Legends for the microscopic demonstrations

1 Introduction/blood

Blood smear

Here is a poor part of the slide for identifying blood cells. Note how the red blood cells are mushed together. It is important that you pick out a favorable part of your slide for viewing the white blood cells.

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Blood smear at 100X

Even at this low power you can provisionally identify the white blood cells. You can scan at this power to help find the rarer cell types and then examine them at high power.

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Neutrophil, oil immersion

Can you make out the granules in the cytoplasm?

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BLOOD SMEAR 10 X

It is very important, when examining blood smears, to choose an appropriate region of the slide to look at. In some places the film of blood will be stretched to thin and the leukocytes distorted or ripped apart. Where the film is too thick the cells will be jammed together and not stain well.

Avoid poor areas like the one under the LEFT hand microscope. If the erythrocytes do not look perfectly round, smooth and easily visible the leukocytes can also be expected to show up poorly in that part of the slide. Do not call over an instructor to help identify the remains of a miserable, frazzled white blood cell in an are like this where the cells are not well preserved.

Instead, spend your time looking in well preserved areas, such as shown in the microscope to the RIGHT.

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NEURTROPHIL

LEFT

Neutrophils are the most abundant nucleated cells of blood. They are unmistakable because their nuclei are differentiated into 3-5 discrete lobs joined by only thin strands of chromatin. Neutrophils are "granulocytes" with specific granules in their cytoplasm. However these granules are hard to see. They stain palely and are very small (~1 micron, about at the limit of resolution through your microscopes using oil immersion.) RIGHT

Neutrophils circulate in blood and then escape into the surrounding tissues where they search for bacteria to phagocytize. As mentioned above, this cell type is immediately recognizable by its complexly shaped nucleus. Here you can easily pick out several neutrophils from the tangle of other cells in the wall of the gut on this basis.

Yes, the cell at the tip of the pointer is a friendly neutrophil.

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ACIDOPHILS AND BASOPHILS AND NEUTROPHILS ARE GRANULOCYTES

LEFT: AN ACIDOPHIL = EOSINOPHIL Acidophils are a minor cell type in blood, constituting about 5% of the leukocytes of blood. They can be recognized by their bi-lobed nuclei and eosinophilic cytoplasmic granules. These granules are large enough to see well, are uniform in size and seem to fill the cytoplasm.

RIGHT: A BASOPHIL

Basophils are even rarer than acidophils in blood, maybe 0.5% of the total leukocytes. You may not come across any on your slide today. Basophil granules are inky black, heterogeneous in size and often are scattered in the cytoplasm instead of filling up the cell. The nucleus typically is elongated and folded into a compact S shape that is hard to make out.

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LYMPHOCYTES

These two microscopes show lymphocytes at 400X and 1000X (oil immersion) magnification. The cell at the right is a -small- lymphocyte with only a narrow rim of cytoplasm along one side. The rest of the cell is the nucleus. Its DNA content makes the nucleus basophilic, blue-staining with H+E. The large lymphocyte to the right has more cytoplasm, hence its name.

The pointer is on a platelet. This is a fragment of a giant bone marrow cell. Platelets do not have nuclei but do have small, somewhat inconspicuous granules. Platelets are sticky and quite frequently form clumps in blood smears.

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MONOCYTE

The monocyte is an agranulocyte, as are lymphocytes. Old monocytes acquire a distinct U or horse-shoe shape to their nuclei. Younger ones have rounded or bean shaped nuclei. They can be distinguished from lymphocytes by their larger, paler-staining nuclei and more extensive cytoplasm. (There is only one monocyte for every 5-10 lymphocytes in blood.)

2 Epithelium

3 Connective tissue, Laboratory I

D-26 Subclavian artery. H+E, low power.

Here you can see connective tissue with various structures running through it. The tissue varies from loose to dense across the field. A layer of especially dense connective tissue surrounds the nerve bundles indicated by the pointer. Ordinary connective tissues stain red with H+E because the dominant component is a protein, collagen.

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D-25 Arterial wall with Masson or "trichrome" stain.

Masson stains make your life easier as you begin to study histology. They color collagen green, whereas almost all other proteins become red. Thus you can easily distinguish the cells from the extracellular proteins of the tissue. It sometimes can be tricky to tell some muscle cells from collagen which may surround them with just H+E. You have slides with Masson staining for quite a few of the tissue of the body. This is quite helpful, but by the time you are ready for your pathology course you will not need such aids (which is a good thing, since those slides will just be plain H+E).

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D-24 Carotid artery, elastic stain.

This special black stain shows off the elastica which, otherwise, would be hard to see. The view is of a portion of an arterial wall. The inner part of the wall contains many, concentrically arranged sheets of elastica (which appear as black lines in section). Farther out in the wall the elastica takes the form of irregularly arranged small fibers.

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D-7 External ear, elastic stain.

This slide shows elastica in two types of tissue. At the left the massive black tissue with holes is elastic cartilage. Ignore it for now as we will come back to it in Lab # 11 dealing with cartilage. To the right you can see small elastic fibers (cut in various orientations) in ordinary connective tissue. Compare the amount of elastica with that of collagen. Why is there so more of the latter?

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D-33 Lymph node, reticulum stain.

The silver ions used here stain carbohydrates black. They shows the tangle of kinked reticular fibers especially well because those delicate fibers have proteoglycans absorbed to their surfaces. The cells found here contain very little polysaccharide and so appear as gray ghosts between the fibers. Obviously, this stain is a poor one for examining cells even though the tissue is packed with them. At the left part of the field is a small seam of ordinary connective tissue (Type I collagen instead of Type III, right? Right

). Even these fibers have some carbohydrate on their surfaces, though not much, and therefore stain tawny-gray instead of black. (OK, so how would YOU describe their color, huh?)

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D-34 Lymph node, H+E.

This slide is for comparison with D-33. The H+E stain shows the cells wonderfully. They are so jammed together that it is impossible to observe the reticular fibers without a special reticulum stain. The function of the reticular fibers is to form a sponge-like network to hold the cells (loosely) in place. Many of these cells are lymphocytes with very little cytoplasm, so the general color of the tissue is bluish due to all of the nuclei (am I right or am I right?).

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D-162 Scalp H+E.

This is a view of skin. A tiny bit of the epithelial layer - the epidermis - is visible at the top of the field. The rest is the dermal layer which is connective tissue. It is very dense. A variety of cellular structures are embedded in the dermis, most notably hair follicles and various glands. Don't worry about figuring out which each is, but you should recognize that they are epithelial structures. In every case they are separated from the surrounding connective tissue by a basement membrane (invisible here).

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D-5 Tendon.

A tendon is composed almost entirely of very coarse bundles of collagen (Type I) in a very regular, compact arrangement. This is dense connective tissue, indeed. The few cells present are squeezed in between the fibers and show up as long skinny nuclei. They are fibrocytes, the cells which synthesized all of the collagen that now traps them in. The clear elongated spaces are just artifacts that formed when the collagen shrank from being dehydrated.

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Tendon, cross section (not in your slide set).

This slide shows a tendon cut in cross section for comparison with D-5. You can appreciate the great width of the individual bundles of collagen, each wrapped in a thin layer of loose connective tissue. Where are the fibroblast cells located?

Your slides do not show dense irregular connective tissue cut in this orientation, which is why this slide is shown to you here.

(any convenient H+E slide for the next two microscopes maybe D-162 and D-26). They should be next to each other so that the students can compare loose with dense connective tissue.

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Dense vx loose CT

LEFT: Loose connective tissue at high power

Note how delicate the fibers are .

Compare this with:

RIGHT: Dense connective tissue at high power

Note how thick the bundles of fibers are and that they run in various orientations.

3 Connective tissue Laboratory II

D-4 Connective tissue spread.

Macrophages have been "vitally stained" with trypan blue here. They are visible as clusters of purple dots outlining their cytoplasm. Their nuclei are palely stained and appear mainly as "holes" in the clusters of cytoplasmic dye particles. The other cell type shown is the fibroblast. Their nuclei are pale and their cytoplasm invisible against the background of the palely stained collagen fibers. The pointer is on the nucleus of a fibroblast. Note that it looks the same as the nuclei of the macrophages. The two cell types would be almost indistinguishable, except for the trypan blue. How did the dye get into the macrophages? Right

I knew that you knew.

One other thing, when you look for these cells on your slide be sure to choose areas where the tissue has been spread very thinly so that you are not looking through a thick layer of cells and fibers.

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D-4 Connective Tissue Spread.

Mast cells are found mainly along small blood vessels (why?). You can easily pick them out after their granules have been stained with neutral red. Can you make out the small arteriole near the mast cells in this field?

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D-4 Connective tissue spread.

One of the stains on this slide is for elastica. The elastic fibers are long and delicate (indicated by the pointer). Spreading the tissue to make this slide stretched the fibers. Therefore they look very straight, unless they broke and curled around like a cut rubber band. What did the stretching do to the collagen fibers? These have been stained (pink) very lightly so as not to obscure your vision of the other fibers and cells. They will appear darker on some of the class slides than on others and on some parts of a slide than other parts. Of course where the tissue is thick the tangle of collagen fibers gives a dark red background.

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D-26 Subclavian Artery.

This is a decent slide for looking at fibroblasts in loose and dense connective tissues. Here, all you see of these cells are their nuclei. Depending upon how dense the region of connective tissue is these elongate nuclei may look darker or paler. In your opinion, is this a region of loose or dense connective tissue? Would the nuclei of the fibroblasts stain darker or paler in dense connective tissue? Why?

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D-3 Umbilical cord.

Your lab book describes the mesenchyme in this tissue thusly: "These cells have multiple plump arms of cytoplasm. The collagenous fibers are too fine to be seen distinctly, and the extracellular space is dominated by amorphous ground substance, rich in hyaluronic aced. This tissue has been known for years to obstetricians as "Whorton's jelly," which indicates its consistency in life. A special metachromatic stain has been used to distinguish the cytoplasm in the arms of the mesenchymal cells from the surrounding amorphous ground substance. Toluidine blue is a purplish compound whose absorption spectrum changes upon complexing with highly charged polysaccharides. Thus, cytoplasm appears pale blue and ground substance, reddish. In many places, the ground substance became shriveled and clumped during the dehydration of the tissue, leaving holes. Note that the mesenchymal cells have much fleshier arms of cytoplasm than do fibroblasts.

The pointer of the microscope is on some pinkish tatters of shriveled and clumped ground substance. It originally filled the clear space between the (greenish) cytoplasmic arms of the adjacent mesenchymal cells. These cells have much more cytoplasm than do the typical fibroblasts of adult tissues. The darker elongate structures are their nuclei.

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D-107 Duodenum.

Delicate wet epithelia are vulnerable to invasive bacteria. This is especially the case in the gut. The connective tissue underneath such epithelia often accumulate large numbers of protective cells. These lymphocytes, neutrophils, acidophils, macrophages and so forth come in from the blood. Here you can see a very cellular connective tissue forming the lamina propria for a simple columnar epithelium. We are not far enough along in the course for you to expect to identify these cell types, but you can try. Highly cellular tissues like this usually are supported by reticular fibers instead of all Type I collagen fibers.

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D-2 Adipose Tissue.

Each clear round holes was once occupied by a fat droplet in an individual fat cells (adipocytes). The fat was dissolved out during the fixation of the tissue, leaving an empty space. The cytoplasm of fat cells is pushed out as a narrow layer at the edge of the cell. The nuclei also lie at the periphery. The nucleus is so much smaller than the whole cell that the plane of section generally misses it. However, the pointer shows a cell with its nucleus visible. Fat cells can occur individually in almost any area of loose connective tissue. When they are so abundant as to make up essential all of the tissue we biologists call them "adipose tissue", (your Ma would simply say "fat tissue".)

Grab your belly or buttocks and estimate how much fat there is just below the skin. Now try it with your neighbor - or with Dr. Lu (who set up these demonstration microscopes) if your neighbor will not cooperate. Thank you Dr. Lu.

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D-129 Sublingual gland.

Here you can see clusters of secretory epithelial cells embedded in connective tissue. Which is the parenchyma and which the stroma? Can you distinguish the two components in this view? Can you pick out collagen fibers and fibroblast nuclei? Most of the epithelial cells in this gland secrete mucus. They are essentially the same cell type as the "goblet cells" that you looked at in the epithelium of the respiratory tract.

4- Muscle

Myoepithelial Cells

  LEFT: Ceruminous gland

RIGHT: Eccrine sweat gland

The secretory portions of these glands have a simple epithelium with a goodly number of myoepithelial cells. The epithelial secretory have round nuclei. The myoepithelial cells (at the pointer) have elongated nuclei. Their cytoplasm typically stains strongly with eosin, Why?

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Skeletal Muscle vs Cardiac Muscle in Cross Section

Compare this is a view of skeletal muscle in cross section (left microscope) with the cardiac muscle, cross section, in the microscope to the right. How many ways can you think of for distinguishing these two types of muscle in cross section? How many of these ways allow you to distinguish the tissue in these two demonstration slides?

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Skeletal Muscle vs Cardiac Muscle in Longitudinal Section

Compare this is a view of skeletal muscle in longitudinal section (left microscope) with that of cardiac muscle, longitudinal section, in the microscope to the right. How many ways can you think of for distinguishing these two types of muscle in cross section? How many of these ways allow you to distinguish the tissue in these two demonstration slides?

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Cardiac Muscle vs Smooth Muscle in Cross Section

Compare this is a view of cardiac muscle in cross section (left microscope) with the smooth muscle, cross section, in the microscope to the right. How many ways can you think of for distinguishing these two types of muscle in cross section? How many of these ways allow you to distinguish the tissue in these two demonstration slides?

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Smooth Muscle, Longitudinal Section, vs Tendon

Compare this view of smooth muscle in longitudinal section (left microscope) with that of tendon, in the microscope to the right. How many ways can you think of for distinguishing these two types of tissue? How many of these ways allow you to distinguish the tissues in these two demonstration slides?

Smooth Muscle, Longitudinal Section, vs Irregular Dense C.T.

Compare the appearance of this smooth muscle in longitudinal section (at the pointer) with that of the surrounding dense irregular connective tissue. How many ways can you think of for distinguishing these two types of tissue? How many of these ways allow you to distinguish the tissues in these two demonstration slides?

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Cross Bands of Skeletal Muscle

These two microscopes show the banding pattern of skeletal muscle in the relaxed and contracted states. Look right where the pointers are pointing. Which microscope shows contracted muscle and which relaxed?

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Muscle spindle

The muscle spindle is a cigar shaped organ embedded in skeletal muscle. Here it is located in an area of perimysium. It consists of a thin sheath of dense connective tissue surrounding several small skeletal muscle fibers. How many of these "intrinsic muscle fibers" can you see. Because this tissue was stained with H&E you cannot see the small nerve endings which penetrate the capsule and twist around the intrinsic muscle fibers. In life the rest of the space within the capsule would be filled with fluid. What is the function of the muscle spindle. What would happen if the spindles in your legs rotted away? Can you see a nerve bundle nearby? How about the endomysium? Can you tell that this is skeletal muscle?

5 Vascular system

Comparison of capillaries with venules

Left microscope: CAPILLARY

Capillaries are small enough in diameter to just accommodate one erythrocyte, aprox. 7.5 microns. Cross sections usually show only one endothelial cell wrapped around to forma a tube. Sometimes the plane of section will go through the nucleus of the endothelial cell. Equally likely it will miss the nucleus and show only a small round lumen surrounded by a narrow ring of cytoplasm. Which is the case here at the tip of the pointer? In very lucky cases you will see tow nuclei, the second being a pericyte. A basement membrane will separate the two cells.

Right microscope VENULE

Small venules have a structure similar to that of capillaries. However, their diameters are larger. Here you see the cross section of a venule showing several red blood cells side by side within it. Can you also see some capillaries in the field?

COMPARISON OF A VENULE WITH AN ARTERIOLE

The pointer is on a venule. An arteriole is off the _________. Typically, the wall of a venule is narrow, with few or no smooth muscle cells and a lumen is large and round (or somewhat collapsed). Often blood cells are retained in the venule. In contrast, arterioles are usually contracted. Their walls are thicker than the diameter of the lumen and have a puckered up inner (lumenal) surface. In life, of course the inner surface would be smooth. An internal elastic membrane is a characteristic feature of all but the smallest arterioles.

ARTERIOLES

Right: Longitudinal section through an arteriole

In this longitudinal (actually somewhat oblique) section the endothelial cells show up as two inner rows of elongated narrow nuclei. Obviously, these cells are elongated in the direction of the length of the arteriole. There is one layer of smooth muscle cells wrapped circularly around the vessels (indicated by the tip of the pointer). These cells are cut in cross section so the elongated nuclei appear small and round. Can you see traces of a connective tissue adventitia outside of the smooth muscle layer? Can you discern an internal elastic membrane?

Left: Cross section through an arteriole

In cross section arterioles typically show a puckered wall around a small lumen. This is due to contraction of the smooth muscle and elastica during fixation. The smooth muscle cells are circularly arranged. They obviously are stubby in tiny arterioles such as this and have elongated curved nuclei.

AORTA

Right: Elastic stain

This view shows the intima and part of the media of the aorta stained for elastica. The pointer runs along the boundary between these two layers. The thickness of the intima is highly variable. As a pathological condition, atherosclerosis, the intima layer has become thickened by the invasion of smooth muscle cells and deposits of cholesterol. The very delicate endothelial lining is damaged or missing over much of the aorta in your slides.

The elastic laminae in the media are fenestrated. Huh?? - Oh yea I know what those are and sure, I can see that they have fenestrations, er, just hwo big should a fenestration look? And their function is to . . . .?

Left H+E

With H+E the elastica is harder to see, but having just seen what the tissue looks like with an elastic stain you should be able to pick out the wavy elastic lamina here, with collagen and fibroblasts in between.

PURKINJE FIBERS

Bands of Purkinje fibers run down along the septum of the heart between the ventricles, mostly along the surface. Here such a band is cut in cross section. These cells are modified cardiac muscle cells. They are notable for:

1. being larger in cross section than ordinary cardiac muscle
cells.

2. having substantial deposits of glycogen around the nucleus.
Since glycogen is a neutral polysaccharide it does not stain with H+E (In fact, glycogen is quite soluble and not even left in place after ordinary H+E procedures). Therefor Purkinje cells typically look empty around their nuclei.

3. The relatively small numbers of myofibrils are dispersed to
the periphery so the outlines of the cells are easily visible.

4. Some of the cells have two nuclei instead of just one.

Because this tissue was taken from a newborn lamb the regular cardiac muscle cells are poorly differentiated. They are small and I, for one, would not be able to recognize them as cardiac muscle. This is a classical preparation for demonstrating Purkinje cells because in the newborn ruminant the cells are unmistakably larger than the rest of the cardiac muscle cells. The muscle cells constitute the myocardium The endocardium here is not much more than a layer of endothelial cells. This is typical of the ventricle. The epicardium is not shown here but it would have fat cells in a substantial layer of loose connective tissue.

6 Glands

DUCTS OF SALIVARY GLANDS

Salivary glands have three kinds of ducts: intercalated, striated (=secretory) and excretory.

To the LEFT is an intercalated duct of the parotid gland. It is a pretty miserable little thing eh?

To the RIGHT is a striated duct of the submandibular gland. Now this is a duct that you can get excited over

It is absolutely essential for you to be able to distinguish mucous from serous secretory cells. How does the cytoplasm of these two cell types differ? How do the nuclei differ. The mucous cells (which secrete mucus) are essentially the same cell type as goblet cells that you looked at in surface epithelium.

The pointer is on a serous demilune. Look at the accompanying figure from a text book to understand the morphology of a "mixed acinus with a serous demilune.

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COMPARISON OF A COMPOUND ACINAR GLAND
WITH A COMPOUND TUBULAR GLAND

The diagram taken from your syllabus shows the difference in morphology between these two forms of glands.

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PANCREAS vs LACRIMAL GLANDS

RIGHT The acini of the pancreas are spherical structures which show 5-10 cells in cross section. The pointer is in the middle of an acinus where the apical ends of the cells come together to form a tiny lumen which they secrete into.

The acinar cells are pyramidal in shape. If you look around (N0, DO NOT MOVE THE STAGE, JUST YOUR EYEBALLS) you should be able to see that the basal parts of the cells are more basophilic (why?) and the apical portions are filled with eosinophilic secretory granules.

LEFT: The lacrimal gland is a branched tubular gland. Note that the lumens of the tubules are much larger and heterogeneous in size than the almost invisible lumens of the acini of the pancreas. Why is this --- YOU figure this out, don't just ask.

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SCALP: LOW POWER,
SHOWING SEBACEOUS GLANDS (at the pointer)
ASSOCIATED WITH HAIR FOLLICLES AND
ECCRIN SWEAT GLANDS (to the lower left).

The sebaceous gland has a stratified epithelium formed by the outpocketing of ectoderm from a hair follicle. The pointer indicates the top of the epithelium in the center of the gland. The basement membrane would surround the gland. Not that the basal cells (where are they located?) are flattened and have dark staining pink cytoplasm. These cells actively divide. As the progeny cells get pushed up they accumulate droplets of lipid, giving them a "foamy" appearance. The amount of lipid increases until the whole cell is just a bag of goo. The nucleus then degenerates, the cell falls apart and the fatty cytoplasm is squeezed up towards the hair follicle as sebum.

Now look at the eccrine sweat glands. The pointer runs past several sections of the secretory portion of the gland. The very base of the pointer runs past two sections through the duct portion of the sweat gland. List the ways that the duct differs from the secretory portion. Can you see these differences? Look around the field. You should be able to identify most of the sections through the sweat glands as being duct or secretory portions.

7 Skin

8 Bone marrow

It is absolutely crucial that you examine appropriate areas of your bone marrow smear. Look through both of these microscopes to see how important this is.

The microscope to the left shows what your field optimally should look like. It should have a pavement of well preserved marrow cells with a minimum of blood.

The microscope to the right shows the sort of poor field that should be avoided. It has mostly blood in it instead of marrow and therefore the marrow cells are poorly preserved. Do NOT call an instructor over to try to name a cell in a poorly preserved area such as this.

Read your manual for directions on finding the right place on your bone marrow smear slide to examine.

The pointer is on a

Mature acidophil

You can also see examples of

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The pointer is on a

Acidophilic myelocyte

You can also see examples of

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The pointer is on a

Basophilic myelocyte

You can also see examples of

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The pointer is on a

Neutrophilic metamyelocyte

You can also see examples of

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Mature neutrophil

You can also see examples of

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Myeloblast/Hemocytoblast

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The pointer is on a

Progranulocyte

You can also see examples of

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The pointer is on a

Basophilic erythroblast
(proerythroblast)

You can also see examples of

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The pointer is on a

Polychromatophilic
erythroblast

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The pointer is on a

Normoblast

You can also see examples of

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The pointer is on a

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The pointer is on a

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The pointer is on a

____________________

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The pointer is on a

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9-Lymphatic system

Plasma cells (D-35, tonsil)

LEFT X 1000 RIGHT X 400

These two microscopes show examples of plasma cells. Between the strands of collagen around the edge of the tonsil happens to be a good place for you to hunt for these cells, although they can be seen throughout the tonsil (usually jammed up against other cells)

Three distinctive features of plasma cells are:

1. Nucleus. The nuclei of plasma cells have large dense clumps of chromatin, located around the nuclear membrane. This produces a characteristic "cart wheel" or "clock face" appearance. Note how much lighter the nucleus looks under oil immersion than at 400-fold magnification. Why? How does the nucleus of a plasma cell differ from that of a lymphocyte?

Do not ask an instructor to answer the questions asked in these demonstrations. Their purpose is to make YOU think about the answers for yourself.

2. Cytoplasm: The cytoplasm of plasma cells is rich in both ribosomes and immunoglobulin protein. Therefore it typically stains deeply with both eosin and hematoxylin dyes. Beware: because the nucleus is located off to one side of the cell a section capturing the nucleus may not show much of the cytoplasm. On your slides hunt around for examples in which the full extent of the cytoplasm of these cells is visible.

3. Golgi: The Golgi apparatus is well developed in plasma cells, why? (If you do not know read pp. 32-35 in your text). The Golgi does not stain well with H+E because it is composed largely of lipid membranes. Thus it appears as a clear, unstained region within the darkly staining cytoplasm of plasma cells. Its is greater in thickness than the depth of focus at high power. Therefore if you very carefully focus up and down you will see a clear area near the nucleus come and go.

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MAIN STRUCTURES OF A LYMPH NODE

RIGHT: outer region

Here is a view of the outer part of a lymph node. You can see the rather unimpressive capsule and the relatively open subcapsular sinus (at arrow). Which of the other structures of the cortex can you observe here - trabeculum, trabecular sinus, nodule, afferent lymph vessel?

LEFT: medulla

The medulla is composed mainly of "cords" of tissue jammed with cells interspersed between "sinuses", which are areas with fewer cells. Both areas have a reticulum of reticular cells supported by reticular fibers. The pointer is on a medullary sinus. Trabeculae of regular connective tissue protrude into the medulla from the capsule. You see one in this section. ..end

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STRUCTURES OF THE TONSIL

LEFT: low power D-35

The tonsil is basically a mucosa of stratified, squamous, nonkeratinized epithelium with masses of lymphocytes in the lamina propria. The lymphocytes form many nodules in the lamina propria, especially in children. The epithelium is folded into wrinkles which dip way down into the lamina propria as crypts. These crypts open to the surface and are lined, of course, with stratified squamous epithelium.

RIGHT: high power D-35 Lymphocytes invade the epithelium, sometimes in such numbers that it is almost impossible to recognize that it is an epithelium. The large nucleus indicated by the pointer is an epithelial cell. Most of the small dark nuclei belong to lymphocytes.

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Cells of the germinal center of a lymph nodule (=lymph follicle)

LEFT: a dendritic antigen presenting cell.

These cells in the germinal center "present" antigens to lymphocytes in the lymph nodules. They are large cells with large pale nuclei. Their cytoplasm is drawn out into long arms. So little cytoplasm surrounds the center of the cell that the nucleus of the dendritic cell looks as if it is bare.

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LYMPHOBLAST

Lymphoblasts have large round nuclei and a discrete rim of cytoplasm. The edge of the cell is usually well seen, unless it is jammed up against some other cell. The trick to looking at cells in nodules (and elsewhere in lymphatic tissues) is to choose places where the cells are not packed to closely together.

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TALL POSTCAPILLARY VENULE OF THE TONSIL

These vascular structures can be found in your lymph node, tonsil and appendix slides. They are essential structures for the circulation pathway of lymphocytes. Can you remember the pathway for lymphocytes through the lymph node?

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RETICULAR CELL OF THE TONSIL

A typical reticular cell has an elongate or triangular shaped nucleus with arms of cytoplasm extending outwards. The arms are draped along reticular fibers that the cells produced. The network of these cells support a profusion of immigrant cell types - lymphocytes, macrophages, plasma cells.

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MACROPHAGES

RIGHT; D-76

Lymph nodes draining the lungs have many macrophages that are filled with dust particles.

LEFT: D- 34

More typically, macrophages ingest cellular debris which can be digested, except for residual lipids. The cytoplasm is eosinophilic and "lumpy looking" due to the indigestible remains in it. Since those remains often are of a lipid nature they get leached out during the processing of the tissue and the cells are sometimes called "foam cells". The nuclei tend to be fairly large and stain fairly palely.

10 Spleen and Thymus

11 Cartilage

Hyaline cartilage, bronchus (D-76)
The cartilage in this tissue is much paler than that in the trachea (D-80, adjacent scope). This is due to a reduced amount of glycosaminoglycans, which can occur with age. Coloration may also vary due to inconsistencies in staining procedures.

Despite variations in staining, hyaline cartilage is one of the more unmistakable tissues of the body. A major feature distinguishing hyaline from other types of cartilage is that fibers here cannot be seen. This gives hyaline cartilage a glassy appearance and led to its name ("hyaline" means "glassy"). What fiber type is found in hyaline cartilage?

Hyaline cartilage, trachea (D-80)
Hyaline cartilage is seen here in C-shaped rings; why do you think that the cartilage supporting the trachea is C- rather than O-shaped?

Individual chondrocytes are found within lacunae and immediately surrounding the lacunae is the territorial matrix. The territorial matrix is poor in collagen but rich in chondroitin sulfate, producing the intense staining seen here.

Fibrocartilage (D-9)

Fibrocartilage is composed of Type I collagen bundles in a cartilage matrix. Note that the chondrocytes are found in lacunae, like the chondrocytes in hyaline cartilage.

Fibrocartilage vs. tendon (D-9)

This tissue was taken from a ligament close to its insertion into bone. In these areas, a tendon or ligament often changes from dense regular connective tissue to fibrocartilage. How would you distinguish between the two tissue types? (Hint: Observe the differences in shape of the cells you see in each tissue. Do you see differences in shape of the white spaces in each tissue?)

Fibrocartilage vs. hyaline cartilage, intervertebral disc (D-8)

Here you can compare two types of cartilage side-by-side. What features can you identify that would distinguish between fibrocartilage and hyaline cartilage? Some things to consider:
Size and shape of chondrocytes
Organization of chondrocytes (are they grouped into nests?)
Size and shape of lacunae
Relative abundance of matrix
Staining and organization of matrix components
Presence/absence of fibers in matrix

Elastic cartilage, epiglottis, elastic stain (D-98)

This stain reveals the many elastic fibers in the matrix of elastic cartilage. You can see that the fibers form a disorganized tangle rather than organized lamellae (such as for fibrocartilage).

Elastic cartilage, epiglottis, H&E stain (D-99)

Elastic fibers here are less evident without special staining (see adjacent scope). However, they will accept the pink eosin dye, so with careful observation, you can see the fibers in the matrix between chondrocytes. How would you distinguish elastic cartilage from hyaline cartilage with H&E? Some things to consider:

Size and shape of chondrocytes
Organization of chondrocytes (are they grouped into nests?)
Size and shape of lacunae
Relative abundance of matrix
Staining and organization of matrix components
Presence/absence of fibers in matrix

12 Bone

SUTURE

LEFT: low power

This is a section through a suture. You must first understand the orientation of the slide. It has been taken perpendicular to the surface of the bone and along the suture. The suture is the junction between two flat bones of the skull. These bones interdigitate like the pieces of a jigsaw puzzle. They are joined by a ligament of dense connective tissue. The cut goes mainly through bone #1 in the diagram below but cuts through the ligament as an island of dense connective tissue and at the tip of the pointer nicked through bone #2. The bone is lamellar, as you can see, with some circumferential lamellae visible at the very top of the field and many Haversian systems elsewhere. The bone looks bluish and funny near the junction of the ligament with the bone. To understand why go to the higher power view in the microscope to the right.

RIGHT; high power

The bone looks funny near the junction with the ligament because the surface of the bone is not cut perpendicular to the surface. In fact, the bone is sectioned right under the surface where the pointer goes across it. Collagen fibers from the ligament extend right into the bone to anchor the ligament. These are called Sharpey's fibers. You can see a cross section of one of these fairly large diameter bundles of collagen fibers marked by the lump on the pointer half way towards the tip. Extending to the left the bone-ligament interface becomes more perpendicular to the plane of section. Here you can see bundles of collagen embedded near the surface of the bone running in the plane of section. You can also see that where the bone surface is cut perpendicular that the very surface of the bone is much more basophilic than the underlying bone. For some reason the osteoblasts at the surface have produced much more ground substance than they did earlier on.

* *

OSTEOCLAST

These cells are characterized by having multiple nuclei (~56-50). Osteoclasts form by the fusion of monocytes, each donating their one nucleus. Chondroclasts are the same cell type but are sometimes given this name when they are chewing up cartilage instead of bone.

* *

ENDOCHONDRAL BONE FORMATION

Left: low power

This slide shows the developmental stages that cartilage goes through as it is replaced by bone. The pointer is in the zone of hypertrophy (or cell enlargement). Can you pick out the other zones labeled on the accompanying picture? Why is the lowest zone in the diagram labeled the "ossification zone?" Where would chondroclasts be found in profusion in this view.

Right: high power

The pointer is on cartilage matrix which has calcified. It stains darker pink than the uncalcified matrix. Are the chondrocytes in this zone alive?

Why does the (hyaline) cartilage matrix appear so red instead of blue on this slide?

* *

ENDOCHONRAL BONE FORMATION

The pointer is on a spicule that has a core of calcified matrix (deep red) surrounded by a layer of bone (paler red). You can see lots of osteoblasts. These cells have a flattened oval shape. Do you see some of them edge on, looking long and thin, and others face on, looking large and plump?

* *

BONE CAN BE HISTOLOGICALLY VIEWED IN TWO WAYS

LEFT: Ground section of bone

A piece of bone was ground down to be about 50 microns thick and is viewed here unstained. No soft tissues remain, just the mineralized matrix. Empty spaces appear black. Haversian systems are easily seen, including the central Haversian canals, the concentric lamellae and the lacunae for the osteocytes. The pointer is on an interstitial lamella. Why is it called interstitial?.

The Haversian canals run along the long axis of a long bone. Was this bone sectioned transversely or longitudinally? Volkmann's canals run at an angle to the Haversian systems and therefore will be visible, if present, as oblique section and oval in appearance.

RIGHT: Decalcified compact bone stained with H+E

Because the collagen fibers are regularly arranged in adult bone the individual lamellae can be seen even when the hydroxyapatite crystals have been dissolved.

The Haversian canal at the pointer contains an endosteum, a capillary, scattered osteoprogenitor cells and a few wisps of C.T. As an artifact of poor preservation these tissues are clumped up in the middle of the Haversian canal here. Try to imagine what they were like in life.

* *

JUXTAPOSITION OF WOVEN AND LAMELLAR BONE

Woven bone can be distinguished by four criteria.

1. More cells

2. Cells larger and more irregular in shape.

3. More ground substance and therefore the matrix stains bluer - often the ground substance is unevenly distributed giving woven bone a mottled appearance.

4. No lamellae (although these will be visible in adult bone only if the plane of section cuts across them.

A "reversal line" marks the junction of the two types of bone. Why does it show up blue? On one of your slides (D 147) you can see equivalent lines between individual lamella within adult bone. What do you make of this? -- NO, not what does Dr. Lu have to say, what do YOU think about this?

The pointer is in the osteoid layer at the surface of the bone under a sheet of osteo...??? er, what are these cells covering the surface of the bone called? How does osteoid (=prebone) differ in chemical composition from decalcified bone matrix. Aha, the tough question for YOU to mull over is why osteoid stains paler than the decalcified matrix.

* *

AN OSTEOBLASST

Describe completely the osteoblast seen under the microscope. (did you remember the Golgi apparatus of it?)

* *

FINGER JOINT

The pointer is on the epiphyseal plate of a finger bone (a carpal). What structure is to the right of the epiphyseal plate? What is to the left. Endochondral bone formation has virtually ceased even though cartilage remains. Can you see traces of the various zones of cartilage maturation characteristic of endochondral bone formation?

* *

Articular cartilage

Articular cartilage caps the articular surface of this bone. The pointer is on the boundary between cartilage and bone. What is distinctive about the this cartilage. Do the cells get smaller towards the surface of the cartilage?

* *

Spongy bone with hematopoietic bone marrow

This spongy = cancellous = trabecular bone is from a vertebra. Where else in the body can you expect spongy bone with red bone marrow?

* *

Circumferential lamellae in decalcified compact bone

Were these lamellae deposited by a periosteum or an endosteum? Nerve, low power, Masson stain.

This slide shows a nerve at low power. It runs as three fascicles, each wrapped up in a perineural sheath. A dense Epineurium surround the entire nerve.

The important part of the perineurium is the sheet of flattened Schwann cells four or five cells deep. It is essentially an epithelium that isolates the inside of the nerve fascicle from the external tissues. Under this sheath is a space (enlarged here as an artifact) filled with fluid. The seam of green staining tissue loose connective tissue within the fascicle is endoneurium. There are also delicate wisps of endoneurium surrounding the individual axons.

13 Urinary System

Kidney (D-43)

Renal corpuscles are round in cortical kidney tissue. Adjacent, you can find a row of cuboidal cells (pointer), which makes up the macula densa. The macula densa and cells in the wall of the afferent arteriole comprise the juxtaglomerular apparatus, which plays a role in the regulation of blood pressure.

Kidney (D-43

)
Here you can see a portion of a proximal convoluted tubule (pointer). In comparison to distal convoluted tubules, proximal convoluted tubules are more numerous, have a more irregular lumen, and have fewer cells per cross section.

Kidney (D-43)

Here you can see a portion of a distal convoluted tubule (pointer). In comparison to proximal convoluted tubules, distal convoluted tubules are less numerous, less acidophilic, have a fairly uniform lumen, and have more cells per cross section.

Kidney (D-43)

Here you can see a collecting tubule or duct (pointer). Its permeability to water is controlled by antidiuretic hormone, or ADH.

Ureter (D-47)
The ureter conveys urine from the kidney to the bladder and is lined with transitional epithelial cells, like the bladder.

* *

Bladder, contracted (D-49)

Like the ureter, the bladder is lined with transitional epithelial cells. The bladder has three layers of smooth muscle tissue which provide support and contractility to the bladder.

Bladder, stretched (D-48)

Here you can see the transitional epithelial lining of the bladder. How would you compare its appearance in this stretched bladder to that in the contracted bladder?

* *

Urethra (D-50)

The epithelial lining of the urethra varies according to distance from the bladder: it progresses from transitional (near the bladder) to pseudostratified/stratified columnar to stratified squamous (near the external opening). How would you classify the epithelium in this particular section?

The clusters of mucus-secreting cells form glands that extend into the lamina propria (so they are referred to as simple glands). These glands are called lacunae of Morgagni, which can also be found within the epithelial layer (where they are referred to as intraepithelial glands).

14 Respiratory System

NB 104: Respiratory System

Monkey nose (D-83)

This is the upper portion of the nasal septum, which has a central core of lamellar bone. The epithelium on either side of the septum is olfactory epithelium. If you look at this under higher magnification on your own slide, you will see that it is a pseudostratified columnar epithelium with microvilli. Underlying the epithelium are numerous glands (Bowmans glands) which open to the epithelial surface through simple ducts. The olfactory cells send their axons to the submucosa, where they form thick bundles of unmyelinated fibers (pointer) that travel to the olfactory bulb in the base of the brain.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

Monkey nose (D-83)
The three conchae are supported by bone and are lined with a typical respiratory epithelium (pseudostratified columnar with cilia and goblet cells). The lamina propria is filled with serous and mucous glands. Note the large venous plexuses (pointer), normally filled with blood, to warm or cool inspired air depending on the conditions.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

* *

Larynx and true vocal cord (D-100)

The true vocal cord is lined with stratified squamous epithelium under which is found fascicles of skeletal muscle (the vocalis muscle). Joining the muscle to the epithelium is a layer of dense connective tissue, the vocalis ligament (pointer). Contraction of the vocalis muscle puts tension on the vocal cord to change the pitch of sounds emanating from your mouth.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

* *

Larynx and false vocal cord (D-100)

The false vocal cord is lined with a somewhat atypical respiratory epithelium (pointer). In the lamina propria, there are very few goblet cells but numerous mucous and serous glands. The false vocal cord apparently plays no part in phonation.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

* *

Trachea (D-80)

The trachea and much of the conduction passageway leading into the lungs is lined with respiratory epithelium (pseudostratified columnar with cilia and goblet cells). The trachea is supported by incomplete, C-shaped rings of cartilage, which are joined at the ends by smooth muscle (pointer). Cartilage serves to keep the trachea open.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

* *

Bronchus (D-75)
Bronchi have a similar structure to the trachea except that they are smaller, contain irregular plates of cartilage (pointer), and have fewer glands.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

Respiratory bronchiole in lung (D-77)
The beginning of the respiratory portion of the lungs starts with the respiratory bronchioles (pointer), where scattered alveoli begin to bud off of the sides of a terminal bronchiole. The epithelium between the alveoli consists of simple squamous/cuboidal cells with a relatively thick underlying layer of smooth muscle. This is the first region of the respiratory pathway where O2/ CO2 exchange can occur.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

Alveolar duct in lung (D-77)
The numbers of alveoli which bud off of the sides of respiratory bronchiole increase until the walls of the duct are merely a continuous row of alveoli. The duct is then known as an alveolar duct (pointer).
nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

Alveolar sac in lung (D-77)
Alveolar ducts are the passages which lead into clusters of alveoli called alveolar sacs (pointer). These alveolar sacs make up by far the greatest part of the lung and have a major role in the exchange of O2 and CO2.

nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs

Interalveolar septum in lung (D-77)

The alveoli are interconnected through pores but are separated by a highly vascular interalveolar septum. Note that capillaries (pointer) are abundant in the septum. Gas exchange takes place between the O2-rich air in the alveolus and the CO2-rich blood in the capillaries. The nuclei that you see in the septum are either those of capillary endothelial cells or of the type I septal cells that line the alveolar walls.

Macrophages in lung (D-77)

Dirt, dust, bacteria, and other foreign particles that find their way into the lung are ingested by the abundant macrophages (pointer). Macrophages roam through the alveoli and in the septae. Because they are often filled with ingested dust particles, they are also called "dust cells."

Type II cells in lung (D-77)

Type II cells (aka giant septal cells) line the alveolar septum and secrete a liquid called surfactant. Surfactant is a phospholipid- and glycolipid-rich secretion that, when released by exocytosis, spreads over the surface of the alveolar walls. It serves to reduce surface tension on alveolar walls, thereby facilitating alveolar expansion during inhalation.

15 Eye and Ear

Eye, Masson stain (D-175)
The cornea consists of an external stratified squamous epithelium, a thick connective tissue layer (the stroma), and a simple squamous epithelium (the endothelium) which lines the anterior chamber. Both the epithelium and the endothelium sit on a thick basement membrane. Note that there are relatively few cells in the stroma, and the nuclei of these cells are very flattened. This is to provide the minimum interference to the passage of light. The thick bundles of collagen are all arranged parallel to the surface of the cornea. This is an example of dense regular connective tissue.

Eye, Masson stain (D-175)
The lens has largely been lost during processing. However, at the edge, the green staining outer capsule (made of a single layer of epithelial cells seen at the pointer) and the elongated, dark red staining lens fibers can be clearly seen. Note that the epithelium is lost towards the back of the lens: this is where the epithelial cells start to elongate into lens fibers (a cluster of nuclei marks this area). The thin, light green remnants of the zonular fibers can be seen streaming across the space between the lens and the ciliary processes. These fibers insert into the lens capsule and into the ciliary processes, and are responsible for changing the accommodation of the lens to allow for near or distant vision.

Eye, Masson stain (D-175)
The ciliary processes (pointer) are pigmented and project from the ciliary body into the posterior chamber. Note how vascular they are - they are responsible for secreting the aqueous humor, which fills the posterior and anterior chambers. The ciliary body consists of the underlying vascular, loose connective tissue and the ciliary muscle, stained red; the ciliary body lies just beneath the green staining connective tissue of the sclera. The contraction and relaxation of this muscle is responsible for the accommodation of the lens, thus allowing us to focus on near or distant objects.

Eye, Masson stain (D-175)
The iris extends anterior to the lens and is covered on its posterior surface by a layer of pigmented epithelial cells (as is the entire inner surface of the eye). The iris sphincter muscle (pointer) is a well-defined layer of smooth muscle, which extends from the tip of the iris just above the epithelium. The iris dilator muscle consists of a poorly visible bunch of myoepithelial cells lying between the epithelium and the sphincter muscle; do not spend any time trying to see this structure. Note that the cells making up the stroma of the iris are pigmented - it is these cells that give the iris its color.

Eye, Masson stain (D-175)
Schlemm's canal (pointer) is seen at the angle of the iris, where it curves around to blend into the cornea. This consists of one or two channels lined with tall endothelial cells. It is through these canals, and the trabecular meshwork in front of them, that aqueous humor drains from the eye into the venous system.

Eye, Masson stain (D-175)
The ora serrata (pointer) is the point at which the sensory retina ends. There is, of course, no vision anterior to the ora serrata.

Eye, Masson stain, low magnification (D-175)
At this low magnification, it is possible to see all the layers of the posterior part of the eye. Starting from the outside, there is a thick, green stained layer of connective tissue - this is the tough, protective sclera that forms the "white" of the eye. Beneath this is a highly vascular layer, the choroid, containing many pigmented cells. Note that vessels nearer the sclera are much larger than those close to the retina, which actually form a capillary layer; these capillaries are responsible for the nutrition of the outer retinal layers. Internal to the choroid is a single layer of pigmented cells, the pigment epithelium, which separates the retina from the choroid and contributes to the blood-brain barrier. Even at this low magnification, it is easy to see six layers of the retina - there are actually nine.

Eye, Masson stain (D-175)
This slide examines an area of the retina, which is detached from the back of the eye, making it easier to see all of the layers. At 40x it is easy to distinguish the thick inner segments of the cones (pointer) from the thinner inner segments of the rods. Remember that cones are responsible for daylight and color vision whereas rods are responsible for vision in dim light. Note that blood vessels are situated only in the inner layers of the retina. In this layer, you can also see isolated large nuclei - these are the ganglion cells that send their axons through the optic nerve to the brain.

Eye, Masson stain (D-175)
The optic nerve consists of the axons of ganglion cells leaving the eye and proceeding to the brain. Where the nerves leave the eye (optic disc), there is no retina; this is known as the blind spot. The axons of the ganglion cells become myelinated as they pass through the disc. The optic nerve is also part of the central nervous system and as such, is surrounded by the three meningeal layers (dura, arachnoid, and pia maters).

Ear, H&E (D-177)
The stria vascularis (pointer) is a stratified cuboidal epithelium that secretes endolymph. It is unusual in that it is vascularized - can you see any small blood vessels? The stria vascularis sits on the spiral ligament, which is attached to bone. Can you recognize the underlying bone?

Ear, H&E (D-177)
The Organ of Corti sits on the basilar membrane (pointer) which consists of collagen and elastic fibers and a thin epithelial layer. It is joined to the spiral ligament, which attaches it to bone. Vibration of the basilar membrane causes movements of the stereocilia of the hair cells, leading to the initiation of a neural impulse.

Ear, H&E (D-177)
The Organ of Corti contains hair cells and supporting cells. There are 3-5 rows of inner hair cells and one row of outer hair cells.

Ear, H&E (D-177)
The spiral ganglion (pointer) contains the cell bodies of afferent bipolar nerves; these nerves transmit signals to the brain. Their dendrites synapse on the sensory hair cells while their axons travel to the brain. Efferent nerve fibers also synapse on the hair cells.

Ear, H&E (D-177)
This slide shows a glancing section through the macula of the saccule. The overlying gelatinous otolithic membrane and the otoliths have been torn off during sectioning.

16 NERVOUS SYSTEM

Axons within a peripheral nerve stained with Masson trichrome stain.

The pointer is on a myelinated axon. The myelin is very poorly preserved, in fact essentially absent. Thus, you can see the axon itself as a dark orange dot at the edge of a round clear space. Myelin originally filled that whole space. Myelin is mostly lipid, which was leeched out during the preparation. The traces of myelin protein clumped to the edge of the myelin space and maybe along the surface of the axon. If the preservation had been better you would have seen some of the protein in the myelin space forming an orange donut. If the preservation had really been good the myelin space would have been filled with a uniform orange staining film of protein. Can you see myelinated axons in various degrees of preservation?

All of the nuclei seen here are of Schwann cells (except for an occasional endothelial cell and scattered fibroblasts in the thicker (green) seams of endoneurium.

* *

Non-myelinated axons with Masson stain

Several nonmyelinated axons run together through the cytoplasm of an elongated Schwann cell, seen here in cross section. You should be able to see several orange dots (representing these axons) in the cytoplasm.

* *

Node of Ranvier

Peripheral nerve, longitudinal section, Masson stain. tthe nuclei seen here are of Schwann cells, (of course).

* *

D-25 Vagus nerve, H+E

These axons are all (or almost all) nonmyelinated. Is this obvious to you? if not, where do you think the myelin sheaths are in your view? Ha, do you see any scattered myelinated fibers?

* *

AUTONOMIC GANGLIA IN THE GI TRACT

LEFT: Myenteric plexus.

The plexus is the lens-shaped bit of tissue between the two muscle layers of the intestine. The nerve cells (= ganglion cells) are large with large pale nuclei. The much more abundant satellite cells have smaller darker nuclei.

RIGHT: Submucosal plexus.

This plexus lies in the submucosa of the GI tract. It is much smaller and less impressive than the myenteric plexus as this view shows. It does contain ganglion cells and satellite cells, however.

* *

Nerve ganglia in the PNS

LEFT a dorsal root ganglion: SENSORY

RIGHT: a sympathetic ganglion: AUTONOMIC

Questions:

What shape do the nerve cell bodies have in the two ganglia?

What are three characteristics that you can use to distinguish these two sorts of ganglia on your slides?

What similar features do these two ganglia have in common?

* *

Peripheral nerve, silver stain.

Silver stains only the axons and cell nuclei. The nuclei, of course belong to Schwann cells. What shape do they have?

LEFT: longitudinal section

RIGHT: cross section.

You can distinguish clusters of nonmyelinated axons from myelinated axons, in both the cross section and longitudinal section Myelinated axons are larger and spread farther apart than nonmyelinated ones.

Central Nervous system

GLIAL CELLS

LEFT: Astrocytes and oligodendrocytes

There are two main types of glial cells in both white and gray matter of the spinal cord. Oligodendrocytes have small darker round nuclei. Astrocytes have larger, paler, more irregularly shaped nuclei. The pointer is on the nucleus of an astrocyte with an oligodendrocyte nearby.

Only the nuclei of these cells can be distinguished. The cytoplasm stains the same as that of all the equally invisible cytoplasmic structures around it. The featureless areas are called neuropil.

RIGHT: Microglia (probably actually probably an endothelial cell)

Microglia are members of the mononuclear phagocyte system, derived from monocytes. They probably function as antigen presenting dendritic cells, patiently awaiting an infection in the spinal cord which they can tell the lymphoid system about. These cells have small elongate nuclei. They would be confused with endothelial cells(of the capillaries that permeate the CNS) instead of with astrocytes or oligodendrocytes.

BRAIN

LEFT: Cerebellum

The cerebellar cortex is a surface layer of gray matter about 2 mm thick. Underneath it are dense tracts of axons running to and from the cortex. The cortex has three layers. The pointer points out the layer of very large Purkinji cells. Above them is the molecular layer with a titanic number of synapses but few cell bodies. Below the Purkinji cells is a layer of closely packed, tiny granule cells. These neurons have small dark nuclei that look similar to lymphocytes. The granule cells send their axons up into the molecular layer. There they make contact with the dendrites of the Purkinji cells. The Purkinji cells send their axons down through the white matter to provide the output from the cerebellar cortex.

RIGHT: Cerebrum

The cerebral cortex is a layer of gray matter about 3 mm deep overlying the white matter of the cerebrum. It is packed with good sized neurons called pyramidal cells. Their axons go downwards and join with each other to form the underlying white matter. Within the cortex the cells are arranged in a functionally distinct series of layers and sublayers. These differ from one another in the size and numbers of neurons and in the connections between them. However, the individual layers are not easily apparent on your slides, so don't worry about them.

Astrocytes

A special staining procedure of the wily histologists selectively stains the cytoplasm of astrocytes. If you look around on slide D 195 you can see some of these spidery-looking cells stained black. The one at the pointer shows a characteristic feature of these cells. Each on them sends at least one cell process out to end on a capillary (visible here as the hole in the tissue). Focus up and down to trace this cell's connection to the capillary. Astrocytes can be found in both gray and white matter of the cerebrum, but if you look in the white matter you will not have to contend with the faintly stained neuron cell bodies of the cortex. You will have to snoop around on your slides to find the appropriately stained areas to look at.

Spinal cord Kluver stain

This special stain leaves myelin blue. The field shows white matter to the left and gray matter to the right. The white matter shows many small blue circles, why? Why is there some blue in the gray matter? And why isn't it in the form of blue circles? You can distinguish the cytoplasm of some of the neurons in the gray matter mainly because their Nissl substance stained darker than the other cytoplasmic structures.

Spinal cord Ventral Horn Kluver stain

The ventral horn of the spinal cord is distinguished by having very large motor neurons. In contrast, the dorsal horn has only small interneurons. Why doesn't the dorsal horn have sensory neurons as large as the neurons of the ventral horn?

D-199 Choroid plexus.

The choroid plexus is made up of two types of tissue. Branching columns of loose connective tissue are surrounded by a simple low cuboidal epithelium of ependymal cells. The connective tissue contains many blood vessels. The epithelial cells secrete cerebral spinal fluid into the ventricles of the brain.

Cerebellum

The cerebellar cortex is a surface layer of gray matter about 2 mm thick. Underneath it are dense tracts of axons running to and from the cortex. The cortex has three layers. The pointer points out the layer of very large Purkinji cells. Above them is the molecular layer with a titanic number of synapses but few cell bodies. Below the Purkinji cells is a layer of closely packed, tiny granule cells. These neurons have small dark nuclei that look similar to lymphocytes. The granule cells send their axons up into the molecular layer. There they make contact with the dendrites of the Purkinji cells. The Purkinji cells send their axons down through the white matter to provide the output from the cerebellar cortex.

Meninges of the spinal cord

The pointer is on the aracnoid layer. It is separated from the pia below by the sub-arachnoid space. The artifactual subdural space separates the arachnoid from the dura.

The subarachnoid space contains cerebral spinal fluid. Nerve rootlets are seen in this space. They emerge all the way along the dorsal and ventral horns of the spinal cord. Then collect together, in the subarachnoid space, into a single dorsal and ventral root between each vertebra.

17 Endocrine System

Herring bodies

Herring bodies are clusters of secretory granules in the axons of the pars nervosa, especially in the distal ends of the axons.

Left Unless tissue sections are made with care the secretory granules lyse and leave a dense, peptide goo in the end of the axon. This is the case for slide D-125 stained with a polychrome stain, shown on the left.

Right: If the tissue is well preserved the Herring bodies show up as oval packets of secretory granules. Here they are stained with H&E.

Cells of the parathyroid gland

The parathyroid has two types of parenchymal cells. The small chief cells are the main source of parathormone. Larger oxyphil cells, with a granular and more eosinophilic cytoplasm are scattered individually or in small clusters. Apparantly they also produce parathormone and their significance is not understood.

Cells of the thyroid.

The thyroid has two types of secretory cells.

Right: Follicular cells. These cells line the follicles and produce two secretory products. What are they? The thin layer of connective tissue below the layer of follicular cells is highly vascular.

Left: parafollicular cells. These cells lie below the layer of follicular cells around a follicle. They are lighter staining and so sometimes called C (for "clear) cells. They are difficult to distinguish and if you do not like these examples - go find better ones yourself.
- geez

Ganglion cells of the adrenal medulla

Ganglion cells are scattered among the chromaffin cells of the adrenal medulla. It is probably not worth wasting too much time looking for them on your slides. Ganglion cells (here as elsewhere) have large pale nuclei with prominent nucleoli.

Right: Slide D-133

Left: Slide D-131

Adrenal gland

Right: Here is a nice section through the entire adrenal cortex. You can easily see the zona glomerulosa, zona fasciculata and zona reticularis. Dr. Lu made a profound discovery about these layers. They all have the same number of letters in their names!

You also can see the capsule of the gland and the medulla

Left: This view contrasts the lowest layer of the adrenal cortex (z. reticularis) with the medulla. Note the many sinusoids in both the cortex and the medulla. Which are larger?

Portal vessels in the pars tuberalis

These small veins run straight down the pars tuberalis.

Where do they start?

Where do they end?

What is their function?

What are the five parts of this portal system:

1. Superior hypophyseal artery

2. _________?_____________

3. _________?_____________

4. _________?_____________

5. Hypophyseal vein

What is the function of this unusual vascular system?

Cells of the anterior pituitary

Can you see acidophils, basophils and chromophobes? Which type is indicated by the tip of the pointer?

18 Female Reproductive System

Primordial follicle (D-58)
In the cortex of the ovary, under the tunica albuginea, you can see numerous primordial follicles. Each primordial follicle contains a large ovum surrounded by only a single layer of flattened follicular cells.

Primary follicle (D-58)
At the pointer is a primary follicle. Its follicular cells have just begun to grow taller and to divide. Compare their shape with that of follicular cells surrounding primordial follicles seen in this field.

The ova in primary follicles are called primary oocytes. They are in prophase of meiosis I; when do they undergo their first meiotic division? What about their second meiotic division?

Secondary follicle (D-58)
At the pointer is a secondary follicle, characterized by the presence of an antral cavity. The ovum is seen here with its surrounding zona pellucida.

Although the ovum is visible in this example, as the follicle grows in size, the probability of sectioning through the ovum decreases. Thus, the ovum may or may not be visible in large follicles.

Mature follicle (D-58)
The theca is well developed around the large mature follicle. The antral space is bordered by a layer of granulosa cells. These cells form an epithelium whose basal lamina should be obvious. External to the basal lamina are the theca interna and theca externa layers; the pointer indicates the boundary between these layers. Blood vessels can be seen traveling through the theca externa.

Cells of the theca interna are plump with round nuclei and vacuolated cytoplasm. How would you describe the appearance of cells in the theca externa? How would you differentiate between the theca interna and externa layers?

Early atretic follicle (D-58)
The pointer indicates a follicle that recently began to undergo atresia and which still contains a lumen. During atresia, granulosa cells are shed from the follicle into the antral space, with the eventual loss of most of the original follicular cells. Only the zona pellucida and glassy membrane are visible in most late atretic follicles (seen in adjacent microscope).

Late atretic follicle (D-58)
The pointer indicates a follicle that is in the advanced stages of atresia and shows only the zona pellucida and glassy membrane. Some late atretic follicles may contain only a zona pellucida; in these cases, the follicle may have been a primary follicle when it degenerated, or the follicle became atretic so long ago that the glassy membrane has time to become completely broken down.

Corpus luteum, low magnification (D-54)
The corpus luteum forms from an empty follicle after ovulation. The wall of the corpus luteum consists of three layers that surround a lumen. The lumen is usually filled with loose connective tissue.

Corpus luteum, high magnification (D-54)
Here you can more clearly see the layers of the corpus luteum wall:
(1) Granulosa lutein cells - These cells appear plumper and lighter staining than theca lutein cells, and make up a layer that is thick and noticeably puckered.
(2) Theca lutein cells - These cells appear smaller and deeper staining than granulosa lutein cells, and make up a layer that is thin and irregularly organized.
(3) Exterior capsule - The capsule immediately surrounds the layer of theca lutein cells and contains blood vessels.

Uterus, follicular/proliferative/estrogenic phase (D-51)
It is difficult to distinguish between the two layers of the endometrium when the tissue is growing and not secreting. However, the glands tend to run in different orientations in each layer: glands run straight towards the surface in the functional layer but are twisted around irregularly in the basal layer. The pointer indicates the boundary between the two.

Uterus, luteal/secretory/progesterone phase (D-53)
The boundary between the functional and basal layers of the endometrium can be seen clearly (pointer). The basal layer is much more cellular. In the functional layer, note the distended and irregular shape of the glands, which actively secrete mucus during the luteal/secretory phase. Much of the mucus is stored in the gland, producing an enlargement that you can see in glands of the functional layer. Are there any coiled arteries (aka spiral or helicine arteries) visible in the field?

Vagina (D-61) and esophagus (D-101)
The vagina bears a resemblance to the esophagus histologically but they differ in the following ways:
(1) Glands - absent in vagina.
(2) Musculature - smooth muscle only in vagina, smooth and skeletal in esophagus.
(3) Muscle layer - less well organized in vagina.
(4) Muscularis mucosa - absent in vagina.

What other criteria could you use to differentiate between the two tissues?

19 Male Reproductive System

Testis (D-67)
The testis is surrounded by an outer capsule of dense connective tissue called the tunica albuginea. Within the testis are many sections of seminiferous tubules. Various cells can be seen within these tubules - from the periphery of each tubule towards the center, you should be able to see (in sequence) spermatogonia, spermatocytes, early spermatids (pointer), and late spermatids.

Testis (D-67)
Sertoli cells are also observed in seminiferous tubules (pointer). Sertoli cells respond to FSH and play a role in spermatogenesis.

Leydig or interstitial cells respond to LH and produce testosterone. They are located between seminiferous tubules.

Testis (D-66)
Here you can see Leydig or interstitial cells (pointer), which secrete testosterone and are found between seminiferous tubules.

Epididymis (D-69)
The epididymis is located adjacent to the testis and separated by the tunica albuginea. The two sets of ducts that make up the epididymis can be differentiated by size and shape; efferent ducts have smaller lumens that appear puckered (pointer).

Duct of the epididymis (D-69)
After detachment from Sertoli cells of the testis, spermatozoa are stored in the epididymis (seen within the lumen). The epithelium consists of columnar and basal cells. Columnar cells exhibit numerous processes that extend into the lumen of the epididymis. Underlying the basal cells are smooth muscle cells (pointer).

Vas deferens (D-65)
The vas deferens contains three distinguishable layers of smooth muscle. The inner and outer longitudinal layers are separated by a layer of circular smooth muscle (pointer).

Seminal vesicle (D-72)
The seminal vesicle is essentially a tube with an elaborate mucosa; the mucosa exhibits numerous folds which greatly increase secretory activity. The folds contain substantial amounts of smooth muscle, found in the lamina propria (pointer).

Prostate (D-70)
The prostate contains compound alveolar glands; unlike the seminal vesicle, it is not structured like a hollow tube. However, the secretory epithelium of the glands bear a resemblance to that seen in the seminal vesicle - in both, the epithelial cells are pseudostratified columnar, and also in both, smooth muscle can be seen in the lamina propria. One major difference is the presence of concretions in alveolar ducts of the prostate (pointer), which are solidified accumulations of prostatic secretion.

20 Digestive system

D-101 Esophagus:

LEFT: Muscularis mucosa

The esophagus has the same basic wall structure as the rest of the GI tract, but the layers are less sharply bounded. The pointer indicates the muscularis mucosa. It actually has two components, a circular and a longitudinal muscle layer. The muscularis mucosa is always made out of smooth muscle even though the muscularis externa changes from smooth muscle to skeletal as it descends.

Where would the lamina propria be? How thick is it?

* *

RIGHT: Muscularis externa

The esophagus is interesting in being one of the few places where one can find interlacing smooth and skeletal muscle fibers. The myenteric plexus extends throughout the GI tract and its representation in the esophagus is visible at the pointer.

* *

Stomach

LEFT: D-103 Monkey H+E

The mucosal glands of the stomach have a simple tubular configuration. They contain a variety of cell types: mucous cells, parietal cells (red, at the pointer), hormone- producing cells of the DNES system, stem cells, and chief cells (at the base of the glands). The chief cells (at pointer) produce digestive enzymes. Therefore they have basophilic cytoplasm and secretory granules in their apical portions. These granules often are not preserved, in which case the cells look empty or foamy in their top parts, instead of showing eosinophilic granules.

The location of the muscularis mucosa near the ends of the glands show that the glands fill the lamina propria of the stomach.

RIGHT: Surface of the stomach

The surface of the stomach is lined with mucous cells. They show up especially well when stained for carbohydrate with PAS. The mucosa is thrown into wrinkles called rugae, too big to be seen in the field of the microscope. These wrinkles flatten out when the stomach is distended with food. Smaller crevices, called pits are seen at the microscopic level. They are permanent features and, of course, lined with sheets of mucus cap cells. The mucosal glands empty at the base of the glands. PAS allows you to easily see the scattered mucus neck cells stained magenta, in the upper portions of the glands.

* *

Duodenum:

RIGHT: Plicae vs villi

You have looked at this slide for a variety of histological structures during the quarter: simple columnar epithelium, smooth muscle, myenteric plexus, cellular connective tissue. You should have no trouble seeing the individual components by now. Make sure, however, that you understand, and can identify, the difference between plicae and villi. In this low power view you can see that the villi are finger-like projections of lamina propria covered with epithelium, whereas the plicae are circular folds in the submucosa covered with mucosa (including villi). It is easy to tell the lamina propria from submucosa because the former is highly cellular, due to an influx of protective lymphatic and blood cells, while the submucosa is a more ordinary pink-staining C.T. layer.

LEFT: Brunner's glands

Brunner's glands are large, compound mucous glands that occupy the submucosa and lamina propria of the upper part of the duodenum. In other words it does not respect the muscularis mucosa, which can be seen as a thin invaded sheet of smooth muscle within the mass of the gland (at pointer). Submucosal glands are found in only one other part of the GI tract: which is it?

This slide is the junction between the stomach and the small intestine. The best way to tell which tissue is which is by the location of Brunner's glands. This is because the gastric glands in this region are only mucus-producing and hence less distinctive and the plicae and villi of the duodenum at the junction are poorly developed.

* *

Duodenum, crypts of Lieberkühn

The surface of the duodenum has finger-like projections sticking out and simple coiled tubular glands dipping inwards. In a well oriented section cut perpendicular to the surface it is a bit tricky to tell where the surface is and what is extending outwards and what inwards. The pointer is on that boundary. The epithelial lined tubes descending below the pointer are "mucosal glands of the duodenum" or, as a synonym, "crypts of Lieberkühn". These glands have two major functions. They are the birth place for epithelial cells which migrate out of the crypts, move to the tips of the villi and there are shed. The Paneth cells at the bottom ends of the glands secrete proteins (mainly lysozyme). Most of the digestive enzymes of the duodenum are secreted by the pancreas.

If the section had been oblique or cut parallel to the surface then a cut through the villi would look like:

- DRAWING -

and where the section went through the lamina propria it would appear as:

- DRAWING -

* *

Colon

LEFT: mucosa

The mucosa of the colon has a smooth epithelial lining with many goblet cells. Simple tubular glands dip in from that surface into the lamina propria. They also contain goblet cells.

RIGHT: muscularis externa

The main specialization of the muscularis externa of the colon is the concentration of the outer longitudinal fibers into three bands ("taenia coli") that run longitudinally along the colon. They serve to contract the length of the colon in an accordion-like way.

21 Liver and Pancreas

Liver (D-118)
The phagocytic Kupffer cells have taken up trypan blue granules and are easily seen lining the liver sinusoids. Note that the endothelial cells lining the sinusoids have not taken up the blue dye.

Liver (D-119)
This is a section of liver that exhibits a portal area. Note the presence of (1) a portal vein, (2) a hepatic artery, and (3) a lymphatic vessel.

Pancreas (D-121)
The large pancreatic acinar cells have lots of zymogen granules near their apex and are easily distinguished from the flattened centro-acinar cells that line the beginning of the duct through which pancreatic secretions will pass.

Pancreas (D-123)
The endocrine cells of the pancreas contain insulin (produced by beta cells) and glucagon (produced by alpha cells). These cells are found in the islets of Langerhans.

22 Oral Cavity

H-86 Lip

LEFT: Transition between the vermilion border and the (external) cutaneous area.

RIGHT: Transition between the vermilion border and the oral mucosa.

As you can see these transitions are gradual.

* *

Papillae of the tongue

The pointer is on a fungiform papilla. The surrounding papillae are fusiform.

* *

Circumvallate papilla.

RIGHT; low power

Here you can see the cleft that surrounds these papillae. Serous glands, the glands of Von Ebner (indicated by the pointer) lie below the papillae and empty into the trench around it.

LEFT; high pwoer

Taste buds line the sides of the circumvallate papillae. They extend through the thickness of the epithelium. Several types of cells make up the taste bud, e.g. hair cells and supporting cells but they are indistinguishable in your slides.

23 Tooth and Gingiva

Tooth and Gingiva

Dentinoenamel junction, ground tooth (D-154)
Which tissue shown here is dentin and which is enamel?

Do the enamel rods run perpendicular to the DEJ?

Do the dentinal tubules run perpendicular to the DEJ?

How would you describe the contour of the DEJ?

Enamel rods, ground tooth (D-154)
The unit of structure of enamel is a prism-shaped "enamel rod." Each ameloblast deposits one rod as it moves back from the dentinoenamel junction to the final outer surface of the enamel. In some places, the rods are nicely lined up in parallel. In others, notably in the complexly shaped crowns of molars, the rods are more irregular in orientation. These regions of "gnarled enamel" are especially hard, a characteristic of greater importance to dental students in the olds days of low speed drills.

Contour lines of Owen and stria of Retzius, ground tooth (D-154)
The pointer indicates a contour line of Owen, created as dentin grows. The line shows up because the density of the dentin varies slightly in its composition. Note that the contour lines of Owen run perpendicular to the dentinotubules. The corresponding stria of Retzius generally are easier to see; these are created as enamel grows.

Which of these lines run parallel to the DEJ?

Which run perpendicular to the surface of the tooth?

Dentinal tubules, ground tooth (D-154)
Dentinal tubules show up in ground sections because they are hollow. Light coming through the tissue gets deflected at air-mineral interfaces; therefore, the tubules appear black. Furthermore, this ground piece of tooth was attached to the slide with a liquid embedding material that seeped into some of the tubules and decreased the optical difference between the tubular lumen and the surrounding matrix. Thus, the tubules show up better in some places than in others. Cementocytes also vary in their visibility for the same reason.

Secondary or cellular cementum, ground tooth (D-154)
Where is secondary cementum typically found on a tooth?

Are cementocytes visible in this preparation? Look carefully to determine if you can see any cells here.

Which cells deposit secondary cementum?

Primary or acellular cementum, decalcified tooth (D-158)
A thin layer of primary or acellular cementum covers the entire surface of the roots of teeth. It has no embedded cementocytes.

How does cementum differ in appearance from dentin?

How thick is the layer of cementum that you see?

What is the function of primary cementum?

Pulp chamber, decalcified tooth (D-158)
The pointer indicates a layer of odontoblasts.
What two functions do these cells have?
Do these cells form an epithelium?

A layer of predentin several microns thick covers the dentin surface.
Does the predentin stain more palely than the dentin?
Do dentinal tubules run through the predentin?

The numerous blood vessels of the pulp can also be seen here.
How would you describe the tissue that forms the pulp?

Dentinal tubules, decalcified tooth (D-158)
Dentinal tubules are "tunnels" that house a small extension of an odontoblast. The tubules show up as parallel, curved lines when cut longitudinally (pointer, left) and as regularly spaced round holes in sections cut parallel to the surface of the dentin (cross section, pointer, right).

Periodontal ligament, decalcified tooth (D-158)
The periodontal ligament (pointer) attaches the tooth to the alveolar bone. The individual collagen fibers run through the cementum and embed into the bone as Sharpey's fibers. The ligament is highly vascular, much more so than most ligaments.

Gingiva, decalcified tooth (D-158)
Enamel has so little organic material that when it is decalcified, nothing is left to stain. The "enamel space" is visible, the region where tooth enamel used to occupy. In contrast, dentin shows up well because it has significant amounts of organic material (mainly type I collagen).

The gingival crevice lies between the enamel and the epithelium of the gingiva. It sometimes contains debris that shows up in the section.

Along the attached and free gingiva, the epithelium is keratinized. However, it is not keratinized in the sulcus. Determine which epithelial cells were part of the epithelial attachment; this part of the epiuthelium is called "junctional epithelium." The epithelial attachment is an extremely important barrier to protect deeper tissues.