Legends for the microscopic demonstrations
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 vs 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.
Location on marrow slides for viewing is crucial
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.
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The pointer is on a:
Mature acidophil
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Acidophilic myelocyte
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Basophilic myelocyte
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Neutrophilic metamyelocyte
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Mature neutrophil
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Myeloblast/Hemocytoblast
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Progranulocyte
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Basophilic erythroblast
(proerythroblast)
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Polychromatophilic
erythroblast
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Normoblast
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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.
8Skin
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.
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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.
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Node of Ranvier
Peripheral nerve, longitudinal section, Masson stain. tthe nuclei seen here are of Schwann cells, (of course).
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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?
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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.
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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?
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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.
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.
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
13Bone
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 OSTEOBLAST
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.
14 Respiratory System
nose
¯
larynx
¯
trachea
¯
bronchi
¯
respiratory bronchioles
¯
alveolar ducts
¯
alveolar sacs
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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 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).
17 Endocrine System
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
Upper esophagus (D-101)
The esophagus has the same basic wall structure as the rest of the gastrointestinal
tract but the layers are less sharply defined. The pointer indicates the muscularis
externa, which actually has two components (circular and longitudinal layers)
and consists primarily of skeletal muscle in the upper esophagus, gradually
converting to smooth muscle as the esophagus descends. In contrast, the muscularis
mucosa is composed of smooth muscle the entire length of the esophagus.
Esophagus (D-101)
The esophagus is one of the few places where interlacing smooth and skeletal
muscle fibers can be found. The myenteric plexus extends throughout the gastrointestinal
tract and its representation in the esophagus is visible at the pointer.
Stomach (D-103)
The mucosal glands of the stomach have a simple tubular configuration and exhibit
a variety of cell types: mucous cells, parietal cells (pointer), and chief cells
are only a few. Parietal cells secrete hydrochloric acid, which functions to
activate the digestive enzymes produced by chief cells. Chief cells contain
basophilic cytoplasm and secretory granules in their apical end. These granules
often are not preserved, giving the cells an empty or foamy appearance at their
apical end.
Stomach (D-104)
The surface of the stomach is lined with mucous cells that show up especially
well when stained for carbohydrate (PAS stain). The mucosa is thrown into wrinkles
called rugae; these are too big to be seen in the field. The rugae flatten out
when the stomach is distended with food.
Smaller crevices called pits can be seen, lined by sheets of mucous cap cells. The mucosal glands empty at the base of the glands. PAS allows you to easily see the mucous neck cells scattered in the upper portion of the glands.
Pyloric-duodenal junction (D-106)
Brunner's glands are large, compound mucous glands that occupy the submucosa
and lamina propria of the upper duodenum; Brunner's glands are not found in
the stomach. Thus, the best way to differentiate between the two organs is by
the presence of these glands The sphincter that marks the boundary between the
stomach and the duodenum is at the pointer.
Duodenum (D-107)
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. Make sure, however, that you understand and identify the
difference between plicae and villi. In this low power view you can see that
villi are finger-like projections of lamina propria covered with epithelium,
whereas plicae are circular folds in the submucosa covered by mucosa (which
includes villi). It is easy to differentiate between lamina propria and 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 layer
of connective tissue.
Duodenum (D-107)
The surface of the duodenum has finger-like projections sticking outward and
simple coiled tubular glands dipping inward. In a well-oriented section cut
perpendicular to the surface, it can be tricky to identify where the surface
is and what is extending outward vs. inward. Tubes that dip inward are mucosal
glands of the duodenum, also called crypts of Lieberkuhn. These glands have
two major functions: (1) they give rise to epithelial cells, which migrate out
of the crypts and up to the tips of villi, where they are shed; and (2) they
house Paneth cells which secrete proteins (mainly lysozymes). Paneth cells are
found at the bottom of the glands (pointer).
Appendix (D-111)
The appendix is an outpocketing from the large intestine and contains simple
glands with many goblet cells. It is specialized in having a large lymphatic
component in the lamina propria. Lymphatic nodules are evident, and lymphocytes
can be found throughout the mucosal connective tissue.
Colon (D-114)
The colon contains a specialization of the muscularis externa: outer longitudinal
fibers are concentrated into three bands called "taenia coli" (pointer).
They serve to contract the length of the colon in an accordion-like fashion.
Colon (D-114)
The mucosa of the colon has a smooth epithelial lining with many goblet cells.
Simple tubular glands (pointer) dip inward from the surface into the lamina
propria.
Ano-rectal junction (D-115)
The transition from the rectum to the anus is marked by an abrupt change in
the epithelial layer. The rectum exhibits simple columnar epithelium containing
the tubular infoldings of glands. The anus, however, exhibits non-keratinized
stratified squamous epithelium at its proximal end and keratinized epithelium
at its distal end.
.
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.
Lip (D-86)
The external surface of the lip is covered with skin while the inner surface
is covered with nonkeratinized, stratified squamous mucosa. The transition between
these surfaces is the vermilion border (aka the lips), which is very lightly
keratinized and especially well vascularized - this causes the vermilion border
to look reddish. The vermilion border lacks glands and requires the tongue to
keep it moistened.
Anterior tongue, musculature (D-93)
Most of the tongue is comprised of skeletal muscle. Note how muscle fascicles
are interlaced in three directions perpendicular to each other, giving almost
unlimited dexterity to this organ.
Posterior tongue, dorsal aspect (D-96)
Mucous glands frequently invade muscles in the posterior tongue. Note that the
epithelium is very lightly keratinized in this part of the tongue.
Lingual tonsils are a special feature, seen here at the surface. Crypts are less well developed in lingual tonsils than in palatine tonsils. Here the crypts are rudimentary because the section goes through only the edge of this tonsil. Notice that lymphocytes have invaded the basal part of the epithelium. Glands empty into the base of the crypts (pointer); their secretions keep the crypts flushed out to prevent infections and subsequent surgical removal.
Hard palate (D-91)
The oral and nasal cavities are separated from each other by the hard and soft
palates. While the soft palate is movable and consists mainly of skeletal muscle,
the hard palate is immovable and contains a bony shelf within. The hard palate
is located anterior to the soft palate.
The oral aspect of the hard palate is covered by stratified squamous keratinized epithelium overlying dense, irregular collagenous connective tissue. The nasal aspect is covered by a combination of respiratory epithelium (pseudostratified columnar) and stratified squamous nonkeratinized epithelium.
Parotid gland (D-126)
This branched, tubulo-acinar gland produces a primarily serous secretion. Its
salivary product contains the enzyme ptyalin, important for carbohydrate breakdown.
As with the submaxillary/submandibular and sublingual glands, the parotid is divided into lobules. Interlobular ducts are found between lobules while striated and intercalated ducts (pointer) are found within lobules.
Sublingual gland (D-129)
This branched, tubulo-acinar gland produces a primarily mucous secretion. Thus,
most of the cells contained within are mucous with only a few darker staining
serous demilunes.
As with the submaxillary/submandibular and parotid glands, the sublingual gland is divided into lobules. Interlobular ducts can be seen between lobules but there are few intralobular ducts (pointer). The intralobular ducts that are present have mainly an excretory function; striated ducts are uncommon and intercalated ducts are nonexistent in this gland.
Submaxillary/submandibular gland (D-128)
This branched, tubulo-acinar gland produces a mixed serous and mucous secretion.
Acini are formed by mucous cells accompanied by half-moon shaped serous cells
(serous demilunes).
As with the parotid and sublingual glands, the submaxillary gland is divided into lobules. Interlobular ducts are found between lobules while striated and intercalated ducts (pointer) are found within lobules.
Submaxillary/submandibular gland, PAS (D-127)
PAS emphasizes the mucous cells, seen here staining purple-red. The mucous cells
can be seen forming an acinus, where each mucous cell is capped by a palely
staining serous demilune (pointer).
Filiform papillae (D-94)
At the pointer is a filiform papilla, a slender structure covered by stratified
squamous keratinized epithelium. It functions to help scrape food off a surface
and imparts a sandpaper-like quality to the tongue of a cat, for instance.
Fungiform papillae (D-94)
At the pointer is a fungiform papilla, a mushroom-shaped structure covered by
stratified squamous nonkeratinized epithelium. The "mushroom cap"
contains taste buds.
Foliate papillae (D-95)
Foliate papillae are located between "trenches" into which the underlying
salivary glands of von Ebner release their products. Foliate papillae also contain
taste buds (pointer).
Circumvallate papillae (D-96)
Circumvallate papillae are covered by stratified squamous epithelium and contain
taste buds (pointer). Surrounding the papillae are "trenches" into
which the salivary glands of von Ebner release their products.
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.