Neurobiology 104                           October 24, 2003

 

 

General Terminology for Organs

 

Histologists use some special terms to describe the general

organization and features of organs.  Here is a list of such

words.  Sometimes the structure alluded to may have a special name in the case of a particular organ.  For example, the adventitia of a muscle is called the epimysium.

 

   = indicates synonyms.

 

   ~ indicates terms with similar meanings, but

customarily used for only certain organs.

 

 

 

­Adventitia­ ~ ­Fibrosa­ ~ ­Capsule­

 

     Layer of dense connective tissue surrounding an organ.

 

 

­Septum­

 

A thin sheet of tissue (esp. C.T.) that separates organs or parts of organs.

 

 

­Trabeculum­ ~ ­Spicule­

 

     A finger-like projection of tissue.  Spicule is

     usually used only for a sliver of hard tissue.

 

 

­Cord­

 

     Tissue which gives the impression of a column of

     material or cells in a section, even though its actual

     3-dimensional geometry may quite different.

 

 

­Hilus­ = ­Root­ ~ ­Pelvis­

 

A localized region where the blood vessels, nerves, etc. enter and leave an organ.

 

 

­Afferent­ / ­Efferent­

 

     Afferent means going towards   (­A­rriving).

     Efferent means going away from (­E­xiting).

 

 

Cortex­ vs ­medulla­

 

     The outer and inner regions of parenchyma of an organ,

     respectively, when they are distinctive.

 

 

­Lobe­ vs ­Lobule­

 

     Lobes are grossly visible subunits organs. 

 

Lobules are microscopic repeating subunits of an organ,

generally demarcated by surrounding C.T. Lobules usually represent units of structure and of function,

for vasculature, drainage, etc.

 

 

­Intralobular­ / ­Interlobular­

 

     Within a lobule / In the C.T. between lobules.

 

 

­Fascicle­

 

     A "bundle": Fascicles are subdivisions of elongated

     tissues, especially of nerves and muscles.

 

     A muscle may have several orders of fascicles.

 

 

­Endo...­ / ­Peri...­ / ­Epi...­

 

     Inner / surrounding / outer (upon)

 

The peri... may surround the epi... or vica versa.

 

 

­Fascia­

 

     A sheet of loose C.T. between two organs.

 

 

­Stroma­ / ­Parenchyma­

 

Stroma refers to the supporting or "house keeping" tissues of an organ (connective tissue, blood vessels, etc.) and    parenchyma to the specialized functional cells, typically epithelial.  The distinction between stroma and parenchyma may break down in organs composed entirely of connective tissue (thus, histologists speak of the "pulp" of the spleen instead of its "parenchyma".)

 

 

­Acinus­ ~ ­Alveolus­

 

     A swollen or round unit of secretory tissue at the end

of a narrower duct: The acinus of an acinar gland is the  smallest unit of secretory tissue secreting into its own terminal duct.  Alveolus often refers to units with a substantial lumen but in some cases (e.g. salivary glands) is used as a synonym for acinus.

 

 

­Stratum­ ~ ­Tunic­ ~ ­Layer­ ~ ­Zona­ ~ ­Theca­ ~ ­Lamina­

 

Various terms used for the individual tissue layers of an organ.  Particular terms usually are used for particular organs.

 

 

­Mucous membrane­ = ­Mucosa­

 

A wet epithelium together with its underlying connective tissue, and covered by a layer of mucous secretion which drains, eventually, to the outside of the body.

 

 

­Lamina­ ­propria­

 

     The connective tissue located directly under a mucosal

     epithelium and specialized to support that epithelium.

 

 

­Submucosa­

 

The tissue, frequently also C.T., underlying a lamina  propria.  The submucosa is not specialized to support the function of the local epithelium directly above it. Large glands, larger arteries and veins, and so forth are usually located in the submucosa.

 

 

­Serosa­

 

The outermost covering of an organ with a free surface in a body cavity.  It corresponds to an adventitia covered with a moist, smooth, slippery, simple squamous epithelium.

 

 

­Mesothelium­

 

     The simple epithelium of a serosa, usually squamous.

 

 

­Peritoneum­

 

     The serosa that lines the body cavity and the organs

     within that cavity.  It consists of mesothelium and an

underlying layer of C.T.  The serosa lining the chambers for the heart and lung is call the pericardium and pleura, respectively.

 

 

­Visceral­ / ­Parietal­

 

Inner / Outer layer when a sheet of epithelium folds over on itself. (E.g. the visceral peritoneum lines the organs within the body cavity whereas the parietal peritoneum lines the walls of the body cavity.)

 

 

­Endothelium­

 

The simple epithelium that lines blood vessels, the heart, lymph vessels and certain other chambers considered to represent lymphatic spaces.

 

 

­Sinusoid­ ~ Sinus

 

     Sinusoids are irregular dilated venules or capillaries.

     They are composed of a layer of fenestrated endothelium

with gaps between the cells, and often are associated with    an abundance of macrophages.  The sinusoids of the liver and spleen are sometimes called sinuses.

 

Sinus can refer to various cavities, depressions or spaces that may or may not be entirely empty of cells.  A sunus may or may not be lined by endothelium or other epithelium.

 

 

 

­Circular­, ­Oblique,­ ­Longitudinal­

 

Orientations of elongated structures (e.g. smooth muscle cells) in the walls of a tubular organ.

 

 

­Transverse­, ­Oblique­, ­Longitudinal­

 

Orientations of the plane of section of an elongate

structure.

­

 

Interstitial­

 

     Tissue or structure situated in an interstice.  An

interstice is a region between one thing and another, especially between closely set parts of an organ, tissue or body.

 

 

­Anastomose­

 

     Branching and fusing into a network.

 

 

­Plexus

 

     An anastomosing tangle of blood vessels, nerves or such.

 

 

Fenestration­

 

     Small hole, pore or "window" in a structure.

 

 

­Fiber­

 

A term for various greatly elongated structures.

 

          A muscle fiber is an elongated muscle cell.

          A collagen fiber is an extracellular protein cord.

          A nerve fiber is an axon in its sheath.

          A lens fiber is an elongated, dead cell remnant.

 

 

­Process­

 

     A narrow extension of a cell or tissue.

 

 

 

 

Some other prefixes denoting relationships between parts:

 

  Extra / endo     outside of / within

  Post / pre~pro   after / before

  meta             beside

  para             opposite

  sub/supra        below/above

         

 

 

 

 

Certain word roots refer to particular tissues or organs

 

 

Sarco, myo       muscle

cardia           heart

adeno            gland

myelo            bone marrow

hemo, hemato     blood

chondro          cartilage

osteo            bone

renal            kidney

pulmonary        lung

gastric          stomach

hepato           liver

lingual          tongue

 

 

 

Several other potential causes of confusion are:

 

1. Structures named from both light microscopy and E.M.

 

   Both names may refer to exactly the same structure:

 

       junctional complex / terminal bar

       Nissl substance of neurons / rough E.R.

 

   or the E.M. term may refer to a crucial, small feature

   within the structure seen by light microscopy:

 

       basement membrane / basal lamina

 

2. Basophilic / acidophilic

 

A basophilic structure has material that picks up hematoxylin dye and therefore has a bluish tinge with H+E regardless of whether or not it also has acidophilic material that attracts the eosin dye.

 

3. Tissues within tissues

 

Connective tissue is a component of muscle tissue.

 

Mesothelium and endothelium are epithelia of connective tissue.

 

4. Be careful not to confuse the nucleus of a cell with a cell under the microscope.