Anatomy and Human Biology2216 Prof. John Campbell

Anatomy and Human Biology2216 Prof. John Campbell

25 August, 2009

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 mucosa of the uterus is called the endometrium.

= indicates synonyms.

~ indicates terms with similar meanings, but

customarily used for only certain organs.

Epithelium (vs. Connective tissue, C.T.):

- covers surfaces.

- is polarized.

rests on a basement membrane.

has a free surface.

- has very little extracellular material.

- has no blood vessels.

- is continuous, with no edges.

epithelial cells are joined and act together.

Epithelia has no collagen.

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.

Laminapropria

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.

Adventitia ~ Fibrosa ~ Capsule

Layer of dense connective tissue surrounding an organ.

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.)

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.)

Stroma / Parenchyma

Stroma refers to the supporting or "house keeping" tissues of an organ (connective tissue, blood vessels, nerves, etc.)

Parenchyma refers to the specialized functional cells, typically epithelial.

(The distinction between stroma and parenchyma may break down in organs composed entirely of connective tissue.)

Lobe vs. Lobule

Lobes and lobules are subdivisions of organs. Lobes are grossly visible subunits. Lobules are microscopic repeating subunits. Lobules usually are demarcated by surrounding C.T. and 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.

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 implies a 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.

Cortex vs. medulla

The outer and inner regions of parenchyma of an organ, respectively, when they are distinctive.

Endo... / Peri... / Epi...

“Inner” / “surrounding” / “outer (upon)”

Beware, A peri... layer may surround the epi... or vice versa.

Circular, Oblique,Longitudinal

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

An oblique layer of muscle would spiral down the tubular structure.

Transverse, Oblique, Longitudinal

Orientations of the plane of section of an elongate

structure on a microscope slide.

Be aware that a longitudinal layer of muscle can be cut transversely or that an oblique layer might be sectioned longitudinally

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.

Hilum = Root ~ Pelvis

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

Afferent / Efferent

Afferent means going towards (Arriving).

Efferent means going away from (Exiting).

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. In particular, cords refer to tissue between enlarged capillaries or lymphatic channels.

Sinusoid ~ Sinus

Sinusoids are irregular, dilated venules or capillaries (venous sinusoids or sinusoidal capillaries). They are composed of a layer of fenestrated endothelium with gaps between the cells, and venous sinusoids usually are associated with abundant 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 sinus may or may not be lined by endothelium or other epithelium.

Anastomose

Branching and fusing into a network.

Plexus

An anastomosing tangle of blood vessels, nerves or whatever.

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.

The suffixes “blast” and “cyte” for a cell type

examples: erythroblast erythrocyte and osteoblast osteocyte

The suffix blast refers to a precursor stage to a more differentiated or fully differentiated cell type.

Typically a “blast cell” actively synthesizes proteins and is capable of division. The “cyte” stage is less active and may be incapable or restricted in its capability to divide. There are exceptions to these generalizations.

A variety of prefixes denote relationships between parts:

Extra / endooutside of / within

Post / pre~proafter / before

metabeside

paraopposite

sub/suprabelow/above

Certain word roots refer to particular tissues or organs

Sarco, myomuscle

cardiaheart

adenogland

myelobone marrow

hemo, hematoblood

chondrocartilage

osteobone

renalkidney

pulmonarylung

gastricstomach

hepatoliver

lingualtongue

Some basics of histological staining

Stains are crucial to histology. Tissue sections are cut so thin for microscopy that they are transparent. Features can be visualized only be absorbing dye molecules onto them. What you see then is actually the dye itself instead of the proteins, mitochondria etc. directly.

Stains range widely in what they will bind to and in color. Some will absorb only to carbohydrates or to lipids or to collagen. Others bind to a wide range of components of a cell. In addition, a tissue can be doubly stained with two dyes of different specificity and color.

It turns out that the most generally useful dye regime is to stain with an acidic dye (which absorbs to base molecules) and with a basic dye for acidic components.

By convention, the acidic dyes used for histology are red to orange in color and the basic dyes purple to blue. the most common pair of dyes is hematoxylin and eosin.

Hematoxylin Basic dye Blue Stains especially nucleic acids

Eosin Acidic dye Red Stains especially proteins

Structures which absorb basic dyes are referred to as basophilic (“base-loving”) Those which absorb acidic stains are acidophilic. The terms basophilic and acidophilic are used so frequently that you should make sure to be comfortable with them.

Basophilic structures stain purple and are most importantly RNA, DNA, cell nuclei. Acidophilic structures stain red and most importantly are proteins and cytoplasm. Eosin is such a standard acidic dye that the term eosinophilic is often used as a synonym for acidophilic.

Do not let the following three deficiencies in terminology confuse you.

1. Structures may be named from both light microscopy and electron microscopy

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:

A basal lamina is a component of a basement membrane.

2. Many structures and cell types have two names. One is descriptive (e.g. myenteric plexus) and the other is a person’s name (Auerbach’s plexus, for the same structure). Histologists are trying to eliminate the use of personal names but many remain deeply entrenched.

3. There can be tissues within tissues, or organs within organs.

Connective tissue is an integral component of muscle tissue.

Mesothelium and endothelium are connective tissue epithelia.

Taste buds are called “organs” although they are parts of the tongue, which is also an “organ”.

1