P104 Histology and Cell Biology Read G&H p 102-108

October 9, 2003

GLANDS

A gland is an epithelial organ which secretes a specific material

Glands:

develop by invagination of a surface epithelium (or neurocrest cells) into the underlying connective tissue.

are numerous, important and diverse.

are classified according to their function and structure.

Cells of exocrine glands secrete apically into a free space

Most exocrine glands secrete thorough a duct.

Cells of endocrine glands secrete basally into the blood.

Endocrine glands are ductless.

Some glands are both endocrine and exocrine, eg liver, stomach.

Today’s lecture concerns only exocrine glands

See G&H Fig. 5-23

Exocrine glands are classified according to:

1. The structure of their ducts and secretory portions.

compound if their ducts branch vs simple if they do not.

branched if their secretory portions branch vs unbranched.

acinar (~ alveolar) if their secretory portions are enlarged

rounded masses at the ends of the ducts.

tubular if their secretory portions are elongated

(most compound glands are “tubuloacinar”).

“Primitive” exocrine glands lie in covering epithelia.

intraepithelial glands, unicellular glands,

secretory epithelium

2. Their type of secretion

Mucous glands/cell s produce a gooey solution with mucus.

Serous glands/cells produce of a watery solution

Most glands which secrete specific proteins are serous

and release the proteins in a watery solution.

Mixed glands contain both serous and mucous cells.

Other secretions such as sebum, lie outside of this scheme

IT IS ESSENTIAL TO BE ABLE TO DISTINGUISH MUCOUS

FROM SEROUS CELLS UNDER THE MICROSCOPE.

_________

Essential terms are in bold type

Glands are named in various ways

(alternative names are equally acceptable.)

1. By organ

If an organ has only one type of gland people speak of the

glands of that organ.

e.g. esophageal glands, uterine glands.

2. By specific name.

e.g. crypts of Lieberkühn, Brunner’s glands

3. By location in an organ

e.g. mucosal glands, submucosal glands

A mucosa includes a wet epithelium and its lamina propria

A submucosa is the layer of C.T. under a mucosa.

The lamina propria is specialized to support the

overlying epithelium. The submucosa is not.

In general

Mucosal glands are small and often lack ducts.

Larger glands lie deeper in the submucosa and do have ducts.

Very large glands may protrude all of the way through the

wall of the organ and form an external glandular organ

with a connecting duct.

4. Some organs fundamentally are glands but are not call glands

e.g. lung, kidney

Ducts are named in three ways.

1. by location

especially intralobular vs interlobular

Lobules are clusters of secretory units that drain through

a single duct. They usually are separated from one another

by sheets of (interlobular) connective tissue.

2. by structure/function

e.g. excretory ducts (with only a conveyance function),

secretory ducts, intercalated ducts

3. by specific names

especially for ducts connecting an outside gland to an organ

e.g. Stensen’s duct, common bile duct, vas deferens

Functions of Glands

1. Secretion

Cells of glands secrete in three ways:

Eccrine = merocrine

The secretory product is packaged in secretory granules

which fuse with the cell membrane to release their contents.

Holocrine

The cell lyses and the entire contents become the secretion.

Sebaceous glands are the only example in humans.

Apocrine

The apical portion of the cell is released as the secretory product but the rest of the cell survives.

A number of supposed apocrine cells turn out, upon

examination with the EM, actually to be merocrine.

Various glands have myoepithelial cells to squeeze secretions

from their secretory units.

Read G+H p 154, Figs 5-24,25.

Myoepithelial cells come embryonically from the epithelium

and lie within the basement membrane around the gland.

2. Cytogenesis

Glands may house the stem cells or reserve stem cells for an epithelium.

e.g. Crypts of Lieberkuhn, uterine glands, sweat glands

3. “Social” functions

e.g. lacrimal (tear) gland, breast, apocrine sweat gland

Functions of Ducts

1. Conveyance of secretions to the surface

This is function of all ducts.

2. Secretion or modification of the secretion

e.g. sweat gland, salivary gland

3. Storage of secretion for periodic release

e.g. prostate, mammary gland