Dr. Randall E. Merchant rmerchan@vcu.edu

GLANDULAR EPITHELIAL TISSUES

OBJECTIVES 1. Identify exocrine glands and their structures at the light microscopic level 2. Classify glands according to: - product distribution - morphology - mode of release of secretory product - type of secretory product 3. Describe the structure of a compound gland

I. Glands

A. General features and functions

1. Originate from lining epithelial cells that penetrate the connective tissue and form secretory units

2. Composed of epithelial cells specialized to synthesize and secrete a specific product 3. Classifications based on product distribution, structure, type of secretion, and mode of

secretion

B. Product distribution

1. Endocrine -lack ducts and, therefore, secrete their products (hormones) into the connective tissue -some hormones eventually enter the bloodstream in order to reach their target cells - some hormones affect cells within the same epithelium (i.e. paracrine)

• unicellular gland cells occur is some epithelia

• multicellular glands composed of secretory (parenchymal) cells and supportive (stromal) cells

2. Exocrine -secrete their products onto surface via ducts

• ducts formed by epithelial cells

• ducts may simply conveyor modify the secretion by adding to or concentrating it

• individual gland cells show polarized distribution of organelles

C. Structure

1. Unicellular - secretory component consists of single cells among non-secreting epithelial cells - e.g. goblet cells - secrete mucus

2. Multicellular - more than one cell with varying complexity, subclassified according to

arrangement of parenchymal cells and ducts

• sheet gland -simplest arrangement, all cells secretory

• ducts - simple (unbranched) or compound (branched)

• secretory unit of the gland:

• tubular - secretory cells arranged as a tube that is straight, branched, or coiled

• acinar (alveolar) - secretory cells arranged as a circle or flask

• tubuloacinar - secretory cells as a tubule that ends in a sac-like dilation

• examples (first named for duct and then by secretory unit): simple tubular, simple coiled tubular, simple branched tubular, simple branched acinar, compound acinar, compound tubuloacinar

3. Compound glands have a connective tissue capsule and septa that subdivide the gland into lobes and lobules

• intralobular ducts -within a lobule

• interlobular ducts -receive numerous intralobular ducts and exit from the lobule surrounded by CT

• interlobar ducts -receive interlobular ducts, in CT between lobes

• one or more excretory ducts drain entire gland 4. Special features of some exocrine glands

Serous demilunes - consists of a “cap” of serous cells around the end of a mucous tubule; appear half-moon shaped in section

Myoepithelial cells - resemble smooth muscle cells in their fine structure but are of

epithelial origin; prominent in sweat and mammary glands, they surround secretory units and aid in the expulsion of secretory products from the gland

Interlobular duct

D. Type of secretion

1. Exocrine • mucous - viscous glycoprotein secretion, functions to protect and lubricate • serous - watery secretion, often rich in enzymes and ions • lipids - oily secretion (sebum) from sebaceous glands and lipid portion of milk in

mammary gland • cerumen - a waxy material formed by the combination of the secretory products of

sebaceous and cerumenous gland with desquamated epidermal cells in the auditory canal

2. Endocrine

• polypeptide or amino acid derivatives • steroid

E. Mode of secretion

1. Merocrine (eccrine) -product released by exocytosis

2. Apocrine -where part of the apical cytoplasm is released along with the secretory product

3. Holocrine -where the entire cell (may be dead or alive) and it's contents are

released 4. Diffusion - secretory product passes through the cell membrane without the formation of secretory granules. Examples are steroid hormones. This method of release is used by endocrine glands only.

Glandular Epithelial Tissues Laboratory You are responsible for identifying the following structures in the “Digital Histology” CD package. Goblet cell Mucigen Sheet gland Simple tubular gland Simple branched tubular gland Body of gland Duct Gastric pit Simple coiled tubular gland Duct Myoepithelial cell Secretory portion Simple branched alveolar gland Acinus (alveolus) Duct Compound acinar gland Interlobular connective tissue Interlobular duct Intralobular connective tissue Intralobular duct Lobule Secretory granule Serous acinus Basal rough endoplasmic reticulum Secretory granules Compound tubulo-alveolar gland Interlobular connective tissue Interlobular duct Intralobular duct Lobule Mucus-secreting tubule Secretory granule Serous acinus (alveolus) Serous demilune