Histology 1.2 (glandular epithelium exocrine glands)

Glandular epithelium + types

Cells specialized to produce secretion (release of products by exocytosis)

2 types:

• Exocrine glands:

  • Excretory ducts that deliver to a specific site

  • Gland product is released on surface

• Endocrine glands:

  • Blood systematic circulation

  • Gland product is released in blood

6 Principles of Exocrine gland classification

1. Number of cells

2. Site of cells

3. Shape of the terminal secretory unit

4. Branching of the terminal secretory unit and collecting ducts

5. Modes of secretion

6. Nature of secretion

1. Number of cells:

• Unicellular

  • Ex. goblet cells (contain mucinogen droplets that +H2O = mucus)

    • Important because mucus produced protects organs such as small intestine

• Multicellular

  • Sweat and sebaceous glands (ex. skin, hair)

  • Intraepithelial glands in many organs (ex. uterus, urinary & respiratory tract)

  • Constitute separate organs (ex. pancreas, salivary and mammary gland)

2. Site of glands

Only applies to multicellular glands:

• Intramural glands

  • Within an epithelium, consist of a secretory unit and a excretory duct

• Extramural glands

  • Constitute a separate organ, (ex. pancreas)

3. Shape of terminal secretory duct (secretory unit)

Tubular gland (longer tube shape)

Alveolar gland (shorter, circular shape)

Methods of cutting tubules

Cross section — horizontal

Oblique section — diagonal

Longitudinal section — vertical

4. Branching of secretory units and collecting ducts

(secretory units attached to collecting ducts)

• Branching of secretory units

  • Simple (1 unit) (only in simple)

  • Simple branched

    • Do not mention in compound

• Branching of collecting ducts

  • Simple = no duct branch

  • Compound = 1+ duct branch

Overview of naming exocrine glands

Simple = 1 unit 1 duct

Simple Branched = 1+ units 1 duct

Compound = 1+ units 1+ ducts

5. Mode of secretion

• Merocrine

  • Thin granules are secreted from cell with cell remaining intact

• Apocrine

  • Portions/drops of the membrane are pinched off and released, with cell remaining otherwise intact

• Holocrine

  • The whole cell disintegrates and thus releases the product

  • Remaining cells divide to reconstitute the gland

6. Nature of secretion

• Serous

  • Usually merocrine secretion

  • Round structure, round nuclei

  • Mainly produces proteins

  • Watery fluid secretion

• Mucous

  • Usually apocrine secretion

  • Predominance of carbohydrates

  • Viscous secretion (thus elongated structure)

  • Everything is squeezed to the bottom because of mucinogen granules

• Mixed

  • Contains some cells producing proteins and other cells producing mucous

Serous nature of secretion

Mucous nature of secretion

Mixed nature of secretion (both mucous and serous)

Myoepithelium

Specialized squamous epithelial cells with power of contraction

• Surrounds glandular acini and ducts of many glands

• Contains actin, myosin, and cytokeratin

  • (Epithelial in origin, not muscle)

Pancreas

Endocrine (islets of Langerhans)

Exocrine pancreas:

• Produces digestive secretions that are discharged into the duodenum via an extensive system of ducts

• A compound tubulo-acinar gland composed of serous secretory cells

  • Groups of acini form lobules, which are separated by connective tissue

Pancreatic Acinus

Simplest secretory unit (a blind sac)

• Acinus lumen continues with a collecting duct called the intercalated duct

  • Smallest, continues to larger ducts in the lobule called striated ducts

    • Found in basal infoldings, mitochondria, and ion transporting cells (where they function to modify final electrolyte concentrations)

Lobule

Many acini and their ducts

• Many lobules form a lobe in the gland

  • Collecting ducts from multiple lobes join together in the major pancreatic duct — the Wirsung duct, which arrives in the duodenum

How to tell between serous or mucous in an image

Serous:

• Nuclei everywhere

Mucous:

• Nuclei are smushed against the membranes because they are pushed away by the mucinogen granules