Histology: Secretory Epithelia & Glands

• Unit 2 focuses on Epithelial Tissue in Human Histology.
• UST General Santos - School of Health Sciences, Department of Medical Technology, 2nd Semester A.Y. 2024-2025

Course Content

• Epithelial Cells
• Epithelial Domains
• Covering or Lining Epithelia
• Secretory Epithelia and Glands
• Transport Across Epithelia
• Renewal of Epithelial Cells

Unit Intended Learning Outcome

• Differentiate the different types of secretory epithelia based on their structure and the products they secrete.

Secretory Epithelia

• Epithelial cells produce and secrete macromolecules. These cells may occur in epithelia with other major jobs or specialized organs called glands.
• Secretory cells synthesize, store, and release macromolecules.
• They also secrete water and electrolytes.
• Unicellular glands and scattered secretory cells are common in simple cuboidal, simple columnar, and pseudostratified epithelium.

Exocrine Glands

• Are formed from covering epithelia.
• These glands are classified as simple or compound based on duct branching and further classified by the shape of their secretory units (tubular, acinar/alveolar, tubuloacinar).

Simple Glands

• Have unbranched ducts.
• Simple tubular glands feature elongated secretory portions.
• These ducts are usually short or absent and can be found, for example, in the mucous glands of the colon, intestinal glands, or crypts of Lieberkühn.
• Branched tubular glands have several long secretory parts that join to drain into one duct.
• Coiled tubular glands has a secretory portion that is very long and coiled.
• Acinar/Alveolar glands have round, sac-like secretory portions.
• Branched Acinar glands have multiple saclike secretory parts entering the same duct
• The multiple saclike secretory parts entering the same duct is commonly found in in sebaceous glands of the skin.

Compound Glands

• Ducts from several secretory units converge into larger ducts.
• Compound tubular glands feature several elongated coiled secretory units, and their ducts converge to form larger ducts. An example is the submucosal mucous glands.
• Compound acinar glands have several sac-like secretory units with small ducts converging at a larger duct. An example is the exocrine pancreas.
• Compound tubuloacinar glands have both tubular and acinar secretory units, and their ducts converge at larger ducts like salivary glands.

Exocrine Gland Secretion

• The three types of exocrine glad secretion are merocrine, holocrine and apocrine.
• Merocrine secretion involves exocytosis of secretory vesicles, leaving the cell intact.
• Holocrine secretion involves disintegration of cells with contents becoming the secretion.
• Apocrine secretion involves pinching off of the apical portion of secretory cells.
• Acne vulgaris arises from blocked ducts in sebaceous glands, resulting from excessive sebum and keratin production triggered by puberty's hormonal changes.

Exocrine Gland Secretions by type

• Mucous: Produces mucous
• Serous: Produces serous
• Seromucous or Mixed

Endocrine Glands

• Lack myoepithelial cells.
• They manufacture steroid or protein hormones.
• Proteins hormones use are released by exocytosis.
• Steroid hormones are released via diffusion through the cell membrane

Transport Across Epithelia

• Involves specific processes in all epithelial cells which permit transcellular transport of the ions and molecules, followed by their release into the intercellular space near capillaries

Epithelial Cell Renewal

• Most epithelial cells maintain a continuously renewing cell population.
• Others (more complex glands, liver) belong to a stable cell population with little mitotic activity, only dividing when stimulated by injury.
• Replacement cells are produced by mitotic activity of self-maintaining adult stem cells.

Learn about secretory epithelia, which produce and secrete macromolecules. Explore exocrine glands and their formation from covering epithelia. Understand the structure and function of these specialized epithelial tissues.