Overview
This lecture explains the structure, classification, and secretion methods of glands, focusing on differences between endocrine and exocrine glands.
Gland Structure and Function
- Glands are organs or cells that secrete substances used by the body.
- Most glands are made of epithelial tissue.
- Glands secrete substances such as mucin, hormones, electrolytes, enzymes, and waste.
Classification of Glands
- Glands are divided into endocrine and exocrine types.
Endocrine Glands
- Endocrine glands secrete hormones directly into the bloodstream or interstitial fluid.
- Examples include the adrenal, thyroid, and pituitary glands.
Exocrine Glands
- Exocrine glands secrete products into ducts or onto surfaces, not into blood.
- Exocrine glands can be unicellular or multicellular.
Unicellular Exocrine Glands
- Do not contain ducts.
- Example: goblet cells secrete mucin to form a protective mucous layer.
Multicellular Exocrine Glands
- Contain a duct system.
- Classified by form and secretion method.
Forms of Multicellular Exocrine Glands
- Simple glands: single duct.
- Compound glands: branching ducts.
- Secretory portion can be tubular (uniform diameter) or acinar/alveolar (sac-like).
- Types: simple straight/coiled/branched tubular, simple/branched acinar, compound tubular, compound acinar, compound tubuloacinar.
Methods of Secretion
- Merocrine: secretion via exocytosis, cell remains intact (e.g., salivary glands).
- Apocrine: cell pinches off part to release products, cell repairs itself (e.g., mammary, some sweat glands).
- Holocrine: entire cell ruptures to release secretion, cells replaced by division (e.g., skin and eyelid glands).
Key Terms & Definitions
- Gland — organ or cell that secretes substances for use in the body.
- Endocrine gland — secretes hormones into blood or interstitial fluid.
- Exocrine gland — secretes products into ducts or onto surfaces.
- Mucin — substance secreted by goblet cells, forms mucus.
- Duct — tube that carries secretions from glands.
- Merocrine — secretion by exocytosis without cell damage.
- Apocrine — secretion by pinching off part of the cell.
- Holocrine — secretion by complete cell rupture.
Action Items / Next Steps
- Review the types and features of each gland classification.
- Prepare for future lectures on individual gland structure and function.