Overview
This lecture covers the structure, types, and classification methods of glands, focusing on their composition, secretion mechanisms, and examples.
General Structure and Function of Glands
- Glands are organs or cells that produce and secrete substances for body use.
- Most glands consist of epithelial tissue.
- Glandular secretions include mucin, hormones, electrolytes, enzymes, and waste products.
Classification: Endocrine vs. Exocrine Glands
- Endocrine glands secrete hormones directly into the blood or interstitial fluid.
- Examples of endocrine glands: adrenal, thyroid, pituitary.
- Exocrine glands secrete products into ducts or onto external surfaces, not into the blood.
- Exocrine glands may be unicellular (no ducts) or multicellular (with ducts).
Unicellular and Multicellular Exocrine Glands
- Unicellular exocrine glands (e.g., goblet cells) secrete mucin and lack ducts.
- Goblet cells create mucus layers over tissues like the trachea.
- Multicellular exocrine glands have duct systems and can be classified by form or secretion method.
Classification by Gland Form
- Simple glands have a single duct; compound glands have branching ducts.
- Secretory portions can be tubular (uniform diameter) or acinar/alveolar (sac-shaped).
- Examples: simple straight tubular, coiled tubular, simple branched tubular (all one duct), simple acinar, simple branched acinar.
- Compound glands include compound tubular, compound acinar, and compound tubuloacinar (mixed tubular and acinar).
Classification by Secretion Method
- Merocrine glands release products via exocytosis without cell damage; example: salivary glands.
- Apocrine glands pinch off cell portions to release products; examples: mammary and some sweat glands.
- Holocrine glands release products by cell rupture and are replaced by new cells; examples: certain skin and eyelid glands.
Key Terms & Definitions
- Gland — Organ or cell that produces and releases substances.
- Epithelial tissue — Tissue type making up most glands.
- Endocrine gland — Gland releasing hormones into blood or interstitial fluid.
- Exocrine gland — Gland releasing products into ducts or onto surfaces.
- Unicellular gland — Single-cell gland, no ducts (e.g., goblet cell).
- Multicellular gland — Gland with multiple cells and duct(s).
- Simple gland — One duct.
- Compound gland — Branching ducts.
- Tubular — Uniform, tube-like secretory portion.
- Acinar/Alveolar — Sac-shaped secretory portion.
- Merocrine — Secretion via exocytosis.
- Apocrine — Secretion via pinched-off cell portions.
- Holocrine — Secretion via complete cell rupture.
Action Items / Next Steps
- Review the structure and functions of individual glands in future lectures or assigned readings.