Week 5: Epithelium 3 - Gland Development Flashcards
What is a gland?
A gland is an epithelial cell or group of cells that produce and release a secretion that differs in composition from tissue fluid or blood.
What is the difference between exocrine and endocrine glands?
Exocrine:
- Release secretions onto a surface
- All exocrine glands have ducts (dedicated channels)
Endocrine:
- Release their secretions (hormones) into blood capillaries. Hormones = chemical messenger that triggers a physiological response in specific target cells, often distant form the endocrine cell.
- No ducts
What type of glands exist?
- endocrine
- exocrine
- unicellular
Describe the formation of exocrine glands.
Cells from surface epithelium divide and invaginate downwards, growing down into underlying tissue. Connecting cells persist to form a duct, and the deepest cells become secretory
Describe the structure of exocrine glands.
Secretory portion/ units contain cells specialised for secretion. Ducts transport secretion out of gland.
Describe the formation of endocrine glands.
Cells from surface epithelium grow down into underlying tissue, connecting cells disappear, deepest cells remain to secrete into capillaries.
What are unicellular glands?
Cells within a surface epithelium e.g., goblet cells in epithelium lining of the respiratory and intestinal tracts.
What are the types of exocrine glands?
Exocrine glands have ducts.
- Simple unbranched glands: unbranched duct, e.g., gastric gland (simple tubular), sweat gland, sebaceous gland (simple acinus
- Compound glands: branched duct system
What are the shapes of exocrine glands?
Acinus/ alveolus
- Secretory unit ‘grape’ shaped
- Located distal to (at ends of) duct system
- Cells usually pyramidal (broad base, close to CT, narrow apex near lumen)
Secretory tubule
- Secretory cells line a tube, e.g., sweat glands, crypts in colon
- Cells are likely to be cuboidal or columnar rather than pyramidal
Describe the structure of compound glands.
Secretory cells form acini that occur in clusters/ clumps = lobule.
Secretory cells and acini need:
- A duct system to convey secretion
- A blood supply for nourishment
- Nerves and/ or blood supply for control of secretion release
- CT spatially supports the secretory cells/ acini, blood vessels, nerves and ducts
- CT septa surround lobules and CT capsule surrounds gland
Cells of secretory units show polarity. A secretory unit = acinus (plural = acini)
What are the features of acini? What types of secretions do they produce.
The appearance of secretory cells is related to the secretion produced. E.g., in the digestive system and respiratory system, acini produce either mucous secretions from mucous acini, or serous secretions from serous acini.
What are myoepithelial cells and what are their role?
- Epithelial cell with muscle-like contractile properties
- Located between secretory cells and the basal lamina
- Basket like arrangement
- Important in controlling timing of secretion release (e.g., saliva, sweat, milk) from a gland
- Contraction triggered by hormones and/ or nervous system
What are the methods of secretions from secretary epithelial cells?
- Merocrine
- Apocrine
- Holocrine
What is merocrine release of secretions?
Only the secretion is released from the cel, via eccrine secretion or exocytosis
This is the mode of release used by most exocrine and endocrine glands
What is apocrine secretion?
Secretion and some cytoplasm is lost.
E.g., secretion of lipid in mammary glands; apocrine sweat glands, lipid is not surrounded by a membrane, hence exocytosis is not possible
