Define gland
an epithelial cell or collection of cells specialised for secretion`
How can glands be classified?
Destination of secretion
Structure of the gland
Nature of the secretion
Method of discharge.
Define exocrine
A gland with ducts
Define endocrine
A ‘ductless gland’ that secretes directly into the blood
How can you classify glands by structure?
unicellular/multicellular
coiled/branched
Define mucous glands
Secretions contain mucus, rich in mucins (highly glycosylated polypeptides). Such cells stain poorly in H&E sections.
Define serous glands
Secretions (often enzymes) are watery and free of mucus. Eosinophilic (pink) in H&E sections.
What are the modes of secretion?
- Merocrine
- Apocrine
- Holocrine
How does Merocine secretion work? (exocytosis)
- Membrane bound vesicle approaches cell surface
- Vesicle fuses with plasma membrane
- Contents of vesicle are in continuity with the extracellular space
- Plasma membrane is very slightly larger
- Membrane retrieved, stabilising cell surface area
How does Apocrine secretion work?
- Non-membrane bound structure (e.g. a lipid) approaches cell surface
- Makes contact and pushes up apical membrane
- Thin layer of apical cytoplasm drapes around droplet
- Membrane surrounding droplet pinches off from cell
- Plasma membrane is very slightly smaller
- Membrane added to regain original surface area
How does Holocrine secretion work?
- Disintegration of the entire cell
- Release of contents
- Discharge of the whole cell
Define endocytosis
Endocytosis is the process of engulfing material initially outside the cell. It is the opposite of exocytosis (merocrine secretion). Endo/Exocytosis are coupled in transepithelial transport.
Define transepithelial transport
- Material is endocytosed at one surface of the cell
- The transport vesicle shuttles it across the cytoplasm
- The material/vesicle is then exocytosed at the opposite surface.
What is the structure of the golgi apparatus?
- Stack of disc-shaped cisternae
- One side of the discs are flattened, other side is concave
- Discs have swelling at their edges (Vesicles that bud off)
- Distal swellings pinch off as migratory Golgi Vacuoles
What is the function of the golgi apparatus?
- Sorting into different compartments
- Packaging through condensation of contents
- Adding sugars to proteins and lipids (Glycosylation)
- Transport
What are the possible destinations of products of the golgi apparatus
- Majority extruded in secretory vesicles
- Some retained for use in the cells (eg lysosomes)
- Some enter the plasma membrane (Glycocalyx)
What mechanisms can control secretion?
Nervous
Endocrine
Neuro-endocrine
Negative feedback
