Lecture 9: Glands introduction Flashcards
What is the definition of a gland?
An epithelial cell or an aggregate of epithelial cells that are specialised for the secretion of a substance
What are the 2 types of glands classified according to their structure?
Endocrine (ductless) and exocrine (ducted)
What is the meaning of an endocrine gland?
- Ductless
- Secrete directly into blood, to let the secretion function at distant parts of the body
- Secrete hormones
What is the meaning of an exocrine gland?
- Ducted
- Secrete into a location or a region of the body through a duct
- Secretions are mostly enzymes or lubricants
- Only cells at the apex of the duct secrete products
What are the types of glands according to modes of secretion?
- Merocrine
- Apocrine
- Holocrine
What is the meaning of a merocrine gland?
Mode of secretion: Fusion of vesicles with apical membrane
What is the meaning of a apocrine gland?
Mode of secretion: Partial loss of cytoplasm
What is the meaning of a holocrine gland?
Complete loss of cytoplasm or cell
What is the mechanism of merocrine secretion?
- Regulated Secreton
- Constitutive secretion
How does regulated merocrine secretion work?
Active process - uses energy
- Secretory granules accumulate in large vesicles
- Active secretion requires signal or simulation( Ca2+)
- Vesicles migrate to cell surface along microtubules by using energy
- In presence of Ca2+ ions, membrane of vesicles fuses with plasmalemma
- Contents are released to extracellular space
- Membrane of vesicles fuses with plasma membrane
How does constitutive merocrine secretion work?
- Secretory product packaged into small vesicles
- Continuously released to the cell surface
- Membranes of vesicles fuses with plasma membrane
How does apocrine secretion work?
- Non-membrane bounded structure 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 transiently smaller
How does holocrine secretion work?
- Secretory cell gradually fills up with secretory granules
- Cell organelles degenerate
- Cells die
- Plasma membrane breaks and contents are released
What are the mechanisms of endocytosis?
- Engulfing of molecules inside the cell via vesicles formation
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
What is the mechanism of phagocytosis?
- Cells (phagocytes) uses pseudopodium to envelop or engulf other cells or particles
- Mainly used by cells of the immune system
What is the mechanism of pinocytosis?
- Process by which liquid droplets are ingested by cells
- Used by all cells, especially smooth muscle cells
What are the types of transepithelial transport?
- Paracellular transport - molecules move through aqueous channels in the intercellular junction
- Transcellular transport - molecules move through lipid cell membranes
- Molecules with appropriate characteristics may be transported by carrier proteins into or out of the cells or by a counter-transport process
- Molecules that are impermeable can bind to cell surface receptors, and engulfed by the cell by endocytosis and then released inside the cell OR expelled by exocytosis
What is the mechanism of glycolysation of newly synthesised proteins in the Golgi apparatus?
- Covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids
What is the importance of glycolysation of proteins?
- Aid protein folding
- Prevents protein digestion by intracellular proteases
- Prevents lipid digestion by intracellular proteases
- Cell recognition (blood groups)
- Role on cell to extracellular matrix attachment
Important function of the biosynthesis-secretory pathway in the ER and Golgi apparatus
What is the role of secretions in cell functions?
- Neurotransmissions
- Cell communication
What are the different mechanisms of secretion control?
- Primarily controlled by negative feedback mechanism
- Humoral
- Neural
- Hormonal
How does the hormonal control mechanism of hormone release work?
- Hypothalamus secretes hormones that
- Stimulate the anterior pituitary gland to secrete hormones that
- Stimulate other endocrine glands to secrete hormones
How does the humoral control mechanism of hormones work?
- Changing level of substance in plasma stimulates
2. Endocrine glands
How does the neural control mechanism of hormones work?
- The nervous system stimulates
2. Endocrine glands
