9 Glands Flashcards
Gland Definition
An epithelial cell or an aggregate of epithelial cells that are specialised for the secretion of a substance
Whats a secreetion?
The production and release of materials by a cell or aggregate
Endocrine (DUCTLESS)
ALL EPITHELIAL CELLS SECRETE THE HORMONES IN THE GLAND
Secrete directly into the extracellular space, then into the interstitial space and then into the blood flowing through them so that secretions can reach distant body parts.
Secretions: hormones.
Endocrine Examples??
Pituitary gland: its beneath the hypothalamus in the brain.
Anterior of pituitary: produce hormones (ACTH, LH, FSH and TSH) which regulate most of the endocrine glands. Also produces prolactin and somatotrophin (growth hormone)
Posterior of pituitary: produce vasopressin (anti-diuretic hormone) which prevents water loss from the kidneys and oxytocin which signals uterus for delivery in pregnant women at the end of gestation.
Endocrine gland
Two more examples
Thyroid glands: produces thyroid hormones T3 ad T4 that control metabolism. Also produces calcitonin which is involved in calcium homeostasis.
Parathyroid gland: produces parathyroid hormone also involved in calcium homeostasis.
Exocrine (DUCTED)
ONLY CELLS IN THE APEX OF THE DUCT SECRETE THE PRODUCTS
These glands secrete into a location or region of the body through a duct and their secretions are mostly enzymes and lubricants.
Exocrine Examples??
Salivary gland
Pancreas
Mammary
Sweat glands
Sebaceous gland
Lachrymal glands
Generation of glands
Happens inutero. Happens about week 4/5 of gestation.
First thing that happens is the mesochymal cells start to produce fibroblast growth factor (FGF 10 mostly). Causes epithelial cells to proliferate down towards the mesochymal signal. If the signals produced are epidermal growth factors it will cause it to grow in the opposite direction. Main genes involved in this is the HOX genes causing epithelial cells to exvaginate (important in limb formation)
Once the daughter cells have proliferated they produce extracellular protein degradation enzymes (elastase eg). These allow the proliferating bud to grow further away from the surface. The bud can then o in three directions:
- Exocrine: the cenetral cells die off (appoptosis) this produces a canal. Elongation factors cause cells to grow further down. At the same time, cells in the apex start to differentiate into secreting cells.
- Endocrine: they start to produce angiogenic factors to stimulate blood vessel growth in and around the epithelial cell. At thsi point the blood vessels are not connected to anything but eventually grow out and join with blood filled vessels.
- Link to mother cells is broken by apoptosis so its now a separate entity. In thyroid follicle the production of colloid between epithelial cells causes expansion of follicle into a sphere.
Gland branching. How does this happen? Whats involved?
What are the two fates? Hows it stopped?
FGF10 released by immature fibroblasts causing the epithelial cells to bud down. Happens in lungs!!
Two different fates:
Tubule branching: ERK1/2 present, mTORC not present
Tubule elongation: ERK1/2 not present,
mTORC present
—> stopped by sonic the hedgehog
Alveolar secretory glands
What specialised cells do they have?
Myoepithelial cells: hybrid of smooth muscle cell and epithelial cell.
Help in ejecting secretions from the duct.
Salivary gland growth
Prebud —> initial bud —> pseudoglandular (starts forming ducts)—> canalicular —> terminal bud
Have acinus duct: berry shaped.
Have cells secreting mucus
Have serous gland cells producing serous
—> therefore producing watery mucus
Myoepithelial cells surround the gland which contract to push secretion in the duct. Striated duct.
Has three types of epithelial: one producing mucus, one producing serous, one producing watery mucus.
Merocrine secretion
Gland example? INSULIN RELEASE
Two secretion pathways?
Vesicle merges with apical membrane of cell. Aka exocytosis.
Example: acinar or endocrine glands of the pancreas ie INSULIN RELEASE
Regulated secretion: secretory granules accumulate in large vesicles and released by exocytosis upon stimulation. Ca2+ needed to work. Golgi modification
Constitutive secretion: secretory product is not concentrated in granules but in small vesicles and are continually released from the cell. Can be used to replenish plasma membrane proteins. Not golgi modified.
Apocrine gland
Partial loss of cytoplasm
Example: lactating mammary gland (fats and protein release), sweat glands in the arm pits.
Example:
Neonatal period: only fats are secreted by apocrine secretion.
Holocrine secretion
Complete loss of cytoplasm/ cell
Example: sebaceous gland in skin or tarsal glands in eyelid.
Sebaceous gland:
Secretory cell gradually fill up with secretory glanules, cell organerlles degenerate, cell dies, PM breaks and the contents (secretum) empties. Dead cells are replaced by mitotic division of the basal cells.
Cytocrine secretion
Cells are released as a secretion eg spermatid in the testis
