PHYS Hypothalamus & Pituitary Gland - Week 11 Flashcards
Position of the pituitary gland compared to the hypothalamus and how are these two structures connected?
Pit. inf. to hypo.
Connected by pit. stalk/infundibulum.
2 x lobes of the pit. gland?
- Anterior lobe – adenohypophysis/anterior pit.
- Posterior lobe – neurohypophysis/posterior pit.
2 x regions of the hypothalamus & state what they secrete and where these secretions travel to and/or are stored?
- Supraoptic nuclei (SON) – secretes vasopressin/ADH
- Paraventricular nuclei (PVN) – magnocellular neurons secrete oxytocin & parvocellular neurons produce releasing factors into median eminence.
These hormones are transported down axons & stored in Herring bodies. - Parvocellular nuclei – secretes hypophysiotropic hormones incl corticotropin-releasing, thyrotropin-releasing, somatostatin, GHRH, donadotropin-releasing, dopamine.
What is the effect of hypophysiotropic hormone secretion?
Hypophysiotropic hormone -> stimulates anterior pit. hormone release via hypothalamic-hypophyseal portal circulatory system -> stimulates endocrine gland -> synthesises & releases particular hormone -> target organ.
What hypothalamic hormone mediates anterior pit. secretion of LH & FSH?
GnRH - gonadotropin-releasing hormone.
What is the target organ of LH & FSH?
Gonads.
What hypothalamic hormone mediates anterior pit. secretion of GH?
GHRH - growth hormone releasing hormone
& SST - somatostatin hormone.
What is the effect of GnRH hypothalamic release?
Increased LH & FSH secretion.
What is the effect of GHRH hypothalamic release?
Increased GH secretion.
What is the effect of SST hypothalamic release?
Decreased GH secretion.
What is the target organ of GH?
Liver & other tissues.
What hypothalamic hormone mediates the release of TSH?
TRH.
What is the effect of TRH hypothalamic release?
Increased TSH secretion.
What hypothalamic hormone inhibits the release of prolactin?
Dopamine.
What hypothalamic hormone mediates the release of prolactin?
Dopamine.
What is the effect of hypothalamic dopamine release?
Decreased prolactin secretion.
What is the target organ of prolactin?
Breasts.
What hypothalamic hormone mediates the release of ACTH?
CRH - corticotropin-releasing hormone.
What is the effect of hypothalamic CRH release?
Increased ACTH secretion.
What is the target organ of ACTH?
Adrenal cortex.
What is the stimulating factor of prolactin?
Still under investigation to date.
Half life of GH. Change when bound to protein.
GH circulates free in plasma w half life of 10-20mins.
40% GH is bound to GHBP (binding protein) – increases half life.
What is the effect of GHRH on GH release?
GH releasing hormone stimulates GH release.
What is the effect of somatostatin on GH release?
Inhibits GH release.
What factors enhance GH secretion?
- Sleep
- Exercise
- Stress
- Post-prandial decline in glucose
- Increase in specific amino acids.
What factors inhibit GH secretion?
- Postprandial hyperglycaemia
- Elevated free fatty acids
- Elevated IGF-1
- Aging
How does GH cause growth & metabolism?
GH binds to target cell receptors -> activates JAK2 & Src family kinases -> initiate intracellular signalling cascades -> regulates gene transcription -> growth & metabolism.
Effects of GH via IGF-1
Increases height via promotion of bone lengthening & mineralisation.
Increased muscle mass via protein synthesis stimulation.
Internal organ growth stimulation (excl. brain).
Effects of GH independent of IGF-1
Promotes lipolysis
Reduces muscle & fat uptake of glucose
Increases gluconeogenesis in the liver.
How are IGFs transported in blood?
BPs.
