Pituitary Gland/ Growth Hormone Flashcards
Where is the pituitary gland located?
beneath the hypothalamus in a socket of bone called the ‘sella turcica’
What is the embryological origin of the pituitary gland?
anterior pituitary (adenohypophysis) arises from evaginations of oral ectoderm (rothke’s pouch)
posterior pituitary (neurohypophysis) arises from neuroectoderm
What is the neurocrine function of the posterior pituitary?
oxytocin is produced by neurosecretory cells in supraoptic nuclei of hypothalamus. adh produced by neurosecretory cells in paraventricular nuclei. both travel down nerve cell axons, where they are stored and released from the posterior pituitary.
how are hormones released from the anterior pituitary?
hormones synthesised in hypothalamus are transported down axons and stored in median eminence before release into hypophyseal portal system. this has a stimulation/inhibition effect on endocrine cells in the AP which then secrete into the bloodstream.
what are the tropic hormones of the hypothalamus?
TRH (PRH) PIH CRH GnRH GHRH GHIH (somatostatin)
What are the actions of growth hormone?
- protein hormone that has signal peptide that must be cleaved before proper folding
- effects mediated by somatomedin (insulin like growth factors), in liver and skeletal muscle
causes:
- long bone growth (GH)
- bone and cartilage growth (IGF’s)
- helps maintain muscle mass, bone mass and promote healing and tissue repair as well as modulating metabolism and body composition
How is growth hormone regulated?
- GHRH increases GH secretion
- GHIH decreases GH secretion
CNS regulates:
- increased GH after deep sleep
- REM sleep decreases GH secretion
- stress increases GH secretion
- exercise increases GH secretion
- also affected by glucose, fatty acid levels, starvation and obesity
How is growth hormone controlled by negative feedback?
long loop:
mediated by IGFs which inhibit release of GHRH from hypothalamus and stimulate the release of somatostatin from hypothalamus.
short loop:
mediated by GH itself via stimulation of somatostatin release
What are the effects of growth hormone deficiency?
- pituitary dwarfism
- delayed or no sexual development in teen years
- responds to GH therapy
What are the effects of growth hormone excess?
- gigantism
- rare and often caused by pituitary adenoma
- in adulthood causes acromegaly
What is the mechanism of action of GH?
activation of JAK’s which causes cross phosphorylation of JAK’s and cross phosphorylation of GH receptors. Activation of signalling pathways and transcription factor and IGF production.
What are the 2 IGF’s in humans?
- IGF1- foetal growth
- IGF2-adults
binding proteins modulate their activity
What are the effects of IGFs binding IGF receptors?
- cell growth
- increase in cell number
- increase in protein synthesis
- increase in lipolysis
note the receptors are cross linked so IGF1 can activate insulin receptor and vice versa.
Aside from growth hormone, how do other hormones have an effect on growth?
- estrogens decrease somatic growth; promote closure of epiphyseal growth plates
- insulin- enhances somatic growth; interacts with IGFs
- thyroid hormones- CNS development
- androgen- muscle mass, puberty, closure of growth plates
- glucocorticoids, inhibit somatic growth
