HPA Axis and Growth Hormone Flashcards
Where is the pituitary gland located
Beneath the hypothalamus in the sella turcica
Where do the two lobes of the pituitary gland originate from
Anterior - projection of ectoderm, upwards from roof of mouth
Posterior - from ectodermal tissue, growing downwards from diencephalon of developing brain
Where do axons from the hypothalamus travel down to reach the pituitary
Infundibulum - pituitary stalk
What are the two posterior pituitary hormones and where are they produced (exact sites)
Oxytocin (OT) and Antidiuretic hormone (ADH)
Synthesised by neurones in supraoptic and paraventricular nuclei of hypothalamus
What stimulates oxytocin release
Suckling in milk let-down reflex
Stimulus of pressure on cervix and uterine wall during childbirth
What are the roles of oxytocin
Cause mammary alveoli to contract to squeeze milk out of them into duct system
Initaites powerful uterine contractions - stimulates uterine smooth muscle cells
What stimulates ADH release
Changes in plasma osmolality - increase will cause more to be released
Haemorrhage will cause ADH to be released
What does ADH cause
Increases permeability of collecting ducts (distal tubule) to water to increase reabsorption of water
Acts on smooth muscle cells of blood vessels to cause vasoconstriction
Where are tropic hormones produced by the hypothalamus stored
Median eminence above anterior pituitary
What 7 tropic hormones are produced by the hypothalamus
TRH - thyrotropin releasing hormone
PRH - prolactin releasing hormone
PIH - prolactin release-inhibiting hormone (dopamine)
CRH - corticotropin releasing hormone
GnRH - gonadotropin releasing hormone
GHRH - growth hormone releasing hormone
GHIH - growth hormone inhibitory hormone (somatostatin)
What hormones are secreted by the anterior pituitary and what hormones stimulate and inhibit this release
Thyroid stimularing hormone - Stim: TRH, Inhib: GHIH
Prolactin - Stim: PRH/TRH, Inhib: PIH and GHIH
Adrenocorticotropin hormone - Stim: CRH
Growth hormone - Stim: GHRH, Inhib: GHIH
Luteinising hormone - Stim: GnRH
Follicle stimulating hormone - Stim: GnRH
What is somatotropin, where is it produced and what stimulates and inhibits its production
Polypeptide hormone produced by somatotrope cells in anterior pituitary
Simt: GHRH
Inhib: somatostatin/GHIH
What does GH stimulate the release of and where from
Insulin like growth factors (IGFs) - somatomedins
Released by cells in liver and skeletal muscle
What are the actions of GH and IGFs
GH - IGF production, stimulation of long bone growth
IGFs - cause muscle hypertrophy, stimulate bone and cartilage growth
GH and IGFs - help maintain muscle and bone mass in adults, promote healing and tissue repair as well as modulate metabolism
How is GH secretion metabolically regulated
Decrease in glucose or free fatty acid increases GH secretion
Increase in glucose or free fatty acid decreases GH secretion
Fasting increases GH secretion
Obesity decreases GH secretion
How is GH secretion regulated by the CNS
Deep sleep causes surge in GH secretion
Light sleep inhibits GH secretion
Stress increases GH secretion
Exercise increases GH secretion
What are the long and short loop mechanisms in GH secretion regulation
Long loop - IGFs inhibit GHRH release, IGFs stimulate somatostatin release, IGFs inhibit GHRH action
Short loop - GH stimulates somatostatin release
How does GH exert its effect on cells
Binds to GH receptor - type of cytokine receptor
Receptor is coupled to Janus kinase and one of its effects is to turn on production of IGFs - mainly IGF-1
IGF-1 activates IGF receptors on target cells
Other GH effects include activation of signalling pathways
What effects does IGF-1 mediate in an adult body
Hypertrophy
Hyperplasia
Increase in rate of protein synthesis
Increase in rate of lipolysis in adipose tissue
Decrease in glucose uptake
What does a deficiency of GH cause
In childhood results in pituitary dwarfism
Responds to GH therapy, get normal growth
What does an excess of GH cause
In children causes gigantism
In adults causes acromegaly
What other hormones influence growth
Insulin
Thyroid hormones
Androgens
Estrogens
Glucocorticoids
