HPA axis Flashcards
Name 6 general pituitary functions
Feeding Stress response Water balance Sleep-wake cycle Thermoregulation Emotions
Where does the pituitary gland sit
Sella turcica which is a small depression in sphenoid (pituitary fossa)
What are the proper names for anterior/ posterior pituitary
Anterior= adenohypophysis Posterior= neurohypophysis
Where is the anterior lobe of pituitary derived from
Upward migration from roof of the mouth called Rathke’s pouch
Composed of glandular secretory epithelial tissue
Where is the posterior lobe of pituitary derived from
Downward migration of neuroectoderm from the diencephalon directly connected to hypothalamus
Do the anterior and posterior lobes share the same venous drainage
Yes
Where does the anterior pituitary gland receive supply from
Superior hypophyseal artery
What is the hypothalamo-hypophysial portal system
Superior hypophyseal artery forms a capillary network around the hypothalamus and blood from this network is transported to secondary capilary plexus surrounding anterior pituitary
What artery supplies the posterior pituitary
Blood supply from inferior hypophyseal artery
Where does pituitary blood supply drain
Into efferent anterior and posterior hypophyseal portal veins
Drains into cavernous sinus
Briefly state what is meant by the HPA axis
- Stimulus causes hypothalamus to secrete a hormone
- This causes pituitary to secrete another hormone
- Act on a target organ which may or may not secrete another hormone
Name 4 stimuli for the thyroid axis
Cold, acute psychosis, severe stress, circadian rhythm
What does the hypothalamus release in response to thyroid axis stimuli?
Thyrotropic releasing hormone
What inhibits release of TRH
- T4 levels
- Somatostatin, dopamine, corticosteroids
What does the pituitary release in response to TRH
TSH
What inhibits TSH release
T3
What does the thyroid gland release in response to TSH
T4 and T3
What are the stimuli for growth hormone release
Circadian rhythm, stress, hypoglycaemia, ghrelin
What stimulates the pituitary gland to release growth hormone
Growth hormone releasing hormone
What does growth hormone stimulate? Effect of this?
Stimulates IGF-1 release from the liver
Growth
What inhibits GHRH release
IGF-1
GH
Whst inhibits growth hormone release
GH
Somatostatin
IGF-1
Role of growth hormone?
Stimulates growth and repair
Regulates carbohydrate metabolism
Effects cell proliferation
What can growth hormone deficiency cause
Inadequate energy and impaired well being
Role in insulin resistance and lipid metabolism and thus deficiency can cause hyperlipidaemia
Decreased bone mineral density
Impaired cardiac function
What is CRH
Corticotropin releasing hormone
What stimulates release of CRH
Circadian rhythm, stress and hypoglycaemia
ADH
What stimulates the pituitary gland to release adrenocorticotropic hormone
- CRH
- ADH
What is the effect of ACTH release
Cortisol release from zona fascilculata of the adrenal gland
What does cortisol inhibit release of
adh
acth
crh
Effect on the body of cortisol release
- Gluconeogenesis and glycogenolysis
- Suppreses immune system
- Aids in fat, protein and carbohydrate metabolism
When does cortisol release peak
Just after waking up
What is cushings?
Excess cortisol
What is the difference between cushings syndrome cushings disease
Syndrome= ACTH independent= adrenal hyperplasia or adrenal adenoma Disease= ACTH dependent= pituitary adenoma
What is addisons
Low cortisol
What stimulates the hypothalamus tol release GnRH
Kisspeptin
What is released from the pituitary when GnRH is released
LH and FSH
What inhibits kisspeptin
Prolactin
What inhibts GnRH release
Oestrogen
Testosterone
What inhibits LH and FSH
Oestrogen
Testosterone
What stimulates prolactin release
Nipple sucking
What does prolactin release from the hypothalamus cause the pituitary to release
Prolactin
What inhibits prolactin release
Dopamine
What is the difference between primary and secondary hormone underactivity
Primary= underactivity at target organ Secondary= underactivity at pituitary
Where is ADH released from
Neurons from supraoptic nuclei
Where is oxytocin released from
Neurons from paraventricular nuclei
Effect of oxytocin
Affects uterine contraction in pregnancy and birth
Stimulates initial release of breast milk post birth
What is the most and least vulnerable hormone to be lost because of a pituitary tumour
Growth hormones- most#
ACTH- last to be lost
What is an addisonian crisis
Rapid drop in ACTH leading to hypovolemic shock, vascular collapse, profound electrolyte abnormalities, confusion and psychosis
