the hypothalamic-pituitary axis Flashcards
what does the HPA regulate
function of thyroid, adrenal and reproductive glands
what does the HPA control
- somatic growth
- lactation
- milk secretion
- water metabolism
explain the anatomy of the pituitary gland
sits within the bone
what is the anterior pituitary made up of
hypophyseal portal system
- primary and secondary plexus
what is the posterior pituitary made up of
2 different nuclei
- paraventricular nucleus
- supraoptic nucleus
explain the development of the adrenal pituitary gland
adenohypophysis
- oral ectoderm of the roof of the stomatodeum
explain the development of the posterior pituitary gland
neurohypophysis
- downgrowth of the forebrain
what are the 5 cell types of the anterior pituitary
- somatotropes
- corticotropes
- thyrotropes
- gonadotropes
- lactotropes
what is the function of the posterior pituitary
neural tissue which is responsible for transport and storage of secretory granules of hormones manufactured in the hypothalamus
where does the pituitary gland get its vascular supply from
the superior hypophyseal artery
how is the anterior pituitary innervated
by paricellular neurons
- hypothalamus to the infundibulum
how is the posterior pituitary innervated
by magnocellular neurons
(paraventricular nuclei and supraoptic neurons)
- hypothalamus to the posterior pituitary
what hormones does the posterior pituitary release?
SON = ADH (anti-diuretic hormones)
PVN = oxytocin
what does ADH do
it is a peptide hormone which has roles in vasoconstriction, reducing urine output, and ultimately increasing blood pressure
how is ADH secreted
- by baroreceptors (which are found on stretch receptors on atria)
- baroreceptors detect stress, pain, increased plasma osmolality or decreased BP - which then activates release of ADH
what happens in the presence of ADH
- urine flow decreases
- urine osmolality increases
what happens in the absence of ADH
- urine flow increases
- urine osmolality decreases
what happens when ADH levels increase
- induces vasoconstriction
- causes bradycardia
- causes a reduction in cardiac output
- also stimulates smooth muscle contraction
why does urine osmolality increase in the presence of ADH
when ADH binds to V2, synthesis of pKa occurs, aquaporin 2 is activated when a lack of H2O is detected
what can abnormally high circulating ADH lead to?
- high urine osmolality
- oedema (due to high plasma volume)
- low plasma osmolality
what can abnormally low circulating ADH lead to
diabetes insipidus
what does oxytocin stimulate
- secretion of breast milk from lactating females
- also contribution to delivery of a foetus
what stimulates oxytocin secretion
- suckling
- vaginal / cervical stimulation during labour
- crying
what is milk production stimulated by
prolactin (from the anterior pituitary)
what is the anterior pituitary responsible for
- the coordination of multiple axis within the body
- 1st level - paricellular neurons in the hypothalamus
- 2nd level - anterior pituitary (hormones be released)
- 3rd level - peripheral endocrine tissues
what does thyrotropin-releasing hormones (TRH) do
TRH stimulates TSH (thyroid-stimulating hormones) and acts on thyrotropes
what do gonadotropin-releasing hormones do
stimulates secretion of FSH (follicle-stimulating hormone) and LH (luteinising hormone) and acts on gonadotropes
what do corticotropin-releasing hormones do
stimulates secretion of ACTH (adrenocorticotropic hormone) and acts on corticotropes
what do growth-hormone releasing hormones do
stimulates secretion of GH (growth hormones) an acts on somatotropes
what are the actions of dopamine
it inhibits secretion and synthesis of prolactin and acts on lactotropes
what does TSH do
it regulates thyroid function via the TSH receptor on the thyroid epithelial cells
TSH stimulates release of T3 and T4 from the thyroid gland to support tropic effects on growth and metabolism
what do FSH and LH do
regulate the function of the gonads in both males and females via the FSH and LH receptors on the gonads
what does ACTH do
it is responsible for stimulating the adrenal cortex via the MC2R - this induces upregulation of circulating cortisol and adrenal androgen - the released cortisol negatively feeds back to inhibit ACTH secretion in the anterior pituitary
what does prolactin do
stimulates manufacture of breast milk via the reduced dopamine from the parvicellular hypothalamic neurons
