Posterior pituitary gland Flashcards
What hormones are secreted from the posterior pituitary gland?
ADH/vasopressin - acts on renal tubules
Oxytocin - acts on mammary gland and uterus
What is the action of ADH?
Acts on distal tubule and collecting duct
Increases permeability to water by increasing aquaporin density on tubule surfaces => more water reabsorbed
Urine volume decreases
Urine conc increases
What are aquaporins?
water channels in the convoluted tubules of the nephron
Always present in all membrane of proximal tubule
Always present on baso-lateral membranes of distal tubule and collecting ducts
Only present in apical membranes of distal tubule and collecting duct if ADH present
What are the clinical signs of dehydration?
prolonged skin tent
dry mucous membrane
sunken eyes
How is dehydration detected?
Osmoreceptors in hypothalamus detect increased osmolarity of ECF => more ADH release
Stretch/volume receptors in atria and veins detect large decrease in distension => nerve impulse to hypothalamus => ALOT more ADH released (emergency response)
What is the major method of correcting dehydration?
thirst stimulation
What are the types of diabetes insipidus?
Neurogenic - inadequate ADH release from pituitary
Nephrogenic - inadequate response within the kidney
How is diabetes insipidus diagnosed?
Injection of exogenous ADH
- if urine concentrated = neurogenic (compensates from failure to produce ADH)
- if urine dilute = nephrogenic (kidney fails to respond to extra ADH)
What congenital deformity can lead to diabetes insipidus?
AQP-2 deficiency (no/limited aquaporins)
What is the function of oxytocin?
Stimulates milk let down
Acts on smooth muscles:
- uterine muscle during parturition
- induces contraction of alveoli of mammary glands
Regulated by neuronal reflexes e.g., suckling
Describe the neuronal transmission controlling oxytocin release
Sensory nerve fibres in teats detect suckling or preparation for milking
impulses sent via superficial sensory pathways and inguinal nerve => thalmus
Thalmus influences cell bodies of neuroendocrine cells
=> secretion of oxytocin from nerve endings in posterior pit gland into circulation
What is the effect of oxytocin on the milk gland?
Increases pressure in alveoli
reduced resistance in excretory ducts and teat canal
=> increased milk outflow
How does oestrogen aid oxytocin action in parturition?
increases the number of oxytocin receptors
How is oxytocin controlled during pregnancy and at parturition?
Oestrogen: progesterone ratio:
- lower in pregnancy => inhibits oxytocin
- higher at birth => stimulates oxytocin
How oxytocin be used to aid surccessful parturition?
Used to induce parturition
Treatment for uterine inertia
Help expel placenta and clear fluid from uterus
