posterior pituitary hormones Flashcards
what are the hormones produced by the posterior pituitary gland
- anti-diuretic hormone (ADH) aka vasopressin (acts on renal tubes)
- oxytocin (actis on mammary gland and uterus)
what are the actions of ADH
- acts on distal tubule and collecting duct
- increases permeability of water
- more water moves out of tubule and is resorbed
- urine volume decreases
- urine concentration increases
how do you assess hydration clincally
- prolonged skin tent
- dry mucous membranes
- sunken eyes
- refractometer
- USG
- urine more concentrated if dehydrated
- colour of urine is darker
- less volume
- high specific gravity
how is dehydration detected and managed by osmoreceptors
- osmoreceptors within the hypothalamus
- respond to an increase in the osmolarity of the of the extracellular fluid
- osmolarity = number of dissolved particles per unit volume
- more concentrated = higher osmolarity
- more ADH released
- more water conserved
how is dehydration detected and managed by volume receptors
- volume receptors in the atria and veins respond to large changes (10%)
- when decrease in distension is detected the nerves send impulses to the hypothalamus
- more (lots, as this is emergency) ADH is released
- water is conserved (not peed out)
are osmoreceptor or volume receptors more sensitive in detecing dehydration
osmoreceptors
what is the major method of correcting dehydration
thirst stimulation
how does ADH increase aquaporin density on the tubule surfaces
- aquaporin-2 is under ADH control
- ADH bind to receptors
- activations of adenyl cyclase
- production of cAMP
- vesicles containing aquaporins move to the cell surface
- inserted via exocytosis
- proportional to plasma ADH concentration
- removed via endocytosis
what is diabetes
refers to increased urine output
what are the 2 types of diabetes insipidous
diabetes insipidous is caused by ADH dysregulation
- neurogenic dibetes insipidus = inadequate ADH release from pituitary
- nephrogenic = inadequate response within the kidney
what does oxytocin do
- stimulates milk let down
- acts on smooth muscle cells (uterine contraction and contraction of mammary alveoli)
- release regulated by neuronal reflexes
explain the neuronal transmission to the hypothalamus from the teat to stimulate oxytocin release
- high density of sensory nerve fibres in the teats detect suckling
- impulses transmitted via superficial sensory pathways and inguinal nerve
- afferent sensory neurons enter the lumbar segments of the spinal cord
- ascend the spinal cord sensory tracts
- to the thalamus, influence cell bodies of neuroendocrine cells
- secretion of oxytocin from nerve endings in posterior pituitary gland into circulation
what are the effects of oxytocin on the mammary gland
- increases pressure within the alveoli
- reduces resistance in excretory ducts
- reduces resistance in teat canal
- resulting in increased milk outflow
describe the neuroendocrine reflex during birth/partuition
- stimulate sensory nerve endings in cervix
- afferent nerve impulses to hypothalamus
- neuroendocrine cells of paraventricular and aupraoptic nuclei depolarize
- secrete oxytocin from pars nervosa (posterior pituitary)
- enters blood circulation
- acts on oxytocin receptors of myometrium
- strong uterine contractions result
