Physiology 6: endocrine control of body volume Flashcards
what is the osmolarity osmolarity of the filtrate when it reaches the distal convoluted tubule
100 mosmol/l (hypotonic)
what is the osmolarity of the cortex vs the medulla
cortex isotonic and osmolarity increases towards the centre and becomes very hypertonic
where do distal tubules empty into
collecting ducts
what happens to urea in the distal tubule
becomes concentrated as low permeability
what is reabsorbed in the early distal tubule
NaKCl co-transport and reabsorption
what is reabsorbed and secreted in the late distal tubule
Ca reabsorption, Na and K reabsorption, H+ secretion
what happens in the early collecting duct
similar to late distal tubule
what happens in the late collecting duct
water permeable depending on ADH levels
what affect does ADH have on kidneys
increases water reabsorption
what type of peptide and hormone is ADH
octapeptide - neurohormone
where is ADH synthesised
supraoptic and paraventricular nuclei in the HYPOTHALAMUS
where is ADH stored
posterior pituitary
how does dehydration trigger ADH release
increased plasma osmolarity is detected by hypothalamic osmoreceptors which triggers an AP to release ADH
how does decreased atrial pressure trigger ADH release
stretch receptors in the left atrium detect low pressure and cause AP to release ADH
what is the Half life of ADH
10-15 minutes
what part of the nephron does ADH affect and how does it work
distal tubule/ collecting duct - uses ATP to insert water channels (aquaporins) into the lumen membrane
what affect does nicotine have on ADH levels
stimulates ADH release
what affect does alcohol have on ADH levels
inhibits ADH release
what affect does high levels of ADH have on urine and vice versa
high ADH = high water permeability = hypertonic urine / low ADH = low water permeability = hypotonic urine
what is central diabetes insipidus
damage to hypothalamus/ pituitary where ADH is not released
what is nephrogenic diabetes insipidus
kidneys to not respond to ADH
what are the symptoms of diabetes insipidus
large volumes of dilute urine + constant thirst
what is the treatment for diabetes insipidus
nephrogenic: thiazide diuretics / central: ADH replacement
what effect does aldosterone have on the kidneys
causes Na reabsorption and H/K secretion
where is aldosterone secreted
adrenal cortex
what can cause aldosterone to be released (3)
increased K in blood, decreased Na in blood, RAAS system
where is K normally reabsorbed and how much is reabsorbed
proximal tubule - 90%
what happens to K in the distal tubule when no aldosterone is released
rest is reabsorbed and no K is excreted in the urine
how does increased [K]plasma directly stimulate aldosterone release
stimulates the adrenal cortex to secrete aldosterone
how does decreased [Na]plasma indirectly stimulate aldosterone release
from the juxtogolmerular apparatus causing renin release
what do the kidneys release renin in response to (3)
decreased NaCl / decreased ECF volume / decreased arterial BP
what does renin do
converts angiotensinogen (liver) –> angiotensin I
what does ACE do (lungs)
convert angiotensin I –> angiotensin II
what does angiotensin II do
causes the release of aldosterone from the adrenal cortex
what cells release renin
granular cells in the juxtaglomerular apparatus
what 3 ways can renin be released by the kidneys
1) reduced pressure in afferent arteriole 2) macula densa senses reduced NaCl 3) increased sympathetic activity (from decreased BP detected by baroreceptors)
what can an increased in the RAAS system causes
hypertension, fluid retention and congestive heart failure (and hypokalaemia)
how can an overactive RAAS system be treated
low salt diet, loop diuretics and ACEi
what effects does atrial natriuretic hormone (ANP) have on the kidneys
decreased Na reabsorption
where is ANP produced and stored
produced in heart and stored in atrial muscle cells
when is ANP released
when atrial muscle cells are stretched due to increased plasma volume (BP)
how does ANP cause plasma volume decrease in the kidneys
by reducing Na reabsorption which causes diuresis which causes decreased plasma volume
what effects does ANP have on the whole body to decrease BP (4)
reduced Na reabsorption / reduced renin production / vasodilation / reduced sympathetic activity
what effects does Parathyroid hormone have on the kidneys
increased Ca reabsorption and decreased phosphate reabsorption
what happens to filtrate (urine) once it leaves the kidneys
traveled down ureters by peristalsis to bladder for temporary storage and then micturition
what happens in the first stage of micturition - the micturition reflex
bladder can hold 250-400ml of urine before stretch receptors initiate micturition and cause involuntary bladder contraction and opening of internal and external urethral sphincter (parasympathetics)
what happens in the second stage of micturition - voluntary control.
deliberate tightening of external sphincter and pelvic diaphragm
what is water diuresis
increased urine flow but no increased solute excretion
what is osmotic diuresis
increased urine flow and increased solutes (usually Na) in urine
