lecture 33 Flashcards
what drives and regulates body water homeostasis?
distribution of water
osmolarity/tonicity
reabsorption
effects of osmotic and volume changes
what portion of out body is water?
55-60%
what portion of total body water is ICF?
2/3
what portion of total body water is ECF?
1/3
What portion of ECF is plasma?
1/5
what portion of ECF is interstitial fluid?
4/5
what is osmolarity based on?
osmotically active ions or solutes
hypo-osmolarity?
lower than usual
what is tonicity?
the effect of a solution on cells
ECF concentration of Na+ and K+?
145 and 4-5mmol/L respectively
ICF concentration of Na+ and K+?
15 and 150mmol/L respectively
what is adjusted to maintain intake and loss of water?
urine output
how much sodium is filtered load is reabsorbed in the PCT?
67%
how much sodium is filtered load is reabsorbed in the thick ascending limb?
25% and only sodium
what percent of sodium in the filtered load is reabsorbed at the DCT?
5%
how much sodium is filtered load is reabsorbed at the collecting duct?
3%
what are the three important places within the nephron where water is reabsorbed?
PCT - 67%
tDLH - 25%
CD - 8%
what is water reabsorption in the PCT driven by?
Na+ reabsorption (isosmotic)
why does the thin ascending limb reabsorb water in the nephron loop?
it has leaky epithelium facilitation water reabsorption via aquaporins and paracellular pathway
water reabsorption in the kidney is mainly facilitated by?
glucose reabsorption
what proportion of water reabsorption does obligatory account for?
92% and not regulated
why does facultative water reabsorption only account for 2-8% of water reabsorption?
tight epithelia
only trans cellular
regulated by ADH
what changes osmolarity?
changing water content, fluid shifts between ECF-ICF to equalise change
what are repercussions of changes in osmolarity?
cell structure can be altered leading to cell functions becoming impaired
what detects changes in total body water?
osmoreceptors in hypothalamus
what is the response to low or high plasma osmolarity?
stimulation of pituitary gland to secrete more or less ADH
what does ADH do?
alters permeability of renal collecting duct
what is diuresis?
high urine volume because water is not being reabsorbed in CD
how does ADH affect the cell?
binds to receptor on basolateral side of collecting duct cells and increases amount of aquaporins in apical membrane
what senses changes in sodium reaching DCT?
macula dense cells
if the sodium reaching DCT is too low what happens?
renin is released from juxtaglomerular cells
what is the receptor that promotes sympathetic activation for low ECF volume?
barorecpotrs
what are the results of renin release from kidney?
decreased Na+ and water lost in urine
