Woods Lecture 8

*only need to know combination for dehydration*  otherwise will only ask to go into details

for changes in osmolarity OR changes in volume but not various combinations of both

1. Increase blood volume + decrease blood osmolarity  by drinking large amount of water

-blood volume increase increases BP detected by baroreceptors and blood osmolarity decrease

detected by very sensitive osmoreceptors

2. Increase blood volume + no change in blood osmolarity  by drinking isotonic saline

3. Increase blood volume + increase blood osmolarity  by drinking large amount of hypertonic

saline

8. Decrease blood volume + increase blood osmolarity  by dehydration due to sweat loss or

diarrhea

-blood volume decrease decreases BP detected by baroreceptors and blood osmolarity increase

detected by very sensitive osmoreceptors

-sweat is hypoosmotic thus contains less ions than the blood it is coming from

-this decreases ECF volume but increases plasma osmolarity (since not many ions leaving)

Decrease in ECF Volume

-volume receptors and baroreceptors detect low volume/low BP causes renin release 

activates RAAS pathway

-AngII hormone released from kidney into bloodstream to get to adrenal cortex to stimulate

Increase in ECF Volume

-osmoreceptors shrink to trigger ADH release from posterior pituitary gland

-water reabsorption increases

BUT plasma osmolarity has increased so WHY are we increasing Na reabsorption?

-because this way achieves max water reabsorption and in the case of dehydration, body more

concerned about maintaining water balance than osmolarity

-once ECF volume back to normal levels, negative feedback sent to stop RAAS activation and Na

reabsorption

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