Physiology 5 + 6 Flashcards
What is the composition of water in the body?
Total = 42L
intracellular fluid = 28L
Extracellular = 14L (3L in plasma, 11L in interstitial fluid)
How does the kidney maintain extracellular fluid?
By controlling sodium levels. Water follows sodium.
How is the extracellular fluid levels measured?
By the baroreceptors:
low pressure - atrial
High pressure - carotid and aortic arch
What happens during vomiting?
You lose water and salt - become hypovolaemic.
What happens during hypovolaemia?
The low and high pressure barrow receptors reduce firing rate - this reduces inhibition on the hypothalamus - this increases ADH.
Also increases sympathetic vasoconstriction.
increases renin production.
What does an increase in ADH do to increase ECF?
It acts on the collecting duct - increases water permeability to reabsorb more water and concentrate the urine.
What is a possible complication of increased ADH during hypovolaemia?
we are only reabsorbing water at the collecting duct, so we might become hyposmotic.
What does sympathetic vasoconstriction achieve during hypovolaemia?
causes vasoconstriction of all blood vessels, to increase blood pressure. Also causes vasoconstriction of afferent arteriole in particular (which maintains GFR as the efferent arteriole is constricted).
What does the release of renin achieve during hypovolaemia?
Renin increases angiotensin II.
What does angiotensin II achieve during hypovolaemia?
It causes constriction of the efferent arteriole - this reduces the hydrostatic pressure in the proximal tubule - and since theres less water, oncotic pressure is higher - this causes increased NaCl reabsorption at the proximal tubule and water.
It causes release of aldosterone from the adrenal gland - this increases sodium chloride and water reabsorption at distal tubule.
What are the effects of angiotensin II on the hypothalamus?
The cause increased release and production of ADH.
They increase thirst and salt appetite.
What are the steps in RAAS?
Liver produces angiotensinogen
juxtaglomerular cells secrete renin
this converts angiotensinogen into angiotensin I
angiotensin convertinge enzyme converts angiotensin in into angiotensin II.
What is the rate limiting step in RAAS?
The release of renin.
What stimulates renin release?
Paracrine activity from the macula dense - causing secretion of renin from the juxtaglomerular cells.
Macula densa - decreased blood flow past or increased sodium chloride.
What inhibits renin release?
Angiotensin II
ADH