kidney homeostasis (9b) Flashcards
(14 cards)
how is water distributed in the body
most of it is in intracellular fluid (cytoplasm)
the rest is in extracellular fluid, most in interstitial fluid and some in plasma
where is our water coming from
mostly beverages then foods then metabolism
where is the water coming out
mostly urine, then losses by skin and lungs, then sweat then feces
how does the thirst mechanism work
osmoreceptors in the hypothalamus react to changes in plasma solute concentration
thirst center in hypothalamus generates thirst sensation, dry mouth from decreased saliva
reinforces drinking drive
what is ADH and how does it work
antidiuretic hormone
responsible for water amount entering urine and control of water reabsorption of water and electrolytes
it travels to the collecting ducts, binds and opens aquaporins for water to flow out of the nephron
ADH is released continuously unless solute concentrations are very low
what happens during urine formation if you have diabetes
there is too much glucose in the filtrate, it increases the osmolality of the filtrate and osmosis at the collecting duct is reduced
the gradient between the filtrate and the medulla is not as large so less water will be reabsorbed even if ADH is present
what hormones regulates blood composition and blood volume by acting on the kidneys
aldosterone
how does aldosterone work
it opens/stimulates the synthesis of more sodium and potassium channels as well as more sodium/potassium transporters
for each sodium absorbed, a chlorine follows (water follows by osmosis) and a potassium is secreted into the filtrate
where is sodium reabsorbed
90% is immediately reabsorbed in the PCT and the rest is reabsorbed in the DCT when it reaches aldosterone receptors
what is the renin-angiotensin mechanism
mechanism that triggers aldosterone release and increases blood volume and blood pressure
how does the renin-angiotensin mechanism work
cells in the juxtaglomerular apparatus in kidneys are stimulated by low BP and release the hormone renin
the liver releases the hormone angiotensinogen
renin + angiotensinogen = angiotensin 1
angiotensin-converting enzyme (ACE) is released from lungs
ACE + angiotensin 1 = angiotensin 2
angiotensin 2 causes vasoconstriction of blood vessels and stimulates the adrenal gland to release aldosterone (also affects posterior pituitary to release ADH)
aldosterone acts on kidneys to stimulate the reabsorption of salt and water
what other hormones have an effect on electrolyte balance
estrogen and glucocorticoids increase sodium reabsorption in the tubule and as a result water retention
what are the renal mechanism for blood pH balance
bicarbonate system
pH rises: bicarbonate ions are excreted and hydrogen ions are retained
pH falls: bicarbonate ions are reabsorbed and hydrogen ions are secreted
when is dialysis required and how does it work
required when 85-90% of kidney function is gone
occurs for 4 hours 3x/week
