Download Hormones and Water balance in urine formation

Hormones and Water
balance in urine
formation
Your kidneys help maintain
the water balance in your body
• It is important that you don’t have too much, or too
little water in you body.
• If you have too much then the nephrons in you
kidneys will take it from your blood stream
• If you have too little water then the nephrons in
your kidneys will try and give as much water back to
the blood (from the urine) as possible
• Two hormones, ADH and Aldosterone, are
important in maintaining this water balance
The Loop of Henle is also important in water balance
• Descending loop is not permeable to ions, but IS
permeable to water (so water leaves the urine as it travels
down, making the urine saltier the lower in the loop it gets)
• Ascending loop is permeable to ions, but NOT water. Ions
are also actively pumped out of the ascending loop. (so
more and more salt leaves the urine as it goes up the
ascending side of the loop)
• Because of these 2 things the “saltiest” part of the nephron
is the bottom of the loop of Henle (and therefore the
saltiest part of a kidney is its Medulla)
• Because the collecting ducts pass through the medulla this
helps pull more water out of the nephron and concentrate
the urine in times of dehydration.
Bigger the
number the
more
concentrated
something is
ADH
• When you become dehydrated:
• Your blood becomes more concentrated
• This makes too much water to move out of your tissues and
into the blood (causing increased osmotic pressure in the
blood)
• This makes the hypothalamus shrink, which triggers it to send
a signal to the pituitary (telling it to release ADH) (NOTE:
This shrinkage also creates the feeling of thirst)
• ADH is:
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A hormone (Antidiuretic Hormone)
Made by the hypothalamus
Stored in the posterior part of the pituitary gland
Released into the blood when the pituitary receives the signal
Then it travels to the kidney where it affects the nephron
• Under “normal” conditions the distal convoluted
tubule and collecting duct of your nephron are NOT
permeable to water.
• This means that less water stays in your blood, and
more water leaves with the urine.
• ADH makes the distal convoluted tubule and collecting
duct become permeable to water.
• This means that now MORE water will be removed
from your urine and put back into the blood
• This helps your body keep enough water in the blood
stream when you are dehydrated
Aldosterone
• When your blood pressure gets too low:
• Special receptors in the blood vessels near the start of each
nephron notice the drop in pressure
(Note this area is called the juxtaglomerular apparatus)
• Special cells in the apparatus release renin, which transforms
angiotensinogen into angiotensin.
• Angiotensin triggers vasoconstriction and the release of
aldosterone from the adrenal gland
• Aldosterone:
• Makes the nephron take more Na+ out of the urine and into
the blood (in the distal convoluted tubule collecting duct)
• This makes more water come out of the urine and into the
blood
• This increases blood volume, and therefore increases blood
pressure