Download Urine Formation

Urine Formation
Filtration: removing maximum waste from the blood
• At the Glomerulus there is very high pressure that
filters a lot of stuff out of the blood stream and into
the nephron (at the bowman’s capsule)
• Things that move out of the blood stream:
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Water
NaCl (and other salt/ions)
Glucose
Amino Acids
H+
Urea/Uric Acid
• Things that stay in the blood:
o Plasma proteins (to big to fit through the “filter”)
o Blood cells (also too big)
o Some water, salts, glucose, amino acids and H+ stay in
behind in the blood
Reabsorption: bringing as much “good stuff”
back into the blood as possible
• All along the Proximal Convoluted Tubule and Loop of
Henle your nephron actively transports glucose, amino
acids and Na+ ions BACK into the blood
• (Negative ions, such as Cl-, will also move back into the
blood because they are following the Na+)
• All of this material moving back into the blood
concentrates the blood, which them causes water to
follow the osmotic gradient and ALSO move back into the
blood.
• This is GREAT because it makes sure you have most of the
good stuff in your blood stream, and your urine is mostly
concentrated waste with a bit of water.
• Unfortunately, reabsorption accidentally brings some
wastes back into the blood stream (urea, uric acid,
ammonia, some extra H+)
Secretion: bringing as much “bad stuff” back out
of the blood as possible
• Along the distal convoluted tubule the nephron actively
transports that small amount of waste that snuck into the
blood during reabsorption BACK out of the blood again
• Some water also goes into the urine during this process,
and so does histamine, excess minerals and any drugs in
your system.
• Then the urine is all collected in the collecting ducts, and
carried to the bladder through the ureters (to eventually
leave the body)