Mammalian System Filter solutes out of blood & reabsorb H 2
O + desirable solutes Key functions filtration fluids (water &
solutes) filtered out of blood reabsorption selectively reabsorb
(diffusion) needed water + solutes back to blood secretion pump out
any other unwanted solutes to urine excretion expel concentrated
urine (N waste + solutes + toxins) from body bloodfiltrate
concentrated urine
Slide 15
Nephron Functional units of kidney 1 million nephrons per
kidney Function filter out urea & other solutes (salt, sugar)
blood plasma filtered into nephron high pressure flow selective
reabsorption of valuable solutes & H 2 O back into bloodstream
greater flexibility & control counter current exchange system
why selective reabsorption & not selective filtration?
Slide 16
Mammalian kidney Proximal tubule Distal tubule Glomerulus
Collecting duct Loop of Henle Amino acids Glucose H2OH2O H2OH2O
H2OH2O H2OH2O H2OH2O H2OH2O Na + Cl - Mg ++ Ca ++ Interaction of
circulatory & excretory systems Circulatory system glomerulus =
ball of capillaries Excretory system nephron Bowmans capsule loop
of Henle proximal tubule descending limb ascending limb distal
tubule collecting duct How can different sections allow the
diffusion of different molecules? Bowmans capsule Na + Cl -
Slide 17
Nephron: Filtration At glomerulus filtered out of blood H2OH2O
glucose salts / ions (Na + / Cl ) urea not filtered out cells
proteins high blood pressure in kidneys force to push (filter) H 2
O & solutes out of blood vessel BIG problems when you start out
with high blood pressure in system hypertension = kidney damage H 2
O & solutes cells & large molecules
Slide 18
Nephron: Re-absorption Proximal tubule reabsorbed back into
blood NaCl active transport of Na + Cl follows by diffusion H2OH2O
glucose HCO 3 - bicarbonate buffer for blood pH
Slide 19
Nephron: Re-absorption structure fits function! Loop of Henle
descending limb reabsorbed H2OH2O structure many aquaporins in cell
membranes high permeability to H 2 O no Na + or Cl channels
impermeable to salt
Slide 20
Nephron: Re-absorption structure fits function! Loop of Henle
ascending limb reabsorbed Na + & Cl structure many Na + / Cl
channels in cell membranes high permeability to Na + & Cl no
aquaporins impermeable to H 2 O
Nephron: Reabsorption & Excretion Collecting duct
reabsorbed H 2 O = through aquaporins excretion concentrated urine
to bladder impermeable lining = no channels in cell membranes
Slide 23
Osmotic control in nephron How is all this re-absorption
achieved? tight osmotic control to reduce the energy cost of
excretion use diffusion instead of active transport wherever
possible the value of a counter current exchange system
Slide 24
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Slide 26
Summary Not filtered out of blood cells u proteins remain in
blood (too big) Reabsorbed back to blood: active transport Na + u
amino acids u glucose Reabsorbed back to blood: diffusion H 2 O u
Cl Excreted out of body urea excess H 2 O u excess solutes
(glucose, salts) toxins, drugs, unknowns why selective reabsorption
& not selective filtration?
