IPHY 3430 10/27/11
Materials filtered into Bowman s
capsule
Water
Ions
glucose, amino acids
wastes (NH3, urea, etc)
a few plasma proteins
everything else in plasma
hopefully no cells
Tubular reabsorption involves transport of
molecules in filtrate back into the blood.
Passive diffusion
Active transport
Pinocytosis
1
Tubular Reabsorption
Glucose (cotransport with Na+; active)
Amino Acids (cotransport with Na+; active)
Na+ (active--about 67% reabsorbed in proximal tubule)
All other positive ions (Ca++, K+, etc) active
Some negative ions (sulfate, phosphate) active Cl- passive
water--passive (by osmosis) following movement of
other molecules Proteins = pinocytosis
Wastes = some urea diffuses back into blood
Tubular reabsorption
Example: glucose (under 320 mg/ml filtered
load)
All glucose
restored to blood
And none left in
filtrate by end of
proximal tubule
tubule
blood
None 2
Tubular reabsorption
Example: glucose over 325 mg/min filtered
load
Carrier molecules for
glucose saturated, so
Some glucose left in filtrate by end of
proximal tubule
tubule
blood
Glucose
left
At the end of the proximal tubule: all glucose, amino acids, many ions except some of the Na+, Cl-, almost all protein, 65% of water, 50% urea
have been reabsorbed back into blood Remaining in filtrate: about 35% of water,
wastes, the rest of Na and Cl, excesses of any
ions, toxins Loop of Henle
Sole purpose is to conserve water
Depends on an extracellular gradient of Na and
Cl concentration 3
4
Descending Loop
Permeable to water
Concentration of
filtrate rises due to
water leaving and
concentrating solute
filtrate
400
300
500
400
600
500
700
600
800
700
900
800
1000
900
1000
1100
1200
1100
1200
At bottom of Loop, another 15-20% of water reabsorbed back into blood Direction of flow
5
Ascending Loop
Not permeable to water
Concentration of filtrate changes due to active
transportfiltrate
of Na and Cl from filtrate
NaCl
100
200
NaCl
600
400
Direction of flow
800
NaCl
1000
1200
By the end of the loop of Henle, 15-20%
more water reabsorbed back into blood
Distal tubule
Active secretion of K+ if necessary
Active secretion of H+ if necessary
CO2 + H20 --> H2CO3--> H+ + HCO3-
(carbonic anhydrase)
6
Collecting Duct
Secretes a variably concentrated urine
depending on needs of the body
filtrate
200
filtrate
200
400
600
800
1000
1200
200
200
200
Dehydration:
Maximal vasopressin
secretion
200
200
Overhydration:
Minimal vasopressin secretion
200
1200
1200
Regulation of body water (colloid osmotic
pressure)
 cop --> hypothalamus--> posterior lobe of
pituitary releases-->  vasopressin --> permeability of collecting duct to water-->
 water reabsorption from filtrate into blood-->
 excretion of dilute, large volume urine -->
 water content of blood -->  cop
7
Regulation of body water (colloid osmotic
pressure)
 cop --> hypothalamus--> posterior lobe of
pituitary releases-->  vasopressin -->  permeability of collecting duct to water-->
 water reabsorption from filtrate into blood-->
excretion of concentrated, small volume urine -->
 water content of blood --> cop
Effect of alcohol on vasopressin
secretion
Renin-angiotensin system helps
vasopressin conserve water, if necessary,
for regulation of body water and blood
pressure
8
Angiotensin II also causes:
 aldosterone release from adrenal gland
--->
 Na+ uptake from urine -->  water
uptake
from urine -->  blood volume -->
 venous return --> stroke volume -->
 cardiac output
net effect of  angiotensin II -->  BP
Additional Na+ regulation
 blood Na+ --> adrenal gland-->  aldosterone secretion -->  active uptake
of Na+ from filtrate in collecting duct -->
 blood Na+
and….
Even more Na+ regulation
 blood Na+ --> heart atrium -->  secretion
of atrial natriuretic peptide -->  absorption of
Na+ from filtrate in collecting duct -->
 blood Na+ 9