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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. - PowerPoint PPT Presentation
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IPHY 3430 10/27/11
Materials filtered into Bowman’s capsule
WaterIonsglucose, amino acidswastes (NH3, urea, etc)a few plasma proteinseverything else in plasmahopefully no cells
Tubular reabsorption involves transport of molecules in filtrate back into the blood.
Passive diffusionActive transportPinocytosis
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) activeSome negative ions (sulfate, phosphate) active
Cl- passivewater--passive (by osmosis) following movement of
other molecules Proteins = pinocytosisWastes = some urea diffuses back into blood
Tubular reabsorption
Example: glucose (under 320 mg/ml filtered load)
tubule bloodAll glucoserestored to bloodAnd none left in filtrate by end of proximal tubule
None
Tubular reabsorptionExample: glucose over 325 mg/min filtered load
tubule blood
Carrier molecules for glucose saturated, soSome glucose left in filtrate by end of proximal tubule
Glucoseleft
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
Descending LoopPermeable to water
300400
400500500600
filtrate
700 600
800 700
900 800
1000 900
1100 1000
1200 11001200
Concentration offiltrate rises due towater leaving andconcentrating solute
At bottom of Loop, another 15-20% of water reabsorbed back into blood
Direction of flow
Ascending LoopNot permeable to waterConcentration of filtrate changes due to active
transport of Na and Cl from filtratefiltrate
1200
1000
800
600
400
200 100
NaCl
NaCl
NaCl
Direction of flow
By the end of the loop of Henle, 15-20% more water reabsorbed back into blood
Distal tubule
Active secretion of K+ if necessaryActive secretion of H+ if necessary
CO2 + H20 --> H2CO3--> H+ + HCO3-(carbonic anhydrase)
Collecting DuctSecretes a variably concentrated urine depending on needs of the body
filtrate200
400600
800
1000
1200
200
1200
Dehydration:Maximal vasopressinsecretion
filtrate
200
200
200
200
200
200
1200
Overhydration:Minimal vasopressin secretion
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
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
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+