renal physiology - fayetteville state universityfaculty.uncfsu.edu/ssalek/biol 670 physiology...
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Renal Physiology
Macroscopic Anatomy
• Kidneys:– Cortex– Medulla– Pelvis
• Ureter• Urinary bladder• Renal arteries and veins
Microscopic Anatomy
• Nephrons– Vascular components: Afferent arteriole,
Glomerular capillary, Efferent arteriole, Peritubilar capillaries, venules
– Tubular component: Bowman’s capsule, proximal tubule, Loop of Henle (descending and acsending), distal tubule, collecting duct
Urine formation
• Glomerular filtration• Tubular reabsorption• Tubular secretion• Excretion
– Excretion rate = filtration rate - reabsorption rate + secretion rate
Glomerular Filtration
• GFR = filtration coefficient * net filtration pressure– Kf = permeability * surface area
• The glomerular membrane– Capillary wall: fenestrated and very permeable– Basement membrane restricts plasma proteins– Podocytes: create filtration slits
GFR and tubule pressures
• Glomerular hydrostatic pressure: favors filtration• Glomerular osmotic pressure: opposes filtration• Bowman’s capsule pressure: opposes filtration• Net filtration pressure = 10 mm Hg
Regulation of GFR• Factors:
– blood pressure in the capillaries
– Capillary surface area
– Membrane permeablility
• Purpose :– Keep GFR
constant
• Increase Kf; increases GFR
• Increase capsule hydrostatic pressure: decrease GFR
• Increase glomerular colloid osmotic pressure; decrease GFR
• Increase glomerularcapillary hydrostatic pressure, increases GFR
Regulation of GFR
• Autoregulation of GFR– Keeps GFR constant in spite of arterial BP– Allows precise control over renal excretion (salt
and water)– Vasoconstriction/vasodilation adjust capillary
pressure back to 60 mmHg• Extrinsic control: Sympathetic inputs• Hormonal /Chemical control
Reabsorption and SecretionReabsorption - movement of solutes from the tubule lumen back toThe capillary
Reabsorption and Secretion
Active transport:Na,glucose, amino acids, Phosphate and calcium
Passive transport:Chloride and water, urea
Secondary active transport
Reabsorption of substancesIs linked to Na by passive transport
Proximal tubule:65% NA H20 and Cl Reabsorbed hereExtensive brush boarderLots of mitochondria
Loop of Henle:Descending thin, ascending thin,no brush boarderDescending thin is site of water reabsorption
Loop of Henleascending thickHi metabolic activityImpermeable to water
Distal tubule
Early:Juxtaglomerular apparatus:Feedback control over GFR and blood flow, ion reabsorptionDiluting segment!
Late and Cortical:Principal and cortical cellsUrea not reabsorbed hereNa reabsorbed under control of aldosteroneH secreted for acid -base balanceWater permeability controlled by ADH
Medullary Collecting Duct
• Reabsorbs < 10% water• Determines final output of water and solutes
in urine• ADH has large control over urine volume
here• Tubular urea absorbed here - helps form a
concentrated urine• H secreted for acid base balance
Regulation of reabsorption• Glomerulotubular balance- rate of reabsorption
matches tubular inflow
Regulation of reabsorption• Hormonal control
Regulation of reabsorption• Sympathetic control• Decreases sodium and water excretion by
by vasoconstriction which reduces GFR
Chapter 22
• Excreting a dilute urine– Counter current exchange
• Excreting a concentrated urine– Counter current exchange and the vasa recta
•Excreting a dilute urine
• Start with 300• Dilute filtrate• PT- solutes and water• Dloh- osmosis• Aloh-reabsorbtion solutes• DT-dilute• CD- no ADH!-> dilute urine!
Renal medulla becomes Salty!
• Na, K, Cl pumped out of Aloh• Active transport of ions from CD to medulla• Passive diffusion of urea to medulla• Little diffusion of water to medulla from
CD
Renal medulla becomes Salty!
Excreting a concentrated urine
• Start with 300• Dilute filtrate• PT- solutes and water• Dloh- osmosis• Aloh-reabsorbtion solutes• DT-dilute• CD- High ADH!-> concentrated urine!
Tloh pumps solutes to medulla
Dloh loses waterpassively
Hyper osmotic fluidMoves to Tloh,
Tloh pumps solutes to medulla, again
Cycle again
Countercurrent multiplier
• Repetitive reabsorption of NaCl from Tloh• Continued inflow of new NaCl from PT
Urea
• Urea builds up in the DT then diffuses to the medulla when it reaches the CT
High permeabilityprevents dissipationof the salty medulla!
• Design a system to monitor and keep blood osmolaratity at 300 mosm
Sketch an osmoreceptor