Kidney Physiology Nikkina Hankins nikkina hankinsbison howard edu
Kidney Physiology Nikkina Hankins nikkina. hankins@bison. howard. edu
• 1200 m. L of blood pass through each glomeruli each minute • Kidneys consume 20 -25% of all oxygen used by the body • Filtrate contains everything found in blood plasma except proteins • Urine contains unneeded substances • Kidneys process 180 L • How much do we urinate in one day?
Urine Formation • Glomerular filtration • Tubular reabsorption • Tubular secretion • Regulation of Urine 4
Glomerular Filtration • Renal corpuscle • Produces cell free and protein free filtrate • Passive process
Filtration Membrane • Allows free passage of water and solutes smaller than plasma • Fenestrated endothelium of glomerular capillaries • Basement membrane • Foot processes of podocytes of the glomerular capsule
Pressures that Affect Filtration • • • Outward pressures • Hydrostatic pressure in glomerular capillaries - HPgc • Colloid osmotic pressure in the capsular space Inward pressures • Hydrostatic pressure in the capsular space - HPcs • Colloid osmotic pressure in the glomerular capillaries - OPgc Net filtration pressure - NFP
Glomerular Filtration Rate • Volume of filtrate formed each minute HPgc = 55 mm Hg OPgc = 30 mm Hg • Net filtration pressure • Total surface area available for filtration • Filtration membrane permeability HPcs = 15 mm Hg NFP = Net filtration pressure = outward pressures – inward pressures = (HPgc) – (HPcs + OPgc) = (55) – (15 + 30) = 10 mm Hg
Regulation of GFR • Intrinsic control - renal autoregulation • Myogenic mechanism • Tubuloglomerular feedback mechanism
Regulation of GFR • Extrinsic control - neural and hormonal mechanism • Sympathetic nervous system mechamism • RAA mechanism
Tubular Reabsorption • Reclaims most tubule contents and returns it to the blood • Selective transepithelial process • Active tubular reabsorption • Passive tubular reabsorption
Transcellular Route of Reabsorption • Sodium • Glucose • Amino Acids • Vitamins • Water
Reabsorptive Capabilities of Different Areas of the Kidney • Proximal convoluted tubule - PCT • Nephron loop • Descending limb • Ascending limb • Distal convoluted tubule - DCT • Collecting duct
Tubular Secretion • Moves selected substances from peritubular capillaries through tubule cells into the filtrate • PCT is main site of secretion • Disposing substances that are tightly bound to plasma proteins • Eliminate substances and end products that have been reabsorbed by passive processes • Ridding body of excess K • Controlling blood p. H
Clinical Evaluation of Kidney Function • Renal Clearance • Urine
Countercurrent Mechanisms • Fluid flows in the opposite directions through adjacent segments of the same tube connected by a hairpin turn. • Multiplier • Exchanger • Medullary osmotic gradient allows kidneys to vary urine concentration
Renal Clearance • Volume of plasma from which kidneys clear a particular substance in a minute • C = renal clearance rate m. L/min • U = concentration of substance in urine mg/m. L • V = flow rate of urine formation m. L/min • P = concentration of substance in plasma mg/m. L
Creatinine Clearance • Clears the kidneys with a C of 140 m. L/min • Freely filtered and barely secreted • Used to measure the renal clearance and activity
Cockcroft Gault Equation • Obtain SCr from blood analysis • SCr is inverse to GFR • Need age, weight (kg) and SCr • m. L/min
Urine • Color and transparency • Odor • p. H • Specific gravity • Micturition
Diuretics
Renal Disorders • Acute kidney injury • Chronic kidney disease
Acute Renal Injury • Rapid decrease in GFR over a period of minutes to days • Accumulation of waste products and inability to regulate fluids, electrolytes, and acid base balance • Prerenal • Intrinsic • Postrenal
Look Ups • RIFLE • AKIN • KDIGO
Chronic Kidney Disease • Progressive deterioration in renal function as shown by an increase in BUN and SCr and decline in Cl. Cr and development of uremic symptoms for at least 3 months • Diabetes is the number one cause of CKD • Hypertension is the number two cause of CKD
Look Ups • Stages of CKD • Equation used for pediatrics Cr. Cl • NKFF/DOQI
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