Human Anatomy and Physiology Renal function

Functions Regulation of water and electrolytes Maintain plasma volume Acid-base balance Eliminate metabolic wastes Hormone secretion

Kidney anatomy

Anatomy Functional unit is the nephron Components Glomerulus Proximal tubule Loop of Henle Distal tubule Common Collecting duct

Nephron anatomy Nephron types Juxtamedullary Cortical Peritubular capillaries Vasa recta

Renal processes Filtration Water and solutes Protein (Not filtered) Blood cells (No filtered) Filtration based on size and charge

Glomerular Filtration Size barrier

Glomerular Filtration

Renal processes Reabsorption 99% of water & solutes Passive - water Active - sodium Proximal tubule (65%)

Reabsorption at cell level Sodium moves passively across the apical membrane and actively into the plasma

Renal processes Secretion Water and solutes (1%)

Secretion at cell level Potassium is transported actively into the cell and passively into the tubular lumen

Urine formation Volume of fluid into kidneys per day 1,640 L Volume filtered into the glomeruli per day 180 L Volume of fluid excreted/day ~ 1.5L Hence L = amount reabsorbed (~99%)

Blood supply GFR will depend on blood supply Blood pressure drop in the glomeruli

Glomerular filtration Total amount of filtrate formed per minute Influenced by: Filtration surface area Filtration membrane permeability Net filtration pressure

Glomerular filtration Measured by a marker Characteristics Freely filtered by the glomerulus Not reabsorbed or secreted Must not alter GFR

Glomerular filtration Inulin Renal clearance GFR x P(In) = U(In) x V

Regulation of GFR 3 mechanisms Renal autoregulation Neural control Renin-angiotension system (JG apparatus)

JG apparatus

Regulation of GFR

Countercurrent multiplication 65% 5% 14% 15%

Urea

Urine concentration Vasopressin: antidiuretic hormone (ADH) Posterior pituitary, increases the number of aquaporin water channels in the CD

Vasa recta Osmotic gradient not washed out Blood supply sluggish Medulla blood flow is 2% of that to the kidneys

Urine concentration The urine to plasma osmolality ratio [U]/[P] Plasma osmolality from mOsm Example: [urine] = 1,200 mOsm, ratio = 4.0

Urine dilution

Atrial natriuretic peptide (ANP) Atrium of the heart, decreases Na + and water reabsorption ADH/ANP

Diuretics Action of Diuretics - Alcohol: inhibits ADH - Caffeine: promotes renal vasodilation, increasing GFR - Drugs: any that inhibit sodium reabsorption

Micturition Mechanism of action Contraction of detrusor muscle Relaxation of sphincters