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URINARY SYSTEM URINARY SYSTEM: OVERVIEW Cellular wastes are toxic if not removed Waste removal (from cells) is performed by blood and lymph Elimination of wastes - Urinary system: H2O, electrolytes, nitrogenous wastes, drugs - Respiratory system: CO2 and H2O - Integumentary system: H2O, electrolytes URINARY SYSTEM: FUNCTIONS Waste removal Maintenance of water/electrolyte balance Regulation of body fluid volume and blood pressure Control of RBC production ANATOMY: MACROSCOPIC Kidneys (2): Filter, reabsorb, secrete Ureters (2): Convey urine to bladder Urinary bladder (1): Collects and stores urine Urethra (1): Conveys urine out of body ANATOMY: KIDNEY Red-brown, bean shaped Enclosed in fibrous capsule Retroperitoneal Surrounded by adipose tissue Continued ... ANATOMY: KIDNEY continued Hilum or Hilus (Indentation; Passage of Vessels, Nerves, etc.) Renal Cortex (Outer) Renal medulla (Inner) - Renal Pyramids (Conical Masses) - Renal Columns (Extensions of Cortical Tissue between Pyramids) ANATOMY: KIDNEY continued Functional Units: Nephrons Renal Papillae (Tip of Pyramid) Minor Calyces (“Cup” receives Urine from Collecting Duct/Renal Papillae) Major Calyces (Receives from Minor C.) Renal Pelvis (Expanded Proximal End Ureter) ANATOMY: URETERS Hollow tubes ~25cm (10”) in length Extend from kidneys to urinary bladder Located retroperitoneally Muscular walls undergo peristalsis Flaps of Mucosa at openings into bladder; prevent backflow ANATOMY: URINARY BLADDER Hollow, muscular, distensible sac Located in true pelvis, subperitoneally Attached to pelvic floor at trigone 3 layers: - Inner muscosa (Transitional E.T. allows filling w/o pressure increase) - Middle detrusor muscle (smooth) - Outer Adventitia Serosa (visceral peritoneum) covers only superior surface ANATOMY: URETHRA Males - Combined Urogenital System - Long urethra (~18 cm) in three subdivisions * Prostatic urethra * Membranous urethra * Penile or spongy urethra Females - Separate reproductive and urinary systems - Short urethra (~4 cm) ANATOMY: MICROSCOPIC Nephron: Functional unit of kidney - Approximately 1 million/kidney - Found Mostly in Renal Cortex - Consists of : * Renal Corpuscle (Glomerulus + Bowman’s Capsule) * Renal Tubules (Proximal & Distal Convoluted Tubules + Loop of Henle) - Collecting Duct – Receives from Multiple Nephrons URINE FORMATION Three Processes: - Filtration - Reabsorption - Secretion Countercurrent Exchange - fluids moving in opposite directions GLOMERULAR FILTRATION Depends on blood pressure (“Pressure Filtration”) Afferent Arteriole carries blood to Glomerulus Small molecules and water move through Walls of Glomerulus into Bowman’s Capsule Fluid is filtrate Includes most substances found in urine Filtrate is similar to plasma (Water, Glucose, Ions, Amino Acids, small Nitrogenous Wastes) TUBULAR REABSORPTION Selective Movement of molecules from renal tubules back into blood PCT Reabsorbs Water, Glucose, Amino Acids, Ions (up to 80% of filtrate) Loop of Henle (& Collecting Duct) Concentrates Urine/Reabsorbs Water & Ions Microvilli for High SA & Absorption TUBULAR SECRETION Primarily in DCT (& Collecting Duct) Additional Molecules move: Blood Renal Tubules Active Transport or Osmosis - Water - Ions (H+, K+, Na+, Cl-) - Some drugs, e.g., penicillin - Creatinine - Nitrogenous wastes URINE PATHWAY Nephron Collecting Duct (Out Renal Papilla of Renal Pyramid) Minor Calyx Major Calyx Renal Pelvis Ureter Urinary Bladder Urethra Outside Body COMPOSITION OF URINE: NORMAL 95% water pH 6.0 (avg.) Urea: From proteins Uric acid: From nucleic acids Creatinine: From creatine phosphate Amino acids: A trace Electrolytes: Vary with diet REGULATION OF FLUID VOLUME Antidiuretic Hormone (ADH) - Released when blood volume drops - Increases permeability of collecting duct to water - Results in: * Increase in Water Reabsorption (decreases water loss) * Increase in Blood Volume REGULATION OF FLUID VOLUME continued Relationship of blood pressure to urine formation - Blood pressure is required for glomerular filtration - If blood pressure falls below a certain point, filtration stops - Results in build-up of nitrogenous wastes