Urinary System (Lecture 30)

Urinary System (Lecture 30) ➤ Main Parts • Kidneys (2): Filter blood and make urine • Ureters (2): Carry urine from kidneys to bladder • Urinary Bladder: Stores urine • Urethra: Passes urine outside the body ➤ Kidneys • Location: On back side of abdomen, below diaphragm (T12–L3) • Shape/Weight: Bean-shaped, ~150 g • Hilum: Entry/exit of artery, vein, ureter • Protected by: Fat and fibrous capsule ➤ Kidney Structure • Cortex: Outer region • Medulla: Inner region with 8–10 pyramids • Renal Pelvis: Funnel-shaped area that collects urine • Flow Path: Pyramids → Papilla → Minor calyx → Major calyx → Renal pelvis → Ureter ➤ Nephron (Basic Unit) • ~1 million per kidney • Parts: o Renal Corpuscle: Glomerulus + Bowman’s capsule o Renal Tubule: PCT → Loop of Henle → DCT → Collecting duct ➤ Types of Nephrons • Cortical (85%): Short loops • Juxtamedullary (15%): Long loops – help concentrate urine ➤ Ureters • Length: 25–30 cm • Function: Move urine by peristalsis • Layers: Outer (fibrous), Middle (muscle), Inner (epithelium) ➤ Urinary Bladder • Function: Urine storage • Wall: 3 layers — outer (connective), middle (detrusor muscle), inner (epithelium) • Capacity: >600 ml; urge felt at 300–400 ml • Trigone: Triangle area with 3 openings (2 ureters, 1 urethra) ➤ Urethra • Male: ~20 cm; Female: ~4 cm • Inner lining: Columnar epithelium • External sphincter: Under voluntary control ➤ Kidney Functions • Remove wastes (urea, creatinine) • Balance water & electrolytes • Regulate blood pH • Make hormones: Erythropoietin, Renin • Activate vitamin D • Gluconeogenesis during fasting Urine Formation (Lecture 31-32) ➤ Urine Formation Steps 1. Glomerular Filtration: Blood is filtered in glomerulus 2. Tubular Reabsorption: Needed substances are reabsorbed 3. Tubular Secretion: Waste and extra ions are added into tubule 🟰 Urine Output = Filtration - Reabsorption + Secretion ➤ Glomerular Filtration • GFR: 125 ml/min or 180 L/day • Filtrate lacks: Proteins, blood cells • Filtration Barrier: Endothelium, basement membrane, podocytes ➤ What Affects GFR • ↑ Blood pressure in glomerulus = ↑ GFR • ↑ Pressure in Bowman’s capsule (e.g., stone) = ↓ GFR • ↑ Plasma proteins (oncotic pressure) = ↓ GFR • Kf: Filtration ability of membrane (normal = 12.5 ml/min/mmHg) ➤ Hormonal Control • Sympathetic nerves, norepinephrine, angiotensin II: ↓ GFR • Prostaglandins, nitric oxide: Help maintain GFR • ADH: Helps concentrate urine ➤ Tubular Reabsorption • PCT: Reabsorbs 65% Na⁺, water, glucose, amino acids • Loop of Henle: • o Descending limb: Water only o Ascending limb: Na⁺, K⁺, Cl⁻ (via NKCC2) – no water DCT & Collecting Tubule: o With ADH: Reabsorbs water o Principal cells: Na⁺ in, K⁺ out o Intercalated cells: Acid–base balance ▪ Type A: Secrete H⁺ in acidosis ▪ Type B: Secrete HCO₃⁻ in alkalosis ➤ Tubular Secretion • Secretes H⁺, drugs, toxins • Helps regulate pH and remove unwanted substances ➤ Acid-Base Regulation by Kidneys • Maintains blood pH = 7.37–7.43 • Uses 3 systems: 1. Buffers (e.g., bicarbonate) 2. Respiratory system (lungs remove CO₂) 3. Renal system (slow but strong – removes H⁺ or HCO₃⁻)