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Unit IV: Regulation Urinary System II Chapter 23: pp. 857-883 Urine Storage and Elimination • Ureters (about 25 cm long) – small flap of mucosa that acts as a valve into bladder – 3 layers: • adventitia • muscularis – urine enters, it stretches and contracts in peristaltic wave • mucosa – lumen very narrow, easily obstructed Connective tissue layer Smooth muscle Mucosa Lamina propria Transitional epithelium Urinary Bladder • Located in pelvic cavity, posterior to pubic symphysis • 3 layers – parietal peritoneum, superiorly; fibrous adventitia rest – muscularis: detrusor muscle – mucosa: transitional epithelium • rugae: • trigone: • capacity: moderately full - 500 ml, max. - 800 ml Mucosa Transitional epithelium Lamina propria Submucosa Detrusor muscle Peritoneum The wall of the urinary bladder Urinary Bladder and Urethra - Female Female Urethra • 3 to 4 cm long • External urethral orifice – between vaginal orifice and clitoris • Internal urethral sphincter – smooth muscle • External urethral sphincter – skeletal muscle Male Bladder and Urethra • 18 cm long • Internal urethral sphincter • External urethral sphincter 3 regions prostatic urethra during orgasm receives semen membranous urethra passes through pelvic cavity spongy urethra to external urethral orifice Urine Formation Stages: Fluid names thru nephron: •Glomerular filtrate –Capsular space •Tubular fluid –PCT DCT •Urine –Collecting duct Glomerular Filtration Turned back:Filtration Membrane Blood cells Plasma proteins Large anions Protein-bound minerals and hormones Most molecules > 8 nm in diameter Glomerulus Podocyte Bloodstream Endothelial cell of glomerular capillary Basement membrane >8nm Filtration slit < 3nm Filtration pore 70-90 nm Foot process of podocyte Passed through filter: Water Electrolytes Glucose Amino acids Fatty acids Vitamins Urea Uric acid Creatinine Capsular space Glomerular Filtration • Damage causes: –Proteinuria – presence of albumin –Hematuria - presence of blood Filtration Pressure Glomerular Filtration Rate (GFR) • Filtrate formed per minute • GFR = 125 ml/min or 180 L/day, male • GFR = 105 ml/min or 150 L/day, female – depends on permeability and surface area of filtration barrier • 99% of filtrate reabsorbed, 1 to 2 L urine excreted/day Effects of GFR Abnormalities • GFR, urine output rises dehydration, electrolyte depletion • GFR wastes reabsorbed (azotemia possible) • GFR controlled by adjusting glomerular blood pressure – autoregulation – sympathetic control – hormonal mechanism: renin and angiotensin Renal Autoregulation of GFR • BP constrict afferent arteriole, dilate efferent • BP dilate afferent arteriole, constrict efferent • Function of the Juxtaglomerular Apparatus • Cannot compensate for extreme BP (<70mmHg) Sympathetic Control of GFR • Strenuous exercise or acute conditions (circulatory shock) stimulate afferent arterioles to constrict • GFR and urine production, redirecting blood flow to heart, brain and skeletal muscles Enzyme Regulation of GFR Tubular Reabsorption and Secretion: Proximal Convoluted Tubules (PCT) Tubular reabsorption: – Reclaims water and solutes from tubular fluid and returns them to the blood • Reabsorbs 65% of GF to peritubular capillaries • active transport – 6% of resting ATP and calorie consumption • Reabsorbs greater variety of chemicals than other parts of nephron – transcellular route - through epithelial cells of PCT – paracellular route - between epithelial cells of PCT Mechanisms of Reabsorption in the PCT Peritubular capillary Tissue fluid Tubule epithelial cells Glucose Na+ K+ K+ Cl– ATP Na+–K+ pump ADP + Pi K+–Cl– symport Tight junction Tubular fluid Na + Glucose Na+ H+ Cl– Anions H2 O Sodium–glucose transport protein (SGLT) (Symport) Na+–H+ antiport Cl––anion antiport Aquaporin Solvent drag Transcellular route Paracellular route Brush border H2O, urea, uric acid, Na+, K+, Cl–, Mg2+, Ca 2+, Pi Blood in Peritubular capillaries has a high Colloid Osmotic Pressure Tubular Secretion of PCT and Nephron Loop Process by which renal tubules extract chemicals from capillary blood and secrete them into the tubular fluid. • Waste removal – urea, creatine, bile salts, ammonia, catecholamines, many drugs • Acid-base balance – secretion of hydrogen and bicarbonate ions • Primary function of nephron loop – water conservation – Counter-current multiplication Water Conservation DCT and Collecting Duct • Function – fluid reabsorption (water conservation) • DCT reabsorbs Na, Cl, and water • Collecting Duct only conserves water – regulated by hormonal action (Aldosterone, ANP, ADH, PTH) • Principal cells – receptors for hormones; involved in salt/water balance • Intercalated cells – involved in acid/base balance Voiding Urine - Micturition Involuntary micturition reflex To pons From pons 5 6 7 Pelvic nerve Sensory fiber Motor fiber Stretch receptors detect filling of bladder, transmit afferent signals to spinal cord. 2 Signals return to bladder from spinal cord segments S2 and S3 via parasympathetic fibers in pelvic nerve. 3 Efferent signals excite detrusor muscle. 4 Full urinary bladder Sacral segments of spinal cord S2 2 1 Parasympathetic ganglion in bladder wall Stretch receptors 4 Internal urethral sphincter (involuntary) Urethra External urethral sphincter (voluntary) 8 5 Somatic motor fiber of pudendal nerve S4 Efferent signals relax internal urethral sphincter. Urine is involuntarily voided if not inhibited by brain. Voluntary control S3 3 Motor fibers to detrusor muscle 1 6 For voluntary control, micturition center in pons receives signals from stretch receptors. If it is timely to urinate, pons returns signals to spinal interneurons that excite detrusor and relax internal urethral sphincter. Urine is voided. 7 If it is untimely to urinate, signals from pons excite spinal interneurons that keep external urethral sphincter contracted. Urine is retained in bladder. 8 If it is timely to urinate, signals from pons cease and external urethral sphincter relaxes. Urine is voided. Test IV - Regulation Chapters 16 and 23 Chapter 24: 885-891 Lab: •Identify organs of endocrine and urinary system •Slides and models •Roles of those organs •Tissue types of urinary system