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 Lamina propria Transitional epithelium Mucosa Connective tissue layer Smooth muscle

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 The wall of the urinary bladder Peritoneum Detrusor muscle Submucosa Lamina propria Transitional epithelium Mucosa

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 Filtration Membrane Capsular space Filtration slit < 3nm Filtration pore 70-90 nm Basement membrane >8nm Passed through filter: W ater Electrolytes Glucose Amino acids Fatty acids Vitamins Urea Uric acid Creatinine Turned back: Blood cells Plasma proteins Large anions Protein-bound Most molecules > 8 nm in diameter Bloodstream Endothelial cell of glomerular capillary Foot process of podocyte minerals and hormones Glomerulus Podocyte

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) 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 Tubular fluid Sodium–glucose transport protein (SGLT) (Symport) Glucose Na+ ATP Na+ Glucose Na+–K+ pump K+ Na+ Na+–H+ antiport ADP + Pi H+ K+ Cl– Cl––anion antiport Cl– Anions K+–Cl– symport H2O Aquaporin Tight junction Solvent drag Transcellular route Brush border H2O, urea, uric acid, Na+, K+, Cl–, Mg2+, Ca 2+, Pi Paracellular route 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 1 Stretch receptors detect filling of bladder, transmit afferent signals to spinal cord. 5 6 7 2 Signals return to bladder from spinal cord segments S2 and S3 via parasympathetic fibers in pelvic nerve. Pelvic nerve 3 Efferent signals excite detrusor muscle. Sensory fiber Motor fiber 4 Efferent signals relax internal urethral sphincter. Urine is involuntarily voided if not inhibited by brain. Full urinary bladder Sacral segments of spinal cord S2 Voluntary control 2 5 For voluntary control, micturition center in pons receives signals from stretch receptors. 1 S3 6 If it is timely to urinate, pons returns signals to spinal interneurons that excite detrusor and relax internal urethral sphincter. Urine is voided. Para- sympathetic ganglion in bladder wall S4 3 Stretch receptors 7 If it is untimely to urinate, signals from pons excite spinal interneurons that keep external urethral sphincter contracted. Urine is retained in bladder. Motor fibers to detrusor muscle 4 Urethra Internal urethral sphincter (involuntary) External urethral sphincter (voluntary) 8 Somatic motor fiber of pudendal nerve 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