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Urinary System! (Chapter 26)!
Lecture Materials!
for!
Amy Warenda Czura, Ph.D.!
Suffolk County Community College!
Eastern Campus!
Primary Sources for figures and content:! Marieb, E. N. Human Anatomy & Physiology 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.! Martini, F. H. Fundamentals of Anatomy & Physiology 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.!
Urinary System Components:! -Kidneys! -Ureters! -Urinary Bladder !! -Urethra!
urinary tract!
Functions:!
- Excretion (kidney):! !remove organic wastes from blood!
- Elimination (UT):! !discharge wastes to environment!
- Regulation of plasma volume and solute! ! concentration (kidney):! -blood volume, BP! -conc. of ions! -stabilize blood pH! -conserve nutrients! -assist liver: deamination, detoxification!
- Other kidney functions:! A. gluconeogenesis during starvation! B. produce renin (regulate BP)! C. produce erythropoietin (RBC production)! D. convert Vitamin D to calcitriol (Ca++^! ! absorption in GI)!
Kidneys! -1% body weight! -retroperitoneal, posterior abdominal wall! -adrenal gland anchored superior! -3 layers CT anchor kidneys:!
- Renal capsule: collagen fibers covering! ! organ!
- Adipose capsule: adipose cushion around ! renal capsule!
- Renal fascia: collagen fibers fused to renal ! capsule and deep fascia of body wall! ! and peritoneum! Renal ptosis = floating kidney: starvation or! ! injury, kidney loose from body wall,! ! could twist blood vessels or ureters!
-Hilum: where renal! arteries, renal! veins, ureters! enter/exit! -Hilum opens to! renal sinus! -Renal sinus lined! with renal capsule,! contiguous with! outside!
Kidney has two layers:!
- Cortex: superficial, contact renal capsule,! ! houses filtration structures (nephrons)!
- Medulla: 6-18 renal pyramids, parallel! ! bundles of collection tubules, apex =! ! papilla, points toward renal sinus! Kidney divided into sections: renal lobes! Renal lobe = renal pyramid + surrounding! ! cortex called renal columns, lobe is! ! complete site of urine production!
Urine production:! nephron (cortex)! collecting ducts (medulla)! ! papilla! minor calyx! major calyx !! renal pelvis! Renal pelvis: fills majority of renal sinus,! ! funnels urine into ureter! Pyelonephritis = inflammation of kidney,! ! infection usually enters from ureter and! ! spreads up through ducts to nephron!
Blood Supply and Innervation to kidney:! -receives 20-25% cardiac output! -highly vascularized, many capillaries! ! involved in filtration (nephrons)!
- Innervation from Renal Plexus controlled by! ! ANS! -Most is sympathetic to!
- Adjust rate of urine formation (change ! BP and flow at nephron)!
- Stimulate release of renin (restricts water! ! and Na+^ loss at nephron)!
Nephron:! -smallest functional unit of kidney! -more than 1 million per kidney! -two major parts:!
- Renal corpuscle = glomerular! ! capsule + glomerulus!
- Renal tubule = proximal convoluted! ! tubule (PCT) + nephron loop + distal! ! convoluted tubule (DCT)!
Two important! capillary beds! associated with! each nephron:!
- Glomerulus: filtration!
- Peritubular capillaries: reclaim filtrate,! ! concentrate urine! Both connected to arterioles only (not for O 2! ! exchange)! afferent arteriole!capillary!efferent arteriole!
Juxtaglomerular Apparatus (JGA):! -consists of two cell types:!
- Endocrine cells of DCT = macula densa!
- Granular cells of afferent arteriole =! ! juxtaglomerular cells! -together cells monitor blood and produce:!
- Renin: enzyme, restricts Na+^ and H 2 O at! ! nephron!
- Erythropoietin: hormone, stimulates RBC! ! production!
Collecting System:! -collecting ducts + papillary ducts! nephrons! 1 collecting duct (renal pyramid)! many collecting ducts! 1 papillary duct! -final osmotic concentration of filtrate! ! adjusted by collecting duct, after this! ! urine is complete and exits kidney:! papillary duct (renal papilla)! minor calyx! ! major calyx! renal pelvis! ureter!
Polycystic kidney disease = genetic, cysts! ! form that cause swelling of kidney! ! tubules, compression reduces function!
Renal Physiology! -urinary system functions to regulate blood! ! volume and conc., remove wastes, and! ! produce urine! Filtrate = everything in blood plasma except! ! large proteins and cells! Urine =metabolic waste, 1% filtrate!
Common wastes:!
- Urea: from catabolism of amino acids!
- Creatinine: from catabolism or damage of! ! skeletal muscle tissue (creatine! ! phosphate is energy storage of muscle)!
- Uric Acid: from recycling of RNA!
- Urobilin: from breakdown of hemoglobin! ! (yellow color)! All wastes excreted as solution in water! Loss of filtering! toxic waste buildup, death! ! in few days! Dialysis = blood filtering machine, used for! ! patients with kidney failure! Urine Formation:!
- Glomerular Filtration: blood hydrostatic! ! pressure forces water and solutes! ! through glomerular wall!
- Tubular Reabsorption: selective uptake of! ! water and solutes from filtrate!
- Tubular Secretion: transport of wastes from! ! capillaries to tubules! 1. Glomerular Filtration! -occurs through filtration membrane:! 1. Fenestrated endothelium of glomerular! ! capillaries (restricts cells)! 2. Podocytes (visceral epithelium of! ! capsule), filtration slits restrict solutes! ! protein sized and larger! 3. Fused basal lamina for both!
-filtration is passive! but all small solutes! escape e.g. glucose,! amino acids etc.!
-filtration depends on:!
- Large surface area!
- High glomerular BP!
- Good permeability! Glomerular Filtration Rate (GFR) = amount of! ! filtrate kidneys produce / minute! ~125ml/min! 180L/day! -99% reabsorbed, 1% lost as urine! -drop in BP =#GFR (#15%BP = 0 GFR)!
Regulation to maintain constant GFR! ! (on handout)!
2. Tubular Reabsorption! -transport proteins in renal tubule cells return! ! substances from filtrate to plasma! -when carrier proteins are saturated by! substance they carry (transporting at max.! velocity) the renal threshold for that! substance has been reached, additional! amounts of substance will be lost in urine!
! e.g. Glycosuria = glucose in urine:! ! glucose levels in blood/filtrate! ! exceed renal threshold! PCT reabsorption:! -PCT reabsorbs 60-70% of filtrate!
- Reabsorption of 99% of organic nutrients! ! by facilitated diffusion and cotransport!
- Passive reabsorption of ions by diffusion!
- Selective reabsorption of ions by active! ! transport: ion pumps controlled by! ! hormones!
- Reabsorption of water by osmosis (water! ! follows ions)! Nephron loop reabsorption:! -functions to concentrate filtrate! -reabsorbs half remaining water and 2/3 Na+^! ! and Cl-^ by countercurrent! ! multiplication: ascending limb pumps! ! ions from filtrate to medulla, high ion! ! conc. then causes water to move by! ! osmosis out of descending limb!
DCT reabsorption:! -aldosterone promotes Na+^ uptake and K+^! ! loss via sodium potassium pump! -parathyroid hormone and calcitriol promote! ! Ca2+^ uptake! -ADH stimulates water uptake!
3. Tubular Secretion! -selectively removes solutes from blood,! ! delivers them to filtrate!
- Dispose of drugs and wastes that were not! ! filtered!
- Eliminate wastes that were reabsorbed!
- Rid body of excess K+!
- Control blood pH: remove H+! CO 2 + H 2 O " H 2 CO 3 " H+^ + HCO 3 -! ! Bicarbonate ions used to buffer blood! ! pH but H+^ must be secreted into filtrate! -secretion carried out mostly by DCT, but! ! some also occurs in collecting ducts!
Control of Water Volume! -obligatory water reabsorption occurs by! ! osmosis in PCT and descending nephron! ! loop (cannot be prevented)! -facultative water reabsorption can occur in! ! DCT and collecting ducts (usually! ! impermeable):!
-if volume exceeds ~500ml, forced relaxation! ! of internal and external urethral! ! sphincters will result in non-voluntary! ! urination/micturition! Incontinence = inability to voluntarily control! ! urine excretion, due to: loss of muscle! ! tone, damage to sphincters, damage to! ! nerves or control centers in brain!
Age Related Changes:! -decline in functional nephrons! -reduction in GFR (damage or #blood flow)! -reduced sensitivity to ADH = dilute urine! -problems with micturition:! ! -incontinence! ! -urinary retention (enlarged prostate)!
