Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Biology 233 Human Anatomy and Physiology Chapter 26 Lecture Outline URINARY SYSTEM kidneys – filter blood and form urine ureters – carry urine from kidneys to bladder urinary bladder – stores urine urethra – voids urine to outside FUNCTIONS OF URINARY SYSTEM 1) Filtration and Reabsorption of Blood – wastes are excreted and nutrients are reabsorbed Excretion of Wastes – excreted in urine nitrogenous wastes urea and ammonia – from amino acids uric acid – from nucleic acids bilirubin – from hemoglobin creatinine – from creatine phosphate foreign drugs and toxins Regulation of Blood Osmolarity, Ion Concentration, and pH osmolarity = number of solute particles / liter of solution ions (electrolyte balance) – Na+, K+, Ca+2, Cl-, phosphate pH – H+, bicarbonate ions water – maintains blood volume and pressure regulated by ADH and aldosterone 2) Secretion of Hormones and Enzymes calcitriol (vitamin D) – increases absorption of dietary calcium erythropoetin – stimulates RBC production renin (enzyme) – RAA pathway; increases blood pressure RENAL (KIDNEY) GROSS ANATOMY paired; kidney bean-shaped (11cm X 6cm) retroperitoneal; superior abdomen Protected by connective tissues: renal capsule (on surface of kidney) – dense irregular CT; protects and shapes kidney adipose capsule – cushions kidney renal fascia – dense irregular CT; anchors kidney to abdominal wall 1 Renal Hilus (Hilum) renal artery and nerves enter renal vein and ureter exit Renal Parenchyma – functional tissues of kidney renal cortex – superficial; pale reddish-brown renal columns – extend toward hilus renal medulla – deep portion; dark reddish-brown renal pyramids (8-18) renal papilla – apex of pyramid renal lobes (8-18) 1 pyramid + surrounding cortex filter blood and form urine urine drains into minor calyx (8-18) major calyces (2-3) renal pelvis – connects calyces to ureter RENAL HISTOLOGY NEPHRON – basic functional unit of kidney renal corpuscle – site of filtration renal tubule – collects filtered fluid, site of reabsorption & secretion Blood Supply to Nephron renal artery – branches extensively afferent arteriole – supplies one renal corpuscle glomerulus – capillary bed in renal corpuscle (filtration site) efferent arteriole – drains renal corpuscle peritubular capillaries & vasa recta – surround renal tubules (site of reabsorption into blood) renal vein Renal Corpuscle – lies in cortex; 2 divisions 1) glomerulus – fenestrated capillary bed endothelial cells with many pores 2) glomerular (Bowman’s) capsule – surrounds glomerulus 2 layers: 1) visceral layer – lines glomerulus podocytes – modified simple squamous epithelium pedicels – foot-like processes wrap around glomerulus filtration slits – spaces between pedicels 2) parietal layer – lines wall of capsule simple squamous epithelium capsular space – between layers of capsule fluid (filtrate) filters out through glomerulus and collects in capsular space 2 Renal Tubule – filtrate from corpuscle flows through some solutes reabsorbed into blood, others secreted into urine 3 divisions: 1) proximal convoluted tubule (PCT) – in cortex drains glomerular capsule simple cuboidal e. w/ microvilli 2) Loop of Henle descending limb – enters medulla ascending limb – returns to cortex thick segment – simple cuboidal e. thin segment – simple squamous e. 3) distal convoluted tubule (DCT) – in cortex simple cuboidal e. collecting ducts – collect urine from several renal tubules papillary ducts – collect urine from several collecting ducts Flow Summary glomerular capsule ---> proximal convoluted tubule ---> Loop of Henle ---> distal convoluted tubule ---> collecting duct ---> papillary duct ---> minor calyx ---> major calyx ---> renal pelvis --->ureter Types of Nephrons cortical nephrons corpuscles in outer cortex short Loop of Henle juxtamedullary nephrons corpuscle near medulla long Loop of Henle, extends deep into medulla juxtaglomerular apparatus – (DCT near glomerulus) endocrine cells involved in blood pressure regulation macula densa – densely packed cells in wall of DCT juxtaglomerular (JG) cells – modified smooth muscle cells in wall of afferent arteriole RENAL PHYSIOLOGY 3 Processes Involved in Production of Urine: 1) Glomerular Filtration – blood filters through walls of glomerular capillaries into glomerular capsule filtrate – water and smaller plasma solutes average production – 180 liters/day (50 gal) 2) Tubular Reabsorption – filtrate passes through renal tubule and 99% of water and many useful nutrients are reabsorbed into blood (1-2 liters of urine/day excreted) 3 3) Tubular Secretion – renal tubule cells secrete additional solutes from from blood into urine (nitrogenous wastes, excess ions, drugs) GLOMERULAR FILTRATION Filtration Membrane – thin, leaky membrane that filters blood 3 layers: glomerular endothelium – large fenestrations water and all solutes pass through blood cells and platelets retained in capillaries lamina densa (basement membrane)– acellular layer prevents filtration of large plasma proteins filtration slits – between pedicels of podocyte cells acellular layer prevents filtration of most plasma proteins Composition of Filtrate – plasma minus plasma proteins water, glucose, amino acids, lipoproteins, nitrogenous wastes, ions, bilurubin, creatinine, vitamins Filtration Pressure (FP) = GHP – (CsHP + BCOP) GHP – glomerular hydrostatic pressure blood pressure that promotes filtration normally high – efferent arteriole smaller that afferent CsHP – capsular hydrostatic pressure resistance in glomerular capsule that opposes filtration BCOP – blood colloid osmotic pressure pressure due to plasma proteins that opposes filtration GLOMERULAR FILTRATION RATE (GFR) – total amount of filtrate formed/minute (average 125ml/minute) high GFR – urine formed so quickly, needed substances may not have time to be reabsorbed (nutrients and water lost in urine) low GFR – wastes filtered out slowly and slow movement of urine in tubules may allow too much reabsorption (wastes accumulate in blood) Regulation of GFR CsHP – constant if urine outflow is unobstructed BCOP – constant if blood volume and plasma protein content are normal GHP – regulated by altering blood flow and pressure in glomerulus altering diameter of afferent and efferent arterioles mesanglial cells – cells in glomerulus that open or close filtration slits 4 3 GFR REGULATORY MECHANISMS – can maintain normal GFR for mean arterial blood pressures between 80-180mmHg 1) Renal Autoregulation – kidneys regulate own GHP in response to changes in local blood flow and blood pressure decreased blood pressure and blood flow in glomerulus triggers dilation of afferent arteriole = increases blood flow constriction of efferent arteriole = increases GHP opening of glomerular filtration slits = more filtration increased blood pressure – stretches afferent arteriole reflex vasoconstriction of afferent arteriole decreases blood flow = decreases GHP = decreases GFR 2) Neural (Autonomic) Regulation sympathetic stimulation (fight or flight) norepinephrine causes vasoconstriction of afferent arterioles decreases blood flow = decreased GHP = decreased GFR 3) Hormonal Regulation Returning Reduced GFR to Normal: RAA pathway – begins with secretion of renin by JG cells (angiotensinogen --> angiotensin I --> angiotensin II) 3 Triggers for RAA Pathway: (all related to reduced GFR) 1) decreased GHP (< BP, < blood volume, blocked renal arteries) 2) sympathetic stimulation 3) decreased solute concentration of filtrate detected by macula densa (slow GFR causes more reabsorption) Effects of Angiotensin II: nephron – constriction of efferent arteriole = >GHP > reabsorption of Na+ and water in PCT = > blood volume adrenal glands – aldosterone secretion > reabsorption of Na+ and water in DCT and collecting duct = > blood volume CNS – thirst = > blood volume secretion of ADH = > reabsorption of water in DCT and collecting duct = > blood volume > CO, venoconstriction, vasoconstriction = >BP capillary beds – vasoconstriction = >BP Returning Increased GFR to Normal: natriuretic peptides (ANP, BNP) (high BP or volume) increased stretching of heart = release of ANP, BNP opening of filtration slits = more filtration dilation of afferent arteriole = > blood flow constriction of efferent arteriole = >GHP < reabsorption of Na+ and water = increased urine volume = < blood volume = < BP 5 TUBULAR REABSORPTION AND SECRETION filtration forms 180 liters/day total blood volume is only 5 liters Tubular Epithelium tight junctions between cells – prevent leakage apical membrane – faces tubular fluid basolateral membrane – faces interstitial fluid peritubular capillaries lie nearby apical and basolateral membranes have different permeabilities due to different transport proteins in their membranes Mechanisms of Reabsorption and Secretion Passive Transport diffusion – ion leakage channels facilitated diffusion – eg. glucose osmosis – aquaporin channels; water follows solutes obligatory water reabsorption – 90% facultative water reabsorption – final 10% regulated by antidiuretic hormone occurs in DCT and collecting duct Active Transport primary – Na+/K+ pumps apical membrane – none basolateral membrane – many Na+ is pumped out of tubule cells into interstitial space creating a concentration gradient (high Na+ in filtrate, low in tubular cells) secondary – use energy from Na+ concentration gradient cotransport – solutes cross with Na+ countertransport – solutes cross opposite to Na+ Proximal Convoluted Tubule all organic nutrients reabsorbed – glucoses, amino acids, lipids majority of water and ion reabsorption (65%) Primary Active Transport Na+/K+ pumps in basolateral membrane pump Na+ out of tubular cells into interstitial space Passive Transport Na+ diffuses into tubule cells from tubular fluid water follows by osmosis less water in tubule = osmolarity of tubule fluid increases other solutes diffuse down their concentration gradients 6 Secondary Active Transport Na+ cotransport – glucose, amino acids, bicarbonate reabsorbed into blood + Na countertransport – H+ secreted into urine (buffered by bicarbonate in tubules) Loop of Henle – 25% of reabsorption countercurrent multiplication ascending limb – no aquaporins – impermeable to water Na+-K+-2Cl- cotransporters – ions are reabsorbed without water following osmolarity in interstitial fluid increases descending limb – aquaporins – water flows out by osmosis osmolarity in descending limb increases more ions to be pumped out in ascending limb + Na and Cl become concentrated in interstitial space of medulla creates a concentration gradient in the medulla Distal Convoluted Tubule filtrate entering from loop of Henle has low osmolarity amount of reabsorption varies Na-Cl cotransport site of PTH activity – promotes reabsorption of Ca+2 site of aldosterone activity – promotes reabsorption of Na+ and secretion of K+ (opposed by natriuretic peptides) Na-H+ countertransport – secrete variable amounts of H+ to maintain pH (reabsorb bicarbonate – related to H+ concentration) Collecting Duct site of aldosterone activity – same as DCT urea reabsorption highly concentrated in tubules – diffuses into interstitial space adds to concentration gradient in medulla site of regulation of body pH secretes or reabsorbs H+ and bicarbonate as needed Water Reabsorption obligatory reabsorption – 85% of water reabsorption occurs in PCT and loop of Henle water always follows reabsorbed solutes by osmosis facultative reabsorption – remaining 15% of water reabsorption occurs in DCT and collecting duct variable amounts of water reabsorbed depending on number of aquaporin channels present facultative reabsorption is regulated by ADH no ADH = no aquaporins = no water reabsorbed more ADH = more aquaporins = more water reabsorption 7 Summary of Hormones Regulating Renal Function 1)RAA Pathway – initiated by factors that reduce GFR increases blood volume increases blood pressure increases GFR, but mildly decreases urine production also increases K+ secretion 2) Antidiuretic Hormone (ADH) released due to increased blood osmolarity and RAA pathway increases water reabsorption decreases urine production diabetes insipidus – hyposecretion of ADH up to 20 liters of urine/day 3) Natriuretic Peptides (ANP, BNP) secreted due to increased stretch of heart (high preload) decreases Na+and water reabsorption suppresses aldosterone and ADH secretion decreases GFR and increases urine production PRODUCTION OF DILUTE OR CONCENTRATED URINE kidneys maintain body fluid volume and osmolarity regulated mainly by ADH increased water intake – increases blood volume and decreases osmolarity less ADH is secreted = fewer aquaporins in DCT and collecting duct solutes are reabsorbed in renal tubule water cannot follow due to lack of aquaporins large volume of dilute urine produced dehydration – decreases blood volume and increases osmolarity more ADH secreted = more aquaporins in DCT and collecting duct water reabsorbed by osmosis high solute concentration gradient in medulla Na+ and Cl- pumped out in ascending loop of Henle urea diffusing out of distal collecting duct large volumes of water can be reabsorbed if enough aquaporins are present small volume of concentrated urine produced diuretics – drugs that inhibit reabsorption of water in kidneys = more urine diuresis – production of large volumes of urine used to treat hypertension (high BP) and edema 8 URINE STORAGE AND ELIMINATION Ureters – carry urine from kidneys to urinary bladder 12 inches long, 1-10mm wide retroperitoneal; enter bladder posteriorly physiological sphincter – pressure in bladder blocks backflow Histology of Ureters mucosa – very elastic; secretes mucus to protect epithelium from wastes in urine transitional epithelium – changes appearance round and many layers when empty flat and few layers when stretched lamina propria – areolar CT; many elastic fibers muscularis – smooth muscle longitudinal and circular layers peristalsis aids flow of urine down ureters adventitia areolar CT + blood & lymph vessels and nerves Urinary Bladder – stores urine trigone – smooth, triangular area in floor of urinary bladder 2 ureteral openings – posterior wall internal urethral orifice (neck) – opening to urethra internal urethral sphincter – smooth muscle, involuntary rugae (folds) in lining of empty bladder Histology of Urinary Bladder mucosa transitional epithelium lamina propria muscularis – detrusor muscle 3 layers of smooth muscle: inner and outer longitudinal layers middle circular layer serosa – visceral peritoneum lining superior surface adventitia – surrounds other surfaces Urethra – carries urine from bladder to exterior Female Urethra – 4cm long; posterior to pubic symphysis external urethral orifice – anterior to vagina Histology mucosa transitional epithelium near bladder stratified squamous at external orifice 9 muscularis – circular smooth muscle external urethral sphincter – skeletal muscle surrounds urethra at pelvic outlet voluntary control over urination Male Urethra – also carries reproductive secretions 3 regions: 1) prostatic urethra – passes through prostate gland mucosa – changes from transitional to stratified columnar muscularis – circular smooth muscle 2) membranous urethra – passes through urogenital diaphragm (muscles and connective tissue across pelvic outlet) mucosa – stratified columnar e. external urethral sphincter – skeletal muscle 3) spongy urethra – passes through penis mucosa – stratified columnar e. for most of length stratified squamous e. near external urethral orofice MICTURITION REFLEX – autonomic reflex micturition – urination stretch receptors in wall of bladder Micturition Center – S2-S3 spinal cord segments (spinal reflex) parasympathetic motor fibers to smooth muscles contraction of detrusor muscle (bladder wall) cerebral cortex perceives fullness – has voluntary control contraction of skeletal muscles in external urethral sphincter and pelvic floor can prevent urination relaxation of external urethral sphincter also relaxes internal sphincter urinary incontinence – lack of voluntary control over urination CLINICAL EVALUATION OF RENAL FUNCTION Composition of Urine 95% water 5 % solutes – ions, urea, creatinine, uric acid, ammonia, pigments, enzymes, hormones, drugs URINALYSIS – examining urine Volume normal 1-2 liters/day Color normal – yellow-amber urobilin from breakdown of hemoglobin pale – dilute urine dark – concentrated urine Turbidity normal – transparent when fresh becomes turbid (cloudy) as it sits 10 Odor normal - mild ammonia pH normal – 4.5-8 (average 6) protein diet – more acidic vegetarian diet – more alkaline Specific Gravity (density compared to water) – indicates solute concentration (specific gravity of water = 1.0) normal – 1.001-1.035 increases when solutes are high Test Strips albuminuria (albumin) – glomerular damage, high BP glucosuria (glucose) – diabetes mellitus hemoglobinuria (hemoglobin) – destruction of RBCs ketonuria (ketones) – diabetes, fasting bilirubinuria (bilirubin) – liver disease Microscopic Examination hematuria (RBCs) – inflammation, kidney stones, trauma pyuria (WBCs) – infection casts – clumps of material (cells) crystals microbes – infection RENAL FUNCTION TESTS – blood tests blood urea nitrogen (BUN) rises when GFR is low (renal disease, urinary obstructiion) plasma creatinine rises when GFR is low creatinine clearance test all creatinine is normally excreted in urine creatinine excreted / minute = GFR plasma concentration of creatinine Dialysis – artificial cleansing of blood through a semipermeable membrane hemodialysis – blood flows through a dialysis membrane wastes diffuse into surrounding dialysis solution solutes removed from blood depend on permeability of dialysis membrane and concentrations of solutes in dialysis solution continuous ambulatory peritoneal dialysis peritoneum is the dialysis membrane peritoneal cavity is filled with dialysis solution solution is drained following exchange 11