Chapter 26 The Urinary System-revised (1).pdf - Chapter 26...

Unformatted text preview: Chapter 26 The Urinary System Organs of Urinary System 1.  Kidneys — organs that produce urine 2.  Urinary tract — organs that eliminate urine •  Ureters (paired tubes) •  Urinary bladder (muscular sac) •  Urethra (exit tube) –  Urination or micturition — process of eliminating urine •  Contraction of muscular urinary bladder forces urine through urethra, and out of body Organs of the Urinary System Kidney Produces urine Ureter Transports urine toward the urinary bladder Urinary bladder Temporarily stores urine prior to urination Urethra Conducts urine to exterior; in males, it also transports semen Rakhi Agarwal, Ph.D. QCC Urinary System Functions •  Three Functions: 1.  Excretion (Kidneys) •  Removal of organic wastes from body fluids 2.  Elimination (UT) •  Discharge of waste products 3.  Homeostatic regulation (Kidneys) –  Regulates blood volume and blood pressure •  By adjusting volume of water lost in urine •  Releasing erythropoietin and renin –  Regulates plasma ion concentrations •  Sodium, potassium, and chloride ions (by controlling quantities lost in urine) •  Calcium ion levels (through synthesis of calcitriol) –  Helps stabilize blood pH •  By controlling loss of hydrogen ions and bicarbonate ions in urine –  Conserves valuable nutrients •  By preventing excretion while excreting organic waste products –  Assists liver –  In detoxifying poisons Rakhi Agarwal, Ph.D. QCC The Kidneys -­‐1% body weight -­‐retroperitoneal, posterior abdominal wall -­‐adrenal gland anchored superior -­‐3 layers CT anchor kidneys: 1. Renal capsule/ fibrous capsule: collagen fibers covering organ 2. Adipose capsule/perinephareBc fat: adipose cushion around renal capsule 3. Renal fascia: collagen fibers fused to renal capsule and deep fascia of body wall and peritoneum Renal ptosis = floaMng kidney: starvaMon or injury, kidney loose from body wall, could twist blood vessels or ureters Rakhi Agarwal, Ph.D. QCC Figure 26-3 The Gross Anatomy of the Urinary System. Esophagus (cut) Diaphragm Left adrenal gland Inferior vena cava Left kidney Celiac trunk Left renal artery Right adrenal gland Left renal vein Right kidney Superior mesenteric artery Hilum Quadratus lumborum muscle Left ureter Abdominal aorta Iliacus muscle Left common iliac artery Gonadal artery and vein Psoas major muscle Peritoneum (cut) Rectum (cut) Urinary bladder Anterior view Rakhi Agarwal, Ph.D. QCC Figure 26-2b The Position of the Kidneys. External oblique Parietal peritoneum Stomach Renal vein Renal artery Aorta Pancreas Ureter Spleen Left kidney Vertebra Connective tissue layers Fibrous capsule Perinephric fat Renal fascia Quadratus lumborum Psoas major Inferior vena cava b A superior view of a transverse section at Rakhi the Alevel garwal, Pindicated h.D. QCC in part (a) -­‐Hilum: where renal arteries, Inner layer of renal veins, fibrous capsule ureters enter/exit Renal sinus Adipose tissue -­‐Hilum opens to in renal sinus Renal pelvis renal sinus Hilum -­‐Renal sinus lined Renal papilla with renal Ureter capsule, a conMguous with outside Figure 26-4a The Structure of the Kidney. Rakhi Agarwal, Ph.D. QCC Renal cortex Renal medulla Renal pyramid Connection to minor calyx Minor calyx Major calyx Kidney lobe Renal columns Fibrous capsule Kidney has two layers: 1.  Cortex: superficial, contact renal capsule houses filtraMon Inner layer of structures (nephrons) fibrous capsule 2.  Medulla: 6-­‐18 renal Renal sinus pyramids, parallel bundles Adipose tissue in renal sinus of collecMon tubules, apex Renal pelvis = papilla, points toward Hilum renal sinus Renal papilla –  Kidney divided into Ureter secMons: renal lobes Figure 26-4a The Structure of the Kidney. •  a Renal lobe = renal pyramid + surrounding cortex called renal columns, lobe is complete site of urine Rakhi Agarwal, Ph.D. QCC producMon Renal cortex Renal medulla Renal pyramid Connection to minor calyx Minor calyx Major calyx Kidney lobe Renal columns Fibrous capsule Urine producBon: nephron (cortex)→ collecMng ducts (medulla) → papilla → minor calyx → major calyx →renal pelvis Renal pelvis: fills majority of renal sinus, funnels urine into ureter Pyelonephri+s = inflammaMon of kidney, infecMon usually enters from ureter and Rakhi spreads u p hrough ducts to nephron Agarwal, Ph.D. QtCC Blood Supply and InnervaBon to kidney: -­‐receives 20-­‐25% cardiac output -­‐highly vascularized, many capillaries involved in filtraMon (nephrons) -­‐InnervaMon from Renal Plexus controlled by ANS -­‐Most is sympatheMc to 1.  Adjust rate of urine formaMon (change BP and flow at nephron) 2. SMmulate release of renin (restricts water and Na+ loss at nephron) Rakhi Agarwal, Ph.D. QCC Nephron: -­‐smallest funcMonal unit of kidney -­‐more than 1 million per kidney -­‐two major parts: 1.  Renal corpuscle = glomerular capsule or Bowman’s capsule + glomerulus 2.  Renal tubule = proximal convoluted tubule (PCT) + nephron loop (loop of Henle) + distal convoluted tubule (DCT) NEPHRON Proximal convoluted tubule Distal convoluted tubule • Reabsorption of water, ions, and all organic nutrients • Secretion of ions, acids, drugs, toxins • Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Cuboidal cells with abundant microvilli Cuboidal cells with few microvilli Mitochondria Renal tubule Renal corpuscle • Production of filtrate Squamous cells Efferent arteriole Afferent arteriole Glomerulus Glomerular capsule Descending limb of loop begins Capsular space Ascending limb of loop ends Nephron loop Squamous cells Low cuboidal cells Descending limb Further reabsorption of water Ascending limb Reabsorption of sodium and chloride ions Thick ascending limb Thin descending limb KEY Filtrate Water reabsorption Variable water reabsorption Solute reabsorption or secretion Variable solute reabsorption or secretion Rakhi Agarwal, Ph.D. QCC Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System (Part 1 of 2). Two important capillary beds associated with each nephron: Peritubular capillaries Efferent arteriole Afferent 1. Glomerulus: filtraMon arteriole 2. Peritubular capillaries: reclaim Renal corpuscle filtrate, concentrate urine. Collecting duct –  Both connected to arterioles Peritubular capillaries only (not for O2 exchange) Distal convoluted tubule Nephron loop Afferent arteriole → capillary → à efferent arteriole b The circulation to a cortical nephron Rakhi Agarwal, Ph.D. QCC Two types of nephrons: 1.  CorBcal nephrons: majority, in cortex, short nephron loops 2.  Juxtamedullary nephrons: 15%, at cortex/medulla interface, long nephron loops, important for water conservaMon and concentrated urine Cortical nephron Juxtamedullary nephron Cortex Medulla Collecting duct Papillary duct Renal papilla Minor calyx a The general appearance and location nephrons the kidneys Rakhi Aof garwal, Ph.D. in QCC Renal Corpuscle: -­‐site of filtraMon -­‐2 parts: Glomerular capsule Glomerular Capsular Visceral epithelium epithelium Capsular capillary (podocyte) space 1.  Glomerular capsule: thin Efferent arteriole Proximal convoluted parietal Distal convoluted tubule tubule epithelium, forms Juxtaglomerular capsule around complex Macula densa glomerulus Juxtaglomerular cells 2.  Glomerulus: fenestrated Afferent arteriole capillaries covered by Golmerulonephri1s = inflammaMon of glomeruli, podocytes = prevents filtraMon, can be result of anMgen/Ab visceral complexes trapped in filtraMon slits following allergy or bloodinfecMon Rakhi Agarwal, Ph.D. QCC epithelium a Important structural features of a renal corpuscle. Figure 26-8b The Renal Corpuscle. Filtration membrane Podocyte nucleus Podocytes = visceral epithelium, intertwine to create filtraMon slits on surface of capillaries, slits smaller than fenestraMons in glomerular capillaries to restrict filtraMon of large molecules Fenestrated endothelium Dense layer Filtration slits Capillary endothelial cell Mesangial cell Pores RBC Pedicels Podocyte Capsular space Capsular epithelium b This cross section through a portion of the glomerulus shows the components of Rakhi Agarwal, Ph.D. Qthe CC filtration membrane of the nephron. Renal Tubule: -­‐reabsorpMon to process raw filtrate into urine -­‐3 parts: 1.  PCT: simple cuboidal epithelium with microvilli, reabsorbs organic nutrients, ions, water, and small plasma proteins from filtrate exiMng glomerular capsule 2.  Nephron loop: simple squamous epithelium, reabsorbs Na+, Cl-­‐, and H2O from filtrate, important to regulate volume and solute conc. of urine, has descending and ascending limbs NEPHRON Proximal convoluted tubule Distal convoluted tubule • Reabsorption of water, ions, and all organic nutrients • Secretion of ions, acids, drugs, toxins • Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Cuboidal cells with abundant microvilli Cuboidal cells with few microvilli Mitochondria Renal tubule Renal corpuscle • Production of filtrate Squamous cells Efferent arteriole Afferent arteriole Glomerulus Glomerular capsule Descending limb of loop begins Capsular space Ascending limb of loop ends Nephron loop Squamous cells Low cuboidal cells Descending limb Further reabsorption of water Ascending limb Reabsorption of sodium and chloride ions Thick ascending limb Thin descending limb KEY Filtrate Water reabsorption Variable water reabsorption Rakhi Agarwal, Ph.D. QCC Solute reabsorption or secretion Variable solute reabsorption or secretion 3. DCT: simple cuboidal epithelium, flat surface, has four important funcMons: NEPHRON Proximal convoluted tubule Distal convoluted tubule • Reabsorption of water, ions, and all organic nutrients • Secretion of ions, acids, drugs, toxins • Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Cuboidal cells with abundant microvilli Cuboidal cells with few microvilli Mitochondria 1.  SecreMon: removal of wastes from peritubular capillaries into filtrate 2.  Reabsorb Na+ and Ca2+ from filtrate 3.  OpMonal H2O reabsorpMon from filtrate under hormonal control 4.  Contribute to formaMon of Juxtaglomerular Apparatus Renal tubule Renal corpuscle • Production of filtrate Squamous cells Efferent arteriole Afferent arteriole Glomerulus Glomerular capsule Descending limb of loop begins Capsular space Ascending limb of loop ends Nephron loop Squamous cells Low cuboidal cells Descending limb Further reabsorption of water Ascending limb Reabsorption of sodium and chloride ions Thick ascending limb Thin descending limb KEY Filtrate Water reabsorption Variable water reabsorption Solute reabsorption or secretion Variable solute reabsorption or secretion Rakhi Agarwal, Ph.D. QCC Juxtaglomerular Apparatus (JGA): -­‐consists of two cell types: 1. Endocrine cells of DCT = macula densa 2. Granular cells of afferent arteriole = juxtaglomerular cells -­‐together cells monitor blood and produce: Glomerular capsule 1. Renin: enzyme, restricts Na+ and H2O Visceral at nephron Capsular Glomerular epithelium epithelium Capsular capillary (podocyte) 2. ErythropoieMn: hormone, s Mmulates RBC producMon space Efferent arteriole Proximal convoluted tubule Distal convoluted tubule Juxtaglomerular complex Macula densa Juxtaglomerular cells Rakhi Agarwal, Ph.D. QCC CollecBng System: -­‐collecMng ducts + papillary ducts nephrons → 1 collecMng duct (renal pyramid) many collecMng ducts → 1 papillary duct -­‐final osmoMc concentraMon of filtrate adjusted by collecMng duct, ager this urine is complete and exits kidney: papillary duct (renal papilla) → minor calyx → major calyx → renal pelvis → ureter Polycys+c kidney disease = geneMc, cysts form that cause swelling of kidney tubules, compression reduces funcMon Cortical nephron Juxtamedullary nephron Cortex Medulla Collecting duct Papillary duct Renal papilla Minor calyx a The general appearance and location of nephrons in the kidneys Rakhi Agarwal, Ph.D. QCC Figure 26-5a The Blood Supply to the Kidneys. Cortical radiate veins Cortical radiate arteries Interlobar arteries Cortex Segmental artery Adrenal artery Renal artery Renal vein Arcuate veins Interlobar veins Medulla Arcuate arteries a A sectional view, showing major Rakhi and Agarwal, Ph.D. QCC arteries veins Figure 26-5b The Blood Supply to the Kidneys. Glomerulus Cortical radiate vein Afferent arterioles Cortical radiate artery Arcuate artery Cortical nephron Arcuate vein Juxtamedullary nephron Renal pyramid Interlobar vein Interlobar artery Minor calyx b Circulation inPh.D. a single Rakhi Agarwal, QCC kidney lobe Renal Physiology •  The Goal of Urine Production –  Is to maintain homeostasis •  By regulating volume and composition of blood •  Including excretion of metabolic waste products •  Filtrate = everything in blood plasma except large proteins and cells •  Urine =metabolic waste, 1% filtrate Rakhi Agarwal, Ph.D. QCC Common wastes: 1.  Urea: from catabolism of amino acids 2.  CreaBnine: from catabolism or damage of skeletal muscle Mssue (creaMne phosphate is energy storage of muscle) 3.  Uric Acid: from recycling of RNA 4.  Urobilin: from breakdown of hemoglobin (yellow color) •  All wastes excreted as soluMon in water •  Loss of filtering → toxic waste buildup, death in few days •  Dialysis = blood filtering machine, used for paMents with kidney failure Rakhi Agarwal, Ph.D. QCC Urine FormaBon: 1.  Glomerular FiltraBon: blood hydrostaMc pressure forces water and solutes through glomerular wall 2.  Tubular ReabsorpBon: selecMve uptake of water and solutes from filtrate 3.  Tubular SecreBon: transport of wastes from capillaries to tubules Rakhi Agarwal, Ph.D. QCC Figure 26-9 An Overview of Urine Formation. Proximal convoluted tubule Distal convoluted tubule Glomerulus Glomerular capsule Collecting duct KEY Filtration occurs exclusively in the renal corpuscle, across the filtration membrane. Nephron loop Water reabsorption occurs primarily along the PCT and the descending limb of the nephron loop, but also to a variable degree in the DCT and collecting system. Variable water reabsorption occurs in the DCT and collecting system. Solute reabsorption occurs along the PCT, the ascending limb of the nephron loop, the DCT, and the collecting system. Variable solute reabsorption or secretion occurs at the PCT, the DCT, and the collecting system. Rakhi Agarwal, Ph.D. QCC Urine storage and elimination Table 26-2 Normal Laboratory Values for Solutes in Plasma and Urine. Rakhi Agarwal, Ph.D. QCC 1. Glomerular FiltraBon -­‐occurs through filtraMon membrane: 1.  Fenestrated endothelium of glomerular capillaries (restricts cells) 2.  Podocytes (visceral epithelium of capsule), filtraMon slits restrict solutes protein sized and larger 3.  Fused basal lamina for both -­‐filtraMon is passive but all small solutes escape e.g. glucose, amino acids etc. Glomerulus Dense layer Efferent arteriole Capillary lumen Afferent arteriole Filtration slit Podocyte Pedicels Pore Capsular space Filtration membrane Rakhi Agarwal, Ph.D. QCC a The glomerular filtration membrane Figure 26-10b Glomerular Filtration. -­‐filtraBon depends on: 1. Large surface area 2. High glomerular BP 3. Good permeability Glomerular FiltraMon 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) Factors Controlling Glomerular Filtration The glomerular hydrostatic pressure (GHP) is the blood pressure in the glomerular capillaries. This pressure tends to push water and solute molecules out of the plasma and into the filtrate. The GHP, which averages 50 mm Hg, is significantly higher than capillary pressures elsewhere in the systemic circuit, because the efferent arteriole is smaller in diameter than the afferent arteriole. The blood colloid osmotic pressure (BCOP) tends to draw water out of the filtrate and into the plasma; it thus opposes filtration. Over the entire length of the glomerular capillary bed, the BCOP averages about 25 mm Hg. Filtrate in capsular space Plasma proteins 50 25 15 10 mm Hg Solutes The capsular colloid osmotic pressure is usually zero because few, if any, plasma proteins enter the capsular space. b Net filtration pressure Rakhi Agarwal, Ph.D. QCC The net filtration pressure (NFP) is the net pressure acting across the glomerular capillaries. It represents the sum of the hydrostatic pressures and the colloid osmotic pressures. Under normal circumstances, the net filtration pressure is approximately 10 mm Hg. This is the average pressure forcing water and dissolved substances out of the glomerular capillaries and into the capsular space. Capsular hydrostatic pressure (CsHP) opposes GHP. CsHP, which tends to push water and solutes out of the filtrate and into the plasma, results from the resistance of filtrate already present in the nephron that must be pushed toward the renal pelvis. The difference between GHP and CsHP is the net hydrostatic pressure (NHP). RegulaBon of FiltraBon Three levels of regulaMon to maintain constant Glomerular FiltraMon Rate: 1. AutoregulaBon -­‐funcMons to maintain constant GFR with normal BP fluctuaMons in systemic arteriole pressure A. Reduced blood flow/ BP triggers: -­‐dilaMon of afferent arteriole -­‐dilaMon of glomerular capillaries -­‐constricMon of efferent arteriole All funcMons to increase pressure at the glomerulus to increase GFR B. High blood flow / BP triggers: -­‐ constricMon of afferent arteriole -­‐ constricMon of glomerular capillaries -­‐dilaMon of efferent arteriole All funcMons to decrease pressure at the glomerulus to decrease GFR Rakhi Agarwal, Ph.D. QCC Figure 26-11 The Response to a Reduction in the GFR (Part 2 of 2). Autoregulation Immediate local response in the kidney Increased glomerular blood pressure Dilation of afferent arterioles Contraction of mesangial cells Constriction of efferent arterioles if sufficient HOMEOSTASIS RESTORED Normal GFR HOMEOSTASIS DISTURBED Decreased GFR resulting in decreased filtrate and urine production Rakhi Agarwal, Ph.D. QCC HOMEOSTASIS Start Normal glomerular filtration rate 2. Hormonal RegulaBon -­‐extrinsic regulaMon aimed at maintaining systemic blood pressure A. Renin: •  Enzyme released by juxtaglomerular apparatus in response to: -­‐decline in BP at kidney -­‐decline in osmoMc concentraMon of filtrate -­‐direct sympatheMc sMmulaMon •  Renin acMvates angiotensin in blood to form Angiotensin II which triggers: -­‐arteriole constricMon to elevate BP -­‐secreMon of aldosterone from adrenal glands (aldosterone promotes sodium reabsorpMon in kidney tubules) -­‐thirst -­‐release of ADH from pituitary (ADH promotes water uptake in tubules) Rakhi Agarwal, Ph.D. QCC Effect: ↑ blood volume, ↓ urine producMon Figure 26-11 The Response to a Reduction in the GFR (Part 1 of 2). Renin–Angiotensin-Aldosterone System Integrated endocrine and neural mechanisms activated Endocrine response Juxtaglomerular complex increases production of renin Renin in the bloodstream triggers formation of angiotensin I, which is then activated to angiotensin II by angiotensin converting enzyme (ACE) in the capillaries of the lungs Angiotensin II constricts peripheral arterioles and further constricts the efferent arterioles HOMEOSTASIS RESTORED Increased glomerular pressure Increased systemic blood pressure Increased blood volume Angiotensin II triggers increased aldosterone secretion by the adrenal glands Angiotensin II triggers neural responses Aldosterone increases Na+ retention Increased fluid consumption Increased stimulation of thirst centers Increased fluid retention Increased ADH production Constriction of venous reservoirs Increased cardiac output Together, angiotensin II and sympathetic activation stimulate peripheral vasoconstriction HOMEOSTASIS Normal glomerular filtration rate Rakhi Agarwal, Ph.D. QCC Increased sympathetic motor tone B. NatriureBc PepBdes: Hormones released in response to stretching in heart or aorta (↑blood volume) Triggers: -­‐dilaMon of afferent arteriole, constricMon of efferent arteriole: Effect: ↑ GFR, ↑ urine producMon, ↓ b...
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