Anatomy & Physiology: Chapter 24 Lecture Slides PDF

Anatomy & Physiology AN INTEGRATIVE APPROACH Third Edition Michael P. McKinley Valerie Dean O’ Loughlin Theresa Stouter Bidle See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. © 2019 McGraw-Hill Education. All rights reserved. Authorized only fo...

Anatomy & Physiology AN INTEGRATIVE APPROACH Third Edition Michael P. McKinley Valerie Dean O’ Loughlin Theresa Stouter Bidle See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. 2 Chapter 24 Lecture Outline © 2019 McGraw-Hill Education 24.1 Introduction to the Urinary System Learning Objectives 1. Identify the structures that compose the urinary system, and provide a description of general function of each. 2. List the functions of the kidneys. © 2019 McGraw-Hill Education 3 24.2 Gross Anatomy of the Kidney Learning Objectives: 3. Describe the location of the kidneys in the body. 4. Name and describe the four tissue layers that surround and support the kidneys. 5. Identify the two distinct regions of the kidney and the components of each. 6. Explain the relationship among minor calyces, major calyces, and renal pelvis. 7. List the structures of the kidney innervated by the sympathetic nervous division. © 2019 McGraw-Hill Education 4 5 24.1 Introduction to the Urinary System Components of the urinary system • Kidneys, filter blood • Remove waste products and convert filtrate into urine • Ureters, transport urine • From kidneys to urinary bladder • Bladder, expandable muscular sac • Stores as much as 1 L urine • Urethra, eliminates urine from body © 2019 McGraw-Hill Education 1 6 24.1 Introduction to the Urinary System Processes that occur as filtrate is converted to urine: • Elimination of metabolic wastes • Regulation of ion levels • E.g., Na+, K+, Ca2+ • Regulation of acid-base balance • Alters levels of H+ and HCO3- • Regulation of blood pressure • Elimination of biologically active molecules • hormones, drugs © 2019 McGraw-Hill Education 2 7 24.1 Introduction to the Urinary System Other functions of kidney • Formation of calcitriol • Production and release of erythropoietin • Secretes erythropoietin (EPO) in response to low blood oxygen • Stimulates red bone marrow to increase erythrocyte production • Potential to engage in gluconeogenesis • During prolonged fasting or starvation • Produces glucose from noncarbohydrate sources; maintain glucose levels © 2019 McGraw-Hill Education 3 8 24.2 Gross Anatomy of the Kidney Kidneys are two symmetrical, bean-shaped organs Size of hand to second knuckle Concave medial border, hilum • Where vessels, nerves, ureter connect to kidney Lateral border convex Adrenal gland rests on superior aspect of kidney © 2019 McGraw-Hill Education 9 Urinary System: Anterior View Figure 24.1a © 2019 McGraw-Hill Education ©McGraw-Hill Education/Christine Eckel Urinary System: Posterior View Figure 24.1b On posterior abdominal wall Lateral to vertebral column Both only partially protected by rib cage Vulnerable to forceful blows to inferior region of back Kidneys positioned posterior to parietal peritoneum In retroperitoneal space Only anterior surface covered with parietal peritoneum © 2019 McGraw-Hill Education 10 24.2a Location and Support 2 Kidney supported by several tissue layers • Fibrous capsule • Directly adhered to external surface of kidney • Dense irregular CT • Maintains kidney’s shape • Protects it from trauma • Prevents pathogen penetration • Perinephric fat • Adipose CT external to fibrous capsule • Cushions and supports kidney © 2019 McGraw-Hill Education • Renal fascia • External to perinephric fat • Dense irregular CT • Anchors kidney to surrounding structures • Paranephric fat • Outermost layer surrounding kidney • Adipose CT • Cushions and supports kidney 11 12 Kidney Figure 24.3 © 2019 McGraw-Hill Education ©McGraw-Hill Education/Rebecca Gray 13 24.2c Innervation of Kidney Each kidney innervated by both divisions of autonomic nervous system • Sympathetic nerves from T10–T12 • Blood vessels of kidney and juxtaglomerular apparatus • Decreases urine production • Parasympathetic nerves from CN X (Vagus) • Specific effects not known © 2019 McGraw-Hill Education 14 Section 24.1 What did you learn? 1. Which structure of the urinary system forms urine, and which structure stores urine? 2. What are the two means by which the kidney helps to regulate blood pressure? © 2019 McGraw-Hill Education 15 Section 24.2 What did you learn? 3. What tissue composes the fibrous capsule that directly adheres to the kidney, and what are its functions? 4. What are the regions of the kidney that drain urine? 5. What three anatomic structures of the kidney are innervated by the sympathetic division of the autonomic nervous system? © 2019 McGraw-Hill Education 24.3 Functional Anatomy of the Kidney Learning Objectives: 1 8. Describe a renal corpuscle and its components. 9. Identify the location, and describe the structure, of the three components of a renal tubule. 10. Name and compare the two types of nephrons and the functional differences between them. 11. State the relationship between collecting tubules and collecting ducts. © 2019 McGraw-Hill Education 16 24.3 Functional Anatomy of the Kidney Learning Objectives: 2 12. Identify the two types of specialized epithelial cells found within distal convoluted tubules and collecting tubules and ducts. 13. Describe the location and structure of juxtaglomerular apparatus. 14. Explain the two actions of granular cells. 15. Describe the function of the cells of the macula densa. © 2019 McGraw-Hill Education 17 18 24.3a Nephron 1 Functional anatomy of the kidney • Nephrons, collecting tubules, collecting ducts (and associated structures) Nephron • Microscopic functional filtration unit of kidney • Consists of: renal corpuscle and renal tubule • All of corpuscle and most of tubules reside in cortex © 2019 McGraw-Hill Education 19 Nephron Structure Figure 24.4a © 2019 McGraw-Hill Education 1 20 Nephron Structure Figure 24.4b © 2019 McGraw-Hill Education 2 21 Histology of Renal Cortex and Medulla Figure 24.6 © 2019 McGraw-Hill Education ©McGraw-Hill Education/Al Telser 22 24.3a Nephron 7 Two types of nephrons: cortical & juxtamedullary • Classified based on two factors • Relative position of renal corpuscle in the cortex • Length of nephron loop 1. Cortical nephrons • Oriented with renal corpuscles near peripheral cortex • Short nephron loop barely penetrates medulla • 85% of nephrons © 2019 McGraw-Hill Education 23 24.3a Nephron 8 Two types of nephrons (continued) 2. Juxtamedullary nephrons • Renal corpuscles adjacent to corticomedullary junction • Long nephron loops extend deep into medulla • Help establish salt concentration gradient in interstitial space • Allows for regulation of urine concentration by ADH © 2019 McGraw-Hill Education 24 Two Types of Nephrons Figure 24.5 © 2019 McGraw-Hill Education 24.3b Collecting Tubules and Collecting Ducts Nephrons drain into a collecting tubule Multiple collecting tubules empty into larger collecting ducts Numerous collecting ducts empty into papillary duct located within renal papilla Specialized epithelial cells (in DCT, CT, CD) • Principal cells • Responsive to hormones aldosterone and antidiuretic hormone (ADH) • Intercalated cells (types A and B) • Both specialized epithelial cells • Help regulate urine pH and blood pH © 2019 McGraw-Hill Education 25 26 24.3c Juxtaglomerular Apparatus 1 Juxtaglomerular (JG) apparatus • Helps regulate blood filtrate formation, systemic blood pressure JG apparatus components: • Granular cells • Modified smooth muscle cells of afferent arteriole • Located near entrance to renal corpuscle • Contract when stimulated by stretch or sympathetic stimulation • Synthesize, store, and release renin © 2019 McGraw-Hill Education 27 24.3c Juxtaglomerular Apparatus 2 JG apparatus components (continued) • Macula densa • Modified epithelial cells in wall of DCT • Located on tubule side next to afferent arteriole • Detect changes in NaCl concentration of fluid in lumen of DCT • Signal granular cells to release renin through paracrine stimulation • Extraglomerular mesangial cells • Just outside glomerulus • In gap between afferent arteriole and efferent arteriole • Communicate with other cells of JG apparatus © 2019 McGraw-Hill Education 28 Juxtaglomerular Apparatus Figure 24.7 © 2019 McGraw-Hill Education 29 Section 24.3 What did you learn? 6. What two structures compose the renal corpuscle? Provide a brief description of each. 7. What is the order of the components of a renal tubule? 8. What differences exist between cortical and juxtamedullary nephrons? 9. Differentiate between the functions of principal cells and the intercalated cells within the kidney. 10. What are the two primary cellular components of the juxtaglomerular apparatus, and how is each stimulated? © 2019 McGraw-Hill Education 24.4 Blood Flow and Filtered Fluid Flow Learning Objectives : 16. Name the arteries that supply the kidney, in sequence from largest to smallest. 17. Describe the two capillary beds through which blood must pass in the kidney. 18. List the veins through which blood leaves the kidney, in sequence from smallest to largest. 19. Distinguish among filtrate, tubular fluid, and urine. 20. Trace the fluid from its formation at the renal corpuscle until it exits the body through the urethra. © 2019 McGraw-Hill Education 30 31 Blood Supply to the Kidneys Figure 24.8 © 2019 McGraw-Hill Education 24.4b Filtrate, Tubular Fluid, and Urine Flow 1 Filtrate • Blood flows through glomerulus • Both water and solutes filtered from blood plasma • Moves across wall of glomerular capillaries and into capsular space • Forms filtrate © 2019 McGraw-Hill Education 32 24.4b Filtrate, Tubular Fluid, and Urine Flow 2 Tubular fluid • New name for filtrate when enters PCT • Flows through 1. PCT 2. Nephron loop 3. DCT 4. Enters collecting tubules 5. Empties into larger collecting ducts 6. Now called urine © 2019 McGraw-Hill Education 33 24.4b Filtrate, Tubular Fluid, and Urine Flow 3 Urine • Enters papillary duct located within renal papilla • Flows within renal sinus of kidney • Minor calyx → major calyx → renal pelvis • Renal pelvis connects to ureter • Ureter connects to urinary bladder • Stores and excretes from body through urethra © 2019 McGraw-Hill Education 34 Structures That Transport Fluids Through the Urinary System 35 Figure 24.9 © 2019 McGraw-Hill Education 36 Section 24.4 What did you learn? 11. What is the pathway that blood follows as it enters via the renal artery and later leaves via the renal vein? 12. What are the three major types of capillaries associated with the nephron? Describe the location and general function of each. 13. What is the pathway of fluid filtered by the kidney from the glomerulus to its eventual excretion? © 2019 McGraw-Hill Education 24.5 Production of Filtrate Within the Renal Corpuscle Learning Objectives: 1 21. Compare and contrast the renal processes of filtration, reabsorption, and secretion. 22. Describe the three layers that make up the glomerular filtration membrane. 23. Give examples of substances that are freely filtered, that are not filtered, and that are filtered in a limited way. 24. Describe the phagocytic function of mesangial cells. © 2019 McGraw-Hill Education 37 38 24.5a Overview of Urine Formation Urine formed through three interrelated processes • Filtration, reabsorption, and secretion Steps of urine formation: 1. Glomerular filtration 2. Tubular reabsorption 3. Tubular secretion © 2019 McGraw-Hill Education 1 Overview of the Processes of Urine Formation Figure 24.10 © 2019 McGraw-Hill Education 39 40 Filtration Membrane Figure 24.11a © 2019 McGraw-Hill Education 41 24.5b Filtration Membrane 1 Filtration membrane characteristics • Porous, thin, negatively charged structure • Formed by glomerulus and visceral layer of glomerular capsule Layers of filtration membrane (innermost to outermost): 1. Endothelium of glomerulus • Fenestrated, allows plasma and dissolved substances to pass • Restricts passage of large structures (e.g., erythrocytes) 2. Basement membrane of glomerulus • Restricts passage of large plasma proteins © 2019 McGraw-Hill Education 42 24.5b Filtration Membrane 2 3. Visceral layer of glomerular capsule • Outermost layer wrapping around glomerular capillaries • Composed of specialized cells called podocytes • Restrict passage of most small proteins Mesangial cells • Specialized cells positioned between glomerular capillary loops • Phagocytic, contractile, and signaling properties © 2019 McGraw-Hill Education Substances Filtered by Filtration Membrane Figure 24.11b © 2019 McGraw-Hill Education 43 24.5c Formation of Filtrate and Its Composition 1 Filtrate • 180 L produced daily • Filtered plasma with certain solutes and minimal amounts of protein • Caught within capsular space and funneled into PCT • Materials not filtered remain in blood, exit renal corpuscle through efferent arteriole • Some filtered material trapped within basement membrane • Phagocytized by mesangial cells © 2019 McGraw-Hill Education 44 24.5c Formation of Filtrate and Its Composition 2 Three categories of substances in blood • Freely filtered • Small substances • E.g., water, glucose, amino acids, ions • Pass easily through filtration membrane • Not filtered • Formed elements and large proteins • Cannot pass through filtration membrane • Limited filtration • Proteins of intermediate size • Usually blocked from filtration • Due to size or due to negative charge © 2019 McGraw-Hill Education 45 24.5 Production of Filtrate Within the Renal Corpuscle Learning Objectives: 1 25. Define glomerular hydrostatic pressure (HPg), and explain why it is higher than the pressure in other capillaries. 26. Name two pressures that oppose HPg. 27. Explain how to calculate the net filtration pressure. 28. Define glomerular filtration rate and factors that influence it. © 2019 McGraw-Hill Education 46 24.5d Pressures Associated with Glomerular Filtration 1 Glomerular hydrostatic (blood) pressure (HPg) • Blood pressure in glomerulus • “Pushes” water and some solutes out of glomerulus • Pushed into capsular space of renal corpuscle • Higher than blood pressure of other systemic capillaries • Required for filtration to occur • Larger diameter of afferent arteriole • Smaller diameter of efferent arteriole © 2019 McGraw-Hill Education 47 24.5d Pressures Associated with Glomerular Filtration 2 Pressures opposing HPg • Blood colloid osmotic pressure (OPg) • Osmotic pressure exerted by dissolved solutes • E.g., plasma proteins • Opposes filtration • Draws fluid back into glomerulus • Capsular hydrostatic pressure (HPc) • Pressure in glomerular capsule due to filtrate • Impedes movement of additional fluid © 2019 McGraw-Hill Education 48 49 Pressures That Determine Net Filtration Pressure If pressures promoting filtration are greater than pressures opposing Difference is net filtration pressure (NFP) HPg (OPg HPc) NFP 60 mm Hg (32 mm Hg 18 mm Hg) NFP 60 mm50 mm Hg 10 mm Hg © 2019 McGraw-Hill Education 24.5d Pressures Associated with Glomerular Filtration 4 Variables influenced by net filtration pressure • Glomerular filtration rate (GFR) • Rate at which the volume of filtrate is formed • Volume per unit of time (usually 1 min) • Increased net filtration pressure • Increases GFR • Increases solutes and water remaining in tubular fluid • Increases substances in urine • Decreases filtrate reabsorption © 2019 McGraw-Hill Education 50 24.5e Regulation of Glomerular Filtration Rate 51 1 Glomerular filtration rate (GFR) is tightly regulated • Helps kidney control urine production based on physiologic conditions • E.g., hydration status GFR influenced by • Changing luminal diameter of afferent arteriole (blood flow) • Altering surface area of filtration membrane (mesangial cell) Processes within kidney itself (intrinsic controls) Processes external to kidney (extrinsic controls) © 2019 McGraw-Hill Education 24.5 Production of Filtrate Within the Renal Corpuscle Learning Objectives: 2 29. Describe what is meant by intrinsic and extrinsic controls, and give examples of each. 30. Compare and contrast the myogenic response and the tubuloglomerular feedback mechanism, which are involved in renal autoregulation. 31. Explain the effects of sympathetic division stimulation on the glomerular filtration rate. 32. Describe the effects of atrial natriuretic peptide on the glomerular filtration rate. © 2019 McGraw-Hill Education 52 24.5e Regulation of Glomerular Filtration Rate 53 2 Renal autoregulation: intrinsic controls • Intrinsic ability of kidney to maintain constant blood pressure and GFR • Maintains in spite of changes in systemic arterial pressure • Functions by two mechanisms 1. Myogenic response 2. Tubuloglomerular feedback mechanism © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 54 3 Myogenic response: Contraction or relaxation of smooth muscle of afferent arteriole in response to stretch • E.g., Decreased blood pressure less stretch of smooth muscle in arteriole • Causes smooth muscle cells to relax, vessels to dilate • Allows more blood into glomerulus • Compensates for lower system pressure • GFR remains normal © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 55 4 Myogenic response (continued) • With increased blood pressure, more stretch of smooth muscle in arteriole • Causes smooth muscle cells to contract • Vessels constrict • Allows less blood into glomerulus • Compensates for greater systemic pressure • GFR remaining normal © 2019 McGraw-Hill Education 56 Renal Autoregulation: Myogenic Response Figure 24.13ac © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 57 5 Tubuloglomerular feedback mechanism • “Backup” to myogenic mechanism response to increased blood pressure • If glomerular blood pressure increased • Amount of NaCl in tubular fluid also increased • Detected by macula densa cells in juxtaglomerular apparatus • Results in further vasoconstriction of afferent arteriole © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 58 6 Limitations to maintaining GFR • Renal autoregulation • Maintains normal glomerular pressure when BP is within certain range, 80 to 180 mm Hg • Decrease in blood pressure below 80 mm Hg • Arterioles at maximum dilation • Decrease in glomerular blood pressure and GFR • If extremely low, cessation of waste elimination in urine • Increase in blood pressure above 180 mm Hg • Arterioles at maximum constriction • Increase in glomerular blood pressure and GFR • Urine formation increasing © 2019 McGraw-Hill Education 59 Renal Autoregulation Figure 24.13d © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 60 7 Neural and hormonal control: extrinsic controls • Involve physiologic processes to change GFR, in contrast to renal autoregulation which attempts to maintain GFR • Decreasing GFR through sympathetic stimulation • During exercise or emergency • Results in decrease in GFR through • Vasoconstriction of afferent and efferent arterioles • Granular cells of JG apparatus release renin, which results in angiotensin II production and contraction of mesangial cells • Contraction of mesangial cells decreases surface area of glomerulus, decreasing GFR • Body therefore conserves water under stressful conditions © 2019 McGraw-Hill Education 61 Review: Renin-Angiotensin Mechanism • MAP below 80 mm Hg triggers the granular cells of the JGA to release renin angiotensinogen (a plasma globulin) renin  angiotensin I angiotensin converting enzyme (ACE)  angiotensin II © 2019 McGraw-Hill Education 62 Effects of Angiotensin II 1. Constricts arteriolar smooth muscle, causing MAP to rise 2. Stimulates the reabsorption of Na+ • Acts directly on the renal tubules • Triggers adrenal cortex to release aldosterone 3. Stimulates hypothalamus to release ADH and activates the thirst center 4. Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption 5. Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration © 2019 McGraw-Hill Education 63 Decreasing GFR Through Sympathetic Stimulation Figure 24.14a © 2019 McGraw-Hill Education 24.5e Regulation of Glomerular Filtration Rate 64 8 Increasing GFR through atrial natriuretic peptide (ANP) • Peptide hormone released from cardiac muscle cells in response to stretch of atria in heart • Increases GFR through • Relaxation of afferent arteriole • Inhibits release of renin, ultimately causing relaxation of mesangial cells • Relaxation of mesangial cells increases filtration membrane surface area, increasing GFR • Net increase in GFR with increased urine volume decreases blood volume and blood pressure © 2019 McGraw-Hill Education Increasing GFR Through ANP Figure 24.14b © 2019 McGraw-Hill Education 65 66 Putting it all together SYSTEMIC BLOOD PRESSURE (–) Blood pressure in afferent arterioles; GFR Stretch of smooth muscle in walls of afferent arterioles Baroreceptors in blood vessels of systemic circulation Granular cells of juxtaglomerular apparatus of kidney GFR Filtrate flow and NaCl in ascending limb of Henle’s loop Release (+) (+) Renin Catalyzes cascade Targets resulting in conversion Vasodilation of afferent arterioles Angiotensinogen (+) Macula densa cells of JG apparatus of kidney Angiotensin II (+) Adrenal cortex (+) Sympathetic nervous system Systemic arterioles (+) Releases Aldosterone Release of vasoactive chemical inhibited Targets Vasoconstriction; peripheral resistance Kidney tubules Vasodilation of afferent arterioles Na+ reabsorption; water follows GFR (+) Stimulates (–) Inhibits Increase Decrease Blood volume Systemic blood pressure Myogenic mechanism of autoregulation Tubuloglomerular mechanism of autoregulation Intrinsic mechanisms directly regulate GFR despite moderate changes in blood pressure (between 80 and 180 mm Hg mean arterial pressure). Pearson Figure 25.12 © 2019 McGraw-Hill Education Hormonal (renin-angiotensin) mechanism Neural controls Extrinsic mechanisms indirectly regulate GFR by maintaining systemic blood pressure, which drives filtration in the kidneys. 67 Section 24.5 What did you learn? 1 14. How does tubular reabsorption differ from tubular secretion? 15. How are the components of the filtration membrane of the glomerulus arranged? 16. What is normally filtered across the glomerular membrane? What is not normally filtered? 17. Certain diseases, kidney trauma, heavy metals, and some bacterial toxins can damage the filtration membrane. What effect would this have on relative permeability of the membrane and the substances that are filtered? © 2019 McGraw-Hill Education 68 Section 24.5 What did you learn? 2 18. What is the value of the NFP if the glomerular hydrostatic pressure (HPg) is 65 mm Hg, OPg is 30 mm Hg, and HPc is 20 mm Hg? 19. What happens to the value of the NFP in question 18 if the HPg increases from 65 mm Hg to 75 mm Hg? 20. If HPg increases, what is the effect on NFP? Is the relationship between HPg and NFP direct or inverse? © 2019 McGraw-Hill Education 69 Section 24.5 What did you learn? 3 21. Does urine production increase, decrease, or stay the same in response to an increase in glomerular filtration rate? 22. What are the three factors that regulate glomerular filtration rate? Does each of these increase, decrease, or maintain GFR? 23. Renal autoregulation is effective with a MAP between 80 and 180 mm Hg. Would renal autoregulation be effective in an individual with a blood pressure of 300/150 mm Hg? A pressure of 70/55 mm Hg? Explain. © 2019 McGraw-Hill Education 24.6 Reabsorption and Secretion in Tubules and Collecting Ducts Learning Objectives: 1 33. Describe five characteristics and conditions that affect tubular reabsorption and secretion. 34. Define the transport maximum of a substance. 35. Explain what is meant by renal threshold. © 2019 McGraw-Hill Education 70 71 Overview of transport processes Figure 24.16 © 2019 McGraw-Hill Education 24.6b Transport Maximum and Renal Threshold Transport Maximum (Tm) • Maximum rate of substance that can be reabsorbed (or secreted) across tubule epithelium per a certain time • Depends on number of transport proteins in membrane Renal threshold • Max plasma concentration of a substance that can be transported in the blood without appearing in the urine • If Tm exceeded, substance excreted in urine © 2019 McGraw-Hill Education 72 73 Clinical View: Glucosuria Excretion of glucose in urine Plasma glucose level above 300 mg/dL Glucose acts as an osmotic diuretic • Pulls water into tubular fluid • Causes loss of fluid in urine Classic symptom of diabetes, along with frequent urination and thirst © 2019 McGraw-Hill Education 24.6 Reabsorption and Secretion in Tubules and Collecting Ducts Learning Objectives: 1 36. Explain the reabsorption of nutrients such as glucose. 37. Describe the process by which protein is transported out of the filtrate and into the blood. 38. List substances for which reabsorption is regulated. 39. Describe how the reabsorption of sodium, potassium, calcium, and phosphate occurs. © 2019 McGraw-Hill Education 74 24.6 Reabsorption and Secretion in Tubules and Collecting Ducts Learning Objectives: 2 40 Describe the reabsorption of water, and compare how it is regulated by the actions of aldosterone and antidiuretic hormone. 41 Describe how pH is regulated by intercalated cells. 42 Identify the three nitrogenous waste products, and describe the fate of each. 43 Give examples of other material eliminated by kidneys. © 2019 McGraw-Hill Education 75 76 24.6c Substances Reabsorbed Completely Nutrient reabsorption • Normally reabsorbed completely • Each nutrient has own specific transport protein • E.g., glucose and sodium transport © 2019 McGraw-Hill Education 1 77 Glucose Reabsorption Figure 24.17 © 2019 McGraw-Hill Education 78 24.6c Substances Reabsorbed Completely Transport of protein • Most not freely filtered (due to size and charge) • Some small and medium-sized may appear in filtrate • Small amounts of large proteins • Transported from tubular fluid in PCT back into blood • Protein moves across the luminal membrane • By pinocytosis • By receptor-mediated endocytosis • Digested by lysosomes or peptidases • Amino acids move by facilitated diffusion back into blood © 2019 McGraw-Hill Education 2 79 Sodium Reabsorption Overview Figure 24.18a © 2019 McGraw-Hill Education 80 24.6d Regulated Na Reabsorption Sodium reabsorption (continued) • Aldosterone • Steroid hormone produced by adrenal cortex • Stimulates protein synthesis of Na+ channels and Na+/K+ pumps • Embedded in plasma membranes of principal cells • Increase in Na+ reabsorption • Water follows by osmosis • Atrial natriuretic peptide • Inhibits reabsorption of Na+ in PCT and collecting tubules • Inhibits release of aldosterone • More Na+ and water excreted in urine • Increases GFR © 2019 McGraw-Hill Education 2 81 Sodium Transport in PCT Figure 24.18b © 2019 McGraw-Hill Education 82 Sodium Transport in DCT, CT, or CD Figure 24.18c © 2019 McGraw-Hill Education 83 Water Transport Overview Figure 24.19a © 2019 McGraw-Hill Education 24.6d Substances with Regulated Reabsorption 3 Water reabsorption • Reabsorbed by • Paracellular transport between cells • Transcellular transport through water transporter proteins, aquaporins • 180 L filtered daily; all but 1.5 L reabsorbed • Tubule permeability varies along its length • 65% reabsorbed in PCT • Aquaporins constant number • Water follows Na+ by osmosis, obligatory water reabsorption © 2019 McGraw-Hill Education 84 85 24.6d Regulated H2O Reabsorption 5 Water reabsorption (continued) • Antidiuretic hormone (ADH) binds to principal cells • Increases migration of vesicles containing aquaporins to membrane • Adds channels to increase water reabsorption • Increases water reabsorption from filtrate into blood • Results in smaller volume of more concentrated urine • Elevated levels during dehydration • Urine noticeably darker color © 2019 McGraw-Hill Education 86 Water Transport in CT and CD Figure 24.19b © 2019 McGraw-Hill Education 87 Potassium Movement Figure 24.20 © 2019 McGraw-Hill Education 24.6d Substances with Regulated Reabsorption 7 Reabsorption and secretion of potassium • It is both reabsorbed and secreted • 60% to 80% reabsorbed in tubular fluid • Dependent on movement of Na+ • Net secretion or reabsorption in collecting tubule • Intercalated cells reabsorb K+ continuously • Principal cells secrete K+ at varying rates • Based on aldosterone level • Stimulates principal cells to secrete K+ • Most powerful stimulant for aldosterone, elevated K+ level © 2019 McGraw-Hill Education 88 PTH Regulation of Calcium Ion and Phosphate Ion Reabsorption Figure 24.21 © 2019 McGraw-Hill Education 89 24.6d Substances with Regulated Reabsorption 9 Hormonal calcium and phosphate balance • Parathyroid hormone (PTH) - raises blood calcium levels • Regulates excretion of Ca2+ and PO43• Inhibits PO43- reabsorption in PCT • Stimulates Ca2+ reabsorption in DCT • Less phosphate available to form calcium phosphate • Calcium deposition in bone decreased • Ca 2+ blood levels increased © 2019 McGraw-Hill Education 90 Bicarbonate Ion and Hydrogen Ion Movement Figure 24.22a © 2019 McGraw-Hill Education 91 24.6d Substances with Regulated Reabsorption 10 Bicarbonate ions, hydrogen ions, and pH • Bicarbonate ions • Move freely across filtration membrane • If filtered HCO3– not reabsorbed, blood too acidic • 80% to 90% reclaimed from tubular fluid • Remaining 10% to 20% taken up from thick segment of ascending limb © 2019 McGraw-Hill Education 92 Movement of Bicarbonate Along the PCT and Nephron Loop 93 Figure 24.22b © 2019 McGraw-Hill Education 24.6d Substances with Regulated Reabsorption 11 Bicarbonate ions, hydrogen ions, and pH (continued) • pH of urine and blood regulated in collecting tubules • If acidic blood, then • HCO3– reabsorbed into blood • H+ excreted within filtrate by • Increase blood pH and decrease urine pH • If alkaline blood, then • Secrete HCO3– and reabsorb H+ • Lower blood pH and increase urine pH © 2019 McGraw-Hill Education 94 Blood too acidic? Reabsorb HCO3 and Secrete H Figure 24.22c © 2019 McGraw-Hill Education 95 24.6e Substances Eliminated as Waste Products 1 Elimination of nitrogenous waste • Nitrogenous waste: metabolic waste containing nitrogen • Main nitrogenous waste products • Urea, molecule produced from protein breakdown • Both reabsorbed and secreted • 50% excreted in the urine • Helps establish concentration gradient in the interstitial fluid • Uric acid, produced from nucleic acid breakdown in liver • Both reabsorbed and secreted • Creatinine, produced from creatinine metabolism in muscle • Only secreted © 2019 McGraw-Hill Education 96 24.6e Substances Eliminated as Waste Products 2 Elimination of drugs and bioactive substances • Most secretion occurring in PCT • Certain drugs • E.g., penicillin, sulfonamides, aspirin • Other metabolic wastes • E.g., urobilin, hormone metabolites • Some hormones • E.g., human chorionic gonadotropin, epinephrine © 2019 McGraw-Hill Education 97 98 Review Cortex 65% of filtrate volume reabsorbed • H2O • Na+, HCO3−, and many other ions • Glucose, amino acids, and other nutrients • H+ and NH4+ • Some drugs Outer medulla Regulated reabsorption • Na+ (by aldosterone; Cl− follows) • Ca2+ (by parathyroid hormone) Regulated secretion • K+ (by aldosterone) Regulated reabsorption • H2O (by ADH) • Na+ (by aldosterone; Cl− follows) • Urea (increased by ADH) • Urea Regulated secretion • K+ (by aldosterone) Inner medulla • Reabsorption or secretion to maintain blood pH described in Chapter 26; involves H+, HCO3−, and NH4+ Reabsorption Secretion © 2019 McGraw-Hill Education 24.6 Reabsorption and Secretion in Tubules and Collecting Ducts Learning Objectives: 3 44. Explain what is meant by the countercurrent multiplier that occurs within the nephron loop. 45. Describe the countercurrent exchange system that maintains the concentration gradient. 46. Discuss the contribution of urea cycling to the concentration gradient. © 2019 McGraw-Hill Education 99 24.6f Establishing the Concentration Gradient 100 1 Concentration gradient • Present in interstitial fluid surrounding nephron • Established by various solutes • E.g., Na+ and Cl– • Progressively increase in concentration from cortex into medulla • Exerts osmotic pull to move water into interstitial fluid • When is ADH present © 2019 McGraw-Hill Education 24.6f Establishing the Concentration Gradient 2 The nephron loop • Countercurrent multiplier involves nephron loop and helps establish gradient • Juxtamedullary nephrons are primarily involved • Descending limb permeable to water, impermeable to salts • Water moves from tubular fluid to interstitial fluid • Salts retained in tubular fluid; becomes concentrated • Ascending limb impermeable to water; salts pumped out • More concentrated the salts, the more is pumped out (e.g. beginning of ascending limb) • Less concentrated the salts, the less is pumped out (e.g. end of ascending limb) • Get salt gradient in interstitial fluid © 2019 McGraw-Hill Education 101 24.6f Establishing the Concentration Gradient 3 Vasa recta • Blood in vasa recta • Travels in opposite direction to tubular fluid of adjacent nephron loop • Countercurrent exchange system • Helps maintain concentration gradient • Water diffuses out of vasa recta capillaries by osmosis • Salt in interstitial fluid enters vasa recta by diffusion • Increases concentration of salt in vasa recta • Vasa recta next runs along descending limb of nephron • Gradients reversed, with salt diffusing out and water in © 2019 McGraw-Hill Education 102 103 Interstitial Fluid Concentration Gradient Figure 24.23 © 2019 McGraw-Hill Education 104 Descending limb permeable to water, impermeable to salts Ascending limb impermeable to water; salts pumped out Vasa Recta permeable to both © 2019 McGraw-Hill Education 24.6f Establishing the Concentration Gradient 4 Urea recycling • Help concentrating process in interstitial fluid • Recycled urea • ½ of solutes of interstitial fluid gradient • Urea removed from tubular fluid in collecting duct by uniporters • Diffuses back into tubular fluid in thin segment of ascending limb • Remains within tubular fluid until it reaches collecting duct • Urea “cycled” between collecting tubule and nephron loop © 2019 McGraw-Hill Education 105 24.6f Establishing the Concentration Gradient 5 Summary of reabsorption and secretion • After filtration • Majority or most other substances reabsorbed or secreted • Nephron loop, vasa recta, and urea recycling • Responsible for establishing concentration gradient of interstitial fluid • Necessary for normal function of ADH • Regulation of specific substances • Hormonal controls • Urine • Composed of water, dissolved substances, waste products • Drained into renal sinus of kidney • Excreted by urinary tract © 2019 McGraw-Hill Education 106 Final Urine Dilute urine Filtrate is diluted in the ascending loop of Henle Concentrated urine Depends on the medullary osmotic gradient and ADH In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine ADH triggers reabsorption of H2O in the collecting ducts Na+ and other ions may be selectively removed in the DCT and collecting duct, decreasing osmolality to as low as 50 mOsm © 2019 McGraw-Hill Education Water reabsorption occurs in the presence of ADH so that 99% of H2O in filtrate is reabsorbed 107 108 Section 24.6 What did you learn? 1 24. What are the significant anatomic and physiologic factors that influence tubular reabsorption and tubular secretion? 25. What is the transport maximum of a substance? How is it different from the renal threshold of the substance? 26. How is glucose reabsorbed across the two membranes of the tubule cells? 27. Why are proteins said to be transported rather than simply reabsorbed in the proximal convoluted tubule? © 2019 McGraw-Hill Education 109 Section 24.6 What did you learn? 2 28. How does Na+ reabsorption occur? Which two hormones are involved? 29. What is the effect of parathyroid hormone on the reabsorption of both PO43− and Ca2+? 30. How is the movement of H+ and HCO3− regulated by type A and type B intercalated cells? 31. What are some examples of drugs and bioactive substances eliminated in the urine? © 2019 McGraw-Hill Education 110 Section 24.6 What did you learn? 3 32. How is the concentration gradient that is essential for normal function of ADH in water reabsorption established and maintained? 33. Which substances are reabsorbed in tubular processing in the different regions of the nephron? Which are secreted? What are the general processes that occur in the different regions of the tubules: (a) PCT, (b) nephron loop, and (c) DCT, CT, and CD? © 2019 McGraw-Hill Education 24.7 Evaluating Kidney Function Learning Objectives: 47. Describe the procedure for measuring the glomerular filtration rate. 48. Explain the formula for calculating the glomerular filtration rate. 49. Define renal plasma clearance and its importance. 50. Identify the substance that may be measured to estimate glomerular filtration rate. © 2019 McGraw-Hill Education 111 24.7a Measuring Glomerular Filtration Rate 112 Glomerular filtration rate (GFR) • The rate filtrate is formed per unit of time • Can be measured with inulin injection • Freely filtered and not reabsorbed nor secreted • Urine collected and measured for volume and concentration • Plasma concentration of inulin measured at given time intervals • GFR = UV/P • U = concentration of inulin in urine • V = volume of urine produced per minute • P = concentration inulin in plasma • Normal GFR 125 mL/min • Less than this indicating decrease in kidney function © 2019 McGraw-Hill Education 113 24.7b Measuring Renal Plasma Clearance Renal plasma clearance test • Another means of assessing kidney function • Measures volume of plasma cleared of substance in given time • If substance neither reabsorbed nor filtered • Clearance equal to GFR • If substance reabsorbed • Clearance lower than GFR © 2019 McGraw-Hill Education 1 114 24.7b Measuring Renal Plasma Clearance Renal plasma clearance test (continued) • If substance filtered and secreted • Clearance higher than GFR • Drug clearance • Affects appropriate dosage level • Creatinine clearance • Clearance only slightly higher than GFR • Can be used to approximate glomerular filtration rate © 2019 McGraw-Hill Education 2 Clinical View: Renal Failure, Dialysis, and Kidney Transplant 115 Renal failure • Greatly diminished or absent renal functions • Often from chronic disease affecting glomerulus or small blood vessels • From autoimmune disease, high blood pressure, diabetes • Once destroyed will not function again • Two main treatments: dialysis or kidney transplantation © 2019 McGraw-Hill Education Kidney Transplant © 2019 McGraw-Hill Education 116 117 Section 24.7 What did you learn? 34. What is the purpose of measuring the glomerular filtration rate? 35. What information is gained by measuring the renal plasma clearance for a specific substance (e.g., medication)? © 2019 McGraw-Hill Education 24.8 Urine Characteristics, Transport, Storage, and Elimination Learning Objectives: 51. Describe the composition of urine and its characteristics. 52. Explain what is meant by specific gravity. © 2019 McGraw-Hill Education 118 119 24.8a Characteristics of Urine 1 Urine • Product of filtered and processed blood plasma • Sterile unless contaminated with microbes in kidney or urinary tract • Characteristics: composition, volume, pH, specific gravity, color and turbidity, smell • Composition • 95% water, 5% solutes • Salts, nitrogenous wastes, some hormones drugs, ketone bodies • Abnormal constituents –glucose, blood cells, proteins © 2019 McGraw-Hill Education 120 24.8a Characteristics of Urine 2 Urine (continued) • Volume • Average 1 to 2 L per day • Variations due to fluid intake, blood pressure, temperature, diuretics, diabetes, other fluid excretion • Minimum of 0.5 L to eliminate wastes from body • Below 0.40, wastes will accumulate in blood • pH • Normally between 4.5 and 8.0 • More acidic with larger amounts protein or wheat in diet • Less acidic with diet high in fruits and vegetables • Influenced by metabolism, infection © 2019 McGraw-Hill Education 121 24.8a Characteristics of Urine • Specific gravity • Density of a substance compared to density of water • Specific gravity slightly higher than water due to solutes • Indicates ability of kidney to concentrate urine • Color • Ranges from almost clear to dark yellow • Depends on concentration of urobilin • With increased volume of urine, lighter color • Smell • Urinoid, normal smell of fresh urine • May develop ammonia smell if allowed to stand • Fruity smell in diabetes © 2019 McGraw-Hill Education 3 24.8 Urine Characteristics, Transport, Storage, and Elimination Learning Objectives: 53. Describe the structure and function of the ureters. 54. Explain the structure of the urinary bladder. 55. List distinguishing characteristics of the female urethra and male urethra. © 2019 McGraw-Hill Education 122 24.8b Urinary Tract (Ureters, Urinary Bladder, Urethra) 123 1 Urinary tract: ureters, urinary bladder, urethra Ureters • Long epithelial-lined fibromuscular tubes • Conduct urine from kidneys to urinary bladder • Retroperitoneal • Originate from renal pelvis as it exits hilum of kidney • Enter posterolateral wall of base of urinary bladder © 2019 McGraw-Hill Education 124 Ureter Cross Section Figure 24.25a © 2019 McGraw-Hill Education 24.8b Urinary Tract (Ureters, Urinary Bladder, Urethra) 125 4 Urinary bladder • Expandable, muscular container • Reservoir for urine • Positioned immediately posterior to pubic symphysis • Anteroinferior to uterus in females • Anterior to rectum and superior to prostate gland in males • Retroperitoneal • Superior surface covered with parietal peritoneum © 2019 McGraw-Hill Education Urinary Bladder Trigone-prone to infection © 2019 McGraw-Hill Education 126 24.8b Urinary Tract (Ureters, Urinary Bladder, Urethra) 127 8 Urethra • Epithelial-lined fibromuscular tube • Exits urinary bladder through urethral opening • Conducts urine to exterior of body • Two sphincters restrict release of urine until bladder pressure is high enough • Internal and external urethral sphincters © 2019 McGraw-Hill Education 24.8b Urinary Tract (Ureters, Urinary Bladder, Urethra) Urethra (continued) • Internal urethral sphincter • Involuntary, superior sphincter • Composed of smooth muscle • Surrounds neck of bladder • Controlled by autonomic nervous system • External urethral sphincter • Inferior to internal urethral sphincter • Formed by skeletal muscle fibers of pelvic diaphragm • Voluntary sphincter controlled by somatic nervous system • Learn control of muscle during “toilet training” © 2019 McGraw-Hill Education 128 9 24.8b Urinary Tract (Ureters, Urinary Bladder, Urethra) 129 10 Urethra (continued) • Female urethra • Single function: to transport urine from urinary bladder to exterior • Lumen lined with stratified squamous epithelium • Opens at external urethral orifice in female perineum • Male urethra • Passageway for urine and semen • Three segments: prostatic urethra, membranous urethra, spongy urethra © 2019 McGraw-Hill Education Female and Male Urethra © 2019 McGraw-Hill Education 130 131 Clinical View: Renal Calculi Also know as kidney stones Formed from crystalline minerals building up in kidney Risk factors • • • Inadequate fluid intake, reduced urinary flow Frequent urinary tract infections Abnormal chemical or mineral levels in urine More common in males Small stones asymptomatic Larger stones obstructed in kidney, renal pelvis, ureter • Severe pain along “loin-to-groin” region Most pass on their own if less than 4 mm diameter May require lithotripsy or ureteroscopy © 2019 McGraw-Hill Education 24.8 Urine Characteristics, Transport, Storage, and Elimination Learning Objectives: 56. Define micturition. 57. Compare and contrast the storage reflex and the micturition reflex. 58. Explain conscious control over micturition. © 2019 McGraw-Hill Education 132 133 24.8c Micturition 1 Micturition • Expulsion of urine from the bladder • Associated with two reflexes • Storage reflex and micturition reflex • Regulated by sympathetic and parasympathetic divisions of the autonomic nervous system, respectively © 2019 McGraw-Hill Education 134 24.8c Bladder innervation 2 • Sympathetic axons • Cause contraction of internal urethral sphincter • Inhibits contraction of detrusor (bladder) muscle and micturition • Parasympathetic division • Contraction of detrusor, relaxation of internal urethral sphincter • Stimulates micturition • Pudendal nerve of somatic nervous system • Innervates external urethral sphincter; contracts to prevent urination © 2019 McGraw-Hill Education 24.8c Storage Reflex Storage reflex • Continuous sympathetic stimulation • Causes relaxation of detrusor to accommodate urine • Stimulates contraction of internal urethral sphincter • urine retained in bladder • External urethral sphincter • Continuously stimulated by pudendal nerve to remain contracted © 2019 McGraw-Hill Education 135 Micturition Reflex Micturition reflex 1) Volume of urine in bladder between 200 to 300 mL Bladder distended and baroreceptors activated in bladder wall activated 2) Visceral sensory neurons signaled by baroreceptors Stimulate micturition center in pons 3) Micturition center Alters nerve signals down spinal cord through pelvic splanchnic nerves 4) Parasympathetic stimulation Causes detrusor muscles to contract Causes internal urethral sphincter to relax © 2019 McGraw-Hill Education 136 137 24.8c Micturition 6 Conscious control of urination • Initiated from cerebral cortex through pudendal nerve • Causes relaxation of external urethral sphincter • Facilitated by voluntary contraction of abdominal and expiratory muscles • After emptying • Detrusor muscle relaxed • Neurons of micturition reflex inactivated • Neurons of storage reflex activated © 2019 McGraw-Hill Education 138 24.8c Micturition 7 Conscious control of urination (continued) • If urination not activated at time of first reflex • Relaxation of detrusor muscle due to “stress-relaxation response” • Micturition reflex activated again after another 200 to 300 mL added • Urination occurs involuntarily between 500 mL and 600 mL • Can empty bladder prior to micturition reflex • Contract abdominal muscles and compress bladder • Initiates micturition reflex by stimulating stretch receptors © 2019 McGraw-Hill Education 139 Clinical View: Urinary Tract Infections UTI occurs when bacteria or fungi multiply within urinary tract Women more prone due to short urethra close to anus Often first develops in urethra, urethritis If spreads to bladder, cystitis May spread up into kidneys, pyelonephritis Symptoms • Painful urination, dysuria • Frequent urination • Pressure in pubic region • Pyelonephritis causing flank pain, back pain, nausea Diagnosed through urinalysis Treated with antibiotics © 2019 McGraw-Hill Education 140 Clinical View: Impaired Urination Incontinence • Inability to voluntarily control urination • May occur due to childbirth, strong detrusor muscle contractions, secondary result of medications, fear response Retention • Failure to eliminate urine normally • Side effects from general anesthesia, enlarged prostate • May require insertion of catheter to allow urine to flow out © 2019 McGraw-Hill Education 141 Section 24.8 What did you learn? 36. What characteristics are used to describe urine? What conditions cause variation in pH of urine? 37. What are the major components of the urinary tract? What tunics are found in each of these? 38. How do the urethras of a male and female differ? 39. What steps lead to micturition? At what point does the reflex overcome conscious control? © 2019 McGraw-Hill Education Urinary System Connections Can you connect the systems? © 2019 McGraw-Hill Education 142