Presentation is loading. Please wait.

Presentation is loading. Please wait.

Anatomy and Physiology, Seventh Edition

Similar presentations

Presentation on theme: "Anatomy and Physiology, Seventh Edition"— Presentation transcript:

1 Anatomy and Physiology, Seventh Edition
Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College Chapter 26 Lecture Outline* *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Chapter 26 Urinary System

3 Urinary System Functions
Filtering of blood: involves three processes- filtration, reabsorption, secretion. Regulation of Blood volume Concentration of blood solutes: Na+, Cl-, K+, Ca2+, HPO4-2 pH of extracellular fluid: secrete H+ Blood cell synthesis Synthesis of vitamin D

4 Urinary System Anatomy

5 Location and External Anatomy of Kidneys
Renal capsule: fibrous connective tissue. Surrounds each kidney Perirenal fat Engulfs renal capsule and acts as cushioning Renal fascia: thin layer loose connective tissue Anchors kidneys and surrounding adipose to abdominal wall Hilum Renal artery and nerves enter and renal vein and ureter exit kidneys Opens into renal sinus (cavity filled with fat and loose connective tissue) Location Lie behind peritoneum (retroperitoneal) on posterior abdominal wall on either side of vertebral column Lumbar vertebrae and rib cage partially protect Right kidney slightly lower than left

6 Internal Anatomy of Kidneys
Cortex: outer area Renal columns: part of cortical tissue that extends into medulla Medulla: inner area; surrounds renal sinus Renal pyramids: cone-shaped. Base is boundary between cortex and medulla. Apex of pyramid is renal papilla, points toward sinus. Calyces Minor: papillae extend into funnel of minor calyx Major: converge to form pelvis Pelvis: enlarged chamber formed by major calyces Ureter: exits at the hilum; connects to urinary bladder

7 The Nephron Functional and histological unit of the kidney
Parts of the nephron: Bowman’s capsule, proximal tubule, loop of Henle (nephronic loop), distal tubule Urine continues from the nephron to collecting ducts, papillary ducts, minor calyses, major calyses, and the renal pelvis Collecting ducts, parts of the loops of Henle, and papillary ducts are in the renal medulla

8 Types of Nephrons Juxtamedullary nephrons. Renal corpuscle near the cortical medullary border. Loops of Henle extend deep into the medulla. Cortical nephrons. Renal corpuscle nearer to the periphery of the cortex. Loops of Henle do not extend deep into the medulla. Renal corpuscle. Bowman’s capsule plus a capillary bed called the glomerulus.

9 Renal Corpuscle Bowman’s capsule: outer parietal (simple squamous epithelium) and visceral (cells called podocytes) layers. Glomerulus: network of capillaries. Blood enters through afferent arteriole, exits through efferent arteriole.

10 Bowman’s Capsule Parietal layer: outer. Simple squamous epithelium that becomes cube-shaped where Bowman’s capsule ends and proximal tubule begins Visceral layer: inner. Specialized podocytes that wrap around the glomerular capillaries

11 Fenestrae: window-like openings in the endothelial cells of the glomerular capillaries.
Filtrations slits: gaps between the cell processes of the podocytes. Basement membrane sandwiched between the endothelial cells of the glomerular capillaries and the podocytes. Filtration membrane: capillary endothelium, basement membrane and podocytes. First stage of urine formation occurs here when fluid from blood in capillaries moves across filtration membrane into the lumen inside Bowman’s capsule. Filtration Membrane

12 Circulation in the Glomerulus
Afferent arteriole: supplies blood to glomerulus Efferent arteriole: drains glomerulus Both vessels have a layer of smooth muscle Juxtaglomerular apparatus: sight of renin production Juxtaglomerular cells- ring of smooth muscle in the afferent arteriole where the latter enters Bowman’s capsule Macula densa- Specialized tubule cells of the distal tubule. The distal tubule lies between the afferent and efferent arterioles.

13 Histology of the Nephron
Proximal tubule: simple cuboidal epithelium with many microvilli Loops of Henle Descending limb: first part similar to proximal tubule. Latter part simple squamous epithelium and thinner Ascending limb: first part simple squamous epithelium and thin, distal part thicker and simple cuboidal Distal tubule: shorter than proximal tubule. Simple cuboidal, but smaller cells and very few microvilli Collecting ducts: form where many distal tubules come together. Larger in diameter, simple cuboidal epithelium. Form medullary rays and lead to papillary ducts

14 Circulation Through the Kidney
Arterial supply: Renal arteries branch from abdominal aorta Segmental arteries branch from renal Interlobar arteries ascend within renal columns toward cortex Arcuate arteries branch and arch over the base of the pyramids Interlobular arteries project into cortex and give rise to afferent arterioles

15 Circulation Through the Kidney
The part of the circulation involved with urine formation Afferent arterioles supply blood to glomerulus Glomerulus Efferent arterioles exit the renal corpuscle Peritubular capillaries form a plexus around the proximal and distal tubules Vasa recta: specialized parts of peritubular capillaries that course into medulla along with loops of Henle, then back toward cortex Circulation Through the Kidney

16 Circulation Through the Kidney
Venous drainage Peritubular capillaries drain into interlobular veins and lead to Arcuates Interlobar veins Renal veins

17 Anatomy and Histology of Ureters and Bladder
Ureters: bring urine from renal pelvis to urinary bladder. Lined by transitional epithelium Urinary bladder: hollow muscular container. In pelvic cavity posterior to symphysis pubis. Lined with transitional epithelium; muscle part of wall is detrusor Trigone: interior of urinary bladder. Triangular area between the entry of the two ureters and the exit of the urethra. Area expands less than rest of bladder during filling

18 Anatomy and Histology of Urethra
Male: extends from the inferior part of the urinary bladder through the penis Female: shorter; opens into vestibule anterior to vaginal opening Internal urinary sphincter: in males, elastic connective tissue and smooth muscle keep semen from entering urinary bladder during ejaculation External urinary sphincter: skeletal muscle surrounds urethra as it extends through pelvic floor. Acts as a valve

19 Urine Formation Nephrons considered functional units the kidney: smallest structural component capable of producing urine

20 Filtration Movement of fluid, derived from blood flowing through the glomerulus, across filtration membrane Filtrate: water, small molecules, ions that can pass through membrane Pressure difference forces filtrate across filtration membrane Renal fraction: part of total cardiac output that passes through the kidneys. Varies from 12-30%; averages 21% Renal blood flow rate: 1176 mL/min Renal plasma flow rate: renal blood flow rate X fraction of blood that is plasma: 650 mL/min Filtration fraction: part of plasma that is filtered into lumen of Bowman’s capsules; average 19% Glomerular filtration rate (GFR): amount of filtrate produced each minute. 180 L/day Average urine production/day: 1-2 L. Most of filtrate must be reabsorbed


22 Filtration Filtration membrane: filtration barrier. It prevents blood cells and proteins from entering lumen of Bowman’s capsule, but is many times more permeable than a typical capillary Fenestrated endothelium, basement membrane and pores formed by podocytes Some albumin and small hormonal proteins enter the filtrate, but these are reabsorbed and metabolized by the cells of the proximal tubule. Very little protein normally found in urine Filtration pressure: pressure gradient responsible for filtration; forces fluid from glomerular capillary across membrane into lumen of Bowman’s capsules Forces that affect movement of fluid into or out of the lumen of Bowman’s capsule Glomerular capillary pressure (GCP): blood pressure inside capillary tends to move fluid out of capillary into Bowman’s capsule Capsule pressure (CP): pressure of filtrate already in the lumen Blood colloid osmotic pressure (BCOP): osmotic pressure caused by proteins in blood. Favors fluid movement into the capillary from the lumen. BCOP greater at end of glomerular capillary than at beginning because of fluid leaving capillary and entering lumen Filtration pressure (10 mm Hg) = GCP (50 mm Hg) – CP (10 mm Hg) – BCOP (30 mm Hg)

23 Filtration Pressure

24 Filtration Colloid osmotic pressure in Bowman’s capsule normally close to zero. During diseases like glomerular nephritis, proteins enter the filtrate and filtrate exerts an osmotic pressure, increasing volume of filtrate High glomerular capillary pressure results from Low resistance to blood flow in afferent arterioles Low resistance to blood flow in glomerular capillaries High resistance to blood flow in efferent arterioles: small diameter vessels Pressure lower in peritubular capillaries downstream from efferent arterioles Filtrate is forced across filtration membrane; fluid moves into peritubular capillaries from interstitial fluid Changes in afferent and efferent arteriole diameter alter filtration pressure Dilation of afferent arterioles/constriction efferent arterioles increases glomerular capillary pressure, increasing filtration pressure and thus glomerular filtration

25 Tubular Reabsorption: Overview
Tubular reabsorption: occurs as filtrate flows through the lumens of proximal tubule, loop of Henle, distal tubule, and collecting ducts Results because of Diffusion Facilitated diffusion Active transport Cotransport Osmosis Substances transported to interstitial fluid and reabsorbed into peritubular capillaries: inorganic salts, organic molecules, 99% of filtrate volume. These substances return to general circulation through venous system

26 Reabsorption in Proximal Tubule
Substances pass through cells of tubule wall. Each cell has Apical surface: surface that faces filtrate. Apical membrane Basal surface: faces interstitial fluid. Basal membrane Lateral surfaces: surfaces between cells Active transport of Na+ across the basal membrane from cytoplasm to interstitial fluid linked to reabsorption of most solutes Because of active transport, the concentration of Na+ is low inside the cell and Na+ moves into nephron cell from filtrate through the apical membrane. Other substances moved by cotransport from the filtrate into the nephron cell are substances which should be retained by the body Substances transported Through apical membrane: Na+, Cl-, glucose, amino acids, and water. Through basal membrane: Na+, K+, Cl-, glucose, amino acids, water Reabsorption in Proximal Tubule

27 Reabsorption in Proximal Tubule
Number of carrier molecules limits rate of transport In diabetes mellitus Concentration of glucose in filtrate exceeds rate of transport High concentration of glucose in plasma (and thus in filtrate) reflected in glucose in the urine Diffusion between cells: from lumen of nephron into interstitial fluid Depends on rate of transport of same solutes through the cells of the tubule K+, Ca2+, and Mg2+ Filtrate volume reduced by 65% due to osmosis of water

28 Reabsorption in Loop of Henle
Loop of Henle descends into medulla; interstitial fluid is high in solutes. Descending thin segment is highly permeable to water and moderately permeable to urea, sodium, most other ions (passive). Water moves out of nephron, solutes in. Volume of filtrate reduced by another 15%. Ascending thin segment is not permeable to water, but is permeable to solutes. Solutes diffuse out of the tubule and into the more dilute interstitial fluid as the ascending limb projects toward the cortex. Solutes diffuse into the descending vasa recta.

29 Reabsorption in Loop of Henle
The wall of the ascending limb of the loop of Henle is not permeable to water. Na+ moves across the wall of the basal membrane by active transport, establishing a concentration gradient for Na+. K+ and Cl- are cotransported with Na across the apical membrane and ions pass by facilitated diffusion across the basal cell membrane of the tubule cells. At the end of the loop of Henle, inside of nephron is 100 mOsm/kg. Interstitial fluid in the cortex is 300mOsm/kg. Filtrate within DCT is much more dilute than the interstitial fluid which surrounds it.

30 Reabsorption in Distal Tubule and Collecting Duct
Active transport of Na+ out of tubule cells into interstitial fluid with cotransport of Cl- Na+ moves from filtrate into tubule cells due to concentration gradient Collecting ducts extend from cortex (interstitial fluid 300 mOsm/kg) through medulla (interstitial fluid very high) Water moves by osmosis from distal tubule and collecting duct into more concentrated interstitial fluid Permeability of wall of distal tubule and collecting ducts have variable permeability to water Urine can vary in concentration from low volume of high concentration to high volume of low concentration

31 Changes in Concentration of Solutes in the Nephron
Urea: enters glomerular filtrate. As volume of filtrate decreases, concentration of urea increases Walls of nephron not very permeable to urea: only 40-60% passively reabsorbed Urate ions, creatinine, sulfates, phosphates, nitrates partially reabsorbed Concentration is high in urine Toxic substances and are eliminated

32 Tubular Secretion Moves metabolic by-products, drugs, molecules not normally produced by the body into tubule of nephron Active or passive Ammonia: produced by epithelial cells of nephron from deamination of amino acids. Diffuses into lumen H+, K+, penicillin, and substances such as para-aminohippuric acid (PAH): actively secreted into nephron

33 Secretion of Hydrogen and Potassium
Hydrogen ions secreted into filtrate by countertransport in proximal tubule H+ either diffuse from peritubular capillaries into interstitial fluid and then into epithelial cells of tubule or derived from reaction between carbon dioxide and water in cells of tubule. Na+ and HCO3- cotransported across basal membrane into interstitial fluid, then diffuse into peritubular capillaries

34 Secretion of Hydrogen and Potassium
H+ and K+ secreted into filtrate by countertransport in distal tubule. Na+ and K+ move by active transport across the basal membrane. Na+ and HCO3- cotransported across basal membrane into interstitial fluid, then diffuse into peritubular capillaries

35 Urine Production In ascending limb of loop of Henle
Na+, Cl-, K+ transported out of filtrate Water remains In distal tubules and collecting ducts Water movement out regulated by ADH If absent, water not reabsorbed and dilute urine produced If ADH present, water moves out, concentrated urine produced In Proximal tubules Na+ and other substances removed Water follows passively Filtrate volume reduced In descending limb of loop of Henle Water exits passively, solute enters Filtrate volume reduced 15%

36 Urine Concentration Mechanism
When large volume of water consumed Eliminate excess without losing large amounts of electrolytes Response is that kidneys produce large volume of dilute urine When drinking water not available Kidneys produce small volume of concentrated urine Removes waste and prevents rapid dehydration Mechanisms that create urine of variable concentration Maintenance of high concentration of solutes in medulla Countercurrent functions of loops of Henle Control of permeability of distal nephron to water

37 Medullary Concentration Gradient
In order to concentrate urine (and prevent a large volume of water from being lost), the kidney must maintain a high concentration of solutes in the medulla Interstitial fluid concentration (mOsm/kg) is 300 in the cortical region and gradually increases to 1200 at the tip of the pyramids in the medulla Maintenance of this gradient depends upon Functions of loops of Henle Vasa recta flowing countercurrent to filtrate in loops of Henle Distribution and recycling of urea

38 Creating/Maintaining High Solute Concentration in Medulla
Active transport of Na+ and cotransport of ions such as K+ and Cl- and other ions out of the thick portion of ascending limb into interstitial fluid Impermeability of thin and thick parts of ascending limb of loop of Henle to water Vasa recta remove excess water and solutes that enter the medulla without destroying the high concentration of solutes in interstitial fluid of medulla Active transport of ions from collecting ducts into interstitial fluid of medulla Passive diffusion of urea from collecting ducts into interstitial fluid of medulla, impermeability of the ascending limb and permeability of the descending limb of the loops of Henle to urea

39 Loops of Henle Juxtamedullary nephrons: long loops.
Walls of descending limbs permeable to water, water moves out into interstitial fluid Walls of ascending limb impermeable to water Solute diffuses out of thin segment of ascending limb as it passes though progressively less concentrated interstitial fluid Na+, K+ and Cl- actively transported out of ascending limb into interstitial fluid Thus, water enters interstitial fluid from descending limbs and solutes enter interstitial fluid from ascending limbs

40 Vasa Recta Countercurrent systems that remove excess water and solutes from medulla: parallel tubes in which fluid flows, but in opposite directions Blood flows through vasa recta to the medulla, vessels turn near tip of renal pyramid, then blood flows in opposite direction Walls are permeable to water and to solutes: as blood flows toward medulla, water moves out, solutes diffuse in. As blood flows back toward cortex, water moves into vasa recta, some solutes diffuse out Diffusion is such that slightly more water and slightly more solute are carried from the medulla by the vasa recta than enter it

41 Loops of Henle and vasa recta function together to maintain a high concentration of solutes in the interstitial fluids of the medulla and to carry away the water and solutes that enter the medulla from the loops of Henle and collecting ducts Water moves out of descending limb and enters vasa recta Solutes diffuse out of ascending thin segment and enter vasa recta, but water does not Solutes transported out of thick segment of ascending enter the vasa recta Excess water and solutes carried away from medulla without reducing high concentration of solutes Concentration of filtrate reduced to 100 mOsm/kg by the time it reaches distal tubule

42 Water and solutes move out of the collecting duct into the vasa recta

43 Urea Responsible for large part of high osmolality in medulla
Descending limbs of loops of Henle permeable to urea; urea diffuses into interstitial fluid Ascending limbs and distal tubules impermeable to urea Collecting ducts permeable to urea; some diffuses out into interstitial fluid Urea flows in a cycle maintaining high urea concentration in medulla

44 Urine Concentrating Mechanisms

45 ADH and the Nephron

46 Renin/Angiotensin/Aldosterone

47 Other Hormones Atrial natriuretic hormone
Produced by right atrium of heart when blood volume increases stretching cells Inhibits Na+ reabsorption Inhibits ADH production Increases volume of urine produced Venous return is lowered, volume in right atrium decreases Prostaglandins and kinins: produced in kidney. Role unclear

48 Autoregulation and Sympathetic Stimulation
Involves changes in degree of constriction in afferent arterioles As systemic BP increases, afferent arterioles constrict and prevent increase in renal blood flow Increased rate of blood flow of filtrate past cells of macula densa: signal sent to juxtaglomerular apparatus, afferent arteriole constricts Sympathetic stimulation: norepinephrine Constricts small arteries and afferent arterioles Decreases renal blood flow and thus filtrate formation During shock or intense exercise: intense sympathetic stimulation, rate of filtrate formation drops to a few mm

49 Clearance and Tubular Load
Plasma clearance: calculated using substances like inulin Volume of plasma cleared of a specific substance each minute Used to estimate GFR Used to calculate renal plasma flow. Calculated using substances like PAH Used to determine which drugs or other substances excreted by kidney Tubular load Total amount of substance that passes through filtration membrane into nephrons each minute

50 Maximum rate at which a substance can be actively absorbed
Each substance has its own tubular maximum Normally, glucose concentration in the plasma (and thus filtrate) is lower than the tubular maximum and all of it is reabsorbed; none of it is found in the urine In diabetes mellitus tubular load exceeds tubular maximum and glucose appears in urine. Urine volume increases because glucose in filtrate increases osmolality of filtrate reducing the effectiveness of water reabsorption Tubular Maximum

51 Urine Movement Hydrostatic pressure forces urine through nephron
Peristalsis moves urine through ureters from region of renal pelvis to urinary bladder. Occur from once every few seconds to once every 2-3 minutes Parasympathetic stimulation: increase frequency Sympathetic stimulation: decrease frequency Ureters enter bladder obliquely through trigone. Pressure in bladder compresses ureter and prevents backflow

52 Micturition Reflex

53 Effects of Aging Gradual decrease in size of kidneys, but only one-third of one kidney necessary for homeostasis Amount of blood flowing through gradually decreases Number of glomeruli decrease and ability to secrete and reabsorb decreases Ability to concentrate urine declines and kidney becomes less responsive to ADH and aldosterone Reduced ability to participate in vitamin D synthesis contributing to Ca2+ deficiency, osteoporosis, and bone fractures

Download ppt "Anatomy and Physiology, Seventh Edition"

Similar presentations

Ads by Google