Urinary System PDF

10.01.2023 Urinary System Prepared by: Mrs. Asma Salem Location of the Kidneys Against the dorsal body wall At the level of T12 to L3 The right kidney is slightly lower than the left Attac...

10.01.2023 Urinary System Prepared by: Mrs. Asma Salem Location of the Kidneys Against the dorsal body wall At the level of T12 to L3 The right kidney is slightly lower than the left Attached to ureters, renal blood vessels. Atop each kidney is an adrenal gland 1  10.01.2023 Organs of the Urinary system Kidneys Ureters Urinary bladder Urethra Coverings of the Kidneys Renal capsule Surrounds each kidney Adipose capsule Surrounds the kidney Provides protection to the kidney Helps keep the kidney in its correct location 2  10.01.2023 Kidney Functions The Kidneys are the primary organs of the Urinary System At less than 1% of body weight, they receive 20-25% of total cardiac output! Functions: Maintain blood volume Maintain fluid & electrolyte composition – Water – Ions Maintain acid/base balance Eliminate metabolic waste, toxic substances Vitamin D activation: Ca2+, PO4 absorption Hormone production – EPO – red blood cell production – Renin – water/salt conservation Acid-base balance in the blood Role of kidney in vitamin D synthesis The kidneys convert vitamin D from supplements or the sun to the active form of vitamin D that is needed by the body. 3  10.01.2023 Regions of the Kidney Renal cortex – outer region Renal medulla – inside the cortex Renal pelvis – inner collecting tube Kidney Structures Medullary pyramids – triangular regions of tissue in the medulla Renal columns – extensions of cortex-like material inward Calyces – cup-shaped structures that funnel urine towards the renal pelvis What is Urine? Urine: a fluid waste product produced by the kidneys Normally contains: water, ions, nitrogenous waste, small soluble compounds Composition changes as a function of blood/kidney regulation Should NOT contain: blood cells, large proteins (presence of these could indicate damage to the kidneys) 4  10.01.2023 Nephron Processes Nephron The Nephron is the working unit of the kidney that produces urine Over 1 million nephrons in each kidney Removes, exchanges, adds materials to/from the blood to regulate blood composition “What stays in the blood?” – Blood IN à Regulated Blood OUT returns to body “What needs to be removed from the blood?” – Blood IN à Removed Waste/Urine OUT leaves the body. 5  10.01.2023 Nephron physiology Nephron contains specialized blood vessels and tubules that regulate exchange of materials to/from the blood : Afferent Arteriole Renal Corpuscle: – Glomerulus – Bowman’s Capsule Efferent Arteriole Proximal Convoluted tubule (PCT) Peri-tubular capillaries Loop of Henle – Descending Limb (thin) – Ascending Limb (thick) Distal Convoluted tubule (DCT) Collecting Duct Nephron Overview of Functions of Parts of a Nephron Vascular component Afferent arteriole —carries blood to the glomerulus Glomerulus —a tuft of capillaries that filters a protein-free plasma into the tubular component Efferent arteriole —carries blood from the glomerulus Peritubular capillaries —supply the renal tissue; involved in exchanges with the fluid in the tubular lumen Tubular component Bowman’s capsule —collects the glomerular filtrate Proximal tubule —uncontrolled reabsorption and secretion of selected substances.almost the reabsorption occurs in PCT about 65% of processes. Loop of Henle —establishes an osmotic gradient in the renal medulla that is important in the kidney’s ability to produce urine of varying concentration Distal tubule and collecting duct — variable, controlled reabsorption of Na+ and H2O and secretion of K+ and H+ occur here; fluid leaving the collecting duct is urine, which enters the renal pelvis Combined vascular/tubular component Juxtaglomerular apparatus —produces substances involved in the control of kidney function. 6  10.01.2023 Types of Nephrons - Cortical nephrons located entirely in the cortex Includes most nephrons - Juxtamedullary nephrons found at the boundary of the cortex and medulla. Blood Flow in the Kidneys 7  10.01.2023 Nephron Processes 3 main processes in the Nephron to regulate blood and produce urine: 1) Glomerular Filtration: Separation of cells and large proteins from plasma, plasma enters nephron 2) Tubular Reabsorption : Valuable substances selectively returned to the blood from the nephron 3) Tubular Secretion: Unneeded substances selectively removed from the blood and added to the nephron Glomerular Filtration Glomerular Filtration is the nonspecific separation of large substances (cells, proteins) from small substances (water, ions, small molecules) Blood enters at the afferent arteriole, passes through the glomerular membrane BLOOD: Large proteins and cells STAY in the blood and exit the efferent arteriole FILTRATE: Water, ions, small molecules enter the filtrate into the nephron tubules at Bowman’s capsule Glomerular Membrane 3 components of glomerular membrane that blood is filtered through: 1) Glomerular capillary wall: simple squamous epithelium with large pores(fenestrations) 2) Basement membrane: collagen and glycoprotein gelatinous layer 3) Capsular Filtration Slits: podocyte cells with processes link together to form filtration slits 8  10.01.2023 Glomerular Filtration Glomerular Filtration Pressure Glomerular Filtration is regulated by various pressures at the glomerular membrane, where capillary blood pressure is the main driving force: Pglom Glomerular capillary blood pressure = 55mmHg – systemic blood pressure – Elevated glomerular capillary BP due to diameter of afferent arteriole (large) vs. efferent arteriole (smaller) Pop Plasma-colloid osmotic pressure = 30mmHg – high protein level in glomerular capillaries vs. Bowman’s capsule PBC Bowman’s capsule hydrostatic pressure = 15mmHg – Fluid in Bowman’s capsule – The sum of these pressures is the: NET glomerular filtration pressure = +10mmHgs 9  10.01.2023 Glomerular Filtration Pressure Glomerular Filtration Rate The rate of glomerular filtration (GFR) is important clinically for assessing kidney health, kidney disease and kidney failure The total rate of filtration at the glomerular membrane depends on : net filtration pressure (NFR) = Pglom + Pop + PBC properties of the glomerular membrane, such as pore size, filtration slit size (Kf) GFR = [(Kf) x (net filtration pressure)] – Total for the entire system, daily average GFR = 115- 125 mL/min 10  10.01.2023 factor decreasing GRF: 1-Increasing plasma colloid osmotic pressure. 2-increase Bowman's capsule pressure. 3-Afferent arteriolar constriction. 5-sympathetic stimulation. GFR Regulation GFR can be altered by: Plasma protein concentration ( affects Pop) Hydration level (affects Pglom and PBC) Urinary tract obstruction (PBC) Mean Arterial Blood Pressure (MAP affectsPglom) MAP is the most variable and will cause the biggest changes, so there are 2 ways the kidneys compensate for MAP 1) Autoregulation – Myogenic mechanism – Tubuloglomerular feedback 2) Sympathetic nervous System 11  10.01.2023 Autoregulation I Autoregulation is the main way kidneys maintain constant GFR as mean systemic arterial blood pressure (MAP) changes: If GFR is too high: afferent arteriole vasoconstriction If GFR is too low: afferent arteriole vasodilation 2 ways this happens: Myogenic Mechanism Tubuloglomerular feedback Autoregulation II 12  10.01.2023 Autoregulation: Myogenic – Myogenic Mechanism: afferent arteriole automatically constricts when stretched by increased MAP – Increased Pglom afferent arteriole vasoconstriction, decreases Pglom to balance GFR Autoregulation: Tubuloglomerular Feedback – Tubuloglomerular feedback: occurs at juxtaglomerular apparatus – ATP and adenosine released by DCT cells (macula densa) if GFR is too high, causes afferent arteriole vasoconstriction (granular cells) – Increased Pglom led to macula densa sense high salt and fluid flow – Macula densa led to release ATP and adenosine – Afferent arteriole vasoconstriction decreases Pglom to balance GFR 13  10.01.2023 Sympathetic GFR Regulation Sympathetic Nervous System stimulation will decrease GFR to decrease urine volume and retain fluids (increase blood volume) SNS led to afferent arteriole vasoconstriction Decreases Pglom, decreases GFR SNS led to mesangial cells and podocyte cell contraction Decreases size of filtration slits, decreases Kf, decreases GFR 14  10.01.2023 Sympathetic GFR Regulation Tubular Reabsorption Tubular Reabsorption: the selective process of returning needed substances from the glomerular filtrate back to the blood Glomerular filtrate contains all fluids, ions, small molecules from blood Starting with PCT, tubules transport valuable substances back to peritubular capillaries to be returned to body Excess materials and waste will stay in the filtrate and exit as urine For normal GFR at 125 mL/min, typically 124 mL/min is returned to blood 99% of water, 100% of sugar, 99.5% of salt is reabsorbed Excess ions, urea, toxins will become concentrated in the filtrate 15  10.01.2023 Transepithelial Transport Reabsorption occurs through the process of transporting substances from the lumen of the tubules to the blood - Substances must pass through 5 layers: Reabsorption by location After renal corpuscle, tubules are: PCT Loop of Henle DCT Collecting Duct 16  10.01.2023 Average Proximal Loop of Henle Distal Convoluted Convoluted Tubule Tubule & Collecting Duct - Na+, 67% of total Na+, 25% of total Na+, 8% of total - Water, 8% of total -Water, 15% of total -Water, 20% of total - Cl- - Cl- - Cl- - Glucose - Amino Acids Reabsorption - PO4 -Urea - K+ Secretion - H+ - Na+ - H+ -ions - Cl- - K+ 17  10.01.2023 Regulation of Water Reabsorption Dilute urine enters the DCT The osmotic gradient in the medulla is used by the DCT and Collecting duct to increase water reabsorption Vasopressin (ADH- anti-diuretic hormone) inserts aquaporins into the DCT and Collecting Duct Graded response, can slightly increase or decrease based on need Up to 20% of total water reabsorption can be increased at the DCT and Collecting Duct Caffeine, alcohol block ADH (increase urine output) 18  10.01.2023 Tubular Secretion: H+ – H+ secretion is regulated in order to maintain acid/base balance – Normally causes urine to be acidic pH = 6 – occurs in PCT, DCT, Collecting Duct H+ ATPase pumps H+/K+ ATPase pumps Na+/H+ cotransporters; antiporters – Balanced with HCO3 - reabsorption 19  10.01.2023 Tubular Secretion: Organic Ions – Organic Ions include hormones, foreign compounds (pesticides, , food additives), drugs (antibiotics, anti-inflammatories) – Two types of non-selective carriers for organic anions organic cations Consequence of general anion/cations group carriers is that drugs compete for carriers during elimination, causes drug interactions Two drugs taken that use the same carrier, will NOT be fully eliminated. Ureters Slender tubes attaching the kidney to the bladder Continuous with the renal pelvis Enter the posterior aspect of the bladder Runs behind the peritoneum Peristalsis aids gravity in urine transport 20  10.01.2023 Urinary Bladder Smooth, collapsible, muscular sac Temporarily stores urine Trigone – three openings Two from the ureters One to the urethrea Urinary Bladder Wall Three layers of smooth muscle (detrusor muscle) Mucosa made of transitional epithelium Walls are thick and folded in an empty bladder Bladder can expand significantly without increasing internal pressure 21  10.01.2023 Urethra Urethra Gender Differences Length Females – 3–4 cm (1 inch) Males – 20 cm (8 inches) Location Females – along wall of the vagina Males – through the prostate and penis Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis Release of urine is controlled by two sphincters Internal urethral sphincter (involuntary) External urethral sphincter (voluntary) Regulation of Water and Electrolyte Reabsorption - Regulation is primarily by hormones - Antidiuretic hormone (ADH) prevents excessive water loss in urine -Aldosterone regulates sodium ion content of extracellular fluid -Triggered by the rennin-angiotensin mechanism Cells in the kidneys and hypothalamus are active monitors 22  10.01.2023 Maintaining Acid-Base Balance in Blood Blood pH must remain between 7.35 and 7.45 to maintain homeostasis Alkalosis – pH above 7.45 Acidosis – pH below 7.35 Most ions originate as byproducts of cellular metabolism Most acid-base balance is maintained by the kidneys Other acid-base controlling systems Blood buffers Respiration Blood Buffers Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations Bind to H+ when pH drops Release H+ when pH rises Three major chemical buffer systems Bicarbonate buffer system Phosphate buffer system Protein buffer system 23  10.01.2023 The Bicarbonate Buffer System Mixture of carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3) Bicarbonate ions (HCO3–) react with strong acids to change them to weak acids Carbonic acid dissociates in the presence of a strong base to form a weak base and water Respiratory System Controls of Acid- Base Balance Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma Increases in hydrogen ion concentration produces more carbonic acid Excess hydrogen ion can be blown off with the release of carbon dioxide from the lungs Respiratory rate can rise and fall depending on changing blood pH 24  10.01.2023 Renal Mechanisms of Acid-Base Balance Urine can Excrete bicarbonate ions if needed Conserve or generate new bicarbonate ions if needed Urine pH varies from 4.5 to 8.0 Developmental Aspects of the Urinary System Functional kidneys are developed by the third month Urinary system of a newborn the Bladder is small not be concentrated Control of the voluntary urethral sphincter does not start until age 18 months Urinary infections are the only common in women than men problems why ? 25