Urinary System - Part 1 PDF

Urinary System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Object...

Urinary System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Objectives List the components of the urinary system. Describe the general functions of the urinary system. Describe the structure and functions of a nephron. Compare glomerular filtration, tubular reabsorption, and tubular secretion. Explain how urine is formed. Indicate the typical components of urine. Describe the structure and function of the ureters, urinary bladder, and urethra. Explain how water balance is maintained in body fluids. Explain how electrolyte balance is maintained in body fluids. Explain how pH balance is maintained in body fluids. Describe the common disorders of the urinary system. 2 Major Structures of the Urinary System Two kidneys: Maintain composition and volume of body fluids by removing wastes and excess substances in the formation of urine. Two ureters Slender tubes that carry urine from the kidneys to the urinary bladder. One urinary bladder Temporary storage of urine. One urethra 3 Kidney Functions Maintainance of body fluid composition Helps maintain blood plasma volume and composition within healthy limits. Secretion of erythropoietin: Stimulates RBC formation when oxygen levels fall below homeostasis. Maintenance of blood pressure Increases blood pressure by secreting renin, which trigger the reninangiotensin mechanism. Conversion of vitamin D: Converts inactive vitamin D to its active form, in response to PTH. 4 Kidney Functions Excretion of nitrogenous wastes: Keeps wastes levels in blood within tolerable limits. Three primary nitrogenous wastes: Urea Uric acid Creatinine 5 Anatomy of the Kidneys Reddish brown, located on both sides of the vertebral column. Lie in retroperitoneal space. Partially protected by floating ribs. Protected by three layers of connective tissue: Enveloped in a fibrous capsule. Surrounded by a thick layer of adipose tissue. Cushioning shock absorber. Renal fascia attaches each kidney to the abdominal wall. 6 Gross Anatomy Hilum: Medial indentation Site where blood vessels, lymphatic vessels, nerves, and ureter exit or enter the kidney. Adult kidney: Approx. 12 cm long, 7 cm wide, 2.5 cm thick. Renal cortex: Outer layer Renal medulla Inner layer Contains renal pyramids: Renal papilla Renal columns 7 Gross Anatomy Minor calyx: Surrounds a renal papilla. Receives urine from renal papilla. Major calyx: Formed by union of minor calyces. Renal pelvis: Formed by union of major calyces. Contiguous with ureter. Ureter: Carries urine from kidney to urinary bladder. Papillary duct 8 Nephron Approximately 1 million nephrons per kidney. Structural and functional units of the kidneys. Originate in renal cortex, dip into renal medulla, return to the renal cortex. Consists of two parts: Renal corpuscle Renal tubule Papillary duct 9 Nephron Bowman’s capsule Renal corpuscle: In renal cortex. Each renal corpuscle is composed of a glomerulus. Glomerulus: Group of capillaries Enclosed in a double walled glomerular capsule. 10 Nephron Renal tubule In renal cortex and renal medulla. Proximal convoluted tubule (PCT) Nephron loop Descending limb (descends into the renal medulla). Ascending limb (ascends back into the renal cortex and is continuous with the distal convoluted tubule). Henle’s loop 11 Nephron Papillary duct Distal convoluted tubule (DCT) Papillary duct Several DCTs unite with a single collecting duct. Collecting duct Extends from renal cortex through renal pyramid and its papilla. Receives tubular fluid from DCTs. Merge together to form papillary ducts in renal papilla. 12 Types of Nephrons Cortical nephrons: 80% Glomerular capsule near the surface of the renal cortex. Nephron loops almost entirely in renal cortex. Important in adjusting the composition of the urine. Juxtamedullary nephrons: 20% Glomerular capsules lie deep in renal cortex, close to renal medulla. Nephron loops penetrate renal medulla. Important role in regulating blood water content. 13 Gross Anatomy Thus, the pathway of urine from nephrons to ureter is as follows: Nephrons→ papillary ducts→ minor calyces→ major calyces→ renal pelvis→ ureter→ urinary bladder. 14 Renal Blood Supply Receive approximately 1,200 ml blood per minute. Renal artery: Brings blood to kidney. Branches to form segmental arteries. Segmental arteries branch to form interlobar arteries. These arteries continue to branch until they finally form arterioles. 15 Renal Blood Supply Afferent glomerular arteriole: Brings blood to a glomerulus. Efferent glomerular arteriole: Takes blood out of glomerulus. Leads to peritubular capillary network. Peritubular capillaries: Surround the cortical portion of the renal tubule. Vasa recta: Surround the nephron loops and collecting ducts within the renal medulla. 16 Renal Blood Supply Blood will leave peritubular capillaries and vasa recta to enter venules. Venules merge to form: Interlobar veins (join to form the renal vein). Renal vein→ carries blood from kidney to inferior vena cava. 17 Juxtaglomerular Complex A contact point between ascending limb of the nephron loop and the afferent and efferent glomerular arterioles. Consists of: Granular cells-smooth muscle cells in the walls of the afferent and efferent glomerular arterioles. Macula densa- tightly packed cells composing the ascending limb. Helps to regulate blood pressure. 18 Three Basic Functions of Nephrons Regulate solute concentration in blood plasma, such as nutrients and ions, which also regulates blood pH. Regulate water concentration in blood plasma, which helps regulate blood pressure. Remove metabolic wastes and excess substances from blood plasma. 19 Four Processes Involved in Urine Formation Glomerular filtration: Moves water and solutes from blood plasma and into glomerular capsule. Formed elements and plasma proteins are usually absent. Fluid within the capsule is called glomerular filtrate: Fluid is renamed tubular fluid after passing into the renal tubule. 20 Four Processes Involved in Urine Formation Tubular reabsorption: Removes useful substances from tubular fluid and returns them to blood plasma. Tubular secretion: Removes wastes from blood. Water conservation: Removes water from tubular fluid of DCT and collecting duct and returns it to blood plasma. 21 Glomerular Filtration A process that forces water and solutes in blood plasma from glomeruli into the glomerular capsules. Two factors cause filtration: Increased permeability of glomerular capillary walls. Elevated blood pressure within the glomeruli. Glomerular capillaries possess numerous pores. Allow water and most dissolved substances to pass across capillary walls. Capillaries are wrapped by cellular extensions from podocytes. Help prevent plasma proteins and formed elements from being filtered. 22 Glomerular Filtration Elevated glomerular blood pressure results from differences in arteriole diameter. Efferent glomerular arteriole has a smaller diameter that the afferent glomerular arteriole. Leads to a greater blood volume, which increases blood pressure→ provides the force for glomerular filtration. Result of glomerular filtration is glomerular filtrate: Same as blood plasma, without the plasma proteins. No formed elements are present. 23 Glomerular Filtration Rate (GFR) Approximately 125 ml/min or 7.5 liters/hour: Most of the glomerular filtrate is reabsorbed. Stable GFR is necessary for healthy kidney function: A change in glomerular blood pressure will impact GFR. Change in systemic blood pressure will alter glomerular blood pressure. 24 Glomerular Filtration Rate (GFR) Three mechanisms help to maintain a stable GFR 1. Renal autoregulation –for smaller, daily fluctuations in systemic blood pressure. 2. Sympathetic control—systemic blood pressure changes. 3. Renin-angiotensin mechanism— for severe drops in systemic blood pressure. 25 Glomerular Filtration Rate Renal autoregulation Involves the response of smooth muscle in the afferent glomerular arteriole wall to changes in systemic blood pressure. Increased blood pressure (increased GFR) increases stretch on afferent glomerular arteriole. Arteriole constricts, ↓blood volume and flow into glomerulus. ↓blood pressure within glomerulus, ↓GFR. Decline in blood pressure causes the arteriole to dilate, allowing more blood volume to enter the glomerulus. ↑blood pressure volume, which keeps the GFR stable. 26 Glomerular Filtration Rate Renal autoregulation Juxtaglomerular complex uses the macula densa to detect tubular fluid flow rate and chemical composition in ascending limb. If GFR increases, fluid moves too quickly, and not enough ions are reabsorbed. Macula densa detects elevated Na+, K+, and Clconcentrations. Granular cells constrict the afferent glomerular arteriole ↓GFR. If GFR decreases, tubular fluid moves too slowly and too many ions are reabsorbed. Macula densa detects the decrease in Na+, K+, and Clconcentrations. The afferent glomerular arteriole relaxes, ↑GFR. 27 Glomerular Filtration Rate Sympathetic control Overrides renal autoregulation in times of large systemic blood pressure shifts or during the “fight or flight” response. If systemic blood pressure decreases, sympathetic stimulation constricts afferent glomerular arterioles. ↓glomerular blood pressure, ↓GFR. ↓ urine formation, which conserves water maintains healthy blood volume and pressure. If systemic blood pressure increases, lack of sympathetic stimulation dilates afferent glomerular arterioles. ↑glomerular blood pressure, ↑GFR. ↑ urine formation, and water excretion which maintains healthy blood volume and pressure. 28 Glomerular Filtration Rate Renin-angiotensin mechanism Is triggered when the juxtaglomerular complex detects a reduced GFR and releases the enzyme renin. Renin is released in response to: Sympathetic stimulation. Drop in blood pressure in afferent glomerular arteriole. Detection of reduced Na+, K+, and Cl- in tubular fluid in ascending limb by the macula densa. 29 Glomerular Filtration Rate Renin-angiotensin mechanism Renin converts angiotensinogen, which is formed by the liver, into angiotensin I. Angiotensin I is converted into angiotensin II by the angiotensinconverting-enzyme (ACE). Angiotensin II Constricts the efferent glomerular arterioles to maintain blood pressure in glomeruli, which maintains an adequate GFR in spite of a decline in systemic blood pressure. 30 Glomerular Filtration Rate Renin-angiotensin mechanism Angiotensin II also acts to restore blood volume and blood pressure by: 1. Constricting systemic arterioles. 2. Stimulating aldosterone secretions which promotes the reabsorption of Na+, which in turn promotes the reabsorption of water by osmosis. 3. Stimulating secretion of antidiuretic hormone (ADH) which promotes water reabsorption. 4. Stimulating thirst, which promotes water intake. ACE inhibitors 31 Glomerular Filtration Rate Natriuretic peptides also affect GFR Secreted by atria of the heart when stretched by excessive blood volume. Promotes water excretion by increasing GFR and inhibiting Na+ reabsorption in the DCT and collecting duct. ↑urine volume. ↓blood volume, ↓blood pressure. Kidney anatomy and urine production (3D) https://anatomy.mheducation.com/html/apr.html?animal=human& Filtration Overview https://anatomy.mheducation.com/html/apr.html?animal=human&id=16981 32