Urinary System PDF

The Urinary System Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Urinary System Consists of the kidneys, ureters, bladder, and urethra Maintains homeostasis by managing the volume and composition of fluid reservoirs, primarily blood Copyright © 2014 Joh...

The Urinary System Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Urinary System Consists of the kidneys, ureters, bladder, and urethra Maintains homeostasis by managing the volume and composition of fluid reservoirs, primarily blood Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Organs of the urinary system in a female Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Urinary System The urinary system or renal system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder and the urethra. The female and male urinary system are very similar, differing only in the length of the urethra. Urine is formed in the kidneys through a filtration of blood. The urine is then passed through the ureters to the bladder, where it is stored. During urination (peeing) the urine is passed from the bladder through the urethra to the outside of the body. About 1-2 liters of urine are produced every day in a healthy human, although this amount may vary according to circumstances such as fluid intake.  Urinary System Urine formation. Average urine production in adult humans is about 1 – 2 L per day, depending on state of hydration, activity level, environmental factors, weight, and the individual's health. Producing too much or too little urine needs medical attention. Polyuria is a condition of excessive production of urine (> 2.5 L/day), Oliguria when < 400 mL are produced, and anuria one of < 100 mL per day. The basic structural and functional unit of the kidney is the nephron. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Urination Urination is the ejection of urine from the urinary bladder through the urethra to the outside of the body.  Urinary System There are several functions of the Urinary System: § Removal of waste product from the body (mainly urea and uric acid) § Regulation of electrolyte balance (e.g. sodium, potassium and calcium) § Regulation acid-base homeostasis § Controlling blood volume and maintaining blood pressure  Kidney functions § Produce erythropoietin § Produce renin § Convert vitamin D to a form that facilitates calcium absorption  Homeostatic Kidney Functions § Regulation of blood ionic composition Na+, K+, Cl– § Regulation of blood pH H+, HCO3– § Regulation of blood volume H20 § Regulation of blood pressure Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Homeostatic Kidney Functions § Maintenance of blood osmolarity § Production of hormones Calcitrol and Erythropoietin § Regulation of blood glucose level § Excretion of metabolic wastes and foreign substances (drugs or toxins) Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Organs of the Urinary System Kidneys – excretory organs that separate waste substances from the blood and discharge them. Ureters – a pair of thick-walled tubes that carry urine from the kidney to the urinary bladder. Urinary bladder – a membranous sac for temporary retention of urine. Urethra – a duct through which urine is discharged and which serves as the male genital duct. The Urinary System: Built for Filtering & Waste Disposal Kidney (one of a pair) Blood-filtering organ; filters water, all solutes heart except proteins from diaphragm blood; reclaims only adrenal amounts body requires, gland excretes rest as urine Ureter (one of a pair) abdominal Channel for urine flow from a aorta kidney to the urinary bladder inferior Urinary Bladder vena Stretchable urine cava storage organ Urethra Urine flow channel between Urinary bladder and body surface Anatomy of the Urinary System Anatomy of the Urinary System Human urinary system: 2. Kidney, 3. Renal pelvis, 4. Ureter,5. Urinary bladder, 6. Urethra. (Left side with frontal section) 7. Adrenal gland Vessels: 8. Renal artery and vein, 9. Inferior vena cava, 10. Abdominal aorta, 11. Common iliac artery and vein With transparency: 12. Liver, 13. Large intestine, 14. Pelvis The order of impurities being excreted from the kidneys: Kidneys → Ureters → Urinary Bladder → Urethra  Renal Anatomy The kidneys are retroperitoneal, partly protected by the lower ribs. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Renal Anatomy The indented area is called the Hilum. This is the entrance for: Renal Artery Renal Vein Ureter Nerves Lymphatics Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  External Layers Connective Tissue, (Superficial to Deep) Renal Fascia - Anchors to other structures Adipose Capsule – Protects and anchors Renal Capsule – Continuous with Ureter Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Internal Renal Anatomy Renal Cortex – Outer layer Renal Medulla – Inner region Renal Pyramids – Secreting Apparatus and Tubules Renal Columns – Anchor the Cortex Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Internal Renal Anatomy Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Internal Renal Anatomy Papillary ducts empty urine into calyces Calyces pass urine to the Ureter Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Blood and Nerve supply of the Kidneys Blood supply Although kidneys constitute less than 0.5% of total body mass, they receive 20–25% of resting cardiac output Nerve Supply Renal Nerves primarily carry sympathetic outflow They regulate blood flow through the kidneys Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Nephrons are the kidney filters. distal Nephrons proximal tubule tubule Bowman’s capsule (orange) (brown) More than 1 million tubes/kidney Filter water and solutes from blood Glomerulus KIDNEY CORTEX Cluster of blood capillaries Bowman’s capsule KIDNEY MEDULLA Proximal tubule, loop of Henle, and distal tubule loop of Henle (yellow) collecting duct (tan)  The Nephron Renal corpuscle filters the blood plasma Renal tubule modifies the filtrate Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Renal Corpuscle The Renal Corpuscle consists of two parts: Ø The Glomerulus is a mass of capillaries. Ø The Glomerular (Bowman’s) Capsule has a visceral layer of podocytes which wrap around the capillaries. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Renal Corpuscle The Glomerulus is a mass of capillaries. It is fed by the Afferent Arteriole and drains into the Efferent Arteriole. Mesangial cells are contractile and help regulate glomerular filtration. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Special vessels transport blood to, in, and away from nephrons. Renal artery delivers 75 gallons of blood/hour efferent arteriole to your kidneys Afferent arteriole: afferent arteriole brings blood to each nephron Blood goes through glomerular glomerular capillaries. capillaries inside Bowman’s collecting capsule duct Blood leaves via the efferent arteriole, which branches into peritubular capillaries threading around peritubular capillaries tubular nephron regions  The Renal Corpuscle The Glomerular (Bowman’s) Capsule has a visceral layer of podocytes which wrap around the capillaries. The filtrate is collected between the visceral and parietal layers. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Histology of a Renal Corpuscle Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Renal Corpuscle The glomerular endothelial cells have large pores (fenestrations) and are leaky. Basal lamina lies between endothelium and podocytes. Podocytes form pedicels, between which are filtration slits. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. The Renal Corpuscle Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  The Renal Tubule The filtrate passes from the glomerular capsule to the renal tubule § Proximal Convoluted Tubule § Nephron Loop § Descending Loop § Ascending Loop § Distal Convoluted Tubule  The Juxtaglomerular Apparatus The ascending loop contacts the afferent arteriole at the macula densa. The wall of the arteriole contains smooth muscle cells; juxtaglomerular cells. The apparatus regulates blood pressure in the kidney in conjunction with the ANS. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Histology of a Renal Corpuscle  The Distal Collecting Tubule and Collecting Duct Principal Cells receptors for ADH and aldosterone Intercalated Cells help to manage blood pH  Two Kinds of Nephrons Cortical nephrons – 80-85% of nephrons Ø Renal corpuscle in outer portion of cortex Ø Short loops of Henle extend only into outer region of medulla Ø Create urine with osmolarity similar to blood Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Juxtamedullary Nephrons Ø Renal corpuscle deep in cortex with long nephron loops Ø Receive blood from peritubular capillaries and vasa recta Ø Ascending limb has thick and thin regions Ø Enable kidney to secrete very concentrated urine Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Cortical Juxtamedullary Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Renal Physiology - Urine Formation Glomerular filtration Tubular reabsorption Tubular secretion Excretion of a solute = glomerular Copyright © 2014 John Wileyfiltration & Sons, Inc. All+ secretion rights reserved. - reabsorption  Glomerular Filtration Ø Driven by blood pressure Ø Opposed by capsular hydrostatic pressure and blood colloid osmotic pressure Ø Water and small molecules move out of the glomerulus. Ø In one day, 150–180 liters of water pass out into the glomerular capsule. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Glomerular filtration Glomerular filtration rate – amount of filtrate formed by both kidneys each minute Homeostasis requires kidneys to maintain a relatively constant GFR Too high – substances pass too quickly and are not reabsorbed Too low – nearly all reabsorbed and some waste products not adequately excreted Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Glomerular Filtration  Glomerular Filtration Rate GFR averages 125mL/min in males and 105mL/min in females Controlled by: Renal Autoregulation Neural Regulation Hormonal Regulation Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Renal Autoregulation Myogenic Mechanism Smooth muscle cells in afferent arterioles contract in response to elevated blood pressure Tubuloglomerular Feedback High GFR diminishes reabsorption Macula Densa inhibits release of nitric oxide Afferent arterioles constrict Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Renal Autoregulation Tubuloglomerular Feedback  Neural Regulation Kidneys are richly supplied by sympathetic fibers. Strong stimulation (exercise or hemorrhage)– afferent arterioles are constricted. Urine output is reduced, and more blood is available for other organs. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Hormonal Regulation Angiotensin II constricts afferents and efferents, diminishing GFR. Atrial Natriuretic Peptide relaxes mesangial cells, increasing capillary surface area and GFR. ANP is secreted in response to stretch of the cardiac atria. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  A Stimulus E Response Renin Water loss reduces Receptors in blood volume. Sensors brain detect Produced by efferent arterioles in the in the brain trigger the increase in juxtaglomerular apparatus release of ADH. blood volume. Signals for ADH secretion Triggers production of angiotensin I → stop. II Stimulates production of aldosterone B ADH makes distal tubules, collecting ducts more Reabsorption of NA+; less water permeable to water. excreted Diuretics C Kidneys D The Promotes the loss of water in urine reabsorb more blood water, so less water leaves volume Example, caffeine in urine. rises.  Manage Fluid Balance & Blood Pressure Receptors in kidneys, elsewhere detect falling sodium level Renin released from renin-secreting cells in the JGA (efferent cells in arteriole juxtaglomerular leaving the apparatus Angiotensinogen glomerulus) converts to angiotensin I Angiotensin II Aldosterone secreted (from adrenal glands) Aldostérone acts distal (afferent Bowman’s proximal on distal tubules tubule arteriole leading capsule tubule into glomerulus) Sodium (and water) reabsorbed  Tubular Reabsorption and Secretion Much of the filtrate is reabsorbed Especially water, glucose, amino acids, and ions Secretion helps to mange pH and rid the body of toxic and foreign substances. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Bowman’s proximal tubule distal tubule capsule filtered plasma Na+,Cl–, K+ H+ nutrients, H2O Na+,Cl–, H+, K+ 1 2 3 H2O Glomerular Tubular Tubular 4 collecting filtration reabsorption secretion duct peritubular capillary Na+ renal cortex H2O renal medulla ascending arm descending arm of loop of of loop of Henle Henle increasing solute H2O Na+ urea concentration in H2O interstitial fluid urine to renal pelvis  Plasma, Filtrate and Urine Compositions Amount Total Amount in 180 L returned to Amount in Amount in of filtrate (/day) blood/d Urine (/day) Plasma (Reabsorbed) Water (passive) 3L 180 L 178-179 L 1-2 L Protein (active) 200 g 2g 1.9 g 0.1 g Glucose (active) 3g 162 g 162 g 0g 24 g 30 g Urea (passive) 1g 54 g (about 1/2) (about 1/2) 0g 1.6 g Creatinine 0.03 g 1.6 g (all filtered) (none reabsorbed) Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Reabsorption Routes Ø Paracellular Reabsorption Passive fluid leakage between cells Ø Transcellular Reabsorption Directly through the tubule cells Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Reabsorption Routes Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Transport Mechanisms Primary Active Transport Uses ATP, like Na+/K+ pumps At rest, accounts for 6% total body ATP use Secondary Active Transport Driven by ion’s electrochemical gradient Symporters move substances in same direction Antiporters move substances in opposite directions Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Water Reabsorption Obligatory Water Reabsorption – 90% Water follows the solutes that are reabsorbed Facultative Water Reabsorption – 10% Regulated by ADH Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Reabsorption and Secretion in PCT Na+ - Glucose Symporters Na+ - H+ Antiporters Aquaporin - 1 Membrane protein permeable to water Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Transport Mechanisms Symporter Antiporter Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Passive Reabsorption in the late PCT Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Reabsorption in the Loop of Henle Relatively impermeable to water, especially the ascending limb Little obligatory water reabsorption Na+ - K+ - 2Cl– symporters Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Reabsorption in the Nephron Loop Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Reabsorption in early DCT Na+ - Cl– symporters reabsorb ions PTH stimulates reabsorption of Ca2+ It also inhibits phosphate reabsorption in the PCT, enhancing its excretion Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Late DCT and Collecting Duct Principal Cells Na+-K+ pumps reabsorb Na+ Aquaporin – 2 reabsorbs water Stimulated by ADH Intercalated Cells Reabsorb K+ + HCO3–, secrete H+ Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Regulation of Water Reabsorption by ADH Facultative Reabsorption Negative Feedback.  Removing Excess Acids The kidneys play a role in maintaining the balance of acids and bases in the blood. Acid-base balance pH of body fluids between 7.37 and 7.43 Buffering capabilities of the kidney Either excrete bicarbonate or form new bicarbonate and add it to the blood Excess H+ may combine with phosphate ions, ammonia, or bicarbonate  tubule cells of peritubular interior tubule wall capillary H2O + CO2 enzyme action (carbonic H2CO3acid) tissue fluid H+ HCO−3 bicarbonate H+ + ammonia enters bloodstream H+ + phosphate excreted in urine  Removing Excess Acids Various factors may cause serious acid-base imbalances. Metabolic acidosis Caused by severe diarrhea or kidney disease Affects the central nervous system Could cause fatal coma Metabolic alkalosis Caused by severe vomiting or dehydration, hormonal disorders, or overuse of antacids Overstimulated nerves may lead to muscle spasms or convulsions  Urine Production Fluid intake is highly variable. Homeostasis requires maintenance of fluid volumes within specific limits. Urine concentration varies with ADH. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Urine Production High intake – Dilute urine of high volume Low intake – Concentrated urine of low volume Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Formation of Dilute Urine Glomerular filtrate and blood have the same osmolarity – 300mOsm/Liter Tubular osmolarity changes due to a concentration gradient in the medulla Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Formation of Dilute Urine When dilute urine is formed, osmolarity in the tubule 1. Increases in the descending limb 2. Decreases in the ascending limb 3. Decreases more in the collecting duct Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Formation of Dilute Urine Tubule Osmolarity ↑ in descending limb ↓ in ascending limb ↓ in collecting duct  Formation of Dilute Urine Thick Ascending Limb Symporters actively resorb Na+, K+, Cl– Low water permeablility Solutes leave, water stays in tubule Collecting Duct Low water permeability in absence of ADH Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Formation of Dilute Urine Tubule Osmolarity ↑ in descending limb ↓ in ascending limb ↓ in collecting duct  Formation of Concentrated Urine Juxtamedullary Nephrons with long loops Osmotic gradient is created by the Countercurrent Multiplier Solutes pumped out of ascending limb, but water stays in tubule Medulla osmolarity is increased Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Formation of Concentrated Urine In presence of ADH, collecting ducts become very permeable to water. Tubular fluid there becomes very concentrated. Movement of water also carries urea into the medulla, contributing to its osmolarity. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Countercurrent Exchange Loop and duct cells require nutrients and oxygen from blood supply. Capillaries that feed them (vasa recta) form loops like those of nephron loops in the medulla. Incoming and outgoing blood will have similar osmolarity. This maintains medulla concentration gradient. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Evaluation of Kidney Function Routine urinalysis primarily evaluates for the presence of abnormalities in the urine: Albumin Glucose Red blood cells Ketone bodies Microbes Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Urine Transportation and Storage Each ureter transports urine from a renal pelvis by peristaltic waves, hydrostatic pressure, and gravity. No anatomical valve at the opening of the ureter into bladder – when bladder fills, it compresses the opening and prevents backflow. The bladder is a hollow, distensible, muscular organ with a capacity averaging 700–800 mL. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Ureters, Bladder, and Urethra in a female Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.  Micturition The discharge of urine involves voluntary and involuntary muscle contractions. Stretch receptors trigger a spinal reflex, which we learn to control in childhood. The urethra carries urine from the internal urethral orifice to the exterior of the body. In males, it discharges semen as well as urine. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Male and Female Urethras Urinary Bladder Kidneys Pathology Polycystic Kidney Disease Polycystic kidney disease Inherited Cysts form that can destroy kidney tissue Frequent urinary tract infections Dialysis Kidney transplant May lead normal lifestyles with proper treatment  Cancer in the Urinary System Urinary system cancer on the rise Easily metastasizes kidney Higher in males Major risk factors include smoking and certain industrial chemicals ureter Wilms tumor: inherited cancer tumor Infections & Drugs in the Urinary System Urinary tract infections are common. Cystitis and pyelonephritis More common in females due to anatomy May be caused by sexually transmitted microorganisms, e.g., chlamydia Nephritis May be caused by various microbes Kidneys are inflamed Fluid builds up making filtration almost impossible Infections & Drugs in the Urinary System Painkillers and other drugs may harm the kidneys. Over-the-counter painkillers Aspirin, acetaminophen, and ibuprofen Take according to directions and drink plenty of water Heavy alcohol use Illegal street drugs Amphetamines Cocaine Heroin Hydronephrose Ureterospasm Disorders of the Urinary System Kidney stones Deposits of uric acid and calcium salts that have settled in renal pelvis; stones may cause blockage Lithotripsy Glomerulonephritis Major causes are chronic high blood pressure and diabetes; damage of kidney capillaries Toxic substances build up Dialysis may be necessary Retrograde Pyelogram Kidney Stones (Nephrolithiasis) Lithotripsy Procedure Ureteroscopy Glomerulonephritis Major causes are chronic high blood pressure and diabetes; damage of kidney capillaries Toxic substances build up Dialysis may be necessary filter where blood flows through semipermeable tubes and exchanges substances with dialysis solution abdominal dialysis solution cavity, lined flowing into with peritoneum abdominal cavity (green) dialysis solution patient’s with unwanted blood inside wastes and tubing solutes draining out 1 Hemodialysis 2 Peritoneal dialysis Bladder Incontinence Overactive Bladder  Urine Retention Prostate Gland Hypertrophy  The Urinary System Chemical testing of a urine sample can be a diagnostic tool Clarity pH Proteins Sugar Illegal drugs Hormones Cancer cells The Challenge: Shifts in Extracellular Fluid Maintaining the Extracellular Fluid The chemical makeup of body fluid changes constantly as water and solutes enter and leave it. Female adult: ~50% Male adult: ~60% Two fluid compartments in humans Inside the cells Outside the cells The Challenge: Shifts in Extracellular Fluid The urinary system adjusts fluid that is outside cells. Extracellular fluid (ECF) Tissue fluid Blood plasma Other fluids, e.g., lymph Intracellular fluid Inside the cells Urinary system Maintains stable conditions in the ECF The Challenge: Shifts in Extracellular Fluid The body loses water in urine, sweat, feces, and by evaporation. § Excretion in urine Excess water and excess or harmful solutes removed § Evaporation from the lungs and skin § Sweating § In feces Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.