Module 11: The Urinary System PDF

References: MLS 1104 LECTURE Module 11 The Urinary System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russo...

References: MLS 1104 LECTURE Module 11 The Urinary System Reference: Seeley’s Essentials of Anatomy & Physiology 11th Edition by Vanputte, Regan Russo Compiled by: Cherry Grace A. Dabucon, MD 1 Urinary System and Fluid Balance 2  Urinary System The urinary system is the major excretory system of the body. Some organs in other systems also eliminate wastes, but they are not able to compensate in the case of kidney failure. Urinary system consists of: 2 kidneys (primary excretory organs) 2 ureters 1 urinary bladder 1 urethra The kidneys each filter a large volume of blood ➔ Wastes from the blood are collected ➔ urine. Urine consists of: (1) excess water (2) excess ions (3) metabolic wastes, including the protein by-product urea (4) toxic substances As long as about one-third of one kidney remains functional, survival is possible 3  Urinary System Functions 1. Excretion remove waste products from the blood metabolic by-products of cell metabolism skin, liver, lungs, and intestines eliminate some of these waste products 2. Regulation of blood volume and blood pressure major role in controlling the extracellular fluid volume in the body 3. Regulation of blood solute concentration concentration of the major molecules and ions, such as glucose, Na+, Cl−, K+, Ca2+, HCO3 −, and HPO4 4. Regulation of extracellular fluid pH excrete variable amounts of H+ 5. Regulation of red blood cell synthesis erythropoietin, which regulates the synthesis of red blood cells in bone marrow 6. Regulation of Vitamin D synthesis controlling blood levels of Ca2+ by regulating the synthesis of vitamin D 4  Components of the Urinary System 1. Kidney Bilateral retroperitoneal organs bean-shaped organs weighs 5 ounces each, about the size of a tightly clenched fist Location: between 12th thoracic and 3rd lumbar vertebra located in the abdominal cavity right kidney just below the liver and the left kidney below the spleen. ureter extends from each kidney to the urinary bladder within the pelvic cavity adrenal gland is located at the superior pole of each kidney kidneys are located behind the parietal peritoneum, & surrounded by adipose tissue. connective tissue layer, the renal fascia, anchors the kidney to the abdominal wall renal arteries extend from the abdominal aorta to each kidney, and the renal veins extend from the 5 kidneys to the inferior vena cava.  Renal capsule: layer of connective tissue surrounds each kidney. Hilum: On the medial side of each kidney where the renal artery and nerves enter and The hilum opens into where the renal vein, ureter, a cavity called the and lymphatic vessels exit renal sinus, a the kidney space containing the renal pelvis, calyces, blood vessels, adipose tissue, and other connective tissues The tip of each renal pyramid is surrounded by a calyx. The calyces connect to the renal pelvis. Urine flows from the tip of the renal pyramid through the calyx and renal pelvis into the ureter 6  The tip of each renal pyramid is surrounded by a calyx. renal pyramids extend from the cortex The calyces connect to the renal pelvis. Urine flows of the kidney to the renal sinus. from the tip of the renal pyramid through the calyx and renal pelvis into the ureter Urine Flow: ➔ formed in the cortex and medulla ➔ tips of the renal pyramids ➔ calyces ➔ renal pelvis ➔ exits the pelvis through the ureter ➔ the urinary bladder, where it is stored ➔ urethra into the external environment 7  THE NEPHRON is the histological and functional unit of the kidney specialized structures including small tubes that are called tubules. approximately 1.3 million nephrons distributed throughout the cortex and medulla of each kidney. The four regions of a nephron are: (1) a renal corpuscle- filters the blood (2) a proximal convoluted tubule- returns filtered substances to the blood (3) a loop of Henle - helps conserve water and solutes (4) distal convoluted tubule- rids the blood of additional wastes The fluid in the distal convoluted tubule then empties into a collecting duct, which carries the newly formed urine from the cortex of the kidney toward the renal papilla deep in the medulla. Near the tip of the renal papilla, several collecting ducts merge into a larger- diameter tubule called a papillary duct, which empties into a calyx 2 Types of Nephrons a. Juxtamedullary nephrons (those near the medulla of the kidney) have loops of Henle that extend deep into the medulla of the kidney b. Cortical nephrons- loops of Henle that do not extend deep into the medulla Structure of a Nephron 8 The Four Regions Of A Nephron are: (1) a RENAL CORPUSCLE- filters the blood Consists of: a. the glomerulus- is a network of capillaries twisted around each other like a ball of yarn b. the Bowman capsule- or glomerular capsule, is an indented, double-walled chamber surrounding the glomerulus. 1. outer layer is constructed of simple squamous epithelial cells 2. inner layer is constructed of specialized cells called podocytes, which wrap around the glomerular capillaries (spaces) 9 Renal Corpuscle has several unique characteristics that make it particularly efficient at filtration—the main function of the kidneys 1. Porous capillaries. highly permeable due to the presence of pores. glomerular capillary pores, neither large proteins nor blood cells can fit through them. 2. Porous inner layer of Bowman capsule. 3. High pressure. An afferent arteriole supplies blood to the glomerulus for filtration. An efferent arteriole transports the filtered blood away from the glomerulus 10 Urine production begins when the filtration membrane filters the blood. The filtered fluid, called filtrate, then enters the lumen, or space, inside the Bowman capsule. Juxtaglomerular apparatus: an important regulatory structure that is located next to the glomerulus consists of: 1. a unique set of afferent arteriole cells and 2. specialized cells in the distal convoluted tubule that are in close contact with each other. a. juxtaglomerular cells b. macula densa. Function: Secretion of the enzyme renin plays an important role in the regulation of filtrate formation and blood pressure 11  The Renal Tubule Once the blood is filtered, the resulting fluid is modified to form urine as it passes through each section of the renal tubule 2. Proximal convoluted tubule. simple cuboidal epithelium have many microvilli, which serves to increase the surface area of these cells 3. the loop of Henle two limbs: (1) the descending limb (2) the ascending limb water and solutes pass through thin walls by diffusion 4. distal convoluted tubule is shorter than the proximal convoluted tubule. simple cuboidal ➔ collecting ducts (simple cuboidal epithelium) carry fluid from cortex through medulla 12  ARTERIES AND VEINS Arteries 1. Renal arteries –a branch of abdominal aorta 2. Interlobar (between the lobes) arteries pass between the renal pyramids. 3. Arcuate (arched) arteries branch from the interlobar arteries. They arch between the cortex and the medulla. 4. Interlobular arteries branch off the arcuate arteries and project into the cortex. 5. Afferent arterioles arise from branches of the interlobular arteries. The afferent arterioles carry blood to the glomerular Capillaries 6. Glomerulus 7. Efferent arterioles carry blood from the glomerular capillaries. 8. Peritubular (around the tubes) capillaries branch from the efferent arterioles. They surround the proximal convoluted tubules, the distal convoluted tubules, and the loops of Henle. 9. Vasa recta (straight vessels) are specialized Veins portions of the peritubular capillaries that extend 10. Interlobular vein 13. Renal artery deep into the medulla of the kidney and surround 11. Arcuate vein 14. IVC the loops of Henle and collecting ducts. 12. Interlobular vein ➔ will return to the general circulation through the 13 veins of the kidneys  Anatomy and Histology of the Ureters, Urinary Bladder, and Urethra 1. Kidneys 2. Ureters are small tubes that carry urine from the renal pelvis of the kidney to the posterior inferior portion of the urinary bladder 3. Urinary bladder is a hollow, muscular container that lies in the pelvic cavity just posterior to the pubic symphysis. It stores urine; thus, its size depends on the quantity of urine present. The urinary bladder can hold from a few milliliters (mL) to a maximum of about 1000 mL of urine its wall is stretched enough to activate a reflex that causes the smooth muscle of the urinary bladder to contract Trigone - triangle-shaped portion of the urinary bladder located between the opening of the ureters and the opening of the urethra - unique and does not expand with the urinary bladder wall as it fills. - causes the trigone to act as a funnel for emptying the urinary bladder. most of the urine flows out of the urinary bladder through the 4. Urethra Cystitis is an inflammation of the tube that carries urine from the urinary bladder to the outside of the body urinary bladder, which usually In males, the urethra extends to the end of the penis (approximately 20 results from a bacterial infection. cm) , where it opens to the outside. Typically, bacteria from outside the The female urethra is much shorter (approximately 4 cm) and opens body enter the bladder. Infection by into the vestibule anterior to the vaginal opening. the bacterium E. coli is the most 14 common cause of cystitis.  Anatomy and Histology of the Ureters, Urinary Bladder, and Urethra Cuboidal when relaxed, squamous when stretched ✓ Transitional epithelium lines both the ureters and the urinary bladder ✓ Contractions of smooth muscle in the ureter & urinary bladder force urine to flow from the bladder through the urethra ✓ At the junction of the urinary bladder and the urethra, smooth muscle forms an internal urethral sphincter that prevents urine leakage from the In males, the internal urethral sphincter urinary bladder contracts to keep semen from entering the ✓ Both males and females have a well- urinary bladder during sexual intercourse defined external urethral sphincter. 15 16  URINE PRODUCTION The “throw away” items end up in the urine, and the “save” items go back into the blood. Filtration is nonselective and separates based only on size or charge of molecules. Filtration does not remove everything in the blood. Filtration removes only those substances small enough to fit through the filtration membrane. Reabsorption it involves removing substances from the filtrate and placing back into the blood Secretion involves taking substances from the blood at a nephron area 17 other than the renal corpuscle and putting back into the nephron tubule 1. Filtration nonspecific process whereby materials are separated based on size or charge. Ex: of size filtration is demonstrated by a drip coffeemaker. In this case, the driving force of filtration is gravity. The kidneys also use size filtration to remove substances from the blood by filtering it, but in this case, the driving force of this filtration is blood pressure. 21% of the blood pumped by the heart each minute flows through the kidneys 9% passes through the filtration membrane into the Bowman capsule to become filtrate 180 liters (L) of filtrate are produced each day, but only about 1% or less of the filtrate becomes urine because most of the filtrate is reabsorbed. Urine =( substances filtered directly from the blood + those that are secreted into the renal tubules ) - reabsorbed substances components prevent many larger molecules from entering the filtrate Ex: antibody molecules are too large to pass through, glucose and amino acids can pass through the filtration membrane into the filtrate. Most plasma proteins are too large to be filtered out of the blood but albumins (smaller) can pass through Therefore, filtrate is NOT protein-free 18 19 Filtration Pressure- pressure gradient which forces fluid from the glomerular capillaries across the filtration membrane into the Bowman capsule outward pressure inward pressure inward pressure 20 Regulation of Filtration blood pressure within the glomerular capillaries is fairly constant afferent and efferent arterioles can either dilate or constrict, the blood pressure is tightly regulated in the glomerular capillaries sympathetic stimulation causes constriction of the kidney arteries ➔ decrease filtrate formation and urine volume Intense sympathetic stimulation ➔ circulatory shock is that the renal blood flow can be so low that the kidneys suffer from lack of O2 (hypoxia) ==permanent kidney damage or complete kidney failure results 2. Tubular Reabsorption - the transport of water and solutes from the filtrate into the blood. Proper tubular reabsorption is critical in preventing the body from becoming overly dehydrated and deficient in important materials Nearly all (99%) of the water and solutes are rapidly returned to the blood via the renal tubules As the filtrate passes through the tubules, many of the substances in the filtrate are removed enter the interstitial fluid → pressure is low in the peritubular capillaries, these substances enter the peritubular capillaries and flow through the renal veins to enter the general circulation 21 By the time the filtrate has reached the end of the proximal convoluted tubule, its volume has been reduced by approximately 65%. Together with Na 22 Reabsorption in the Loop of Henle loop of Henle and its two limbs. The two limbs differ in the type of epithelial tissue present in each. This difference in cell type is linked to the permeability of each limb to water and solutes simple squamous epithelial tissue highly permeable to water Simple squamous Water moves by epithelium osmosis out of the but it has become descending limb, while impermeable to water some solutes move by permeable to solutes diffusion into the descending limb filtrate has reached the end of the thin segment, the volume of the filtrate has been reduced by another 15% 23  Process of reabsorption in the thick segment of the ascending limb of the loop of Henle. simple cuboidal epithelium impermeable to both water cells of the thick segment house multiple types of transport proteins including ATP-powered pumps and carrier molecules this active transport of solutes that contributes to the kidneys’ ability to conserve water Active transport by Na+ Cotransport moving K + and Cl− across the membrane 24  Reabsorption in the Distal Convoluted Tubule and Collecting Duct reabsorption of these solutes is generally under hormonal control and depends on the current conditions of the body not always permeable to water; however, hormone regulation can change their permeability to water hormone Anti Diuretic Hormone➔ reabsorption of water Three major hormonal mechanisms are involved in regulating urine concentration and volume: (1) the renin-angiotensin-aldosterone mechanism (RAA) (2) the antidiuretic hormone (ADH) mechanism, and (3) the atrial natriuretic hormone (ANH) mechanism 25  Tubular Secretion the movement of nonfiltered substances from the blood into the filtrate. include toxic by-products of metabolism and drugs or molecules not normally produced by the body. tubular secretion can be either active or passive. For example, a. ammonia is a toxic by-product of protein metabolism. It is produced when the epithelial cells of the renal tubule remove amine groups from amino acids, which diffuse into the lumen of the renal tubule. b. H+, K+, and penicillin, are actively secreted by either active transport or counter transport processes into the renal tubule. An example of counter transport process in the kidney is the secretion of H+, which plays a major role in regulating body fluid pH 26  180L filtrate enters Urine Concentration Mechanism the Nephron: Kidneys’ ability to control the volume and concentration of the urine depends on three factors: (1) countercurrent mechanisms -where fluid in separate structures flows in opposite directions relative to each other. -As the fluids pass by each other, materials can be exchanged between the fluids 2. medullary concentration gradient -interstitial fluid in the medulla of the kidney has a very high solute concentration compared with that of the cortex -high solute concentration of the interstitial fluid develops from The kidneys reabsorb and secrete (1) the actions of the countercurrent urea multiple times, which helps mechanisms and create a high concentration of solutes (2) the recycling of the protein in the renal medulla. This process is breakdown product, urea called urea recycling 3. hormonal mechanisms High-protein diet increase urine concentration 27  Hormonal Mechanisms Three major hormonal mechanisms are involved in regulating urine concentration and volume: (1) the renin-angiotensin-aldosterone mechanism, (2) the antidiuretic hormone (ADH) mechanism, (3) the atrial natriuretic hormone (ANH) mechanism 1. Renin-Angiotensin-Aldosterone Mechanism renin-angiotensin-aldosterone mechanism is initiated under low blood pressure conditions. 1. blood pressure decreases 2. Constriction of afferent arteriole 3. cells of the juxtaglomerular apparatuses in the kidneys secrete the enzyme renin 4. converts angiotensinogen, a plasma protein produced by the liver, to Angiotensin-converting enzyme (ACE) angiotensin I. Angiotensin-converting enzyme (ACE) is an enzyme produced by capillaries of organs such as the lungs. ACE converts angiotensin I to angiotensin II a. Angiotensin II increases blood pressure and increases the sensation of thirst, and salt appetite b. stimulates the adrenal cortex to secrete aldosterone (increases reabsorption of Na and water in distal convoluted tubules and collecting ducts.) 28 2. Antidiuretic Hormone Mechanism secreted by neurons in the posterior pituitary when the solute concentration of the blood or the interstitial fluid increases promotes water conservation in the kidneys by increasing the permeability of the distal convoluted tubules and collecting ducts to water➔allows more water to be reabsorbed from the filtrate and the kidneys to produce a small volume of concentrated urine 3. Atrial Natriuretic Hormone increased blood pressure triggers the atrial natriuretic hormone (ANH) mechanism secreted from cardiac muscle cells in the right atrium of the heart when blood pressure in the right atrium increases above normal acts on the kidney to decrease Na+ reabsorption increases urine volume while reducing blood volume and blood pressure 29  Control of the Micturition Reflex by Higher Brain Centers Activated by stretch (pressure) of the urinary bladder The micturition reflex is an automatic reflex, but it can be inhibited or stimulated by higher centers in the brain. A. Voluntary initiation of micturition requires an increase in action potentials sent from the cerebrum to facilitate the micturition reflex and to voluntarily relax the external urethral sphincter. B. Higher brain centers prevent micturition by sending action potentials through the spinal cord to decrease the intensity of the autonomic reflex that stimulates urinary bladder contractions and to stimulate nerve fibers that keep the external urethral sphincter contracted. Note: The ability to voluntarily inhibit micturition develops at the age of 2–3 years. Micturition Reflex 1. micturition reflex is activated by stretch of the urinary bladder wall. As the urinary bladder fills with urine, pressure increases, stimulating stretch receptors in the wall of the urinary bladder. 2. Action potentials produced by stretch receptors are carried along pelvic nerves to the sacral region of the spinal cord Parasympathetic action potentials cause the urinary bladder to contract. 3. Decreased action potentials carried by somatic motor nerves cause the external urethral sphincter to relax 30  Body Fluid Compartments 1. The intracellular fluid compartment includes the fluid Intracellular fluid contains a relatively high inside all the cells of the body. concentration of ions, such as K+, magnesium Approximately two-thirds of all the water in the body is in the (Mg2+), phosphate (PO43−), and sulfate (SO42−), intracellular fluid compartment. compared to the extracellular fluid. It has a lower concentration of Na+, Ca2+, Cl−, and 2. The extracellular fluid compartment includes all the fluid HCO3− than does the extracellular fluid outside the cells. The extracellular fluid compartment includes, interstitial fluid, plasma, lymph, and other special fluids, such as joint fluid, and cerebrospinal fluid 31  Exchange Between Fluid Compartments 2. Ion Concentration Regulation The cell membranes that separate the body fluid Regulating the concentrations of positively charged compartments are selectively permeable. ions, such as Na+, K+, and Ca2+, in the body fluids is Water continually passes through them, but ions particularly important. dissolved in the water do not readily pass through the cell Action potentials, muscle contraction, and normal cell membrane. membrane permeability depend on the maintenance of Water movement is regulated mainly by hydrostatic a narrow range of these concentrations. pressure differences and osmotic differences Negatively charged ions, such as Cl−, are secondarily between the compartments. regulated by the mechanisms that control the positively Osmosis controls the movement of water between the charged ions intracellular and extracellular spaces. The negatively charged ions are attracted to the positively charged ions; when the positively charged Regulation of Extracellular Fluid Composition ions are transported, the negatively charged ions 1. Thirst Regulation move with them 2. Ion Concentration Regulation 1. Thirst regulation: Water intake is controlled by the thirst center located in the hypothalamus When the concentration of ions in the blood increases, it stimulates the thirst center to cause thirst When water is consumed, the concentrations of blood ions decreases, due to a dilution effect; this causes the sensation of 32 thirst to decrease  3. Calcium Ions 1. Sodium ions (Na+) Increases and decreases in the extracellular concentration are the dominant ions in the extracellular fluid. of Ca2+ have dramatic effects on the electrical properties of About 90 to 95% of the osmotic pressure of the excitable tissues extracellular fluid results from sodium ions and a. Parathyroid hormone (PTH), secreted by the parathyroid from the negative ions associated with them. glands, increases extracellular Ca2+ concentrations. Stimuli that control aldosterone secretion b. Calcitonin produced by Thyroid gland influence the reabsorption of Na+ from reduces the blood Ca2+ concentration when it is too high. nephrons of the kidneys and the total amount of prolonged lack of sun exposure Na+ in the body fluids. c. vitamin D3 increase intestinal Ca absorption (Inc Ca+) Sodium ions are also excreted in sweat. Without vitamin D3, the transport of Ca2+across the wall of the digestive tract is very low. This leads to inadequate Ca2+ absorption 2. Potassium Ions (K+ ) Electrically excitable tissues, such as muscles and 4. Phosphate and Sulfate Ions nerves, are highly sensitive to slight changes in the are reabsorbed by active transport in the kidneys. extracellular K+ concentration. The rate of reabsorption is slow, so that if the The extracellular concentration of K+ must be concentration of these ions in the filtrate exceeds the maintained within a narrow range for these tissues to nephron’s ability to reabsorb them, the excess is excreted function normally. into the urine. Aldosterone plays a major role in regulating the As long as the concentration of these ions is low, nearly all of concentration of K+ in the extracellular fluid. them are reabsorbed by active transport. PTH stimulates phosphate excretion in the kidneys, which results in low blood levels of phosphate 33  Regulation of Acid-Base Balance Buffers chemicals resist change in pH of a solution buffers in body contain salts of weak acids or bases that combine with H+ three classes of buffers: a. proteins, b. phosphate buffer, c. bicarbonate buffer Respiratory system involvement in acid-base: Kidney Involvement in acid-base: responds rapidly to changes in pH nephrons secrete H+ into urine and directly increased respiratory rate raises blood pH (more regulate pH of body fluids alkalotic) due to increased rate of carbon dioxide more H+ secretion if the body pH is elimination from the body decreasing (acidic) Respiratory alkalosis less H+ secretion if pH is increasing reduced respiratory rate reduces pH (more acidic) (alkaline) due to decreased rate of carbon dioxide elimination from the body Respiratory acidosis 34 More alkaline (Alkalosis) 35 More acidic (Acidosis) 36 Acidosis Alkalosis Acidosis occurs when the blood pH falls below 7.35. Alkalosis occurs when the blood pH increases The central nervous system malfunctions, and the above 7.45. individual becomes disoriented and, as the A major effect of alkalosis is hyperexcitability condition worsens, may become comatose. of the nervous system. Peripheral nerves are affected first, resulting in Acidosis is separated into two categories. spontaneous nervous stimulation of muscles. a. Respiratory acidosis results when the respiratory Spasms and tetanic contractions result, as system is unable to eliminate adequate amounts of can extreme nervousness or convulsions. CO2 from the blood. Carbon dioxide accumulates in Tetany of respiratory muscles can cause death. the blood, causing the pH of the body fluids to decline. Alkalosis is separated into two categories. b. Metabolic acidosis results from excess production a. Respiratory alkalosis results from of acidic substances, such as lactic acid and ketone hyperventilation, as can occur in response bodies, because of increased metabolism or to stress. decreased ability of the kidneys to eliminate H+ b. Metabolic alkalosis usually results from the in the urine. rapid elimination of H+ from the body, as occurs during severe vomiting or when excess aldosterone is secreted by the adrenal cortex. 37 38  Hemodialysis substitute for the excretory functions of the kidney. Blood is usually taken from an artery, passed through the tubes of the dialysis machine, and then returned to a vein During hemodialysis, blood flows through a system of tubes composed of a selectively permeable membrane. Dialysis fluid, which has a composition similar to that of normal blood (except that the concentration of waste products is very low), flows in the opposite direction on the outside of the dialysis tubes. Waste products, such as urea, diffuse from the blood into the dialysis fluid. Other substances, such as Na+, K+, and glucose, can diffuse from the blood into the dialysis fluid if they are present in higher than normal concentrations, because these substances are present in the dialysis fluid at the same concentrations found in normal blood. Kidney transplants are sometimes performed on people who have severe renal failure. The 39 major cause of kidney transplant failure is rejection by the recipient’s immune system Urinary System and Fluid Balance 40