Urinary System PDF

Urinary System Water control and nitrogen disposal DR AKEEM  Organs of the Urinary system  Kidneys  Ureters  Urinary bladder  Urethra  Functions of the Urinary System  Elimination of waste products  Nitrogenous wastes  Toxins  Drugs  Regulate aspects of home...

Urinary System Water control and nitrogen disposal DR AKEEM  Organs of the Urinary system  Kidneys  Ureters  Urinary bladder  Urethra  Functions of the Urinary System  Elimination of waste products  Nitrogenous wastes  Toxins  Drugs  Regulate aspects of homeostasis (filtration, active absorption, passive absorption and secretion)  Water balance  Electrolytes  Acid-base balance in the blood  Blood pressure  Red blood cell production  Activation of vitamin D  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, and nerves at renal hilus  Atop each kidney is an adrenal gland  Kidney Structures Each kidney has: (i) a concave medial border (ii) the hilum, (iii)convex lateral border Nerves enter the kidney through hilum, as well as blood and lymph vessels enter and exit  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  Regions of the Kidney  Renal cortex – outer region  Renal medulla – inside the cortex  Renal pelvis – inner collecting tube  Renal pelvis is the expanded upper end of the ureter It is divided into two or three major calyces Several small branches called minor calyces arise from each major calyx Division Kidney can be divided into an outer cortex and an inner medulla Renal medulla consists of conical or pyramidal structures called the medullary pyramids Medullary rays arise from the base of each medullary pyramid Medullary rays are parallel arrays of tubules that penetrate the cortex Size An adult kidney is about 12cm (5 inches) long ,6cm (2.5 inches) wide, and 3cm (1 inch) thick  Anatomy of the Kidney Main structures of the mammalian kidney: renal cortex renal medulla renal pelvis nephrons  Blood Flow in the Kidneys Figure 15.2c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 15.7  Anatomy of the Nephron Glomerulus Proximal tubule Loop of Henle Distal tubule  Nephron Each kidney is composed of about 4 million nephrons Nephron is the functional unit of kidney Each nephron consists of: (i) a dilated portion, the renal corpuscle (ii)the proximal convoluted tubule (iii)the thick and thin limbs of Henle’s loop (iv)the distal convoluted tubule (v)the collecting tubules and ducts  Renal corpuscles Each renal corpuscle is about 200µm in diameter It consists of a tuft of capillaries called glomerulus Glomerulus is surrounded by a double-walled epithelial capsule called Bowman’s capsule It consist of internal layer (visceral layer) and external layer(parietal layer) of Bowman’s capsule Visceral layer envelopes the capillaries of the glomerulus Parietal layer forms the outer limit of the renal corpuscle  Renal corpuscle and blood filtration Between visceral and parietal layer is urinary space Urinary space receives the fluid filtered through capillary wall and visceral layer Each renal corpuscle has a vascular pole and urinary pole Afferent arteriole enters and efferent arteriole leaves through vascular pole proximal convoluted tubule begins at urinary pole Renal corpuscle cont’d Glomerulus  The glomerulus sits within a glomerular capsule (the first part of the renal tubule)  Renal Tubule  Glomerular (Bowman’s) capsule  Proximal convoluted tubule  Loop of Henle  Distal convoluted tubule  Types of Nephrons  Cortical nephrons  Located entirely in the cortex  Includes most nephrons Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Types of Nephrons  Juxtamedullary nephrons  Found at the boundary of the cortex and medulla Figure 15.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide  Glomerulus This is the only place in the system where the blood is actually “filtered.” Blood pressure is used to push plasma through capillary walls and into the Bowman’s capsule.  Proximal tubule Nutrients (salts, vitamins, etc.) are moved out of the tubule through active transport. Water follows the nutrients by osmosis.  Loop of Henle Tissue around the Loop of Henle is salty, from active transport and diffusion of sodium chloride. The salty conditions allow water to diffuse out of the loop. Distal tubule Active transport is used to move more nutrients out of the concentrated urine. Some ions, drugs, and toxins are actively pumped into the tubule. Collecting Duct More water leaves the tube by osmosis, since the tube is surrounded by salty tissue. Some urea leaves by diffusion, and may be cycled through the system.  The juxtaglomerular apparatus (JGA) The juxtaglomerular apparatus (JGA) is a specialized structure located in the kidneys, near the glomerulus, which is a crucial component of the nephron—the functional unit of the kidney. The JGA plays a vital role in regulating blood pressure, blood volume, and the filtration rate in the kidneys.  Macula Densa: The macula densa is a group of specialized cells located in the wall of the distal convoluted tubule (DCT), which is a segment of the renal tubule. The macula densa cells are chemoreceptors that detect changes in the concentration of sodium chloride (NaCl) in the tubular fluid passing through the DCT. They play a key role in regulating the glomerular filtration rate (GFR) by sensing changes in NaCl levels and initiating feedback responses. Juxtaglomerular (JG) Cells: Juxtaglomerular cells are specialized smooth muscle cells found in the walls of the afferent arterioles—the small arteries that supply blood to the glomerulus. JG cells produce and release the enzyme renin in response to signals from the macula densa. Renin is a critical component of the renin- angiotensin-aldosterone system (RAAS), which plays a central role in regulating blood pressure and sodium and water balance in the body. Extraglomerular Mesangial Cells: These cells are located outside the glomerulus and assist in communication between the macula densa and the juxtaglomerular cells. They are believed to be involved in paracrine signaling within the juxtaglomerular apparatus.  Function of The juxtaglomerular apparatus (JGA) GFR Regulation: When the macula densa cells detect low sodium chloride levels in the distal convoluted tubule, they signal the juxtaglomerular cells to release renin. Renin acts as an enzyme and converts angiotensinogen (a protein produced by the liver) into angiotensin I. Angiotensin I is further converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), which is mainly present in the lungs. Angiotensin II and Blood Pressure Regulation: Angiotensin II is a potent vasoconstrictor, causing the blood vessels to narrow and increasing peripheral resistance. It also stimulates the release of aldosterone from the adrenal glands, leading to increased reabsorption of sodium and water in the kidneys. This, in turn, helps increase blood volume and blood pressure. Negative Feedback Loop: As blood pressure and sodium levels return to normal, the macula densa senses the changes and reduces its signaling to the juxtaglomerular cells, leading to a decrease in renin release. This negative feedback loop helps maintain blood pressure and GFR within the desired range.  Which of these happens during filtration? 1. Salt is actively pumped out. 2. Water is removed osmotically from the filtrate. 3. Plasma moves from capillaries into the capsule. 4. Toxins are actively removed from plasma.  ? What drives filtration in the glomerulus 1. Osmosis 2. Smooth muscle contractions 3. Salt gradients 4. Blood pressure  Which of these aids in water recovery from the filtrate? 1. Active transport of water out of the tubules. 2. Active transport of sodium out of the filtrate. 3. Peristalsis in the Loop of Henle. 4. Concentration of urea in the urine.  Functions of the Kidney (i)Filter The kidney filter gallons of fluid from the bloodstream every day (ii) Waste processing The kidneys then process this filtrate, allowing wastes and excess ions to leave the body in urine while returning needed substances to the blood in just the right proportions (iii) Elimination Although the lungs and the skin also play roles in excretion, the kidneys bear the major responsibility for eliminating nitrogenous wastes, toxins, and drugs from the body  Cont’d (iv)Regulation The kidneys also regulate the blood’s volume and chemical makeup so that the proper balance between the water and salts and between acids and bases is maintained (v) Other regulatory functions By producing the enzyme renin,they help regulate blood pressure Their hormone erythropoietin stimulates red blood cell production in the bone marrow (vi)Conversion Kidney cells also convert vitamin D to its active form  The result of the complex process is production of urine Metabolic waste products are eliminated Urine produced in the kidneys passes through the ureters to the bladders Temporarily stored in bladder and released to the exterior through the urethra  Volume of urine The two kidneys produce about 125mL of filtrate per minute Of this amount,124mL is absorbed in the organ Only 1mL is released into the ureters as urine About 1500mL of urine is formed every 24h  homeostatic functions of kidneys Regulate the fluid and electrolyte balance of the body Are site of production of renin , a substance that participates in the regulation of blood pressure Erythropoietin is also produced in kidneys. Erythropoietin is a growth factor glycoprotein of 30kDa which stimulates the production of erythrocytes  Homeostasis The urinary system maintains homeostasis in several ways: Removal of urea (nitrogenous waste) from the bloodstream. Control of water and salt balance in the bloodstream. Involved in blood pressure regulation. Blood pressure  Renin-angiotensin-aldosterone system (RAAS) Renin is an enzyme released by the kidneys in response to a drop in blood pressure. Renin catalyzes the production of angiotensin, a hormone that causes arterioles to constrict, raising blood pressure. This also causes water retention. How does this maintain homeostasis of blood pressure? For example in case of low blood pressure The stimulation of sympathetic nervous system and RAAS Increased SNS will increase vasoconstriction RAAS will produce; Angiotensin II which is a potent vasoconstrictor Aldosterone retains water and sodium (blood volume) Antidiuretic hormone; also known as vasopressin (osmolality in blood) causes water reabsorption in the kidneys. It is produced by the hypothalamus and released by the pituitary gland 1. Renin Release: The process begins in the kidneys when they detect a decrease in blood flow or a drop in blood pressure. Specialized cells in the kidneys called juxtaglomerular cells release an enzyme called renin into the bloodstream. 2. Conversion of Angiotensinogen to Angiotensin I: Renin catalyzes the conversion of a protein called angiotensinogen, which is produced in the liver, into angiotensin I. 3. Conversion of Angiotensin I to Angiotensin II: Angiotensin I circulates in the blood until it reaches the lungs. There, an enzyme called angiotensin-converting enzyme (ACE), primarily produced by the lungs but also present in other tissues, converts angiotensin I into angiotensin II. 4. Effects of Angiotensin II: Vasoconstriction: Angiotensin II is a potent vasoconstrictor, which means it narrows the blood vessels, leading to an increase in systemic vascular resistance. This constriction of blood vessels elevates blood pressure. Release of Aldosterone: Angiotensin II stimulates the adrenal glands to release a hormone called aldosterone. Thirst Stimulation: Angiotensin II acts on the hypothalamus to stimulate thirst, leading to an increase in fluid intake. Aldosterone Effects: Aldosterone is a hormone that acts on the kidneys, specifically in the distal tubules and collecting ducts. Its main function is to increase sodium reabsorption in the kidneys while promoting the excretion of potassium and, to a lesser extent, hydrogen ions. By reabsorbing more sodium, water follows, leading to increased fluid retention and expanded blood volume. Increased Blood Volume: With increased fluid retention due to aldosterone's action, the blood volume rises, resulting in an increase in cardiac output (the amount of blood the heart pumps per minute). This leads to an increase in blood pressure. Negative Feedback Loop: Once the blood pressure and blood volume return to their normal range, the RAAS is inhibited. High blood pressure, increased blood volume, and high sodium levels are sensed by the kidneys, which reduces renin release, thereby decreasing the production of angiotensin II and aldosterone. By adjusting blood vessel constriction, fluid balance, and electrolyte levels, the RAAS helps to maintain blood pressure and overall cardiovascular homeostasis. However, excessive activation of the RAAS can lead to hypertension (high blood pressure), which is associated with various cardiovascular complications. Consequently, drugs that target the RAAS, such as ACE inhibitors and angiotensin receptor blockers (ARBs), are commonly used to treat hypertension and related conditions.  Erythropoietin A second response to low blood pressure is the release of erythropoietin, another hormone. Erythropoietin travels to the bone marrow and stimulates the production of new blood cells. How does this maintain homeostasis? The kidneys produce two important hormones. What do they control? 1. Blood pressure and volume 2. Blood clotting 3. Blood sugar 4. Blood oxygen Urea removal  Amino acid metabolism Amino acids are the building blocks of protein. If not needed for building protein, then can be metabolized for energy, or broken apart and the carbon chains used to make fat. Metabolism requires removal of the amine unit (NH3).  Ammonia and Urea Ammonia is toxic and highly water soluble. The liver turns ammonia into urea, which is less toxic and less soluble.  Regulating water Antidiuretic hormone (ADH, also called vasopressin) is part of a negative feedback system that regulates water in the mammalian body. ADH increases the permeability of the distal tubule, allowing greater water recovery.  W Caffeine and alcohol are diuretics. Alcohol O inhibits ADH release, while caffeine interferes R K with its activity. Part of the symptoms of a hangover are due to dehydration. T O G E What causes the dehydration? And why is a T cup of coffee not a good cure for a hangover? H E R  If a person were given a dose of ADH, what would happen? 1. More water lost through kidneys. 2. More potassium secreted by nephron. 3. More water retained in the kidneys. 4. More sodium secreted by nephron.  Final thinking question: The kangaroo rat is adapted to desert life. It survives on very little water. List some ways in which its kidneys might be different from the human kidney to allow it to conserve as much water as possible.  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  Urinary Bladder  Smooth, collapsible, muscular sac  Temporarily stores urine Figure 15.6  Urinary Bladder  Trigone – three openings Two from the ureters One to the urethrea Figure 15.6  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  Urethra  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)  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  Urethra Gender Differences  Function  Females – only carries urine  Males – carries urine and is a passageway for sperm cells  Micturition (Voiding)  Both sphincter muscles must open to allow voiding The internal urethral sphincter is relaxed after stretching of the bladder Activation is from an impulse sent to the spinal cord and then back via the pelvic splanchnic nerves The external urethral sphincter must be voluntarily relaxed  Maintaining Water Balance  Normal amount of water in the human body Young adult females – 50% Young adult males – 60% Babies – 75% Old age – 45%  Water is necessary for many body functions and levels must be maintained  Distribution of Body Fluid  Intracellular fluid (inside cells)  Extracellular fluid (outside cells) Interstitial fluid Blood plasma The Link Between Water and Salt  Changes in electrolyte balance causes water to move from one compartment to another Alters blood volume and blood pressure Can impair the activity of cells  Maintaining Water Balance  Water intake must equal water output  Sources for water intake  Ingested foods and fluids  Water produced from metabolic processes  Sources for water output  Vaporization out of the lungs  Lost in perspiration  Leaves the body in the feces  Urine production  Maintaining Water Balance  Dilute urine is produced if water intake is excessive  Less urine (concentrated) is produced if large amounts of water are lost  Proper concentrations of various electrolytes must be present 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  Developmental Aspects of the Urinary System  Functional kidneys are developed by the third month  Urinary system of a newborn Bladder is small Urine cannot be concentrated  Developmental Aspects of the Urinary System  Control of the voluntary urethral sphincter does not start until age 18 months  Urinary infections are the only common problems before old age  Aging and the Urinary System  There is a progressive decline in urinary function  The bladder shrinks with aging  Urinary retention is common in males