Urinary System PDF

The Urinary System - many products that are produced as a result of metabolism are harmful and must be removed by the body. A few of the body’s waste products are summarized in the table below. Waste Origin of waste Organ of...

The Urinary System - many products that are produced as a result of metabolism are harmful and must be removed by the body. A few of the body’s waste products are summarized in the table below. Waste Origin of waste Organ of excretion Ammonia - deamination of amino acids by the liver Kidneys - highly toxic Urea - deamination of amino acids by the liver Kidneys - ammonia combined with carbon dioxide forms urea (less toxic than ammonia) Uric acid - product of the breakdown of nucleic acids Kidneys CO2 - waste product of cellular respiration Lungs Bile pigments - breakdown of red blood cell pigment, hemoglobin Liver Lactic acid - product of anaerobic respiration Liver Solid waste - by product of digestible and indigestible material Intestine  blood Renal artery Kidney – filters wastes See next page Renal vein Abdominal aorta – brings blood to the kidneys Inferior vena cava – brings filtered blood to heart Ureter – carries urine from kidneys to bladder Bladder – stores urine Urethra – releases urine out of the body  Renal Cortex - Contains nephrons Renal Medulla - Contains loops of Henle from nephrons Renal Pelvis - funnels urine to ureter Renal Capsule - fibrous and tough for protection Contains millions of Nephrons – filters blood  Proximal Distal blood Bowman’s convoluted convoluted The Nephron capsule tubule tubule Afferent arteriole Glomerulus Efferent arteriole Ascending blood loop of Henle Collecting duct Descending loop of Henle Loop of Henle Blood vessels surround the tubules. Blood is filtered as water, ions and small molecules are absorbed or secreted. There are three main steps: 1. Filtration 2. Absorption 3. Secretion Urine Formation 1. Filtration - blood enters into the glomerulus through the afferent arteriole - the glomerulus is a network of porous, thin-walled capillaries and is surrounded by Bowman’s capsule - Blood pressure forces plasma components into Bowman’s capsule - water, ions, small nutrients (glucose, amino acids) and waste such as urea can pass into the filtrate but larger components such as blood cells, platelets and proteins remain in the capillaries - this filtered plasma which enters the tubule is called the filtrate 2. Reabsorption a) proximal convoluted tubule - “good” components of filtrate are reabsorbed into blood of peritubular capillaries - active transport reabsorbs glucose, aa and other nutrients - specialized ion pumps transport K+, Na+ and Cl- from the filtrate into the fluid surrounding the tubule - this makes the filtrate hypoosmotic to the interstitial flued causing water to move out by osmosis - special membrane proteins called aquaporins act as water channels to allow for more water to flow out of the tubule - by the end of the proximal tubule, the fluid is isotonic with the surrounding cells. b) Loop of Henle  Descending Loop: - the cells of the medulla have an increased concentration of Na+ ions which increase in a gradient starting from the area closest to the cortex and moving toward the inner pelvis of the kidney - this gradient acts to remove water by osmosis from the filtrate as it moves down the loop of Henle.  Ascending Loop: - so much water has been removed that the filtrate is very concentrated - therefore as filtrates moves up the ascending loop of the Henle, Na+ and Cl- ions pass from the filtrate into the medulla by diffusion. - further salt is removed by active transport closer to the top of the ascending loop. - the water that left the descending loop cannot re-enter because the ascending loop is impermeable to water c) Distal Tubule - additional water and salts are removed d) Collecting ducts - permeable to water but not salt - concentration of solutes increases with depth as fluid descend into the medulla causing further removal of water through the ducts, greatly increasing the concentration of the urine - near the bottom of the medulla, the walls of the collecting ducts contain passive urea transports, - this allows some urea to pass into the interstitial fluid, adding to the concentration gradient of solutes in the medulla 3. Secretion - involves the removal of waste products from the blood and interstitial fluid - involves active transport of substance such as H+ ions, creatinine, and drugs (e.g. aspirin, antibiotics, birth control) out of the blood and into the filtrate - K+ and H+ are secreted into filtrate at the distal tubule - pH is regulated by the quantitative secretion of H+ and the reabsorption of bicarbonate. - the distil tubule is also acted upon by anti-diuretic hormone to regulate the amount of water removed or conserved by the body. - the fluid from a number of nephrons moves from the distal tubules into a common collecting duct, which carries the filtrate (now called urine) to the renal pelvis, to the ureter and finally to the bladder.  ammonia glucose drugs ADH acts here blood enters amino K+ acids H2O Cl- H+ H+Na+ Cl- HCO3- Na+ HCO3- K+ Filtration filtrate Secretion impermeable to water Reabsorption CORTEX active transport H2O Na+ blood leaves Na+ Cl- H2O (contains blood cells permeable to water and proteins that Na+ H2O are too large) H2O Na+ Na+ urea H2O Cl- Na+ H2O Na+ Na+ Na+ urine MEDULLA H2O passive Cl- Increasing Na+ transport Na+ Na+ concentration Na+ Na+ renal pelvis ureter bladder Kidneys and Water Balance - anti-diuretic hormone is secreted by the pituitary gland - when the body needs to conserve water → ADH increases the permeability of the distal tubules and collecting duct, this allowing more water to be removed from the filtrate - when the body needs to eliminate excess water → ADH is inhibited and more water is excreted in the urine - alcohol and caffeine block the release of ADH and thus increase the volume of urine Kidneys and pH Balance - kidneys regulate the acid-base balance of the body - healthy blood pH is approx. 7.4 - cellular respiration produces carbon dioxide which forms carbonic acid in the blood. This acid can ionize to produce H+ ions (which lowers the pH) and HCO3- (bicarbonate ion) - active transport can be used to pull hydrogen ions into the nephric filtrate Kidneys and Blood Pressure - kidneys play a role in regulating blood pressure by adjusting for blood volume - receptors in the juxtaglomerular apparatus (near the glomerulus) detect low blood pressure and release the enzyme, rennin - rennin converts a protein called angiotensinogen (produced by the liver) into angiotensin - angiotensin has two functions: i. causes constriction of blood vessels (blood pressure increases when the diameter of the blood vessels is reduced) ii. stimulates the release of aldosterone from the adrenal gland - aldosterone acts on the nephrons to increase Na+ reabsorption - as NaCl reabsorption increases, the osmotic gradient increases and more water moves out of the nephron by osmosis Video: Amoeba Sisters: Excretory System https://www.youtube.com/watch?v=q5qaGHfdmYM Video: The Excretory System: From Your Heart to the Toilet - CrashCourse Biology #29 https://www.youtube.com/watch?v=WtrYotjYvtU Homework: Complete the Urinary System Homework Questions posted on D2L.