Urinary System Chapter 24 Urinary system - Functions Removal of nitrogenous waste, mainly urea Maintain electrolyte balance, Maintain pH or acid-base balance and Maintain water balance of the body. Urinary System Urinary system of humans is formed of a pair of Kidneys, a pair of ducts called Ureters, a Urinary Bladder to store urine and Urethra the duct that carries urine outside the body. Each kidney lies attached to back wall partly covered by 12th rib. It is a flat bean shaped organ. Median side has an indentation, hilum. Renal Capsule, a transparent fibrous membrane, covers each kidney. In addition a fat capsule and a fibrous renal fascia surround the kidney and keep it in position. Take notice, peritoneum only covers anterior surface of kidneys. Therefore, kidneys are retroperitoneal organs. Kidney - structure Outer part, Cortex of kidney, appears granular in section. Cortex appears lighter in color and has abundant blood supply. Inner part, Medulla of kidney, appears striated. It has nephron loop and collecting ducts passing through it. Renal columns are extensions of cortex into medulla and separate medullary pyramids from one another. Collecting ducts  papillary duct  minor calyx  major calyx pelvis  ureters  urinary bladder  urethra  urine released outside = micturition. Ureters are a pair of urinary ducts that collect urine from kidneys to urinary balder. Renal Blood Supply Renal arteries arise from descending aorta and one enters hilum of its side. Renal artery segmental artery  lobar artery  interlobar artery arcuate artery  interlobular artery or cortical radiate artery  afferent arteriole  glomerulus  efferent arteriole  Peritubular capillaries / Vasa recta  Venules  interlobular vein  arcuate vein  interlobar vein  renal vein. Renal veins leave the hilum and join inferior vena cava. Nephron – the functional unit of kidney Each kidney has about 1 million Nephrons. Each nephron is formed of a Glomerular capsule, PCT – proximal convoluted tubule, Nephron Loop or Loop of Henle with descending and ascending limbs, DCT – distal convoluted tubule and a collecting duct. Glomerulus glomerular capsule PCT  descending limb ascending limb DCT collecting duct. Each nephron has Renal Corpuscle formed of outer cup shaped Glomerular capsule and inner Glomerulus formed of a bunch of blood capillaries. Afferent arteriole brings blood to glomerulus and Efferent arteriole takes it away from glomerulus. Efferent arteriole then wraps around different parts of nephron as Peritubular capillaries. Urine formation Urine formation takes place by 3 processes – Filtration, Reabsorption and Secretion. Filtration: Glomerular capillaries are highly permeable. The inner membrane of glomerular capsules has a many gaps in it. Inner wall of glomerular capsule is lined by Podocytes with many feet like extensions. Fenestrae are the gaps between these extensions. Diffusible part of blood having water, glucose, amino acids, urea, ions, enter space of glomerular capsule. Reabsorption: Useful substances are reabsorbed from the filtrate. Primary site of reabsorption is PCT and all glucose, most amino acids and majority of salts are absorbed in PCT. Water follows passively. Secondary site is DCT. Most of the reabsorption is active. Secretion: Some substances like, K+ and H+ do not filter from blood, but are actively secreted into filtrate. Others filter in small quantity, like creatinine, and are secreted actively into filtrate. Excretion: The urine with wastes like urea, uric acid and creatinine (3 nitrogenous wastes) and excessive salts or amino acids, leaves body with variable amount of water. Nephrons – 2 types Nephron is the functional unit of kidney. Cortical Nephrons lie in outer part of cortex and have a short loop of Henle barely entering medulla. Juxtamedullary nephrons (15%) lie near border of cortex and medulla and have long loop of Henle present in most of medulla. Juxtaglomerular Apparatus Juxtaglomerular Apparatus = JGA is formed of 3 types of cells Grannular cells around afferent arteriole Macula densa in DCT facing cleft of afferent and efferent arterioles Mesangial Cells in the cleft (mesangial cells in glomerular capsule are not included in JGA) JGA secretes renin Renin converts Angiotensinogen  angiotensin 1 Angiotensin-1 changes to Angiotensin-2 in blood vessels and stimulates adrenal medulla to secrete aldosterone Recap 1 Urinary System 1. Urinary system removes ----waste materials, maintain -----balance and ------balance. 2. Urine is formed in ------and is stored in ------. 3. ----- carries urine from kidneys to bladder and ------carries urine to outside. 4. Each kidney has about 1 million of functional units ------. 5. Each nephron has renal corpuscle formed of ------and ------. 6. Filtrate moves from ------ Glomerular capsule  ------ loop of Henle  ------ collecting duct and becomes urine. 7. Renal artery  ------A.  lobar A. ------A. arcuate A.  ------ ------tubule  glomerulus  ------8. Collecting ducts  ------duct medullary ------ ------calyx  ------calyx  pelvis  ------9. ------are extensions of cortex into medulla and separate medullary pyramids from one another. 10. Urethra in females is ------than urethra in males. 11. Urine formation takes place by 3 processes ------, ------, and ------. 12. Filtration takes place in------. Useful substances like ------and ------pass out in filtrate, also harmful substances like ------pass out in filtrate. Recap 2 Urinary System 1. Kidney has to actively secrete some substances, like ------and ------, that do not filter out in filtrate. 2. 3 nitrogenous substances eliminated in urine are ----, -----, and ------. 3. Most of the reabsorption takes place in ------; most of the secretion takes place in ------. 4. Glomerular capillaries are many times more permeable than ordinary capillaries due to presence of ------in them and slits between feet of ------. 5. Juxtaglomerular Apparatus consists of ------, and ------cells. 6. ------is a patch of closely placed slender cells in side of DCT facing afferent arteriole. 7. ------cells are swollen smooth muscle fibers mostly around afferent arteriole but some around efferent arteriole. 8. ------released by posterior pituitary causes the walls of DCT and Collecting ducts to become permeable so that lot of water is ------from urine. 9. Kidneys release ------that stimulates adrenal cortex to release aldosterone hormone that causes greater reabsorption of Na+ followed by water. 10. ------is a small triangular area in urinary bladder having 2 openings of ureters and a 3rd for urethra. 11. The counter current systems of kidney are ------and ------. 12. Kidneys can excrete ------urine due to activity of counter current systems.