Renal Physiology Part 1 PDF

Urinary system Dr. Muhammed Malik Al-Ani PhD. Pharmacology & Toxicology 1  Anatomy of urinary system 2 Kidneys: clean and filter blood 2 Ureters: tubes that take urine to bladder 1 Urinary bladder: stores urine until eliminated...

Urinary system Dr. Muhammed Malik Al-Ani PhD. Pharmacology & Toxicology 1  Anatomy of urinary system 2 Kidneys: clean and filter blood 2 Ureters: tubes that take urine to bladder 1 Urinary bladder: stores urine until eliminated 1 Urethra: removes urine from body Kidneys: a bean shaped organs lie on the posterior wall of the abdomen to either side of the vertebral column. 2  Wt of kidney 150 g in males 135 g in females 3  Functions of the urinary system 1- Excrete wastes and foreign substances such as: § Nitrogenous wastes (urea, creatinine, and uric acid) § Toxins § Drugs 2- Maintain blood osmolarity: Plasma osmolarity = 300 mOsm prevents any unwanted movement of fluid into or out of the body’s cells § Maintain water balance. § Regulates blood electrolyte levels (sodium, potassium,…) § Regulate blood glucose level. 4  Functions of the urinary system 3- Regulate blood volume (which affects blood pressure) § Conserve water in case of need (as in fasting) § Eliminates excess water (as after drinking lots of water) 4- Regulate blood pressure § Secretes Renin which promotes the production of angiotensin which increases blood pressure. 5- Regulatesblood pH by maintaining proper balance between acids & bases: § Excretes excess H+ ions. § Conserves bicarbonate ions (HCO3-). 5  Functions of the urinary system 6- Produces hormone ERYTHROPOIETIN which stimulates erythrocyte production in bone marrow. 7- Activation of vitamin D which allows calcium uptake from GIT to blood. 6  The nephron - Is the basic functional unit of the kidney. - Number: 1 million nephrons/ kidney. - They filter the blood and form urine. - It has two components: § Renal corpuscle § Renal tubule 7  Renal corpuscle - Consists of two parts: 1- Glomerulus: a network of fenestrated capillaries that lies between 2 arterioles. üA large afferent arteriole for incoming blood (mixed with wastes) üA narrow efferent arteriole for outgoing blood (filtered and free of wastes) 2-Bowman’s capsule: a double-walled structure of epithelial cells that forms a cup within which the glomerulus sits. 8  Tubular component - This is a tube formed by a single layer of epithelial cells. Allows filtrate to pass through nephron and it is the site of tubular secretion & reabsorption - It begins with the Bowman’s capsule and consists of: § Proximal convoluted tubule § Loop of Henle: which is made of ü Descending limb ü Ascending limb § Distal convoluted tubule § Collecting duct 9 There are two types of nephron 10  Urine formation Urine formation in nephrons occurs by: 1. Glomerular filtration 2. Tubular reabsorption 3. Tubular secretion 4. Urinary excretion 11  Glomerular filtration - Movement of water, solutes & ions out of the glomerular capillary into Bowman`s capsule. - It filters every thing except RBCs and proteins. - It depends on net filtration pressure (NFP) which depends upon the following forces: § Glomerular hydrostatic pressure: it pushes water and solutes out (from the capillary into Bowman`s capsule). It is about 60 mm Hg. § Bowman`s capsule hydrostatic pressure: it pushes water and solutes in (from Bowman`s capsule into the capillary). It is about 18 mm Hg. § Glomerular colloid osmotic pressure: it pulls water and solutes in (from Bowman`s capsule into the capillary). It is about 32 mm Hg. 12 The NFP 13  Glomerular filtration rate (GFR) - Is the volume of plasma filtered by the glomeruli of both kidneys per minute. - Normal value of GFR = 125 ml/min (7.5 L/h , 180 L/day) - GFR is auto-regulated by the following mechanisms: 1. Extrinsic mechanisms: § Hormonal mechanisms: ü Renin-Angiotensin II system ü Natriuretic peptides. § Neural mechanism. 2. Intrinsic mechanisms: § Myogenic mechanism. § Tubulo-glomerular feed-back mechanism 14  Extrinsic mechanisms (outside of the kidney) A. Hormonal mechanisms: - Renin-Angiotensin II system: Cause vasoconstriction of efferent arteriole. If blood pressure decreases, angiotensin-II increases and causes efferent vasoconstriction to: q Increase the glomerular capillary hydrostatic pressure and maintains the GFR so that the kidney keep functioning. q Decrease the peritubular capillary hydrostatic pressure to facilitate more water absorption in these capillaries. 15 16 - Natriuretic peptides: Made by the heart in case of increased blood volume and blood pressure. They cause vasodilation of afferent arteriole to increase the GFR and water excretion. ANP – atrial natriuretic peptide B. Neural mechanism: Sympathetic stimulation cause vasoconstriction of afferent arteriole Decrease RBF (important in shock to reduce blood flow to the kidney to maintain blood flow to other organs) 17 * SYMPATHETIC control 18  Intrinsic mechanisms (inside of the kidney) A. Myogenic mechanism: via increasing afferent resistance - Increase RBF à stretching of afferent arteriole à afferent arteriole smooth muscles contract àRBF decreased. 19  Intrinsic mechanisms (inside of the kidney) B. Tubulo-glomerular feed-back mechanism - Mediated through the juxtaglomerular apparatus. - The juxtaglomerular apparatus lies between afferent arteriole, efferent arteriole, and distal convoluted tubule of the same nephron. And it consists of the following: § Macula densa: these are modified cells in the distal convoluted tubule. They act as chemoreceptors sensitive to changes in Na+ content of the fluid in the distal convoluted tubule. § Juxtaglomerular cells: these are modified cells in the afferent arterioles as they enter the glomeruli. They acts as baroreceptors and respond to decrease in blood pressure or hypovolemia and respond by secreting renin. 20 Juxtaglomerular apparatus 21  The tubulo-glomerular feed-back mechanism - In case of increased pressure: (the GFR is high now and must be decreased) Increase glomerular hydrostatic pressure à increase GFRà increased Na+ delivery to macula densa à macula densa secretes adenosine (a vasoconstrictor) à adenosine causes vasoconstriction of afferent arteriole à decreases glomerular hydrostatic pressure à decreases GFR. - In case of decreased pressure: (the GFR is low now and must be increased) Decreased glomerular hydrostatic pressure à decreased GFR à decreased Na+ delivery to macula densa à macula densa secrete nitric oxide & prostaglandin (both are vasodilators) à vasodilation of afferent arteriole à increased glomerular hydrostatic pressure à increased GFR. 22 The tubulo-glomerular feed-back mechanism 23