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The Urinary System Mr O. Tada 1 Introduction Functions Gross structure & function Micro-structure of Kidney (Nephron) Urine formation Hormones & Kidney function Micturition Maintenance of Acid-Base balance 2 Functions Produces Urine (formed from blood) Maintain volume of extracellular fluid Maintain ionic balance in extracellular fluid Maintain pH and osmotic concentration of the extracellular fluid Excrete toxic metabolic by-products such as urea, ammonia, and uric acid 3 Structure & Function Kidney Pair of Organs Bean-Shaped--Most Species Heart-Shaped—Horses Lobulated—Cattle Blood Supply Renal Artery Brings blood to Kidney Arises directly from aorta Renal Vein Brings blood away from Kidney Empties into the Caudal Vena Cava 4 Divisions Cortex Outer Portion Contains upper parts of nephrons (Glomeruli and Tubules) Medulla Inner Portion Contains lower parts of nephrons (Loops of Henle and Collecting Ducts) Renal Pelvis -Drains kidney and connects ureters Renal Hilus Indented area on concave edge Ureter, Blood Vessels, Nerves and Lymphatics enter or leave 5 Structure & Function Ureter Smooth muscle lined tube Conveys urine from renal pelvis to bladder Enter bladder through uretero-vesicular junction Acts as a valve Prevents backflow Urinary Bladder Hollow muscular organ (Smooth Muscle) Stores Urine (Stretches) Lined with Transitional Epithelium Flatten when filling occurs 6 Structure & Function Urethra Caudal continuation of the neck of the bladder Conveys urine from bladder to exterior Urine release into urethra controlled by external sphincter Skeletal muscle 7 All in one! 8 Micro-structure of Kidney (Nephron) The functional unit of the kidney Numbers range from 250,000 (cat) to 4 million (cow) per kidney Components i. Glomerulus ii. Bowman's Capsule iii. Proximal Tubules iv. Loop of Henle v. Distal Tubules 9 This is it!!! 10 Nephron > Glomerulus Tufts of Capillaries Afferent arterioles Conduct blood to glomerulus Efferent arterioles Conduct blood away from glomerulus Function: Filtration of Blood 11 Nephron > Capsule & Prox tubule Bowman's Capsule a. Collect Glomerular Filtrate b. Conduct filtrate into proximal tubules Proximal Tubules a. Conduct filtrate into Loop of Henle b. Very convoluted (Surrounded by Peritubular Capillaries) c. Reabsorb, Secrete, & Excrete 12 Nephron > Loop of Henle Play important role in concentration of urine Divisions Descending limb thin segment simple squamous epithelium Ascending limb thick segments simple cuboidal epithelium 13 Nephron > Distal & J. App Distal tubules a. Convey urine from Loops of Henle b. Also convoluted (Surrounded by peritubular capillaries) c. Reabsorb, Secrete, and Excrete d. Feed Collecting tubules and ducts Juxtaglomerular Apparatus a. Junction between distal tube and glomerulus b. Contain unique cell types i. Macula Densa in tubules ii. Juxtaglomerular cells in arterioles 14 Nephron cont’d c. Function: i. Regulate renal blood flow ii. Regulate glomerular filtration iii. Secrete Renin --Involved in production of angiotensin II Two Types of Nephrons a. Cortical i. Short loops of Henle ii. Only go into Outer medulla b. Juxtamedullary i. Long loops of Henle ii. Can go clear to renal pelvis 15 Principal roles of Nephron Glomerular filtration of water and solutes from the blood Tubular reabsorption of water and conserved molecules back into the blood Tubular secretion of ions and other waste products from surrounding capillaries into the distal tubule 16 Urine Formation Filtration in the glomerulus and nephron capsule Re-absorption in the proximal tubule Tubular secretion in the Loop of Henle !!!More details coming NOW!!! 17 Glomerular Filtration Glomerulus favors filtration Peritubular capillaries favor reabsorption Slit pores at glomerulus filter larger molecules Macula densa sensitive to changes in ionic concentrations (Na+ and Cl-) Juxtaglomerular cells secrete Renin and initiates Angiotensin II Increases water reabsorption by tubules to peritubular capillaries 18 Tubular Re-absorption & Secretion Re-absorption Path a. Tubular Lumen b. Tubular Epithelium c. Interstitial Fluid d. Capillary Secretion Path Just the opposite 19 Re-absorbed Molecules a. Amino Acids & Glucose b. Use carrier proteins coupled with Na+ to enter tubular cells c. Water reabsorption follows osmotic gradient from lumen to epithelium to capillaries d. Other diffusible substances follow water by diffusion because they increase in concentration in the lumen --Proximal Tubule Reabsorption (65% of H2O, Na+, Cl-, and 100% of Glucose and Amino Acids) 20 Secreted Molecules a. H+ is secreted throughout tubules b. K+ is secreted in distal and collecting tubules c. Ammonia is secreted --Depends on acid-base balance Species differences: a. Desert Kangaroo Rat i. Only long loops of Henle ii. Can live on Metabolic H2O b. Humans, Cattle, & Swine i. Few long loops (1/3 to 1/5 of total) ii. Void large amounts of dilute urine c. Dogs, Cats, Camels, Sheep, and Goats i. Many long loops of Henle ii. Produce relatively concentrated urine 21 Hormones in the Kidney Antidiuretic Hormone/Vasopressin Synthesized by hypothalamus, secreted by posterior pituitary (or neurohypophysis) Low Blood [ADH] = increased H20 excretion or a dilute urine High Blood [ADH] = increased solute excretion or a concentrated urine ADH allows H2O reabsorption by late distal tubules and collecting ducts thus facilitating the concentration of urine ADH facilitating the formation of "water channels" on the luminal membrane of tubule and ductal epithelial cells ADH also increases the permeability of the collecting ducts to urea ADH decrease blood flow of the vasa recta Without ADH the late distal tubules and collecting ducts nephron are impermeable to H2O 22 Angiotensin II Causes Efferent arteriole to constrict Increases GFR Increases water reabsorption by tubules to peritubular capillaries Increases vasoconstriction of peripheral blood vessels Causes the secretion of Aldosterone 23 Aldosterone Produced in adrenal cortex (Mineralocorticoid) Involved in K+ regulation Causes secretion in distal tubules, collecting tubules and ducts Causes H2O reabsorption (increase blood volume & pressure) 24 Parathyroid Hormone Causes a reabsorption of Ca++ Secretion of Phosphorus Controls formation of Vitamin D Activated in kidney Vitamin D promotes Ca++ absorption from intestine 25 Micturition (Urinating) Transfer of Urine to the Urinary Bladder From Glomerulus to Renal Pelvis (hydrostatic pressure) From Renal Pelvis to Bladder (peristalsis of the ureter) Micturition Reflexes Micturition: Emptying of Bladder Involuntary or Voluntary Control Sympathetic Control --closure of sphincter during ejaculation 26 Acid-Base Balance Relationship of pH to H+ Concentration Normal = pH 7.4 Severe Acidosis = pH 7. a. H+ concentration doubled Severe Alkalosis = pH 7.7 H+ concentration halved Mechanism of H+ Secretion by the Kidneys Na+/H+ antiporter secretes H+ a. Occurs along whole nephron b. 85% in Proximal tubules Secreted H+ combines with: Bicarbonate, Phosphate, Ammonia 27 Role of Respiratory System Respiratory System also controls pH of extracellular fluids Bicarbonate from hydration reaction binds CO2 Releases H+ with CO2 at alveoli Increased H+ and CO2 in extracellular fluid cause increase ventilation 28 Chemical Buffer Systems and Mechanisms System can buffer acids and bases in extra-cellular fluids Bicarbonate Acid buffer: HCl + NaHCO3 --> H2CO3 + NaCl Base buffer: NaOH + H2CO3 --> NaHCO3 + H2O Phosphate Acid buffer: HCl + Na2HPO4 --> NaH2PO4 + NaCl Base buffer: NaOH + NaH2PO4 --> Na2HPO4 + H2O Proteins i. Amino-end (basic) buffer acids ii. Carboxy-end (acidic) buffer bases iii. Hemoglobin most abundant buffer in body 29