The Urinary System Chapter 16

Waste Excretion Chemical reactions in the body result in waste products that may be potentially harmful, therefore must be eliminated. –Examples of metabolic waste products: Carbon dioxide, Urea, Salts –Methods of elimination: Respiratory system, urinary system, digestive system, sweat The urinary system is the most important route of waste-product removal in the body. It removes nearly all the soluble waste products from blood and transports out of the body. –Also removes excess water from the body.

The Urinary System Parts of urinary system: Two kidneysTwo kidneys –Make urine and carry out other vital functions. Two uretersTwo ureters –Carry urine to the urinary bladder. Urinary bladderUrinary bladder –Collects, stores and releases urine. UrethraUrethra –Carries urine from the body to the external environment. ffffffffff

Terminology nephro/reno = kidney Nephrology- the study of the kidney. Diuresis- producing and passing large amounts of urine Oliguria- passing small amounts of urine Anuria- no urine is passed from the body Dysuria- difficult urination Hematuria- blood in urine Polyuria- increased urine volume.

Kidney Function Must maintain homeostasis through a variety of processes. –Blood filtration, reabsorption, and secretion Blood is filtered, useful substances are returned to circulation and waste products are secreted. –Fluid balance regulation Makes sure body has enough water to maintain healthy environment. –Acid-base regulation Ability to remove hydrogen and bicarbonate ions from blood. –Electrolyte regulation Na+, K+, Cl- can be fatal outside of normal levels –Hormone production Kidneys produce erythropoietin- necessary for red blood cell production Produce some prostoglandins Influenced by Antidiuretic Hormone (posterior pituitary) and Aldosterone (adrenal cortex)

Location of the kidneys In dorsal part of abdomen, ventral to and on either side of first few lumbar vertebrae. Are retroperitoneal to the abdominal cavity and are considered outside abdominal cavity. In most domestic animals, right kidney is slightly more cranial than left. Perirenal fat surrounds and helps protect from exertion from other organs. Move somewhat with the movement of the diaphragm

Gross Anatomy of the Kidney Bean shaped and covered by fibrous connective tissue capsule. Reddish brown in color Generally a smooth surface –Cattle have multiple lobed kidney which gives it a lumpy appearance Hilus: indented area on medial side of kidney –Ureters, nerves, blood and lymph vessels enter/leave kidney Renal Pelvis: funnel-shaped area inside hilus –Forms beginning of ureter –Lined with stretchable transitional epithelium –Cattle lack a renal pelvis

Gross Anatomy of the Kidney Cortex- outer portion of the kidney. –Rough granular appearance, reddish brown in color Medulla- inner portion around the renal pelvis. –Smooth appearance –Dark purple outer area and gray- red inner area. –Varies with species can be multipyramidal (multilobar) or unipyramidal (unilobar). Calyx- funnel-like extension of the renal pelvis that the medullary pyramids drain into. –Calyces funnel fluid into renal pelvis

Microscopic Anatomy of the Kidney Nephron- basic functional unit of the kidney whose job is to filter, reabsorb and secrete. –Smallest part of the kidney –Number varies per kidney and species 1 million in human, sheep, pigs 200,000 in cat –Composed of: Renal Corpuscle –Bowman’s capsule and glomerulus Proximal Convoluted Tubule (PCT) Loop of Henle Distal Convoluted Tubule (DCT)

Renal Corpuscle Located in cortex of kidney. Function is to filter blood in first stage of urine production. –This filtrate is called glomerular filtrate Made up of Glomerulus (tuft of glomerular capillaries), and Bowman’s capsule (double walled capsule that surrounds the glomerulus). –Bowman’s capsule has inner visceral layer and outer parietal layer. Space between these two layers is known as the capsular space and is continuous with the proximal convoluted tubule.

Proximal Convoluted Tubule (PCT) Continuation of the capsular space of the Bowman’s capsule. Longest part of the tubular system of the nephron. –Glomerular filtrate becomes tubular filtrate (primitive urine). Epithelial cells are cuboidal and have a brush border on lumen side that increases the surface area.

Loop of Henle Continued from PCT Descends into medulla of the kidney and the ascends back to cortex. Descending portion –Epithelial cells like PCT and brush border At bottom of loop, epithelium flatten to simple squamous epithelial cells and loses brush border Ascending loop wall becomes thicker again –No brush border

Distal Convoluted Tubule (DCT) and Collecting Ducts DCT is a continuation of ascending portion of Loop of Henle –Not as twisted as PCT The DCT from all nephrons empty into a series of collecting ducts which carry tubular filtrate through medulla and eventually empty it into renal pelvis that becomes ureter. The DCT and Collecting Ducts are the sites of action for: –Antidiuretic Hormone (ADH) –Regulation of K+ –Acid-base balance

Nerve Supply to the Kidneys Supplied by sympathetic portion of autonomic nervous system. –Sympathetic stimulation decreases the diameter of blood vessels leading to the kidney Controls the blood flow through the glomerular capillaries. Is not essential for kidney function, –Why transplanted kidneys will work.

Blood Supply to the Kidneys Kidneys have very large blood supply. All circulating blood passes through kidney every 4 or 5 minutes. Composed of: –Renal artery –Afferent glomerular arterioles –Glomerular capillaries –Efferent Glomerular arterioles –Peritubular capillaries –Renal vein

Blood Supply Renal artery –Branches off of aorta and enters kidney at hilus –Divides smaller and smaller until becomes afferent glomerular arterioles Afferent glomerular arterioles –Carry blood into the glomerular capillaries of the renal corpuscle. Glomerular capillaries –Continuation of afferent glomerular arterioles. –Filter plasma from blood in capsular space – called glomerular filtrate. –Only place in body where blood that enters and leaves capillaries is still oxygenated blood.

Blood Supply Efferent Glomerular arterioles –Receive (arterial) blood from glomerular capillaries –Divide into peritubular capillaries Peritubular capillaries –Surround nephron and converge to form venules the become renal vein. –Oxygen transfer occurs here. –Usable substances are removed from tubular filtrate and reabsorbed. –Other waste substances are secreted into filtrate here as well. Renal vein –Leaves kidney at hilus and joins abdominal portion of the caudal vena cava. Purest blood in body.