The Urinary System

1. The Urinary System Chapter 16

2. 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.

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

4. 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.

5. 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)

6. 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

8. 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

9. 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

11. 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)

12. 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.

14. 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.

15. 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

16. 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

17. 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.

18. 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

19. 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.

20. 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.