The Urinary System Part I 04 24 2014 An Introduction to the Urinary System The urinary system removes most physiological wastes 26 1 Urinary System Functions Three Functions of the Urinary System 1 Excretion Removal of organic wastes from body fluids 2 Elimination Discharge of waste products 3 Homeostatic regulation of blood plasma volume and solute concentration Structures and Functions of the Urinary System Kidneys organs that produce urine Urinary tract organs that eliminate urine o Ureters paired tubes o Urinary bladder muscular sac o Urethra exit tube of body Homeostatic Functions of the Urinary System 1 Regulates blood volume and blood pressure o By adjusting volume of water lost in urine o Releasing erythropoietin and renin 2 Regulates plasma ion concentrations Urination or micturition process of eliminating urine o Contraction of muscular urinary bladder forces urine through urethra and out o Sodium potassium and chloride ions by controlling quantities lost in urine o Calcium ion levels through synthesis of calcitriol 3 Helps stabilize blood pH 4 Conserves valuable nutrients 5 Assists liver o By controlling loss of hydrogen ions and bicarbonate ions in urine o By preventing excretion while excreting organic waste products o In detoxifying poisons Also during starvation deaminates amino acids so other tissues can metabolize them for energy 26 2 The Kidneys The Kidneys Located on either side of vertebral column Left kidney lies superior to right kidney Superior surface capped by adrenal gland Position is maintained by o Overlying peritoneum o Contact with adjacent visceral organs o Supporting connective tissues o Floating Kidney Each Kidney Is Protected and Stabilized By three concentric layers of connective tissue o 1 Fibrous capsule innermost layer A layer of collagen fibers Covers outer surface of entire organ o 2 Perinephric fat capsule Suspensory fibers damaged kidney displaced can cause pain distortion or ureter blood vessels during movement A thick layer of adipose tissue Surrounds renal capsule o 3 Renal fascia outermost layer A dense fibrous outer layer Anchors kidney to surrounding structures Typical Adult Kidney Is about 10 cm long 50 5 cm wide and 3 cm thick 4 in 2 2 in 1 2 in Weighs about 150 g 5 25 oz Hilum Renal Cortex Point of entry for renal artery and renal nerves Point of exit for renal vein and ureter Superficial portion of kidney in contact with renal capsule Reddish brown and granular Renal Pyramids Base abuts cortex Tip renal papilla projects into renal sinus 6 to 18 distinct conical or triangular structures in renal medulla Renal Columns Bands of cortical tissue separate adjacent renal pyramids Extend into medulla Have distinct granular texture Renal Lobe Consists of Ducts discharge urine into minor calyx a cup shaped drain o Renal pyramid o Overlying area of renal cortex o Adjacent tissues of renal columns Produces urine Renal Papilla Major Calyx Renal Pelvis Formed by four or five minor calyces Large funnel shaped chamber Consists of two or three major calyces Fills most of renal sinus Connected to ureter which drains kidney Blood Supply to the Kidneys 1200 mL of blood flows through kidneys each minute Kidneys receive 20 25 of total cardiac output Kidney receives blood through renal artery Blood flow o From renal artery segmental arteries interlobar arteries arcuate arteries cortical radiate interlobular arteries afferent arterioles glomerulus efferent arteriole peritubular capillaries venules cortical radiate interlobular veins arcuate veins interlobar veins renal vein Renal Nerves Innervate kidneys and ureters Enter each kidney at hilum Follow tributaries of renal arteries to individual nephrons Sympathetic Innervation o Adjusts rate of urine formation by changing blood flow and blood pressure at nephron o Stimulates release of renin Restricts losses of water and salt in urine by stimulating reabsorption at nephron renin angiotensin system stimulates aldosterone release Nephrons functional unit of the kidney from adrenal cortex Microscopic tubular structures in cortex of each renal lobe Each kidney has approximately 1 25 million nephrons Where urine production begins The Nephron Consists of renal tubule and renal corpuscle Renal corpuscle Spherical structure consisting of o Glomerular capsule Bowman s capsule o Cup shaped chamber o Capillary network glomerulus Long tubular passageway Renal tubule o Begins at renal corpuscle Glomerulus Consists of 50 intertwining capillaries Blood delivered via afferent arteriole Blood leaves in efferent arteriole o Flows into peritubular capillaries o Which drain into small venules o And return blood to venous system through a venule Filtration Occurs in renal corpuscle Blood pressure space Note blood leaves the capillary network through the efferent arteriole and NOT o Forces water and dissolved solutes out of glomerular capillaries into capsular o Produces protein free solution filtrate similar to blood plasma except lacks proteins Three Functions of the Renal Tubule 1 Reabsorb useful organic nutrients that enter filtrate 2 Reabsorb more than 90 of water in filtrate 3 Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus Segments of the Renal Tubule Located in cortex o Proximal convoluted tubule PCT o Nephron loop loop of Henle U shaped tube Extends partially into medulla medulla important for their function o Distal convoluted tubule DCT In juxtamedullary nephrons the nephron loop extends deeper into the Organization of the Nephron Traveling along tubule filtrate tubular fluid gradually changes composition o Due to reabsorption and secretion of substances Changes vary with activities in each segment of nephron Each Nephron Empties into the collecting system o A series of tubes that carries the filtrate away from nephron Collecting ducts o Receive fluid from many nephrons o Each collecting duct Begins in cortex Descends into medulla Carries fluid to papillary duct that drains into a minor calyx Cortical Nephrons 85 of all nephrons Located mostly within superficial cortex of kidney Nephron loop Loop of Henle is relatively short Efferent arteriole delivers blood to a network of peritubular capillaries Juxtamedullary Nephrons 15 of nephrons Nephron loops extend deep into medulla Peritubular capillaries connect to vasa recta capillary network of juxtamedullary nephrons found surrounding the loop of Henle The Renal Corpuscle Each renal corpuscle is 150 250 m in diameter
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