Chapter 26 The Urinary System Part I 04 25 2014 Describe the structures of the urinary system and explain their function Kidneys o Organs that produce urine Urinary Tract o Organs that eliminate urine o Ureters Paired tubes o Urinary Bladder Muscular sac o Urethra Exit tube Explain the function of the urinary system Three Functions of the Urinary System o 1 Excretion o 2 Elimination Urination or Micturition The process of eliminating urine Contraction of muscular urinary bladder forces urine through urethra and out of body o 3 Homeostatic Regulation of Blood Plasma Volume and Solute Concentration Explain how the urinary system maintains homeostasis within the body 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 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 o By controlling loss of hydrogen ions and bicarbonate ions in urine 4 Conserves Valuable Nutrients o By preventing excretion while excreting organic waste products 5 Assists Liver o In detoxifying poisons o Also during starvation deaminates amino acids so other tissues can metabolize them for energy Describe the anatomy of the kidney Located on either side of vertebral column Left kidney lies superior to right kidney Superior surface capped by adrenal gland Position Maintained By o Overlying peritoneum o Contact with adjacent visceral organs o Supporting connective tissues o Floating Kidney Suspensory fibers damaged kidney displaced can cause pain distortion or ureter blood vessels during movement 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 A thick layer of adipose tissue o 3 Renal Fascia outermost layer A dense fibrous outer layer Anchors kidney to surrounding structures Typical Adult Kidney o 10 cm long 50 5 cm wide 3 cm thick 4 in x 2 2 in x 1 2 in o Weighs about 150 g 5 25 oz Hilum Renal Cortex o Point of ENTRY for renal artery and renal nerves o Point of EXIT for renal vein and ureter o Superficial portion of kidney in contact with renal capsule o Reddish brown and granular Renal Pyramids o 6 18 distinct conical or triangular structures in renal medulla Base abuts cortex Tip renal papilla projects into renal sinus Renal Columns o Bands of cortical tissue separate adjacent renal pyramids o Extend into medulla o Have distinct granular texture Renal Lobe o Consists Of Renal Pyramid o Ducts discharge urine into Minor calyx a cup shaped drain Overlying area of renal cortex Adjacent tissues of renal columns o Produces Urine Renal Papilla Major Calyx Renal Pelvis o Formed by 4 or 5 minor calyces o Large funnel shaped chamber o Consists of 2 or 3 major calyces o Fills most of renal sinus o Connected to ureter which drains kidney Describe the blood supply to the kidneys Kidneys receive 20 25 of total cardiac output 1200 mL of blood flows through kidneys each minute 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 Explain the function of the renal nerves Renal Nerves o Innervate kidneys and ureters o Enter each kidney at hilum o Follow tributaries of renal arteries to individual nephrons o Sympathetic Innervation Adjusts rate of urine formation by changing blood flow and blood pressure at nephron Stimulates release of renin Restricts losses of water and salt in urine by stimulating reabsorption at nephron renin angiotensin system stimulates aldosterone release from adrenal cortex Describe the structure of the nephron and explain its function Nephron functional unit of the kidney o Microscopic tubular structures in cortex of each renal lobe Each kidney has approximately 1 25 million nephrons o Where urine production begins Consists of o 1 Renal tubule o 2 Renal corpuscle Organization of the Nephron composition o Traveling along tubule filtrate tubular fluid gradually changes Due to reabsorption and secretion of substances o Changes vary with activities in each segment of nephron Each Nephron empties into the collecting system What is found in the renal corpuscle Renal Corpuscle o Spherical structure o Each renal corpuscle is 150 250 m in diameter Consists Of o 1 Glomerular Capsule Bowman s Capsule Forms outer wall of renal corpuscle Encapsulates glomerular capillaries o 2 Cup shaped chamber o 3 Capillary network glomerulus Knot of fenestrated capillaries Capillaries are enveloped by podocytes Podocytes cells that have complex processes or feet pedicles that wrap around the capillaries Filtration Slits narrow gaps between pedicles Allows small substances to pass out of capillary Explain the difference between the renal tubule and the glomerulus Renal Tubule o Lone tubular passageway o Begins at renal corpuscle o Functions 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 o Segments of Renal Tubule Located in cortex 1 Proximal Convoluted Tube PCT 2 Nephron Loop Loop of Henle U shaped tube Extends partially into medulla In juxtamedullary nephrons loop extends deeper into the medulla important for their function 3 Distal Convoluted Tubule DCT Glomerulus o Consists of 50 intertwining capillaries o Blood delivered via afferent arteriole o Blood leaves in efferent arteriole Flows into peritubular capillaries which drain into small venules and return blood to venous system o Note Blood leaves the capillary network through the efferent arteriole and NOT through a venule Differences Explain where filtration reabsorption and secretion takes place on the nephron What is filtered reabsorbed and or secreted Filtration o Occurs in renal corpuscle o Blood Pressure 1 Forces water and dissolved solutes out of glomerular capillaries into capsular space 2 Produces protein free solution filtrate similar to blood plasma except lacks proteins o Filtration membrane prevents large molecules from passing o Blood Pressure forces water and small
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