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This 11 page Class Notes was uploaded by Jess Graff on Monday May 2, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 4 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 05/02/16
BMS 508.03 4/22/2016 Chapter 26 Urinary System Urinary System Functions • 3 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 • Functions of the Urinary System 1. Kidneys — organs that produce urine 2. Urinary tract — organs that eliminate urine • Ureters (paired tubes) • Urinary bladder (muscular sac) • Urethra (exit tube) 3. Urination or micturition — process of eliminating urine • Contraction of muscular urinary bladder forces urine through urethra, and out of body • Homeostatic Functions of the Urinary System • Regulates blood volume and blood pressure • By adjusting volume of water lost in urine • Releasing erythropoietin and renin • Regulates plasma ion concentrations • Sodium, potassium, and chloride ions (by controlling quantities lost in urine) • Calcium ion levels (through synthesis of calcitriol) • Helps stabilize blood pH • By controlling loss of hydrogen ions and bicarbonate ions in urine • Conserves valuable nutrients • By preventing excretion while excreting organic waste products • Assists liver • In detoxifying poisons The Kidneys • The Kidneys • Are located on either side of vertebral column • Left kidney lies superior to right kidney • Superior surface capped by adrenal gland • Position is maintained by: • Overlying peritoneum • Contact with adjacent visceral organs • Supporting connective tissues • Each Kidney Is Protected and Stabilized • By 3 concentric layers of connective tissue • Fibrous capsule • A layer of collagen fibers • Covers outer surface of entire organ • Perinephric fat • A thick layer of adipose tissue • Surrounds renal capsule • Renal fascia • A dense, fibrous outer layer • Anchors kidney to surrounding structures • Typical Adult Kidney • Is about 10 cm long, 5.5 cm wide, and 3 cm thick (4 in. 2.2 in. 1.2 in.) • Weighs about 150 g (5.25 oz) • Hilum • Point of entry for renal artery and renal nerves • Point of exit for renal vein and ureter • Sectional Anatomy of the Kidneys • Renal sinus • Internal cavity within kidney • Lined by fibrous renal capsule • Bound to outer surfaces of structures in renal sinus • Stabilizes positions of ureter, renal blood vessels, and nerves • Renal Cortex • Superficial portion of kidney in contact with renal capsule • Reddish brown and granular • Renal Pyramids • 6 to 18 distinct conical or triangular structures in renal medulla • Base abuts cortex • Tip (renal papilla) projects into renal sinus • Renal Columns • Bands of cortical tissue separate adjacent renal pyramids • Extend into medulla • Have distinct granular texture • Kidney Lobe • Consists of: • Renal pyramid • Overlying area of renal cortex • Adjacent tissues of renal columns • Produces urine • Renal Papilla • Ducts discharge urine into minor calyx, a cup-shaped drain • Major Calyx • Formed by four or five minor calyces • Renal Pelvis • Large, funnel-shaped chamber • Consists of two or three major calyces • Fills most of renal sinus • Connected to ureter, which drains kidney • Nephrons • Microscopic, tubular structures in cortex of each renal lobe • Where urine production begins • 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 • Segmental Arteries • Receive blood from renal artery • Divide into interlobar arteries • Which radiate outward through renal columns between renal pyramids • Supply blood to arcuate arteries • Which arch along boundary between cortex and medulla of kidney • Afferent Arterioles • Branch from each cortical radiate artery (also called interlobular artery) • Deliver blood to capillaries supplying individual nephrons • Cortical Radiate Veins • Also called interlobular veins • Deliver blood to arcuate veins • Empty into interlobar veins • Which drain directly into renal vein • Renal Nerves • Innervate kidneys and ureters • Enter each kidney at hilum • Follow tributaries of renal arteries to individual nephrons • Sympathetic Innervation • Adjusts rate of urine formation • By changing blood flow and blood pressure at nephron • Stimulates release of renin • Which restricts losses of water and salt in urine • By stimulating reabsorption at nephron • The Nephron • Consists of renal tubule and renal corpuscle • Renal tubule • Long tubular passageway • Begins at renal corpuscle • Renal corpuscle • Spherical structure consisting of: • Glomerular capsule (Bowman’s capsule) • Cup-shaped chamber • Capillary network (glomerulus) • Glomerulus • Consists of 50 intertwining capillaries • Blood delivered via afferent arteriole • Blood leaves in efferent arteriole • Flows into peritubular capillaries • Which drain into small venules • And return blood to venous system • Filtration • Occurs in renal corpuscle • Blood pressure • Forces water and dissolved solutes out of glomerular capillaries into capsular space • Produces protein-free solution (filtrate) similar to blood plasma • Three Functions of the Renal Tubule • Reabsorb useful organic nutrients that enter filtrate • Reabsorb more than 90% of water in filtrate • Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus • Segments of the Renal Tubule • Located in cortex • Proximal convoluted tubule (PCT) • Distal convoluted tubule (DCT) • Separated by nephron loop (loop of Henle) • U-shaped tube • Extends partially into medulla • Organization of the Nephron • Traveling along tubule, filtrate (tubular fluid) gradually changes composition • Changes vary with activities in each segment of nephron • Each Nephron • Empties into the collecting system • A series of tubes that carries tubular fluid away from nephron • Collecting ducts • Receive fluid from many nephrons • 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 • The Renal Corpuscle • Each renal corpuscle is 150–250 µm in diameter • Glomerular capsule • Is connected to initial segment of renal tubule • Forms outer wall of renal corpuscle • Encapsulates glomerular capillaries • Glomerulus • Knot of capillaries • The Glomerular Capsule • Outer wall is lined by simple squamous capsular epithelium • Continuous with visceral epithelium that covers glomerular capillaries • Separated by capsular space • The Visceral Epithelium • Consists of large cells (podocytes) • With complex processes or “feet” (pedicels) that wrap around specialized dense layer of glomerular capillaries • Filtration Slits • Are narrow gaps between adjacent pedicels • Materials passing out of blood at glomerulus: • Must be small enough to pass between filtration slits • The Glomerular Capillaries • Are fenestrated capillaries • Endothelium contains large-diameter pores • Blood Flow Control • Special supporting cells (mesangial cells) • Between adjacent capillaries • Control diameter and rate of capillary blood flow • The Filtration Membrane • Consists of: • Fenestrated endothelium • Dense layer • Filtration slits • Filtration • Blood pressure • Forces water and small solutes across membrane into capsular space • Larger solutes, such as plasma proteins, are excluded • Filtration at Renal Corpuscle • Is passive • Solutes enter capsular space • Metabolic wastes and excess ions • Glucose, free fatty acids, amino acids, and vitamins • Reabsorption • Useful materials are recaptured before filtrate leaves kidneys • Reabsorption occurs in proximal convoluted tubule • The Proximal Convoluted Tubule (PCT) • Is the first segment of renal tubule • Entrance to PCT lies opposite point of connection of afferent and efferent arterioles with glomerulus • Epithelial Lining of PCT • Is simple cuboidal • Has microvilli on apical surfaces • Functions in reabsorption • Secretes substances into lumen • Tubular Cells • Absorb organic nutrients, ions, water, and plasma proteins from tubular fluid • Release them into peritubular fluid (interstitial fluid around renal tubule) • The Nephron Loop (Loop of Henle) • Renal tubule turns toward renal medulla • Descending limb • Fluid flows toward renal pelvis • Ascending limb • Fluid flows toward renal cortex • Each limb contains: • Thick segment • Thin segment • The Thick Descending Limb • Has functions similar to PCT • Pumps sodium and chloride ions out of tubular fluid • Ascending Limbs • Of juxtamedullary nephrons in medulla • Create high solute concentrations in peritubular fluid • The Thin Segments • Are freely permeable to water • Not to solutes • Water movement helps concentrate tubular fluid • The Thick Ascending Limb • Ends at a sharp angle near the renal corpuscle • Where DCT begins • The Distal Convoluted Tubule (DCT) • The third segment of the renal tubule • Initial portion passes between afferent and efferent arterioles • Has a smaller diameter than PCT • Epithelial cells lack microvilli • Three Processes at the DCT • Active secretion of ions, acids, drugs, and toxins • Selective reabsorption of sodium and calcium ions from tubular fluid • Selective reabsorption of water • Concentrates tubular fluid • The Juxtaglomerular Complex (JGC) • An endocrine structure that secretes: • Hormone erythropoietin • Enzyme renin • Formed by: • Macula densa • Juxtaglomerular cells
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