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Chapter 15 Urinary System Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 1 Pretest True or False • • • • • The functional unit of the kidney is the nephron. The outer portion of the kidney is known as the renal medulla. The indentation in the kidney is known as the hilum. The glomerulus is made up of loose connective tissue. The double-layered epithelial cup that surrounds the glomerulus is Bowman’s capsule. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 2 Pretest, cont. True or False 6. The ureters transport urine from the urinary bladder to the outside. 7. Rugae located in the wall of the urinary bladder allow the bladder to expand. 8. The urethra in a male functions only in the transport of urine. 9. Glucose is reabsorbed into the body in the renal tubule. 10. Micturition is the act of expelling urine. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 3 Introduction to the Urinary System • Functions of the urinary system – Rids body of waste products – Maintains appropriate fluid volume • By regulating amount of water excreted in the urine – Maintains normal pH of the blood – Secretes erythropoietin: controls red blood cell production – Secretes rennin: helps maintain normal blood pressure Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 4 Components of the Urinary System • Consists of: – Kidneys: produce urine – Ureters: transport the urine away from kidneys to urinary bladder – Urinary bladder: stores urine until it is excreted from the body – Urethra: tubular structure that carries urine from urinary bladder to the outside of body Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 5 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 6 Components of the Urinary System, cont. Kidneys • Primary organs of the urinary system • Functions: – Filter the blood – Remove wastes – Excrete the wastes in the urine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 7 Components of the Urinary System, cont. Location • Located between T-12 and L-3 vertebrae • Right kidney: slightly lower than left – Liver displaces it downward 3. Renal fascia: connective tissue that holds kidney in place Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 8 Components of the Urinary System, cont. 4. Perirenal fat: thick layer of adipose tissue that surrounds each kidney 5. Renal capsule: tough, fibrous connective tissue – Encases each kidney – Provides support for the soft tissue inside Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 9 Components of the Urinary System, cont. Macroscopic Structure • Bean-shaped 2. Hilum: indentation in kidney – Where ureter and renal vein leave the kidney – Where renal artery enters the kidney – Leads to a large cavity within the kidney (renal sinus) Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 10 Components of the Urinary System, cont. 3. Renal cortex: outer, reddish region of kidney 4. Renal medulla: inner, reddish-brown region of kidney – Consists of a series of renal pyramids Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 11 Components of the Urinary System, cont. 5. Renal pyramids – Appear striated • Contain straight tubular structures and blood vessels – Wide bases of pyramids: are adjacent to the cortex – Pointed ends of pyramids: renal papillae • Directed toward center of kidney Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 12 Components of the Urinary System, cont. 6. Renal columns: formed by portions of the renal cortex – Extend into spaces between adjacent pyramids Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 13 Components of the Urinary System, cont. 7. Renal pelvis: central region of kidney – – Continuous with ureter Consists of a large cavity: collects urine as it is produced Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 14 Components of the Urinary System, cont. c. Calyces: cuplike projections of the renal pelvis • Minor calyx: surrounds the renal papillae of each pyramid – Collects urine from that pyramid • Major calyx: made up of several minor calyces – From the major calyces: urine flows into renal pelvis 1)Then flows into ureter Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 15 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 16 Components of the Urinary System, cont. Nephrons • Functional unit of the kidney • Each kidney: contains over a million nephrons • Located in the cortex and medulla of kidney Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 17 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 18 Components of the Urinary System, cont. 4. Parts of a nephron a. Renal corpuscle consists of: • Glomerulus: cluster of capillaries • Glomerular capsule (Bowman’s capsule): doublelayered epithelial cup that surrounds glomerulus • Pathway of blood through glomerulus – Blood enters glomerulus through an afferent arteriole – Blood is filtered in glomerulus: filtrate enters glomerular capsule – Blood leaves glomerulus through an efferent arteriole Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 19 Components of the Urinary System, cont. b. Renal tubule: carries fluid away from Bowman’s capsule • Proximal convoluted tubule: highly coiled • Nephron loop (Henle’s loop): descends, makes a U-turn, ascends back toward the cortex • Distal convoluted tubule: highly coiled Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 20 Components of the Urinary System, cont. Collecting Ducts 1. Urine passes from nephrons into collecting ducts a. Flows from collecting ducts into minor calyces Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 21 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 22 Components of the Urinary System, cont. Ureters • Transport urine from renal pelvis to urinary bladder • Descend from renal pelvis • Enter urinary bladder on the posterior inferior surface Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 23 Components of the Urinary System, cont. 4. Wall of ureter a. Fibrous coat: outer layer consisting of fibrous connective tissue b. Muscular layer: middle layer consisting of smooth muscle • Function: peristalsis to propel the urine through the ureter c. Mucosa: inner layer • Function: secretes mucus to coat and protect surface of the cells Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 24 Components of the Urinary System, cont. Urinary Bladder • Located in pelvic cavity • Temporary storage reservoir for urine • Size and shape varies with: – Amount of urine it contains – Pressure from surrounding organs Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 25 Components of the Urinary System, cont. 4. Layers of urinary bladder a. Mucosa: consists of a mucous membrane • Rugae: folds that occur when bladder is empty – Allow bladder to expand as it fills b. Submucosa: consists of connective tissue with elastic fibers c. Muscularis: composed of smooth muscle interwoven in all directions • Collectively called the detrusor muscle – Contraction: expels urine from bladder Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 26 Components of the Urinary System, cont. 5. Trigone: formed by three openings in the floor of the urinary bladder – Two openings: from ureters • Small flaps of mucosa: cover openings – Act as valves: allow urine to enter bladder – Prevent it from backing up from bladder into ureters – Third opening: urethra • Band of the detrusor muscle: encircles this opening – Forms the internal urethral sphincter Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 27 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 28 Components of the Urinary System, cont. Urethra • Thin-walled tube • Conveys urine from urinary bladder to outside of body • Sphincters that control flow of urine through urethra: a. Internal urethral sphincter: surrounds urethra where it leaves the urinary bladder • Consists of smooth (involuntary) muscle b. External urethral sphincter: encircles urethra where it passes through pelvic floor • Consists of skeletal (voluntary) muscle Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 29 Components of the Urinary System, cont. 4. Females: urethra is short – External urethral orifice • Opens to outside just anterior to vaginal opening Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 30 Components of the Urinary System, cont. 5. Males: urethra is much longer – Transports both urine and semen – Parts of the male urethra: • Prostatic urethra: passes through the prostate gland • Membranous urethra: short region that penetrates pelvic floor and enters penis • Spongy urethra: longest region – Extends the entire length of the penis – External urethral orifice: opens to the outside at the tip of penis Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 31 Components of the Urinary System, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 32 Urine Formation Glomerular Filtration • Blood plasma – Moves across filtration membrane in the renal corpuscle – Enters glomerular capsule • Filtration membrane consists of: – Capillary endothelium of the glomerulus – Endothelium of the capsule Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 33 Urine Formation, cont. 3. Filtration pressure: force that moves the fluid across the membrane 4. Filtrate: fluid that enters the capsule 5. Blood flows through the kidneys: at a rate of 1200 ml per minute 6. Filtration membrane: acts as a barrier – Prevents blood cells and protein molecules from entering the capsule Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 34 Urine Formation, cont. Tubular Reabsorption • 180 liters (45 gallons) of filtrate are formed in a 24-hour period – Reduced to 1-2 liters of urine 2. Tubular reabsorption – Movement of substances from the filtrate in the kidney tubules: into the blood • Changes the volume and composition of the filtrate – Substances that are useful to body: are reabsorbed (e.g., glucose, water, sodium) – Wastes remain in the filtrate: excreted in Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 35 Urine Formation, cont. 3. Amount of reabsorption that takes place: – Proximal convoluted tubule: 65% – Nephron loop (loop of Henle): 15% – Distal convoluted tubule: 19% 4. 1% of filtrate: excreted as urine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 36 Urine Formation, cont. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 37 Urine Formation, cont. Tubular Secretion 1. Transport of molecules and ions into the filtrate from the blood – Includes: • Waste products of cellular metabolism (e.g., urea) – Become toxic if allowed to accumulate in body • Some drugs (e.g., penicillin) • Hydrogen ions – Helps to regulate the pH of the blood • Potassium ions, creatinine, histamine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 38 Urine Formation, cont. 2. Urine consists of: – Substances that are filtered minus the substances that are reabsorbed in the tubules – Plus the substances that are added by tubular secretion Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 39 Urine Formation, cont. Regulation of Urine Concentration and Volume 1. Aldosterone: secreted by adrenal gland – Acts on the kidney tubules: increases reabsorption of sodium • When sodium is reabsorbed: water follows by osmosis – Reduces urine output Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 40 Urine Formation, cont. 2. Antidiuretic hormone (ADH): released from pituitary gland a. Presence of ADH: less water is lost from body • Makes distal convoluted tubule and collecting duct more permeable to water – More water is reabsorbed – Reduces amount of urine excreted – Makes urine more concentrated b. Absence of ADH: more water is lost from body • Makes tubules less permeable to water – Less water is reabsorbed – Increases volume of urine – Makes urine dilute Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 41 Urine Formation, cont. 3. Atrial natriuretic hormone (atriopeptin): produced by special cells in the heart – Promotes excretion of sodium and water – Acts directly on kidney tubules • Inhibits secretion of ADH, renin, and aldosterone – Decreases blood volume and blood pressure Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 42 Urine Formation, cont. 4. Renin: enzyme produced by kidney – Secreted in response to: • Low blood pressure • Decreased blood sodium concentration – Promotes production of angiotensin II in the blood • Powerful vasoconstrictor: increases blood pressure • Stimulates adrenal gland to secrete aldosterone – Acts on kidney tubules to conserve sodium and water • Increases blood volume and, consequently, increases blood pressure Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 43 Urine Formation, cont. Micturition • Act of expelling urine from the bladder • Bladder: – Can hold up to 1 liter (1000 ml) of urine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 44 Urine Formation, cont. 3. Micturition reflex – When bladder contains 200-400 ml of urine • Stretch receptors in bladder wall triggers micturition reflex • Automatic and involuntary response • Impulses are transmitted to detrusor muscle – Can be inhibited or stimulated by higher brain centers Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 45 Posttest True or False • • • • The urinary system helps to regulate the blood pressure. The renal pelvis collects urine as it is produced. The nephron is made up of the glomerulus and Bowman’s capsule. Blood enters the glomerulus through the efferent arteriole. • The renal tubule carries fluid away from the glomerular capsule toward a collecting duct. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 46 Posttest, cont. True or False 6. Urine is expelled from the urinary bladder through contraction of the detrusor muscle. 7. The calyx consists of three openings and is located in the floor of the urinary bladder. 8. The urethral orifice controls the passage of urine through the urethra. 9. Erythropoietin increases reabsorption of sodium and reduces urine output. 10. In the absence of ADH, the urine is more dilute. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc. 47