Chapter 26 – The Urinary System

Lesson 2 Chapter 26 – The Urinary System Unit 10 Study Guide The Urinary System The urinary system includes the kidneys, the ureters, the urinary bladder, and the urethra. Overview o Kidneys, ureters, urinary bladder & urethra o Urine flows from each kidney, down its ureter to the bladder and to the outside via the urethra The kidneys maintain the purity and constancy of fluids in our internal environment. They filter gallons of fluid from the bloodstream, ridding the body of metabolic wastes, toxins, and excess ions, while returning needed substances to the blood. 1 Lesson 2 Chapter 26 – The Urinary System 2 Major Functions: - Eliminating nitrogenous wastes, toxins, and drugs from the body. Regulating the volume and chemical makeup of the blood. Maintaining the balance between water and salts and between acids and bases. Other Functions: - Producing renin to help regulate blood pressure and kidney function. Producing the hormone erythropoietin (stimulates red blood cell production). Metabolizing vitamin D to its active form. Internal/External Anatomy: Kidney - - Paired kidney-bean-shaped organ Found just between the peritoneum & posterior wall of abdomen o Retroperitoneal along with adrenal glands & ureters o At the level of T12 to L3 Protected by 11th & 12th ribs with right kidney lower Kidneys are bean-shaped and lie in a retroperitoneal position in the superior lumbar region. They receive some protection from the lower rib cage. The right kidney is crowded by the liver and lies slightly lower than the left. The medial surface contains a cleft (hilus). The ureters, renal blood vessels, lymphatics, and nerves enter or exit the kidney at the hilus. Three layers of supportive tissue surrounds each kidney:  Renal capsule – closest, provides a strong barrier that prevents infection from surrounding regions from spreading to the kidneys.  Adipose capsule – middle layer, fatty tissue which helps protect kidneys and hold them in place.  Renal fascia – outermost dense fibrous connective tissue, anchors kidneys to surrounding structures. Internal anatomy:  Cortex - outer region, contains the nephrons  Medulla - middle region, contains the renal pyramids  Pelvis - flat, funnel-shaped tube continuous with the ureter, branching sections form the major calyces, each of which subdivides further The calyces collect urine, which drains from the papillae (tips of renal pyramids) and empties into the pelvis. Urine then flows through the pelvis and into the ureter which transports it to the bladder to be stored. The walls of the calyces, pelvis, and ureter contract rhythmically and propel the urine along by peristalsis. Lesson 2 Chapter 26 – The Urinary System 8 – 18 minor calyces 2 – 3 major calyces 3 Lesson 2 Chapter 26 – The Urinary System 4 Blood Supply to Kidneys The renal artery (from the abdominal aorta) enters the kidney at the hilum, where it divides into five interlobar arteries, each an end artery. At the junction of the renal medulla and cortex, the interlobar branches divide into arcuate arteries, which course at right angles to the interlobar arteries. The interlobular arteries arise at right angles to the arcuate arteries and penetrate through the renal cortex. The afferent arterioles, which arise from the interlobular arteries, divide within the cortical tissue to form the glomerular capillary network. The capillaries then reunite to form the efferent arterioles. The subsequent course of the efferent arterioles varies, depending on whether they are located superficially in the cortex or are situated in the juxtamedullary cortex. Superficial efferent arterioles feed a plexus of peritubular venous capillary vessels. These vessels supply the proximal and distal tubules and portions of the loops of Henle and the collecting ducts before joining the interlobular veins and returning to the inferior vena cava through the arcuate, interlobar, and renal veins. Juxtamedullary efferent arterioles also supply the venous capillary network and give rise to the vasa recta, small-diameter vessels that penetrate deep into the medulla. These vessels provide most of the oxygen supply to the loop of Henle and join together to form the arcuate veins. The juxtaglomerular apparatus is between the afferent and efferent arterioles and the macula densa, a specialized group of cells in the distal convoluted tubule. Lesson 2 Chapter 26 – The Urinary System The Nephron Each kidney contains over one million tiny blood processing units called nephrons which carry out the process of urine formation.  Filtration occurs in the glomerulus, which receives blood from an afferent arteriole.  Glomerular blood is drained by an efferent arteriole, which delivers blood to peritubular capillaries that surround the nephron tubules.  The glomerular (Bowman’s) capsule and the proximal and distal convoluted tubules are located in the cortex.  The loop of Henle is located in the medulla.  Filtrate from the distal convoluted tubule is drained into collecting ducts, which plunge through the medulla to empty urine into the calyces. Parts of the nephron and processes that occur:      Glomerulus - tuft of capillaries; filtration Bowman's (renal) capsule - enlarged, cupshaped capsule which surrounds the glomerulus; collects filtrate Proximal convoluted tubule - tubular reabsorption Loop of Henle - sodium and water balance Distal convoluted tubule - tubular secretion Cortical nephrons – most nephrons are located in the cortical. Juxtamedullary nephron has longer loop of henle in medulla. 5 Lesson 2 Chapter 26 – The Urinary System Structure of Renal Capsule May be called bowman’s space, capsular space, Bowman’s capsule. o Glomerular capillaries arise from afferent arteriole & form a ball before emptying into efferent arteriole – glomerulus o Bowman’s capsule – 2 layers  Podocytes (modified simple squamous epithelial cells) cover capillaries to form visceral layer  Simple squamous cells form parietal layer of capsule  A space in between – capsular space Two hormone products of Juxtaglomerular: Erythropoietin (stimulates RBC production) 6 Lesson 2 Chapter 26 – The Urinary System 7 Renin (Renin activates angiotensinogen, a precursor found in the bloodstream, leading to the formation of angiotensin I, which is converted to angiotensin II. Angiotensin II is the most potent vasoconstrictor known. It also stimulates the secretion of aldosterone.) Ureters The ureters are a pair of tubes that carry urine from the kidneys to the urinary bladder. The ureters are about 10 to 12 inches long and run on the left and right sides of the body parallel to the vertebral column. Gravity and peristalsis of smooth muscle tissue in the walls of the ureters move urine toward the urinary bladder. The ends of the ureters extend slightly into the urinary bladder and are sealed at the point of entry to the bladder by the ureterovesical valves. These valves prevent urine from flowing back towards the kidneys. Lesson 2 Chapter 26 – The Urinary System 8 Urethra The urethra is the tube through which urine passes from the bladder to the exterior of the body.  The female urethra is around 2 inches long and ends inferior to the clitoris and superior to the vaginal opening.  In males, the urethra is around 8 to 10 inches long and ends at the tip of the penis. The urethra is also an organ of the male reproductive system as it carries sperm out of the body through the penis. The flow of urine through the urethra is controlled by the internal and external urethral sphincter muscles. The internal urethral sphincter is made of smooth muscle and opens involuntarily when the bladder reaches a certain set level of distention. The opening of the internal sphincter results in the sensation of needing to urinate. The external urethral sphincter is made of skeletal muscle and may be opened to allow urine to pass through the urethra or may be held closed to delay urination.  Females o length of 1.5 in., orifice between clitoris & vagina  Males o 18-20 cm from neck of bladder to tip of penis o 3 regions of urethra  prostatic urethra, membranous urethra & spongy urethra Urinary Bladder The urinary bladder is a sac-like hollow organ used for the storage of urine. The urinary bladder is located along the body’s midline at the inferior end of the pelvis. Urine entering the urinary bladder from the ureters slowly fills the hollow space of the bladder and stretches its elastic walls. The walls of the bladder allow it to stretch to hold anywhere from 600 to 800 milliliters of urine.  Posterior to pubic symphysis  In females is anterior & inferior to uterus  In males lies anterior to rectum – between the rectum and the symphysis publis  Mucosal lining has folds (rugae) that disappear as bladder fills and distends. Lesson 2 Chapter 26 – The Urinary System 9