17 -1 Chapter 18 The Urinary System

18-1: The Urinary System Functions of the urinary system: Excretion Excretion—removal of waste products Elimination Elimination—discharge of waste products Regulate homeostasis Kidneys urine Kidneys perform excretion; produce urine uretersurinary bladderurethra Urinary tract includes ureters, urinary bladder, & urethra Micturition Micturition (urination) 17 -2

Homeostatic mechanisms Regulate blood volume & blood pressure Regulate plasma concentrations Stabilize blood pH Conserve valuable nutrients 17 -3

18-1 Checkpoint 1. Name the three primary functions of the urinary system. 2. Identify the components of the urinary system. 3. Define micturition

18-2: The Kidneys retroperitoneally Located retroperitoneally fibrous capsule Kidney covered by fibrous capsule & cushioned by adipose tissue Anatomy of the Kidneys Hilum Hilum—location of ureter, blood vessels & nerve entrance/exit renal cortex Outer edge is renal cortex nephrons Contains nephrons (begin urine formation)

renal medulla Inner kidney is renal medulla renal pyramids Contains numerous renal pyramids Renal columns Renal columns between renal pyramids Renal lobe Renal lobe = renal pyramid + renal columns minor calyx Urine discharged into minor calyx major calyces Minor calyces merge to form major calyces renal pelvis Major calyces merge to form renal pelvis Renal pelvis connects to ureter 17 -6

Blood Supply to Kidneys renal artery Kidney receives blood from renal artery Enter kidney & branch numerous times to deliver blood to nephrons afferent arterioleefferent arteriole Blood enters nephron through afferent arteriole & exits through efferent arteriole Peritubular capillaries Peritubular capillaries surround nephron renal vein Venules & veins combine in kidney & drain into renal vein 17 -8

The Nephron renal corpuscle Begins at the renal corpuscle glomerulus filtration filtrate Consists of a glomerulus that performs filtration (forms filtrate) renal tubule Filtrate leaves glomerulus & enters renal tubule proximal convoluted tubuleloop of Henledistal convoluted tubule Consists of proximal convoluted tubule, loop of Henle, & distal convoluted tubule collecting duct Nephron empties into collecting duct in renal medulla to form urine

Nephron functions Convert filtrate to urine Reabsorb nutrients & water from filtrate Glomerulus Glomerulus begins filtration of fluids & forms filtrate Proximal convoluted tubule Proximal convoluted tubule draws water out of filtrate, increases solutes in filtrate

Loop of Henle Loop of Henle removes water & ions Distal convoluted tubule Distal convoluted tubule performs secretion & reabsorption, regulates blood pressure Collecting system Collecting system receives fluid from nephrons & delivers urine to minor calyces

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18-2 Checkpoint 1. How does the position of the kidneys differ from most organs in the abdominal cavity? 2. Why might large proteins and substances not pass into the glomerulus from the afferent arteriole? 3. Damage to which part of the nephron would interfere with the control of blood pressure?

18-3: Kidney Physiology Urine Urine production maintains homeostasis by regulating volume & composition of blood Nephron Processes Filtration Filtration (occurs in glomerulus) Blood pressure forces water into glomerulus Small filtered molecules become filtrate

Reabsorption Reabsorption (occurs in proximal convoluted tubule) Removal of water & solute molecules from convoluted tubules Reabsorbed substance go back into blood Secretion Secretion (occurs in distal convoluted tubule) Transports solutes from convoluted tubules

Properties of Normal Urine Composition & concentration varies with individuals Typical characteristics 93 – 97% water Should be clear yellow Average pH 6.0 antidiuretic hormone (ADH) Release of antidiuretic hormone (ADH) reduces urine formation; forms concentrated urine

18-3 Checkpoint 1. A decrease in blood pressure would have what effect on filtration? 2. What processes occur in the proximal and distal convoluted tubules? 3. What effect would low levels of antidiuretic hormone (ADH) have on urine production?

18-5: Ureters, Bladder & Urethra The Ureters Ureters conduct urine from kidneys to urinary bladder Waves of peristalsis push urine toward bladder Calculi kidney stones Calculi (kidney stones) may form within kidney, ureters or bladder

The Urinary Bladder Bladder Bladder is hollow, muscular organ that stores urine trigone Bottom of bladder (trigone) contains ureter openings & urethral opening internal urethral sphincter Urethral entrance contains internal urethral sphincter (involuntary control) Detrusor muscle Detrusor muscle of bladder contracts to expel urine from bladder

The Urethra Extends from bladder to exterior of body Longer in males, conducts urine & semen in males external urethral sphincter Urethral exit contains external urethral sphincter (voluntary control)

Micturition Reflex & Urination Micturition reflex Micturition reflex forces urine out of bladder & urethra Stretch receptors in bladder wall trigger nervous system Neurons trigger detrusor muscle to contract Both sphincters relax & urine is released Urine volume over 500 mL forces sphincters open

18-5 Checkpoint 1. What is responsible for the movement of urine from the kidneys to the urinary bladder? 2. An obstruction of a ureter by a kidney stone would interfere with the flow of urine between what two structures? 3. Control of the micturition reflex depends on the ability to control which muscle?