PowerPoint Lecture Outlines to accompany

Hole’s HumanAnatomy and Physiology

Tenth Edition

Shier Butler Lewis

Chapter

20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20-1

Chapter 20Urinary System

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Location of Kidneys

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Kidneys

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Renal Blood Vessels

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Renal Blood Vessels

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Glomerular Capsule

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Nephron and Associated Blood Vessels

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Renal Cortex and Renal Medulla

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Juxtaglomerular Apparatus

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Types of Nephrons

• cortical nephrons• 80% of nephrons

• juxtamedullary nephrons• regulate water balance

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Blood Supply of Nephron

The capillary loop of the vasa recta is closely associated with the nephron loop of the juxtamedullary nephron

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Summary of Blood Flow Through Kidney and Nephron

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Urine Formation

• Glomerular Filtration• substances move from blood to glomerular capsule

• Tubular Reabsorption• substances move from renal tubules into blood of peritubular capillaries• glucose, water, urea, proteins, creatine• amino, lactic, citric, and uric acids• phosphate, sulfate, calcium, potassium, and sodium ions

• Tubular Secretion• substances move from blood of peritubular capillaries into renal tubules• drugs and ions

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Glomerular Filtration

Glomerular filtrate passes through the fenestrae of the capillary endothelium

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Glomerular Filtrate and Urine Composition

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Glomerular Filtration Rate

Net Filtration Pressure = force favoring filtration – forces opposing filtration (glomerular capillary ( capsular hydrostatic pressure hydrostatic pressure) and glomerular capillary osmotic pressure )

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Amounts of Glomerular Filtrate and Urine

average amounts over a 24 hour period

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Control of Filtration Rate

• Increased sympathetic impulses decrease GFR by causing afferent arterioles to constrict• Renin-angiotensin system (shown)• Autoregulation

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Tubular Reabsorption

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Tubular Reabsorption of Water and Ions

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Sodium and Water Filtration, Reabsorption, and Excretion

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Tubular Secretion

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Secretion of Ions

In distal convoluted tubules, potassium ions or hydrogen ions may be passively secreted in response to active reabsorption of sodium ions

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Countercurrent Mechanism• helps maintain the NaCl concentration gradient in the medullary interstitial fluid

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Countercurrent Mechanism of Vasa Recta

• fluid in ascending limb becomes hypotonic as solute is reabsorbed• fluid in descending limb becomes hypertonic as it loses water by osmosis

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Effect of ADH on Renal Tubules

• without ADH, DCT and collecting duct are impermeable to water• with ADH, DCT and collecting duct become permeable to water• with ADH, water is reabsorbed by osmosis into hypertonic medullary interstitial fluid

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Urea and Uric Acid Excretion

Urea• product of amino acid catabolism• plasma concentration reflects the amount or protein in diet• enters renal tubules through glomerular filtration• 50% reabsorbed• rest is excreted

Uric Acid• product of nucleic acid metabolism• enters renal tubules through glomerular filtration• 100% reabsorbed• 10% secreted and excreted

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Renal Clearance

• the rate at which a chemical is removed from the plasma• tests of renal clearance

• inulin clearance test• creatinine clearance test• paraminohipparic acid test

• tests of renal clearance used to calculate glomerular filtration rate

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Elimination of Urine

• nephrons• collecting ducts• renal papillae• minor and major calyces• renal pelvis• ureters• urinary bladder• urethra• outside world

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Ureters

• 25 cm long• extend downward posterior to the parietal peritoneum• parallel to vertebral column• in pelvic cavity, join urinary bladder• wall of ureter

• mucous coat• muscular coat• fibrous coat

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Location of Male and Female Urinary Bladders

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Urinary Bladder

Longitudinal section and posterior view of male urinary bladder

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Cross Section of Urethra

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Male and Female Urethras

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Micturition

• bladder distends and stretch receptors stimulated• micturition center activated in sacral portion of spinal cord• parasympathetic nerve impulses cause detrusor muscle to contract• need to urinate is sensed

• voluntary contraction of external urethral sphincter prevents urination

• when decision is made to urinate, external urethral sphincter relaxes, detrusor muscle contracts, and urine is expelled

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Life-Span Changes

• kidneys appear scarred and grainy • kidney cells die• by age 80, kidneys have lost a third of their mass• kidney shrinkage due to loss of glomeruli• proteinuria may develop• renal tubules thicken• harder for kidneys to clear certain substances• bladder, ureters, and urethra lose elasticity• bladder holds less urine

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Clinical Application

Glomerulonephritis

• inflammation of glomeruli• may be acute or chronic• acute glomerulonephritis usually occurs as an immune reaction to a Streptococcus infection• antigen-antibody complexes deposited in glomeruli and cause inflammation• most patients recover from acute glomerulonephritis• chronic glomerulonephritis is a progressive disease and often involves diseases other than that caused by Streptococcus• renal failure may result from chronic glomerulonephritis

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