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Chapter 18
The Urinary System
Introduction
• Maintains homeostasis
– removes and restores solutes and fluids
• Organs
– two kidneys - main filtering organs, produce
urine
– two ureters
– one bladder
– one urethra
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Corporation. ALL RIGHTS RESERVED.
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Functions of the Urinary System
• Excretion - nitrogenous, drugs and toxins
• Maintaining blood volume and
concentration
– balance of water and dissolved salts
• pH regulation
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Corporation. ALL RIGHTS RESERVED.
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Functions of the Urinary System
• Blood pressure maintenance
– renin
• Erythrocyte concentration
– erythropoietin
• Vitamin D production
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Corporation. ALL RIGHTS RESERVED.
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The External Anatomy of the
Kidneys
• Hilum - passage area for ureters, vessels,
nerves
• Surrounding layers
– renal capsule - innermost, barrier
– adipose capsule - middle, protection
– renal fascia - outer, anchors kidney
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Corporation. ALL RIGHTS RESERVED.
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The Internal Anatomy of the
Kidneys
• Medulla - inner area
– renal pyramids - tips point inward
• Cortex - outer area
– cortical material between pyramids
– cortex and renal pyramids contain nephrons
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Corporation. ALL RIGHTS RESERVED.
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The Internal Anatomy of the
Kidneys
• Nephrons - functional units of the kidney
• Minor calyx
– funnel shaped, collects urine from pyramid
ducts
• Major calyces - formed from minor calyces
– join to form renal pelvis
– renal pelvis narrows to form ureter
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Corporation. ALL RIGHTS RESERVED.
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The Anatomy of the Nephrons
• Nephron - microscopic renal tubule
• Bowman’s glomerular capsule - doublewalled globe
– podocytes - innermost layer
– parietal layer - outermost layer
• Endothelial-capsular membrane - filter
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Corporation. ALL RIGHTS RESERVED.
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The Anatomy of the Nephrons
• Renal tubule
– proximal convoluted tubule
– descending limb, loop and ascending limb of
Henle
– distal convoluted tubule
• Collecting ducts
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Corporation. ALL RIGHTS RESERVED.
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Blood and Nerve Supply to the
Nephrons
• Renal arteries - transport 1200 mL of blood
per minute
• Interlobar arteries
• Arcuate arteries
• Interlobular arteries
• Afferent arterioles divide into glomerular
capillaries
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Corporation. ALL RIGHTS RESERVED.
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Blood and Nerve Supply to the
Nephrons
•
•
•
•
•
Efferent arterioles
Peritubular capillaries
Interlobular veins drain into arcuate vein
Interlobar veins
Renal veins
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Corporation. ALL RIGHTS RESERVED.
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Physiology of the Nephrons
• Functions
– control blood concentration and volume
– regulate blood pH
– remove toxins from blood
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Corporation. ALL RIGHTS RESERVED.
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Urine Formation
• Urine formation
– glomerular filtration
– tubular reabsorption
– tubular secretion
• Urine - 95% water, urea, uric acid,
electrolytes
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Corporation. ALL RIGHTS RESERVED.
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The Ureters: Anatomy and Function
• Extensions of the renal pelvis
• Connect to urinary bladder
• Function - transport urine to urinary
bladder
• Urine movement
– peristalsis, gravity, hydrostatic pressure
©2006 by Thomson Delmar Learning, a part of the Thomson
Corporation. ALL RIGHTS RESERVED.
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The Urinary Bladder and the
Micturition Reflex
• Urinary bladder held in position by
peritoneum
• Trigone - region between openings of
ureters and urethra
• Detrusor muscle – three-layered smooth
muscle
• Internal urinary sphincter - involuntary
control
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Corporation. ALL RIGHTS RESERVED.
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The Urinary Bladder and the
Micturition Reflex
• Micturition - expulsion of urine from
bladder
• External urinary sphincter - voluntary
control
• Bladder capacity
– 700-800 mL
– 200-400 mL - conscious of need to urinate
– micturition reflex stimulated
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Corporation. ALL RIGHTS RESERVED.
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The Urethra: Female Position
• Urethra - connects bladder to the outside
• Females
– located in wall of vagina
– 3.8 cm long
– between clitoris and vaginal opening
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Corporation. ALL RIGHTS RESERVED.
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The Urethra: Male Position
• Males
– 20 cm long
– passes through prostate gland and penis
– opens at tip of penis
– transports urine and semen
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Corporation. ALL RIGHTS RESERVED.
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Animation
• This animation presents an overview of
how urine is formed.
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Corporation. ALL RIGHTS RESERVED.
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