Chapter 20
Urinary System
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Elimination of Waste
Products Summary
• Skin (perspiration)
• Dissolved salts
• Intestines (defecation)
• Solid wastes and water
• Lungs (exhalation)
• Carbon dioxide and water vapor
• Kidneys (urination)
• Nitrogenous wastes and salts dissolved in water to form urine
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Urinary System
• Excretion of nitrogenous wastes, salts, and
water
• Two kidneys
– Form the urine
• Two ureters
• One bladder
• One urethra
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Figure 20-1 The organs of the
urinary system of a female
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Functions of the Urinary System
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•
•
•
Excretion
Aids in maintaining acid-base balance
Renin helps maintain blood pressure
Erythropoeitin stimulates red blood cell
production
• Secretion of waste products in the form of
urine
• Elimination of urine from the bladder where
it is stored
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Kidneys
• Two bean-shaped organs located
retroperitoneally
• Adipose capsule
• Renal fascia
• Hilum
• Renal pelvis
• Medulla and cortex
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Figure 20-2 The internal structure of
a kidney
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Medulla and Cortex
• Cortex is the outer granular layer
– Consists of the functional unit called the
nephron
• Medulla is the inner striated layer
– Consists of radially striated cones called renal
pyramids
– The papilla empties into the calyces, which join
together to empty into the renal pelvis
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Nephron (1 of 2)
•
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•
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Basic structural and functional unit
Each kidney has over 1 million
Afferent arteriole
Bowman’s capsule
Glomerulus
Efferent arteriole
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Nephron (2 of 2)
•
•
•
•
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)
Collecting tubule
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Figure 20-3 Structure of the nephron
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Path of Urine Formation (1 of 2)
Blood enters the afferent arteriole
Glomerulus Bowman’s capsule
Becomes filtrate PCT Loop of
Henle DCT Collecting tubule
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Path of Urine Formation (2 of 2)
Collecting tubule
– At collecting tubule, approximately 99% of the filtrate has
been reabsorbed
Formed urine goes to the renal pelvis
ureter bladder urethra urinary
meatus
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Urine Formation in the Nephron
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•
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Filtration
Reabsorption
Secretion
Urinary output and urinalysis values
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Figure 20-5 Filtration, reabsorption, and secretion are the main
functions of the nephrons
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Control of Urinary Secretion
• Chemical control
– Aldosterone
– ADH
– diuretics
●
Nervous control
– Action of nerve impulses on the blood vessels leading
to the kidney
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Urinary Output
• 1,000-2,000ml of urine/day
• Volume will vary with diet, fluid intake,
temperature and physical activity
• Urinalysis
– Examines the urine
– Most common noninvasive diagnostic test done
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Ureters
• Two ureters
– One for each kidney
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•
•
•
Carries urine to the bladder for storage
About 10-12 inches long and ¼-inch wide
Mucous membranes line ureters
Smooth muscle fibers
– Peristalsis to push urine down the ureter to the bladder
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Urinary Bladder/Urethra
• Hollow muscular organ
• Stores up to about 1 pint (500 ml) of urine
• Involuntary contractions of the bladder can
be controlled to some extent by the nervous
system
• Urine leaves the bladder through the
urethra, then passes through the opening
called the urinary meatus
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Urination
• Micturition
• Level of urine in the bladder is sensed by
stretch receptors
• Requires coordinated contraction of the
bladder muscles and the relaxation of the
sphincters
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Disorders of the Urinary System
(1 of 2)
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Acute kidney failure
Chronic renal failure
Glomerulonephritis
Acute glomerulonephritis
Chronic glomerulonephritis
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Disorders of the Urinary System
(2 of 2)
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Hydronephrosis
Pyelitis/Pyelonephritis
Kidney stones or renal calculi
Cystitis
Incontinence
Neurogenic bladder
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Effects of Aging (1 of 2)
• Kidneys shrink
• Changes result in decreased renal blood
flow
• Kidney compromised in removing waste
products
• Decreased glomerular filtration rate
– Drug dosages have to be adjusted
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Effects of Aging (2 of 2)
• Glucose reabsorption also decreases
– Hyperglycemia
• Loss of muscle tone in the urinary bladder
• Urinary incontinence
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Dialysis
• Passage of dissolved molecules through a
semipermeable membrane
• Used for kidney failure
• Hemodialysis
• Peritoneal dialysis
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Kidney Transplants
• Living donor transplant
• Unrelated donor who has died
• Most important complication
– Rejection of kidney by the recipient
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