chapter 17 - the urinary system urinary system - fnc. producing & excreting urine essential...
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• Chapter 17 - The Urinary System
• Urinary system - fnc. producing & excreting urine
• Essential function in maintaining homeostasis & survival:
– body fluid volumes
– levels of chemicals (electrolytes)
– normal composition of blood (clean waste products - if not > uremia uremic poisoning )
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• Kidneys - two
• Location - posterior back, above waist
– R little lower than L
– Under muscles of back -
& retroperitoneal
– Cushion of fat - place
• Renal arteries - large
– 20% total blood vol/min
– High blood flow & normal B/P essential for urine formation
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• Internal Structure of the Kidneys -
– Cortex - Outer layer
– Medulla - Inner port.
– Pyramids - Triangular divisions of medulla
– Papilla - narrow, end of a pyramid
– Pelvis - Expansion of upper end of ureter
– Calyx - Divisions in renal pelvis where the papilla open into
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Microscopic Structure
• Nephron - microscopic unit– Millions in each
kidney (2 million)– Shaped like a funnel
w/ convoluted stem– Two principle
components:– Renal corpuscle (2)– Renal tubule (4)
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– Renal corpuscle - 2 parts
– Bowman’s capsule - cup-shaped top of the nephron (sacklike)
– Glomerulus -network of blood capillaries tucked into Bowman’s capsule• Afferent arteriole -
delivers blood (larger)• Efferent arteriole -
drains blood (smaller)• Creates hydrostatic
pressure > filtration
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– Renal Tubule – (4)
– Proximal convoluted tubule - 1st segment, lies nearest to Bowman’s capsule (bends)
– Loop of Henle - extension of proximal tubule - straight descending limb, hairpin loop, & straight ascending limb
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– Distal convoluted
tubule - distal to loop of Henle, extension of the ascending limb
– Collecting tubule - straight part of renal tubule, distal tubules of several nephrons join into these collecting ducts
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• Renal corpuscles,
proximal & distal convoluted tubules - located in cortex
• Loop of Henle & collecting ducts - located in medulla
• Urine exits from the pyramids thru the papilla & enters calyx & renal pelvis > to ureters
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• Functions -• Efficient formation of urine is vital• Filtration - 1st step in urine formation-
fluid, electrolytes, & waste products from metabolism
• Secretion - in tubules, additional waste products
• Reabsorption - useful substances the body needs
• Protein metabolism > nitrogenous waste• Artificial kidney - may be used if kidneys
fail to fnc. appropriately
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– Waste Products - toxins, products that contain nitrogen (urea & ammonia)
– Regulating chemical levels - chloride, sodium, potassium, & bicarbonate
– Water and Salt Balance - retaining or excreting
– B/P Regulation - hormone secretion from juxtaglomerular apparatus to make constrict & raise B/P
• Normal Characteristics of Urine - pg. 441– Color - Components
– Odor - pH - Specific Gravity
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• Filtration - Bowman’s capsules of the renal corpuscles
– Blood pressure causes filtration thru membrane
– If B/P drops below certain level < filtration & urine formation <
– Glomerular filtration rate = 125ml/min
– Glomerular filtrate = 180 liters/day
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• Reabsorption - mov’t of substances out of renal tubules into blood capillaries (peritubular capillaries)
– Occurs in tubule sections
– 97% to 99% of water (178 liters) by proximal tubule
– Glucose - proximal tubules /glycosuria - DM
– Sodium ions - actively transported
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• Secretion - movement of
substances into the urine in the distal & collecting tubules from the blood
– Assists in maintaining acid-base balance
– Hydrogen & potassium ions, certain drugs are actively transported to urine
– Ammonia - diffusion
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• Control of Urine Volume -
• Hormone control of water & substance reabsorption
• ADH (antidiuretic hormone) - – From posterior pituitary gland
– Decreases the amt. of urine by making collecting tubules permeable to water > reabsorption of water
– “water-retaining” hormone
– “urine-decreasing” hormone
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• Aldosterone -– Hormone secreted form adrenal cortex
– Controls reabsorption of sodium by stimulating the tubules to reabsorb salt at a faster rate
– Also increases tubular water reabsorption
– “salt- and water-retaining” hormone
• ANH (atrial natriuretic hormone) - – Form heart’s atrial wall
– Opposite effect of aldosterone
– Stimulates tubules to secret more Na & therefore water -“salt- and water-losing”
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• Abnormal excretion of urine -
• Anuria - absence of urine
• Oliguria - scanty amt. of urine
• Polyuria - an unusually large amt. of urine
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• Ureters - Urine
begins draining from the renal pelvis – Narrow tubes (1/4
in. wide, 10-12 in. long)
– Lines w/ mucous membrane
– Thick muscular wall - peristaltic mov’t.
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• Urinalysis - – Physical, chemical, & microscopic
examination of urine
– Reveals information about the fnc. of the body
– Changes in appearance or characteristics of urine may indicate disease process
– Characteristics of urine provide general indicators of the composition of urine -
• Color - Turbidity (cloudiness)
• Odor - Specific Gravity (density)
– Char. may indicate “something” is wrong, BUT will not provide detailed information
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• Chemical Analysis -
– Information about:
• pH - urea concentration
• Presence: glucose, acetone, albumin, bile
– Urine specimen - spun in a centrifuge and suspended particles are forced to the bottom of the tube (microscope - look for abnormal cells & other particles (casts))
– Usually ordered in addition to routine urinalysis (microscopic)
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• Urinary Bladder -
• Lies in pelvis behind pubic symphysis
• If full - projects upward into the lower abdominal cavity
• Renal colic - pain associated w/ urinary tract
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– Elastic fibers &
involuntary muscle fibers in walls - expands - contracts
– Lined w/ mucous membrane
• Rugae - surface is wrinkled & lays in folds
• Trigone - triangular area - posterior surface - tightly fixed (for opens)
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• Urethra -
– Lowest part of urinary tract
– Exit to the exterior
– Covered by the same sheet of mucous membrane (infection can spread up the urinary tract)
• F - 1 1/2 inches
• M - 8 inches
– passageway of reproductive fluid
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• Micturition -
• Urination, voiding
• Passage of urine from body or emptying bladder
• Reflex in infants & small children (trained between 2 to 3 yrs.)
• Two sphincters assist in holding urine in bladder
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• Internal urethral
sphincter - bladder exit, involuntary
• External urethral sphincter - below neck of bladder, striated muscles - voluntary
• Accommodates to great varying volumes w/out need to void
• 150 ml (need) voiding at 350 ml (adults)
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• Emptying reflex -
occurs when walls stretch & nervous impulses are sent to the 2nd, 3rd, & 4th sacral segments of the spinal cord
• Bladder wall contracts Internal sph. relaxes > urine into ureter
• If external sph. relaxes - voiding occurs
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• Higher centers in the brain also fnc. in
voiding - integrate bladder contraction, internal & external sph. relaxation w/ cooperative pelvic & abdominal muscles.
• Retention - kidneys work but no urine
• Suppression - kidneys don’t work, but bladder will fnc.
• Incontinence - pt. voids involuntarily