• 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 )
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
• 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
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)
– 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
– 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
– 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
• 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
• Functions • Efficient formation of urine is vital
• Filtration - 1st step in urine formationfluid, 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
– 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
– Odor
- Components
- pH
- Specific Gravity
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
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
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
• 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
• 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”
•
•
•
•
Abnormal excretion of urine Anuria - absence of urine
Oliguria - scanty amt. of urine
Polyuria - an unusually large amt. of
urine
• Ureters - Urine
begins draining
from the renal
pelvis
– Narrow tubes
(1/4 in. wide, 1012 in. long)
– Lines w/ mucous
membrane
– Thick muscular
wall - peristaltic
mov’t.
• 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
• 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)
• Urinary Bladder -
• Lies in pelvis
behind pubic
symphysis
• If full - projects
upward into the
lower abdominal
cavity
• Renal colic - pain
associated w/
urinary tract
– 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)
• 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
• 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
• 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)
• 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
• 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