Download The Urinary System

The Urinary System
Function
• Maintain the consistency of fluids in the body
• Similar to a water purification plant
Facts
• Kidneys filter 200 liters of fluid every day
• Removes metabolic waste, ions, toxins from
the bloodstream
• Help regulate blood pressure and secretes
erythropoietin
Organs
• Kidneys
• Ureters
• Urinary
bladder
• Urethra
Kidney Location
• Superior lumbar region
• T12 to L3
• Receive some protection from the
lower ribs
• Right kidney is crowded by liver so it
lies slightly lower than left kidney
• Weighs 150g (0.33 lbs)
• 12cm long, 6cm wide, 3cm thick
(about size of large bar of soap)
Internal Anatomy
• Three regions:
– Cortex
– Medulla
• Contains renal
pyramids
– Pelvis
• Collects urine to
send down
ureter to bladder
Blood Supply
• Under normal conditions, the renal arteries
deliver approximately ¼ of blood supply to the
kidneys every minute
Nephrons
• Each kidney contains over one million
tiny processing units called nephrons
• They carry out the process of making
urine
• Each consists of:
Glomerulus – mass of capillaries
Bowman’s capsule – structure that collects
filtrate from glomerulus
Glomerulus
• Endothelium is very porous
• Large amounts of solute-rich, protein
free fluid pass from the blood to the
Bowman’s capsule
• This fluid (or filtrate) is raw material
that is processed by the renal tubules
to form urine
Renal Tubule
• Filtrate leaves the glomerulus
and travels through a set of
small tubes = tubules
• About 3 cm long
• Three parts:
1) Proximal convoluted tubule
(closer to glomerulus)
2) Loop of Henle
3) Distal convoluted tubule
Collecting Ducts
• Receive filtrate from many nephrons
• Give renal pyramids striped appearance
2
1
1
3
1
4
1
5
6
7
Quiz
• Click Here
Kidney Physiology
• Of the approximately 1000mL of blood that
passes through the glomeruli each minute,
650mL is plasma
• About of 120mL of plasma is forced into the
renal tubules
• Equivalent to filtering entire blood plasma 60
times a day = 47 gallons
• Kidneys consume 20-25% of all oxygen used
by body at rest
Filtrate vs. Urine
• Once filtrate has moved through the collecting
ducts, it has lost most of its water, nutrients
and essential ions
• What remains is called urine and contains
mostly metabolic wastes
• About 1.5L of the 180L of filtrate leaves the
body as urine
• Rest is returned to circulation
Urine Formation
Three processes:
1) Glomerular
filtration
2) Tubular
reabsorption
3) Tubular secretion
Glomerular Filtration
• For the most part, filtration is a passive,
nonselective process in which fluids and
solutes are forced through a membrane by
hydrostatic pressure
• Very efficient because of high permeability
and high blood pressure
• 55mm Hg in contrast to other capillaries in
body at 18mm Hg
Tubular Reabsorption
• Our total blood volume is filtered into the
renal tubules about every 45 minutes
• If some was not reclaimed, all of our plasma
would be drained away within an hour
• This reclaiming process is called tubular
reabsorption
Tubular Reabsorption
• All organic nutrients (glucose, amino acids) are
completely reabsorbed but the reabsorption of water
and ions are regulated by hormones
• Which hormone regulates the reabsorption of water
by adjusting the permeability of the collecting ducts?
Antidiuretic hormone
• Reabsorption of:
– Cations (Na+, K+, Mg2+, Ca2+)
– Anions (HCO3-, Cl-)
HCO3- is bicarbonate; where did that come from?
Small Intestine
Tubular Secretion
• Disposing of certain drugs (penicillin, phenobarbital –
seizures and anxiety)
• Eliminates urea
– CO(NH2)2
– How body eliminates nitrogen
• Eliminates uric acid
– C5H4N4O3
– Uric acid is a product of the breakdown of purine
nucleotides. Which ones are purines?
adenine (A) and guanine (G)
– High blood concentrations of uric acid can lead to
a type of arthritis known as gout
GOUT
Gout
Formation of Dilute Urine
• Simple process because no water is absorbed
in the renal tubules
Formation of Concentrated Urine
• Antidiuretic hormone (ADH) inhibits urine
output by increasing reabsorption of water
• During maximum ADH secretion, 99% of water
is reabsorbed and returned to blood
Diuretics
• Chemicals that increase
urinary output
– Alcohol inhibits ADH
release
– Caffeine, drugs for
hypertension and edema
from congestive heart
failure inhibit sodium ion
reabsorption which inhibits
water reabsorption
Characteristics of Urine
• Generally clear and pale to deep yellow in color
• Color results from the body’s destruction of
hemoglobin and creation of by-product bilirubin
• More water = pale urine, and vice versa
• Pink or brown urine can result from foods like
beets or rhubarb or due to bile pigments or blood
in urine
• Cloudy urine may indicate infection of some part
of urinary tract
Characteristics of Urine
Odor
– Fresh urine has a slight odor
– Urine that is allowed to stand
develops an ammonia odor due to
bacteria
– Some foods or drugs can create
unusual odor
– In persons with diabetes, urine
can smell fruity when glucose is
high
Chemical Composition
• 95% of urine is water
• 5% is solutes
– Urea
• breakdown of
amino acids
– Creatinine
• Helps regenerate
ATP, more in
skeletal muscles
– Uric acid
• Breakdown of
purines
Kidney Stones
• Caused by Ca, Mg, or uric acid salts
crystallizing in kidney
• Most are smaller than 5mm so they pass
without problems
• Larger crystals can obstruct ureter
• Prevention includes adequate hydration
• Treatment includes shock wave lithotripsy
(using ultrasound to break up stones)
Pyelonephritis
• Infection of entire kidney
• In females, usually caused
by E. coli bacteria from
anal area into urinary tract
• Severe cases can result in
abscesses that cause
kidney to fill with pus
• If left untreated, kidneys
can be damaged
• Causes:
Renal Failure
– Repeated damage from infections
– Physical injury to kidneys
– Crush injury to skeletal muscles (releases
myoglobin that clogs renal tubules)
– Heavy metal poisoning (Hg or Pb)
– Organic solvent poisoning (paint thinner,
acetone, dry-cleaning fluid, etc.)
– Inadequate blood supply (can occur in
arteriosclerosis)
Physiology of Renal Failure
• Filtrate formation decreases or stops
• Nitrogen waste builds up
• Blood pH becomes more acidic
Hemodialysis
• Artificial kidney
• Patient’s blood is passed through membrane
tubing that is permeable and wastes diffuse
out of blood
• Usually done 3-4 times per week and each
session takes 4-8 hours
• Life threatening kidney failure only becomes
obvious after about 75% of renal function has
been lost
• Only permanent solution is kidney transplant
Ureters
• Tubes that take urine
from each kidney to
bladder
• Each begins at L2
• Stretching of ureters
causes peristalsis to
push urine down
Urinary Bladder
• Smooth, collapsible,
muscular sac that
temporarily stores
urine
• A moderately full
bladder holds about
500mL of urine (2
cups)
Urethra
• Thin walled muscular tube that drains
urine from the bladder to outside the
body
• Has sphincters:
Internal – involuntary sphincter keeps
urethra closed when urine is not being
passed
External – voluntary sphincter that relaxes
during voiding of urine
Urinary Tract Infections
• Overall, 40% of all women get UTIs
–Urethra is only 3-4 cm long
–Proximal to anal opening
–Improper toilet habits
–Sexual intercourse can cause vaginal
bacteria to move into urethra
Incontinence
• Inability to control urination
– Infants have not learned to control external sphincter
– In older adults, the sphincter malfunctions
Crash Course
• Video
About 12 minutes