The Urinary System

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The Urinary System
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Function

• Maintain the consistency of fluids in the body
• Similar to a water purification plant

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Facts

• Kidneys filter 200 liters of fluid every day
• Removes metabolic waste, ions, toxins from the
  bloodstream
• Help regulate blood pressure and secretes
  erythropoietin

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Organs

• Kidneys
• Ureters
• Urinary bladder
• Urethra

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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)

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Internal Anatomy

• Three regions
• Cortex
• Medulla
• Contains renal pyramids
• Pelvis
• Collects urine to send down ureter to bladder

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Blood Supply

• Under normal conditions, the renal arteries
  deliver approximately ¼ of blood supply to the
  kidneys every minute

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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
• Bowmans capsule structure that collects
  filtrate from glomerulus

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Glomerulus

• Endothelium is very porous
• Large amounts of solute-rich, protein free fluid
  pass from the blood to the Bowmans capsule
• This fluid (or filtrate) is raw material that is
  processed by the renal tubules to form urine

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Renal Tubule

• Filtrate leaves the glomerulus and travels
  through a set of small tubes tubules
• About 3 cm long
• Three parts
• Proximal convoluted tubule (closer to glomerulus)
• Loop of Henle
• Distal convoluted tubule

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Collecting Ducts

• Receive filtrate from many nephrons
• Give renal pyramids striped appearance

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Quiz

• Click Here

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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

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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

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Urine Formation

• Three processes
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion

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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

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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

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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

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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

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GOUT
Gout
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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

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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

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Characteristics of Urine

• Generally clear and pale to deep yellow in color
• Color results from the bodys 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

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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

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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

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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)

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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

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Renal Failure

• Causes
• 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)

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Physiology of Renal Failure

• Filtrate formation decreases or stops
• Nitrogen waste builds up
• Blood pH becomes more acidic

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Hemodialysis

• Artificial kidney
• Patients 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

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Ureters

• Tubes that take urine from each kidney to bladder
• Each begins at L2
• Stretching of ureters causes peristalsis to push
  urine down

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Urinary Bladder

• Smooth, collapsible, muscular sac that
  temporarily stores urine
• A moderately full bladder holds about 500mL of
  urine (2 cups)

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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

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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

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Incontinence

• Inability to control urination
• Infants have not learned to control external
  sphincter
• In older adults, the sphincter malfunctions

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Crash Course

• Video
• About 12 minutes