Maintaining%20the%20Excretory%20System

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Maintaining the Excretory System
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Water Balance

• Increased water intake is adjusted for by
  increasing urine output
• The kidneys rely on the nervous and endocrine
  systems to help maintain a balance of water

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FYI

• DO NOT COPY
• Average adult loses 2 L of water a day
• Urine
• Perspiration
• Exhalation
• Drop in fluid intake
• 1 ? thirst
• 5 ? extreme pain, collapse
• 10 ? death

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Regulating ADH

• ADH (antidiuretic hormone) regulates the osmotic
  pressure in the kidneys to increase water
  absorption
• If released, more concentrated urine is produced
• ADH is released from the hypothalamus
• Shrinking of hypothalamus cells, due to
  dehydration, also creates a sensation of thirst

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• Osmoreceptors
• Nerves in hypothalamus (located in the brain)
  that detect change in osmotic pressure
• High Osmotic Pressure
• Water moves into blood stream ? hypothalamus
  shrinks ? signals release of ADH from pituitary
• ADH causes increased reabsorption of water in
  kidneys, prevents osmotic pressure from
  increasing any further

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Negative Feedback Loop
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ADH and the Nephron

• 85 of the water filtered into the nephron is
  reabsorbed in the proximal tubule
• ADH makes the upper part of the distal tubule and
  collecting duct permeable to water
• This allows NaCl in the intercellular spaces to
  create an osmotic pressure that draws water from
  the tubule back into the blood

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ADH Inhibitors

• Alcohol and caffeine are diuretics
• Increase the output of urine and decreases the
  release of ADH
• Intensifies thirst and leads to dehydration

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Kidneys and Blood Pressure

• Kidneys regulate blood pressure by regulating
  blood volume
• Aldosterone acts on nephrons to increase Na
  reabsorption
• If there is a decrease in blood pressure,
  aldosterone is produced, which increases Na
  absorption and therefore brings more water into
  the blood, increasing its volume (and therefore,
  pressure)

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Negative Feedback Loop
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Kidneys and Blood pH

• The blood pH is maintained by acid-base buffer
  systems
• The most important acid-base buffer system is the
  following equation
• H HCO3- ? H2CO3 ? H2O CO2
• pH increases pH decreases
• Turn to page 317

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pH continued

• The kidneys help to maintain this balance by
  balancing H and HCO3-
• If the blood is too acidic, H is excreted and
  HCO3- is reabsorbed and returned to the blood

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Kidney Disorders

• Kidneys are affected when other systems break
  down
• Kidney disorders can be detected by urinalysis
• Important to remember that constituents of urine
  may change throughout the day due to
• Dietary intake
• Physical activity
• Stress
• Fatigue
• Urine is always more concentrated first thing in
  the morning. (Why?)

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Urinary Tract Infection

• Bacterial or viral infection of the bladder ?
  cystitis
• Infection of the urethra ? urethritis
• More common in women than in men
• Symptoms
• Burning sensation during urination
• Frequent urination
• Bloody or brown urine
• Can result in permanent damage to kidneys,
  possible kidney failure

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Kidney Stones

• Kidney stones are collections of mineral salts
  from the blood
• These sharp stones become lodged in the pelvis or
  the ureter, causing severe pain
• Ultrasound can be used to break up these stones
  so that they will be passed in the urine
  (previously, only surgery could remove the kidney
  stones)

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Well Mr. Osborne, it may not be kidney stones
after all.
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Bright's Disease

• Aka Nephritis
• Describes many diseases characterized by
  inflammation of the nephrons
• Eg.) microbes destroy blood vessels of the
  glomerulus ? affects permeability
• Proteins pass into nephron, cant be reabsorbed
• Creates osmotic gradient