Gas and Fluid Concentration

• fluid gain must be equal to fluid loss
• water intake (2.5L)

  • food 700mL
  • metabolic water 200 mL
  • drinking 1.6L
• Water loss (2.5L)

  • lungs 300mL
  • skin 500mL
  • kidneys 1.5L
  • alimentary canal 200mL
• selective reabsorption in the nephron

  in the proximal convoluted tubule and loop of henle

  water via osmosis, Cl- and K+ leave the nephron
• active reabsorption in the nephron

  distal convoluted tubule and collecting duct

  Na+ and Water (controlled by ADH) leaves tubule
• Aldosterone acts to increase sodium in blood from filtrate and increase potassium to be secreted back to the nephron, by targeting the PCT, DCT and collecting duct
• Nephron structure

  A) glomerular capsule

  B) glomerulus

  C) afferent arteriole

  D) efferent arteriole

  E) proximal convoluted tubule

  F) loop of Henle

  G) distal convoluted tubule

  H) collecting duct

  
• Negative feedback loop of osmoregulation due to water loss (ADH)


  1. Stimulus - decrease in water in blood plasma (increase osmotic pressure)

  2. Receptor - osmoreceptor in hypothalamus (detects high OP)

  3. Modulator - hypothalamus sends a message to posterior pituitary to release ADH

  4. Message - ADH is released into the bloodstream

  5. Effector - nephron - DCT and collecting duct

  6. Message - permeability of DCT and collecting duct to water in increased so water is diffused to surrounding capillary network

  7. Response - increase in the amount of water reabsorbed into the blood plasma

  8. Feedback - increase in water in blood plasma (decrease osmotic pressure)
• regulating water intake behaviourally

  1. stimulus - decrease in water in blood (increased osmotic pressure)
  2. receptor - osmoreceptor in hypothalamus (detects high OP)
  3. modulator - thirst centre in hypothalamus
  4. message - person feels thirsty due to dry mouth
  5. effector - mouth (dry), skeletal muscles in arm
  6. message - person responds to feeling of thirst by drinking water
  7. response - water is drunk and absorbed into blood from alimentary canal
  8. feedback - increase in water in blood plasma (decreased osmotic pressure)
• dehydration

  use or loss of more fluid than you take in

  caused by severe diarrhea, vomiting, medications, illnesses, not drinking enough, hot weather
• water intoxication

  disruption of brain function due to drinking too much water

  increases the amount of water in blood which dilutes electrolytes such as sodium
• alcohol is a diuretic which increases the amount of urine produced by inhibiting ADH from being release which has a dehydrating effect
• control of breathing

  • diaphragm and intercostal muscles controlled by respiratory centre in medulla oblongata
  • diaphragm stimulated by phrenic nerve
  • intercostal muscles stimulated by intercostal nerves
• peripheral chemoreceptors

  • aortic bodies - in walls of aorta
  • carotid bodies - found in carotid arteries
  • sensitive to changes in oxygen, carbon dioxide and hydrogen levels in blood plasma
• central chemoreceptors

  • in medulla oblongata
  • sensitive to changes in carbon dioxide in blood and hydrogen levels in cerebrospinal fluid
• oxygen must fall significantly before breathing rate and depth increases
• a large decrease in oxygen concentration will cause a nerve impulse to travel to the respiratory centre which will relay a nerve impulse back to the respiratory muscles to cause an increase in breathing rate and depth
• a slight increase in carbon dioxide will cause a marked increase in breathing rate and depth
• an increase in carbon dioxide causes an increase is hydrogen
• carbon dioxide dissolves in water to form carbonic acid which breaks down to form hydrogen ions and bicarbonate ions
• inhalation:

  • peripheral chemoreceptor impulse to respiratory centre of medulla oblongata
  • stimulates nerve impulses to pass along phrenic and intercostal nerves
  • phrenic nerve stimulates diaphragm to contract
  • intercostal nerve stimulates intercostal muscles to contract
  • increases volume of thoracic cavity (stretch receptors) decreasing pressure in lungs and the individual breathes in
• exhalation

  • walls of lungs stimulated (stretch receptors) - nerve impulse from vagus nerve prevents further stimulation
  • thoracic cavity decreases in volume and pressure increases causing exhalation
• holding your breath causes build up of carbon dioxide in blood plasma which stimulates involuntary impulses to inspiratory muscles to take a breath
• hyperventilation is when the rate of breathing is too fast and more air is exhaled than inhaled causing reduced carbon dioxide in the blood which causes narrowing blood vessels to the brain. The individual would then feel light-headed or dizzy and be forced to take more air in
• hyperventilation can be caused by physical stress or can be voluntary and usually corrects itself as chemoreceptors unstimulated by carbon dioxide causes a reduced breathing rate
• Changes in carbon dioxide concentration:

  1. stimulus - increase in carbon dioxide concentration, increase in hydrogen, decrease pH
  2. receptor - chemoreceptors in respiratory centre, carotid and aortic bodies
  3. modulator - respiratory centre in medulla oblongata
  4. message - message sent along phrenic and intercostal nerves
  5. effector - respiratory muscles (diaphragm and intercostal muscles)
  6. response - increase in stimulation of respiratory muscles (contraction/relaxation), increase in breathing rate and depth
  7. feedback - decrease in carbon dioxide, decrease in hydrogen, increase in pH