Respiratory System

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Respiratory System

• 6.4 D6

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Partial Pressure

• Partial pressure the pressure exerted by each
  component in a mixture.
• The pressure of a gas in a mixture is the same as
  the pressure it would exert in the same volume
  and temperature alone.

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Oxygen Dissociation Curves

• Oxygen binds to hemoglobin of erythrocytes.
• (oxyhemoglobin HbO2)
• Each hemoglobin can bind a maximum of 4 molecules
  of oxygen (1 for each heme group)
• If the maximum number of oxygen molecules have
  attached, the hemoglobin is fully saturated.

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When the pO2 is 100mmHg, the HbO2 is 100 (That
means there are 4 O2 bonded to each hemoglobin
molecule. See Fig 1, page 700
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• The amount of saturation of hemoglobin depends on
  the concentration of oxygen in the air
• pO2 depends on the concentration of oxygen in the
  air and the air pressure.
• If O2 decreases, the pO2 decreases
• If air pressure decreases, pO2 decreases

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Oxygen Dissociation Curve

• The pO2 in the lungs is high (100mm Hg), which
  encourages hemoglobin to become saturated with
  pO2.
• The pO2 in the muscles is low (20 mm Hg) which
  encourages pO2 to dissociate from hemoglobin and
  enter the cells where they are needed.

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High Altitudes

• At higher altitudes, the air pressure decreases,
  and so does the pO2.
• The means that the saturation of hemoglobin is
  lower
• i.e. less oxygen bonded to hemoglobin and
  therefore less oxygen transported by the rbcs

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• The reduced air pressure also reduces the rate of
  diffusion of gases across the respiratory
  membrane
• As a result, less oxygen is available for the
  body cells
• This can cause altitude sickness
• SYMPTOMS shortness of breath, headaches,
  dizziness, tiredness, nausea, alkalemia (high
  blood pH)

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• Your body will adjust after a few days.
• Increase ventilation rate (shallower, more
  frequent breaths
• The kidneys will excrete akaline urine (blood
  remains acidic, continues increased ventilation
  rate)
• Over time, when O2 supply is reduced, the body
  will secrete the hormone erythropoietin (EPO)
  which will increases the number of red blood
  cells in the body.

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• An increase in rbc, means and increase in O2
  absorption, which means more O2 for the body
  cells.
• People who permanently live at high altitues will
  also have a greater lung surface area and larger
  vital capacity than those living at sea level.

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Altitude and Athletic Training

• Endurance athletes (long-distance runners and
  triathletes) often train at high altitudes for a
  few weeks to increase their rbc so they have more
  O2 and therefore more ATP energy for their event

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Sea Level

• At sea level, air pressure is 760 mm Hg
• 21 oxygen
• pO2 0.21 x 760 159 mm Hg
• pO2 of air in the alveoli is 100 mm Hg
• Because water vapour added, and
• pO2 in active muscles is 20 mm Hg

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Oxygen Dissociation Curve

• Sigmoid shaped curve (S-shape)
• Caused by cooperative binding
• When the first oxygen molecule binds, the
  hemoglobin changes slightly in shape
• This makes it easier for the next molecule to
  bind

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Fetal Hemoglobin

• A pregnant mother and her unborn baby have
  separate circulatory systems
• The fetus hemoglobin must be capable of taking
  oxygen from the mothers hemoglobin in the
  placenta.

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Fetal hemoglobin

• Fetal hemoglobin (HbF) is structurally different
  from normal hemoglobin (HbA)
• This causes it to have a higher affinity for
  oxygen.
• So oxygen will dissociate from maternal
  hemoglobin and bind to fetal hemoglobin

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Myoglobin

• When oxygen reaches the muscles, the oxygen is
  taken over and stored by myoglobin.
• Therefore, myoglobin must have a higher affinity
  for oxygen than hemoglobin

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• Myoglobin is made of 1 polypeptide chain
  (hemoglobin is made of 4)
• Therefore, only 1 heme group and therefore
  myoglobin can only bind one oxygen molecule.
• So no cooperative binding
• Curve is not sigmoidal

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The Bohr Effect

• The pH of the blood is directly related to the
  CO2 concentration
• As CO2 in the blood increases, pH lowers (gets
  more acidic)
• Why?

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WHY?

• Remember, 70 of CO2 is transported to the lungs
  as bicarbonate ions.
• The formation of bicarbonate produces H
• And an increase in H means a more acidic
  environment
• CO2 H2O ? H2CO3 (carbonic acid)
• H2CO3 ? H HCO3-
• So more CO2 means more H which means more acidic
  environment (ie lower pH)!!!

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The Bohr Effect

• Remember
• A change in pH will change the ionization of a
  protein
• This will change the shape and functionality of
  the protein
• A lower pH will cause the oxygen dissociation
  curve of hemoglobin to shift to the right
• This is known as the BOHR SHIFT

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Bohr Shift

• This means that the saturation of hemoglobin is
  reduced (does not hold on to O2 as well)
• Which means, that more O2 is released from the
  hemoglobin
• So increased CO2 concentration will reduce the
  saturation of hemoglobin and release more oxygen
  to the cells
• This is good because pH is lower when cells are
  respiring and need more O2 anyway!