The Respiratory System

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The Respiratory System Ventilation moving air
into and out of lungs Gas exchange diffusion
through lung tissue Oxygen utilization in cell
respiration
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The conducting and respiratory zones
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Properties of lungs Compliance- ability to
expand when stretched Elasticity- ability to
return to original size Surface tension exerted
by fluid in alveoli Surfactant helps prevent
alveoli from collapsing RDS-surfactant lacking
in the lungs of premature babies ARDS- alveolar
permeability and reduced surfactant
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Ventilation is a mechanical process
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Restrictive disorders- vital capacity is
reduced FEV is normal Obstructive disorders-
FEV is reduced, vital capacity is normal, e.g.,
asthma Bronchoconstriction- resistance to air
flow Inflammation- clogs air passages Emphysema-
destruction of alveoli COPD- obstructive and
restrictive chronic bronchitis and emphysema
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Partial pressures of oxygen and carbon
dioxide Most O2 in blood is bound to RBCs (0.3ml
out of 20 ml/100 ml blood is dissolved in
plasma) Increasing PO2 in blood increases rate
of diffusion to tissues Arterial levels are
significant because they reflect lung function
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Regulation of breathing

• Voluntary
• Somatic motor neurons controlled by centers in
  medulla oblongata and pons
• Involuntary
• Feedback from receptors that detect changes in
  blood chemistry

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Chemoreceptor control of breathing

• Mostly controlled by chemoreceptors in medulla
• CO2 can cross blood-brain barrier
• Increased CO2 lowers blood pH
• Peripheral receptors are affected by H
  concentration
• Oxygen levels do not change as fast

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Blood CO2 levels are most immediately
affected by changes in breathing (affects blood
pH) Carotid and aortic bodies respond to changes
in pH Oxygen levels do not change as
fast Sensitivity to oxygen augments sensitivity
to carbon dioxide (ventilation rate
increases at high altitude)
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Hemoglobin and oxygen transport Loading (in
lungs) deoxyhemoglobin becomes oxyhemoglobin
reversed in tissues Affinity for oxygen
decreases in lower pH and higher
temperature 2,3-DPG (unique to RBCs) also
reduces affinity of oxyhemoglobin for oxygen
(this works if oxygen levels are low or in
anemia) Net effect favors unloading of oxygen
into tissues
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Carbon dioxide transport and acid-base
balance Carbon dioxide is converted to carbonic
acid by carbonic anhydrase in red blood
cells Hydrogen ions are produced these
combine with hemoglobin This promotes unloading
of oxygen from hemoglobin
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pH balance Hypoventilation- acidosis Hyperventil
ation- alkalosis Normal blood pH is 7.35-7.45
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Compensations for exercise and high
altitude Exercise ventilation increased oxygen
delivery to tissues increased by vasodilation in
creased temperature lowers affinity for oxygen
so is released to tissues lactate threshold-
higher in physically fit people (they have
higher maximal oxygen uptake)
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Adaptations to high altitude
Polycythemia can be dangerous
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Summary

• Designed for ventilation, gas exchange, and
  transport of gases through blood
• Muscles of respiration are controlled
  autonomically through medulla oblongata and pons
• Chemoreceptors detect changes in carbon dioxide,
  hydrogen, and oxygen levels in the blood
• Environmental factors affect affinity of
  hemoglobin for oxygen
• Ventilation helps regulate acid-base balance in
  blood
• Respiratory system adapts to extremes of
  exercise and high altitude