The Respiratory System and Its Regulation

1
chapter
6
The Respiratory System and Its Regulation
2
External Respiration

• Pulmonary ventilation involves inspiration and
  expiration.
• Pulmonary Diffusion is the exchange of oxygen and
  carbon dioxide between the lungs and the blood.

3
RESPIRATORY SYSTEM
4
Process of Inspiration and Expiration
5
Lung Volumes Measured by Spirometry

• Reprinted, by permission, from J. West, 2000,
  Respiratory physiology The essentials
  (Baltimore, MD Lippincott, Williams, and
  Wilkins), 14.

6
Pulmonary Diffusion

• Replenishes blood's oxygen supply that has been
  depleted for oxidative energy production
• Removes carbon dioxide from returning venous
  blood
• Occurs across the thin respiratory membrane

7
Laws of Gases

• Dalton's Law The total pressure of a mixture of
  gases equals the sum of the partial pressures of
  the individual gases in the mixture.
• Henry's Law Gases dissolve in liquids in
  proportion to their partial pressures, depending
  on their solubilities in the specific fluids and
  depending on the temperature.

8
Partial Pressures of Air

• Standard atmospheric pressure (at sea level) is
  760 mmHg.
• Nitrogen (N2) is 79.04 of air the partial
  pressure of nitrogen (PN2) 600.7 mmHg
• Oxygen (O2) is 20.93 of air PO2 159.1 mmHg.
• Carbon dioxide (CO2) is 0.03 PCO2 0.2 mmHg.

9
Did You Know?

• The solubility of a gas in blood and the
  temperature of blood are relatively constant.
  Differences in the partial pressures of gases in
  the alveoli and in the blood create a pressure
  gradient across the respiratory membrane. This
  difference in pressures leads to diffusion of
  gases across the respiratory membrane. The
  greater the pressure gradient, the more rapidly
  oxygen diffuses across it.

10
Comparison of Pressure (mmHg) in the Pulmonary
and Systemic Circulations

• Reprinted, by permission, from J. West, 2000,
  Respiratory physiology The essentials
  (Baltimore, MD Lippincott, Williams, and
  Wilkins), 36.

11
Anatomy of the Respiratory Membrane
12
Partial Pressures of Respiratory Gases at Sea
Level
13
Key Points

• Pulmonary Diffusion
• Pulmonary diffusion is the process by which gases
  are exchanged across the respiratory membrane in
  the alveoli to the blood and vice versa.
• The amount of gas exchange depends on the partial
  pressure of each gas.
• Gases diffuse along a pressure gradient, moving
  from an area of higher pressure to lower
  pressure.
• (continued)

14
Key Points (continued)

• Pulmonary Diffusion
• Oxygen diffusion capacity increases as you move
  from rest to exercise.
• The pressure gradient for carbon dioxide exchange
  is less than for oxygen exchange, but carbon
  dioxides membrane solubility is 20 times greater
  than oxygen, so CO2 crosses the membrane easily.

15
Oxygen Transport

• Hemoglobin concentration largely determines the
  oxygen-carrying capacity of blood.
• Increased H (acidity) and temperature of a
  muscle allow more oxygen to be unloaded there.
• Training affects oxygen transport in muscle.

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Oxyhemoglobin Dissociation Curve
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Carbon Dioxide Transport

• Dissolved in blood plasma (7 to 10)
• As bicarbonate ions resulting from the
  dissociation of carbonic acid (60 to 70)
• Bound to hemoglobin (carbaminohemoglobin) (20 to
  33)

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ArterialVenous Oxygen Difference
19
Did You Know?

• The increase in (a-v)O2 difference during
  strenuous exercise reflects increased oxygen use
  by muscle cells. This use increases oxygen
  removal from arterial blood, resulting in a
  decreased venous oxygen concentration.

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Factors Affecting Oxygen Uptake and Delivery

• 1. Oxygen content of blood
• 2. Amount of blood flow
• 3. Local conditions within the muscle

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Key Points

• External and Internal Respiration
• Oxygen is largely transported in the blood bound
  to hemoglobin and in small amounts by dissolving
  in blood plasma.
• Hemoglobin saturation decreases when PO2 or pH
  decreases or if temperature increases. These
  factors increase oxygen unloading in a tissue
  that needs it.
• Hemoglobin is usually 98 saturated with oxygen,
  which is higher than what our bodies require, so
  the blood's oxygen-carrying capacity seldom
  limits performance.
• (continued)

22
Key Points (continued)

• External and Internal Respiration
• Carbon dioxide is transported in the blood as
  bicarbonate ion, in blood plasma or bound to
  hemoglobin.
• The (a-v)O2 differencea difference in the oxygen
  content of arterial and venous bloodreflects the
  amount of oxygen taken up by the tissues.
• Carbon dioxide exchange at the tissues is similar
  to oxygen exchange except that it leaves the
  muscles and enters the blood to be transported to
  the lungs for clearance.

23
Regulators of Pulmonary Ventilation at Rest

• Higher brain centers
• Chemical changes within the body
• Chemoreceptors
• Muscle mechanoreceptors
• Hypothalamic input
• Conscious control

24
Pulmonary Ventilation

• Ventilation (VE) is the product of tidal volume
  (TV) and breathing frequency (f)
• VE TV x f