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chapter
6
The Respiratory
System and Its
Regulation
Anatomy of the Respiratory System
Transportation of Oxygen and
Carbon Dioxide
1. Pulmonary ventilation (breathing): movement of air into and out of
the lungs
Air is drawn in the lungs via the nose and the mouth. It is drawn in
via the mouth when the demand for air exceeds what the nose
can bring in.
From the nose and mouth the air travels through the pharynxlarnyx-trachea-and into the left and right bronchi-bronchiolesalveoli
Gas exchange occurs in the alveoli. This is known as the
respiratory zone.
Boyle’s Law
• The pressure within the lungs is less than the
pressure outside of the body.
• Because the respiratory tract is open to the
outside, air (oxygen) rushes into the lungs
during inspiration.
Pulmonary Ventilation
Inspiration: active process involving the diaphragm
(flattens out) and the external intercostal muscles (move
ribs and sternum out of the way.
–Pressure in the lung is less than the air pressure
outside the body, air following the pressure gradient
coming into the lung
Expiration: usually a passive process involving
relaxation of the inspiratory muscles; pressure
increases in the lungs and air is forced out
–Active process during forced breathing
Pulmonary Diffusion
• Gas exchange in the lungs
• Replenishes blood's oxygen supply that has been
depleted for oxidative energy production
• Removes carbon dioxide from returning venous blood
Pulmonary Volumes
• Tidal Volume: Amount of air leaving and
entering lungs with each breath
• Vital Capacity: The greatest amount of air
that can be expired after a maximal
inspiration
• Residual Volume: Amount of air left in the
lungs after a maximal expiration’
• Total Lung Capacity: The sum of vital
capacity and residual volume.
Blood Flow to the Lungs at Rest
• At rest the lungs receive approximately 4 to
6 L/min of blood flow, depending on body
size.
Respiratory Membrane:
Gas Exchange
• Gas exchange between the air in the alveoli and the
blood in the pulmonary capillaries occurs across the
respiratory membrane. This membrane consists of the:
Alveolar wall
Capillary wall
Basement membranes (0.5-4.0 microns thick)
• Gases will move along a concentration gradient based
on partial pressures
• The air we breath is composed of 79.04% Nitrogen,
20.93% oxygen and 0.03% carbon dioxide.
Anatomy of the Respiratory
Membrane
Gas Exchange Cont.
• If the pressure on each side of the
membrane is equal, the gases would be in
equilibrium and would not move.
• When the deoxygenated blood goes into the
lungs for oxygen the pressure within the
capillaries is lower than in the alveoli
therefore, the oxygen will move from the
alveoli into the capillaries to be transported
back to the heart.
Oxygen Transport
• Oxygen is transported bound to hemoglobin (protein)
(>98%) or dissolved in plasma (<2%)
• Hemoglobin concentration largely determines the oxygencarrying capacity of blood
• 1 liter of plasma= 3mL of oxygen (a total of 3-5L of blood
plasma in the body for a total of 9-15 mL of Oxygen
• A resting body needs at least 250 mL of oxygen per minute
• Hemoglobin contains approximately 4-6 billion red blood
cells allowing blood to transport nearly 70 times more
oxygen than can be dissolved in plasma.
• Oxygen carrying capacity seldom limits performance in
healthy individuals
Blood Oxygen-Carrying Capacity
• Each 100mL of blood contains an average of 14 to 18g of
hemoglobin (protein that transports oxygen) in men and 12-16g
in women. (1 L = 1,000 mL)
• Each gram of hemoglobin can combine with 1.34 mL of oxygen,
so the oxygen carrying capacity of blood is approximately 16-24
mL per 100 mL of blood.
• When fully saturated with oxygen a man (5 L of blood) will have
approximately 188 mL to 241 mL of oxygen.
• During rest, the blood passes through the lungs and is in
contact with the alveoli for .75 seconds, enough time to become
98-99% saturated with oxygen
• At high intensities the contact time is reduced and the saturation
of oxygen is slightly reduced.
Carbon Dioxide Transport
• Bicarbonate ions: Bicarbonate ions (released by
hemoglobin) maintain the pH balance by offsetting the
hydrogen ions (H+) that are the result of carbon
dioxide in the blood. Accounts for 60-70%
transportation of carbon dioxide in the blood
• Dissolved in blood plasma: 7-10% of carbon dioxide
is transported this way.
• Bound to hemoglobin (carbaminohemoglobin)
20-30% of carbon dioxide is transported in this
manner.
Gas Exchange at the Muscles:
Arterial–Venous Oxygen Difference
A-Vo2 Difference
• The amount of oxygen in the arterial blood
as opposed to the amount of oxygen in the
venous blood.
• The blood is less in the venous blood
because it has be delivered to the cells of
the body.
Oxygen Transport in the Muscle
• Oxygen is transported in the muscle to the
mitochondria by a molecule called
myoglobin.
• Gives the muscle a red colored appearance
Factors Affecting Oxygen Uptake
and Delivery
1. Oxygen content of blood: Under normal conditions,
hemoglobin is about 98% saturated with oxygen
2. Amount of blood flow: Increased blood flow
increases oxygen delivery however, it also has to
make up for the diminished amount of oxygen in
the blood.
3. Local conditions within the muscle: Increase in
physical stress means increase in muscle temp,
which means increase in oxygen delivery. Increase
in muscle activity also means increase in lactate
production which improves oxygen delivery.
Regulation of Pulmonary Ventilation
• Higher brain centers
– Expiratory centers
– Inspiratory centers
• Chemoreceptors
• Mechanoreceptors in the active muscles and the lung
muscles
• Hypothalamic input
• Conscious control