The Respiratory
System
Gas Exchange and Transport
Presented by: Shannel Morgan, Marie Rene, JC Rodriguez
Pulmonary
Gas
Exchange
Pulmonary Gas Exchange
Pulmonary gas exchange or external respiration
is the process of removing CO2 from blood and
replenishing oxygen supply.
It occurs between alveoli and the blood of lungs.
Pulmonary gas exchange occurs by diffusion and
depends on pressure gradient.
Inspired air consists of a mixture of gases
including oxygen and carbon dioxide with
individual pressures called pressure gradient.
Pulmonary Gas Exchange
Differences in the partial pressures between the
gases in the alveoli and blood create a pressure
gradient across the respiratory membrane.
When the partial pressures of O2 and CO2 are
different gas exchange occurs.
Diffusion occurs as the freshly inspired air in the
alveoli is high in O2, the O2 diffuses across the
respiratory membrane into the blood where the
concentration of O2 is low. This blood is now
‘oxygenated’ and is sent to the tissues of the body
for use.
Figure 1: Oxygen from the inhaled air diffuses through the walls of the alveoli and the capillaries into
the red blood cells, which carry it through the blood to the body tissues. Carbon dioxide produced by
the body’s tissues returns to the alveoli via the blood. It then diffuses across the capillary and
respiratory membranes into the air space to be removed by expiration
Systemic Gas
Exchange
Systemic Gas Exchange
 The exchange of gases between blood in systemic capillaries
and body cells is called internal respiration.
 Oxygen molecules move rapidly out of the blood through the systemic capillary membrane into
the interstitial fluid and cell tissues.
Carbon dioxide molecules leave cells , diffuse through the interstitial fluid then enters systemic
capillaries eventually transported to lungs for elimination from the body.
Systemic Gas Exchange
Diffusion results in the movement of oxygen from an area of high partial pressure (Po2, 100 mm
Hg) to lower partial pressure ( Po2, 40 mm Hg) in cells where it’s needed.
Diffusion is also responsible for movement of carbon dioxide from an area of high partial pressure
(Pco2, 46 mm Hg) to lower partial pressure ( Pco2,43 mm Hg) in the systemic capillaries.
Systemic Gas Exchange
Figure 2: Oxygen diffuses out of the capillary and into cells, whereas carbon dioxide diffuses out of cells and
into the capillary.
Figure 3
Blood
Transportation
of Gases
Blood Transportation of Gases
Blood transports the respiratory gases, oxygen and carbon dioxide in both dissolved or combined
states with other chemicals.
Respiratory gases dissolve in the plasma , and rapidly form a chemical union with hemoglobin or
water.
Once gas molecules bound to another molecule, their plasma concentration decreases, and more
gas can diffuse into the plasma.
Transport
of Oxygen
Transport of Oxygen
The total amount of oxygen that blood can transport is 20.4 ml in 100ml of blood,
only about 1.3 ml is dissolved.
Oxygen combines with blood to form oxyhemoglobin (Hb02) so that it can be
carried to the tissues.
Oxygenated blood is found in the systemic arteries and pulmonary veins.
Transport of Oxygen
The difference in oxygen saturation results from the release of oxygen from
oxyhemoglobin to supply body cells.
In summary, oxygen travels in two forms, as dissolved O2 in the plasma and as a
combination of O2 and hemoglobin (oxyhemoglobin).
Oxyhemoglobin carries vast majority of the total oxygen transported
TRANSPORT Of CARBON
DIOXIDE
Transport of Carbon Dioxide
Carbon dioxide is a by-product of cellular metabolism and plays a vital role in
regulating pH of body fluids.
If carbon dioxide accumulates in the body beyond normal limits, it can quickly
become toxic.
Elimination of excess Co2 from the body occurs when it enters the alveoli and
expelled during expiration.
Transport of Carbon Dioxide
Co2 must be transported in the blood in one of three forms, carbon dioxide,
carbaminohemoglobin and bicarbonate.
Approximately, 10% of the total amount of carbon dioxide in blood is carried in
the dissolved form.
This dissolved Co2 produces Pco2 of the blood plasma.
Transport of Carbon Dioxide
 About 20% of the total CO2 transported in the blood is in the form of
carbaheminoglobin ( HbCO2).
Carbaheminoglobin is formed by the union of carbon dioxide and hemoglobin.
When Co2 dissolves in water, some of the Co2 molecules associate with water
(H20) to form carbonic acid.
Transport of Carbon Dioxide
• Once formed some of the carbonic acid molecules dissociate to form hydrogen
and bicarbonate ions.
• The rate of this process is increases dramatically within red blood cells because
the presence of an enzyme called carbonic anhydrase.
Quick
Check
Question 1: What is Internal Respiration?
Answer: The exchange of gases that occurs between blood in systemic
capillaries and the body cells is called internal respiration
Question 2: In what form does most oxygen
travel in the blood?
Answer: Oxygen combines with the hemoglobin in the blood to form
oxyhemoglobin (HbO2) so that it can be carried to the tissues and used
by the body cells.
Question 3: In what three forms does
carbon dioxide travel in the blood?
Answer: Carbon dioxide is transported in the blood to the lungs in one
of three forms:
• 1. As dissolved carbon dioxide (CO2)
• 2. As carbaminohemoglobin (HbCO2)
• 3. As bicarbonate ions (HCO3−).
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