Describe the process of gas exchanges in the lungs and tissues. Describe how oxygen and carbon dioxide are transported in the blood. Flashcards
What is the role of blood in gas exchange, and what processes are involved?
Blood returning from the body delivers carbon dioxide (CO₂) to the lungs and picks up oxygen (O₂) during external respiration (pulmonary gas exchange).
In the systemic circuit, blood delivers oxygen (O₂) to body tissues and picks up carbon dioxide (CO₂).
External respiration is the gas exchange between the alveoli and blood (pulmonary gas exchange), while internal respiration is the exchange between the blood and tissue cells (systemic capillary gas exchange).
All gas exchanges obey the laws of diffusion, where gases move from areas of higher concentration to areas of lower concentration.
Q: What happens during external respiration?
During external respiration, reduced oxygen blood (dark red) in the pulmonary circuit is transformed into oxygen-rich blood (scarlet) as it picks up oxygen (O₂) and unloads carbon dioxide (CO₂) in the lungs.
The color change of blood is due to oxygen binding to hemoglobin in the lungs, while CO₂ is released.
Because the alveoli always have more oxygen than the blood, oxygen diffuses from the alveoli into the pulmonary capillaries, where the blood has less oxygen.
Q: What happens during internal respiration and how does it differ from external respiration?
During internal respiration, tissue cells remove oxygen (O₂) from the blood and release carbon dioxide (CO₂) into the blood.
The concentration of CO₂ is much higher in the pulmonary capillaries than in the alveolar air, so CO₂ diffuses from the blood into the alveoli, where it will be expelled during expiration.
Blood draining from the lungs into the pulmonary veins is rich in oxygen and poor in carbon dioxide, in contrast to the blood entering the lungs from the body.
How is oxygen transported in the blood?
Most oxygen is transported by attaching to hemoglobin molecules inside red blood cells (RBCs) to form oxyhemoglobin.
A small amount of oxygen is carried dissolved in the plasma.
How is carbon dioxide transported in the blood?
Carbon dioxide (CO₂) is 20 times more soluble in plasma than oxygen.
Most CO₂ is transported in plasma as bicarbonate ion (HCO₃⁻), which plays a crucial role in buffering blood pH.
CO₂ is enzymatically converted to bicarbonate ion inside red blood cells. The newly formed bicarbonate ions then diffuse into the plasma.
How is carbon dioxide carried inside red blood cells (RBCs)?
20-30% of carbon dioxide is carried inside RBCs bound to hemoglobin.
Carbon dioxide binds to hemoglobin at a different site than oxygen, so it does not interfere with oxygen transport.
How is carbon dioxide released from its bicarbonate form in the blood?
Before carbon dioxide can diffuse into the alveoli, it must first be released from its bicarbonate ion form.
Bicarbonate ions (HCO₃⁻) enter red blood cells where they combine with hydrogen ions (H⁺) to form carbonic acid (H₂CO₃).
Carbonic acid quickly splits to form water (H₂O) and carbon dioxide (CO₂).
The carbon dioxide then diffuses from the blood into the alveoli.
What is hypoxia, and how does carbon monoxide poisoning affect oxygen transport?
Hypoxia is a condition where there is inadequate oxygen delivery to body tissues. It can be recognized in light-skinned individuals by a bluish skin color (cyanosis), and in dark-skinned individuals, it is visible in the mucosae and nailbeds.
Hypoxia can result from anemia, pulmonary disease, or impaired blood circulation.
Carbon monoxide (CO) poisoning is a unique form of hypoxia. CO competes with oxygen for binding sites on hemoglobin, but binds more readily to hemoglobin than oxygen, displacing oxygen.
Carbon monoxide poisoning is dangerous and may not show typical hypoxia signs like cyanosis. Victims experience confusion, a throbbing headache, and in rare cases, cherry red skin.
Treatment involves administering 100% oxygen to clear carbon monoxide from the body.
What occurs during internal respiration, and how is carbon dioxide and oxygen exchanged in the tissues?
Internal respiration is the exchange of gases between the blood and tissue cells, opposite of what happens in the lungs.
Oxygen leaves the blood and carbon dioxide enters the blood.
Inside red blood cells (RBCs), carbon dioxide combines with water to form carbonic acid, which then releases bicarbonate ions (HCO₃⁻), with the help of the enzyme carbonic anhydrase.
Bicarbonate ions diffuse into the plasma to be transported.
At the same time, oxygen is released from hemoglobin, diffuses into the cells, and is used in cellular processes.
As a result, venous blood in the systemic circulation is poorer in oxygen and richer in carbon dioxide compared to the blood leaving the lungs.
