The transport of respiratory gases, specifically oxygen (O2) and carbon dioxide (CO2), between the lungs and the tissues of the body is a crucial physiological process.
This transport is essential for cellular respiration, which is the process by which cells produce energy.
Here's an overview of how these gases are transported in the human body:
Oxygen Transport
1. Oxygen Uptake in the Lungs:
Oxygen is inhaled into the lungs, where it diffuses across the alveolar-capillary membrane into the blood.
2. Binding with Hemoglobin:
In the blood, oxygen binds to hemoglobin, a protein found in red blood cells.
Hemoglobin can carry up to four oxygen molecules at a time. This oxygen-hemoglobin complex is referred to as oxyhemoglobin.
3. Transport to Tissues:
Oxygenated blood is then circulated through the body via the arteries and arterioles to the capillaries, where oxygen is released to the tissues.
4. Oxygen Release:
The release of oxygen from hemoglobin is influenced by various factors, including the concentration of oxygen and carbon dioxide in the blood, blood pH, temperature, and the presence of 2,3-bisphosphoglycerate (2,3-BPG).
Carbon Dioxide Transport
1. CO2 Production:
Carbon dioxide is produced as a waste product of cellular respiration and must be removed from the body to maintain homeostasis.
2. Transport Forms:
CO2 is transported in the blood from the tissues to the lungs in three main forms:
Dissolved CO2: A small amount of CO2 is transported dissolved in the plasma.
Bicarbonate (HCO3-): The majority of CO2 is transported in the form of bicarbonate ions. CO2 reacts with water in the presence of the enzyme carbonic anhydrase, forming carbonic acid, which then dissociates into bicarbonate and hydrogen ions.
Carbaminohemoglobin: CO2 also binds directly to hemoglobin, but at a different site than oxygen, forming carbaminohemoglobin.
3. CO2 Release in the Lungs:
When blood reaches the lungs, the processes that converted CO2 into bicarbonate and carbaminohemoglobin are reversed.
CO2 is released from hemoglobin, converted back from bicarbonate to CO2 gas, and then exhaled.
Regulation of Gas Transport
The transport and release of O2 and CO2 are finely regulated to meet the metabolic demands of the body.
This regulation involves changes in blood flow, hemoglobin affinity for oxygen, and the rate and depth of breathing, all of which are influenced by neural and chemical controls.