What happens between the inhale and the exhale is highly complex. Once the air reaches your lungs to inflate them it is also simultaneously filling the alveoli within them. The alveoli (millions of them) are microscopic sacks that you could think of as balloons. The alveolar membrane is the gas-exchange surface. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveoli is taken up by the blood in the alveolar blood vessels, to be transported to all the cells in the body.
Each human lung contains about 300 million alveoli (feature 1 in answer to your question). Each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area. An adult alveolus has an average diameter of 200 to 300 micrometres (feature 2), with an increase in diameter during inhalation (feature 3). The membranes of alveoli are only one cell thick, a thickness that when stretched (they are elastic) provides a greater surface area and also facilitates a more expedient gas exchange.
Capillaries are only 1 cell thick, and those that surround alveoli are also fenestrated. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste chemical substances between blood and surrounding tissues.
In humans, mature red blood cells (RBC) are flexible biconcave disks that lack a cell nucleus and most organelles. 2.4 million new erythrocytes are produced per second. Because RBCs have lost their nucleus upon maturity they only live for about 3 months and then are phagocytized by macrophages.
Another item of importance:
Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. The proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region. By adsorbing to the air-water interface of alveoli with the hydrophilic headgroups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
Each human lung contains about 300 million alveoli (feature 1 in answer to your question). Each alveolus is wrapped in a fine mesh of capillaries covering about 70% of its area. An adult alveolus has an average diameter of 200 to 300 micrometres (feature 2), with an increase in diameter during inhalation (feature 3). The membranes of alveoli are only one cell thick, a thickness that when stretched (they are elastic) provides a greater surface area and also facilitates a more expedient gas exchange.
Capillaries are only 1 cell thick, and those that surround alveoli are also fenestrated. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste chemical substances between blood and surrounding tissues.
In humans, mature red blood cells (RBC) are flexible biconcave disks that lack a cell nucleus and most organelles. 2.4 million new erythrocytes are produced per second. Because RBCs have lost their nucleus upon maturity they only live for about 3 months and then are phagocytized by macrophages.
Another item of importance:
Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. The proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region. By adsorbing to the air-water interface of alveoli with the hydrophilic headgroups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
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hmm the smaller an object the greater will the surface area be.. if you open your lungs the alveoli will cover a tennis court and its circular shape as well helps :)
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their large number.