Respiration: It's not just about "breathing" anymore!
Ask a student to list "the most basic human needs" and they sometimes answer... "The ABC's! Airway, breathing, circulation". In so doing, the student has referenced only one basic human need (oxygenation) and barely scratched the surface explaining this one. "Respiration" has 2 phases: 1) physiological respiration: getting oxygen in to the body, all the way to the mitochondria of each cell, and 2) cellular respiration: the biochemical actions that occur within mitochondria to turn oxygen and glucose in to ATP, the energy that sustains life.
Physiological Respiration: 4 phases
1. Ventilation: (Or what we usually mean when we say the word "respiration" or count "respirations" when we do vital signs.) This is where molecules of oxygen are drawn from the atmosphere all the way to the alveoli. It requires perfect functioning of the neuromuscular connections from the respiratory control centers in the medulla, to the motor neurons that serve the muscles of respiration, an intact lung-chest apparatus, open cartilagenous and non-cartilagenous airways and sufficient membrane surface for gasses to diffuse across. But ventilation has a flip-side as well since these same structures are the means of blowing CO2 back out of the body and into the atmosphere.
2. Pulmonary Gas Exchange: This is what happens at "the business end" of the airway. The single-cell thickness of the alveolar wall is almost contiguous with the single cell thickness of the associated capillary wall. Gasses move very easily across these membranes. Carbon dioxide diffuses 20 times faster than oxygen, however. When oxygen crosses the alveolar capillary membrane and becomes dissolved in the plasma, it stays there only briefly. This is because it is exposed to high affinity binding sites on hemoglobin molecules that are crammed into each red blood cell.
3. Gas Transport: This is exactly what it sounds like. This is the movement of those hemoglobin bound oxygen molecules from the capillary vasculature of the lung, to the heart, out the aorta, through multiple arteries to the circulatory bed of each organ system.
4. Peripheral Gas Exchange: Once the oxygen-rich red blood cells enter capillary beds that nourish individual cells, the same process of gas diffusion occurs but in reverse. In the tissues, the concentration of oxygen is very low (the cells have consumed it). As a result oxygen will duffuse from the hemoglobin down its concentration gradient. Similarly, but reversed, the CO2 concentration in the tissues is high (because it's constantly generated as a waste product). It too will diffuse down its concentration gradient, enter the capillary, bind to hemoglobin and be carried to an alveolar capillary membrane where it releases itself from the hemoglobin molecule and can be blown off in each exhalation.
Cellular Respiration:
The oxygen brought to the cells is used by the mitochondria to make ATP. This process is sometimes called oxydative phosphorylation or just oxydative metabolism. This is done within each mitochondria through step-wise oxydation-reduction chemical interactions which (oddly enough) require a lot of oxygen. The purpose of all these reactions is to turn fuel (glucose and fatty acids, primarily) into ATP. The molecules of ATP are used within the cell to maintain life.
Ask a student to list "the most basic human needs" and they sometimes answer... "The ABC's! Airway, breathing, circulation". In so doing, the student has referenced only one basic human need (oxygenation) and barely scratched the surface explaining this one. "Respiration" has 2 phases: 1) physiological respiration: getting oxygen in to the body, all the way to the mitochondria of each cell, and 2) cellular respiration: the biochemical actions that occur within mitochondria to turn oxygen and glucose in to ATP, the energy that sustains life.
Physiological Respiration: 4 phases
1. Ventilation: (Or what we usually mean when we say the word "respiration" or count "respirations" when we do vital signs.) This is where molecules of oxygen are drawn from the atmosphere all the way to the alveoli. It requires perfect functioning of the neuromuscular connections from the respiratory control centers in the medulla, to the motor neurons that serve the muscles of respiration, an intact lung-chest apparatus, open cartilagenous and non-cartilagenous airways and sufficient membrane surface for gasses to diffuse across. But ventilation has a flip-side as well since these same structures are the means of blowing CO2 back out of the body and into the atmosphere.
2. Pulmonary Gas Exchange: This is what happens at "the business end" of the airway. The single-cell thickness of the alveolar wall is almost contiguous with the single cell thickness of the associated capillary wall. Gasses move very easily across these membranes. Carbon dioxide diffuses 20 times faster than oxygen, however. When oxygen crosses the alveolar capillary membrane and becomes dissolved in the plasma, it stays there only briefly. This is because it is exposed to high affinity binding sites on hemoglobin molecules that are crammed into each red blood cell.
3. Gas Transport: This is exactly what it sounds like. This is the movement of those hemoglobin bound oxygen molecules from the capillary vasculature of the lung, to the heart, out the aorta, through multiple arteries to the circulatory bed of each organ system.
4. Peripheral Gas Exchange: Once the oxygen-rich red blood cells enter capillary beds that nourish individual cells, the same process of gas diffusion occurs but in reverse. In the tissues, the concentration of oxygen is very low (the cells have consumed it). As a result oxygen will duffuse from the hemoglobin down its concentration gradient. Similarly, but reversed, the CO2 concentration in the tissues is high (because it's constantly generated as a waste product). It too will diffuse down its concentration gradient, enter the capillary, bind to hemoglobin and be carried to an alveolar capillary membrane where it releases itself from the hemoglobin molecule and can be blown off in each exhalation.
Cellular Respiration:
The oxygen brought to the cells is used by the mitochondria to make ATP. This process is sometimes called oxydative phosphorylation or just oxydative metabolism. This is done within each mitochondria through step-wise oxydation-reduction chemical interactions which (oddly enough) require a lot of oxygen. The purpose of all these reactions is to turn fuel (glucose and fatty acids, primarily) into ATP. The molecules of ATP are used within the cell to maintain life.
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