Overview of Cell Respiration
by T.H. Mathis
Ambient air is made up of 20.9% oxygen and several inert gases. Under ideal conditions, only a quarter of that oxygen we breathe is transferred to blood, through the alveoli in the lungs. About three quarters of the oxygen in inspired (breathed) air is still present as it is expired. Therefore, if we inspire 500 CCs of air each time we breathe, 104.5 CCs is oxygen. We expire, or breathe out 78.3 CCs of oxygen, retaining 26.1 CCs of oxygen per breath, to do the work of respiration. This is about 70% of one ounce per breath that is used by the body. This is about 70% of one ounce per breath that is used by the body.
In health, an individual will have a respiratory system that will saturate 94-96% of the hemoglobin as it passes by the lungs. When a person is at rest, is elderly, loses fitness, or develops any number of circulatory or respiratory illnesses, the efficiency of the lungs decreases, lowering the oxygen saturation of the blood. Human blood should carry a dissolved oxygen level of about 4 ppm.
The total body water (TBW) content of adult men varies from 55% of body weight in the obese to 65% in thin individuals. Values for adult women are about 10% less. About two thirds of TBW is intracellular fluid and one third extra cellular. TBW content is normally regulated by a combination of factors; including the thirst mechanism.
The mention of adenosine triphosphate (ATP) is necessary to the topic of aerobic and anaerobic respiration. ATP is the molecular net product of a sequence of processes collectively termed respiration. In aerobic cell respiration, ambient air, normally entrained with 20.9% oxygen, is inhaled and gas exchange occurs in the alveoli of the lungs.
The lung is a diffusion organ, as is the placenta. (In the case of mother and fetus, there typically is no commingling of blood; nutrients and oxygen are delivered from the mother's blood but diffused through the placenta for utilization by the fetus). Because the lungs consist largely of air tubes and elastic tissue, it is a spongy, elastic organ with a very large internal surface area for gas exchange. In normal adults this surface area is estimated to be approximately the size of a tennis court.
At the cellular level, anaerobic respiration occurs in a deficiency of oxygen in tissues of higher species and produces much less energy than the aerobic process: about 0.25 attojoules per glucose molecule versus 0.06 attojoules in aerobic
.
The normal pH value in the human body is 7.35 to 7.45, slightly alkaline. Remember that the range of pH is zero to 14, with a pH value of 7 considered neutral; lower numbers indicate acidity and higher numbers indicate alkalinity. Anaerobic energy production occurs, ultimately creating a byproduct, lactic acid, hence reducing pH, toward the acidic.
The lower the acidity of the plasma, the less oxygen will be taken up by the hemoglobin or the more will be lost by it. This is called the Bohr Effect. The main factor governing pH of the plasma is the amount of carbon dioxide in the bloodstream (writer's note: carbon dioxide and oxygen are the yin/yang of respiration); CO2 reacts with water to form carbonic acid, which then dissociates hydrogen ions to cause a fall in pH.
In addition, anaerobic respiration results in incomplete breakdown of glucose, producing ethyl alcohol, toxic to most living tissue. If the oxygen supply in an aerobic system becomes seriously depleted, the process is arrested at an intermediate stage, and anaerobic glycolosis takes over, giving the lactate that appears in overworked muscles.
The fundamental formula for life is Oxygen + Nutrients = Energy.
