The Respiratory Life Cycle In Human Body ....
Life depends upon a series of complex chemical reactions, metabolism, occurring in the cells of living matter. The energy needed to drive all these reactions is ultimately derived from a particular reaction called tissue or cellular respiration. The combustion of the carbon in compounds such as glucose, with the gas oxygen, produces the gas carbon dioxide with the evolution of heat and chemical energy. The vitality of the organism therefore depends upon a supply of oxygen and glucose and upon the removal of carbon dioxide.
Oxygen is present in the atmosphere in the proportion of one part in five, the remaining four parts being the inert gas, nitrogen. The rhythmic move¬ments of the chest wall and the diaphragm, that we call breathing, produm a mass movement of air between the atmosphere and the lungsventilation. Oxygen in the inspired air passes through the walls of the microscopic air sacs, alveoli, in the lungs, and through the walls of the blood vessels, pulmonary alveolar capillaries, that lie in close proximity and thus into the blood. The process of permeation of gas is called diffusion. The process whereby a balance is maintained in all parts of the lungs between the volume of air ventilating the local alveoli and the volume of blood per fusingthe local alveolar capillaries is called distribution.
Oxygen transport to the tissues is a function of the blood circulation. The oxygen gas is carried in the blood to a small extent dissolved in the plasma. but mostly in the red cells in chemical combination with the protein, haemoglobin. The oxygenated compound with haemoglobin, oxyhaemo¬globin, is bright red and gives its characteristic colour to arterial blood which is satUrated with oxygen since it has passed through the pulmonary alveolar capillaries.
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The arterial blood is pumped by the heart to the tissues, and its excess oxygen content diffuses into the tissue cells together with glucose that is ultimately derived from food. Excess carbon dioxide that has accumulated
in the cells moves in the opposite direction, into the blood, and continues by way of the veins to the heart and then on in the pulmonOy circulation to the pulmonary capillaries.
The venous blood is tinged with a dark blue colour, which is the colour of haemoglobin as distinct from bright red oxyhaemoglobin. The pulmonary capillary blood gives up its excess carbon dioxide to the air in the alveoli, and this air is then expired. The whole process of ventilation, gaseous exchange in the lungs by diffusion and distribution, and transport of gases to and from the tissue cells by the circulation and cellular respiration is called, simply, respiration.
The acute life-threatening conditions all interfere with cellular respiration. Either there is not enough oxygen in the blood reaching the tissues, or there is too much carbon dioxide; or the circulation itself is inadequate; or there is not enough fuel (glucose) reaching the cells.
Human cells are not all equally sensitive to the effects of inadequate respiration. The cells in muscle, for example, can manage with an in-adequate supply of oxygen for long periods because they have an alter-native chemical source of energy to respiration. During violent exercise much more energy is needed than can be provided by the circulation in the form of oxygen. The alternative source results in the production of lactic acid, and the accumulation of this material ultimately poisons the cell. The exercise cannot be continued indefinitely, because the destruction of the excess lactic acid itself demands oxygen. The muscle is said to have accumulated an oxygen debt during the exercise, and must rest and repay this debt to rid itself of the lactic acid.
Many tissues have no alternative to respiration, but their metabolic activities (and hence their demands for oxygen) are small. Such tissues, like skin, tendon, and bone, can endure a disturbance of tissue respiration for long periods. Other tissues or organs, however, are very sensitive to such disturbances because their metabolic activities are very great and the importance of their efficient functioning to the whole organism is critical. The three most important organs in this context are the brain, the heart and the kidneys.
The brain is the most sensitive to the effects of anoxia (absence of oxygen): its delicate mechanisms, the seat of consciousness and inteliect, emotion and volition, everything that distinguishes man from the lesser orders of life, crumble irreversibly if they are deprived of oxygen for as little as four minutes. This is the length of time available to the bystander if the acute emergency of cerebral anoxia develops. Long before four minutes the consciousness is impaired. The patient's vision goes dark, he feels sick and becomes dizzy as his mechanisms of balance falter, and then he loses consciousness and falls to the ground. Recovery is nonetheless usually complete if an oxygen supply is restored to the brain before four minutes have passed.
The heart is a little less delicate: its anoxia-time is of the order of eight minutes. After this period the electrical activity in the cardiac muscle fibres that is intimately associated with their ability to contract becomes dis-orderly and the circulation ceases, so that circulatory arrest is added' as another cause to whatever caused the primary artgxia.
The kidney is less clear-cut in its sensitivity, but it is usually said to be able to recover from acute anoxia which does not last longer than about
30 minutes. The flow of urine may cease before this time, but provided tissue oxygenation is restored before 30 minutes, eventual recovery can be expected.
One problem peculiar to the kidney is that even if the damage is still reversible it may be so severe that the kidney cannot start functioning adequately for several days after the anoxic incident. During this period the kidney can secrete only a very dilute urine, so that waste products like urea which are normally excreted by the kidney accumulate in the body and poison the patient. To tide the patient over this period of renal inefficiency and to keep him alive until his own kidneys start working properly again, various techniques have been devised to remove the poisons from the patient, e.g. the artificial kidney.
The various acute conditions threatening life, and simple measures used in their treatment are discussed in more detail below.
Life depends upon a series of complex chemical reactions, metabolism, occurring in the cells of living matter. The energy needed to drive all these reactions is ultimately derived from a particular reaction called tissue or cellular respiration. The combustion of the carbon in compounds such as glucose, with the gas oxygen, produces the gas carbon dioxide with the evolution of heat and chemical energy. The vitality of the organism therefore depends upon a supply of oxygen and glucose and upon the removal of carbon dioxide.
Oxygen is present in the atmosphere in the proportion of one part in five, the remaining four parts being the inert gas, nitrogen. The rhythmic move¬ments of the chest wall and the diaphragm, that we call breathing, produm a mass movement of air between the atmosphere and the lungsventilation. Oxygen in the inspired air passes through the walls of the microscopic air sacs, alveoli, in the lungs, and through the walls of the blood vessels, pulmonary alveolar capillaries, that lie in close proximity and thus into the blood. The process of permeation of gas is called diffusion. The process whereby a balance is maintained in all parts of the lungs between the volume of air ventilating the local alveoli and the volume of blood per fusingthe local alveolar capillaries is called distribution.
Oxygen transport to the tissues is a function of the blood circulation. The oxygen gas is carried in the blood to a small extent dissolved in the plasma. but mostly in the red cells in chemical combination with the protein, haemoglobin. The oxygenated compound with haemoglobin, oxyhaemo¬globin, is bright red and gives its characteristic colour to arterial blood which is satUrated with oxygen since it has passed through the pulmonary alveolar capillaries.
•
The arterial blood is pumped by the heart to the tissues, and its excess oxygen content diffuses into the tissue cells together with glucose that is ultimately derived from food. Excess carbon dioxide that has accumulated
in the cells moves in the opposite direction, into the blood, and continues by way of the veins to the heart and then on in the pulmonOy circulation to the pulmonary capillaries.
The venous blood is tinged with a dark blue colour, which is the colour of haemoglobin as distinct from bright red oxyhaemoglobin. The pulmonary capillary blood gives up its excess carbon dioxide to the air in the alveoli, and this air is then expired. The whole process of ventilation, gaseous exchange in the lungs by diffusion and distribution, and transport of gases to and from the tissue cells by the circulation and cellular respiration is called, simply, respiration.
The acute life-threatening conditions all interfere with cellular respiration. Either there is not enough oxygen in the blood reaching the tissues, or there is too much carbon dioxide; or the circulation itself is inadequate; or there is not enough fuel (glucose) reaching the cells.
Human cells are not all equally sensitive to the effects of inadequate respiration. The cells in muscle, for example, can manage with an in-adequate supply of oxygen for long periods because they have an alter-native chemical source of energy to respiration. During violent exercise much more energy is needed than can be provided by the circulation in the form of oxygen. The alternative source results in the production of lactic acid, and the accumulation of this material ultimately poisons the cell. The exercise cannot be continued indefinitely, because the destruction of the excess lactic acid itself demands oxygen. The muscle is said to have accumulated an oxygen debt during the exercise, and must rest and repay this debt to rid itself of the lactic acid.
Many tissues have no alternative to respiration, but their metabolic activities (and hence their demands for oxygen) are small. Such tissues, like skin, tendon, and bone, can endure a disturbance of tissue respiration for long periods. Other tissues or organs, however, are very sensitive to such disturbances because their metabolic activities are very great and the importance of their efficient functioning to the whole organism is critical. The three most important organs in this context are the brain, the heart and the kidneys.
The brain is the most sensitive to the effects of anoxia (absence of oxygen): its delicate mechanisms, the seat of consciousness and inteliect, emotion and volition, everything that distinguishes man from the lesser orders of life, crumble irreversibly if they are deprived of oxygen for as little as four minutes. This is the length of time available to the bystander if the acute emergency of cerebral anoxia develops. Long before four minutes the consciousness is impaired. The patient's vision goes dark, he feels sick and becomes dizzy as his mechanisms of balance falter, and then he loses consciousness and falls to the ground. Recovery is nonetheless usually complete if an oxygen supply is restored to the brain before four minutes have passed.
The heart is a little less delicate: its anoxia-time is of the order of eight minutes. After this period the electrical activity in the cardiac muscle fibres that is intimately associated with their ability to contract becomes dis-orderly and the circulation ceases, so that circulatory arrest is added' as another cause to whatever caused the primary artgxia.
The kidney is less clear-cut in its sensitivity, but it is usually said to be able to recover from acute anoxia which does not last longer than about
30 minutes. The flow of urine may cease before this time, but provided tissue oxygenation is restored before 30 minutes, eventual recovery can be expected.
One problem peculiar to the kidney is that even if the damage is still reversible it may be so severe that the kidney cannot start functioning adequately for several days after the anoxic incident. During this period the kidney can secrete only a very dilute urine, so that waste products like urea which are normally excreted by the kidney accumulate in the body and poison the patient. To tide the patient over this period of renal inefficiency and to keep him alive until his own kidneys start working properly again, various techniques have been devised to remove the poisons from the patient, e.g. the artificial kidney.
The various acute conditions threatening life, and simple measures used in their treatment are discussed in more detail below.
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