Pulmonary alveolus - Wikipedia
Figure 6A shows an alveolar capillary of a monkey lung with an .. a close relationship between the air spaces and the blood capillaries over a. The Alveoli and Gas Exchange | Control of Respiration | Links . The lungs and alveoli and their relationship to the diaphragm and capillaries. Images from. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in Gas Exchange Between Alveoli and Capillaries.
The rate at which oxygen is used by the body is one measure of the rate of energy expended by the body. Breathing in and out is accomplished by respiratory muscles.
Lung Structure and the Intrinsic Challenges of Gas Exchange
The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli. Three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs: Ventilation is the process by which air moves in and out of the lungs. Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the gas in the alveoli and the blood in the capillaries in the lungs.
Oxygen is collected from environmental air, transferred to blood in the lungs, and transported by blood flow to the periphery of the cells where it is discharged to reach the mitochondria by diffusion. The transfer of oxygen to the mitochondria involves several structures and different modes of transports. It begins with ventilation of the lung, which is achieved by convection or mass flow of air through an ingeniously branched system of airways.
In the most peripheral airways, ventilation of alveoli is completed by diffusion of oxygen through the air to the alveolar surface.
Oxygen movement from alveoli to capillaries (video) | Khan Academy
The transfer of oxygen from alveolar air into the capillary blood occurs by diffusion across the tissue barrier; it is driven by the oxygen partial pressure difference between alveolar air and capillary blood and depends on the thickness about 0. Convective transport by the blood depends on the blood flow rate cardiac output and on the oxygen capacity of the blood, which is determined by its content of hemoglobin in red blood cells.
The last step is the diffusive discharge of oxygen from the capillaries into the tissue and cells, which is driven by the oxygen partial pressure difference and depends on the quantity of capillary blood in the tissue. In this process the blood plays a central role and affects all transport steps: Blood also serves as carrier for both respiratory gases: Metabolism, or, more accurately, the metabolic rate of the cells, sets the demand for oxygen.
At rest a human consumes about ml about 15 cubic inches of oxygen each minute. With exercise this rate can be increased more than fold in a normal healthy individual, but a highly trained athlete may achieve a more than fold increase. As more and more muscle cells become engaged in doing work, the demand for ATP and oxygen increases linearly with work rate. This is accompanied by an increased cardiac outputessentially due to a higher heart rate, and by increased ventilation of the lungs; as a consequence, the oxygen partial pressure difference across the air—blood barrier increases and oxygen transfer by diffusion is augmented.
This range of possible oxidative metabolism from rest to maximal exercise is called the aerobic scope. The upper limit to oxygen consumption is not conferred by the ability of muscles to do work, but rather by the limited ability of the respiratory system to provide or utilize oxygen at a higher rate. Muscle can do more work, but beyond the aerobic scope they must revert to anaerobic metabolism, with the result that waste products, mainly lactic acidaccumulate and limit the duration of work.
The limit to oxidative metabolism is therefore set by some features of the respiratory system, from the lung to the mitochondria. Knowing precisely what sets the limit is important for understanding respiration as a key vital process, but it is not straightforward, because of the complexity of the system. Much has been learned from comparative physiology and morphologybased on observations that oxygen consumption rates differ significantly among species.
For example, the athletic species in nature, such as dogs or horseshave an aerobic scope more than twofold greater than that of other animals of the same size; this is called adaptive variation. Then, oxygen consumption per unit body mass increases as animals become smaller, so that a mouse consumes six times as much oxygen per gram of body mass as a cowa feature called allometric variation.
Furthermore, the aerobic scope can be increased by training in an individual, but this induced variation achieves at best a 50 percent difference between the untrained and the trained state, well below interspecies differences.
Within the aerobic scope the adjustments are due to functional variation. For example, cardiac output is augmented by increasing heart rate. Mounting evidence indicates that the limit to oxidative metabolism is related to structural design features of the system. The total amount of mitochondria in skeletal muscle is strictly proportional to maximal oxygen consumption, in all types of variation. In training, the mitochondria increase in proportion to the augmented aerobic scope.
Mitochondria set the demand for oxygen, and they seem to be able to consume up to 5 ml 0. If energy ATP needs to be produced at a higher rate, the muscle cells make more mitochondria. It is thus possible that oxygen consumption is limited at the periphery, at the last step of aerobic metabolism.
Exhaling reverses theses steps. Diseases of the Respiratory System Back to Top The condition of the airways and the pressure difference between the lungs and atmosphere are important factors in the flow of air in and out of lungs. Many diseases affect the condition of the airways. Asthma narrows the airways by causing an allergy-induced spasms of surrounding muscles or by clogging the airways with mucus.
Bronchitis is an inflammatory response that reduces airflow and is caused by long-term exposure to irritants such as cigarette smoke, air pollutants, or allergens. Cystic fibrosis is a genetic defect that causes excessive mucus production that clogs the airways. The Alveoli and Gas Exchange Back to Top Diffusion is the movement of materials from a higher to a lower concentration. The differences between oxygen and carbon dioxide concentrations are measured by partial pressures.
The greater the difference in partial pressure the greater the rate of diffusion. Respiratory pigments increase the oxygen-carrying capacity of the blood. Humans have the red-colored pigment hemoglobin as their respiratory pigment. Hemoglobin increases the oxygen-carrying capacity of the blood between 65 and 70 times.
Each red blood cell has about million hemoglobin molecules, and each milliliter of blood contains 1. Effectiveness of various oxygen carrying molecules. Carbon dioxide concentration in metabolically active cells is much greater than in capillaries, so carbon dioxide diffuses from the cells into the capillaries. Water in the blood combines with carbon dioxide to form bicarbonate.
This removes the carbon dioxide from the blood so diffusion of even more carbon dioxide from the cells into the capillaries continues yet still manages to "package" the carbon dioxide for eventual passage out of the body. Details of gas exchange.
In the alveoli capillaries, bicarbonate combines with a hydrogen ion proton to form carbonic acid, which breaks down into carbon dioxide and water. The carbon dioxide then diffuses into the alveoli and out of the body with the next exhalation. Control of Respiration Back to Top Muscular contraction and relaxation controls the rate of expansion and constriction of the lungs. These muscles are stimulated by nerves that carry messages from the part of the brain that controls breathing, the medulla.Alveolar-Capillary Gas Exchange
Two systems control breathing: Both are involved in holding your breath. Although the automatic breathing regulation system allows you to breathe while you sleep, it sometimes malfunctions. Apnea involves stoppage of breathing for as long as 10 seconds, in some individuals as often as times per night. This failure to respond to elevated blood levels of carbon dioxide may result from viral infections of the brain, tumors, or it may develop spontaneously. A malfunction of the breathing centers in newborns may result in SIDS sudden infant death syndrome.
As altitude increases, atmospheric pressure decreases. Above 10, feet decreased oxygen pressures causes loading of oxygen into hemoglobin to drop off, leading to lowered oxygen levels in the blood. The result can be mountain sickness nausea and loss of appetite. Mountain sickness does not result from oxygen starvation but rather from the loss of carbon dioxide due to increased breathing in order to obtain more oxygen. Farabee, all rights reserved.
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