26.16
Respiración externa e interna
La respiración externa se produce en los pulmones y es el primer paso en el recorrido del oxígeno por el interior del cuerpo. Cuando inhalamos, el oxí…
La respiración externa implica el intercambio de oxígeno y dióxido de carbono entre los alvéolos y los capilares pulmonares de los pulmones.
Este intercambio gaseoso siempre se produce desde una zona de mayor presión parcial a la más baja o de Palta a Pbaja.
El oxígeno se difunde desde el aire alveolar, donde la PO2 es de 105 mmHg, a la sangre dentro de los capilares pulmonares, donde la PO2 es de 40 mmHg.
De manera similar, el dióxido de carbono es conducido desde la sangre a una PCO2 de 45 mmHg al aire alveolar con una PCO2 de 40 mmHg.
En la respiración interna, el oxígeno se transfiere de los capilares sistémicos a las células de tejido de todo el cuerpo, mientras que elCO2 se mueve en la dirección opuesta.
Los capilares sistémicos tienen una PO2 más alta que las células de tejido porque el oxígeno se gasta para la producción de ATP en las células, lo que hace que el oxígeno se difunda de los capilares a las células.
Por el contrario, la producción de CO2 por metabolismo activo da como resultado una mayor PCO2 en las células que en los capilares sistémicos, lo que hace que el CO2 se difunda de las células a estos capilares.
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Q1: What is the difference between external and internal respiration?
External respiration occurs in the lungs, where oxygen diffuses from alveoli into pulmonary capillaries and carbon dioxide moves from blood into alveoli. Internal respiration happens at body tissues, where oxygen transfers from systemic capillaries to tissue cells for ATP production, while CO2 produced by cellular metabolism diffuses from cells back into capillaries. Both processes follow partial pressure gradients.
Q2: How do partial pressure gradients drive gas exchange in the lungs?
Gas always moves from higher to lower partial pressure. In external respiration, alveolar oxygen at 105 mmHg diffuses into pulmonary capillaries at 40 mmHg. Simultaneously, blood carbon dioxide at 45 mmHg moves into alveolar air at 40 mmHg. These pressure differences create the driving force for gas exchange across the alveolar membrane.
Q3: Why does oxygen diffuse from capillaries into tissue cells during internal respiration?
Tissue cells consume oxygen rapidly during ATP production through cellular respiration, lowering their oxygen partial pressure below that of systemic capillaries. This pressure gradient causes oxygen to diffuse from capillaries into cells. Conversely, CO2 accumulates in cells from metabolism, creating a higher PCO2 in cells than capillaries, driving CO2 diffusion outward.
Q4: What factors reduce the rate of gas exchange in external respiration?
Decreased partial pressure gradients, reduced surface area, and increased diffusion distance all slow gas exchange. Conditions like emphysema reduce alveolar surface area, while pulmonary edema extends diffusion distance by accumulating interstitial fluid. Drugs such as morphine slow respiratory rate, decreasing oxygen and carbon dioxide exchange rates between alveoli and blood.
Q5: How does altitude affect oxygen diffusion into the blood?
At higher altitudes, both total atmospheric pressure and oxygen partial pressure decline, reducing the pressure gradient between alveolar air and pulmonary capillaries. This slower oxygen diffusion results in decreased blood oxygen levels, causing high-altitude sickness symptoms including breathlessness, headache, fatigue, insomnia, nausea, and dizziness.
Q6: Why is the large surface area of alveoli important for gas exchange?
The vast surface area provided by alveoli, combined with abundant surrounding capillaries, enables efficient gas exchange between air and blood. This extensive interface maximizes the opportunity for oxygen and carbon dioxide molecules to cross the thin respiratory membrane. Conditions reducing this surface area, such as emphysema, significantly impair gas exchange efficiency.
Q7: How does the thin respiratory membrane facilitate gas exchange?
The thin respiratory membrane minimizes diffusion distance, allowing oxygen and carbon dioxide to cross quickly between alveolar air and blood. Red blood cells pass single-file through narrow capillaries, further reducing diffusion distance and maximizing contact time with the alveolar membrane. This structural efficiency enables rapid, effective gas exchange during both external and internal respiration.