Question

Explain how gaseous exchange takes place at alveoli and explain the regulation of respiration by the brain.

Answer 1

The movement of oxygen gas from the outer environment to cells present in the tissues, and vice- versa for the transportation of carbon dioxide gas. The respiration is of two types namely, aerobic and anaerobic. Both the process starts with the glycolysis cycle.

Complete answer:
The gaseous exchange in the alveoli-
When the air enters the lungs, the procedure of gaseous exchange begins. The capillaries present in the pulmonary artery are situated in the proximity of the alveolar wall. Due to this the gaseous exchange enhances. Carbon dioxide and oxygen, gets exchanged by diffusion across the alveolar membrane. This exchange takes place from higher partial pressure to the lower partial pressure, till the time the equilibrium is not obtained. In this process, there is no involvement of an active or secretory type of transport mechanism.

In the outer air, the concentration of oxygen is higher, that is about 20-25%, whereas the concentration of carbon dioxide is lower, that is about 0.04%. The partial pressure of oxygen in the alveoli is 100mm Hg and in the veins it is about 40mmHg. This gradient helps in the transport of oxygen. The partial pressure of carbon dioxide in veins is 46 mmHg and in alveoli it is 6mmHg. This pressure gradient helps in the diffusion of the gas.

The regulation of respiration by brain-
The respiratory center is present in the medulla oblongata of the brain, which controls the function of breathing. In the respiratory center an expiratory and inspiratory center is present. The axons present in the nerve cells of this center leads to intercostal muscles via the diaphragm and intercostal nerves through the phrenic nerves. These fibers then transmit the signal to the internal and external intercostal muscles. Hence, the walls of alveoli stretch during inspiration by the signal sent by receptors. These signals are sent to stimulate the expiratory center, via the vagus nerve. This sequence is termed as Hering- Breuer reflex.

The medulla also consists of a pneumotaxic center that is related to breathing and aids for ensuring the rhythmic breathing. The inspiratory part, present in the respiratory center, sends impulses to the pneumotaxic center, during inspiration. Then, the expiratory center gets activated, and the working of the inspiratory center gets inhibited through this reflex action.

Note: There are specific enzymes for catalyzing each reaction even on the cellular level. The main function of enzymes in the respiration reaction is assisting the transferred electrons from one molecule to the other. This transfer of electrons is termed as redox reactions, where a molecule loses an electron which gets coincided with another substance by adding that lost electron.