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Mechanism of Respiration and Regulation of Respiration

Aerobic respiration, Anaerobic respiration, Pulmonary ventilation or breathing, Inhalation, Expiration, Breathing externally
For all organisms to survive, including humans, oxygen is necessary. Amoeba, a single-celled organism, breathes through its surface. Stomata are minute pores that plants use to breathe. Humans, too, breathe through minute pores, namely trachea. How does food provide us with energy? Respiration is the act of oxidizing food to release energy and carbon dioxide by taking oxygen into the tissues (from the lungs).

Definition - Respiration is a physiological process as well as a biochemical process. In the biochemical process of respiration, oxygen is inhaled and carbon dioxide is released when food is oxidized. Cellular respiration is what this process is called.

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)

The exchange of oxygen between cells and the external environment is a physiological phenomenon. Cellular respiration, however, is not possible without physiological respiration.

Our bodies require energy for every cell. Glucose is a major fuel used by the cells to generate energy. Life depends upon constant energy supply to the cells. Types of respiration include:

Aerobic respiration - Oxygen is required for aerobic respiration. To provide energy, glucose is broken down and oxygen is used to break it down. This results in the release of water and carbon dioxide. It can be expressed as follows:

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (2870kJ)

Anaerobic respiration - Oxygen is not present when it occurs. This process results in incomplete oxidation of glucose, converting it into carbonic compounds such as ethyl alcohol or lactic acid. A small amount of energy is released alongside carbon dioxide. A process called alcoholic fermentation is performed by yeast anaerobically. The process goes as follows:

C6H12O6→2C2H5OH+2CO2+Energy (247kJ)

For aerobic respiration, not enough oxygen reaches the muscles during strenuous exercise. The muscles release energy anaerobically by respiring. Lactic acid fermentation is the process. Here is an example:

C6H12O6 → Lactic acid + CO2 + Energy

As part of the entire respiratory cycle, the following steps are taken:
  • Pulmonary ventilation or breathing
  • Breathing externally
  • Transportation of oxygen to the tissues
  • Respiration internally
  • Transportation of carbon dioxide from tissues

Pulmonary ventilation or breathing

During this process, air enters and leaves the lungs. Furthermore, respiration eliminates carbonic acid during the process of supplying atomic number 8 to the alveoli. Respiration is primarily governed by the intercostal muscles, so the diaphragm is most responsible. The areas between the twelve pairs of ribs area unit occupied by eleven pairs of intercostal muscles. The intercostal muscles area unit divided into 2 layers, the external and internal intercostal muscles. Diaphragm could be a muscular dome that separates the body part and abdominal cavities. Breathing takes place as a result of fluctuations in the thoracic cavity's pressure and volume. Changes in lung pressure affect the direction of airflow within the lungs. Air moves from high pressure locations to low pressure places.

There are two processes that are involved in breathing:


A decrease in the air pressure combined with a volume increase in the thoracic cavity cause it. Expansion of the thorax occurs when the external intercostal muscles together with the diaphragm are simultaneously contracted. In response to contraction of the diaphragm and external intercostals (downward movement), the lung volume increases!

Following are the events involved:
In the first instance, it is the external intercoastal muscles that contract and the internal intercoastal muscles that relax. The thoracic cavity is expanded as the external intercostal muscles flex. The diaphragm is lowered, and the thoracic cavity is further enlarged due to contraction of the diaphragm. The lungs grow in tandem with the expansion of the thorax. During the breathing process, the lungs fill with air to equalize the pressure inside, causing the pressure within to decrease.


An increase in air pressure and a reduction in the size of the thoracic cavity led to this phenomenon.

Among the events involved are:
Intercoastal muscles contract internally, while external intercoastal muscles relax internally. The contraction of the internal intercostal muscle causes the ribs to be pulled thoracic cavity to become smaller as the diaphragm is pulled up. Due to the compression of lungs, the pressure of air increases, which results in the lungs being compressed.

Breathing externally

Alveolar capillaries, which bridge the respiratory membrane, are responsible for transferring gas between the alveoli and blood. It is dependent on pressure differences that oxygen and carbon dioxide diffuse, e.g., between the atmosphere and the blood, or between the blood and tissues. When the respiratory process takes place, gas exchange occurs between the alveolus and the capillary at its surface. O2 and CO2 molecules migrate at varying partial pressures from one section of the atmosphere to another by diffusion. Alveoli have an O2 pressure of 104mmHg. Blood oxygen saturation is 40mmHg. There is a CO2 pressure of 40mmHg in the alveoli and a CO2 pressure of 45mmHg in the blood. In alveolar capillaries, the venous blood contains high levels of CO2 while the oxygen levels are low. From higher to lower levels (venous blood to alveoli), CO2 diffuses until equilibrium has been achieved. Throughout the alveoli and blood vessels, O2 diffuses in a reciprocal manner.

Regulation of respiration

There are two mechanisms that regulate respiration:
  • Neural or nervous mechanism
  • Chemical mechanism
Neural or nervous mechanism - Respiratory centers, afferent and efferent nerves are involved in the nervous system.

Respiratory centers - The respiratory centres in the medulla oblongata and the pons absorb sensory information about oxygen and carbon dioxide levels in the blood and utilise it to regulate breathing muscles. The stimulation of these respiratory muscles results in alveolar ventilation through respiratory movements. The respiratory centres are positioned in the reticular formation of the brainstem and operate differently depending on how they are organised.

There are two groups of respiratory centers:
  • Pontine center
  • Medullary center
Each group consists of two centers:
Pontine centers –
  • apneustic center
  • Pneumotaxic center
Medullary center -
  • Expiratory center
  • Inspiratory center
Apneustic center - The Apnuestic center is located in lower Pons.
Function - By acting directly upon the inspiratory center, the center increases depth of inspiration.

Pneumotaxic center - Upper Pons is where it is located. The parabrachial nucleus gives rise to it.
Function - This organ includes the apnoeic center, which controls the medullary respiratory centers. Inspiratory centers are always controlled, so their activity plays a role in controlling the duration of inspiration.

Expiratory center - In the medulla oblongata, it is posterior and laterally to the inspiratory center. Respiratory neurons, also called respiratory centers, are located in the ventral group of the medulla. This structure contains neurons from nucleus retro-ambiguous, nucleus ambiguous, and others.
Functions - Due to the inhibition instilled by forced breathing, the inspiratory center becomes active when forced breathing is used. Its inactivity is due to quiet breathing, which is dominated by the inspiratory center.

Inspiratory center - The inspiration center is located at the top of the medulla oblongata. Dorsal respiratory group is another name for this center. A tractus solitarius forms the nucleus of this group.
Functions - Inspiration is the function.
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