Transport of Carbon Dioxide (from tissues to lungs)

Blood transports carbon dioxide with comparative ease because of its high solubility. Active tissues constantly produce CO2. This CO2 is transported to the lungs in three ways:

  1. CO2 is physically dissolved in blood plasma (only 5-7% of the total CO2 is transported).

  2. CO2 directly combines with haemoglobin of RBCs to form carbaminohaemoglobin (about 21-23% only).

  3. As bicarbonate it is dissolved in plasma but produced in RBCs catalyzed by the enzyme carbonic anhydrase and then diffuses into plasma (largest fraction of CO2, about 75% to 80%) to be transported in this manner.





Regulation of respiration

Groups of neurons located bilaterally in the medulla and pons that control the respiratory rhythm constitute the respiratory centers. Three groups of respiratory centers have been identified;

Dorsal respiratory group: present in the dorsal part of medulla oblongata. Since this group controls only inspiration it is also called inspiratory centre; its neurons generate the basic respiratory rhythm and the signals are transmitted to the diaphragm. When the stimulation ceases, these muscles relax and expiration takes place.

Ventral respiratory groups control inspiration and expiration; this group of neurons is stimulated by the impulses sent by the stretch receptors in the lung alveoli stimulated by their expansion.

Pneumotaxic centre transmits signals to the neurons of the dorsal respiratory centre and inspiratory neurons of the ventral respiratory group; it controls the switch off point of inspiration and thereby smoothens the transition between inspiration and expiration.

Cellular respiration

Cellular respiration can be defined as the process of step-wise biological oxidation of organic molecules to release energy, which is stored in readily usable form in ATP. During the process molecules oxygen is used and CO2 and water are produced.


Respiration that takes place in the presence of O2 is called aerobic respiration. It is more efficient as 38 molecules of ATP are released on the oxidation of one glucose molecule.

Common respiratory disorders and their prevention

Table showing common respiratory disorders and their prevention.





Bronchial asthma

It is an allergic disease caused due to certain foreign substance in the air.

Causes difficulty in breathing and coughing because excess mucous secretion may narrow down (clog) the bronchioles.

Avoiding exposure to the foreign substance is the best preventive measure.


Inflammation of bronchi caused by infection. It can also be caused by smoking and by exposure to air pollution.

Regular coughing with greenish blue sputum.

Avoiding exposure to smoke and dust prevents bronchitis.


Acute inflammation caused by diplococcus infection in the alveoli of the lung.

It causes fever, pain and serve cough. Most of the air space is occupied by fluid and dead W.B.C.

Avoid crowded places where infection is prevalent.


It is a bacterial infection that spreads through droplets of infected persons.

It can affect many other organs but pulmonary T.B. is most common symptoms. It is accompanied by low fever. In extreme cases blood may come out while coughing.

BCG vaccine can prevent T.B. well ventilated dwellings and proteins rich diet is also essential for T.B. patients.

Occupational lung hazards

Caused due to exposure to harmful substance like silica, asbestos, dust etc. present in the environment where a person works.

It is expressed after exposure of 10-15 years or more. It causes fibrosis of the lungs.

Such diseases can be prevented by minimizing the exposure to such substances by using protective masks and clothing. Regular health check- up is necessary.

Explore NIOS Notes