Question

Describe how carbon dioxide is taken into blood at the tissue capillaries, transported in the blood, and discharged at the lung capillaries. Be complete.

Answer 1

When air is inhaled through the nostrils, it is warmed, moistened and cleaned by the mucus and fine hair present in the nasal cavity. The air travels through the trachea, bronchi, bronchioles and finally reaches the alveoli in the lungs.

The alveoli are small pouch-like structures which are richly supplied with blood capillaries. The capillaries have walls which are made up of only one layer of epithelial cells. Due to the pressure difference and also the difference in the concentration of CO2 and O2 in the capillary blood and the alveolar cavity, there is an exchange of these two gases by diffusion. The CO2 diffuses into the alveolar cavity from the blood in the capillaries and O2 diffuses into the blood from the inhaled air in the alveoli.

Arteries take oxygenated blood to all the cells in the body. Arteries divide to form smaller blood vessels called arterioles which further divide into extremely fine capillaries. This is required so that O2 and nutrients reach every cell of all the body tissues. This is also important so that CO2 and other waste matters like urea are collected from the cells.

At the tissue level, this exchange of materials takes place by simple diffusion.

The capillaries join together to form venules which form the veins which ultimately take the blood to the right atrium of the heart.

The impure blood, carrying CO2 is sent to the lungs by the heart through blood vessels called the pulmonary arteries. The pulmonary arteries reach the lungs where they divide to form the extremely fine capillaries covering the alveoli like a mesh. The blood in the capillaries give off the CO2 by diffusion into the lungs, from where it is exhaled out of the body and the whole cycle is repeated again.