Respiratory System

Respiratory System

» The most important organ of the respiratory system of human is lungs where the exchange of gases takes place.
» All those organs comes under respiratory system which help in exchange of gases are - Nasal passage, Pharynx, Larynx or Voice box, Trachea, Bronchi, Bronchioles, Lungs etc.
»Nasal passage : Its main function is related to sniffing. Its inner cavity is lined with mucous membrane. This secretes approximately half litre of mucous everyday. This prevents the particles of dust, bacteria or other small organisms from entering into the body. It makes the air wet entering into the body and equalizes it with the temperature of the body.
»Pharynx : It is situated behind the nasal cavity a common passage for both . respiratory and digestive system.
»Larynx : Pharynx open into anterior wider part of trachea called larynx The opening is called glottis. A cartilaginous flop like structure cover the glottis called epiglottis which prevent the entry of food during swallowing A pair of vocal cord is present inside the larynx help in producing sound
» Trachea : From the base of larynx a tube is arises, passes through the neck and reaches up to middle of thorax Is called trachea. It is supported by ā€˜Cā€™ shaped cartilaginous ring. Internally trachea is lined by ciliated and
»Bronchi : In the thorocic region trachea divides into two branches called bronchi. Each bronchus enters into the lung of its own side. After entering into the lung bronchous of each side divide and redevide into very fine tube called bronchioles. Finally bronchioles give rise alveoli or alveolar sac. Alveoli are the side of gaseous exchange.


There is a pair of lungs in the thoracic cavity. It color is pink, red, and looks like sponge. Right lung is larger in comparison to left lung. Each lung is surrounded by a membrane which is called pleural membrance. There is a network of blood capillaries. Here Oxygen enters into the blood and CO2 release out from blood.

The process of respiration can be divided into four parts

1. External respiration
2. Transportation of gases
3. Internal respiration
4. Cellular respiration

1. External respiration

This is divided into two parts -
(a) Breathing : In lungs air is taken and given out at a certain rate which is called breathing.
» Everyday approximately 400 ml water is excreted out through breathing.

(a) Exchange of gases : The exchange of gases takes place inside lungs. This gaseous exchange takes place on the basis of concentration gradient through normal diffusion.
» The exchange of oxygen and carbon dioxide gases takes place due to then difference in partial pressures. The direction of diffusion is both side.

2. Transportation of gases

The process of reaching of gases (oxygen and carbon dioxide) from lungs to the cells of body and coming back again to the lungs is called the transportation of gases.
» Transportation of oxygen takes place by haemoglobin present in blood.
» Transportation of carbon dioxide from cells to lung takes place by haemoglobin only to the extent of 10 to 20%.

3. Internal respiration

Inside the body, gaseous exchange takes place between blood and tissue fluid which is called internal respiration.

4. Cellular respiration

Glucose is oxidised by oxygen reached into the cell. This process is called cellular respiration.

Production of energy

By the oxidation of pyruvic acid one atom of ATP, five atoms of NADH and one atom of NADH2 are formed. From one atom of NADH three atoms of ATP and from one atom of NADH2 two atoms of ATP are obtained. Hence, from one atom of pyruvic acid l + (3x5) + (2xl) = 18 atoms of ATP are formed. From one atom of glucose two atoms of pyruvic acid are formed, by which 36 atoms of ATP are released. During the glycolysis, two atoms of ATP are obtained. Hence, during oxidation of one atom of glucose total 2 + 36 = 38 ATP atoms are obtained.

Respiratory substances

Carbohydrate, fat and protein are the main respiratory substances. At first, oxidation of glucose takes place, then fat. After the consumption of carbohydrate and fat oxidation of protein start.