Mechanism of Respiration: Humans, like all other living organisms, require oxygen to thrive. The mechanics of respiration in human beings takes place in two events: inspiration and expiration (inhale and exhale). The respiratory mechanism is the act of inhaling air into the lungs and is known as inspiration. Expiration is the process of removing air from the lungs. Amoeba and other unicellular organisms breathe through their skin.

Plants breathe through tiny pores known as stomata. Humans, too, breathe efficiently to generate energy. How can food provide us with energy? Respiration is an oxidative process for releasing energy from food. In the process, the oxygen is absorbed into the tissue (from the lungs) to oxidise the food and release energy and carbon dioxide. Read the complete article to know more about the mechanism of respiration in human beings.

What is the Respiratory Mechanism?

The physiological and biochemical aspects of respiration differ from each other. Bio-chemically, respiration involves the production of energy, typically with the intake of oxygen and liberation of carbon dioxide from the oxidation of food. It is called cellular respiration.

\({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}{\rm{ +  6}}{{\rm{O}}_{\rm{2}}} \to \,{\rm{6C}}{{\rm{O}}_{\rm{2}}}{\rm{ +  6}}{{\rm{H}}_{\rm{2}}}{\rm{O +  Energy}}\,\left( {{\rm{ATP}}} \right)\)

Physiologically it involves the movement of oxygen from the outside environment to the cells and vice-versa. However, physiological respiration is necessary to sustain cellular respiration.

Types of Respiration

Every cell in our body needs energy. One of the main fuels that is used to provide energy to the cells is glucose. Cells need a constant supply of energy to sustain life. Respiration can be classified into two types:

1. Aerobic Respiration: It occurs in the presence of oxygen. In aerobic respiration, the glucose is completely broken down with the help of oxygen to provide energy. Carbon dioxide and water are released as end products. This can be summed up in the following equation:
   \({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}{\rm{ +  6}}{{\rm{O}}_{\rm{2}}} \to {\rm{6C}}{{\rm{O}}_{\rm{2}}}{\rm{ +  6}}{{\rm{H}}_{\rm{2}}}{\rm{O  +  Energy}}\,\left( {{\rm{2870}}\,{\rm{kJ}}} \right)\)
2. Anaerobic Respiration: It occurs in the absence of oxygen. In this process, the glucose is incompletely oxidized into some carbonic compounds such as ethyl alcohol or lactic acid; relatively small amounts of energy are released along with the liberation of carbon dioxide. Yeast performs anaerobic respiration that is called alcoholic fermentation. This can be summed up as follows:
   \({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}} \to {\rm{2}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH  +  2C}}{{\rm{O}}_{\rm{2}}}{\rm{ +  Energy}}\,\left( {{\rm{247}}\,{\rm{kJ}}} \right)\)
   During strenuous exercise, not enough oxygen reaches the muscles for aerobic respiration. Therefore, the muscle cells respire anaerobically to release energy. It is called lactic acid fermentation. This can be shown by the following equation:
   \({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}} \to {\rm{Lactic}}\,\,{\rm{acid}} + {\rm{C}}{{\rm{O}}_{\rm{2}}} + {\rm{Energy}}\)

Physiological Anatomy of Human Respiratory System

The human respiratory system consists of a group of organs that help to breathe. Lungs are the primary organs of the respiratory system that comprises about \(600-700\) million alveoli (air sacs). The other main parts of this system are the trachea (windpipe) and bronchi for air passages. The associated body parts are blood vessels and the muscles that facilitate breathing.

Fig: Respiratory System-Elaborating the Internal Structure of Lung

Mechanism of Breathing

The entire Mechanism of breathing involves the following steps:

1. Breathing (Pulmonary ventilation): The mechanism of breathing involves the inspiration and expiration of air with the movement of the diaphragm and intercostal muscles. During inhalation, external intercostal muscles contract. At the same time, the diaphragm contracts and flattens. These actions increase the volume of the thoracic (chest) cavity, and the air (oxygen) is forced into the lungs. On the contrary, exhalation occurs when the thoracic cavity is reduced, and the air (carbon dioxide) is expelled out.

Fig: Mechanism of Breathing

2. External Respiration: It involves the diffusion of oxygen and carbon dioxide between the alveoli and the pulmonary capillaries due to the partial pressure difference. The solubility of oxygen in the blood is not high, hence there is a big difference in the partial pressure of oxygen in the alveoli versus in the blood of the pulmonary capillaries. The partial pressure of oxygen in the alveoli is about \(104\,{\rm{mm}}\,{\rm{Hg}},\) and it is about \(40\,{\rm{mm}}\,{\rm{Hg}}\) in the capillary blood. The difference is about \(64\,{\rm{mm}}\,{\rm{Hg}}.\) This strong pressure gradient forces oxygen from the alveoli into the blood across the respiratory membrane.

The partial pressure of carbon dioxide between the alveolar air and the blood of the capillary is also different. However, the partial pressure difference is far less than that of oxygen, about \(5\,{\rm{mm}}\,{\rm{Hg}}{\rm{.}}\) The partial pressure of carbon dioxide in the capillary blood is about \(45\,{\rm{mm}}\,{\rm{Hg}}\) and, in the alveoli, it is about \(40\,{\rm{mm}}\,{\rm{Hg}}.\) It is because the solubility of carbon dioxide in the blood is much greater than that of oxygen.

3. Internal Respiration: The gaseous exchange process that takes place in the tissues is called internal respiration. The oxygen after dissociating from the haemoglobin reaches the tissues or cells. The oxygen causes the complete breakdown of the glucose molecules (food) into carbon, water, and energy. The energy remains stored in the form of ATP (Adenosine Triphosphate) and is further utilized to perform several living activities. This mechanism of internal respiration is also named Cellular Respiration.

Fig: Exchange of Gases between Alveolus and Body tissues

4. Transport of Oxygen: Oxygen is carried through the blood from the respiratory organs to the different tissues. Oxygen can be carried in two forms:

1. Through plasma
2. Through Red Blood Cells \(\left( {{\rm{RBCs}}} \right)\)

Only about \(3\) per cent is dissolved in plasma. Haemoglobin transports about \(97\) per cent of the oxygen in the form of oxyhemoglobin.

\({\rm{H}}{{\rm{b}}_{\rm{4}}}{\rm{ +  4}}{{\rm{O}}_{\rm{2}}} \to {\rm{H}}{{\rm{b}}_{\rm{4}}}{{\rm{O}}_{\rm{8}}}\,\left( {{\rm{oxyhemoglobin}}} \right)\)

Each haemoglobin molecule consists of four \({\rm{F}}{{\rm{e}}^{ + 2}}\) ions. Each of the four \({\rm{F}}{{\rm{e}}^{ + 2}}\) ions in the haemoglobin molecule can bind with one molecule of oxyhaemoglobin, so oxyhaemoglobin carries \(1\) to \(4\) molecules of oxygen according to its degree of saturation with oxygen.

\({\rm{H}}{{\rm{b}}_{\rm{4}}}{{\rm{O}}_{\rm{8}}} \to {\rm{dissociates}}\,{\rm{to}}\,{\rm{give}}\, \to \,{\rm{Hb  +  }}{{\rm{O}}_{\rm{2}}}\)

Fig: Exchange of Gases through Alveolus

5. Transport of Carbon Dioxide: Carbon dioxide is transported in the blood in the below-mentioned three ways:
1. In dissolved state: About \(5-7\) per cent of carbon dioxide is transported, being dissolved in the plasma of blood.
2. In the form of bicarbonate: Carbon dioxide produced by the tissues diffuses passively into the blood and passes into the red blood corpuscles, where it reacts with water to form carbonic acid \(\left( {{{\rm{H}}_2}{\rm{C}}{{\rm{O}}_3}} \right).\)
\({\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}}\)
The enzyme carbonic anhydrase found in \({\rm{RBCs}}\) catalyzes this reaction, and instantly, the carbonic acid dissociates into hydrogen ions \(\left( {{{\rm{H}}^ + }} \right)\) and bicarbonate ions \(\left( {{\rm{HCO}}_3^ – } \right).\)
\({\rm{C}}{{\rm{O}}_{\rm{2}}} + {{\rm{H}}_{\rm{2}}}{\rm{O}} \to {{\rm{H}}^{\rm{ + }}} + {\rm{HCO}}_{\rm{3}}^{\rm{ – }}\)
Hydrogen ions combine with the haemoglobin to form haemoglobinic acid \(\left( {{\rm{H}}{\rm{.Hb}}} \right),\) and bicarbonate ions combined with sodium or potassium present in the blood to form sodium bicarbonate \(\left( {{\rm{NaHC}}{{\rm{O}}_3}} \right)\) or Potassium bicarbonate \(\left( {{\rm{KHC}}{{\rm{O}}_3}} \right).\) Almost \(70\) per cent of carbon dioxide is transported from tissues to the lungs in this form.
3. In combination with the amine group of protein: (carbaminohemoglobin): In addition to the above two methods, carbon dioxide reacts directly with the amine radicals \(\left( {{\rm{N}}{{\rm{H}}_2}} \right)\) of haemoglobin molecules and forms a carbanionhemoglobin molecule \(\left( {{\rm{Hb}}.{\rm{C}}{{\rm{O}}_2}} \right).\)
\({\rm{C}}{{\rm{O}}_{\rm{2}}} + {\rm{NHbN}}{{\rm{H}}_{\rm{2}}} \to {\rm{HbNH}}{\rm{.COOH}}\)
Almost \(23\) per cent of carbon dioxide is carried to the lungs and released out of the body through exhalation.

Disorders Associated with Mechanism of Respiration

Some common respiratory diseases that obstruct the smooth breathing process and mechanism of respiration are as follows:

1. Pneumonia: It is caused primarily due to a bacterium, namely Streptococcus pneumoniae. It is an acute inflammation of the alveoli in the lungs.
2. Tuberculosis: It is caused by Mycobacterium tuberculosis. It is the inflammation of the lungs that slowly gets worse.
3. Emphysema: It occurs when the fragile and delicate links between alveoli are damaged due to smoking.
4. Acute Respiratory Distress Syndrome: It is a severe condition that causes fluid to build up in the lungs. Slowly the fluid leaks from small blood vessels and collects in the alveoli. Because of this, the blood cannot pick up the oxygen from the alveoli and causes damage to the heart and kidneys.

Important Facts

1. Respiration and breathing are interconnected processes.
2. Respiration is a biochemical process that involves the liberation of energy, while breathing is a physical process of gaseous exchange.
3. Respiration is an involuntary process that is regulated by the medulla oblongata.
4. Hemocyanin in molluscs and arthropods, hemerythrin in some annelids are the respiratory pigments similar to the haemoglobin found in human blood.
5. Carbon monoxide is a toxic gas that has a great affinity with haemoglobin and forms carboxyhemoglobin, hence reducing the oxygen-carrying capacity of haemoglobin.

Summary

Respiration can be briefly described as an energy-releasing process involving the gaseous exchange. It is an essential life process that enables a person to perform life-sustaining activities. The main organ involved in the mechanism of respiration is a pair of lungs that consists of millions of air sacs that take part in the exchange of respiratory gases between the blood and lungs. In this article, learners will learn how respiratory gases are carried from the lungs to every cell of our body.

FAQs about Mechanism of Respiration in Human Beings

Q.1. What is the definition of respiration?
Ans: Respiration is the process of production of energy by inhaling oxygen and exhaling carbon dioxide from the oxidation of food.

Q.2. What is the name of respiration that occurs in the presence of oxygen?
Ans: Respiration that occurs in the presence of oxygen is called aerobic respiration.

Q.3. What is the difference between breathing and respiration?
Ans: Breathing is a physical process involving the inhalation of oxygen and exhalation of carbon dioxide. Respiration is a biochemical process that occurs at the cellular level and produces energy.

Q.4. What is the mechanism of internal respiration?
Ans: Internal respiration is the process of diffusion of oxygen from the blood into the tissues.

Q.5. What is the importance of respiration?
Ans: Respiration is the process that releases energy which is further utilized to perform several living activities.