1. Oxygen transport: Oxygen combines with hemoglobin in red blood cells to form oxyhemoglobin. Oxyhemoglobin reaches different parts of the body. Oxyhemoglobin breaks down in body cells and oxygen and hemoglobin are released. As a result, body cells get the necessary oxygen.
Hb4 + 4O2 → 4Hbo2
Actually hemoglobin reacts with 4 oxygen molecules to form Hb4o8.
Hb4 + O2 → Hb4o2
Hb4o2 + O2 → Hb4o4
Hb4o4 + O2 → Hb4o6
Hb4o6 + O2 → Hb4o8
This reaction is extremely fast and takes less than 0.01 second. Temperature, pH and red blood cell diphosphoglycerate affect this reaction.
2. Transport of carbon dioxide: Carbon dioxide reacts with hemoglobin in body cells to form carbaminohemoglobin compound. Carbaminohemoglobin comes from the compound body cells to the walls of the alveoli. The compound breaks down in the walls of the alveoli and turns into carbon dioxide and hemoglobin. Carbon dioxide is then released from the body.
CO2 + HbNH2 → HbNHCOOH
Hemoglobin acts as the sole carrier for transporting oxygen and carbon dioxide in the human body. That is, oxygen and carbon dioxide transport is not possible without red blood cells.

Hemoglobin is a spherical molecule. It is composed of iron called heme and protein called globin. 100 cc of blood contains 15.8 grams of hemoglobin in men and 13.7 grams in women. Heme and globin ratio in hemoglobin is 1:25. 33.33% of Heme is iron. Adult human blood contains only 4-5 grams of iron. Its chemical symbol is (C712H1130O245N214S2Fe)4 and molecular weight is 64,450 daltons. Heme is ferrous iron and globin is a polypeptide protein. Each hemoglobin contains 4 heme and 4 globin proteins. Hence it is written as Hb4.

The red proteinaceous molecule present in human red blood cells that transports oxygen and carbon dioxide is called hemoglobin.

The part of blood that transports oxygen and carbon dioxide is called the respiratory pigment. The main pigments in animals are Haemoglobin of Vertebrates, Haemocyanin of Molluscs and Arthropods, Heme-erythrin of Brachiopods and Cypanculids and Chlorocrurin of Polychaetes.

In the diffusion process CO2 enters the red blood cells and reacts with water with the help of carbonic anhydrase enzyme to produce HCO3. Carbonic acid breaks down into H+ and HCO3- ions. Some HCO3- moves from the red blood cells into the plasma. As much HCO3- enters the blood from the red blood cells as Cl- enters the red blood cells from the plasma. This is called chloride shift or hamburger reaction. The chloride shift reaction is called the Hamburger reaction after the first describer, German physiologist Hartog Jacob Hamburger. This reaction maintains the acid-base balance (pH = 7.4) in the blood.
CO2 + H2O → H2CO3
H2CO3 → H+ + HCO3-
HCO3- ← Exchange → Cl-

10% of CO2 is transported in blood as carbamino compounds. Carbon dioxide reacts with hemoglobin in body cells to form carbaminohemoglobin compound. Carbon dioxide is transported as a carbaminohemoglobin compound.
CO2 + HbNH2 → HbNHCOOH

Oxidation of carbohydrates in body cells produces CO2. The CO2 produced enters the lungs through the blood and is exhaled. CO2 is transported in the blood in three ways. namely-
(i) As physical solution: 5% CO2 is transported in blood as physical solution. CO2 dissolves in the water of the blood plasma to form carbonic acid and is transported.
CO2 + H2O → H2CO2)
(ii) As carbamino compounds: 10% of CO2 is transported in blood as carbamino compounds. Carbon dioxide reacts with hemoglobin in body cells to form carbaminohemoglobin compound. Carbon dioxide is transported as a carbaminohemoglobin compound.
CO2 + HbNH2 → HbNHCOOH
(iii) As bicarbonate compound: 85% of CO2 is transported in blood as bicarbonate compound. It is transported in two ways. as NaHCO3 and KHCO3.
In the diffusion process CO2 enters the red blood cells and reacts with water with the help of carbonic anhydrase enzyme to produce HCO3. Most carbonic acid breaks down into H+ and HCO3- ions.
CO2 + H2O → H2CO3
H2CO3 → H+ + HCO3-
K+ and HCO3- combine inside red blood cells to form KHCO3. Some HCO3- moves from the red blood cells into the plasma and combines with Na+ to form NaHCO3. As much HCO3- enters the plasma from the red blood cells as Cl- enters the red blood cells from the plasma. This is called chloride shift reaction or Hamburger reaction.
In red blood cells: K+ + HCO3 →KHCO3
In plasma : Na+ + HCO3 → NaHCO3
About 25-33% oxygen enters the collars under normal conditions. 100 ml blood transports 19-20 ml oxygen in 100 ml blood 14-15 ml CO2.

Through diffusion, oxygen enters the capillary blood from the walls of the alveoli. Then it reaches different cells of the body. Oxygen is transported in the blood in two ways. namely-
(i) Physical solution: 2% oxygen is transported in blood as physical solution. That is, in every 100 ml of blood, 2 ml of oxygen is transported as a physical solution.
(ii) As chemical compounds: 98% oxygen is transported as chemical compounds in the blood. Hemoglobin in red blood cells combines with oxygen to form oxyhemoglobin. Oxyhemoglobin reaches different cells of the body from the heart. When body cells lack oxygen, oxyhemoglobin breaks down and oxygen and hemoglobin are released. As a result, body cells get the necessary oxygen.
Hb4 + 4O2 → 4Hbo2

1. Transport of O2: Through diffusion, oxygen enters the capillary blood from the walls of the alveoli. Then it reaches different cells of the body. Oxygen is transported in the blood in two ways. namely-
(i) Physical solution: 2% oxygen is transported in blood as physical solution. That is, in every 100 ml of blood, 2 ml of oxygen is transported as a physical solution.
(ii) As chemical compounds: 98% oxygen is transported as chemical compounds in the blood. Hemoglobin in red blood cells combines with oxygen to form oxyhemoglobin. Oxyhemoglobin reaches different cells of the body from the heart. When body cells lack oxygen, oxyhemoglobin breaks down and oxygen and hemoglobin are released. As a result, body cells get the necessary oxygen.
Hb4 + 4O2 → 4Hbo2

2. Carbon Dioxide Transport: Oxidation of carbohydrates in body cells produces CO2. The CO2 produced enters the lungs through the blood and is exhaled. CO2 is transported in the blood in three ways. namely-
(i) As physical solution: 5% CO2 is transported in blood as physical solution. CO2 dissolves in the water of the blood plasma to form carbonic acid and is transported.
CO2 + H2O → H2CO2)
(ii) As carbamino compounds: 10% of CO2 is transported in blood as carbamino compounds. Carbon dioxide reacts with hemoglobin in body cells to form carbaminohemoglobin compound. Carbon dioxide is transported as a carbaminohemoglobin compound.
CO2 + HbNH2 → HbNHCOOH
(iii) As bicarbonate compound: 85% of CO2 is transported in blood as bicarbonate compound. It is transported in two ways. as NaHCO3 and KHCO3.
In the diffusion process CO2 enters the red blood cells and reacts with water with the help of carbonic anhydrase enzyme to produce HCO3. Most carbonic acid breaks down into H+ and HCO3- ions.
CO2 + H2O → H2CO3
H2CO3 → H+ + HCO3-
K+ and HCO3- combine inside red blood cells to form KHCO3. Some HCO3- moves from the red blood cells into the plasma and combines with Na+ to form NaHCO3. As much HCO3- enters the plasma from the red blood cells as Cl- enters the red blood cells from the plasma. This is called chloride shift reaction or Hamburger reaction.
In red blood cells: K+ + HCO3 →KHCO3
In plasma : Na+ + HCO3 → NaHCO3
About 25-33% oxygen enters the collars under normal conditions. 100 ml blood transports 19-20 ml oxygen in 100 ml blood 14-15 ml CO2.

1. Volume, structure and thickness of airways.
2. O2 and CO2 pressure in alveoli.
3. Solubility and diffusivity of O2 and CO2.
4. Physiological relationship of gases present in alveolus and blood.