Oxyhaemoglobine dissociation curve moving:

1. to the left (up) – is observed:

• at temperature decreasing;

• pH increasing (alkalosis);

• hypocapnia;

• in blood reaching lungs;

• in new-borns;

• in mountaineers;

• in fliers;

• in cosmonauts.

Essence: at less oxygen partial pressure in atmosphere to form more oxyhaemoglobine in blood.

2. To the right (down) – is observed:

• at hyperthermia;

• at fever;

• pH decreasing (acidosis);

• carbonic acid content increasing;

• in blood reaching tissues (for example, working muscles).

Essence: at the same oxygen partial tension oxygen forming is less and free oxygen comes to the tissue where it’s necessary for redox reactions performing in them.

Carbon dioxide transport

Carbon dioxide transmission and transfer is realized by same mechanisms. Carbon dioxide tension:

• in tissues – maximal – 60 mm merc col.;

• in venous blood outflowing from tissues – 46 mm;

• in alveoles where venous blood inflows – 38 mm merc col;

• in atmosphere – 0,2 mm merc col.

It’s quite naturally that pressure and tension gradient in different organism environments and compartments provides carbonic dioxide transition from tissues to blood, from blood into alveoles and from alveoles into surrounding space.

Carbon dioxide forms

Particularly, like oxygen, in little amounts it can dissolves (3-6%). Rest part comes into chemical connections both in plasma and in erythrocytes. Chemical substance of carbonic dioxide with water – carbonic acid (H₂CO₃) – appears in plasma. It takes place because partial tension of this gas is more than in blood, that’s why it transfers into blood plasma where is connected to water. Carbonic acid part in plasma is connected to sodium chloride as the result of which soda is formed (NaHCO₃). Plasma transports carbonic dioxide in composition of these compounds. Its rest part reaches erythrocytes where under influence of special erythrocytic enzyme carboanhydrase the possibility of its connection with water is significantly increased with carbonic acid forming. Little amount of this acid is binded with potassium chloride with potassium bicarbonic (KHCO₃) formation. Finally, carbon dioxide part is binded to amine group of haemoglobine with the carbohaemoglobine (KHCO₂) forming. Thus, in erythrocytes carbonic dioxide is transported in a structure of H₂CO₃, KHCO₃ and HbCO₂.

When blood reaches alveoles, same enzyme carboanhydrase acts on the contrary: it helps H₂CO₃ dissociation and CO₂ comes into alveoles as the result of these processes. As oxygen partial pressure in alveoles is higher than in blood the gas passes in blood, in red blood cells with oxyhaemoglobine forming in them. Being more powerful acid than carbonic, ohyhaemoglobine takes the bases from bicarbonates and thus provides carbonic dioxide releasing. The result: CO₂ passes into alveoles. In tissues oxyhaemoglobine transformes into haemoglobine giving bases connected with it, increasing blood saturation with CO₂. These examples testify to the fact that oxygen plays essential role in CO₂ forming and releasing.

But at all these reactions CO₂ tension in venous blood remains big (46 mm merc col) and it doesn’t differ significantly from its tension in arterial blood. Thus, there exists carbonic dioxide arterio-venous difference equal to 6 mm merc col.

There is quite natural question: why organism has big amount of CO₂? The answer is the following: it is essential respiration regulator.