Oxygen transport.

Oxygen partial pressure:

• in atmosphere is equal to 159 mm merc col.;

• in alveoles – 102-105 mm merc col;

• in venous blood reaching alveoles – 40 mm merc col;

• pressure gradient for oxygen between alveoles and blood is about 60 mm merc col.

Thus, oxygen due to this difference of partial pressure and its tension in different environments passes from atmosphere into alveoles and then in blood and tissues. How oxygen is transmitted?

Oxygen transfer conditions

It is known that blood transfers 300-350 ml of oxygen for 1 minute under relative rest state (this ziphra significantly increases at physical work). One can differentiate 2 factors of oxygen transfer:

• large alveolar surface (60-100 square meters);

• oxygen fast diffusion ability – at this difference between alveoles and blood in 1 mm merc col 200 ml of oxygen will diffund; at a real difference that is 60 mm merc col – 12000 ml of oxygen (!even in course of intensive physical loading this ziphra is not more than 4000-5000 ml!). You see data about oxygen diffuse ability: it predominates the level necessary for intensive physical trainings in 2,5-3,0 times.

Oxygen transport forms

Particularly oxygen can be dissolved (in 100 ml of blood – up to 0,3 ml of oxygen, thus, in all blood – about 15 ml). Of course, it can’t solve the problem of oxygen transport. Main chemical substance necessary for oxygen transport is oxyhaemoglobine. It was estimated that 1 g of haemoglobine can transmit approximately 1,31 ml of oxygen. 100 ml of blood contains about 14-16 g of haemoglobine, so, they can carry 18-21 ml of oxygen. This index is known as oxygen blood capacity – is is defined as oxygen amount transporting with 100 ml of blood till its full saturation. This index can change. It is rised up in course of physical training, at polycitaemia; reduced – at blood diseases for instance at anaemias.

Formed oxyhaemoglobine amount depends on oxygen partial pressure in blood. This dependence is linear that is proved by following data. At oxygen partial pressure equal to 0, oxyhaemoglobine isnt’t formed; 10 mm merc col. – 10% oxyhaemoglobine; 20 mm.- 30%; 40 mm. – 70%; 70 mm.- 90%; 100 mm. – 96%. If we connect all this points we shall receive curve describing dependence between oxygen tension in blood and amount of forming oxyhaemoglobine. This curve name is oxyhaemoglobine dissociation curve. One can make some important conclusions from this curve:

1. At oxygen partial tension decreasing in blood up to 80-70 mm merc col (it corresponds to such partial pressure in mountains at a high 2500-3000 meters above sea level) amount of formed oxyhamoglobine decreases insignificantly, i.e. its amount is less only on several per cents than on plain. It gives the possibilities to successful work of mountaineers, highland workers and also to life in highlands without any additional devices and forces. At a high level above 4000 metres we’ll not be able to breath without additional oxygen coming from gas cylinder.

2. Venous blood is rich in oxyhaemoglobine, i.e. it is saturated by oxygen. At partial tension in venous blood equal to 40 mm merc col, up to 70% of oxyhaemoglobine is formed in blood.

3. Difference between oxyhaemoglobine content in arterial and venous blood is 25-26%. Oxyhaemoglobine content in arterial blood is 95-96%, in venous – 70%. This index is named arterio-venous difference. It is rised up in course of physical training, at polycitaemia; reduced – at blood (at anaemias) and heart disorders.