Blood circulation in lungs

Lung circulation peculiarity: circulation small circle vessels are relatively short, resistance in them is less; that’s why pressure in them is in 5-6 times lower comparatively to aortal. Lung vessels capacity may be increased or decreased. Thus, due to this mechanism, lung filling with blood may varies in the limits of 10-25 per cent from common blood amount in organism. It provides blood depot creation. Lung net vessels big ability to stretching creates favourable conditions for easy blood stream and volume change. Inspiration leads to blood regional content increasing and to regional resistance decreasing to blood in course of usual breathing or even in course of hyperventillation.

At hypertony in reflexogenic zones vessels with parallel reflectory heart activity weakening and large circle vessels dilation lung circle reflectory filling takes place. Due to this blood pressure is leveled and blood distribution between circulation big and small circles occurs. At pulmonal arteries pressure increasing, when small circle is overfilled with blood, reflexes from pulmonal artery receptors occurs on large circle vessels. As the result of this blood amount is increased in large and is decreased - in small circle. It prevents blood stagnation in lungs and provides heart activity and blood circulation as a whole.

Lecture 14 Blood physiology – blood functions. Blood physico-chemical peculiarities. Erythrocytes and erythropoiesis.

Blood system includes:

• circulating blood;

• haematopoiesis organs;

• blood destruction organs;

• regulative organs.

Circulating blood - is internal environment liquid or tissue, contained into blood circulation system. Its amount is 6-8 % from body weight; in average – 4,0-6,0 litres. In women this amount is on 1,0-1,5 l less in comparison to men.

Blood amount:

• in new-borns - 15 per cent from body weight (11,0-20,0 %);

• in 1 year - 10 %;

• in boys it is bigger than in girls.

Normovolemy - normal blood volume.

Hypovolemy - blood volume decreasing. Reasons:

• haemorrhagias (bleedings);

• hard physical activity;

• hyperthermy.

Hypervolemy – blood volume increasing. Reasons:

• liquid big amount usage;

• oligoanuria (kidneys and urinary tract pathology).

2/3 of blood is concentrated in veins, 1/3 - in arteries; 1/3 (1,5 l) – in blood depot:

• spleen;

• liver;

• skin et al.

Deponated volume decreasing main reasons:

• physical activity;

• environment or body temperature increasing;

• tissular hypoxy;

• bleedings.

Deponated volume increasing main reasons:

• pregnancy;

• hyperadrenalinaemia and other cases.

There is definite correlation in blood between plasma and formed elements – haematocrit. Normal values:

• in men - 40-48 per cent;

• in women - 36-44 per cent;

• in new-borns – 55-60 per cent;

• in 1 month - 40-45 per cent;

• in 1 year – 35-40 per cent;

• in capillary blood - 32 per cent.

Main blood functions:

1. Transport – oxygen, nutrients delivery to peryphery, carbonic dioxide and metabolites removal.

2. Protective:

• immunity;

• phagocytosis;

• complement system;

• haemostasis;

• fibrinolysis;

• antioxidant system and so on.

3. Regulatory:

1. humoral regulation:

• hormones;

• mediators et al.;

2. physico-chemical regulation:

• temperature;

• osmotic pressure;

• oncotic pressure;

• acid-alkaline equillibrium and others.