Capillary circulation and its peculiarities

Circulation in this part provides its main function – exchange between blood and tissues. That’s why main link in this system – capillaries – they are called exchangeable vessels. Thir function is tightly linked with vessels they are originated from - arterioles and vessels they come into (inflow) – venules. There exist direct arterio-venous anastomoses, connecting them out off capillaries. Mentioned vessels plus lymphatic capillaries are microcirculation system. This is main link of blood circulation system. Main reasons of diseases biggest part are in this region. Capillaries are the base of this system. Under rest state in norma only 25-35 per cent of them are opened, i.e. in working state; if more – one can see haemorrhagias and even organism death from internal bleeding, because blood is accumulated in capillaries and doesn’t reach heart.

Capillaries are located in intercellular spaces and that’s why metabolism occurs between blood and intercellular fluid.

Capillary exchange factors:

1. Hydrostatic pressure difference between capillary origin and its end (30-40 mm and 10 mm merc col correspondingly).

2. Low blood movement velocity (0,05 m/sec).

3. Filtration pressure (difference between oncotic pressure in intersticium and hydrostatic pressure in arterial capillary end – 15 mm merc col.). At its increasing – liquid comes into vessels and cellular dehydratation is developed.

4. Reabsorbtion pressure (difference between hydrostatic pressure in venous capillary end and oncotic pressure in intersticium – 15 mm merc col.). At its increasing – liquid (fluid) maily comes into tissues and oedemas are developed (for example, at proteins deficiency).

Capillary pulse (or Kwinke pulse) – pseudopulse, linked with rhythmical oscillations at small arteries dilation in course of ventricules systole. It is easily observed at thermal procedures: if one attaches mirror to lips small vessels pulsation is seen. But more often such pulse is pathology sign: aortal insufficiency, thyreotoxicosis.

 

Venous circulation

Veins are cavitary vessels, approximately 70-80 per cent of blood are located in them; they possess large ability to stretching and comparatively low elasticity. Their internal surface has valves (with exception of shallow veins, portal veins and cava veins) which:

· encourage blood stream to the heart;

· prevent its regurgitation (movement ahead);

· protect heart from excessive energy consumption to blood oscillative movements overcoming.

Blood in veins come rapidly despite low pressure in them. Why?

· Pressure gradient in blood circulation arterial and venous ends;

· heart residual force;

· thorax suckering action (respiratory pump);

· sceletal muscles contractions (muscular pump);

· diaphragm activity.

 

Venous pulse – pressure and volume fluctuations in veins in course of one cardiac cycle delt with blood outflow dynamics into right atrium in systole and dyastole different phases. These fluctiations are transmitted in retrograde direction (ahead); one can find them out in large veins located near heart – usually cava or jugular. Pulse wave distribution velocity is 1-3 m/sec. This pulse wave reason differs from that for arterial pulse. Vein pulse reason is blood outflow stoppage from veins to heart in course of atrial and ventricular systole. In this moment blood stream is lacked in large veins that results in pressure rising up in them. This pulse is registrated graphically and this curve is named as phlebogram.

3 phlebogram waves:

· wave “a” - occurs in course of right atrium systole: blood outflow from veins to heart is stopped and pressure in rised up in them;when atrium is relaxed blood begins to pass in its cavity, pressure in vein is reduced and curve reaches its initial level;

· wave “c” – new wave after drop which corresponds to pulse of neighbouring carotid artery and reflects fluctuation of its wall. Carotid artery push is communicated to vein and causes occurence of increased pressure rapid wave in it. After such short-termed rising pressure is falling down because blood outflows in atrium constantly and atrium is in dyastole;

· wave “v” - after atriums filling pressure in vein is increased again, blood stagnation and venous wall stretching take place; all this causes third wave appearence.

Venous pulse can be investigated both graphically and by palpation.

 

Lymphatic circulation

It’s necessary for fluid and substance (proteins) excessive amount, particles (microbes and others) removal; it serves as messengers between blood and cells. Blood comes into lymph, lymph – in tissues, from tissues in blood and on the contrary.

Lymphatic system:

· lymphatic capillaries;

· lymphatic vessels;

· lymphatic nodes.

Lymphatic capillaries - capillaries beginning blindly, which consist of endothelial tubules systems penetrating tissues. Their cavity is wider comparatively to blood capillary, endotheliocytes are larger, fissures between them are bigger, basal membrane is absent. Some organs don’t have any lymphatic capillaries such as cutaneous (skin) epithelium, mucosae, placenta, brain.

Lymphatic vessels look like blood vessels, but they are thinner, muscular layer is less developed and there are many constrictions (valves) in them. Valves are pair intime plicas directed one opposite other and creating activity like in locks (sluices).

Lymphatic nodes perform very significant role in organism. One can tell about following main functions:

1) haemopoiesis (lymphopoiesis);

2) filtration – lack of:

· side bodies;

· bacterias;

· tumor (particularly malignant) cells;

· toxines;

· side proteins;

3) immunity –

· plasmocytes production;

· antibodies production;

· T- and B-lymphocytes differentiation;

4) participating in metabolism of:

· proteins;

· fats;

· vitamins.

 

Lymph

This is product of blood, cells, intersticial fluid. That’ s why its content is similar to all these compounds. Its reaction is alkaline, it has proteins (fibrinogen and other coagulation factors), lymphocytes, salts, fats and other substances. Daily production is up to 2,0 l of lymph.

Lymph types (according to lymphocytes number):

· peripheral (0,5 x 10⁹/l);

· central (passing through lymphatic nodes where lymphocytes amount is from 2,0 to 20,0 x 10⁹/l).

Lymph formation stages:

· tissular liquid formation;

· proper lymph formation;

· lymph movement through vessels.

Tissular fluid formation occurs in capillaries. Tissues and blood osmotic pressure difference is essential for this. Under physiological conditions lymph formation from tissular fluid is insignificant (because filtration and reabsorbtion pressures are equal - see above). At oncotic pressure reducing (at protein deficiency in fasting) filtration pressure is rised up and reabsorbtion pressure is decreased. Fluid in such a case will come in tissues that leads to swelling (oedema) development. But such phenomenon will be in course of physical training too: filtration pressure increases due to capillary presure increasing (the result of hydrostatic pressure increasing in magistral vessels). Fluid amount in tissues will grow too (muscles increase their weight to 20 per cent). Lymphatic vessels begin their active functionning and take fluid excessment off.

But tissular liquid is not yet a lymph. It becomes itself when fluid passes into lymphatic vessels. Lymph formation is a rather complicated process. One can differentiate both physico-chemical reactions (diffusion, permeability, osmotic pressure) and secretory process (cellular secretion) in it. There are some substances increasing lymph formation. They are known as lymphogonic: peptones, hystamine et al. Some food products also possess lymphogonic features: crabs, squids, strawberry et al. Leeches action is based on this.

Lymph movement is realized due to:

· lymphatic vessels walls contraction (8-20 times per 1 minute);

· negative pressure in thorax;

· muscular contractions (intramuscular lymphatic heart). This mechanism lymph movement through vessels is essential for massage performance. At hypodynamy when this mechanism is disturbed, lower extremities oedemas are developed.

Lymph while proteins return from intercellular fluid to blood participates in fluid balance (equillibrium) support into tissues.

 

Lecture 13