In the human body, the arterial bed of the circulatory system functions according to the principle “from large to small”. The blood supply to organs and tissues is carried out by the smallest vessels, to which blood flows through medium and large arteries. This type is called main when numerous arterial basins are formed. Collateral circulation is the presence of connecting vessels between the branches of the main arteries. Thus, the arteries of different basins are connected through anastomoses, acting as a backup source of blood supply in case of obstruction or compression of the main supply branch.
Physiology of collaterals
Collateral circulation is the functional ability to ensure uninterrupted nutrition of body tissues due to the plasticity of blood vessels. This isroundabout (lateral) blood flow to organ cells in case of weakening of blood flow along the main (main) path. Under physiological conditions, it is possible with temporary difficulties in blood supply through the main arteries in the presence of anastomoses and connecting branches between the vessels of neighboring pools.
For example, if in a certain area the artery that feeds the muscle is squeezed by some tissue for 2-3 minutes, then the cells will experience ischemia. And if there is a connection of this arterial basin with the neighboring one, then the supply of blood to the affected area will be carried out from another artery by expanding the communicating (anastomosing) branches.
Examples and vascular pathologies
As an example, consider the nutrition of the gastrocnemius muscle, the collateral circulation of the femoral artery and its branches. Normally, the main source of its blood supply is the posterior tibial artery with its branches. But a lot of small branches from neighboring basins from the popliteal and peroneal arteries also go to it. In the event of a significant weakening of the blood flow through the posterior tibial artery, blood flow will also be carried out through the opened collaterals.
But even this phenomenal mechanism will be ineffective in pathology associated with damage to the common main artery, from which all other vessels of the lower limb are filled. In particular, with Leriche's syndrome or a significant atherosclerotic lesion of the femoralarteries, the development of collateral circulation does not allow to get rid of intermittent claudication. A similar situation is observed in the heart: if the trunks of both coronary arteries are damaged, collaterals do not help get rid of angina pectoris.
Growth of new collaterals
Collaterals in the arterial bed are formed from the laying and development of arteries and the organs they feed. This happens even during the development of the fetus in the mother's body. That is, a child is already born with the presence of a collateral circulation system between the various arterial basins of the body. For example, the circle of Willis and the blood supply system of the heart are fully formed and ready for functional loads, including those associated with interruptions in the blood filling of the main vessels.
Even in the process of growth and with the appearance of atherosclerotic lesions of the arteries at a later age, a system of regional anastomoses is continuously formed to ensure the development of collateral circulation. In the case of episodic ischemia, each tissue cell, if it experienced oxygen starvation and had to switch to anaerobic oxidation for some time, releases angiogenesis factors into the interstitial space.
Angiogenesis
These specific molecules are, as it were, anchors or markers, in place of which adventitial cells should develop. A new arterial vessel and a group of capillaries will also be formed here, the blood flow through which will ensure the functioning of cells without interruptions in blood supply. This means that angiogenesis, that is, the formation of new blood vessels, isa continuous process designed to meet the needs of a functioning tissue or prevent the development of ischemia.
Physiological role of collaterals
The importance of collateral circulation in the life of the body lies in the possibility of providing backup blood circulation for parts of the body. This is most valuable in those structures that change their position during movement, which is typical for all parts of the musculoskeletal system. Therefore, collateral circulation in the joints and muscles is the only way to ensure their nutrition in conditions of constant change in their position, which is periodically associated with various deformations of the main arteries.
Because twisting or compression causes the arteries to narrow, the tissues to which they are directed may experience occasional ischemia. Collateral circulation, that is, the presence of roundabout ways of supplying tissues with blood and nutrients, eliminates this possibility. Also, collaterals and anastomoses between pools allow increasing the functional reserve of the organ, as well as limiting the extent of the lesion in the event of acute obstruction.
This safety mechanism of blood supply is typical for the heart and brain. In the heart there are two arterial circles formed by branches of the coronary arteries, and in the brain there is a circle of Willis. These structures make it possible to limit the loss of living tissue during thrombosis to a minimum instead of half the mass of the myocardium.
In the brain, the circle of Willis limitsthe maximum volume of ischemic damage to 1/10 instead of 1/6. Knowing these data, we can conclude that without collateral circulation, any ischemic episode in the heart or brain caused by thrombosis of a regional or main artery would be guaranteed to lead to death.
