It is composed of the arterial system originating from the ventricle, the venous system flowing back to the atrium, and the reticular capillaries connecting the arteries and veins
This entry is missingOverview, add relevant content to make the entry more complete, and it can also be upgraded quickly. Hurry upeditCome on!
The vascular system consists of the arterial system originating from the ventricle, the venous system flowing back to the atrium, and the reticular capillaries connected between the arteries and veins.Blood is ejected from the ventricles through arteriesblood capillaryThe vein circulates into the atrium again, and can not be circulated continuously. According to the different circulation routes, it can be divided into large (body) circulation and small (lung) circulation.
The great circulation starts from the left ventricle, which contracts to pump arterial blood rich in oxygen and nutrientsaorta, reaching the capillaries of various parts of the body through various arterial branches, andHistiocyteConduct material exchange, that is, oxygen and nutrients in blood are absorbed by tissue cells, and metabolites of tissue cells andcarbon dioxideIt enters the blood and forms venous blood.Then it passes through all levels of veins and finally converges into superior and inferior vena cava to inject into the right atrium.The minor circulation starts from the right ventricle. When the right ventricle contracts, the blood returned from the major circulation (including venous blood containing metabolites and carbon dioxide) is pumped into the pulmonary artery, and reaches the capillary network around the alveoli through all branches of the pulmonary artery. Gas exchange is carried out with the air in the alveoli through the capillary walls and alveolar walls, that is, carbon dioxide is discharged and oxygen is taken in,It turns blood into arterial blood rich in oxygen, and then flows back to the left atrium through the pulmonary vein.
reason
Announce
edit
As can be seen above, the artery is formed byventricleThe blood vessels sent out interrupt their branches during the journey, forming large, medium and small arteries.Because of the great pressure, the artery wall is thick and the lumen section is round.The arterial wall is composed of intima, media and adventitia. The surface of the intima is composed of a smooth cavity surface of a single layer of flat epithelium (endothelium). The adventitia is connective tissue. The middle membrane of the great arteries is rich in elastic fibers. When the heart shrinks and shoots blood, the wall of the great arteries expands. When the heart relaxes, the wall of the great arteries retracts elastically to continue to push the blood;Middle and small arteries, especially the middle membrane of small arteries, have developed smooth muscle.It contracts and relaxes under innervation to maintain and regulate blood pressure and regulate blood flow in its distribution area.Vein is the blood vessel that guides blood back to the heart, and small veins originate fromCapillary networkDuring the journey, it gradually converges into the middle vein and the great vein, and finally opens in the atrium.The vein has thin wall, less smooth muscle and elastic fiber, weak elasticity and contractility due to low pressure, and the lumen is oblate on the section.The number of veins is more than that of arteries. Due to the different locations, the veins of the head and neck, trunk, and limbs can be divided into deep and shallow ones. The deep veins are accompanied by the arteries of the same name. In the middle and distal segments of the limbs, one artery has two veins.The superficial veins run in the subcutaneous tissue.The anastomoses between veins were abundant.The structure of vein wall can also be divided into inner membrane, middle membrane and outer membrane. In most veins, the inner membrane is reflexed to form a half moon shaped vein valve to ensure the centripetal flow of blood.Capillaries are tiny vascular networks connected between arteries and veins, with a diameter of only 7-9 μ m and thin walls, mainly composed of one layerendothelial cellsComposition, with certain permeability, blood flows slowly in the capillary network, which is conducive to the material exchange between tissue cells and blood.
