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It is provided with two pairs of valves, the lower pair being placed at its entrance into the subclavian vein, the upper in most cases about 4 cm above the clavicle. The portion of vein between the two sets of valves is often dilated, and is termed the sinus.
The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption of lipids , by allowing products that have been carried by lymph in the thoracic duct to enter the ...
The left and right external jugular veins drain into the subclavian veins. The internal jugular veins join with the subclavian veins more medially to form the brachiocephalic veins. Finally, the left and right brachiocephalic veins join to form the superior vena cava, which delivers deoxygenated blood to the right atrium of the heart. [2]
No valve divides the superior vena cava from the right atrium. The superior vena cava is made up of three layers, starting with the innermost endothelial tunica intima . The middle layer is the tunica media , composed of smooth muscle tissue, and the outermost and thickest layer is the tunica adventitia , composed of collagen and elastic ...
As the valve forms, the vein wall where the leaflets attach, becomes dilated on each side. These widenings form the pockets, hollow cup-shaped regions, on the cardial side, known as the valvular sinuses. [22] The endothelial cells in the sinuses are able to stretch twice as much as those in areas without valves. [22]
It is formed by the folding of the serous layer over the remnant of the lower part of the left superior vena cava (duct of Cuvier), which becomes obliterated during fetal life, and remains as a fibrous band stretching from the highest left intercostal vein to the left atrium, where it is continuous with a small cardiac vein, the vein of the ...
After nourishing the heart muscle, blood returns through the coronary veins into the coronary sinus and from this one into the right atrium. Backflow of blood through its opening during atrial systole is prevented by the Thebesian valve. The smallest cardiac veins drain directly into the heart chambers. [10]
Anastomoses provide alternative routes for blood to flow through in case of blockages. Veins can have valves that prevent the backflow of the blood that was being pumped against gravity by the surrounding muscles. [8] In humans, arteries do not have valves except for the two 'arteries' that originate from the heart's ventricles. [9]