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The externa, alternatively known as the tunica adventitia, is composed of collagen fibers and elastic tissue—with the largest arteries containing vasa vasorum, small blood vessels that supply the walls of large blood vessels. [3] Most of the layers have a clear boundary between them, however the tunica externa has a boundary that is ill-defined.
Blood vessels function to transport blood to an animal's body tissues. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system.
The umbilical arteries are one of two arteries in the human body, that carry deoxygenated blood, the other being the pulmonary arteries. The pressure inside the umbilical artery is approximately 50 mmHg. [4] Resistance to blood flow decreases during development as the artery grows wider. [5]
It contains one vein, which carries oxygenated, nutrient-rich blood to the fetus, and two arteries that carry deoxygenated, nutrient-depleted blood away. [6] Occasionally, only two vessels (one vein and one artery) are present in the umbilical cord. This is sometimes related to fetal abnormalities, but it may also occur without accompanying ...
Transverse section of the human spleen, showing the distribution of the splenic artery and its branches. Section of the spleen, showing the termination of the small bloodvessels. Posterior abdominal wall, after removal of the peritoneum, showing kidneys, suprarenal capsules, and great vessels.
The middle coat (tunica media) is distinguished from the inner (tunica intima) by its color and by the transverse arrangement of its fibers. In the smaller arteries , it consists principally of smooth muscle fibers in fine bundles, arranged in lamellae and disposed circularly around the vessel.
The dorsal scapular artery (or descending scapular artery [3]) is a blood vessel which supplies the levator scapulae, rhomboids, [4] and trapezius. It most frequently arises from the subclavian artery (the second or third part), [3] but a quarter of the time it arises from the transverse cervical artery. [5]
The aortic root is the portion of the aorta beginning at the aortic annulus and extending to the sinotubular junction. It is sometimes regarded as a part of the ascending aorta, [2] and sometimes regarded as a separate entity from the rest of the ascending aorta.