Arteries have a smaller bore and thick walls. Veins have a larger bore and thin walls. Capillaries have a larger bore and the wall is of one cell in thickness. There are thick muscle layers and elastic fibers present. The elasticity helps to change the pulsating flow of blood. There are thin muscle layer and less elastic fibers present in veins. So, they are less elastic. No muscles or elastic fibers are present. There is no exchange of materials. These are responsible for the exchange of gases and nutrients.
All veins except the pulmonary veins carry deoxygenated blood. People who smoke often have cold hands and feet. What might explain this condition in terms of Is the vertebral artery a branch of the aortic arch? What conditions contribute to elevated blood levels of alkaline phosphatase? Are lymphocytes produced in the bone marrow and then migrate to the thymus gland and lymph nodes What is heart disease?
What is the primary cause of heart disease and what symptoms does it How does blood flow back to the heart from the lower extremities, since it is fighting against gravity? The arterioles play a key role in regulating blood flow into the tissue capillaries. About 10 percent of the total blood volume is in the systemic arterial system at any given time. The wall of an artery consists of three layers.
The innermost layer, the tunica intima also called tunica interna , is simple squamous epithelium surrounded by a connective tissue basement membrane with elastic fibers. The middle layer, the tunica media , is primarily smooth muscle and is usually the thickest layer. It not only provides support for the vessel but also changes vessel diameter to regulate blood flow and blood pressure.
The outermost layer, which attaches the vessel to the surrounding tissue, is the tunica externa or tunica adventitia. This layer is connective tissue with varying amounts of elastic and collagenous fibers. The connective tissue in this layer is quite dense where it is adjacent to the tunic media, but it changes to loose connective tissue near the periphery of the vessel.
Capillaries, the smallest and most numerous of the blood vessels, form the connection between the vessels that carry blood away from the heart arteries and the vessels that return blood to the heart veins. The primary function of capillaries is the exchange of materials between the blood and tissue cells. Capillary distribution varies with the metabolic activity of body tissues.
Tissues such as skeletal muscle , liver , and kidney have extensive capillary networks because they are metabolically active and require an abundant supply of oxygen and nutrients.
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