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The Arteries and Veins

Table of Contents
The Lungs
The Trachea
The Testes
The Submaxillary Gland
The Liver
The Stomach and Duodenum
The Blood
The Arteries and Veins
The Adipose Tissue
The Skin
The Pituitary Gland
The Pancreas
The Thyroid
The Kidney
The Spinal Cord
The Cerebellum
The Elastic Cartilage
The Bone
The Smooth Muscle
The Striated Muscle


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Along with the heart and the blood, the arteries and veins make up what is called the circulatory, or cardiovascular, system. The circulatory system works to provide the body with four main services; the transportation of nutrients and wastes, the circulation of hormones, the transportation of oxygen and carbon dioxide, and finally the maintenance of body temperature.


While the heart is the pump which circulates the blood that supplies these nutrients, the arteries and veins are the roadways that carry the blood throughout the body to all its tissues and cells.


The arteries, branching from the aorta leaving the heart, are the blood vessels that carry blood away from the heart to the tissues of the body. The arteries are composed of three layers; an outermost layer of connective tissue, a layer of smooth muscle and elastic tissue, and finally a layer of endothelium tissue. The hollow center of the artery where the blood travels is called the lumen. Arteries have the capacity to dilate and constrict; the major arteries leaving the heart expand and collapse slightly in response to the surge of blood caused by the pumping heart. Also, the arteries can expand and constrict in response to nervous stimulation. Nerve impulses control the size of the arteries in response to changes in blood pressure and activity. The arteries travel into different cavities and tissue of the body, branching off into smaller arterioles and finally tiny capillaries.


Microscopic capillary beds, made of endothelial cells, are found in all tissues and work to deliver oxygen to cells, while harvesting carbon dioxide. The capillaries leaving the tissues grow in size, becoming venules, and eventually veins.


Veins are the blood vessels that carry deoxygenated blood from the tissues to the heart, where it can be pumped into the lungs, oxygenated, and eventually be sent back to the tissues via the arteries. Because the pumping action of the heart has little effect on the blood traveling through the veins, the walls of the veins are much thinner than that of the arteries, and its lumen is larger. The lower blood pressure in the veins also makes it more difficult for blood to travel back towards the heart against the force of gravity. In order to accommodate this difficulty, the veins have one-way valves to prevent backflow of the blood away from the heart. Deoxygenated blood enters the heart via the superior and inferior vena cava.

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