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Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste and carbon dioxide away from the tissues. [2] Some tissues such as cartilage, epithelium, and the lens and cornea of the eye are not supplied with blood vessels and are termed avascular.
In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. [1] [2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels).
The endothelium (pl.: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. [1] The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall.
Veins have less smooth muscle and connective tissue and wider internal diameters than arteries. Because of their thinner walls and wider lumens they are able to expand and hold more blood. This greater capacity gives them the term of capacitance vessels. At any time, nearly 70% of the total volume of blood in the human body is in the veins. [3]
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.
In plant anatomy, tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and the vascular tissue. Epidermis – Cells forming the outer surface of the leaves and of the young plant body. Vascular tissue – The primary components of vascular tissue are the xylem and phloem. These transport fluids and ...
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium.
The human body consists of biological systems, that consist of organs, that consist of tissues, that consist of cells and connective tissue. The history of anatomy has been characterized, over a long period of time, by a continually developing understanding of the functions of organs and structures in the body.