Which tissue layer does not contain any blood vessels or connective tissue?
Connective tissue may or may not be avascular - it depends on the composition of the connective tissue. Avascular tissue is any tissue that does not contain blood vessels or lymphatics. Examples include epithelial tissue layers and the cornea. Elastic fibers, a form of connective tissue is avascular, but muscle is vascular.
whereas most tissue are vascular (contain blood vessels), epithelium is avascular, meaning it lacks blood vessels. epithelial cells receive their nutrients from capillaries in the underlying connective tissue. although blood vessels do not penetrate epithelial sheets, nerve endings do; that is, epithelium is innervated (supply organ with nerve).
Blood vessels can be termed as organs, since an organ is a group of http://wiki.answers.com/dictionary/Tissues that perform a specific http://wiki.answers.com/dictionary/Function or group of functions. The function of blood vessels is to circulate blood to various parts of the body. The tissues that make up blood vessels(arteries and veins) are- endothelial tissue(endothelium)-tunica intima, smooth muscle or muscular tissue- tunica media and connective tissue- tunica externa, while capillaries only contain endothilial tissue.
Connective tissues are based on fibrous proteins, and include bones, cartilage, tendons, ligaments, and adipose tissue (stores fat). Blood and lymph are generally classified as "fluid connective tissue" although they do not have a fixed structure and are normally constrained by epithelial cells, such as those lining the blood vessels.
connective The outer layer of a blood vessel (artery or vein) is called the tunica externa or tunica adventitia. See <A href="http://training.seer.cancer.gov/module_anatomy/unit7_3_cardvasc_blood1_classification.html">http://training.seer.cancer.gov/module_anatomy/unit7_3_cardvasc_blood1_classification.html</A> pericardium is the layer of the blood vessel that is made of tough connective tissue.