There are many organ systems in the human body, each of which needs constant replenishment of nutrients and removal of metabolic products. For this purpose, blood, which is the main transport medium, copes. In this context, it is natural to ask the question of which tissues are devoid of blood vessels. What they are called and how they are fed should be considered in more detail.
Nutrition for articular cartilage
When considering what tissues are devoid of blood vessels, there are two obvious answers to consider. The first is cartilaginous, the second is derivatives of the epidermis of the skin. Cartilaginous hyaline tissue is an example of a connective tissue that forms a protective shock-absorbing shell for the joints. In other cartilages of the body, such as the larynx, auricles, annulus fibrosus and valvesheart blood vessels are present. But in the cartilage that provides protection for the joints, they are not. The nutrition of the articular cartilage is achieved due to the synovial fluid and substances dissolved in it. Also, blood vessels are completely absent in the cornea of the eye, which is supplied by tear fluid.
Derivatives of the epidermis
All derivatives of the epidermis of the skin known in biology are not provided with blood. Such tissues are devoid of blood vessels, which the epidermis itself does not have. It represents dying cells that do not need to be provided with nutrients. Hair, unlike nails and epidermis, has signs of life. Their nutrition is provided by the hair follicle.
Epithelial tissue
Despite indirect communication with the blood supply system, epithelial tissue does not have its own arteries and veins. This answers the question of which tissues are devoid of blood vessels. Why? It should be de alt with in more detail. Any epithelium is a collection of cells located on the basement membrane. The latter is a semi-permeable structure through which nutrients dissolved in the intercellular fluid pass freely. The blood vessels themselves do not penetrate the basement membrane, which is made up of fibrillar proteins.
Epithelial tissue nutrition is achieved through simple diffusion and active transport of substances from the interstitial fluid. There theyenter through the capillary fenestra and freely pass the basement membrane, reaching the epithelial cells. At the same time, nutrients in their greater mass are spent on meeting the needs of the germ layer of the epithelium. The farther away from it, the less nutrition the epithelial tissue receives. However, this is sufficient for its functioning.
To the question of which tissues are devoid of blood vessels in humans, one should answer that they are epithelial, since they are associated only with the intercellular fluid. From it, the epithelium receives nutrition, and metabolic products can be dumped into the opening cavity, and not into the blood. A special situation is observed in the case of the intestinal epithelium, which, in addition to excretion, is able to absorb substances from the intestine.
So, which tissues lack blood vessels? Answer: all epithelial, limited from the vessels by the basement membrane, but indirectly communicating with the circulatory system. Therefore, normally, all nutrients from the intestines also enter the intercellular space and later diffuse into the blood.
