Structure of Hair and Hair Follicles

‭Structure of Hair and Hair Follicles‬ ‭ These are p cells polyhedral, poorly pigmented and therefore stacked on top of each other.‬ ✪ ‭Around this cord, there is the cortex or bark or even cortical zone which is thicker and which is‬ ‭made of elongated cells, parallel to the axis of the hair and these cells havelong contain keratins and‬ ‭melanin, melanosomes and these cells are responsible for hair coloring. There is a third zone at this‬ ‭stem, which is called the epidermis which is an outer layer which is made of cells flattened,‬ ‭keratinized and this Keratin is different from the keratin located in the cells of the epidermis‬ ‭because it is harder. The second part of the hair is the shaft, an area which is included in the‬ ‭epidermis and here again we go find the three parts, the three constituents:the medulla, the bark and‬ ‭the epidermis but what is particular is that this root is housed in a structure derived from the‬ ‭epidermis: the hair follicle (a kind of cylindrical bag) which is an invagination of the epidermis.‬ ‭ To the surface of the epidermis, a sort of cylindrical depression dug into the epidermis and inside‬ ✪ ‭this depression is the root of the hair. The basal part of this type of cylinder is swollen and forms‬ ‭what is called the bulb pileu. At Level of this bulb there is a kind of depression where a certain‬ ‭quantity of connective tissue comes from the dermis, this depression is the papilla. Here is a‬ ‭representation of the hair: We see the oblique insertion, the shaft on the outside and the rootwith the‬ ‭same constitution in 3 layers but we see that this stem, this root is inserted in a structure which is‬ ‭the hair follicle which comes from the epidermis and there is a more or less cylindrical invagination‬ ‭and at the level of the extremity terminal a depression in which there is connective tissue coming‬ ‭from the dermis. This hair follicle is made up of different layers of cells, different sheaths: one outer‬ ‭sheath which actually includes all the layers of the epidermis at the level of the surface then which‬ ‭things a little at the level of the deepest part to keep that the deep layers towards the papilla. Then,‬ ‭there is an inner epithelial sheath located between the outer epithelial sheath and the hair root.‬ ‭ This Internal epithelial sheath is not constant but only at the level of the deepest part of the root‬ ✪ ‭and in particular it stops at the level of the junction of the sebaceous gland.‬ ‭They are actually at the level of the hairs glands that are sebaceous and therefore this internal‬ ‭epithelial sheath stops at the level of the junction of the sebaceous gland. There is also a fibrous‬ ‭sheath made of different types of fibers.‬ ‭ The deepest part of this hair follicle and hair root is a shovel the matrix and this matrix is the‬ ✪ ‭place where the cells are located which are at the origin, which will proliferate and which are at the‬ ‭origin of the different layers of the hair: the bark, the marrow, the epidermis. And therefore there‬ ‭are melanocytes which are in significant proportion in this area: melanocytes which produce‬ ‭melanin which distribute it to the keratinocytes. And so this matrix is in close contact with the‬ ‭dermal papilla so there is a sort of depression at the level of this matrix which is filled by dermis‬ ‭and at this level there are numerous capillaries and this area of the dermis with its capillaries which‬ ‭will allow nutrition and regulation of proliferating cells in the matrix.‬ ‭ There is a muscle called the mohair actor scale which is inserted at the level of the hair bulb‬ ✪ ‭therefore in the lower part of this bulb pile therefore of this kind of epidermal cylinder which sinks‬ ‭into depth and it is also inserted at the level of the epidermis therefore quite on the surface and‬ ‭when it contracts, it causes a modification of the inclination of the hair, it That's what gives you‬ ‭goosebumps. Around this bile follicle there is a capillary network which is very abundant and there‬ ‭are also myelinated nerve endings.‬ ‭ Hair growth occurs discontinuously therefore there are periods of rest, there is no true‬ ✪ ‭synchronization between the different regions and this growth of hair is linked to hormonal‬ ‭impregnation by hormones sexual, thyroidiennes, adrenals therefore during the regeneration of a‬ ‭hair, it is the cells of the external sheaths which become active and which will reconstitute the‬ ‭matrix therefore if the hair has been torn off the outer sheath persists and from it there is‬ ‭regeneration of the matrix first and then all the different elements.‬