The upper part named acroinfundibulum, the keratinization of epithelium turns into the “epidermal mode”, with formation of stratum granulosum and stratum corneum like a similar manner to epidermis [1, 14, 16]. Axial keratin filaments (microfibrils) that are formed from multiple hard α-keratin intermediate filaments (α-KIF) molecules, packs each cortex cells. Flat and square-shaped cuticle cells are adhered tightly to the cortex cells proximally. Lanugo, vellus and terminal hairs follow the same basic architectural principles. On entering the hair bulb matrix, they proliferate and undergo terminal differentiation to form the hair shaft and inner root sheath. The matrix proteins are separated to three major subgroups according to their amino acid compositions [29]. No unique molecular markers associated with the telogen follicle are determined yet; however, estrogen receptor expression is reported to be limited to the telogen papilla fibroblasts. These continually divide and push upwards, gradually hardening. However, any apoptosis is occurred in dermal papilla due to the expression of suppressor bcl-2 [11]. inferior bulb of jugular vein a dilatation of the internal jugular vein just before it joins the brachiocephalic vein. It may be small or large, white or pigmented. Bulge stem cells are then activated to self-renew and replenish the hair germ stem cells. 2  Through the anagen I–V, hair stem cells proliferate, encloses the dermal papilla, grow downwards to the skin and begin to proliferate hair shaft and IRS, respectively. The hair assumes its color via the amount and the type of the phagocytized major pigment [1, 3, 16, 25]. The bone morphogenic protein-4 (BMP-4) as a growth factor plays an essential role in suppressing follicular growth and differentiation at telogen stage [16]. In contrast to EDA and EDAR, members of the bone morphogenic protein (BMP) family of secreted signaling molecules seem to be inhibitors of placode formation. The root of the hair is made up of protein cells and is nourished by blood from nearby blood vessels. The volume and secretory activity of follicular papilla and also the number of matrix stem cells determine the size of the anagen hair bulb, the duration of anagen phase and the diameter of the hair shaft [11, 26, 27]. Enhanced knowledge on the normal dynamics of the hair provides understanding the basis of how the follicle behaves during a disease. Yesterday's Angel β-Catenin is the downstream mediator of WTN signaling. HeadquartersIntechOpen Limited5 Princes Gate Court,London, SW7 2QJ,UNITED KINGDOM. There are 11 type I hair keratins, designated K31–K40, and 6 type II hair keratins, designated K81–K86, and the remainder are epithelial keratins [24]. Contact our London head office or media team here. Bending the hair stimulates the nerve endings allowing a person to feel that the hair has been moved. Hair follicle density is much more condense in the forehead and follicular infundibular volume is also bigger. The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis (Figure 1). Eventually, the lower hair follicle becomes reduced to an epithelial strand, bringing the dermal papilla into close proximity of the bulge [36]. Most healthy individuals have adequate nutrients in their diet; however some people do not have access to good nutrition, others have medical illnesses that predispose them to nutritional deficiency which influence scalp / body hair.Nutrition is a complex subject – the effects of correct nutrition are indirect and often slow to appear. Outer root sheath (ORS) generates two bulges along the side of the hair follicle, the proximal bulge serves as a reservoir for epithelial stem cells and the distal bulge evolves to sebaceous glands. Hair follicle IP has a unique characteristic of recurring in a cyclic pattern. The topic of the structure of a hair follicle is included in some courses in health sciences, including subjects such as nursing, skin care, hair care, beauty therapy and various holistic therapies. Hair shaft is consisted of three layers: cuticle, cortex and in certain cases medulla. Structure and Function of Hair . The ultimate signal from this primitive dermal papilla to the epithelial placode cells indicates a rapid proliferation and differentiation. About 54 functional keratin genes (28 type I and 26 type II keratins) have been identified to date. Based on the observations: the hair follicle has no need for intact innervation, vascularization or other extrafollicular components to maintain cycling, and the basic oscillator system which controls hair cycling is located presumably in the follicle [42]. It is important just because of the large follicular infundibular volume that is associated with more follicular reservoir ability [1, 13]. Accuracy cannot be guaranteed. Hair follicle development is related to the interactions between epithelial and mesenchymal cells. It holds a knot of capillaries that provides nutrients to the growing hair follicle. There are several types of nerve endings associated with the hair follicle: free nerve endings, lanceolate nerve endings, Merkel cells and pilo-Ruffini corpuscles. Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft. This connection, anchoring the hair shaft to the hair follicle, is so tight. The hair follicle can be a target for therapeutic agents. At the lower tip of the hair bulb it consists of a single layer of cuboidal cells, becoming multilayered in the region of the upper hair bulb. Telogen stage lasts for 2–3 months. This is also where the sebaceous gland and the hair bulb is. The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis (Figure 1). The hair bulb forms the base of the hair follicle. The anatomy of the hair… The hair medulla contains structural proteins that are markedly different from other hair keratins and eosinophilic granules that are filled by an amino acid, citrulline and eventually form internal coatings within the membranes of mature cells [14, 16, 17]. . They migrate in a downward direction. The shedding period is believed to be an active process and independent of telogen and anagen thus this distinct shedding phase is named exogen [16, 33]. After the keratinization of the presumptive club hair, the epithelial strands begin to involute and shorten progressively followed by the papilla which condenses, moves upward and locates to rest below the bulge. Nerves related to the hair follicle are identical to the dermal nerve network including sensory afferents and autonomic sympathetic nerves. See terms of use. Medulla is located in the center of the hair shaft preferably presented in coarser fibers. The first “coat” that is formed is fine, long, variably pigmented lanugo hair, which is shed in an anterior to posterior wave during last trimester of gestation. The bulb is the stocking-like structure that surrounds the papilla and germinal matrix. The hair bulb grows around a bud of vascular connective tissue called the dermal papilla, which provides the hair with its sole source of nutrition. 3. These imbricated surfaces also facilitate removal of dirt and desquamated cells from the scalp. Each of the three layers of IRS undergoes abrupt keratinization. Bilgen Erdoğan (May 3rd 2017). Several molecular pathways, growth factors, proteins and genes play substantial roles for the development of the hair follicle. Thereafter, the epithelial placode expands and generates the primary hair germ (stage 2). All hair lost at the root will contain a bulb. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too. Activation of this β-catenin pathway seems to be essential for the epithelial ability of the hair follicle production [7]. contained might not be completely up to date. The immunology of hair is very amazing and complicated. The column eventually reduces to a nipple and forms secondary hair germ below the club. Vellus hairs are thin (<30 μm), short (<2 mm) and mostly nonmedullated. The papilla of a hair follicle comprises of many veins that give supplements to help in the development, development, and cycling of the hair. Hair follicle has a continuous growth and rest sequence named hair cycle. The hair shaft and IRS are derived from the matrix cells. Yesterday's Angel Melanocytes reside among matrix stem cells to produce the pigment of the hair. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. This specialized immune environment of IP is required to prevent destructive immune reactions in critical regions. This is an oval-shaped indentation at the base of the bulb that contains blood vessels which deliver nutrients to each follicle and hair shaft. The upper follicle remains constant, while the lower part has continuous cycles of regeneration [1, 2, 16, 18]. 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