It also contains hormones that affect hair growth and structure during different stages of life, like puberty. Temperature regulation (sweat glands to cool down; goosebumps to keep warm). Huxley layer is keratinized above the Henle’s layer at the region known as Adamson’s fringe. A hair bulb is just one of many structures of or associated with hair follicles. The nearness of broad veins move supplements and oxygen to the lower layers of the epidermis. The isthmus is the lower portion of the upper part of hair follicle between the opening of the sebaceous gland and the insertion of arrector pili muscle. In the precortical matrix, these melanosomes are transferred to the hair shaft keratinocytes and formed a pigmented hair shaft. Skin is the largest organ in the body. Several microfibrils come together to form larger units called macrofibril which represents almost 50% of the cortex material. The bulb is home to several types of stem cells that divide every 23 to 72 hours, faster than any other cells in the body. Available from: Fundamentals of Sexually Transmitted Infections, Regression and involution stage of hair follicle cycle, Active hair shaft shedding stage of hair follicle cycle, Fully keratinized, dead hair formed at telogen stage, Fine hairs on the fetus body; shed in utero or within the first weeks after birth, Non-pigmented, and generally non-medullated; short hairs, Consists of rapidly proliferating keratinocytes that move upwards to produce the hair shaft, Onion-shaped portion of hair bulb surrounded by hair matrix cells, consists of mesenchymally derived tissues, Lowermost portion of the hair follicle, includes the follicular dermal papilla and the hair matrix, The lower portion of the upper part of hair follicle between the opening of the sebaceous gland and the insertion of arrector pili muscle, Uppermost portion of the hair follicle extending from the opening of the sebaceous gland to the surface of the skin, Segment of the outer root sheath located at insertion of arrector pili muscle, Guides the hair shaft and helps to take a shape; coats the hair shaft up to the isthmus level, Extends along from the hair bulb to the infundibulum and epidermis serves as a reservoir of stem cells, Significant mesenchymal follicular layer that adheres to the basement membrane of the hair follicle and interacts with the follicular dermal papilla, Blond/red hair: predominance of pheomelanin, Bakırköy Dr. Sadi Konuk Research and Training Hospital, İstanbul, Turkey. They migrate in a downward direction. 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. 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]. By interlocking with the cuticle cells of inner root sheath, they contribute to the follicular anchorage of the growing hair. Our team is growing all the time, so we’re always on the lookout for smart people who want to help us reshape the world of scientific publishing. The hair bulb forms the base of the hair follicle. During the telogen stage, the hair shaft is transformed to club hair and finally shed. The bulb holds several types of stem cells that divide every 23 to 72 hours, faster than any other cells in the body. The first sign of catagen is the termination of melanogenesis in the hair bulb. The hair bulb is where hair production takes place. From dermis, wall of hair follicle. Eventually, the lower hair follicle becomes reduced to an epithelial strand, bringing the dermal papilla into close proximity of the bulge . A hair bulb is just one of the structures of or associated with hair follicles. Almost 85–90% of all scalp hairs are in anagen. The bulb is the stocking-like structure that surrounds the papilla and germinal matrix. In addition, the thyroid gland should be checked as the quality of your life depends on its function. The arrector pili muscle, takes place between the hair bulge area and dermoepidermal junction. By Gürkan Yardımcı, Server Serdaroğlu and Zekayi Kutlubay. 4. 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 follicle is an organ found in mammalian skin. 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 suprabulbar region of the follicle, below the isthmus and above the hair bulb, is comprised of three layers from outermost to innermost: outer root sheath, inner root sheath and hair shaft (Figure 2). How? Basically terminal hairs are found on scalp, eyebrows and eyelashes at birth while the rest of the body is covered with vellus hairs. 2 The anatomy of the hair… We share our knowledge and peer-reveiwed research papers with libraries, scientific and engineering societies, and also work with corporate R&D departments and government entities. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. β-Catenin is the downstream mediator of WTN signaling. & Treatments, Vitamins The inner root sheath hardens before the presumptive hair within it, and so it is thought to control the definitive shape of the hair shaft. The featured regulatory proteins in anagen phase are BMPs, sonic hedgehog, several WNT proteins and receptors. The telogen stage is defined as the duration between the completion of follicular regression and the onset of the next anagen phase. In humans, hair has various functions such as protection against external factors, sebum, apocrine sweat and pheromones production and thermoregulation. The presence of hairless gene mutation contributes to the failure of dermal papilla migration toward the bulge area in catagen phase . The hair shaft is composed of three parts – the cuticle, the cortex and the medulla. Insulin like growth factor-1 (IGF-1), fibroblast growth factor-7 hepatic growth factor (HGF), and vascular endothelial growth factor (VEGF) are thought to be important for anagen maintenance . Connective tissue root sheath (outer) from dermis, wall of hair follicle. The ultimate signal from this primitive dermal papilla to the epithelial placode cells indicates a rapid proliferation and differentiation. Furthermore, the hair pigment, melanin, is a potent free-radical scavenger. Hair starts growing at the bottom of a hair follicle. Catagen phase is consisted of eight different stages. It is ceased in early the anagen-catagen transition, restarted with the down-regulation of key enzymes of melanogenesis, followed by hair follicle melanocyte apoptosis. beard, trunk, axilla and genital area) by the influence of androgens differentiate to terminal hairs, which are long (>2 cm), thick (>60 μm), pigmented and medullated. There is an active division of the cells in the bulb. There are cells at the base of the bulb that divide to produce new hair cells. gustatory b's taste buds. *Address all correspondence to: email@example.com, Edited by Zekayi Kutlubay and Server Serdaroglu. Until recently, the IP of the hair follicle is considered to be restricted to the matrix region during the anagen phase. Functional deterioration of antigen presenting cells. These imbrications are crucial. Companion layer cells show numerous intercellular connections to the inner root sheath and are thought to migrated distally along with the inner root sheath to the isthmus region and to form the plane of slippage between the inner and outer root sheaths [1, 3, 14, 16]. Hair development is a continuous cyclic process and all mature follicles go through a growth cycle consisting of growth (anagen), regression (catagen), rest (telogen) and shedding (exogen) phases (Figure 3). Submitted: June 14th 2016Reviewed: December 15th 2016Published: May 3rd 2017. The innermost layer is the cuticle of IRS whose cells interlock with those of the hair cuticle. In this chapter, the basic anatomy and the amazing and complicated biology of the hair follicle is reviewed. Built by scientists, for scientists. The hair bulb consists of epithelial cells that surround the papilla. 2. About 54 functional keratin genes (28 type I and 26 type II keratins) have been identified to date. This consecutive signaling process finally leads to the production of the mature follicle. contained might not be completely up to date. These imbricated surfaces also facilitate removal of dirt and desquamated cells from the scalp. 3. attached together), dead, keratinized cells. However recent progress in our understanding of the biology and pathology of hair follicles should lead more effective therapies for hair disorders. In addition to producing the main structural components of hair, they also produce the hair keratins, and their associated proteins (KAPs) . Catagen is a process of bulbar involution. Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft. During catagen the proximal of the hair shaft is keratinized and forms the club hair, whereas the distal part of the follicle is involuted by apoptosis [16, 38]. Thereafter, the epithelial placode expands and generates the primary hair germ (stage 2). Hair shaft diameters represent little variations and hairs are found to be thicker in androgen dependent areas. Inner root sheath (IRS) contains three layers: Henle’s layer, Huxley layer and cuticle layer. The bulb is always present when it comes from the source (that is, the follicle). Hair production involves a specialized keratinization process. These cells take place in certain functions of the follicle such as acting as a sensory organ and serving as an immunologic sentinel for the skin . Lanugo, vellus and terminal hairs follow the same basic architectural principles. Login to your personal dashboard for more detailed statistics on your publications. Hair shaft is the first part of the hair that is above skin. Anatomy and Physiology of Hair, Hair and Scalp Disorders, Zekayi Kutlubay and Server Serdaroglu, IntechOpen, DOI: 10.5772/67269. Fig, 8 The derma/ papilla. Other immune privileged sites include the anterior chamber of the eye, testis, brain and placenta. Hair in particular is slow to respond to any stimulus. The infundibulum, the uppermost portion of the hair follicle extending from the opening of the sebaceous gland to the surface of the skin, is a funnel-shaped structure filled with sebum, the product of the sebaceous glands. The papilla provides blood supply to the hair follicles for healthy hair. Your hair is made of two parts - the hair follicle and the hair shaft. It has the following parts : 1. Hair and naif structure and function HAIR ANATOMY Two main types of hair are present after birth, ... (fig.8), which is located in the center of the hair bulb and surrounded by the epidermally derived germinative epithelium. Lineage studies have proven that bulge cells are multipotent and that their progeny generate the new lower anagen hair follicle . Hair is consisted of two distinct structures: follicle—the living part located under the skin and hair shaft—fully keratinized nonliving part above the skin surface. Catagen lasts approximately 2 weeks in humans, regardless of the site and follicle type . Excretion (the skin is sometimes referred to as the \"third kidney\"). I think some of these companies make very generalized claims about their products. All hair lost at the root will contain a bulb. Hair protects our bodies from harmful objects. As the follicle extends to its maximum length, matrix cells proliferate and differentiate into the cells of the new hair. Each of the three layers of IRS undergoes abrupt keratinization. Moreover the follicular papilla is an essential source of growth factors [1, 3, 16, 28]. The main function of the hair follicle is to produce a hair shaft or fiber. 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 . at bottom of bulb; dermal tissue protrudes into hair bulb, knot of capillaries supplies nutrients and signals hair to grow. Brief introduction to this section that descibes Open Access especially from an IntechOpen perspective, Want to get in touch? hair bulb the bulbous expansion at the proximal end of a hair, in which the hair shaft is generated. Most of these are tiny, colorless vellus hairs. Activation of this β-catenin pathway seems to be essential for the epithelial ability of the hair follicle production . Hair follicle development is related to the interactions between epithelial and mesenchymal cells. Free nerve endings transmit pain, lanceolate nerve endings detect acceleration, Merkel cells responsible of pressure sensation and pilo-Ruffini corpuscles detect tension. Thought, Therapies Hair covers almost all of our body except for the palms of our hands, soles of the feet, and lips. Hair is one of the characteristic features of mammals and has various functions such as protection against external factors; producing sebum, apocrine sweat and pheromones; impact on social and sexual interactions; thermoregulation and being a resource for stem cells. Subsequently, hair matrix melanocytes begin to develop pigment and the form of the hair shaft begins to arise; in anagen VI, hair bulb and adjacent the dermal papilla formation is realized and the new hair shaft appears from the skin. The papilla: The bottommost part of the bulb, the papilla connects to the follicle root and is where nutrients, oxygen, and energy are delivered from the blood vessels. In the hair bulb, living cells divide and grow to build the hair shaft. 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. The only living cells of a hair are in and near the hair bulb. Hair follicle melanocytes and their precursors reside in the hair matrix and along the outer root sheath of anagen hair follicles.
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