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. Different hair and epithelial keratins are expressed in the various concentric layers of the hair follicle, with hair keratins found primarily in the cortex and hair cuticle [1, 2]. 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. Eventually, the lower hair follicle becomes reduced to an epithelial strand, bringing the dermal papilla into close proximity of the bulge [36]. The perifollicular sheath collapses and vitreous membrane thickens. Six portion of the anagen stage is demonstrated. About 54 functional keratin genes (28 type I and 26 type II keratins) have been identified to date. Excretion (the skin is sometimes referred to as the \"third kidney\"). The cortex comprises the bulk of the shaft and also contains melanin [2, 15, 16]. Canonical (β-catenin dependent) WNT (wingless-type integration site) signals are candidates for the initial dermal message, and it is believed that they precede other activators and regulators of appendage development. It is surrounded by mesenchymal cells that eventually transformed to the fibrous sheath. To date our community has made over 100 million downloads. 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. The hair follicle IP is maintained by several factors [32]: Downregulation of MHC class I expression in the proximal ORS and matrix cells. The hair papilla is an intrusion of the underlying dermis into the hair bulb. Telogen stage lasts for 2–3 months. Accuracy cannot be guaranteed. Ithas various functions including: 1. The IRS is derived from the lower and laterally located matrix cells, whereas the hair shaft is originated from upper and centrally located cells. In humans, hair has various functions such as protection against external factors, sebum, apocrine sweat and pheromones production and thermoregulation. 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. The hair assumes its color via the amount and the type of the phagocytized major pigment [1, 3, 16, 25]. It may be small or large, white or pigmented. Each of the three layers of IRS undergoes abrupt keratinization. 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. 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. Healthy looking hair is in general a sign of good health and good hair-care practices. There are cells at the base of the bulb that divide to produce new hair cells. Nerves related to the hair follicle are identical to the dermal nerve network including sensory afferents and autonomic sympathetic nerves. 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. The actions of EDA/EDAR and WNT promote placode formation, whereas BMP signaling represses placode fate in adjacent skin [6]. ... bulge area is spar ed, a new hair bulb and 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. Probably, the hair cycle clock is controlled by regulating the balance of the interactions between the follicle epithelium and the surrounding mesenchyme. Lineage studies have proven that bulge cells are multipotent and that their progeny generate the new lower anagen hair follicle [21]. Medulla is located in the center of the hair shaft preferably presented in coarser fibers. Only few differentiated corneocytes remain and the invagination of the epidermis in this area must be considered as highly permeable for topically applied compounds [19]. Brief introduction to this section that descibes Open Access especially from an IntechOpen perspective, Want to get in touch? By interlocking with the cuticle cells of inner root sheath, they contribute to the follicular anchorage of the growing hair. Angel Thoughts by IvyRose. Hair follicle IP occurs during anagen [30]. When they reach the upper part of the bulb, they arrange themselves into six concentric layers. . a school giving instruction in one or more of the fine or dramatic arts a comic character, usually masked, dressed in multicolored, diamond-patterned tights, and carrying a wooden sword or magic wand TAKE … The aim of this chapter is to enhance the knowledge of the complex anatomy and physiology of the hair in a simple manner (Table 1) [2, 5]. Several microfibrils come together to form larger units called macrofibril which represents almost 50% of the cortex material. It's fed by capillaries. Protection (against sun, rain, bugs, infection, etc).Skin has two main parts - the epidermis anddermis.The epidermis has fivelayers. The hair follicle also contains melanocyte stem cells, which are located in the bulge and in the secondary hair [33–35]. Thereafter, the epithelial placode expands and generates the primary hair germ (stage 2). 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. Cuticle has also important protective properties and barrier functions against physical and chemical insults [14–16]. Skin is the largest organ in the body. The inception of anagen phase is presented by the onset of the mitotic activity in the secondary epithelial germ located between the club hair and dermal papilla in telogen hair follicle [5, 16]. However, evidence has accumulated that the IP of the hair follicle extends to the bulge region and is present at this site during the entire hair cycle. The bulb is always present when it comes from the source (that is, the follicle). At the isthmus level, epithelium keratinization begins with the lack of granular layer named “trichilemmal keratinization” [14, 16]. 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]. In the hair bulb, living cells divide and grow to build the hair shaft. Bulge stem cells are then activated to self-renew and replenish the hair germ stem cells. The papilla provides blood supply to the hair follicles for healthy hair. Above the insertion of the arrector pili muscle, sebaceous glands and, in some certain regions, apocrine glands are opened into the follicle. 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). It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. Almost 85–90% of all scalp hairs are in anagen. Hair shaft diameters represent little variations and hairs are found to be thicker in androgen dependent areas. The root of the hair is made up of protein cells and is nourished by blood from nearby blood vessels. The hair bulb is the bulb-shaped structure at the base of the hair follicle of which it is a part. These imbrications are crucial. Melanocytes reside among matrix stem cells to produce the pigment of the hair. The ones located in several areas like scalp, eyebrows and eyelashes are thicker, longer and pigmented and are called terminal hairs. Hairs are threads of fused (i.e. Outer root sheath (ORS) extends from the epidermis at the infundibulum and continues to the hair bulb and its cells change considerably throughout the follicle. Yesterday's Angel During the hair cycle phases, there are some alterations in the density of perifollicular vascularization due to the upregulation of vascular endothelial growth factor expression [1]. Local production of potent immunosuppressants like TGF-β1, IL-10 and α-MSH. Hair follicle has a continuous growth and rest sequence named hair cycle. Many genes play substantial role in this interaction and also in hair follicle cycling [3–5]. Melanin synthesis is established in lysosome-related organelles named melanosomes. One of the main functions of hair is to act as a sensitive touch receptor. Although care has been taken when compiling this page, the information These imbricated surfaces also facilitate removal of dirt and desquamated cells from the scalp. The protein products of these genes are presented during the different phases of hair cycle, indicating that they are so important for the normal development and distribution of follicles as well as for the ongoing growth process [4, 5]. 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 [36]. Human hair follicle morphogenesis occurs only once. 3. Thought See terms of use. The arrector pili muscle, takes place between the hair bulge area and dermoepidermal junction. 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). 3. Free nerve endings transmit pain, lanceolate nerve endings detect acceleration, Merkel cells responsible of pressure sensation and pilo-Ruffini corpuscles detect tension. Hair loss with a white bulb at the beginning of each hair there is the bulb (that white dot). 4,18 Although they vary in size and shape depending on location, the basic structure of the hair follicle is similar – rapidly proliferating matrix cells in the hair bulb and a hair shaft composed of intermediate filaments and associated proteins enveloped by a dermal sheath. β-Catenin is the downstream mediator of WTN signaling. The hair follicle is one of the characteristic features of mammals serves as a unique miniorgan (Figure 1). During the migration of the cells from the hair bulb to compose the cortex, the shapes of them become more fusiform. Fiber length is often dependent on the duration of the anagen or actively growing phase of the follicle [17]. 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. at bottom of bulb; dermal tissue protrudes into hair bulb, knot of capillaries supplies nutrients and signals hair to grow. 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]. The column eventually reduces to a nipple and forms secondary hair germ below the club. It holds a knot of capillaries that provides nutrients to the growing hair follicle. The hair follicle is an organ found in mammalian skin. Hair covers almost all of our body except for the palms of our hands, soles of the feet, and lips. It’s based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. The initial “message” for the development of all types of skin appendages is from the dermal mesenchyme (stage 0) and hair follicle development begins with the accumulation of epithelial cells to form epithelial placode after the initial mesenchymal signals (stage 1). Enhanced knowledge on the normal dynamics of the hair provides understanding the basis of how the follicle behaves during a disease. The innermost layer is the cuticle of IRS whose cells interlock with those of the hair cuticle. Hair follicle melanocytes and their precursors reside in the hair matrix and along the outer root sheath of anagen hair follicles. Inner root sheath (IRS) contains three layers: Henle’s layer, Huxley layer and cuticle layer. 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. 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]. By Gürkan Yardımcı, Server Serdaroğlu and Zekayi Kutlubay. Until recently, the IP of the hair follicle is considered to be restricted to the matrix region during the anagen phase. The hair also plays important roles for the individual’s social and sexual interaction [1, 2]. The hair follicle represents an immune privileged (IP) site, which is defined basically as a location in the body where foreign tissue grafts can survive for longer periods of time without immune rejection. Built by scientists, for scientists. Melanin production inside the active anagen hair bulb may, therefore, help to buffer cell stress induced by reactive oxygen species. This is caused by premature breakage, typically a … Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft. Cutaneous vascularization is provided by arterioles, which are concentrated at the lower portion of the hair follicle and compose vascular network. 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]. Flat and square-shaped cuticle cells are adhered tightly to the cortex cells proximally. The division of the cells in the bulb leads to the production of the cells of the hair shaft. This might be provided by the rhythmic secretions of growth/modulatory signals from follicle epithelium or mesenchyme as well as the rhythmic alterations in the expressions of corresponding receptors [40]. Bulb. Ectodysplasin (EDA) and its receptor (EDAR) are another important pathways involved in the placode stage of hair morphogenesis. There are several types of nerve endings associated with the hair follicle: free nerve endings, lanceolate nerve endings, Merkel cells and pilo-Ruffini corpuscles. Functional deterioration of antigen presenting cells. Hair shaft synthesis and pigmentation only take place in anagen [11]. The hair bulb consists of epithelial cells that surround the papilla. Angels help in life's everyday situations, not just in cases of high drama. 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. Perifollicular nerves related neuromediator and neuropeptides, that is, substance P, calcitonin gene-related peptide influence follicular keratinocytes and hair follicle cycling [1, 3, 16]. In utero, type and distribution of each hair follicle over the entire body are determined. At the end of anagen, mitotic activity of the matrix cells is diminished and the follicle enters a highly controlled involutionary phase known as catagen. The hair shaft consists of a cortex and cuticle cells, and a medulla for some types of hairs. 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]. Help us write another book on this subject and reach those readers. Contact our London head office or media team here. The ultimate signal from this primitive dermal papilla to the epithelial placode cells indicates a rapid proliferation and differentiation. 2. 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. More pages in this category(in alphabetical order): More pages in this category (in alphabetical order): This is in the Structures of the Skin section of the health glossary. These continually divide and push upwards, gradually hardening. Papilla. After these first two cycles, hair starts to grow in an asynchronous “mosaic” pattern rather than in waves [2]. 3. Glossary of terms for hair anatomy and physiology. The IRS coats and supports the hair shaft up to the isthmus level where the IRS disintegrates [3, 14, 16]. attached together), dead, keratinized cells. The hair is classified into three main ethnic subgroups (Asian, African and European). Hair shaft diameters, hair follicle density and follicular infundibulum volume are some of them. During the telogen stage, the hair shaft is transformed to club hair and finally shed. Follicular papilla, which is derived from a condensation of mesenchymal cells at the early stages of follicular embryogenesis, is one of the most important players during the induction and maintenance of the follicular epithelial differentiation. 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. Bending the hair stimulates the nerve endings allowing a person to feel that the hair has been moved. 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. The follicle is the essential unit for the generation of hair. This phase can last up to 6–8 years in hair follicles [1, 11, 18]. The immunology of hair is very amazing and complicated. The nearness of broad veins move supplements and oxygen to the lower layers of the epidermis. 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]. 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. & Treatments, Vitamins 2  I think some of these companies make very generalized claims about their products. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides, and immune cells. In the second stage of development, hair germ elongates into a cord of epithelial cells and forms the hair peg (stages 3 and 4). Several molecular pathways, growth factors, proteins and genes play substantial roles for the development of the hair follicle. 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]. This material is copyright. We are IntechOpen, the world's leading publisher of Open Access books. As the follicle extends to its maximum length, matrix cells proliferate and differentiate into the cells of the new hair. Hair follicle density is much more condense in the forehead and follicular infundibular volume is also bigger. . Most of these are tiny, colorless vellus hairs. The only living cells of a hair are in and near the hair bulb. Vellus hairs are thin (<30 μm), short (<2 mm) and mostly nonmedullated. In the precortical matrix, these melanosomes are transferred to the hair shaft keratinocytes and formed a pigmented hair shaft. The matrix proteins are separated to three major subgroups according to their amino acid compositions [29]. The dermal pupil is located inside the bulb. 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. The mouse EDAR mRNA is expressed in the epithelium before placode formation, and then becomes restricted to placodes, whereas the EDA mRNA is still expressed even after placode formation [3, 6, 8]. The hair shaft is composed of three parts – the cuticle, the cortex and the medulla. However, production of hair pigment (black eumelanin and/or the reddish pheomelanin) only occurs in the specialized hair follicle pigmentary unit, located above and around the dermal papilla during anagen III–VI. Anatomy and Physiology of Hair, Hair and Scalp Disorders, Zekayi Kutlubay and Server Serdaroglu, IntechOpen, DOI: 10.5772/67269. It is responsible for determining the follicle type. Huxley layer is keratinized above the Henle’s layer at the region known as Adamson’s fringe. Hair follicles remain in late anagen for variable lengths of time, depending on hair type and species. 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. By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers. Other immune privileged sites include the anterior chamber of the eye, testis, brain and placenta. It is important just because of the large follicular infundibular volume that is associated with more follicular reservoir ability [1, 13]. A hair without a bulb, then, means the hair was lost prior to the root. The ORS of the hair follicle also contains melanocytes, Langerhans cells and Merkel cells. Follicular epithelium, mesenchyme, neuroectodermal cell populations and also perifollicular vascular and neural systems demonstrates cyclic changes in differentiation and apoptosis. 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. The papilla of a hair follicle comprises of many veins that give supplements to help in the development, development, and cycling of the hair. Catagen phase is consisted of eight different stages. Submitted: June 14th 2016Reviewed: December 15th 2016Published: May 3rd 2017. There is less interest for the mechanism of the hair shedding but from the patient’s perspective it is probably the most important part of the hair growth. 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. All hair lost at the root will contain a bulb. The principal challenge is to define the underlying “oscillator” system. Open Access is an initiative that aims to make scientific research freely available to all. The bulb also contains hormones that affect hair growth and structure during different stages of life, such as during puberty and during pregnancy. It is the lowermost layer of the integumentary system in vertebrates. 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. It sits at the very top of the dermis (top layer of skin). The bulb of the terminal hairs is located in the subcutaneous fat; however, the bulb of vellus hairs is in the reticular dermis. In addition to producing the main structural components of hair, they also produce the hair keratins, and their associated proteins (KAPs) [24]. Furthermore, the hair pigment, melanin, is a potent free-radical scavenger. The second signal arises from epithelial placode and constitutes a cluster of adjacent mesenchymal cells which later develops the dermal papilla (DP). The anatomy of the hair… Activation of this β-catenin pathway seems to be essential for the epithelial ability of the hair follicle production [7]. The duration of growth and rest cycles is coordinated by many endocrine, vascular and neural stimuli and depends not only on localization of the hair but also on various factors, like age and nutritional habits. The club hair itself is formed from cortical and cuticle cells only, and it is characterized by a lack of pigmentation [2, 37]. BMPs in the subcutaneous fat are capable of maintaining follicles in a “refractory” telogen, and cessation of this inhibitory activity by BMPs enables the follicle to progress to a “competent” telogen with a hair germ that is responsive to anagen-initiation signals and capable of entering a new anagen phase [2, 41]. In this chapter, the basic anatomy and the amazing and complicated biology of the hair follicle is reviewed. At the base of the hair follicle are sensory nerve fibers that wrap around each hair bulb. The hair follicle can be a target for therapeutic agents. The bulb is the stocking-like structure that surrounds the papilla and germinal matrix. The hair follicle serves as a reservoir for epithelial and melanocyte stem cells and it is capable of being one of the few immune privileged sites of human body. Catagen lasts approximately 2 weeks in humans, regardless of the site and follicle type [37]. Hair in particular is slow to respond to any stimulus. The degree of axial symmetry within the hair bulb determines the curvature of the final hair structure [35]. Thought, Therapies Hair follicle development is related to the interactions between epithelial and mesenchymal cells. This specialized immune environment of IP is required to prevent destructive immune reactions in critical regions. The hair bulb is the bulb-shaped structure at the base of the hair follicle of which it is a part. During the development of bullous peg (stages 5–8), the hair bulb and the main cell layers of the mature hair follicle are also formed [2–4, 6]. The hair bulb is where hair production takes place. The matrix cells are localized to the lowermost portion of the follicle and surround all sides of the follicular papilla. Hair production involves a specialized keratinization process. Since the bulge represents the hair follicle stem cell niche, sustained IP in this region may be essential for the survival of the follicle. Hair production takes place, Zekayi Kutlubay and Server Serdaroglu, IntechOpen, the outermost anatomy and physiology of morphogenesis. In vertebrates constitutes a cluster of adjacent mesenchymal cells that divide to produce the pigment of the interactions between layers!, Langerhans cells and is nourished by blood from nearby blood vessels which deliver nutrients the. To produce a hair, hair has various functions such as protection against external factors sebum. 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