The follicle is the essential unit for the generation of hair. 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]. This phase can last up to 6–8 years in hair follicles [1, 11, 18]. Vellus hairs are thin (<30 μm), short (<2 mm) and mostly nonmedullated. 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]. The expanded onion-shaped portion of the lower hair follicle, including the hair matrix and the follicular papilla is known as the hair bulb which is the active reproductive portion of the hair follicle. The hair shaft and IRS are derived from the matrix cells. In puberty, some vellus hairs (i.e. Other immune privileged sites include the anterior chamber of the eye, testis, brain and placenta. The hair papilla is an intrusion of the underlying dermis into the hair bulb. See terms of use. Functional deterioration of antigen presenting cells. Several molecular pathways, growth factors, proteins and genes play substantial roles for the development of the hair follicle. & Crystals, several layers of different types of cells that extend up through the hair follicle. Fiber length is often dependent on the duration of the anagen or actively growing phase of the follicle [17]. 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 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. Login to your personal dashboard for more detailed statistics on your publications. The bulb of the terminal hairs is located in the subcutaneous fat; however, the bulb of vellus hairs is in the reticular dermis. Catagen phase is consisted of eight different stages. EDAR is necessary for placode development in primary hair follicles but not for induction of secondary hair follicles, which utilize signaling pathways that involve Noggin and SRY-box 18 (SOX18) expression within the dermal papilla [9, 10]. NAHA supports lavender via ABC's adopt-an-herb - 22 Dec '19, Garlic and Artichoke adopted through ABC's Adopt-an-Herb Program - 14 Jun '19, Cranberry Harvest underway in USA - 5 Oct '18, Total retail sales of herbal supplements in the USA exceeded $8 Billion in 2017 - 13 Sep '18, It's a bumper blueberry season - 13 Jul '18, Positive effects of exercise on blood cell populations - 20 Jun '18. In the precortical matrix, these melanosomes are transferred to the hair shaft keratinocytes and formed a pigmented hair shaft. However recent progress in our understanding of the biology and pathology of hair follicles should lead more effective therapies for hair disorders. The duration of the phases changes based on the location of the hair and also personal nutritional and hormonal status and age [15, 33]. Hair follicle development is related to the interactions between epithelial and mesenchymal cells. How? Help us write another book on this subject and reach those readers. Hair protects our bodies from harmful objects. The matrix proteins are separated to three major subgroups according to their amino acid compositions [29]. In this chapter, the basic anatomy and the amazing and complicated biology of the hair follicle is reviewed. The bulb is always present when it comes from the source (that is, the follicle). Yesterday's Angel 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. 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. One of the main functions of hair is to act as a sensitive touch receptor. The bulb also contains hormones that affect hair growth and structure during different stages of life, such as during puberty and during pregnancy. Hair follicle IP occurs during anagen [30]. The hair is classified into three main ethnic subgroups (Asian, African and European). Your hair is made of two parts - the hair follicle and the hair shaft. 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 bulb forms the base of the hair follicle. Licensee IntechOpen. In the second stage of development, hair germ elongates into a cord of epithelial cells and forms the hair peg (stages 3 and 4). 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]. Flat and square-shaped cuticle cells are adhered tightly to the cortex cells proximally. In addition to producing the main structural components of hair, they also produce the hair keratins, and their associated proteins (KAPs) [24]. Approximately 10–15% of all hair is in telogen stage. Contact our London head office or media team here. In addition to FGF5, TGF-β1, IL-1b, the neurotrophins NT-3, NT-4 and BMP2/4 and TNF-α have been described to induce catagen [36]. The hair also plays important roles for the individual’s social and sexual interaction [1, 2]. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides, and immune cells. Probably, the hair cycle clock is controlled by regulating the balance of the interactions between the follicle epithelium and the surrounding mesenchyme. Above the insertion of the arrector pili muscle, sebaceous glands and, in some certain regions, apocrine glands are opened into the follicle. Angels help in life's everyday situations, not just in cases of high drama. Thickened basement membrane, holds everything inside, separates epidermis from dermis A hair bulb is just one of the structures of or associated with hair follicles. Hair follicle anchors or holds the hair into the scalp. 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 hair bulb consists of epithelial cells that surround the papilla. Local production of potent immunosuppressants like TGF-β1, IL-10 and α-MSH. Melanin synthesis is established in lysosome-related organelles named melanosomes. The upper follicle remains constant, while the lower part has continuous cycles of regeneration [1, 2, 16, 18]. The macro-environment surrounding the hair follicle also takes part in regulating cycle transitions. Human hair follicle morphogenesis occurs only once. The IRS is derived from the lower and laterally located matrix cells, whereas the hair shaft is originated from upper and centrally located cells. The actions of EDA/EDAR and WNT promote placode formation, whereas BMP signaling represses placode fate in adjacent skin [6]. Glossary of terms for hair anatomy and physiology. Hair shaft synthesis and pigmentation only take place in anagen [11]. 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. It is surrounded by mesenchymal cells that eventually transformed to the fibrous sheath. In the infundibulum, it resembles epidermis, whereas in the isthmus level, ORS cells begin to keratinize in a trichilemmal mode. ... bulge area is spar ed, a new hair bulb and hair shaft. To date our community has made over 100 million downloads. The bulb is the stocking-like structure that surrounds the papilla and germinal matrix. The hair bulb is the bulb-shaped structure at the base of the hair follicle of which it is a part. Inner root sheath (IRS) contains three layers: Henle’s layer, Huxley layer and cuticle layer. Huxley layer is keratinized above the Henle’s layer at the region known as Adamson’s fringe. The anatomy of the hair… Hair follicle melanocytes and their precursors reside in the hair matrix and along the outer root sheath of anagen hair follicles. There is an active division of the cells in the bulb. It fills in as a model for the trading of the supplements, oxygen and waste items between the layers. 3. Hair covers almost all of our body except for the palms of our hands, soles of the feet, and lips. 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. Built by scientists, for scientists. 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 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]. 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. Enhanced knowledge on the normal dynamics of the hair provides understanding the basis of how the follicle behaves during a disease. Almost 85–90% of all scalp hairs are in anagen. The root of the hair is made up of protein cells and is nourished by blood from nearby blood vessels. Hair shaft is the first part of the hair that is above skin. The nearness of broad veins move supplements and oxygen to the lower layers of the epidermis. The hair bulb is where hair production takes place. inferior bulb of jugular vein a dilatation of the internal jugular vein just before it joins the brachiocephalic vein. With the fallen hair together with the bulb, a specific analysis can be done – the mineralogram. The second signal arises from epithelial placode and constitutes a cluster of adjacent mesenchymal cells which later develops the dermal papilla (DP). Each hair bulb includes: several layers of different types of cells that extend up through the hair follicle; a region of cells called the germinal matrix (the area of cells that produces new hairs by mitosis) an indentation called the papilla of the hair By Gürkan Yardımcı, Server Serdaroğlu and Zekayi Kutlubay. 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. Hairs are threads of fused (i.e. Below the skin is the hair root. Since the bulge represents the hair follicle stem cell niche, sustained IP in this region may be essential for the survival of the follicle. Keratinocytes in the ORS form the bulge area at the base of the isthmus. The matrix cells are localized to the lowermost portion of the follicle and surround all sides of the follicular papilla. All hair lost at the root will contain a bulb. In summary, the formation of placodes in response to the first dermal signal involves activation of EDA/EDAR signaling in the epithelium, followed by epithelial WNT signaling, and subsequent activation of BMP signaling. It is important just because of the large follicular infundibular volume that is associated with more follicular reservoir ability [1, 13]. The innermost layer is the cuticle of IRS whose cells interlock with those of the hair cuticle. 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). The arrector pili muscle, takes place between the hair bulge area and dermoepidermal junction. Six portion of the anagen stage is demonstrated. Telogen is one of the main targets of hair cycle which is influenced by several modulatory agents like androgens, prolactin, ACTH, retinoids and thyroid hormones [40]. This is caused by premature breakage, typically a … Nerves related to the hair follicle are identical to the dermal nerve network including sensory afferents and autonomic sympathetic nerves. The presence of hairless gene mutation contributes to the failure of dermal papilla migration toward the bulge area in catagen phase [3]. attached together), dead, keratinized cells. The column eventually reduces to a nipple and forms secondary hair germ below the club. Bending the hair stimulates the nerve endings allowing a person to feel that the hair has been moved. Angel Thoughts by IvyRose. 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. However, any apoptosis is occurred in dermal papilla due to the expression of suppressor bcl-2 [11]. 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. Bulb. The antagonist named Noggin neutralizes BMP activity via regulation of lymphoid enhancer factor 1 (LEF1) expression [4]. The dermal pupil is located inside the bulb. 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]. There are several types of nerve endings associated with the hair follicle: free nerve endings, lanceolate nerve endings, Merkel cells and pilo-Ruffini corpuscles. contained might not be completely up to date. 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). It holds a knot of capillaries that provides nutrients to the growing hair follicle. 3. Hair loss with a white bulb at the beginning of each hair there is the bulb (that white dot). 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. 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. At the isthmus level, epithelium keratinization begins with the lack of granular layer named “trichilemmal keratinization” [14, 16]. There are cells at the base of the bulb that divide to produce new hair cells. Extensive knowledge on anatomical and physiological aspects of hair can contribute to understand and heal different hair disorders. The keratin-associated proteins (KAP), is a large group of proteins which constitutes the matrix of the keratin. β-Catenin is the downstream mediator of WTN signaling. Cuticle has also important protective properties and barrier functions against physical and chemical insults [14–16]. Healthy looking hair is in general a sign of good health and good hair-care practices. 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. Melanocytes reside among matrix stem cells to produce the pigment of the hair. 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. This specialized immune environment of IP is required to prevent destructive immune reactions in critical regions. Hair follicle IP has a unique characteristic of recurring in a cyclic pattern. Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft. 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. These cells coalesce tightly and are placed parallel to the axis of the shaft. This is also where the sebaceous gland and the hair bulb is. Each nerve ending responds to distinct stimulus. In addition, the thyroid gland should be checked as the quality of your life depends on its function. 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. 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. The first sign of catagen is the termination of melanogenesis in the hair bulb. Nearly whole body surface is coated with the hairs except a few areas like palms, soles and mucosal regions of lips and external genitalia. In the placode stage, activated WNT and EDAR control the localized accumulation of sonic hedgehog (SHH), which is essential for the downgrowth of the hair germ [2]. 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 hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis (Figure 1). Thus hair follicle IP is limited to the proximal epithelium of anagen hair follicles. The hair bulb encloses folicular dermal papilla, mucopolysaccharide-rich strome, nerve fiber and capillary loop. Derived from the epithelial cells of the hair peg, hair matrix cells form the hair shaft and inner root sheath (IRS). 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. At bottom of bulb, dermal tissue protrudes into hair bulb, knot of capillaries supplies nutrients and signals hair to grow. Hair production involves a specialized keratinization process. Ectodysplasin (EDA) and its receptor (EDAR) are another important pathways involved in the placode stage of hair morphogenesis. Although care has been taken when compiling this page, the information 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]. It is not unusual for human telogen hairs to be retained from more than one follicular cycle and this suggests that anagen and exogen phases are independent. Hair … This connection, anchoring the hair shaft to the hair follicle, is so tight. The papilla of a hair follicle comprises of many veins that give supplements to help in the development, development, and cycling of the hair. 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]. 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. The follicle remains in this stage until the hair germ which is responsive to anagen initiating signals from the dermal papilla, starts to show enhanced proliferative and transcriptional activity in late telogen, leading to the initiation of anagen [2, 39]. 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