Introduction. Human physiology is the study of the functioning of the normal body, and is responsible for describing how various systems of the human body work. (Seeley R.R., Stephens T.D. and Tate P. Anatomy and Physiology. a: longitudinal section, b: cross section.(Marieb E.N. and Hoehn K. Human Anatomy and Physiology. Figure (): Tracheobronchial Tree.(Seeley R.R., Stephens T.D. and Tate P. Anatomy and Physiology. medical-site.info The Coaching Habit. Essentials of human physiology for pharmacy / by Laurie J. Kelly p. ; cm. — (CRC .
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Textbook of medical physiology / Arthur C. Guyton, John E. Hall.—11th .. the majesty of the human body and its many functions and that it stimulates students to. BiolHuman Anatomy and Physiology-Syllabus/Course Calendar and Physiology PDF textbook is also available for you to access. Both items are free. T W ELF TH EDITION Stuart Ira Fox Pierce College TM medical-site.info i 22/07/10 PM HUMAN PHYSIOLOGY, TWELFTH EDITION Published by.
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 addition to producing the main structural components of hair, they also produce the hair keratins, and their associated proteins KAPs [ 24 ]. Melanocytes reside among matrix stem cells to produce the pigment of the hair. During their differentiation phase, matrix cells phagocytose melanin or pheomelanin from the dendritic elongations of melanocytes.
The hair assumes its color via the amount and the type of the phagocytized major pigment [ 1 , 3 , 16 , 25 ]. 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.
It is responsible for determining the follicle type. 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 ].
Moreover the follicular papilla is an essential source of growth factors [ 1 , 3 , 16 , 28 ]. Molecular structure Keratin proteins can be divided into two major families: the type I acidic keratins and the type II basic-neutral keratins.
About 54 functional keratin genes 28 type I and 26 type II keratins have been identified to date. 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 keratin-associated proteins KAP , is a large group of proteins which constitutes the matrix of the keratin. The matrix proteins are separated to three major subgroups according to their amino acid compositions [ 29 ].
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 ]. Hair follicle innervation and vascularization Nerves related to the hair follicle are identical to the dermal nerve network including sensory afferents and autonomic sympathetic nerves.
Smaller nerve fibers form a circular layer around the bulge area of terminal follicles and the bulb area of vellus follicles. There are several types of nerve endings associated with the hair follicle: free nerve endings, lanceolate nerve endings, Merkel cells and pilo-Ruffini corpuscles.
Each nerve ending responds to distinct stimulus. Free nerve endings transmit pain, lanceolate nerve endings detect acceleration, Merkel cells responsible of pressure sensation and pilo-Ruffini corpuscles detect tension. Perifollicular nerves related neuromediator and neuropeptides, that is, substance P, calcitonin gene-related peptide influence follicular keratinocytes and hair follicle cycling [ 1 , 3 , 16 ].
Cutaneous vascularization is provided by arterioles, which are concentrated at the lower portion of the hair follicle and compose vascular network. 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 ].
Immunology of hair follicle The immunology of hair is very amazing and complicated. 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. This specialized immune environment of IP is required to prevent destructive immune reactions in critical regions.
Other immune privileged sites include the anterior chamber of the eye, testis, brain and placenta. Hair follicle IP has a unique characteristic of recurring in a cyclic pattern.
Until recently, the IP of the hair follicle is considered to be restricted to the matrix region during the anagen phase. 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.
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 follicle IP occurs during anagen [ 30 ]. Thus hair follicle IP is limited to the proximal epithelium of anagen hair follicles. During anagen, melanogenesis is activated in the hair bulb and suggests that hair follicle melanocyte autoantigens play a key role as potential immune targets [ 28 , 31 ].
Functional deterioration of antigen presenting cells. Absence of lymphatics. Establishment of extracellular matrix barriers to hinder immune cell trafficking. Expression of non-classical MHC class 1. Expression of fas ligand.
Pigmentation of hair follicle Hair shaft pigmentation ensures multiple benefits including UV protection, thermoregulation and sexual perceptions. Furthermore, the hair pigment, melanin, is a potent free-radical scavenger.
Melanin production inside the active anagen hair bulb may, therefore, help to buffer cell stress induced by reactive oxygen species.
In contrast to the continuous melanogenesis observed in epidermal melanocytes, follicular melanogenesis is a cyclic phenomenon. 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.
Hair follicle melanocytes and their precursors reside in the hair matrix and along the outer root sheath of anagen hair follicles. Melanin synthesis is established in lysosome-related organelles named melanosomes. In the precortical matrix, these melanosomes are transferred to the hair shaft keratinocytes and formed a pigmented hair shaft. The hair follicle also contains melanocyte stem cells, which are located in the bulge and in the secondary hair [ 33 — 35 ].
Physiology of the hair 4. The duration of the phases changes based on the location of the hair and also personal nutritional and hormonal status and age [ 15 , 33 ]. The hair cycle. Anagen 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 ].
The anagen is the active growth phase in which the follicle enlarges and takes the original shape and the hair fiber is produced.
Six portion of the anagen stage is demonstrated. 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. 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.
This phase can last up to 6—8 years in hair follicles [ 1 , 11 , 18 ].
Hair shaft synthesis and pigmentation only take place in anagen [ 11 ]. The degree of axial symmetry within the hair bulb determines the curvature of the final hair structure [ 35 ]. Fiber length is often dependent on the duration of the anagen or actively growing phase of the follicle [ 17 ]. 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 ].
Catagen 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.
Catagen lasts approximately 2 weeks in humans, regardless of the site and follicle type [ 37 ]. 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 ].
Catagen phase is consisted of eight different stages. The first sign of catagen is the termination of melanogenesis in the hair bulb. Follicular epithelium, mesenchyme, neuroectodermal cell populations and also perifollicular vascular and neural systems demonstrates cyclic changes in differentiation and apoptosis. However, any apoptosis is occurred in dermal papilla due to the expression of suppressor bcl-2 [ 11 ]. Catagen is a process of bulbar involution.
The perifollicular sheath collapses and vitreous membrane thickens. Eventually, the lower hair follicle becomes reduced to an epithelial strand, bringing the dermal papilla into close proximity of the bulge [ 36 ]. The epithelial strand begins to elongate and finally reaches to just below the insertion of pilar muscle.
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.
Awards and recognition for Dr. Kramer is a former research scientist and university professor Lincoln College of New England, Southington CT who founded Ingenium Patents LLC which specializes in providing services to inventors and companies developing new products.
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Institutional Subscription. Instructor Ancillary Support Materials. Free Shipping Free global shipping No minimum order. Covers the physiology, anatomy, nutrition, biochemistry and cell biology of humans, showing how they are distinguished from other animals Includes medical literature and internet references, example test questions, and a list of pertinent words at the end of each chapter Provides unique perspective into all aspects of what makes up and controls humans.
Medical researchers and graduate students of physiology.