Why is Hair Important?

The hair is considered as the characteristic feature of mammals and it possesses numerous functions including providing protection against external factors and dealing with the production of pheromones, apocrine sweat, and sebum. It is found to have a great impact on sexual and social interactions. It functions in thermoregulation and is found to be a storage site of the stem cells.

Structure of Hair

The hair is considered a keratinous filament growing from the epidermal layer of the skin and is composed of nonliving keratinized cells. The epidermal penetration zone of the dermis is the origination site of the hair and this structure is referred to as the hair follicle. The hair shaft in the region of the hair is not connected to the follicle and the majority of this region is found in the external region of the skin. The balance region found below the surface layer of the skin is called the hair root. The hair root is positioned dipinto the dermis at a region called the hair bulb and it encompasses a layer, called hair matrix that undergoes active cell division. The hair papilla is enclosed by the hair bulb and is composed of numerous connective tissues, blood capillaries, and nerve endings positioned in the dermis of the skin.

The basal layer of the epidermis generates the epidermal layer that is conveyed to the surface region of the dead skin. The basal cells detected in the hair bulb undergo division and move out of the hair root as the growth of the hair shaft is detected. The central core of the hair is known as the medulla and is enclosed by the cortex. The cortex is a layer composed of compressed keratin cells enclosed by an external layer called the cuticle. 

Texture of Hair

The texture of the hair is determined by the structure and shape of the cortex and the medulla. The shape of these structures is found to be influenced by the shape of the hair follicle.The production of keratinocytes is the initial step in the production of hair in the body.The basal cells generate the keratinocyte and the newly formed cells are positioned in the hair bulb. The hair shaft is found to push in the direction of the surface through the follicle, the process of keratinization completes and the hair is completely positioned on the surface layer of the skin. The externally visible shaft is considered dead and possesses keratin. The wall layer of the hair follicle is composed of three concentric layers, where the internal root sheath is enclosed by the root of the growing hair. The position of the basal cell in the hair matric gives rise to the formation of these types of cells. The external root sheath surrounds the hair root. 

The structure is mainly composed of basal cells positioned at the basal region of the hair root and the region is comparatively more keratinized than the other regions. The glassy membrane of the hair is composed of clear and thick connective tissue that originate din the hair root. The hair follicle is composed of numerous layers of cells that are generated from the basal cells detected in the hair root and the hair matrix. The cells found in the hair matrix undergo differentiation and division to form multiple layers of hair.

Function of Hair

The hair provides numerous functions in the body encompassing sensory input, protection, communication, and thermoregulation. The skull is protected from exposure to the sun by the hair. The hair identified in the nose, eyes, and ears prevent the entry of dust or any hazardous substances from the external environment. They also prevent allergies from developing in the respective regions of the body. The hair detected in the eyebrows avoids the formation of sweat and other substances affecting the eye. The sensory innervation detected in the hair root plexus aids in the sensory function of the hair. The hair is highly sensitive to the movement of the air and this characteristic aids in the detection of hazardous substances or insects in the environment. Arrector pili also connect to the hair root and the smooth muscle and contract in response to sympathetic stimulation. The hair traps a layer of air and supports the insulation of heat. They have a greater impact on the life of organisms surviving in colder conditions, where heat is retained in the body for maintaining homeostasis.

Growth of Hair

The hair undergoes eventual shedding and regrowth through three stages including the anagen phase, catagen phase, and telogen phase. The rapid division of cells is detected during the anagen phase and is found to take place for 2-7 years. The catagen phase requires 2-3 weeks and it mediates a transition from the active growth of the hair follicle. The telogen phase of the hair growth lasts for 2-4 months and is followed by the next anagen phase, the basal cells detected in the hair matrix generate a new hair follicle and mediate the expulsion of old hair. About 50 hairs are found lost in a day. The hair loss is found to take place as the number of hairs lost per day is much higher than the number of hairs replaced. 

Aging is found to have a major impact on the growth of hair. The melanin is found to provide the color of the hair and is generated from the melanocytes detected in the papilla. The variation in the type of melanin pigment detected codes for the formation of diverse types of hair. The melanin production is found to be lowered during the process of aging consequently, the hair turns white or grey.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

• B.Sc. Biochemistry and Molecular biology
• Bachelor of Molecular and cellular biology
• M.Sc. Biological science
• M.Sc. in Biomolecular chemistry
• Masters in Biotechnology

Related Concepts

Homeostasis, keratinocytes, and vellus hair