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Hair and growth of hair
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We view our hair very differently from most of our fellow mammals. We pluck it and shave it, bleach it and color it, and curl it and straighten it as an expression of individual style. But for all the consideration and attention our hair seems to get, most of us don’t know very much about its origins and primary functions. To see hair in its entirety, you have to first go to the roots. This article covers hair structure and function, hair types, growth of hair and the hair cycle.

Hair Structure and Function

In mammals, hair is the collective name for all the fine, thread-like filaments that grow outward from the epidermis. When hair is very dense, as it is in many animals, it is usually called fur or wool. Each tiny hair filament grows outward from a deep, pouch-like depression within the epidermis called a follicle, and extending into the follicles is a group of capillaries and nerves called the papilla. The papilla is the center of hair growth; it is the blood supply of the hair and contains the cells that form individual hair shafts. As cells at the base of the hair divide, they force cells above them to move upward. Gradually, the cells moving upward die and harden into the hair shaft, which is composed of two layers, the cuticle and the cortex. The outer cuticle layer is made up of flat cells that overlap one another kind of like fish scales. Below this is the cortex. Cortex contains all the hair’s pigment and a tough, fibrous protein called keratin.
Hair is characteristic of all mammals, and all mammals are built with the structural components needed to produce hair. The increased density of hair we see in mammals living in colder regions indicates that the primary outward function of hair is in regulating body temperature by insulating the body. The exceptions to this general rule are animals that have been bred to reduce or eliminate this visible hair. Some hairs, like the whiskers on cats, have a specialized sensory function and are extremely sensitive like our fingers. Other functions of hair include camouflage and protection against harmful particles and pathogens. Keeps harmful particles suspended in the air like dust and sand from entering the body, and plays a part in the removal of pathogens within the body as seen in the very rapid growth of hair from moles. Plants and insects also have outward-growing filaments that serve similar functions as hair in mammals. In plants, these “hairs” are called “trichomes”, and in insects and spiders they are called “insect bristles”.
In mammals, hair is the collective name for all the fine, thread-like filaments that grow outward from the epidermis. When hair is very dense, as it is in many animals, it is usually called fur or wool. Each tiny hair filament grows outward from a deep, pouch-like depression within the epidermis called a follicle, and extending into the follicles are groups of capillaries and nerves called the papilla. The papilla serve as the hair’s blood supply and provide the cells that form individual hair shafts. Hair is lubricated by sebaceous glands within the hair follicles.

Hair Function in Mammals

All mammals are built with the structural components needed to produce hair. The increased density of hair we see in mammals living in colder regions indicates that the primary outward function of hair is in regulating body temperature by insulating the body. The exceptions to this general rule are animals that have been bred to reduce or eliminate this visible hair. Some hairs, like the whiskers on cats, have a specialized sensory function and are extremely sensitive like our fingers. Hair prevents particles suspended in the air -- like dust and sand -- from entering the body, and can serve also in the removal of pathogens from within the body, as seen in the very rapid growth of hair from moles. Other functions of hair include camouflage and protection against the harmful ultraviolet component of sunlight. Plants and insects also have outward-growing filaments that serve similar functions as hair in mammals. In plants, these “hairs” are called “trichomes”, and in insects and spiders they are called “insect bristles”.

                     
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