Human hair anatomy - Structure and composition of your hair
Arterioles form an exemplary network with capillary branches supplying sweat glands, sebaceous glands, hair follicles and the dermis. The epidermis has no blood supply. It obtains nutrition and oxygen from interstitial fluid derived from blood vessels in the papillae of the dermis.
Form a network throughout the dermis and the deeper layers of the epidermis. Sensory nerve endings: Nerve endings that are sensitive to touch, change in temperature, pressure and pain are widely distributed in the dermis. The skin is an essential sensory organ through which individuals are aware of their environment.
Nerve impulses, generated in the nerve endings in the dermis, are conveyed to the spinal cord by sensory (somatic cutaneous) nerves, then to the sensory area of the cerebrum where the sensations are perceived.
Sweat glands are found widely distributed throughout the skin and are most numerous in the hand's palm, soles of the feet, axillae and groins. They are composed of epithelial cells. The bodies of the glands lie coiled in the subcutaneous tissue. Some ducts open on the skin surface at tiny depressions or pores, and others open into hair follicles. Glands opening into hair follicles do not become active until puberty. In the axilla, they secrete an odourless milky fluid which, if decomposed by surface microbes, causes an unpleasant odour. The functions of this secretion are not known. Sympathetic nerves stimulate sweat glands in response to raised body temperature and fear.
The essential function of sweat secreted by glands opening on to the skin surface is regulating body temperature. Evaporation of sweat secreted by glands opening on to the skin surface is in regulating body temperature. Evaporation of sweat on the surface takes heat from the body, and the amount produced is governed by the temperature-regulating centre in the hypothalamus. Excessive sweating may lead to dehydration and severe depletion of body sodium chloride unless water and salt intake are appropriately increased. After 7 to 10 days of exposure to high environmental temperatures, the amount of salt lost is substantially reduced, but water loss remains high.
A down-growth of epidermal cells forms these into the dermis or subcutaneous tissue called hair follicles. At the base of the follicle, there is a cluster of cells called the bulb. The multiplication of the bulb cells forms the hair, and as they are pushed upwards, away from their source of nutrition, the cells die and become keratinised. The part of the hair above the skin is the shaft and remainder, the root.
The colour of the hair is genetically determined and depends on the amount of melanin present. White hair is the result of the replacement of melanin by tiny air bubbles.
The arrectores pilorum are little bundles of involuntary muscle fibers attached to the hair follicles. Contraction makes the hair stand erect and raises the skin around the hair, causing 'goose flesh'. Sympathetic nerve fibers stimulate the muscles in response to fear and cold. Although each muscle is very small, the contraction of a large number generates an appreciable amount of heat, especially when accompanied by shivering, i.e. involuntary contraction of the skeletal muscles.
The sebaceous glands consist of secretory epithelial cells derived from the same tissue as the hair follicles. They pour their oily secretion, sebum, into the hair follicles, so they are present in the skin of all parts of the body except the palms of the hands and the feet soles. They are most numerous in the skin of the scalp, face, axillae and groins. In regions of transition from one type of superficial epithelium to another, such as lips, eyelids, nipples, labia minora and glans penis, there are sebaceous glands independent of hair follicles, secreting sebum directly on to the surface.
Hair has a say in deciding how you look and what you look to be. Countless studies about hair are being undertaken, which consider different aspects of the hair in the fields of science, including biology, dermatology, cosmetics, forensic sciences and medicine.
