The hair structure is very unique and it’s one of the defining characteristics of both humans and animals. Hair consists mainly of keratin (a fibrous structural protein constituting the outermost layer of skin in mammals and other skin appendages).
The presence of keratin in hairs gives them an elastic property, enabling hair tissues to resist damage from friction caused by scratching, patting, and rubbing, or minor trauma caused by falls.
Hairs project from hair follicles found in almost all parts of the skin, except the lips, soles of the feet, and palms. Generally, the part of hairs exposed at the skin surface is called the hair shaft, while the part anchored in hair follicles is called the hair root.
The hair shaft consists of three layers; the cortex, medulla, and cuticle.
The cuticle: It is the outermost layer of the hair shaft. This layer consists of overlapping cells that look like fish scales, which strengthen and protect the hair shaft. The cuticle protects the hair shafts’ inner parts. It is highly keratinized (contains a large number of cells with keratin).
The cuticle also controls the water content of the hair fiber, by regulating the amount of water that can pass through it, and enter the cortex. This helps maintain the flexibility of hairs.
The cortex: It is the layer between the cuticle and medulla. It forms the main bulk of the hair shaft. The melanin pigment is located within the cortex, which provides the hair shaft with its color.
The melanin pigment found in the cortex is divided into two types; phenomenon, and eumelanin. Pigments of eumelanin dark colors (black and brown), while pheomelanin produces light colors (yellow, blonde, e.t.c.) Hair color is derived from the combination of eumelanin and pheomelanin pigments in ratios. However, eumelanin is the most prevalent.
The medulla: It is the innermost layer of the hair shaft. Also known as the hair shafts’ marrow, or pith, is not present in all hair — it is present in thick large hair. Generally, medullas are not found in fine and blonde hair.
Functions of Hair.
Hair has numerous functions. Animal hair is very important for both animals and human beings. Human hair also has crucial functions. Let’s look at these functions.
Functions of Animal Hair.
Warmth: Hairs help keep animals warm. When the temperature drops, the hairs trap a layer of air close to the skin of the animal. Since air is a poor conductor but a good insulator of heat, this layer of air prevents heat from escaping from the animal into the environment. The greater the number of hairs, the greater the layer of air trapped, and the greater the insulating property.
The color of animal hair also affects its insulating capability. White hair is has a greater insulating capability than brown hair. Brown hair contains pigments that give it its color, while white hair is devoid of these pigments, giving it its white color.
Because white hair lacks pigments, air can replace the spaces meant for these pigments. Hence, white hairs can trap a greater amount of air than brown hairs, and also has a greater insulating capability.
To buttress this point, consider polar bears. Polar bears that are found in the cold regions of the arctic have thick white coats. These white coats increase the insulating property of their hairs and help them warm.
Human beings also use the furry coats of animals to make clothes that keep them warm in cold temperatures.
Sensory Function: Just like the skin, hairs also act as sensory organs. Sensory nerve fibers can be found at the base of hair follicles. This sensory nerve fibers transmit sensory impulses to the brain when the hairs are touched, bent, or drawn out. In some animals, there are specific hairs that serve as sensory units; the whiskers.
Animals use whiskers as a complementary sensory organ, especially in the dark. Animals like cats might find it difficult to rely on only their eyes to find prey at night. Whiskers, however, make this task easier.
Protection: The hair of animals also serve as a means of protection in some animals, and even self-defense. Manes of horses, for example, could protect their necks from the bites of predators – if the bite isn’t very ferocious. Animals like hedgehogs and porcupines have spiny skin. These spiny hairs can be used to ward off predators.
Camouflage: Animal hair is used by some animals for camouflage. The arctic fox for example uses their hairy coat for camouflage. Their coat color changes with the seasons. In summer, its coat is brown to blend in with the tundra grasses, while in winter, its coat turns white to blend in with the snow.
Functions of Human Hair.
Thermoregulation: Human hair helps the body maintain constant internal body temperature. When external temperature drops, the hair erector muscles contract, raising the skin hairs. This enables the hairs to trap a large amount of air close to the skin and prevent internal body heat from escaping into the environment.
When the external temperature rises, the hair erector muscles relax, making the hairs on the skin lie flat. This prevents the hairs from trapping air close to the skin, hence allowing internal body heat to escape into the environment.
Health Determiner: Our hairs could also be used to determine if we are sick or not. Changes in the outlook of our hairs could be signs of underlying health conditions. For example, a person with brittle hair could have Cushing’s syndrome.
Of course, this doesn’t mean that anyone with brittle hair has Cushing’s syndrome, but it is a symptom of the disease. A person with dry scalp or hair could be lacking fat. Thinning hair could also be a sign of low body protein. Even early grey hairs could be a sign of extreme stress.
Industrial Use: Due to the human hair’s unique properties like its chemical composition, high tensile strength, and slow degradation rate, it is used in making varieties of products. For example, a human hair is used in making cosmetic brushes, wigs, eyelashes, beards, and the like. It could also be used as fertilizer.