hair

hair, slender threadlike outgrowth from the skin of mammals. In some animals hair grows in dense profusion and is called fur or wool. Although all mammals show some indication of hair formation, dense hair is more common among species located in colder climates and has the obvious function of insulation against the cold. Other functions include camouflage and protection against dust and sand. The long, sensitive hairs, called tactile hairs, that are located around the mouth area of most mammals are extremely sensitive to touch. Each hair filament originates in a deep pouchlike depression of the epidermis, called a hair follicle, which penetrates into the dermis. The root of the hair extends down into the hair follicle and widens into an indented bulb at its base. Extending into the indentation is the papilla, the center of hair growth, which contains the capillaries and nerves that supply the hair. Newly dividing cells at the base of the hair multiply, forcing the cells above them upward. As the cells move upward, they gradually die and harden into the hair shaft. The hair shaft has two layers, the cuticle and the cortex. The cuticle (outer layer) consists of flat, colorless overlapping cells; below the cuticle is the cortex, containing pigment and a tough protein called keratin; it forms the bulk of the hair shaft. Coarse hair, such as that of the scalp, contains an additional inner core called the medulla. Hair is lubricated by sebaceous glands that are located in the hair follicle. Illness or stress may lessen the secretion of pigment, which normally gives color to hair, and cause the hair shaft to whiten. However, the normal process of whitening that comes with age is determined by heredity. In humans, scalp hairs are generally shed every two to four years, while body hairs are shed more frequently. Straight-textured hair, round in cross section, is common among Native Americans, Eskimos, and Mongoloid peoples. Kinky or woolly hair, flat in cross section, prevails among the dark peoples of Africa, Australia, and elsewhere. Wavy or curly hair, common among Caucasians, is oval in cross section. The color of hair is determined by the amount of pigment and air spaces in the cortex and medulla. Hair color and texture are inherited characteristics.

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hair

Threadlike outgrowths of the skin. Babies shed a layer of downy, slender hairs (lanugo) before or just after birth. The fine, short, unpigmented hairs (vellus) then grow. Starting at puberty, terminal hair, longer, coarser, and more pigmented, develops in the armpits, crotch, sometimes on parts of the trunk and limbs, and, in males, on the face. Scalp hair, eyebrows, and eyelashes are different types. The number of scalp hairs, which grow about 0.5 in. (13 mm) per month, averages 100,000–150,000. The hair shaft (above the skin) is dead tissue, composed of keratin. Only a few growing cells at the base of the root are alive. Hair is formed by cell division at the base of the follicle (a tiny pocket in the skin), part of a cycle of growing, resting, and falling out. Vellus lasts about four months, scalp hairs three to five years.

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hair

1. any of the threadlike pigmented structures that grow from follicles beneath the skin of mammals and consist of layers of dead keratinized cells

2. a growth of such structures, as on the human head or animal body, which helps prevent heat loss from the body

3. Botany any threadlike outgrowth from the epidermis, such as a root hair

4. a fabric or material made from the hair of some animals

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hair [her]

(zoology)

A threadlike outgrowth of the epidermis of animals, especially a keratinized structure in mammalian skin.

The hairy coat of a mammal, or of a part of the animal.

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Hair

Nonliving, specialized epidermal derivatives characteristic only of modern mammals. However, it is now thought that hair was present in at least some therapsid reptiles. It consists of keratinized cells, tightly cemented together, which arise from the matrix at the base of a follicle. A follicle is a tubular epidermal downgrowth that penetrates into the dermis and widens into a bulb (the hair root) at its deep end. The follicle, together with a lateral outgrowth called the sebaceous gland, forms the pilosebaceous system. Rapid cell production in the matrix, and differentiation in the regions immediately above, produces a hair shaft which protrudes from the follicle mouth at the skin surface. See Gland

Hairs are not permanent structures but are continually replaced throughout the life of a mammal. In some species, for example, the rat, hamster, mouse, chinchilla, and rabbit, the replacement pattern is undulant, and waves of follicular activity can be traced across the body. In other species, for example, humans, cats, and guinea pigs, each follicle appears to cycle independently of others in the immediate area.

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Hair

Happiness (See JOY.)

Absalom

hair entangled in branches, he was left dangling. [O.T.: II Samuel 18:9]

Aslaug

used hair as cloak to meet king. [Norse Myth.: Walsh Classical, 35]

Beatles

famous English rock group whose initial appeal was derived partly from their moplike haircuts. [Br. Hist.: NCE, 253]

Bes

shaggy-haired, shortlegged god with tail. [Egyptian Myth.: Leach, 138]

Buffalo Bill

(William F. Cody, 1846–1917) American cowboy and showman whose image was fortified by his long blond hair. [Am. Hist.: NCE, 390]

Cousin Itt

Addams’s relative; four feet tall and completely covered with blond hair. [TV: “The Addams Family” in Terrace, I, 29]

Custer, General George

(1839–1876) American army officer whose image included long, yellowish hair. [Am. Hist.: NCE, 701]

Enkidu

hirsute companion of Gilgamesh. [Babyl. Myth.: Gilgamesh]

Godiva, Lady

(d. 1057) Leofric’s wife who rode through Coventry clothed only in her long, golden hair. [Br. Hist.: Payton, 274]

Gruagach

“the hairy one”; fairy lady. [Scot. Folklore: Briggs, 206–207]

hippies

1960s “dropouts of American culture” usually identified with very long hair adorned with flowers. [Popular Culture: Misc.]

Hair

rock musical celebrating youthful exuberance as evidenced by growing long hair. [Am. Mus.: On Stage, 517]

Mullach, Meg

long-haired and hairy-handed brownie. [Scot. Folklore: Briggs, 284–285]

Rapunzel

her golden tresses provide access to tower loft. [Ger. Fairy Tale: Rapunzel]

Samson

the Hercules of the Israelites; rendered powerless when Delilah cut off his hair. [O.T.: Judges 13–16]

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hair - [back-formation from hairy] The complications that make something hairy. "Decoding TECO commands requires a certain amount of hair." Often seen in the phrase "infinite hair", which connotes extreme complexity. Also in "hairiferous" (tending to promote hair growth): "GNUMACS elisp encourages lusers to write complex editing modes." "Yeah, it's pretty hairiferous all right." (Or just: "Hair squared!")