- 1. One of the fine, keratinized filamentous epidermal growths arising from the skin of the body of mammals except the palms, soles, and flexor surfaces of the joints; the full length and texture of h. varies markedly in different body sites. SYN: pilus (1) [TA]. 2. One of the fine, hairlike processes of the auditory cells of the labyrinth, and of other sensory cells, called auditory h., sensory h., etc. SYN: thrix [TA]. [A.S. haer]- bamboo h. h. with regularly spaced nodules along the shaft caused by intermittent fractures with invagination of the distal h. into the proximal portion, with intervening lengths of normal h., giving the appearance of bamboo; seen in Netherton syndrome; autosomal recessive trait. SYN: trichorrhexis invaginata.- burrowing hairs SYN: ingrown hairs.- club h. a h. in resting state, prior to shedding, in which the bulb has become a club-shaped mass.- downy h. [TA] fine, soft, lightly pigmented fetal h. with minute shafts and large papillae; it appears toward the end of the third month of gestation. SYN: lanugo [TA], primary h., lanugo h..- exclamation point h. the type of dystrophic anagen h. found at margins of patches of alopecia areata; the bulb is absent.- Frey hairs short hairs of varying degrees of stiffness, set at right angles into the end of a light wooden handle; used for assessing sensation.- ingrown hairs hairs that grow at more acute angles than is normal, and in all directions; they incompletely clear the follicle, turn back in, and cause pseudofolliculitis. SYN: burrowing hairs.- kinky h. tightly curled or bent h.. See kinky-h. disease.- lanugo h. SYN: downy h..- nettling hairs sharp-pointed barbed hairs of certain caterpillars which cause a dermatitis when brought in contact with the skin.- primary h. downy h..- pubic h. [TA] one of the pubic hairs; the h. of the pubic region just above the external genitals. SYN: pubes (1) [TA].- ringed h. a rare condition in which the h. shows alternate pigmented and bright segments, the latter due to air cavities within the cortex. SYN: pili annulati.- Schridde cancer hairs thick lusterless hairs scattered in the beard and the temporal region, said to occur in cancerous patients but found also in persons with other cachectic conditions.- spun glass h. SYN: uncombable h. syndrome.- stellate h. h. split in several strands at the free end.- taste hairs hairlike projections of gustatory cells of taste buds; electron micrographs show them to be clusters of microvilli.- twisted hairs SYN: pili torti, under pilus.- hairs of vestibule of nose [TA] one of the hairs growing at the nares, or vestibule of the nose. SYN: vibrissa [TA].
* * *hair 'ha(ə)r, 'he(ə)r n, often attrib1) a slender threadlike outgrowth of the epidermis of an animal esp one of the usu. pigmented filaments that form the characteristic coat of a mammal2) the hairy covering of an animal or a body part esp the coating of hairs on a human headhair·like -.līk adj
* * *n.a threadlike keratinized outgrowth of the epidermis of the skin. It develops inside a tubular hair follicle. The part above the skin consists of three layers: an outer cuticle; a cortex, forming the bulk of the hair and containing the pigment that gives the hair its colour; and a central core (medulla), which may be hollow. The root of the hair, beneath the surface of the skin, is expanded at its base to form the bulb, which contains a matrix of dividing cells. As new cells are formed the older ones are pushed upwards and become keratinized to form the root and shaft. A hair may be raised by a small erector muscle in the dermis, attached to the hair follicle.
* * *(hār) [L. pilus; Gr. thrix] 1. a long, slender filament. 2. in most mammals, one of the filamentous appendages growing out of the skin, consisting primarily of keratin, and comprising a cylindrical shaft and a root, which is contained in a follicle. The base of the root expands to form the hair bulb, which rests upon and encloses the hair papilla. The three phases from production of a hair to its final shedding are called the hair cycle (q.v.). In anatomical terminology, hairs in different locations are given specific names, e.g., pili, capilli, tragi, vibrissae, pubes, hirci.
Hair in longitudinal section (A), and in cross section (B), showing the surrounding root and dermal sheaths.
Medical dictionary. 2011.