hair (redirected from Vellus hair)

hair (har) pilus; a threadlike structure, especially the specialized epidermal structure composed of keratin and developing from a papilla sunk in the dermis, produced only by mammals and characteristic of that group of animals. Also, the aggregate of such hairs.hair´y

Hair in longitudinal section (A), and in cross section (B), showing the surrounding root and dermal sheaths.

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bamboo hair  trichorrhexis nodosa.

beaded hair  hair marked with alternate swellings and constrictions, as in monilethrix.

burrowing hair  one that grows horizontally beneath the surface of the skin.

club hair  one whose root is surrounded by a bulbous enlargement composed of keratinized cells, preliminary to normal loss of the hair from the follicle.

ingrown hair  one that emerges from the skin but curves and reenters it.

lanugo hair  lanugo.

resting hair  see telogen.

sensory hairs  hairlike projections on the cells of sensory epithelium.

taste hairs  clumps of microvilli that form short hairlike processes projecting into the lumen of a taste pore from the peripheral ends of the taste cells.

Taste hairs protruding from the pore of a taste bud.

terminal hair  the coarse hair on various areas of the body during adult years.

twisted hair  one which at spaced intervals is twisted through an axis of 180 degrees, being abnormally flattened at the site of twisting.

vellus hair  vellus (1).

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hair (hâr) n. 1. Any of the cylindrical, keratinized, often pigmented filaments characteristically growing from the epidermis of a mammal. 2. A growth of such filaments, as that forming the coat of an animal or covering the scalp of a human. 3. One of the fine hairlike processes of a sensory cell.

hair

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hair

1. a threadlike keratinized epidermal structure developing from a follicle sunk in the dermis, produced only by mammals and characteristic of that group of animals. Also, the aggregate of such hairs.

2. various other threadlike structures.

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auditory h's

hairlike attachments of the epithelial cells of the inner ear.

awn hair

in cats, a short thick, bristly hair underneath the top coat.

hair beds

coat hairs occur in groups of about three primary follicles and a variable number of secondary follicles.

burrowing hair

one that grows horizontally in the skin.

hair cells

sensory neuroepithelial cells which have hair-like processes; found in organ of Corti, ampullary crests and utricle and saccule of the inner ear.

club hair

a hair whose root is surrounded by a bulbous enlargement composed of keratinized cells, preliminary to normal loss of the hair from the follicle.

hair coat

see coat (1).

cover hair

see guard hair (below).

hair follicle

one of the tubular invaginations of the epidermis enclosing the hair roots and from which the hairs grow.

Longitudinal section of hair follicle. By permission from Smith BP, Large Animal Internal Medicine, Mosby, 2001

hair follicle unit

see apopilosebaceous complex.

hair granuloma

granuloma in the esophageal wall caused by swallowed hairs acting as foreign bodies.

hair growth cycle

a period of growth, called anagen, is followed by a transitional stage, called catagen, and then a period of inactivity in the hair follicle, called telogen, lasting until the cycle starts again. The duration of each stage varies with the species, anatomical location, genetic influence, and a variety of environmental and physiological factors.

guard hair

the coarse, stiff and often longer and more prominent hairs in a haircoat with an undercoat. For example, the darkly colored, outer hairs of a German shepherd dog. Called also primary hair, master hair, cover hair.

ingrown hair

one that has curved and re-entered the skin.

lanugo hair

the fine hair on the body of the fetus.

master hair

see guard hair (above).

primary hair

see guard hair (above).

ringed hair

see thrix annulata.

secondary hair

finer and growing from a more superficial follicle than a guard hair; forms the undercoat.

sensory h's

hairlike projections on the surface of sensory epithelial cells.

sinus hair

the vibrissae or whiskers located on the muzzle and face of many species has an endothelium-lined blood sinus between the inner and outer layers of the dermal portion of the follicle with a rich nerve supply. This structure serves to increase sensory perception.

specialized hair

includes auditory, guard, sensory, tactile, taste, tylotrich hairs (see this list).

hair streams

the hairs in the coat of animals are inclined in one or other direction so that collectively they create streams that meet at vortices or cowlicks.

tactile h's

hairs particularly sensitive to touch.

taste h's

short hairlike processes projecting freely into the lumen of the pit of a taste bud from the peripheral ends of the taste cells.

tipped hair

one with a different, usually darker, color at the tip; seen in Chinchilla cats.

tylotrich hair

special hairs that act as rapid-adapting mechanoreceptors; large, primary follicles with a ring of neurovascular tissue around them. Always associated with a tylotrich pad, a local area of epidermal thickening with a layer of highly vascular and well-innervated connective tissue below.