hair follicle

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follicle

 [fol´ĭ-k'l]
a sac or pouchlike depression or cavity. adj., adj follic´ular.
atretic ovarian follicle an involuted ovarian follicle.
dental follicle the structure within the substance of the jaws enclosing a tooth before its eruption; the dental sac and its contents.
gastric f's lymphoid masses in the gastric mucosa.
graafian follicle see graafian follicle.
hair follicle one of the tubular invaginations of the epidermis enclosing the hairs, and from which the hairs grow.
Diagram of a hair follicle showing layers of hair schematically. From Copstead, 1995.
lymph follicle (lymphatic follicle)
2. lymphatic nodule (def. 2).
Naboth's f's (nabothian f's) Naboth's cysts.
ovarian follicle the ovum and its encasing cells, at any stage of its development.
primary ovarian follicle an immature ovarian follicle consisting of an immature ovum and the few specialized epithelial cells surrounding it.
primordial ovarian follicle an ovarian follicle consisting of an ovum enclosed by a single layer of cells.
sebaceous follicle a hair follicle with a relatively large sebaceous gland, producing a relatively insignificant hair.
solitary f's
1. areas of concentrated lymphatic tissue in the mucosa of the colon.
2. small lymph follicles scattered throughout the mucosa and submucosa of the small intestine. Called also solitary glands.
thyroid f's discrete cystlike units filled with a colloid substance rich in iodine; they constitute the lobules of the thyroid gland.
vesicular ovarian follicle graafian follicle.

hair fol·li·cle

[TA]
a tubelike invagination of the epidermis from which the hair shaft develops and into which the sebaceous glands open; the follicle is lined by a cellular inner and outer root sheath of epidermal origin and is invested with a fibrous sheath derived from the dermis.
Synonym(s): folliculus pili [TA]

hair follicle

n.
A deep narrow pit that is formed by the tubular infolding of the epidermis and that encloses the root of the hair.

hair follicle

Etymology: AS, haer + L, folliculus, a small bag
a tube-like opening in the epidermis where the hair shaft develops and into which the sebaceous glands open.
enlarge picture
Hair follicle

hair fol·li·cle

(hār fol'i-kĕl) [TA]
A tubelike invagination of the epidermis from which the hair shaft develops and into which the sebaceous glands open; the follicle is lined by cellular inner and outer root sheaths of epidermal origin and is invested with a fibrous sheath derived from the dermis.
Synonym(s): folliculus pili [TA] .

hair follicle

a sheath of epidermal tissue surrounding the root of a HAIR (2). The follicle is supplied by a sebaceous gland and erectile muscles for the hair. see SKIN.

Hair follicle

A tube-like indentation in the skin from which a single hair grows.

hair follicle

invagination of fetal epidermis and dermis to form a deep, narrow pit, from which a hair papilla (hair root) and resultant hair shaft develop, and into which the local sebaceous gland opens

follicle

a sac or pouchlike depression or cavity.

atretic follicle
an involuted ovarian follicle.
conjunctival follicle
focal accumulations of hypertrophied lymphoid tissue in conjunctiva, indicative of an inflammatory reaction.
cystic follicle
ovarian follicle that has not ruptured, is grossly enlarged, may be multiple and on both ovaries. Caused by insufficient luteinizing hormone. Affected cows may be nymphomaniac in behavior, but most are anestrous and anovulatory. See also cystic ovarian degeneration.
dental follicle
the structure within the substance of the jaws enclosing a tooth before its eruption; the dental sac and its contents.
dominant follicle
in the ovary, hormones secreted by the largest follicle will cause others to regress.
gastric follicle
lymphoid masses in the gastric mucosa.
graafian follicle
a maturing ovarian follicle among whose cells fluid has begun to accumulate, leading to the formation of a single cavity and leaving the ovum located in the cumulus oophorus; called also vesicular ovarian follicle.
hair follicle
see hair follicle.
hemorrhagic follicle
see corpus hemorrhagicum.
lymph follicle, lymphatic f
1. a small collection of actively proliferating lymphocytes in the cortex of a lymph node.
2. a small collection of lymphoid tissue in the mucous membrane of the gastrointestinal tract; such collections may occur singly (solitary lymphatic follicle) or closely packed together (aggregated lymphatic follicles).
ovarian follicle
the ovum and its encasing cells, at any stage of its development.
primary ovarian follicle
an immature ovarian follicle consisting of an immature ovum and the few specialized epithelial cells surrounding it.
primordial follicle
an ovarian follicle consisting of an ovum enclosed by a single layer of cells.
sebaceous follicle
a hair follicle with a relatively large sebaceous gland, producing a relatively insignificant hair.
solitary follicle
1. areas of concentrated lymphatic tissue in the mucosa of the colon.
2. small lymph follicles scattered throughout the mucosa and submucosa of the small intestine. Called also solitary glands.
thyroid follicle
discrete cystlike units filled with a colloid substance, constituting the lobules of the thyroid gland.
vesicular ovarian follicle
graafian follicle.
wool follicle
site of origin of wool fiber.

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.

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