hair follicle

follicle /fol·li·cle/ (fol´ĭ-k'l) a sac or pouchlike depression or cavity.follic´ular

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atretic ovarian follicle  an involuted ovarian follicle.

dominant ovarian follicle  the growing ovarian follicle in a given menstrual cycle that matures completely and forms the corpus luteum.

gastric follicles  lymphoid masses in the gastric mucosa.

graafian follicles  vesicular ovarian f's; maturing ovarian follicles among whose cells fluid has begun to accumulate, leading to the formation of a single cavity and leaving the oocyte located in the cumulus oophorus.

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

Folliculus pili (hair follicle). (A), Longitudinal section, comprising the infundibulum, isthmus, stem, and bulb; (B), transverse section of follicle, showing the hair shaft and surrounding follicular sheaths.

intestinal follicles  see under gland.

lingual follicles  nodular masses of lymphoid tissue at the root of the tongue, constituting the lingual tonsil.

lymph follicle , lymphatic follicle

1. lymph node.

2. lymphatic nodule (2).

Naboth's follicles , nabothian follicles cystlike formations due to occlusion of the lumina of glands in the mucosa of the uterine cervix, causing them to be distended with retained secretion.

ovarian follicle  the oocyte and its encasing cells, at any stage in its development.

primary ovarian follicles  immature ovarian follicles, each comprising an immature oocyte and the specialized epithelial cells (follicle cells) surrounding it.

primordial ovarian follicle  an immature ovarian follicle that has not undergone recruitment and consists of an oocyte enclosed by a single layer of cells.

sebaceous follicle  a hair follicle with a relatively large sebaceous gland, producing a relatively insignificant hair.

solitary follicles  small lymph follicles scattered throughout the mucosa and submucosa of the small intestine.

thyroid follicles  discrete, cystlike units of the thyroid gland that are lined with cuboidal epithelium and are filled with a colloid substance, about 30 to each lobule.

vesicular ovarian follicles  graafian f's.

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hair follicle

n.

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

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Hair follicle

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

Mentioned in: Hair Transplantation, Sunscreens

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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.

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follicle

a sac or pouchlike depression or cavity.

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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.

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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.