1. Linton, Christina P.

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ALOPECIA - Hair loss, usually on the scalp.


ANAGEN - Phase of hair growth; lasts for variable periods of time depending on body site. Hairs in this phase have pigmented, malleable proximal ends.


ARRECTOR PILI MUSCLE - Bundles of smooth muscle fibers that are attached to the deep part of the hair follicles and act to pull the hairs erect.


BULB - Lowermost portion of the hair follicle.


CANITIES - Graying of hair.


CASTS - Remnants of the inner root sheath that may mimic nits. Unlike nits (which are firmly attached), hair casts slide freely along the shaft. Also called pseudonits.


CATAGEN - Regression phase in between the telogen and anagen phases; driven by massive keratinocyte apoptosis, which leads to involution of the lower two thirds of the hair follicle.


CICATRICIAL ALOPECIA - Irreversible loss of hair follicles with disappearance of follicular ostia. Also called scarring alopecia.


CORTEX - Comprises the bulk of the hair shaft and contains melanin; situated between the medulla (in larger hairs) and cuticle.


CLUB HAIR - Hair characteristic of the telogen phase in which the bulb has become a club-shaped mass.


CUTICLE - Covers the hair shaft to provide protection; may be completely lost at the end of long hairs. The integrity and properties of the cuticle greatly impact the appearance of the hair.


EFFLUVIUM - Process of increased daily hair shaft shedding (more than 25-100 hairs per day).


EXCLAMATION POINT HAIR - Short broken hairs whose distal ends are broader than the proximal ends; indicative of alopecia areata.


EXOGEN - Phase of active hair shaft shedding.


HIRSUTISM - Excessive growth of terminal hairs in a "male pattern" in a female patient that is related to hormonal factors (androgen overproduction or increased end-organ sensitivity to androgens). The "male pattern" may involve the upper lip, chin, cheeks, central chest, breasts, lower abdomen, and/or groin.


HYPERTRICHOSIS - The growth of excessive amounts of hair on any area of the body; may be generalized or localized and congential or acquired and involve lanugo, vellus, or terminal hairs.


LANUGO HAIR - Fine, pigmented hair on the fetal body that is shed in utero or during the first weeks of life; somewhere between vellus and terminal hair in length and form; occurrence in postnatal life (hypertrichosis lanuginosa) may indicate a serious problem.


MADAROSIS - Loss of eyelashes and/or eyebrows.


MATRIX - Rapidly proliferating keratinocytes that terminally differentiate to produce the hair shaft.


MEDULLA - The central axis of some hairs; contains a column of large vacuolated and keratinized cells; surrounded by the cortex.


MINIATURIZATION - Terminal-to-vellus hair conversion in conditions such as androgenic alopecia. The miniaturized follicles still display an arrector pili muscle.


OPHIASIS - Confluent hair loss along the temporal and occipital scalp; usually a feature of alopecia areata.


POLIOSIS - Circumscribed patches of white or gray hair. May be associated with several syndromes, including vitiligo, regressing melanoma, and alopecia areata. Migrating patches without hair loss may represent a forme fruste of alopecia areata.


PILOERECTION - Erection of the hair shaft due to the action of the arrector pili muscle.


PILOMOTOR REFLEX - Contraction of the smooth muscle of the skin resulting in "gooseflesh" appearance; caused by mild application of tactile stimulus or by local cooling.


PILOSE - Hairy.


ROOT - The part of the hair that is embedded in the hair follicle.


SHAFT - The visible hair that arises from the bulb. Made up of the medulla (in the center of larger hairs) and the cortex and covered by the cuticle.


SCHIZOTRICHIA - Splitting of the hairs at their ends.


TELOGEN - Period of relative quiescence; lasts for variable periods of time depending on body site. Hairs in this phase are clubbed with depigmented, rounded-up proximal ends (also called club hairs).


TERMINAL HAIR - Produced by large hair follicles located in the subcutis; hairs are generally pigmented, medullated, and >0.03 mm in diameter.


TRICHOLOGIA - A nervous habit of plucking at the hair.


TRICHOPHAGIA - Habitual biting of the hair or swallowing of plucked hairs.


TRICHORRHEXIS - A condition in which the hairs tend to break or split.


TRICHOTILLOMANIA - A compulsion to pull out one's own hair from the scalp, eyebrows, or eyelashes.


TUFTING - Doll's hair-like bundling of follicular units; usually a feature of cicatricial alopecia.


VELLUS HAIR - Produced by very small (but functionally active, cycling) hair follicles located in the dermis; thin (<=0.03 mm diameter), short, often depigmented, and usually nonmedullated hair shaft; arrector pili muscle absent.

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