Hair, Trichology

Lanugo comedones (bundlehairs)

Bundle of very fine lanugo hair in sebum. It can be lifted with tweezers without causing damage.

Trichology

The study of hair

Exogen

end of the telogen phase

how many hairs per square inch

200-300 hairs

Dermal papilla

Area of the follicle that contains the nerve endings and blood supply that provide nourishment to the entire follicle structure. Not a part of the follicle, it serves the follicle. The blood supply also carries hormones which can affect the growth of hair. In the dermal papilla, capillaries extend to the walls of the follicle and practically come in contact with it.

The Bulge

Area to which the arrector pili muscle is attached. Believed to be the storage area for hair follicle stem cells

Layers of hair

The cuticle The cortex The medulla

Hair growth stages

The hair growth cycle is a cycle of events that is repeated as long as nourishment is available. ACT Anagen - growing phase - Active Catagen - transitional phase - Change Telogen - inactive or dormant - Tired

Anagen

Active stage, in which hair germ cells in the dermal cord begin to multiply by mitosis, extending downward, eventually reaching full anagen level (anagen 6). The matrix is active, encapsulating the dermal papilla and the hair bulb is darker. Hairs remain in anagen for 2 to 3 weeks. Terminal hairs on the head for about two years. During anagen the follicle receives nourishment through the dermal papilla.

Pilo-sebaceous unit

Consists of the hair follicle and a sebaceous gland. The sebaceous gland opens into the top third of the hair follicle. It produces sebum that empties into the pilo-sebaceous unit to lubricate the hair and skin surface. Attached to the follicle below the sebaceous gland is the arrector pili (pilorum) muscle. This muscle causes hair to stand on end, when cold to keep heat, or when we are frightened. The arrector pili is located midway between the bulb and the sebaceous gland.

Hair germ

Consists of undifferentiated cells, which produce new hair when stimulated by circulating hormones and enzyme action.

Ambisexual hairs

Develops in both sexes at puberty. Influenced by increased gonadal and androgen production. Axilla, pubis, lower limbs, abdomen in both sexes. Growth varies widely between the sexes, individuals of same sex and body sites.

Club hair

Develops in catagen. The bulb of the hair dries out and become brush like. Held in place by cells of the inner root sheath.

Inner Root Sheath

Encases the hair root. Holds the hair in the follicle by interlocking with the cuticle of the hair. Consists of 3 layers: 1 The cuticle, innermost layer that interlocks with the hair cuticle. Point down. 2 Huxley's layer, middle and thickest layer 3 Henle's layer, outer layer, single layer of cells. Lying between the outer root sheath and the Huxley's layer.

Telogen

Final phase in hair growth cycle. Known as resting or dormant stage. Telogen hairs are also known as club or bed hairs. The follicle remains dormant until stimulated into anagen and the whole process is repeated. Telogen only lasts for a few weeks. The club hair ofter remains in the follicle until a new hair is produced. In most areas of the body telogen hairs are more numerous that anagen hairs.

Infundibulum

Funnel shaped opening of the follicle.

Hair is

Keratinized structures growing out if hair follicles. Hair is a dead, inert structure, composed of hard keratin. Sulfur, nitrogen and carbon are in the composition of hair. A hair cannot conduct short wave. The part of the hair laying within the follicle is the hair root. The portion above is the shaft. The base of the root is the bulb.

Asexual hairs

Hair present at birth. Found in scalp, eyebrows, eyelashes. Forearm and legs in both sexes of all ages. Influenced by growth hormones but not by steroids.

Regrowth hairs

Hair that grows through the skin after treatment by electrolysis. The follicle was only partially destroyed. The hair can be much finer in texture, paler, shallower and slower to regrow than untreated hair.

Ingrown hairs

Hairs the continue to grow just beneath the surface of the skin and often become infected. It should be freed from the skin so it can rise above the surface. If the hair is not infected it can be treated with electrolysis. If it is, it should be cut and wait until the infection is cleared.

Keratin

Hard, horny substance that resists digestion by pepsin and is insoluble in water, organic substances, dilute acids and alkalis.

Medulla

Innermost layer of the hair. Can be continuous or discontinuous. Contains proteins that give hair its body. Made of round cells. Loosely connected keratinized cells. Also called the pith or marrow. Fine hair lacks this layer but all wavy hair has it. The curlier the hair the stronger this layer is.

Catagen

Known as transitional stage. The shortest hair growth stage. This is a casting off, a reversal of the anagen growth process called retrograde morphogenic transformation. The cells go thru a period of degeneration during this phase. The hair separates from the dermal papilla and starts to rise in the follicle. Now the hair is held in the follicle by the cells of the inner root sheath and receives nourishment from cell in the follicle wall. As the hair moves up, the part of the follicle that was left behind disintegrates. This part is called transient or temporary. This part never disappears totally, instead it forms the epidermal cord. Which is a chain like structure that allows it to maintain contact with the dermal papilla.

Types if hair

Lanugo -Only present in the fetus and shed before birth. Vellus (secondary), an appendage of the sebaceous gland, receiving nourishment from the gland itself. If stimulated by the glandular system may develop into a terminal hair. Terminal (terciary), deeper, longer, coarser than vellus hairs. it terminates or connects to the dermal papilla.

Cortex

Middle layer of the hair. Bulk of hair. Made of elongated keratinized cells cemented together and the pigment (melanin granules) that gives hair its color. If melanin is absent then the hair is white or gray. This layer gives hair its strength and elasticity.

Sexual hairs

More pronounced in men due to progesterone production by the testes. Beard, mustache, nasal passages, ears and external body hair (back, chest). Influenced by increased androgen hormone production by the gonads. Testosterone hormone levels in men are 15-30% higher that women.

Cuticle

Outermost layer that gives hair its strength. It protects inner layers and give hair elasticity. Composed of single layer of transparent cells that overlap like scales and point towards the tip of hair. This allows the cuticle of the follicle to interlock with the cuticle of the hair, holding it in place.

Hair follicles

Sac like indentations of the epidermis. The hair take its shape, size and direction from the hair follicle. Consist of these layers: 1 Inner root sheath - Cuticle - Huxley's layer - Henley's layer 2 Outer root sheath 3 Vitreous membrane 4 Connective tissue

Epidermal cord

Slender cord of hair germ cells which enables the retreating follicle to remain in contact with the dermal papilla.

Outer Root Sheath

Surrounds inner root sheath. Forms follicle wall. Its continuous with the mitotic layer of epidermis (stratum malpighii). It does not grow upward with the hair, stays in place. It is the permanent source of hair germ cells from which new hairs develop when stimulated by circulating hormones and enzymes. Important to destroy these cells to prevent further growth.

Connective Tissue

Surrounds the follicle and the sebaceous gland. It's an extension of the papillary layer of the dermis and it includes the dermal papilla (blood supply) There are two layers of connective tissue, both consisting of collagen and elastin fibers.

Hair Bulb

The bulb is the lower part of the follicle and is wider than the upper part. In the bulb region is the matrix where new hair cells and a new root sheath cells are made. An indentation at the bottom of the bulb contains the blood supply (dermal papilla) that provides nourishment to the hair. Melanocytes are contained here that give hair pigmentation.

Nerve supply to the follicle

The nerve supply to the skin is contained within the dermis and around the hair follicles, reaching the base of the epidermis. They form the skin's sensory nerve supply.

Pili multigemini

Two or more hairs emerge from the same her follicle. This is caused by a follicle having more than one papilla. Each hair is complete with its own inner and outer root sheath.

Tombstones

When a telogen hair is removed by electrolysis, sometimes the follicle also contains a new anagen hair that has not grown out of the skin. The anagen hair progresses towards the surface.

how is the follicle of a wavy, curly or kinky hair

the follicle of a wavy or curly hair has a simple curve. that of a kinky hair tends to form a "S" curve. The degree of follicle curvature is related to the flatness of the hair shaft.