Hair Hair is found in association with thin skin except for the lips, nipples, and portions of the external reproductive organs. There are three general types of hair: Lanugo – covers the fetus by the 5 th or 6 th month of development. It is delicate and unpigmented. Vellus – replaces most of lanugo hair. Short fine and unpigmented. Terminal – long course and pigmented (scalp, eyebrows, eyelashes immediately following birth) Terminal hair at puberty – for males: arms, chest, legs, and pubic region (90%); for females: (35%).

Hair Structure Two main parts: Shaft and Root The base of the root expands to form the hair bulb. The entire hair is composed of columns of dead keratinized cells arranged in three concentric layers: the medulla (center), the cortex, and the cuticle.

Hair

Hair Color As with skin, varying amounts of melanin cause different shades of hair. The exception is red hair which is caused from a blend of melanin containing iron. With age, melanin in hair fades or decreases resulting in gray or white hair.

Hair Growth Hair is produced in cycles: growth and resting stages. During growth, hair is formed by cells in the matrix of the hair follicle. Hair grows longer as cells are added to the base of the root. During the resting phase the hair growth stops and the follicle shortens holding the hair in place. After resting the hair is released from the follicle and replaced. Different hair has different lengths of each period. So what happens with alopecia?

Hair Muscles Associated with each hair follicle is a smooth muscle called the arrector pili muscle. It extends from the dermal root sheath to the papillary layer of the dermis. At an oblique angle to the surface of the skin. Cause of goose bumps, the wrinkled appearance of the scrotum, and nipples.

Nails Functions: protects the ends of the digits, aids in manipulation and grasping of small objects, and are used for scratching. Consists of proximal nail root and distal nail body.

Nail Structure Root is covered by skin. Lateral and proximal edges also covered in skin = nail fold. Edges held in place by nail groove. The stratum corneum of the nail fold grow onto the nail body as the eponychium (what is the common name?). Under the free edge of the nail is the hyponychium which is a thickened region of the stratum corneum. The nail root and body are attached to the nail bed, the proximal portion of which is the matrix. The nail matrix produces the nail. The lunula is seen through the nail body as a white cresent. The matrix is thicker here.

Glands Sweat glands (merocrine): coiled tubular glands located in the dermis. Pore formed at surface where duct opens. Aids in temperature regulation. Sweat glands (apocrine): open into hair follicles found in the axillae and genitalia. Become active at puberty and are influenced by sex hormones. Secretion is organic and is metabolized by bacteria quickly resulting in an odor (BO).

More Glands Sebaceous (Holocrine): Located in the dermis and are simple or compound alveolar. Secrete sebum, an oily white substance rich in lipids. Prevent drying of hair and skin and also protection against some forms of bacteria.