composition: a shaft, most of which is superficial to the surface, a root that penetrates the dermis and sometimes the subcutaneous layer, and a hair follicle
Functions: Protects from the sun, heat loss, and entry of foreign particles into the eyes, nose and ears. They also function in sensing light touch
is the superficial portion of the hair which projects above the surface of the skin
- is the portion of the hair deep to the shaft that penetrates the dermis and sometimes the subcutaneous layer.
Hair: Hair follicle
- -surrounding the root of the hair
- -is made up of an external and an internal root sheath
- - the base of each hair follicle and its surrounding dermal root sheath is and onion shaped structure, the bulb
- -this structure houses a nipple shaped indentation called the papillae of the hair
Hair: Hair matrix
- a germinal layer of cells found in the bulb of hair.
- -they arise from the stratum basale.
- -they are responsible for the growth of existing hair and produce new hairs when old hairs are shed.
Hair: arrector pili muscle
- -muscle surounding a hair
- -it extends from the superficial dermis of the skin to the dermal root sheath around the side of the hair follicle.
- -under emotional or physiological stress, such as cold or fright, autonomis nerve endings stimulate the arrector pili muscles to contract, which pulls the hair shaft perpendicular to the skin surface
Hair: Hair root plexuses
-surrounding each hair follicle are dendrites of neurons that are sensitive to touch which generate nerve impulses if their hair is moved.
- new hairs develop from division of the hair matrix cells in the bulb; hair replacement and growth occue in a cyclical pattern consisting of growth, regression and resting stages.
vellus hairs (peach fuzz)
short fine pale hairs that are barely visible to the naked eye.
long coarse heavily pigmented hair
is due to the type and amount of melanin in its keratinized cells
Sebaceous (oil) glands
- are usually connected to hair follicles; they are absent from palms and soles.
- -they produce sebum
- oily substance secreted from sebaceous glands
- -coats the surface of hairs and helps keep them from drying and becoming brittle
- -also helps prevent the excessive evaporation of water from skin and keeps it soft and pliable and inhibits the growth of some bacteria
-caused when sebaceous glands are clogged
Sudoriferous Glands (sweat glands)
- the cells of these glands release sweat or perspiration into hair follicles or onto skin surfaces through pores
- two types of glands: Eccrine glands and Apocrine glands
Eccrine sweat glands
- -simple coiled tubular glands
- have an extensive distribution; their ducts terminate at pores at the surface of the epidermis. They are involved in thermoregulation and waste removal and are stimulated during emotional stress
insensible and sensible perspiration
-insensible is when sweat evaporates from the skin before it is perceived as moisture
- sensible is sweat that is secreted in larger amounts and is seen as moisture on the skin
Apocrine sweat glands
are limited to the skin of axillae, groin, and areilae; their ducts open into hair follicles. Apocrine sweat glandsare stimulated during emotional stress and sexual excitement
Ceruminous sweat glands
are modified sudoriferous glands that secret cerumen. They are found in the external auditory canal (ear canal)
are hard, dead, keratinized epidermal cells over the dorsal surfaces of the distal portion of digits.
visible portion of the nail
free edge (nail)
the part of the nail that may extend past the distal end of the digit
is the portion of the nail that is buried in a fold of the skin
the whitish crescent shaped area of the proximal end of the nail body
- the proximal protion of the epithelium deep to the nail root is the nail matrix
- -where cells divide by mitosis to produce growth