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The Stratum Germinativum or Basale
- This layer rests on the basement membrane. Its low-
ermost layer of cells is called the stratum basale.^
- This layer is the layer that produces new epidermal
cells by mitosis.^
- Melanocytes of this layer produce melanin. This
pigment is responsible for skin color and protection
from the harmful ultraviolet rays of the sun.^
- Dark-skinned individuals have more active
melanocytes.^
- Albinism is a genetic condition that results from the
absence of melanin.
The Dermis
- The dermis is also called the corium or true skin
and is composed of dense connective tissue.^
- Blood and lymph vessels, nerves, muscles, glands,
and hair follicles are found in the dermis.^
- It is divided into two portions: the papillary portion
below the epidermis and the reticular portion above
the subcutaneous tissue.^
- The subcutaneous tissue can be called the
hypodermis.
The Appendages Of The Skin
- The appendages of the skin include hair, nails, seba-
ceous glands, ceruminous or wax glands, and sweat
glands.
Hair
- Hair covers the entire body except the palms of the
hands, the soles of the feet, and parts of the external
genitalia.^
- Each individual hair is made of three parts: the outer
cuticle, the cortex, which is the principal por-tion
with pigment granules, and the inner medulla with air
spaces.^
3.^ The visible portion of a hair is called the shaft.^
4.^ The root of a hair is in a hair follicle.^
5. When the arrector pili smooth muscle con-tracts, it
causes a hair to stand on end and causes “goose
flesh.”
Chapter 6Hair Growth- Hair growth begins with the cells deep in the hair
follicle at the hair bulb growing by mitosis and
nourished by blood vessels.^ - Hair grows in cycles and rests between cycles.
Hair Texture- Hair texture can be classified as straight, curly, or
tightly curly, and is due to genetic factors.^ - Hair in the alpha keratin chain is elastic; when
stretched, it is in the beta keratin chain.
Hair Color- Hair color is determined by complex genetic
factors.^ - Gray hair occurs when pigment is absent in the
cortex.^ - White hair results from both the absence of pigment
and air bubbles in the shaft.^ - Heredity and other unknown factors cause hair to
turn gray.
Nails- A nail is a modification of epidermal cells made of
very hard keratin.^ - The lunula is the white crescent at the proximal end of
a nail caused by air mixed with the keratin.^ - The nail body is the visible portion of a nail. The nail
root is the part covered by skin.^
4.^ The nail grows from the nail bed.^ - The cuticle is stratum corneum that extends over
the nail body.
Sebaceous Glands- Sebaceous glands produce sebum and are found
along the walls of hair follicles.^ - Sebum, an oil, gives a cosmetic gloss to skin and
moisturizes it.^ - Sebaceous secretion is controlled by the endocrine
system, increasing during puberty and late preg-
nancy and decreasing with age.