b. It also contains muscle cells, blood vessels, and
nerve cell processes.
c. Dermal blood vessels supply nutrients to all skin
cells and help regulate body temperature.
d. Nervous tissue is scattered throughout the dermis.
(1) Some dermal nerve cell processes carry
impulses to muscles and glands of the skin.
(2) Other dermal nerve cell processes are
associated with sensory receptors in the skin.
ACCESSORY STRUCTURES OF THE SKIN
a. Nails are protective covers on the ends of F
b. They consist of keratinized epidermal cells.
2. Hair follicles
a. Hair covers nearly all regions of the skin.
b. Each hair develops from epidermal cells at the base
of a tubelike hair follicle.
c. As newly formed cells develop and grow, older
cells are pushed toward the surface and undergo
d. A hair usually grows for a while, rests, and then is
replaced by a new hair.
e. Hair color is determined by genes that direct the
type and amount of pigment in hair cells.
f. A bundle of smooth muscle cells and one or more
sebaceous glands are attached to each hair follicle.
3. Skin glands
a. Sebaceous glands secrete sebum, which softens
and waterproofs both the skin and hair.
b. Sebaceous glands are usually associated with hair
c. Sweat glands are located in nearly all regions of
d. Each sweat gland consists of a coiled tube.
e. Eccrine sweat glands, located on the forehead,
neck, back, palms, and soles, respond to elevated
body temperature or emotional stress.
f. Sweat is primarily water but also contains salts
and waste products.
g. Apocrine sweat glands, located in the axillary
regions, groin, and around the nipples, moisten the
skin when a person is emotionally upset, scared, in
pain, or sexually aroused.
REGULATION OF BODY TEMPERATURE
Regulation of body temperature is vital because
heat affects the rates of metabolic reactions. Normal
temperature of deeper body parts is close to a set point of
1. Heat production and loss
a. Heat is a by-product of cellular respiration.
b. When body temperature rises above normal, more
blood enters dermal blood vessels and the skin
INTRODUCTION (PAGE 171)
The skin, the largest organ in the body, and its accessory
structures constitute the integumentary system.
SKIN AND ITS TISSUES (PAGE 171)
Skin is a protective covering, helps regulate body
temperature, houses sensory receptors, synthesizes
chemicals, and excretes wastes. It is composed of
an epidermis and a dermis separated by a basement
membrane. A subcutaneous layer, not part of the skin, lies
beneath the dermis. The subcutaneous layer is composed of
areolar tissue and adipose tissue that helps conserve body
heat. This layer contains blood vessels that supply the skin.
a. The epidermis is stratiF
ed squamous epithelium
that lacks blood vessels.
b. The deepest layer, called the stratum basale,
contains cells that divide and grow.
c. Epidermal cells undergo keratinization as they are
pushed toward the surface.
d. The outermost layer, called the stratum corneum,
is composed of dead epidermal cells.
e. Production of epidermal cells balances the rate at
which they are lost at the surface.
f. The epidermis protects underlying tissues against
water loss, mechanical injury, and the effects of
g. Melanin, a pigment produced from the amino
acid tyrosine, provides skin color and protects
underlying cells from the effects of ultraviolet light.
h. Melanocytes transfer melanin to nearby epidermal
i. All humans have about the same concentration
of melanocytes. Skin color is largely due to the
amount of melanin in the epidermis.
(1) Each person inherits genes for melanin
(a) Dark skin is due to genes that cause large
amounts of melanin to be produced;
lighter skin is due to genes that cause
lesser amounts of melanin to form.
(b) Mutant genes may cause a lack of melanin
in the skin.
(2) Environmental factors that inﬂ
uence skin color
include sunlight, ultraviolet light, and X rays.
These factors darken existing melanin and
stimulate additional melanin production.
(3) Physiological factors inﬂ
uence skin color.
(a) The oxygen content of the blood in dermal
vessels may cause the skin of light-
complexioned persons to appear pinkish or
(b) Carotene in the subcutaneous layer may
cause the skin to appear yellowish.
(c) Disease may affect skin color.
a. The dermis is a layer composed of dense irregular
connective tissue that binds the epidermis to