Chapter 6 Integumentary System Introduction Two or more tissues grouped together and performing specialized functions define a

c. organ
2. The largest organ(s) in the body is (are) the _______________. (p. 171)

d. skin
6.2 Skin and Its Tissues

3. Functions of the skin include _________________. (p. 171)

e. all of the above

a. A protective covering

b. Synthesizes various chemicals
5. The epidermis is composed of layers of _____________ tissue. (p. 172)

keratinized stratified squamous epithelium

The epidermis is the outermost layer of the skin and is composed of keratinized stratified squamous epithelium. The dermis is the inner, thicker layer, and includes various tissues, such as connective tissue, epithelial tissue, smooth muscle tissue, nervous tissue, and blood. The epidermis and dermis are separated by a basement membrane that is anchored to the dermis by short fibrils.

The subcutaneous layer contains adipose tissue that acts as an insulator, conserving internal body heat and preventing the entrance of heat from the outside. This layer also contains the major blood vessels that supply nutrients and oxygen to the skin.

As new cells in the epidermis are produced, they are pushed upwards from the basement membrane towards the outside of the skin. As they get further from their nutrient source they die. As the process occurs, the maturing cells undergo a hardening process (keratinization) during which the cytoplasm develops strands of tough, fibrous, waterproof proteins called keratin. These dead cells form many tough, waterproof layers. These dead cells are rubbed away as newer cells replace them.

The layers in the epidermis are:

An important function of the skin is to protect the deeper tissues from the harmful effects of sunlight. One method of accomplishing this is the production of melanin, the dark pigment produced by melanocytes in the deeper layers of the epidermis and in the upper layers of the dermis. Melanin absorbs light energy and protects deeper tissues. Although melanocytes are found deep in the epidermis, the pigment can be found in any of the nearby cells due to the melanocytes’ long, pigment-containing extensions that pass upward between neighboring epidermal cells. These extensions can then transfer the granular melanin to these other cells by a process called cytocrine secretion. As a result, the neighboring cells often contain more melanin than the melanocytes themselves.

Melanin also absorbs ultraviolet radiation in sunlight.

Factors such as sunlight, UV light from sunlamps, and X rays affect skin color by rapidly darkening existing melanin, and by stimulating melanocytes to produce more pigment.

The dermal blood supply affects skin color. For example, when the blood is well oxygenated, the hemoglobin makes the skin appear pinkish. When the blood is not well oxygenated, the hemoglobin is darker and the skin appears bluish (cyanosis). In the presence of high levels of carotene in the blood, the skin may exhibit a yellowish cast. Illnesses may also affect skin color.

The dermis is composed largely of irregular dense connective tissue that includes tough collagenous fibers and elastic fibers in a gel-like substance. It has fingerlike projections called papillae that help form the fingerprints. The dermis also includes muscle tissue. It is usually smooth muscle, but striated muscle is also present in certain portions such as the face to help with voluntary facial movements. The dermis contains both sensory and motor nerves. It also contains blood vessels, hair follicles, sebaceous glands, and sweat glands.

The dermal nervous tissue has both sensory and motor fibers. Sensory fibers include Pacinian corpuscles, which are stimulated by heavy pressure and Meissner’s corpuscles, which are sensitive to light touch. The motor fibers stimulate dermal muscles and glands.

Stratified squamous epithelial cells in the region known as the nail root form nails. The whitish half-moon-shaped area called the lunula marks the nail root. As these cells are pushed outward, they are keratinized into a hard tissue that slides forward over the nail bed to which it remains attached.

Genes that direct the type and amount of pigment produced by epidermal melanocytes determine hair color.

Bright red hair contains an iron pigment (trichosiderin) that does not occur in hair of any other color. Gray hair is the result of a mixture of pigmented and unpigmented hair.
19. Explain the function of sebaceous glands. (p. 180)

Sebaceous glands contain groups of specialized epithelial cells and are usually associated with hair follicles. They are holocrine glands that secrete an oily substance called sebum (a mixture of fatty materials and cellular debris) that serve to keep the hair and skin soft, pliable, and relatively waterproof.
20. The sweat glands that respond to elevated body temperature and are commonly found on the forehead, neck, and back are ______________. (p. 180)

c. eccrine glands

Body temperature regulation is vitally important because even slight shifts in body temperature can disrupt the rates of metabolic reactions.

In intense heat, the nerve impulses stimulate the skin and other organs to release heat. The muscles, when active, release heat. The peripheral blood vessels dilate (vasodilation) which allows more of the warmed blood to be close to the outside for dispersal of heat by radiation. The deeper blood vessels constrict (vasoconstriction) forcing more blood to the surface. The heart rate increases to circulate the blood faster. The sweat glands are also stimulated to add perspiration to the skin for evaporation.

1. Radiation—C

2. Conduction—B

3. Convection—A

As excessive body heat is lost, the brain triggers responses in skin structure. For example, the muscles in the walls of the dermal blood vessels contract, decreasing the blood flow. The sweat glands become inactive and skeletal muscles throughout the body contract slightly (shivering).

The air can only hold so much of the water molecules. If it is already saturated, the person who is sweating will not have evaporation occur and they will be wet and uncomfortable.

If the break in the skin is very shallow, the epithelial cells along the margin are stimulated to reproduce more rapidly. These newly produced cells simply fill in the gap. A deeper break involves the blood vessels. The clot will form and tissue cells will seep into the area and dry. This will then form a scab for underlying protection. Fibroblasts then produce fibers that bind the edges of the wound together. Growth factors are released to stimulate damaged tissue replacement. Healing continues beneath the scab, which sloughs off, when healing is complete.

A first-degree burn is a superficial partial-thickness burn. An example would be a sunburn. A second-degree burn is a deep partial-thickness burn. Any burn that blisters is a second-degree burn. A third-degree burn is a full-thickness burn. It can burn away all the skin and muscles leaving bone exposed.

Skin grafts are one possible treatment. An autograft is a piece of skin from the victim. A homograft is one from a cadaver. Skin grafts leave scarring.