(Students: Bolded, italicized, and underlined sections will be on the exam)
The Integumentary System
I. Function of the System:
A. The integumentary system has multiple roles. It is comprised on the skin and
skin derivatives; (hair, nails, glands and receptors) which do the following:
• Protects the body's internal living tissues and organs
• Protects against invasion by infectious organisms
• Protects the body from dehydration
• Protects the body against abrupt changes in temperature
• Helps dispose of waste materials
• Acts as a receptor for touch, pressure, pain, heat and cold
• Stores water, fat, and vitamin D
II. Main Parts of the System:
A. Skin: The skin is the largest organ in the body (12-15% of body weight) with a
surface area of 1-2 meters.
• Layers occur in the skin: the dermis and epidermis.
1. Epidermis: The outer part of the skin. It is made of layers of epithelial
tissue. Cells at the bottom layers keep dividing and forming new cells.
These cells push the cells above them closer to the surface. At the surface,
the cells die, and are then constantly rubbing off. Dandruff is dead cell
material from the scalp. Basal cells are the innermost layer of the epidermis.
Cells at the bottom of the epidermis called melanocytes, and these produce
the pigment melanin. Melanin is the protein that gives skin its darker color
to better protect it from harmful UV rays.
2. Dermis: The inner part of the skin. It is thicker than the epidermis, and
consists of a connective tissue layer under the epidermis which contains
nerve endings, sensory receptors, capillaries, and elastic fibers. Beneath
the dermis is a layer of fatty tissue.
B. Follicles and Glands:
• Hair Follicles and Oil Glands: Hair follicles are lined with cells that synthesize
the proteins that form hair. A sebaceous gland (that secretes the oily
coating of the hair shaft), capillary bed, nerve ending, and small muscle are
associated with each hair follicle. Oil produced by the oil glands keeps the
hair and skin from drying out. If the sebaceous gland becomes plugged and
infected, then it becomes a skin blemish (or pimple). Dandruff is made of
dead hair follicles.
• Sweat Glands: The sweat glands open to the surface through the skin pores of
the dermis. They remove water and salts from blood flowing through the
skin. The water and salts make up sweat. Sweat leaves the skin through the
pores, and as it evaporates, the skin is cooled. Eccrine glands are a type of
sweat gland linked to the sympathetic nervous system; they occur all over
the body. Apocrine glands are the other type of sweat gland, and are larger
and occur in the armpits and groin areas; these produce a solution that
bacteria act upon to produce "body odor".
C. Hair and Nails :
• Hair: Hair is a type of protein. Hair, scales, feathers, claws, horns, and nails are
animal structures derived from skin. The hair shaft extends above the skin
surface, the hair root extends from the surface to the base or hair bulb.
Genetics controls several features of hair: baldness, color, texture.
• Nails: Nails are made of a protein called keratin. They consist of highly
modified epidermal cells. The nail arises from the nail bed, which is thickened
to form a lunula (or little moon). Cells forming the nail bed are linked together
to form the nail.
D. Skin and Homeostasis: Skin functions in homeostasis include protection,
regulation of body temperature, sensory reception, water balance, synthesis of
vitamins and hormones, and absorption of materials. The skin's primary functions
are to serve as a barrier to the entry of microbes and viruses, and to prevent water
and extracellular fluid loss. Acidic secretions from skin glands also retard the
growth of fungi. Melanocytes form a second barrier: protection from the
damaging effects of ultraviolet radiation. When a microbe penetrates the skin (or
when the skin is breached by a cut) the inflammatory response occurs. Heat and
cold receptors are located in the skin. When the body temperature rises, the
hypothalamus sends a nerve signal to the sweat-producing skin glands, causing
them to release about 1-2 liters of water per hour, cooling the body. The
hypothalamus also causes dilation of the blood vessels of the skin, allowing more
blood to flow into those areas, causing heat to be convected away from the skin
surface. When body temperature falls, the sweat glands constrict and sweat
production decreases. If the body temperature continues to fall, the body will
engage in thermiogenesis, or heat generation, by raising the body's metabolic rate
and by shivering.
Water loss occurs in the skin by two routes.
1. evaporation 2. sweating
In hot weather up to 4 liters per hour can be lost by these mechanisms. Skin
damaged by burns is less effective at preventing fluid loss, often resulting in a
possibly life threatening problem if not treated.
E. Skin and Sensory Reception : Sensory receptors neurons in the skin include
those for pain, pressure (touch), and hot and cold temperature. Deeper within
the skin are Meissner's corpuscles, which are especially common in the tips of the
fingers and lips, and are very sensitive to touch. Pacinian corpuscles respond to
pressure. Temperature receptors: more cold ones than hot ones.
F. Skin and Synthesis : Skin cells synthesize melanin and carotenes, which give the
skin its color. The skin also assists in the synthesis of vitamin D. Children lacking
sufficient vitamin D develop bone abnormalities known as rickets.
G. Skin Is Selectively Permeable: The skin is selectively soluble to fat-soluble
substances such as vitamins A, D, E, and K, as well as steroid hormones such as
estrogen. These substances enter the bloodstream through the capillary
networks in the skin. Patches have been used to deliver a number of therapeutic
drugs in this manner. These include estrogen, scopolamine (motion sickness),
nitroglycerin (heart problems), and nicotine (for those trying to quit smoking).
III. Interaction with Other Systems:
The integumentary system interacts with every system, since it provides a barrier for
the internal organs that protects every cell in every organ system from harmful
organisms. Also, it helps to regulate overall body temperature, and reduces water
loss in every cell throughout the body. Some examples of systems that directly
interact with the system include:
• The Nervous System: Receptors in skin send sensory information to the brain.
The autonomic nervous system regulates peripheral blood flow and sweat
glands. Also, nerves control muscles connected to hair follicles.
• The Excretory System: Excess body salts and fluids are expelled from the body
through the pores in the skin.
• IV. Some Diseases and Disorders:
• Melanoma: Although melanoma is the least common type of skin cancer, it is
the most serious form of the disease. It occurs in certain cells in the skin
called melanocytes, which are found in the outermost layers of the skin (the
epidermis). Melanocytes produce the protective pigment called melanin that
gives skin its natural color. Melanoma begins when melanocytes become
malignant, which means they are abnormal and grow uncontrollably. Cells
can become malignant through random changes or mutations that can occur
in a cell’s genetic code. Melanoma strikes people of all ages, all races, all
economic levels and both sexes. It is already the most common cancer for
women 25 to 29 and the second most common cancer for women 30 to 34
and melanoma is increasing faster than any other cancer. An American's
lifetime risk of developing melanoma is about one in 75.
• Eczema (ek'ze-mah) and dermatitis (der'ma-ti'tis) are inflammatory conditions of
the skin. Cause of the inflammation can be allergy, infection, poor circulation,
or exposure to physical factors such as chemicals, heat and cold, or sunlight.
• Birthmarks are congenital (present at birth) disorders of the capillaries in the
dermis of the skin. Usually they are only of concern for cosmetic reasons. A
strawberry birthmark is a mass of soft, elevated tissue that appears bright red
to deep purple in color. In 70% of patients, strawberry birthmarks disappear
spontaneously by the age of seven. Port-wine stains appear as flat, dull red or
bluish patches that persist throughout life.
• Vitiligo (vit-i-li'-go) is the the development of patches of the white skin because
the melanocytes in the affected area are destroyed, apparently by an
autoimmune response.
• A mole is an elevation of the skin that is variable in size and is often pigmented
and hairy. Histologically, a mole is an aggregation or "nest" of melanocytes in
the epidermis or dermis. They are a normal occurrence, and most people have
10 to 20 moles, which appear in childhood and enlarge until puberty.