The Integumentary System

Transcription

1 (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.

2 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.

3 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.

4 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.

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