integumentary system: (skin)

Integumentary system:

The skin is also known as the cutaneous membrane. It is waterproof and expandable within limits. Also referred to as simply the integument, the skin is a structural marvel. Most of the skins functions, though not all, are protective. It protects deeper tissues from many things:

Mechanical damage, such as bumps and cuts. The skin is physical barrier containing pressure receptors (nerves), which alert the brain to danger
Chemical damage, such as acid and basic burns. The skin has relatively impermeable keritinized cells and pain receptors
Bacterial damage and infection. The skins secretions are acidic, inhibiting bacteria and forming what is known as the "acid mantle". Blood vessels in the skin also contain and move leukocytes of all sorts which destroy pathogens and foreign substances
Ultraviolet radiation, radiation that causes damage. Melanin produced from the melanocytes offer protection
Thermal damage, too much heat or chill. Contains heat, cold, pain receptors to register the threat
Desiccation, drying out. Keritinized cells are waterproof, holding the water in the body

The skin aids in the cooling of the body by producing sweat and rushing blood to the surface of the skin (flush). The skin also helps to keep the heat in by not letting the skin flush. Sweat is also used to excrete urea and uric acid

The skin modifies cholesterol molecules to make them into vitamin D, using sunlight

The integument's is made up of two kinds of tissue. The outer dermis, or epidermis is made up of stratified squamous epithelium and is full of keratin and hardened, or cornified. The underlying dermis is made up of dense fibrous connective tissue. A blister is caused when the two are separated by burning or friction. Deep to the dermis is the subcutaneous tissue, essentially areolar tissue containing many fat cells. Not really considered part of the skin, it "glues" the skin to underlying organs and tissues. The subcutaneous tissue also serves at a sort of shock absorber and insulates to maintain heat

The epidermis is an epithelial tissue, and accordingly avascular. The epidermis in and of itself contains many parts:

The deepest layer of the epidermis is the stratum germinativum. It lays closest to the dermis and contains only dermal cells that receive adequate nourishment diffused from the dermis. These cells constantly undergo mitosis, germinating and creating new cells to be pushed upward to replace the old ones constantly shed
As the cells move upward and outward, they become part of the stratum granulosum
From the stratum granulosum the new skin cells then move to the clear stratum lucidum. From here on, they are dead
The stratum corneum is the upper layer of keritinized, squamous cells. it is waterproof, with no circulation or nerve receptors. The

corneum is shed about every thirty-five to forty-five days

Melanin is a pigment which ranges in color from pale yellow to black. It is produced by cells called melanocytes, found mainly in the stratum germinativum. When exposed to sunlight, which stimulates the melanocytes to make more melanin, tanning occurs. The germinativum cells phagocytize, or eat, the melanin. The consumed melanin forms a protective pigment shield of sorts over the superficial side of the cells nuclei to protect the dna from ultraviolet radiation. Freckles and moles occur when melanin accumulates in one spot

The dermis underlies the epidermis, "epi" meaning above. Leather is the treated dermis of animals such as cows. The dense fibrous connective tissue that makes up the dermis has two primary regions:

The papillary region is the upper of the two dermal regions. It is uneven and have finger-like projections on the superior surface, called dermal papillae, which indent the overlying epidermal layers. Many dermal papillae contain capillary loops, which provide the nourishment to the lower layers of the epidermis. Others contain free nerve endings which are pain receptors, or Meissner's corpuscles, touch receptors. On the palms, fingertips, toes and soles of the feet, the papillae are arranged in definite swirling patterns to increase the gripping ability. They are genetically determined and are well equipped with sweat glands, leaving behind one's distinctive and identifying fingerprints
The reticular layer is the deepest integumentary layer. It houses blood vessels, sweat glands, oil glands, and deep pressure receptors known as Pacinian corpuscles. Also here are many phagocytes and throughout the dermis to prevent bacteria from penetrating

Both collagen and elastic fibers are located throughout the dermis. Collagen is responsible for the toughness of the dermis, attract and bind water, helping to keep the skin hydrated. Elastic fibers give it the ability to stretch while we are young. As we age, the numbers of both fibers decrease and the subcutaneous fat is lost, thus giving way to sagging and wrinkling

Blood vessels are abundant in the dermis. They help to regulate body temperature. If blood flow is restricted for a length of time, decubitus ulcers form. These occur mostly in bedridden patients who are not turned or are dragged across the bed a number of times. The skin first becomes blanched at pressure points, especially over bony projections. They flush if the pressure is relieved. But if the pressure is not, then the cells die, small cracks and breaks appear in the skin, and there is most often permanent damage to the blood vessels

The dermis also contains many nerves and nerve endings with special receptor nerve end organs

Three pigments contribute to skin color. The amount and kind (yellow, brown or black) melanin, the amount of carotene (an orange-yellow pigment from vegetables), and the of oxygen bonded to hemoglobin in the dermal blood vessels. When hemoglobin is poorly oxygenated, both the blood and skin take on a blue is cast. The condition is called cyanosis. Sometimes cyanosis can be caused by heart failure. In dark skin people, the darker melanin shields the cyanosis, but can be seen in the mucous membranes and nail beds:

Redness or erythema indicates embarrassment, fever, hypertension, inflammation or allergy
Pallor, paleness or blanching can mean fear, anger, anemia, low blood pressure or impaired blood flow
Yellowing, or jaundice, usually signifies liver problems. The bile coloring leaks out and deposits in other tissues
Black and blue, bruising is bleeding under the skin. The blood had escaped from circulation and has clotted in tissue spaces. The clotted masses are known as hematomas. An usual tendency to bruise may show a deficiency of vitamin C or hemophilia (bleeder's disease)

Cutaneous glands are all exocrine glands that release their secretions on the surface of the skin. The fall into two groups, being sebaceous glands and sweat glands. They are formed by the cells of the stratum germinativum, and push into the deeper tissue. Ultimately, they reside almost totally in the dermis

Sebaceous glands are oil glands. They are found throughout the skin, except in the palms and the sole of the foot. The ducts usually empty into the hair follicles, though some open directly onto the skin surface itself. The secretion of these glands is called sebum, a mixture of oily substances and fragmented cells. Sebum is a lubricant to keep the skin soft and moist, and prevents hair from becoming brittle and splitting. Sebum also contains chemicals to kill bacteria. They become more active during adolescence, when more male sex hormones are produced

Sweat glands, or sudoriferous glands, are spread throughout the skin-- more than 2.5 million per person. There are two types of sweat glands:

Eccrine glands are the more numerous of the two. They produce sweat. Sweat a sterile solution made up mostly of water, with some sodium chloride, urea, uric acid, and traces of vitamin C. It is acidic with a pH of about four to six, which inhibits the growth of bacteria. The sweat comes out of funnel-shaped pores, though the pores commonly referred to on the face are actually the external outlets of hair follicles. The eccrine sudoriferous glands are important to the bodies ability to cool itself. They are supplied with nerve endings that cause them to secrete whenever external or internal temperature rises. When it evaporates off they skin, it carries large quantities of heat with it. One can lose up to seven liters of water in this manner
Apocrine glands are mostly confined to the axillary (armpit) and genital areas of the body. They are larger then the eccrine sweat glands, and empty their secretions into hair follicles. Their secretions contain fatty acids and proteins in addition to the usual sweat contents. It may have a milky or yellowish appearance. The sweat is odorless, but bacteria use the proteins and acids to grow and create the characteristic odor we all know and hate. The apocrine glands begin to function during puberty, with the influence of androgens (male sex hormones). Their exact purpose is not yet known, as they play a minimal role in thermoregulation, but they are stimulated by nerves during pain and stress

Hair is a protective structure. It is produced by a hair follicle, and is made up of dead cells by the time it has reached the surface of the skin. The part of the hair enclosed by the follicle is the root, the visible part, the shaft. The cells are supplied by the prolific stratum germinativum in the matrix of the hair bulb at the inferior end of the follicle. As the cells are pushed out, they become keritinized and die. Each hair consists of a core, the medulla, surrounded by a bulky cortex, surrounded in turn by a cuticle only one cell layer thick. The cells in the cuticle overlap like shingles to help keep the hair from matting. This it the most keritinized layer, providing strength and compacting the deeper layers. At the tip of the shaft, the cuticle wears off, causing split ends. Hair color comes form melanocytes in the matrix, and contain all three kinds of melanin in differing amounts. When the shaft is oval, the hair is wavy. Flat hair is wavy or kinky. Round hairs make up straight tresses. Hair is found everywhere but the palms, soles, and lips of humans. We are born with all of the hair follicles we will ever have, but hormones cause hair to grow at different time in our lives. Hair follicles are compound structures. The inner sheath is formed of epithelial tissue and forms the hair. The outer sheath is dermal tissue. The dermal tissue supplies blood and nourishment to the hair root of epithelial tissue and reinforces t. It's nipple-like papilla in the bottom of the follicle provides blood to the matrix. The hair is slanted, attached to the arrector pili, which pulls it upright when we are cold or stressed, though it is not very useful in humans

Nails are scale-like modifications of the epidermis. Each terminates in a free edge, with a body and a root. The borders of the nails are overlaid by folds of skin called nail folds. The thick, proximal nail fold is most commonly known as the cuticle. Stratum germinativum makes up the nail bed, thickening proximal to the nail into the nail matrix. Nails, like hair and stratum corneum, are dead, pushed up from the germinativum. The nail appears pink only due to the richly vasulated tissue underneath. The exception to this is the lunula, a region over the matrix

Athletes foot is an itchy, red peeling of the skin between the toes from a fungal infection

Boils and carbuncles are inflamed hair follicles and sebaceous glands on the dorsal neck. Carbuncles are composite boils often caused by the bacteria Staphylococcus aureus

Cold sores, or fever blisters, are small, fluid-filled blisters that sting and itch. They are caused by a herpes simplex infection. The virus localizes in a cutaneous nerve, where it remains dormant until activated. The trigger may be sun, stress, or a fever. Most often the blisters occur in the oral mucosae

Contact dermatitis is itchy, red swelling of the skin, progressing into blisters. It is an allergic response to chemicals, such as those in poison oak or ivy

Impetigo is characterized by pink, water-filled lesion that develop a yellowed crust and rupture. It is caused by a highly contagious staphylococcus infection, common in school-aged children

Psoriasis is a chronic condition. Red epidermal lesions are formed, covered by dry, silvery scales. A severe case may lead to disfigurement, the cause unknown. Psoriasis may be hereditary, brought on by trauma, infection, hormonal changes or stress

Burns are cellular damage and death caused by heat, electricity, ultraviolet radiation, or chemicals. Burns present two major hazards. Fluid is lost, with proteins and electrolytes. This can lead to circulatory shock. Lost fluids must be replaced immediately. The volume of fluid lost can be estimated using the nines, how much body surface has been burned. This method divides the body into eleven areas, each representing nine percent of the body's total surface, with area about the genitals, the perineum, making the last one percent. Later, infection is a major concern. The acid mantle is lost, and the deep tissue is exposed. Burned skin in sterile for about twenty-four hours. The patients immune system becomes depressed, adding to the problem within one or two days after burning

Burns are classified as first-, second-, and third-degree burns. In fist-degree burns, the skin becomes red and swollen. Only the epidermis is damaged. After the initial discomfit, the burn heals quickly, and is not a major threat. Sunburns are usually first-degree burns. Second-degree burns damage the epidermis and the papillary region of the dermis, and involved blistering. A sufficient amount of epithelial cells are left to regrow the damaged tissue. Both are called partial-thickness burns. Third-degree burns are full-thickness. The affected area is blanched or blackened. The is little or no pain, because the nerves have been too damaged. In such cases, regeneration is not possible, and skin must be regrafted. Burns are critical if over twenty-five percent of the body has second-degree burns, over ten percent of the body has third-degree burns, or third-degree burns exist on the face, hands, or feet. Facial burns are dangerous to air passages. Joint injuries are a difficulty when scar tissue forms, which may limit movement

Most skin tumors are benign; a wart or neoplasm, for example. Some, however, are not so lucky. Skin cancer is the one most common type of cancer, with a tendency to move to other areas of the body. The cause of most skin cancers is not known, but one of the more important risk factors is over-exposure to ultraviolet radiation. Also to consider are genetics, and predisposition from infection, chemicals, or physical trauma

Basal cells carcinoma is the least malignant and most common of skin cancer. Cells of the stratum germinativum are altered so they no longer produce keratin, and enter the dermis and subcutaneous tissues. Most often, it appears in sun-exposed areas of the skin as a shining, dome-shaped node. Later, it becomes an ulcer with an edge of the same character. Basal cells carcinoma is slow-growing, and seldom metastasizes before diagnosis. Ninety-nine percent of the time, the cancer is fully cured by surgery

Squamous cell carcinoma also arises in the germinativum, but not those cells in direct contact with the basement membrane. The lesion shows as a scaly, red papule that slowly changes into an ulcer with a firm, raised border. Most often, this cancer appears on the scalp, ears, dorsum of the hands, and lower lip. It metastasizes quickly, moving to the near lymph nodes. If caught early and treated with radiation or surgery, the chances of curing the growth are good. The cause is believed to be sun-related

Malignant melanoma is a cancer in the melanocytes. Making up only about five percent of skins cancers, it is the most deadly. It can begin wherever there is pigment, but most often occurs in pigmented moles. It usually appears as a spreading brown or black patch the metastasizes quickly into surrounding blood vessels and lymph nodes. The chances of survival are increased with early diagnosis. The ABCD rule is suggested by the American Cancer Society. Look for Asymmetry in pigmented spots. Border irregularity. Colors, such as black, brown, tan, even blue or red. Diameter, be cautious of growth

During the fifth and sixth months of fetal development, an infant is covered with lanugo. Lanugo is a coat of downy hair usually shed by birth. When the child is born, the skin is covered in vernix caseosa, a white, cheese-like substance produced by the sebaceous glands. It's purpose is to protect the baby's skin in the womb. The newborn skin is very thin and translucent. It is quite common for there to be accumulations in the sebaceous gland, appearing as white spots on the infants nose and forehead, called milis. Usually, they disappear by the third week after birth

During adolescence, the skin and hair become more oily as sebaceous glands become more active. Acne may occur, but usually subsides in early adulthood. Later in life, abrasion, chemicals, sun, wind, and other such factors can cause pimples, scales, or various kinds of dermatitis, or skin inflammation. In old age, subcutaneous tissue is lost, as are elastic fibers and collagen. The skin become sagging and thin. This is sped by the suns harsh ultraviolet radiation. By fifty, the number of hair follicles has dropped by a third, and continues to fall, causing baldness, or alopecia. Many men become obviously bald, male pattern baldness. The fine, tiny, colorless hairs in the "bald" spots are vellus. Grey hair is caused by a delayed-action gene that, when active, causes melanin to be decreased in the hair

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