SKIN &BODY MEMBRANES 1-Mucous membranes line the body systems that have openings to the environment. (RS, DS, US, & RS). The epithelium of a mucous membrane (mucosa) varies. Mucosa is composed of epithelium resting on a loose connective tissue membrane called a lamina propria The mucus secreted keeps the lining epithelial cells wet and acts as lubricant. The epithelium of a mucous membrane (mucosa) varies with the different organs involved:. The mucosa of the esophagus & vagina is stratified squa-mous epithelium; the mucosa of the trachea is ciliated epithelium; the mucosa of the stomach is columnar epithelium. 2-Serous Membranes : Simple squamous epithelium that line some closed body cavities and cover the organs in these cavities. It secrete serous fluid, which prevents friction a-pleura : are the membranes of the thoracic cavity. The parietal pleura lines the chest wall. and the visceral pleura covers the lungs. b-pericardium around the heart The parietal pericardium lines the thoracic cavity the visceral pericardium, or epicardium, is on the surface of the heart muscle c-peritonium around the viscera The parietal peritonium lines the abdominal wall. - the visceral peritonium covers the abdominal organs - Connective tissue membranes These are made of connective tissue with no epithelial cells at all. It cushions organs moving against each other during muscle activity.Of these membranes: 1-Superficial fascia between skin and muscles, the adipose tissue. 2-Periosteum around bones 3-Synovial membrane,lines joints 4-Meninges, around the brain and spinal cord. Mainly, the integumentary system is composed of three parts: 1. The skin, 2. its accessory structures (hair $sweat glands), and 3. The subcutaneous tissue below the skin. * The skin is considered an organ; composed of different tissues. 1-Protects deeper tissues from: -mechanical damage -chemical damage (acids & bases) -bacterial damage -ultraviolet radiation (sunlight) Thermal (heat or cold) damage -desiccation (drying out) 2-aids in heat regulation -in cold: vasoconstriction -in hot: vasodilation + sweating 3-aids in excretion of urea & uric acid 4-synthesize vitamin D A-The epidermis: made of stratified squamous keratinizing epithelial tissue and is thickest on the palms and soles. The cells that are most abundant are called keratinocytes, and no capillaries present between them. Subdivided into four or five sublayers, two of these are of greatest importance: - the innermost layer, the stratum germinativum, the outermost layer, the stratum corneum. Stratum Germinativum (basale) To germinate means to grow. Basal means the base or lowest part. The stratum germinativum is the base of the epidermis, the innermost layer in which mitosis takes place. New cells are continually being produced, pushing the older cells toward the skin surface. These cells produce the protein keratin, and as they get farther away from the capillaries in the dermis, they die. Stratum Corneum -the outermost epidermal layer, -consists of many layers of dead cells; all that is left is their keratin which is a fibrous protein that makes the epidermis: - a tough protective layer - relatively waterproof (prevent evaporation, prevents the entry of water). -a barrier to pathogens and chemicals. * Stratum Corneum rubs and flakes slowly leading to totally new epidermis every days Cells in the skin 1-Keratinocytes 2-Langerhans Cells,originate in the red bone marrow, and are quite mobile. Part of immune response such as the production of antibodies. 3-Melanocytes produce another protein,a pigment called melanin. In people with dark skin, the melanocytes continuously produce large amounts of melanin. The melanocytes of lightskinned people produce less melanin. The activity of melanocytes is genetically regulated. People with dark skin already have good protection against the damaging effects of ultraviolet rays. -Melanin also gives color to hair,iris &choroid. B-Dermis It is a strong stretchy envelope that hold the body together It is made of an irregular type of fibrous connective tissue. Fibroblasts produce both collagen and elastin fibers. Collagen fibers are strong, and elastin fibers are able to recoil after being stretched. Strength and elasticity are two characteristics of the dermis. With increasing age, however, the deterioration of the elastin fibers causes the skin to lose its elasticity. The junction of the dermis with the epidermis is uneven. Capillaries are abundant here to nourish not only the dermis but also the stratum germinativum. N.B. The epidermis has no capillaries of its own. Within the dermis are the accessory skin structures: hair and nail follicles, sensory receptors, and several types of glands. *Colour of skin three pigments contribute to skin colour: 1-melanin 2-karotine 3-oxyhemoglobin *Appendages of the skin 1-Hair follicles mitosis takes place in the hair root; new cells produce keratin, die, and become the hair shaft. 2. Nail folliclesat the ends of fingers and toes; mitosis takes place in the nail root; the nail itself is dead, keratinized cells. 3. Receptorsdetect changes in the skin: touch, pressure, heat, cold, and pain; provide information about the external environment that initiates appropriate responses. 4. Sebaceous glands(oil glands) secrete sebum into hair follicles or to the skin surface. -sebum inhibits the growth of bacteria and prevents drying of skin and hair. -if its duct is blocked by sebum,whitehead appears, with oxidation become blackhead -active infection leads to acne. 5. Ceruminous glandssecrete cerumen in the ear canals. It prevents drying of the eardrum. 6. Apocrine sweat in axillae and genital area; activated by stress and emotions. Begins function at puberty, minimal role in thermoregulation. 7. Eccrine sweat glandsall over the body, most numerous on face, palms, soles. Activated by high external temperature or exercise; sweat on skin surface is evaporated by excess body heat. Excretion of small amounts of NaCl and urea is a very minor function. 8. Arteriolessmooth muscle of its wall permits constriction or dilation. Vasoconstriction in cold temperatures decreases dermal blood flow to conserve heat in the body core. Vasodilation in warm temperatures increases dermal blood flow to bring heat to the surface to be lost. Vasoconstriction during stress shunts blood away from the skin to more vital organs, such as muscles, to permit a physical response, if necessary.