THE INTEGUMENTARY SYSTEMWhat is an organ? A group of two or more tissues that performs a specific function is called an organ.What is a system?A group of two or more organs that work together towards a common goal is a system.A. SKINWhat are the components of the integumentary system?The skin and organs that are embryonic epidermal derivatives comprise the integumentary system. These include hair, nails, glands, and enamel of teeth.1. ANATOMYDescribe each of the following:Epidermis – The epidermis is the outer, thinner, waterproof portion of the skin. It is composed of keratinized stratified epithe-lium divided into four (thin skin) or five (thick) distinct layers or strata.Dermis -- The epidermis is attached to the dermis, the inner, thicker portion of skin. It is composed of elastic and collagenous connective tissues and bears a vascular supply. The dermis is very thick on the palms and soles, and tends to be thicker on the dorsal body surfaces than on the ventral surfaces.Hypodermis - Deep to the dermis is the hypodermis (subcutaneous layer or superficial fascia). The hypodermis isnot a true part of the skin. It is formed from areolar and adipose tissues and serves to attach the dermis to under-lying tissues, give protection from mechanical blows, and store energy.292. PHYSIOLOGYList and give a brief description of the seven functions of the skin.Regulation of body temperature -- In response to strenuous exercise or high environmental temperature, evaporation of sweat from the skin surface lowers body temperature to normal. Sweating ceases when temperatures are low. Increased blood flow to the skin also participates in regulation of temperature.Protection -- Skin covers the body and provides a physical barrier that protects underlying tissues from physical abrasion, microbial invasion, dehydration, and ultraviolet (UV) irradiation.Sensation -- Skin contains abundant nerve endings and receptors that detect stimuli related to temperature, touch, pressure, and pain.Excretion -- In addition to thermoregulation, sweat also is the vehi-cle for excretion of a small amount of salts and several organic compounds.Immunity -- Certain cells of the epidermis are important compon-ents of the immune system, working to fend off foreign invaders.Blood reservoir -- Blood vessels in the dermis carry 8-10% of total blood volume in a resting adult. This blood can be moved quickly to skeletal muscles to facilitate exercise.Synthesis of vitamin D -- One step in the activation of vitamin D requires UV light. This occurs as blood passes through the skin.3. EPIDERMISList the four cell types of the epidermis, give the percent of the total population of epidermal cells, and give a brief description of each.Keratinocytes -- (90%) produce the keratin that waterproofs and protects the skin and underlying tissues. Anchoring junctions between cells called desmosomes “weld” cells together to form a formidable membrane.30Melanocytes -- (8%) produce the brown-black pigment melanin thatabsorbs ultraviolet light. The cells produce melanin then transfer it to the keratinocytes in the stratum spinosum for distribution throughout the layers of the epidermis. Once inside a keratinocyte, melanin clusters over the apical side ofthe nucleus, giving it protection from the UV irradiation that penetrates it.Langerhans cells -- (1%) involved in immune function, working with lymphocytes called helper T cells.Merkel cells -- (1%) make contact with the flattened portion of a sensory nerve ending called a tactile (Merkel) disc and are thought to function in the sense of touch.Describe each of the following strata of the epidermis:Stratum basale -- single layer of cells, mostly mitotic keratinocytes, resting on basement membrane; gives rise to new cells of the epidermis; also contains the melanocytes and Merkel cells.Stratum spinosum -- 8-10 rows (sheets) of spiny-shaped cells derived from the keratinocytes below; receive melanin from melanocytes; no longer mitotic.Stratum granulosum -- 3-5 rows of cells that begin producing and accumulating the molecule keratohyalin, a precursor of keratin.Stratum lucidum -- 3-5 rows of clear, flattened, dead cells packed with eleidin, the intermediate molecule in the formation of keratin; only present in thick skin.Stratum corneum -- 25-30 rows of flattened dead cells, completely filled with keratin; gives the skin a water-proof, anti-microbial,and abrasion-resistant barrier. Can absorb water to keep skin hydrated.4. DERMISDescribe the papillary dermis.The outermost portion (top one-fifth) of the dermis is the papillary dermis. It consists of areolar connective tissue rich in fine elastin fibers. Its surface area is greatly increased by small, hill-like projections called dermal papillae. Each papilla contains loops of blood capillaries.31Describe the reticular dermis.The deeper layer is the reticular dermis. It consists of dense irregular connective tissue rich in interlacing bundles of collagen and coarse elastin fibers.What is the function of the dermis?The combination of elastin and collagen, particularly in the reticular dermis, gives the skin strength, elasticity (the ability to return to shape after stretching), and extensibility (the ability to stretch). The dermis has a large blood supply, especially in areas of skin used fortemperature regulation. This is the blood supply for the epidermis as well.B. GLANDS1. SEBACEOUS (OIL) GLANDS 2. SUDORIFEROUS (SWEAT) GLANDS a. ECCRINE b. APOCRINEDescribe each of the following exocrine glands of the skin.Sebaceous glands -- secrete sebum, a mixture of lipids, proteins, and salts onto the surface of the epidermis. It forms a protective film, in combination with sweat, called the acid mantle, that lubricates the skin and hair, prevents evaporation of water through the epidermis, and is anti-microbial.Eccrine sweat glands -- are most common, being found over most of the skin. Secretion is copious and about 90% water. It is used as the body’s principal means of losing body heat via evaporation. The glands are poorly functional prior to the age of two; therefore, young children are poor thermoregulators in the heat.Apocrine sweat glands -- found mainly in the skin of the axillary region, pubic region, areolar regions of the breasts, and the beard area of men. Beginning at about puberty, they produce only a very small amount of a viscous milky fluid. The role of this secretion is unknown, but it is released in response