THE INTEGUMENTARY SYSTEM What 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 SKIN What 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 ANATOMY Describe each of the following Epidermis The epidermis is the outer thinner waterproof portion of the skin It is composed of keratinized stratified epithelium 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 is not a true part of the skin It is formed from areolar and adipose tissues and serves to attach the dermis to underlying tissues give protection from mechanical blows and store energy 29 2 PHYSIOLOGY List 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 vehicle for excretion of a small amount of salts and several organic compounds Immunity Certain cells of the epidermis are important components 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 EPIDERMIS List 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 30 Melanocytes 8 produce the brown black pigment melanin that absorbs 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 of the 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 DERMIS Describe 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 31 Describe 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 for temperature regulation This is the blood supply for the epidermis as well B GLANDS 1 SEBACEOUS OIL GLANDS 2 SUDORIFEROUS SWEAT GLANDS a ECCRINE b APOCRINE Describe 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 to emotional stress and sexual excitement The glands apparently correspond to the scent glands of other mammals The secretion does not have a disagreeable odor 32 C THERMOREGULATION HOMEOSTASIS OF BODY TEMPEATURE