Integumentary System Chapter 6 Sections 1 & 2 Objectives • Describe what constitutes an organ, and name the large organ of the integumentary system • Discuss the functions of the skin • Describe the structure of the layers of the skin • Summarize the factors that determine skin color Introduction • Review: two or more tissues grouped together to perform specialized functions constitutes an organ • The skin is the largest organ in the body by weight • The skin and its accessory structures together make up the integumentary system • Skin is composed of several types of tissues such as, stratified squamous epithelium, dense irregular connective, and adipose tissues (see figure 6.1 p.180) • It is a versatile organ of the body and vital in maintaining homeostasis Characteristics & Functions of the Skin • It prevents harmful substances and microorganism from entering the body • It lessens water loss by diffusion from deeper tissues • It regulates body temperature • It houses sensory receptors • Contains epidermal dendritic cells or Langerhans cells which initiated the immune response to phagocytize harmful microorganisms • It excretes small amounts of waste • Some skin cells produce the vitamin D precursor, which when exposed to sunlight changes to an inactive form of vitamin D. Skin & its Tissues • The skin, also known as the cutaneous membrane, has two distinct layers: • The epidermis • The dermis The Epidermis • The outer layer of the skin • It’s a thin layer, averaging 0.07-0.12 mm thick • Composed of stratified squamous epithelium • It lacks blood vessels • Can have five distinct layers • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale The Epidermis Overall Stratum corneum • Is the outermost layer • Consists of many layers of keratinized, dead epithelial cells that are flattened and non-nucleated • Keratinization is the process of older skin cells, called keratinocytes, thickening and developing many desmosomes while hardening at the same time • Keratin is a tough, fibrous, waterproof protein that is stored in those cells Stratum lucidum • Found between the stratum corneum and stratum granulosum on the soles of your feet and the palms of your hands • Cells appear clear • Nuclei, organelles and cell membranes are no longer visible • This layer is missing where the skin is thinner Stratum granulosum • Found beneath the stratum corneum • Consists of 3-5 layers of flattened cells that contain shrunken fibers of keratin and shriveled nuclei Stratum spinosum • Lies beneath the stratum granulosum • Composed of many layers of cells with centrally located, large, oval nuclei, and developing fibers of keratin • Cells become flattened as new layers develop Stratum Basale • The deepest layer of the epidermis • Consists of a single row of cuboidal or columnar cells • Can grow and divide because the cells receive nutrients from the nearby dermis layer • Also contains melanocytes The Epidermis Overall Melanocytes • Are specialized cells that produce the dark pigment melanin from the amino acid tyrosine in organelles called melanosomes • Melanin provides skin color and absorbs UV radiation in sunlight • They lie in the stratum basale of the epidermis • The number of melanocytes is the same for all human regardless of racial origins • It is the amount of melanin produced that determines how dark your skin is, as well as, genetic factors and environmental factors The Dermis • The boundary between the dermis and the epidermis is uneven • Two distinct layers: • Dermal papilla • Dermis Dermal papilla (Papillary Layer) • Are cone-shaped and extend from the dermis layer into the uneven ridges of the epidermis • Composed of areolar connective tissue • They increase the surface area where epidermal cells receive oxygen and nutrients from the capillaries • They are found all over in the skin of the body, but are most abundant in the hands and feet • They form friction ridges that leave a patterned impression better known as a fingerprint Dermis layer (Reticular Layer) • Composed of dense irregular connective tissue with a tough collagenous fibers and elastic fibers embedded in a gel-like ground substance • The network of these fibers, give skin its toughness and elasticity • The dermis on average is 1.0-2.0 mm thick • On the eyelids it is 0.5 mm • On the soles of the feet it is 3.0 mm • Also contains: muscle fibers, accessory structures, nerve cell processes, and sensory receptors The Dermis