Integumentary SystemIntegumentary System Chapter 6 Sections 1 & 2Chapter 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 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 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