Skin outline - CHAPTER 5 The Integumentary System The...

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CHAPTER 5: The Integumentary System The integumentary system or integument is the largest system of the body. - 16% of body weight; 1.5 to 2 square meters in area The integument is made up of 2 parts: 1. the cutaneous membrane , or skin, and 2. the accessory structures The cutaneous membrane is made up of 2 parts: 1. the outer epidermis or superficial epithelium (epithelial tissues) and 2. the inner dermis , composed of connective tissues The accessory structures include hair, nails, and multicellular exocrine glands. These structures generally originate in the dermis and extend through the epidermis to the skin’s surface. The integument interacts with the circulatory system through blood vessels in the dermis, and with the nervous system through sensory receptors for pain, touch, temperature etc. Below the dermis is a subcutaneous layer of loose connective tissue, also known as the superficial fascia or hypodermis (where hypodermic injections are administered). The functions of skin and its subcutaneous layer include: 1. Protection of underlying tissues and organs against shock, abrasion, fluid loss and chemical attack. 2. Excretion of salts, water, and organic wastes by glands. 3. Maintenance of body temperature by insulation (heating) and sweat evaporation (cooling). 4. Synthesis of vitamin D3 (converted to calcitriol for calcium regulation). 5. Storage of lipids. 6. Detection of touch, pressure, pain and temperature. The Epidermis, p. 155 The epidermis is an avascular stratified squamous epithelium that relies on diffusion of nutrients and oxygen from capillaries in the dermis. The most abundant cells in the epidermis are the keratinocytes (so called because they contain large amounts of the protein keratin). Most of the body is covered by thin skin , which has only 4 layers of keratinocytes in the epidermis. The palms of the hands and soles of the feet are covered with thick skin , which has 5 layers of keratinocytes in its epidermis. Layers of the Epidermis, p. 155 The 5 layers or strata of keratinocytes in the thick skin of the epidermis are (from the deep basal lamia to the free surface) the: 1. stratum germinativum 2. stratum spinosum 3. stratum granulosum 4. stratum lucidum , and the 5. stratum corneum The stratum germinativum (“germinative layer”) is attached to the basal lamina by hemidesmosomes, forming a strong bond between the epidermis and the dermis. - Stratum germinativum forms epidermal ridges that determine our fingerprint pattern, and dermal papillae or tiny mounds. - Stratum germinativum has many germinative (stem) cells, called basal cells , which replace keratinocytes that are shed at the skin’s surface.
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- Skin surfaces that have no hair have many Merkel cells in their stratum germinativum that respond to touch by releasing chemicals that trigger nervous system responses.
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