BI13_Ch5 Text Notes


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ANATOMY AND PHYSIOLOGY 1 TEXT NOTES Chapter 5 – The Integumentary System 1. THE SKIN a. Integumentary System – the skin and its derivatives (sweat and oil glands, hair, and nails). b. The skin has a surface area of 1.5 to 2.2 square meters, weighs 4 to 5 kg (9 to 11 lbs), and accounts for approximately 7% of total body weight in the average adult. c. The skin varies in thickness from 1.5 to 4.0 mm or more, and is composed of two different regions, the epidermis and the dermis. d. Hypodermis (Superficial Fascia) – subcutaneous tissue found just below the dermis. Strictly speaking, it is not part of the skin, but shares some of the skin’s protective functions. i. The hypodermis is also called the superficial fascia because it is superficial to the tough connective tissue wrapping (facia) of the skeletal muscles. ii. The hypodermis consists mostly of adipose tissue. This acts as a shock absorber and insulator for the body. iii. The hypodermis anchors the skin to the underlying structures (mostly muscles), but loosely enough that the skin can slide relatively freely over those structures. iv. The hypodermis thickens markedly when a person gains weight. e. Epidermis i. Epidermis – composed of epithelial cells and is the outermost protective shield of the body. ii. The epidermis has no vascularization. Nutrients reach the epidermis by diffusing through the tissue fluid from blood vessels in the dermis. iii. Structurally, the epidermis is a keratinized stratified squamous epithelium consisting of four distinct cell types (keratinocytes, melanocytes, Langerhans’ cells, and Merkel cells) and four or five distinct layers. 1) Cells of the Epidermis. a) Keratinocytes (Keratin Cells) – most epidermal cells are keratinocytes. Their chief role is to produce keratin , the fibrous protein that helps give the epidermis its protective properties. i) Keratinocytes are tightly connected to one another by desmosomes. ii) Keratinocytes originate from the stratum basale, which undergoes almost continuous mitosis. iii) Keratinocytes are pushed toward the skin surface and by the time they reach it, they are dead, keratin-filled plasma membranes. File: 092bce38c02f25d845796a8e8b7e23f153c76524.doc Updated: 8/14/09
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TEXT NOTES Chapter 5 Page 2 b) Melanocytes – spider-shaped epithelial cells that synthesize the pigment melanin . They are found in the deepest layers of the epidermis. i) As melanin is made, it is accumulated in membrane- bound granules called malanosomes that are moved along actin filaments by motor proteins to the ends of the melanocyte’s processes. Here, they are taken up by keratinocytes, accumulate on the superficial side of the nucleus, forming a pigment shield that protects the nucleus from ultraviolet (UV) radiation. .
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