Chapter 4 - Bio 2870 - CHAPTER 4 There are only 4 general types of tissue found in the human body epithelial connective muscle and nervous tissue

Chapter 4 - Bio 2870 - CHAPTER 4 There are only 4 general...

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CHAPTER 4-There are only 4 general types of tissue found in the human body: epithelial, connective, muscle, andnervous tissue.Epithelial Tissue– do not have a lot of intercellular matrix and is classified by its cells-can be found in two forms: 1.Epithelial linings(skin, internal lining of digestive system, body cavities)2.Epithelial Glandswhich are modified epithelial cells (sweat glands, sebaceous glands which release oil, carotid gland, pituitary gland).Internalized epithelia will form glands. A gland forms when a plasma membrane invaginates inward inside a cell, but never pinches off to form a vesicle. Any gland of your body is derived from epithelial cells.Important characteristics of Epithelial tissue:-Epithelial tissue is cellular- tissue is made up of cells bound together.-Epithelial cellsare polar- they look different on one end than they do on another.-Epithelial tissue is avascular- does not have its own blood supply and is far away from capillaries.-Epithelial tissue is very regenerative– there are stem cells located deep down in the interior of the skin that can give rise to new skin cells.Functions of Epithelial Tissue:-They form a physical protective barrier to the environment (Ex:Skin). It is a selective barrierand allows certain things to pass/not pass through. -Epithelial Tissue is loaded with sensory structures(Ex:Temperature, Pain, Vibration, etc). -Very common function of epithelial tissue is secretion(Ex:The serous membrane that line body cavities.) and absorption. (Ex:Small intestine we have epithelial cells absorbing various nutrients during digestion)Epithelial Tissue ModificationsAPICAL SURFACE MODIFICATIONS-The upper surface of the cell is the Apical Surface. (Area that faces the lumen or the external environment). Epithelial tissue also contain Apical Surface Modificationswhich include:1.Ciliawhich contain microtubulesand are motile. Cilia are considered cytplasmic extensions of the cell.2.Microvillicontain actin filaments(microfilaments) which increase the surface area of the cell for absorption and secretion. Microvilli also function for structural support, are non-motile, and are considered cytoplasmic extensions of the cell.Many microvilli are especially located in the Gastrointestinal (GI) tract.Stereocilliaare NOTa type of cilia. They are a long type of Microvilli(contain microfilaments).-As cells move up towards the surface of the skin, they eventually die, and release a protein called keratin. This leads to Keratinization (cornification) of the skin’s surface of skin. (A layer of protein called keratin on surface of skin). This is not an apical surface modification because it is not a physical extension of the cell. It is just stuff laying on the surface.
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