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CHAPTER 4: THE TISSUE LEVEL OF ORGANIZATION Four types of tissues: (Powerpoint) Epithelial, Connective Tissue, Muscle Tissue (bottom right- cells that contract), Neural Tissue (bottom right)- composed of neurons specialized for communication I. Epithelial Tissue (top left) A. Characteristics: mostly made of cells that are held together tightly and stacked; line all passages that communicate with the outside world 1. Cellular- tend to stick together (cell junctions), very little matrix between them, made mostly of cells 2. Polar- one side is different than the other- one side has cilia , golgi towards top, nucleus toward bottom a. Basal lamina- (bottom) functions to connect the epithelial tissue to whatever is underneath 3. Avascular- no blood vessels- has to receive its nutrients and dispose of wastes w/o blood vessels- not extremely thick and will exchange with blood vessels which normally lie beneath- cells at top die as they get further from blood 4. Regenerative- capacity to continually replace dying cells- continually reproduce more cells from stem cells B. Specializations 1. Cilia, microvilli 2. Intercellular connections: tight junctions-hold cells very tightly and form barriers so even water cannot get through, desmosomes- connection just for purpose of holding cells together, gap junctions- very tiny pores that allow small items to pass to adjacent cell 3. Basal lamina secreted matrix that forms attachment for epithelium to connective tissue 4. Germinative cells stem cells that continually regenerate the epithelium C. Functions (locations of epithelia) function tied closely to its structure 1. Physical protection all kinds of barriers; skin, digestive tract- protect from water loss, abrasion 2. Allow selective permeability lungs, digestive tract, kidneys, blood vessels 3. Transmit sensations intimately connected with the nervous system 4. Produce secretions glandular epithelium D. General Classification 1. Complexity: Simple (single layer), Stratified (multiple layers)... View Full Document

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