Chapter 4 intro and histology

Chapter 4 Intro and Histology
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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)
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