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Chapter 4 – Tissue Level of Organization

Chapter 4 – Tissue Level of Organization. What is a tissue?. A tissue is a collection of cells and cell products that perform a limited number of functions. Four Tissue Types. Epithelial (skin/outer layer/glands) tissue Connective tissue (never exposed to the outside)

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Chapter 4 – Tissue Level of Organization

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  1. Chapter 4 –Tissue Level of Organization What is a tissue? A tissue is a collection of cells and cell products that perform a limited number of functions.

  2. Four Tissue Types Epithelial (skin/outer layer/glands) tissue Connective tissue (never exposed to the outside) Muscle tissue (in muscles) Neural tissue (nerves, spinal cord, brain)

  3. Epithelial Tissue • Characteristics: • Cells are in close proximity, tightly packed • Exposed to the environment (skin/free surface) or an internal passageway (digestive, respiratory, reproductive, urinary tracts) • Have a basement membrane that attaches connective tissue to underlying layer • No blood vessels – where do nutrients come from? • Damaged and lost, so continually replaced

  4. Functions of Epithelia Provides physical protection Controls permeability Provides sensation Produces specialized secretions (glands)

  5. Intercellular Connectionsin Epithelial Tissues • Epithelial cell membranes have proteins called cell adhesion molecules (CAMs) • The adhesion molecules and intercellular cement (made of composed protein-polysaccharide mixture) hold neighboring cells together • Types: • Tight junctions – layers of lipids tightly bound by proteins on the cell membranes • Gap junctions – embedded membrane proteins hold them together • Desmosome – membranes bound together by intercellular cement

  6. Layer Types of Epithelial • Simple – single layer of cells over a basement membrane • Thin cells • Only in protected, internal parts • Stratified – several layers of cells above the basement membrane • A little greater protection • Survive mechanical and chemical stresses better

  7. Intercellular Connections • Tight junctions • Formed by fusion of neighboring cell membranes • Found in the digestive tract • Gap junctions • Allow for an electrical current and small molecule exchange • Commonly found in cardiac and smooth muscle tissue and the liver • Desmosome • Reinforced with fine protein filaments • Top layers of skin and between heart cells

  8. Cell Shapes in Epithelial Tissue • Three types: • Squamous epithelium • Squama – plate • Thin and flat cells with the thickest part containing the nucleus • Cuboidal epithelium • 3D are hexagonally shaped, under microscope are cubed • Often form a neat row • Columnar epithelium • Taller hexagonally shaped cells • Nuclei are located closer to the basement membrane

  9. Cell Layers & Shapes • Psuedostratified Ciliated Columnar Epithelia • What’s the break down of the name? • Transitional Epithelia • Expandable and flexible, but thins out • Balloon/Bladder

  10. Where are these cells? Where secretion takes place Found where absorption takes place Found where mechanical stresses are severe Respiratory tracts, male reproductive tract

  11. Glandular Epithelia • Two glands: • Endocrine (ductless; hormones into blood or tissue fluid) • Exocrine (ducts for external/internal secretion) • Secretion mode: • Secrete either into a duct (crosses an apex) or into a blood vessel (across the base) • Merocrine – secretion through exocytosis • Apocrine – portion of the cell, including cytoplasm is shed with secretion • Holocrine – cell fills with secretion and then bursts

  12. Glandular Epithelia • Secretion type: • Serous glands – watery with enzymes • Mucous glands – thick, but slippery • Mixed glands – more than one type • NOTE: mucous is the descriptive adjective; mucus is the noun or actual product

  13. Connective Tissue • A matrix (most of the tissue volume; formed by ground substance and extracellular protein fibers) that supports scattered cells – seems like conglomerate of unrelated tissues • Widely distributed throughout the body • Three components: • Specialized cells • Protein fibers • A surrounding fluid, ground substance

  14. Functions & Types of Connective Tissues Support and protection Transport materials Store energy Defend the body Types: Connective Tissue Proper Fluid Connective Tissue Supporting Connective Tissue

  15. Connective Tissue Proper – Cell Types Major Cell Types: Fibroblasts – most abundant Microphages – scattered, can be fixed or free Fat Cells/ Adipocytes – amount of fat varies Mast Cells – full of enzymes, near blood vessels

  16. Connective Tissue Proper – Fiber Types • Collagen fibers – long & straight; strong & flexible • Most common fiber in Connective Tissue Proper • Elastic fibers – contain protein elastin; branched and wavy • Stretch, but return to original length • Reticular fibers – thinner than collagen • Form branching, interwoven network in organs

  17. Connective Tissue Proper • Categorized as loose or dense connective tissue • LOOSE: least specialized, contains cells and fibers of Connective Tissue Proper and blood vessels • Layer between skin and muscles • Provides padding

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