Introduction To Basic Tissue Types Connective and Epithelial Flashcards
Tissue
Aggregates or groups of cells organized to perform one or more specific functions, cells with in a tissue work collaboratively to form functional units 4 basic types of tissue Epithelial Connective Nervous Muscular
Hierarchical organization of animal body
Organ system -> Organ -> Tissue -> Cell
Epithelial Tissue
Epithelium continuous sheet of epithelial cells, covers exterior body surfaces, lines interior body cavities and/ or forms secretory portion of glands
3 major functions in animal body
Protection, Absorbtion, Secretion
Characteristics of epithelial cells
Closely approved to each other, adhere to each other by specialized cell junctions composed of cell-cell adhesion molecules
Exhibit polarity- 3 distinct domains apical (free surface), lateral, basal
Lower most cells of epithelium are always attached by basal surface to underlying basement membrane
Classification of epithelia
Classified by two criteria number of cells and shape of cells
Number of layers- simple (one cell layer thick), stratified (more than one cell layer thick), pseudostratified (looks stratified but all cells resting on basement membrane, not all cells will reach free surface)
Shape of cells on surface layer- squamous (flat), cuboidal (width, depth, height approximately equal), columnar (height exceeds width)
Apical domain modifications
In many epithelia apical domain exhibits structural surface modifications that carry out specific functions Microvilli Cilia Stereocilia Primary cilium
Microvilli
Small finger like cytoplasmic projections of luminal plasma membrane increase surface area of cell; have core of actin filaments that are cross linked by several actin binding proteins which confer rigidity
Cells which transport fluid and absorb metabolites have closely packed tall microvilli, cells which transport less have smaller more irregularly shaped microvilli
Individual not seen in light microscopy but enough closely packed per cell in kidney and small intestine they can be seen as striated or brush border
Cilia
Motile hair like extension of apical plasma membrane with micro tubule-based internal structure associated with motor proteins; can move fluid and particles across epithelial surface
Longer than microvilli, give crew-cut appearance to epithelial surface
Primary cillia
Solitary projections found on almost all eukaryotic cells; immotile; function as signal detectors; generate and transmit signals from extracelluar part of cell
Stereocilia
Unusually long immotile microvilli located on sensory cell of inner ear and in parts of male reproductive tract; visible with light microscopy
Organization of epithelial tissues
Organized in 2 ways Sheets- cover or line a free surface, in some locations have specific name Endothelium Endocardium Mesothelium Transitional epithelium
Glands
Endothelium
Epithelial lining of blood and lymphatic vessels, simple squamous
Endocardium
Epithelial lining of heart, simple squamous
Mesothelium
Epithelial lining of closed cavities of body, simple squamous
Transitional epithelium
Epithelial lining of lower urinary tract, stratified with special characteristics to allow for distention
Connective tissue
Forms continuous compartment throughout animal body, provides structural and functional support for other 3 tissue types; composed of cells suspended within tissue-specific ECM composed of protein fibers suspended in watery gel (“ground substance”); cells do not adhere to each other
Subdivided into 3 groups
Embryonic connective tissue (mesenchyme)
Specialized connective tissue (bone, cartilage, blood, hematopoietic tissue, and adipose tissue)
Connective tissue proper
ECM connective tissue
ECM consists of protein fibers and ground substance, provides structural, biochemical, and mechanical support for connective tissue; provides pathway for cell migration and allows for diffusion of small molecules
Fibroblasts
Principal cell type of connective tissue, synthesize the ECM they reside in; don’t usually see entire fibroblast in H & E stain but will see fibroblast nuclei as elongated or disk like structure, sometimes with nucleolus
Connective tissue cell types
Primarily fibroblasts, also have resident cell population, wandering cell population
Myofibroblasts
Display properties of both fibroblasts and smooth muscle cells, elongated and spindly with contractile proteins but unlike smooth muscle cells no external lamina and usually exist as isolated cell. Do not see in stain.
Fiber types in connective tissue
Collagen, elastic, reticular
Collagen fibers
Most abundant structural component of connective tissue, confer flexibility and tensile strength (resistance to pulling forces); in light microscopy appear as eosinophilic ( eosin is red and bonds with cations) wavy structures of variable width and length; they are bundles of fine thread-like subunits
Elastic fibers
Allow tissues to respond to stretch and distention; thinner than collagen fibers, arranged in branching pattern to form 3d network; stain with eosin (eosin is red, reacts with cations) but can be difficult to see with collagen
Reticular fibers
Provide a supporting framework for cellular constituents of various tissues and organs, they are a form of collagen, have a mesh-like pattern or network; networks of reticular fibers found at boundary between epithelia and connective tissue also surround adipocytes, small blood vessels, nerves, and muscle cells
Do not stain with H&E
