Introduction To Basic Tissue Types Connective and Epithelial

Question 1

Tissue

Answer 1

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

Question 2

Hierarchical organization of animal body

Answer 2

Organ system -> Organ -> Tissue -> Cell

Question 3

Epithelial Tissue

Answer 3

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

Question 4

Characteristics of epithelial cells

Answer 4

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

Question 5

Classification of epithelia

Answer 5

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)

Question 6

Apical domain modifications

Answer 6

In many epithelia apical domain exhibits structural surface modifications that carry out specific functions
Microvilli
Cilia
Stereocilia
Primary cilium

Question 7

Microvilli

Answer 7

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

Question 8

Cilia

Answer 8

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

Question 9

Primary cillia

Answer 9

Solitary projections found on almost all eukaryotic cells; immotile; function as signal detectors; generate and transmit signals from extracelluar part of cell

Question 10

Stereocilia

Answer 10

Unusually long immotile microvilli located on sensory cell of inner ear and in parts of male reproductive tract; visible with light microscopy

Question 11

Organization of epithelial tissues

Answer 11

Organized in 2 ways
Sheets- cover or line a free surface, in some locations have specific name
Endothelium
Endocardium
Mesothelium
Transitional epithelium

Glands

Question 12

Endothelium

Answer 12

Epithelial lining of blood and lymphatic vessels, simple squamous

Question 13

Endocardium

Answer 13

Epithelial lining of heart, simple squamous

Question 14

Mesothelium

Answer 14

Epithelial lining of closed cavities of body, simple squamous

Question 15

Transitional epithelium

Answer 15

Epithelial lining of lower urinary tract, stratified with special characteristics to allow for distention

Question 16

Connective tissue

Answer 16

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

Question 17

ECM connective tissue

Answer 17

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

Question 18

Fibroblasts

Answer 18

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

Question 19

Connective tissue cell types

Answer 19

Primarily fibroblasts, also have resident cell population, wandering cell population

Question 20

Myofibroblasts

Answer 20

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.

Question 21

Fiber types in connective tissue

Answer 21

Collagen, elastic, reticular

Question 22

Collagen fibers

Answer 22

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

Question 23

Elastic fibers

Answer 23

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

Question 24

Reticular fibers

Answer 24

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

Question 25

Ground substance

Answer 25

Part of ECM that occupies space between cells and fibers; viscous clear substance consisting of glycosaminoglycans, proteoglycans, mutiadhesive glycoproteins, and large amounts of water
Lost in H&E

Question 26

Connective Tissue Proper

Answer 26

Can be subdivided into
Loose connective tissue ie areolar tissue- characterized by loosely arranged fibers and abundant cells of various types, located beneath epithelia that covers body surfaces and line internal surfaces of body, associated with epithelium of glands and surrounds smallest blood vessels; most cells in loose connective tissue are transient wandering cells that migrate in from local blood vessels
Dense connective tissue- can be subcateglorized as
Dense irregular connective tissue and dense regular connective tissue
Dense irregular connective tissue- characterized by abundant fibers and few cells, contains mostly collagen fibers relatively little ground substance, fibers are arranged in bundles in various direction conferring strength fibroblasts are most abundant cell type
Dense regular connective tissue- characterized by ordered and densely packed arrays of fibers and cells, main functional component of tendons, ligaments, aponeuroses, little ground substance, cells producing fibers packed between fiber bundles