Tissues
• Whole body contains only 200 different cells types that are organized into tissues
• The extracellular fluid surrounding the cells organized into tissues is called interstitial fluid
• Four primary tissue classes
– epithelial tissue
– connective tissue
– muscular tissue
– nervous tissue

Epithelial Tissue
• Covers the entire surface of the body
– includes skin, lining of the lung, lining of the digestive tract, lining of the urinary tract, lining of the reproductive tract
– barrier between what is IN the body and what is
OUT of the body
– controls what substances enter/exit the body and what substances stay in/out of the body
• Primary tissue type found in exocrine glands
– secrete substances out of the body (sweat, saliva, digestive system juices)
• Classification of epithelial tissue is based on:
– the shape of the cells that make up the tissue
– the number of layers of epithelial cells

Epithelial Tissue: Basic Structure
• Made of epithelial cells that are connected to adjacent cells by proteins called tight junctions
– create “sheets” of epithelial cells
• similar in structure to a six-pack of cans
• Anchored to the body by a structure called the basement membrane
• Epithelial cells have 2 sides
– apical side of the cell faces toward the OUTSIDE of the body
– basal side of the cell faces toward the INSIDE of the body

Shape of Epithelial Cells
• Cell shape
– squamous (flattened cells)
• cell width is larger than cell height
• cells have flat nuclei
– cuboidal (cube-like cells)
• cell width is equal to cell height
• spherical nuclei
– columnar (column-like cells)
• cell height is larger than cell width
• tall nuclei

Layering of Epithelial Cells
• Simple
– one cell layer thick
– transports substances into or out of the body
• Stratified
– more than one cell layer thick
– protects body from mechanical damage (abrasion, puncture…)
• Pseudo stratified
– one cell layer thick made of cells with differing heights
– gives false impression of stratified epithelium

Epithelia: Simple Squamous
• Single layer of squamous epithelial cells

Epithelia: Simple Cuboidal
• Single layer of cuboidal epithelial cells

Epithelia: Simple Columnar
• Single layer of columnar cells

Epithelia: Pseudostratified Columnar
• Single layer of cells with different heights; some do not reach the surface of the body

Epithelia: Stratified Squamous
• Multiple layers of squamous cells with flat nuclei

Epithelia: Stratified Cuboidal and Columnar
• 2-3 layers of cuboidal/columnar cells
• Both are rare in the body

Epithelia: Transitional
• The shape of the cells will change based on the amount of stress (stretch) on the tissue
• Can appear as cuboidal or columnar when not stretched or squamous when stretched

Connective Tissue
• Most abundant tissue type
• 4 primary types
– Connective tissue proper
• loose
• dense
– Cartilage
– Bone
– Blood

Structural Elements of Connective Tissue
3 structural elements (components) of connective tissue
• Cells
• Ground substance
• unstructured (gel-like) material that fills the space between cells ( interstitial space )
• Fibers
• very large proteins extracellular proteins which make a web-like structure holding tissues together
• Ground substance + fibers = Extracellular Matrix

Structural Elements of Connective Tissue

Cells
There are 4 different cell types which are responsible for building ( blast = “ to build ”) the 4 different types of connective tissue
• Fibro blasts
– connective tissue proper
• Chondro blasts
– cartilage
• Osteo blasts
– bone
• Hemocyto blast
– blood

Fibers
3 primary types of extracellular fibers provide different physical characteristics to connective tissue types
• Collagen
– very thick and strong, do not stretch
– provides tough structure to tissue
• Elastic
– thin and strong, allow for stretch and then recoil
(return to original length) when released
• Reticular
– thin and fragile, do not stretch
– provide delicate structure to tissue

Loose Connective Tissue Proper: Areolar

Loose Connective Tissue Proper: Adipose
• Stores lipids to use as fuel, insulation and protection

Loose Connective Tissue Proper: Reticular

Dense Connective Tissue Proper: Regular
• Many parallel collagen fibers with a few elastic fibers
• Attaches muscles to bone ( tendons ) and bone to bone
( ligaments )

Dense Connective Tissue Proper: Irregular
• Many non-parallel collagen fibers with a few elastic fibers

Connective Tissue: Cartilage
• 3 types
– Hyaline
– Fibrocartilage
– Elastic
• Made of chondrocytes found in a lacuna (“pit”) within the firm but flexible extracellular matrix comprised of a network of collagen fibers