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…)• Pseudostratified

– 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

• Fibroblasts – connective tissue proper

• Chondroblasts – cartilage

• Osteoblasts – bone

• Hemocytoblast– 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