TISSUES

TISSUE TYPESFour major tissue types• Epithelial tissue• Connective tissue• Muscle tissue• Nervous tissue

EPITHELIAL TISSUE• Sheets of cells covering body surfaces or lining

body cavities• Form boundaries between different

environments– e.g., Epidermis of skin separates inside and outside

of body– e.g., Epithelium lining urinary bladder separates

underlying cells from urine

EPITHELIAL TISSUE• Many diverse functions– Protection– Absorption– Filtration– Excretion– Secretion– Sensory reception

EPITHELIAL TISSUE• Classification

According to shape:- Squamous cells:

Flattened like fish scales

- Cuboidal cells: Cube-shaped

- Columnar cells: Column-shaped

• Classification according to cell arrangement:- Simple : one layer- Stratified: more than one layer• Simple epithelial- Simple squamous: usually forms membranes- Simple cuboidal: commonly in glands and their

ducts- Simple columnar: lines the entire digestive tract- Pseudostratified columnar: mainly functions in

absorption and secretion

EPITHELIAL TISSUE

• Stratified epithelial- Stratified squamous: most common stratified epithelialIs found in sites that receive a good deal of abuse or friction such as the esophagus, mouth and outer skin- Stratified Cuboidal and Columnar:Found mainly in the ducts of large glands

EPITHELIAL TISSUE

CONNECTIVE TISSUE• Found everywhere in the body–Most widely distributed primary tissue

• Four main classes– Loose connective tissue (Provides a matrix of

support and cushing) eg. Adipose tissue – Cartilage– Bone tissue– Blood

CONNECTIVE TISSUE• Major functions– Binding and support– Protection– Insulation– Transportation

• Which of these functions are accomplished by bone and cartilage? Fat? Blood?

NERVOUS TISSUE• Main component of the nervous system– Brain, spinal cord, and nerves– Regulates and controls body functions

• Two main cell types– Neurons

• Generate and conduct nerve impulses

– Supporting cells• Non-conducting cells

that support, insulate, and protect neurons

MUSCLE TISSUE• Highly cellular• Well vascularized• Responsible for most types of body movement• Possess myofilaments– Actin and myosin

• Three types– Skeletal muscle– Cardiac muscle– Smooth muscle

TISSUE REPAIR• Injured cells release growth factors– Stimulate cells to divide and migrate

• Two major tissue repair means:– Regeneration• Replacement of destroyed tissue with same type of tissue

– Fibrosis• Replacement with fibrous connective tissue (scar tissue)

• Type of repair dependent upon– Type of tissue damaged– Severity of injury

TISSUE REPAIR• The regenerative capacity of different tissues

varies widely– Some tissues regenerate extremely well• e.g., Epithelial, bone, blood-forming tissue

– Some tissues have a moderate regenerative capacity• e.g., Smooth muscle, dense regular connective tissue

– Some tissues have a weak regenerative capacity• e.g., Skeletal muscle, cartilage

– Some tissues have a virtually no functional regenerative capacity• e.g., Cardiac muscle, nervous tissue

TISSUE REPAIR• In non-regenerative tissue and severe wounds,

damaged tissue is replaced by fibrosis

• Resulting scar tissue is strong, but lacks flexibility, elasticity, and function of normal tissue