Histology: the study of tissues

Tissues A group of interrelated cells that function together and perform specialized activities 4 Types of Tissues in the body Epithelial Connective Muscle Nervous

Epithelial Tissue AKA: Epithelium (epi- upon or above) Functions: (P) Protection (S) Secretions (A) Absorption (F) Filtration

Epithelial Tissue Characteristics Closely packed flat cells Avascular (a- without vasc- blood supply), needs are met through diffusion from neighboring cells

Epithelial Tissue Location Coverings or linings of organs Always has a surface exposed to open space or the outside of the body (apical surface) Underside always attached to connective tissue by a basement membrane Mitosis is frequent to replace damaged cells since they are “exposed”

Epithelial Tissue Epithelial tissue is classified two ways By the cell shape By the number of cell layers Some may contain goblet cells….these cells are filled with and release mucus. (This type lines the digestive tract and are sometimes referred to as mucosae)

Epithelial Cell Shapes Squamous- (squashed) flat, nucleus near surface Cuboidal- (cube) thicker, square shaped with central nucleus

Epithelial Cell Shapes Columnar- (column) elongated cells, some have microvilli (fingerlike projections that increase surface area), some have cilia (tiny hair-like structures that help move materials along)

Epithelial Cell Shapes Transitional- appearance ranges from flat to columnar, cells can stretch and compress (different shapes in the same layer)

Arrangement of Layers Simple- single layer, thinness allows substances to permeate easily Stratified- (strat-layers) multiple layers, protection for areas that endure large amounts of stress, cells grow from the bottom layer up Pseudostratified- (psuedo-false) one layer, but appears to be multilayered. All cells are attached to the basement membrane, but not all the cells reach the surface

Types of Epithelium Simple Squamous- single, flat cell layer, nucleus in middle of the cell

Types of Epithelium Simple Cuboidal- Single layer of cubed shaped cells, nucleus in the middle

Types continued Simple Columnar- single layer of rectangular cells, nucleus at base, Non-ciliated- contains goblet cells (mucous) and microvilli (increase surface area) in some areas

Simple Columnar- Ciliated- single layer of rectangular cells, nucleus at the base

Types- continued Stratified Squamous- Several layers, larger at the bottom and flattened out at the top, bottom replaces top as the superficial layers shed, can produce keratin

Types- Continued Stratified Cuboidal- two or more layers, cubed shaped cell

FYI Stratified Columnar- several layers on columnar in superficial layers Found in few places of the body (epiglottis, urethra) *you will not be responsible for the identification of this type

Types Pseudostratified Columnar- single layer, nucleus at different levels, all cells attached to basement membrane

Types Transitional- range from squamous to cuboidal appearance

Practice Looks for at Home Review Epithelia Page 1. Simple Squamous 2. Simple Squamous 3. Simple Cuboidal 4. Simple Cuboidal 5. Simple Columnar 6. Simple Columnar 7. Pseudostratified Columnnar 8. Pseudostratified Columnnar (Ciliated) 9. Transitional 10. Transitional 11. Stratified Squamous 12. Stratified Squamous 13. Stratified Squamous 14. Stratified Squamous (Keratinized) 15. Stratified Squamous (Keratinized 16. Stratified (High) Cuboidal 17. Stratified Cuboidal