Biological sciences6

BIOLOGICAL SCIENCES

By:

MARIA KRISIA FAE DELOS REYES DE ASIS, BSN-RN

TISSUE LEVEL OF ORGANIZATION

COVERING AND LINING EPITHELIUM- classified according to two characteristics:

1. Arrangement of cells in layers- Depends on the function

a. SIMPLE EPITHELIUM- a single layer of cells

that functions in DIFFUSION, OSMOSIS, FILTRATION, SECRETION, and ABSORPTION

TISSUE LEVEL OF ORGANIZATION

b. PSEUDOSTRATIFIED EPITHELIUM- appears to have multiple

layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface

- cells that do not extend to the apical surface may contain cilia (TRACHEA & LUNGS); others (GOBLET CELLS) secrete mucus

TISSUE LEVEL OF ORGANIZATION

- they are actually simple epithelium because all cells are attached to the basement membrane. However, they appear like stratified epithelium, thus the term pseudostratified; pseudo meaning “false”

TISSUE LEVEL OF ORGANIZATION

c. STRATIFIED EPITHELIUM- consists of two or more

layers of cells that protect underlying tissues and locations where there is considerable wear and tear

HARD PALATE

TISSUE LEVEL OF ORGANIZATION

2. Cell shapesa. SQUAMOUS CELLS

- arranged like floor tiles and are thin, which allows the rapid passage of substancesb. CUBOIDAL CELLS

- as tall as they are wide and are shaped like cubes or hexagons. May have microvilli at apical surface (secretion/absorption)

TISSUE LEVEL OF ORGANIZATION

c. COLUMNAR CELLS- consists of two or more

layers of cells that protect underlying tissues and locations where there is considerable wear and teard. TRANSITIONAL CELLS

- change shape from flat to cuboidal. Ex. Uterus, urinary bladder

URINARY BLADDER

TISSUE LEVEL OF ORGANIZATION

- Combining the two characteristics, the types of covering and lining epithelia are as follows:

I. SIMPLE EPITHELIUMA. SIMPLE SQUAMOUS EPITHELIUMB. SIMPLE CUBOIDAL EPITHELIUMC. SIMPLE COLUMNAR EPITHELIUM

(CILIATED AND NON-CILIATED)D. PSEUDOSTRATIFIED COLUMNAR

EPITHELIUM (CILIATED AND NON-CILIATED)

TISSUE LEVEL OF ORGANIZATION

II. STRATIFIED EPITHELIUMA. STRATIFIED SQUAMOUS EPITHELIUM

(KERATINIZED AND NON-KERATINIZED)

B. STRATIFIED CUBOIDAL EPITHELIUM*C. STRATIFIED COLUMNAR EPITHELIUM* D. TRANSITIONAL EPITHELIUM

* - based on the shape of the cells at the APICAL surface

GASTROINTESTINAL TRACT

Transitional epithelium