Histology

4 Basic Tissue Types

4 Basic Tissue Types

Epithelial, Connective, Muscle, Nervous

Epithelium

-Its job is to cover

-Skin, Serous Membranes

Epithelia

Layers of cells covering internal and external surfaces

Glands

Composed of secreting cells derived from epithelia

Shape of Epithelial Cells

-Irregular, fitting closely together like puzzle pieces

Apical (Free) Surface

Exposed to the environment or internal chamber/passageway

Cilia

Hair-like projection from Apical surfaces that move objects along the surface

Microvilli

Finger-like projection from Apical surfaces that increase surface area and absorption

Basement Membranes

Protein fibers that connect epithelium to underlying connective tissue

Avascular

Epithelial Cells have no blood vessels. They obtain nutrients from deeper tissues through diffusion

Continual Regeneration of Epithelial Cells

Stem Cells or Germinative Cells found near the Basement Membranes are constantly creating new cells because Epithelial Cells are always being lost from the surface.

Where Epithelial Cells are Found

-Inner surfaces of passageways through organs

-Covering outer surfaces of organs (visceral)

-Making up glandular tissue

Functions of Epithelial Cells

-Physical Protection

-Controls Permeability (Things moving from 1 tissue to another)

-Provides Sensation

-Produce Secretions

Gland Cells

Cells that produce secretions

Glandular Epithelium

A surface on which most or all cells produce secretions

Exocrines

Secretions discharged onto the Apical surface of the epithelium

Endocrines

Secretions released into surrounding tissue (Hormones)

How Epithelial Tissues are Classified

-Amount of Layers

-Cell Shapes

Simple Epithelial Tissue

Only 1 layer of cells often in protected areas of the body

Stratified Epithelial Tissue

Several layers of cells in areas of heavy stress

Squamous

Thin and flat cell shape with flat nucleus

Cuboidal

Cube shaped with more rounded nucleus

Columnar

Rectangular shaped with oval upright nucleus (typically toward the bottom of the cell)

What to look for to determine cell type

Nucleus

Location of simple squamous epithelium

-Lines ventral body cavities

-Lines heart + blood vessels

-Lines Alveoli of lungs and kidney tubules

Function of simple squamous epithelium

-Reduce Friction (Very Smooth)

-Control vessel permeability

-Absorb and Secrete

Location of simple cuboidal epithelium

-Glands

-Ducts

-Portions of Kidney Tubules

-Thyroid Gland

Function of simple cuboidal epithelium

-Limited protection

-Absorb and Secrete

Location of simple columnar epithelium

-Stomach Lining

-Intestine

-Gallbladder

-Uterine tubes

-Upper respiratory tract

Function of simple columnar epithelium

-Protection

-Absorb and Secrete

Location of stratified squamous epithelium

-Skin surface

-mouth lining, throat, esophagus

-rectum, anus, vagina

Function of stratified squamous epithelium

-Protection from abraison, pathogens, and chemicals

Location of stratified cuboidal epithelium

-Ducts of large glands

-Rare

Function of stratified cuboidal epithelium

-Used in secretion

-2 layers

Location of stratified columnar epithelium

-Pharynx

-Epiglottis

-Anus

-Urethra

-Rare

Function of stratified columnar epithelium

-Protection

-Secretion

Location of pseudostratified ciliated columnar epithelium

-Nasal cavity

-trachea

-bronchi

-male reproductive tract

Function of pseudostratified ciliated columnar epithelium

-Trap and move pollutants

-Filter out debris

-Secretion

-Protection

Merocrine Glands

Secrete using exocytosis

Apocrine Glands

lose part of the cell to discharge their secretion

Holocrine Glands

the entire cell disintegrates to release its secretion

Location of transitional epithelium

-Bladder

-Ureters

Function of transitional epithelium

Permits expansion and recoil after stretching