Histology“study of tissues”

Types of Tissue

1. Epithelial

2. Connective

3. Muscle

4. Nervous

Functions of Epithelial Tissue• Covers & protects• Lines cavities• Secretion & Glands

– Mucus– Hormones– Sweat

• Excretion– Kidneys

• Absorption– Lining of gut – Lining of respiratory tract

General Characteristics of Epithelial Tissue

• Limited intercellular space or matrix• Continuous sheets packed tightly together• Avascular, contains no blood vessels

– Nutrients move through diffusion

• Basement membrane adheres it to connective tissue– Integrins bind cytoskelton of cells to basement

membrane

• Because they go through so much wear and tear they have a high mitotic rate

Classification of Epithelial Tissues

Simple Squamous Epithelial

• One layer, flat scale like cells

• Substances can diffuse/filter easily– Examples

• Alveoli• Blood vessels• Pleural membranes

Simple Squamous Epithelial

Simple Cuboidal Epithelium

• One layer of cuboidal cells resting on basement membrane– Examples

• Glands and ducts• Ducts & tubules of

kidneys

Tubules in kidneys

Simple Columnar Epithelium

• Adapted for secretion• Examples

– Lines stomach– Uterus & ovaries– Eyes

• Modifications– Goblet cells

• Have vesicles filled with mucus – Microvilli & Cilia

• Plasma membrane extends out

Pseudostratified Columnar Epithelium

• All the cells touch the basement membrane

• Irregular placement of nuclei

• Not all reach the top layer

• Lots of goblet cells and cilia

• Examples– Lining air passages– Segment of male

urethra

Pseudostratified Columnar Epithelium

Stratified Squamous (Keratinized) Epithelium

• Multiple layers• Flatted cells on

surface• Dead keratinized

cells at surface– Examples

• Skin, kertin provides protection

Stratified Squamous (Keratinized) Epithelium

Stratified Squamous (Non-keratinized) Epithelium

• Look for nuclei at superior border• Flattened cells at surface• Many layers• Surface is moist

– Examples• Vagina• Mouth• esophagus

Stratified Squamous (Non-keratinized) Epithelium

Stratified Cuboidal Epithelium

• Two or more rows of cuboidal cells

• Arranged randomly– Examples

• Sweat gland ducts• Pharynx• epiglottis

Stratified Cuboidal Epithelium

Stratified Columnar Epithelium

• Only most superficial cells are columnar in appearance

• Protective epithelium– Examples

• Male urethra• Mucosa layer near

anus

Stratified Columnar Epithelium

Stratified Transitional Epithelium

• Found in areas subject to stress and tension

• Prevent tearing• When stretched cell

change shape from cuboidal to squamous– Examples

• Bladder

Glandular Epithelium• Glandular secretions rely on

highly regulated cellular activity that requires using stored energy

• Mulitcellular or unicellular(goblet cell)

• Exocrine Glands -release secretion into ducts– Salivary glands– Sebaceous glands– Sweat glands– lacrymal glands

• Endocrine Glands- ductless glands that release secretions(hormones) directly into blood– Pituitary gland– Thyroid gland– adrenal

Thyroid gland Islet of Langerhans

Exocrine Glands• Apocrine glands

– Secretion collect in tip(apex) of gland– Secretions are released when distended end

is pinched off– Cell loses cytoplasm and is damaged– Recovery is quick and cell continues to

release secretions• Mammary glands• Sweat glands

• Holocrine glands– Collect secretions inside the cell– Rupture completely to release secretion– Cell is destroyed

• Sebaceous glands

• Merocrine glands– Secretion is released directly through plasma

membrane– No loss of cytoplasm or damage to cells– Most common gland

• Salivary glands• Sweat glands not associated with hair

Exocrine Glands

Apocrine gland

Holocrine gland

Merocrine gland