Histology: Epithelial Tissue Types and Structure

• Histology is the study of the microscopic structure of tissues and organs, which is important for understanding tissue function

The four basic types of tissues that make up the human body:

• Epithelial tissue covers surfaces and lines organs
• Connective tissue supports, binds, and fills spaces
• Muscle tissue moves body parts
• Nervous tissue sends and receives signals

Epithelial Tissues

• Cover the outside of the body and lines organs inside.

Types of Epithelial Tissue, By Cell Shape:

• Squamous: flat cells
• Cuboidal: cube-shaped cells
• Columnar: tall, column-like cells

By Number of Layers:

• Simple: one layer of cells
• Stratified: multiple layers
• Pseudostratified: looks like many layers, but all cells touch the base and some don’t reach the surface

Special Type:

• Transitional epithelium: found in areas like the bladder, stretches and changes shape

Simple Epithelium (One Layer)

• Found in areas where absorption and filtration happen a lot

Simple Squamous Epithelium (Flat Cells):

• Function: Exchange, transport, absorption, filtration
• Location: lining of heart, blood vessels, and lymph vessels, lung alveoli, kidney, and lining of body cavities like pleura and pericardium

Simple Cuboidal Epithelium (Cube-Shaped Cells):

• Function: Secretion and absorption
• Location: Most glands, and covers the ovary

Simple Columnar Epithelium (Tall Cells):

• Function: Absorption and secretion
• Location: Lining of stomach, intestines, and gallbladder
• Features: May contain goblet cells (mucus-secreting) and have cilia or microvilli

Pseudostratified Columnar Epithelium:

• Function: Protection, secretion, and movement of mucus by cilia
• Location: Lining of trachea, bronchi, and nasal cavity
• Features: Appears layered but all cells touch the basement membrane and may have goblet cells and cilia

Stratified Epithelium (Multiple Layers)

• Stratified Squamous Keratinized (Dry) is located in the Epidermis of skin, and its function is Protection, prevents water loss
• Stratified Squamous Nonkeratinized (Moist) is located in the Mouth, esophagus, larynx, vagina, and anal canal, and its function is Protection, keeps surface moist
• Stratified Cuboidal Epithelium is located in Ducts of sweat glands, and developing ovarian follicles, and its function is Protection and secretion
• Stratified Columnar Epithelium is located in the Conjunctiva, and ducts of some glands, and its function is Protection
• Transitional Epithelium has dome-shaped cells when relaxed and flattened when stretched, Located in the Bladder, ureters, and renal calyces, and its function is Protection and ability to stretch (distension)

Glandular Epithelium

• A gland is one or more cells that make and release a product (called a secretion)

Two main types of glands:

• Exocrine Glands have ducts and Release secretions onto surfaces or into ducts
• Examples are sweat glands, pancreas, salivary glands, and goblet cells
• Endocrine Glands are Ductless and Release secretions into blood or fluid around cells
• Examples are thyroid, pituitary, and adrenal glands