Epithelial Tissue - What Is Epithelial Tissue - Functions Of Epithelial Tissue - Epithelial Cells

Summary

Epithelial tissue, one of the body's four primary tissue types, lines the respiratory and digestive tracts, skin, and various glands. It's characterized by tightly packed cells, an apical surface exposed to internal or external environments, and a basal surface attached to a basement membrane. Epithelium is avascular, receiving nutrients from its surfaces, and is innervated, with cells capable of self-reproduction. It serves protective, sensory, secretory, and absorptive functions. Classified by shape into squamous, cuboidal, columnar, and pseudostratified, and by layers into simple, stratified, and pseudostratified. Special types include transitional epithelium in the urinary tract and keratinized stratified squamous epithelium in the skin's outer layer.

Takeaways

• 🔬 Epithelial tissue is one of the four major types of tissue in the body.
• 📍 It is found throughout the body, including the respiratory tract, digestive tract, skin, oral cavity, and glands.
• 💧 Epithelial tissues are composed of tightly packed cells with minimal extracellular space and lack blood vessels.
• 🌐 They have an apical surface exposed to internal or external environments and a basal surface attached to a basement membrane.
• 🌱 Epithelial cells can reproduce themselves and are innervated, providing a rich supply of nerves.
• 🛡️ Epithelial tissue serves protective functions, such as the skin shielding from harmful substances.
• 👂 It plays a role in sensory functions in the skin, nose, eyes, and ears.
• 💧 Epithelial cells are involved in secretion, such as hormones, sweat, digestive juices, and mucus.
• 🌀 It is important for absorption, like nutrients in the gut, and gas exchange in the lungs.
• 🔄 Epithelial tissue can be classified by cell shape (squamous, cuboidal, columnar, pseudostratified) or by the number of cell layers (simple, stratified, pseudostratified).
• 🔬 Specialized cells include goblet cells that secrete mucus and ciliated cells that move mucus away from the lungs.
• 🌿 Transitional epithelium can change from a relaxed to a stretched state and is found in the urinary tract.
• 🧪 Keratinized stratified squamous epithelium is found in the outer layer of the skin, with dead cells filled with keratin at the top.

Q & A

What are the four major types of tissue in the body?

The four major types of tissue in the body are epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

Where can epithelial tissue be found in the body?

Epithelial tissue can be found lining many structures of the respiratory tract, the digestive tract, the epidermis of the skin, the oral cavity, and many of the glands in the body.

What are the common characteristics of epithelial tissues?

Epithelial tissues are comprised of tightly packed cells with little extracellular space, have an apical or free surface exposed to internal or external environments, a basal surface attached to a basement membrane, lack blood vessels (are avascular), and are innervated with a rich supply of nerves.

How do epithelial tissues receive nutrients since they are avascular?

Epithelial tissues receive nutrients from their apical free surface or by diffusion across their basal surface from the underlying connective tissue.

What are the important functions of epithelial tissue?

Epithelial tissues provide protection, sensory functions, secretion of substances like hormones, sweat, digestive juices, and mucus, and are involved in absorption of nutrients and gas exchange.

How can epithelial cells be classified based on their shape?

Epithelial cells can be classified as squamous (flat), cuboidal (similar to a cube), columnar (taller than wide), pseudostratified (varying heights, all connect to the basement membrane), and sometimes containing goblet cells or having cilia or microvilli.

What is the difference between simple, stratified, and pseudostratified epithelium?

Simple epithelium is one cell layer thick with all cells in direct contact with a basement membrane. Stratified epithelium has two or more layers with only the basal layer in contact with the basement membrane. Pseudostratified epithelium contains cells of varying heights, not all reaching the apical surface, but all connecting to the basement membrane.

What are transitional epithelium and where are they found?

Transitional epithelium can be in a relaxed or stretched state, with rounded cells at the top in a relaxed state and flattened cells in a stretched state. These are found in the urinary tract.

What is keratinized stratified squamous epithelium and where is it found?

Keratinized stratified squamous epithelium is composed of dead cells filled with keratin in the top layers, which makes them strong but lacking organelles and nuclei. This type of epithelium is found in the epidermis or outer layer of the skin.

Why is the ability of epithelial cells to reproduce themselves important?

The ability of epithelial cells to reproduce themselves is important because they undergo severe wear and tear, especially in areas like the skin, respiratory tract, and digestive tracts.

What is the role of microvilli in the intestine?

Microvilli are tiny finger-like projections that increase the surface area for digesting and absorbing nutrients in the intestine.