Epithelial Tissue Histology Explained for Beginners | Corporis

Summary

This video introduces epithelial tissue, one of the four major tissue types in the human body, and its role in covering surfaces and secreting substances. Patrick explains how epithelial cells are structured, categorized by shape and layering (simple, stratified, pseudostratified), and highlights their polarity and connection to the basement membrane. He also discusses glandular epithelium, differentiating between endocrine glands, which release hormones internally, and exocrine glands, which release substances like enzymes externally. The video includes histological examples from the respiratory system and digestive tract, offering practical insights into identifying epithelial cells under a microscope.

Takeaways

• 🧬 Epithelial tissue, one of the four tissue types in the human body, covers internal and external surfaces and performs essential functions like protection and secretion.
• 🫀 Epithelium forms the functional bulk of organs such as the liver, which is 80% epithelial cells, and plays a role in protecting and secreting substances.
• 🔬 Epithelial cells are polar with distinct apical (top) and basal (bottom) sides, separated by a basement membrane, and supported by the lamina propria, a connective tissue layer.
• 🌱 Epithelial cells come in three shapes: squamous (flat), cuboidal (cube-shaped), and columnar (tall). Their arrangement determines their classification.
• 📏 Epithelia can be classified by layers: simple (one layer), pseudostratified (appearing layered but not), and stratified (multiple layers).
• 🦠 Pseudostratified epithelium appears to have multiple layers due to cells of varying heights, but all cells are attached to the same basement membrane.
• 🧪 Stratified epithelium can become keratinized, as seen in skin where cells die, lose their nuclei, and form a tough, protective layer of keratin.
• 💧 Glandular epithelium forms glands that can be either endocrine (releasing hormones into the bloodstream) or exocrine (releasing substances outside the body or into body cavities).
• 🌙 Endocrine glands, such as the pineal gland and Leydig cells in the testes, secrete hormones into the bloodstream to regulate various body functions.
• 💧 Exocrine glands, such as salivary glands and goblet cells in the GI tract, secrete substances like enzymes and mucus outside the body or into cavities.

Q & A

What are the two main jobs of epithelial tissue in the human body?

The two main jobs of epithelial tissue are: 1) forming layers of cells that cover internal and external surfaces, such as the lining of blood vessels and skin, and 2) secreting different substances either within or outside the body.

What is meant by epithelial cells being 'polar'?

Epithelial cells are considered 'polar' because they have distinct top and bottom poles. The basal pole touches the basement membrane, while the apical pole faces the lumen, which is the inside of a tube like a blood vessel or bronchi.

How do epithelial cells receive oxygen and nutrients if they are avascular?

Since epithelial cells are avascular (without blood vessels), they receive oxygen and nutrients through diffusion from capillaries located in the underlying connective tissue called the lamina propria.

What are the three main shapes of epithelial cells, and where might you find each type?

The three main shapes of epithelial cells are: 1) Squamous, which are flat and found in the lining of blood vessels, 2) Cuboidal, which are cube-shaped and found in glands like the seminiferous tubules, and 3) Columnar, which are column-shaped and found in the gastrointestinal tract for secretion and absorption.

What is pseudostratified epithelium, and how is it different from stratified epithelium?

Pseudostratified epithelium is a type of simple columnar tissue that appears to have multiple layers but actually does not. All cells are attached to the same basement membrane but vary in height, making them look stacked. In contrast, stratified epithelium has two or more layers of cells.

What is keratinized epithelium, and where is it found?

Keratinized epithelium is a type of stratified epithelium where cells far from the lamina propria die, lose their nuclei, and get filled with keratin. It is found in the skin, where the top layer consists of dead cells filled with keratin for protection.

What is transitional epithelium, and in which organ is it commonly found?

Transitional epithelium consists of multiple layers of epithelial cells that transition from one shape to another. It is most commonly found in the bladder, an organ that needs to stretch as it fills with urine.

What is the difference between exocrine and endocrine glands?

Exocrine glands secrete substances outside the body or into cavities within the body, like the salivary glands or goblet cells in the GI tract. Endocrine glands secrete hormones into the bloodstream to communicate with other parts of the body, such as the thyroid or Leydig cells in the testes.

What is the function of cilia on the apical surface of some epithelial cells?

Cilia are hair-like structures on the apical surface of epithelial cells that move in a coordinated manner to propel substances along the surface. They are especially common in the respiratory system, where they help clear mucus and debris from the lungs.

How do epithelial cells communicate with neighboring cells?

Epithelial cells communicate with neighboring cells through their lateral faces using structures like gap junctions (allowing tiny particles like ions to pass), tight junctions (allowing specific proteins to pass), and desmosomes (helping anchor cells together).