Characteristics of epithelia include all of the following except
A polarity.
B extracellular matrix.
C regeneration.
D avascularity.
E attachment.
The correct answer and explanation is :
The correct answer is:
B) Extracellular matrix.
Explanation:
Epithelial tissue is one of the four primary tissue types in the body and serves as a protective covering for internal and external surfaces. It also plays roles in absorption, secretion, and sensation. The defining characteristics of epithelia include:
- Polarity (Option A) – Epithelial cells have an apical (top) surface that is exposed to the external environment or internal lumen and a basal (bottom) surface attached to the basement membrane. This structural polarity is essential for the specialized functions of epithelial cells, such as secretion and absorption.
- Regeneration (Option C) – Epithelial cells have a high capacity for regeneration. They frequently undergo mitosis to replace damaged or lost cells, which is crucial for tissues subjected to frequent wear and tear, such as the skin and the lining of the digestive tract.
- Avascularity (Option D) – Epithelial tissue lacks blood vessels. Instead, it relies on diffusion from underlying connective tissue for nutrients and oxygen. This characteristic ensures a controlled environment for selective absorption and secretion.
- Attachment (Option E) – Epithelial tissue is anchored to a basement membrane, a specialized structure that separates it from underlying connective tissue. This attachment provides structural support and stability.
Why Extracellular Matrix is Incorrect:
Unlike connective tissue, which has an abundant extracellular matrix (ECM) made of fibers (e.g., collagen, elastin) and ground substance, epithelial tissue is characterized by closely packed cells with minimal extracellular matrix. The basement membrane, which supports epithelial cells, is different from the extensive ECM found in connective tissues.
Thus, while epithelial cells interact with a basement membrane, they do not have the abundant extracellular matrix seen in connective tissues, making option B (extracellular matrix) the correct choice as the exception.