Question

Assertion: Epithelial tissues protect the under lying and over lying tissues. Reason: Materials are exchanged at the surfaces across the epithelial tissues.

Short answer

Both the assertion and reason are correct, but the reason does not correctly explain the assertion.

Step-by-step solution

Verify the assertion

Epithelial tissue is indeed a type of tissue that covers the external surface of the body and lines hollow organs, body cavities, and ducts. It is also forms glands. Thus, its primary function includes protection of the underlying tissues. Hence, the assertion is correct.

Verify the reason

Epithelial tissues serve as barriers and gateways for substances to be exchanged between the body and its external environment, or between different sections of the body. So the reason, stating that materials are exchanged at the surfaces across the epithelial tissues, is correct.

Connect the reason with the assertion

Even though both the assertion and reason are true, the reason does not accurately explain why epithelial tissues protect the underlying and overlying tissues. They do facilitate exchange of materials, but their protective role is primarily due to their barrier function, not their exchange function.

Key concepts

Tissue Protection

Epithelial tissues are essential to the body’s first line of defense, acting as protective barriers that shield the underlying tissues from physical damage, chemical exposure, and bacterial invasion. These tissues are tightly packed cells with minimal intercellular spaces, which not only helps in reducing the risk of injuries but also prevents the entry of pathogens.

The protective role of epithelial tissue also extends to absorption and secretion, where it helps in selectively allowing substances into the body, maintaining homeostasis. This selective gatekeeping is crucial for protecting internal systems from toxins and unregulated material intake. Moreover, epithelial cells are often replaced throughout life due to their regenerative ability, meaning that they constantly renew the protective barrier.

Material Exchange in Tissues

One of the vital functions of epithelial tissues pertains to their role in the exchange of materials. These tissues are strategically located at sites of substance transfer, such as the lining of the intestines and the alveoli in the lungs, where nutrient uptake and gas exchange occur, respectively.

The exchange process is facilitated by the specialized structure of the epithelial cells. For instance, certain epithelial cells have microvilli—tiny, fingerlike projections that increase the surface area available for absorption or transport of materials. This morphological adaptation enhances the efficiency of the epithelial tissue in nutrient absorption and waste elimination, providing a pathway for vital substances to enter and exit the body. It's important to note, however, that while facilitating exchange, epithelial tissues still maintain a selective barrier to ensure that only the necessary materials are allowed through.

Epithelial Barrier Function

The barrier function of epithelial tissues is a key component of their role in the body. Junctions between epithelial cells, such as tight junctions, adherens junctions, and desmosomes, play a vital role in maintaining the integrity of the barrier. Tight junctions seal the spaces between cells, ensuring that substances must pass through the cells rather than between them—this selectivity is crucial in controlling the passage of molecules, thus maintaining the internal environment.

In addition, the epithelium can secrete mucus, which serves as an additional physical barrier to trap pathogens and particulate matter. The mucus also contains antimicrobial peptides and enzymes that help destroy potential invaders before they can cause harm. Thus, while epithelial tissues actively engage in the exchange of materials, their fundamental configuration is designed to preserve an optimal internal environment by asserting a strong barrier function.