Question

Which one of the following acts as a physiological barrier preventing the entry of microorganisms in the human body?
A. Skin
B. Epithelium of urogenital tract
C. Tears
D. Monocytes

Answer 1

First line of defense countering the pathogens is provided through the physiological barriers. Mechanisms underlying the dynamic mucociliary clearance, and skin forms these types of barriers.

Complete answer:
-The physiological barriers include the processes that occur in the body against the pathogenic response. They assist in removing pathogens from the body. The type of physiological barrier differs as per the situation and location of the pathogenic action. These barriers form a part of an innate immune system thus preventing the body from the entry of microorganisms.
-Tears present in eyes are the physiological barriers that prevent the entry of microbes inside the human body. Lysozyme enzymes are present in the tears as well as in the saliva. Peptidoglycan is the component of the cell wall present in the microorganisms. Lysozymes work by inhibiting the peptidoglycan synthesis in the cell wall.
-Skin and epithelium of the urogenital tract provides physical barriers against the entry of pathogens in the immune system. Moreover, monocytes are the type of white blood cells which give rise to the macrophages. They provide non-specific resistance to the microbes. Thus they act as a second line of defense.

Hence, the correct answer is option (D).

Note: Tears present in eyes, saliva present in mouth and HCL present in stomach acts as a physiological barrier which forms part of an innate immune system. They prevent the entry of microbes in the body.