IMMUNOLOGY

Detailed explanation-1: -Physical barriers include skin, mucus, digestive tract membranes, and traps of respiratory and urogenital which traps entering microorganisms. >

Detailed explanation-2: -The human body has three primary lines of defense to fight against foreign invaders, including viruses, bacteria, and fungi. The immune system’s three lines of defense include physical and chemical barriers, non-specific innate responses, and specific adaptive responses.

Detailed explanation-3: -Innate immunity can be viewed as comprising four types of defensive barriers: anatomic (skin and mucous membrane), physiologic (temperature, low pH and chemical mediators), endocytic and phagocytic, and inflammatory. Table 1 summarizes the non-specific host-defense mechanisms for each of these barriers.

Detailed explanation-4: -The main components of the immune system are the thymus, spleen, Lymph Nodes, bone marrow and white blood cells. A brain is not involved in elicitation of immune response but regulates the function of the whole body. Hence option A is correct.