Exercises: The body's defences

The diagram shows the body's three lines of defence. Write the name of the lines labelled A, B, and C, ordering them from outermost to innermost, and indicate which of them is specific to each infectious agent.

Name four body barriers that hinder the entry of microorganisms (skin, mucous membranes, tears, gastric acid...) and explain how each of them protects the body.

Explain what an antibody is, which cells produce it, and why each antibody only acts against a specific infectious agent.

When you get a splinter, the area becomes red, warm, and swollen. Explain what is happening, what this response is called, which blood cells travel to the site, and why this reaction, although annoying, is beneficial.

Compare the non-specific and specific immune responses: speed of action, cells involved, memory against the same agent, and an example of how each acts during the same infection.

Fever is a controlled increase in body temperature during many infections. Reason why it can be considered a defence mechanism and not just a symptom, and explain in which situations it should indeed be treated.

A patient undergoing chemotherapy is diagnosed with pneumonia caused by Pneumocystis jirovecii, a harmless fungus that coexists in the respiratory tract of healthy people without causing any harm. Analyse this clinical case: a) Justify why this infection is described as "opportunistic", supporting your answer with the state of the patient's defences following treatment. b) If a healthy family member lives in close contact with him, predict whether they will fall ill from this same fungus and explain your reasoning. c) Design two specific preventive measures that the hospital or family environment should implement to protect him from other common pathogens.

While walking through a park in spring, Marcos starts sneezing non-stop, his eyes water, and the skin on his neck turns red. A friend tells him: "You've caught a very aggressive bacterium; take an antibiotic quickly to cure yourself". a) Refute the two scientific errors in his friend's statement, explaining what is actually happening in Marcos's immune system in response to pollen. b) The doctor prescribes an "antihistamine" drug. Predict and explain what effect this medication will have on his blood vessels and mucous membranes based on the action that histamine exerts during an allergic reaction.

In a study, the amount of antibodies in a person's blood against a pathogenic bacterium is measured at two different times: after the first contact (day 1), antibodies take 10 days to appear and reach a maximum level of 15 units; after a second infection one year later (day 365), antibodies reach 250 units in just 2 days. a) Interpret these results, justifying the difference in speed and quantity based on the function of memory lymphocytes. b) Justify how vaccines take advantage of this same biological principle to protect us without having to suffer from the disease.