Exercises: The body's defences

The diagram shows the body's three lines of defense. Write the name of the lines labeled 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, stomach 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.

Explain what phagocytes are, which group of blood components they belong to, and why they are said to "eat" microbes.

Explain what role mucus and the mucous membranes of the airways play as a defensive barrier against microorganisms.

Explain what lymphocytes are and what two major tasks they carry out within the specific immune response.

State whether these statements are true or false and justify your answer: a) fever must always be brought down immediately with medication; b) antibodies are proteins made by the body itself; c) the first time a microbe enters, the specific response takes longer than the non-specific one.

Explain what inflammation is and what its four characteristic signs are in the affected area.

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 nonspecific 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. Explain why it can be considered a defense mechanism and not just a symptom, and explain in which situations it should indeed be treated.

A small scratch heals on its own, without treatment. Describe the chain of defenses that acts from the moment the skin is broken until the wound closes, indicating which line of defense intervenes at each moment.

People whose spleen has been removed are advised to get more vaccines and to watch out for any infection. Explain what relationship the spleen has with white blood cells and why its absence weakens the defenses without canceling them out.

During the flu, the glands in the neck swell. Explain what the lymph nodes are, what happens inside them during an infection, and why their swelling indicates that the defenses are at work.

Against the same bacterium, the phagocytes act first and the lymphocytes afterward. Compare both responses: order of arrival, way of recognizing the invader, and what remains in the body when each one finishes its work.

An extensive burn is a serious emergency even if there is no infection at first. Explain, relating it to the lines of defense, why burned skin puts life in danger and what risk appears in the following days.

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. Analyze this clinical case: a) Justify why this infection is described as "opportunistic", supporting your answer with the state of the patient's defenses 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.

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.

A person claims: "Getting the flu vaccine is useless; my aunt got vaccinated in November and in January she was in bed with the flu, feeling unwell and coughing." Refute their conclusion using your knowledge of the immune response: a) Justify why the flu virus can infect a vaccinated person if it has undergone minor mutations in its surface antigens and why this requires changing the vaccine every year. b) Predict and justify what the course of infection would have been like in their aunt had she not been vaccinated, explaining the role of the antibodies and lymphocytes generated by the previous vaccine.