Every day you breathe in, touch, and eat microorganisms on the bus, at the open-air market, or at recess, and you almost never get sick. Your body doesn't let just anything in: it has several lines of defense, one behind the other, and disease appears only when all of them fail.
Three lines of defense
Ximena scrapes her knee playing soccer at recess. The broken skin bleeds, the area turns red, and within a few days it heals without the infection spreading to the rest of the body. How does the body organize its defenses to stop invaders depending on how far they get?
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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…
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.
A continuous, tough layer that blocks physical entry
Mucous membranes with mucus and cilia
The mucus traps microorganisms and the cilia sweep them outward
Tears
They wash away particles and microbes from the eye
Stomach acid
Gastric juice is so acidic that it destroys many microorganisms in food
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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.
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.
Whether you get a splinter or a mosquito bites you at the market, your skin reacts in almost the same way: it turns red, feels warm, and hurts. Why does the body use the same response against such different aggressors?
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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…
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.
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…
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.
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…
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.
When defense goes astray: opportunistic infections and allergies
A patient undergoing chemotherapy has weakened defenses, and Marcos sneezes in a park full of pollen without having any infection. What happens when the immune system fails or overreacts?
In an allergy, the body treats pollen as if it were an invader. Some cells release histamine, which widens the blood vessels and makes the mucous membranes produce mucus and swell: sneezing, watery eyes, red skin. It is the same response as inflammation, but with no infection at all.
Antihistamines block the action of histamine, so they reduce the widening of the vessels and the swelling of the mucous membranes. Antibiotics work only against bacteria: they don't act against viruses, fungi, or allergies.
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A patient undergoing chemotherapy is diagnosed with pneumonia caused by Pneumocystis jirovecii*, a harmless fungus that coexists in the respiratory tract of healthy…
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…
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.
If you had measles as a child, you can be around sick people your whole life without getting a single spot. How does the body "remember" a virus for decades?
Back to the beginning: the body "remembers" the measles virus because it keeps memory lymphocytes that respond within a few days and with lots of antibodies.
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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…
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.