What is the function of the mucus in the small int

Question 1 of 5

What is the function of the mucus in the small intestine?

A. To protect the intestinal immune system from invaders B. To produce short-chain fatty acids C. To act as a diffusion barrier and contain antimicrobial proteins D. To transport nutrients to the epithelial cells

Correct Answer: C

Rationale: Mucus acts as a barrier with antimicrobial proteins ; protection is broader, SCFAs are microbiota-derived, not nutrient transport .

Question 2 of 5

Vaccination against many infectious diseases has provided enormous benefit in developed countries, leading to the virtual eradication of diseases such as polio, measles, smallpox, and others. However, efforts to create long-lasting vaccines against some viral infections, like Influenza and HIV, have not been successful to date because:

A. Viruses like HIV and Influenza undergo antigenic variation to evade previous immune responses B. Viruses like HIV and Influenza spread too rapidly in the population for a vaccine to be effective C. Viruses like HIV and Influenza have RNA, rather than DNA genomes, and are resistant to current vaccine strategies D. Viruses like HIV and Influenza infect via mucosal surfaces, a route that is not well protected by current vaccine strategies

Correct Answer: A

Rationale: Antigenic variation allows Influenza/HIV to evade immunity; speed , RNA , or mucosa are challenges but not primary.

Question 3 of 5

NK cells can be activated following recognition of a virus-infected cell, if that cell has down-regulated expression of MHC class I proteins on its surface. However, NK cells can also recognize infected cells or tumor cells, even if they still express MHC class I proteins. In this latter case, activating receptors on NK cells are recognizing:

A. Molecules on the target cell up-regulated by cellular or metabolic stress B. Cytokines secreted by the virus-infected or tumor cell C. MHC class I-like decoy molecules encoded by the virus D. Mutated self-proteins expressed by the tumor cell

Correct Answer: A

Rationale: Stress molecules (e.g., MICA) activate NK cells ; cytokines , decoys , or mutations are less common triggers.

Question 4 of 5

The B cell co-receptor, composed of CD19/CD21/CD81, is a receptor that binds to complement fragments such as C3dg. When an antigen bound by the BCR on a B cell has also been tagged with C3dg, the B cell co-receptor is stimulated together with the BCR. Signaling through the co-receptor:

A. Inhibits BCR signaling by leading to ITAM dephosphorylation B. Inhibits BCR signaling by leading to PIP_3 dephosphorylation C. Enhances BCR signaling by recruiting and activating PI 3-kinase D. Enhances BCR signaling by bringing the Src-kinase together with Ig-Î± and Ig-Î²

Correct Answer: C

Rationale: Co-receptor boosts BCR via PI 3-kinase ; not inhibition (A, B) or Src alone .

Question 5 of 5

Some complement proteins

A. induce antibody formation by phagocytic cells B. help trigger the inflammatory response C. are released by natural killer cells to attack cancer and virus-infected cells D. replace T cells in the cell-mediated response

Correct Answer: B

Rationale: Complement proteins enhance inflammation by attracting immune cells and promoting pathogen destruction, not inducing antibodies, NK cell activity, or replacing T cells.

What is the function of the mucus in the small intestine?

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