Nokea
Which of the following statements is most correct? Immunoglobulin gene rearrangement:
- A. Occurs after transcription of an immunoglobulin gene
- B. Creates a complete V exon in the germline DNA
- C. Creates a complete V exon in the B cell DNA
- D. Both A and B are correct
Correct Answer: C
Rationale: The correct answer is C because immunoglobulin gene rearrangement creates a complete V exon in the B cell DNA. This process happens during B cell development, where segments of V, D, and J gene regions are rearranged to form a functional immunoglobulin gene. This rearrangement occurs before transcription, so option A is incorrect. Option B is incorrect because the V exon is not complete in the germline DNA, but rather created through rearrangement in the B cell DNA. Option D is incorrect as it combines two incorrect statements.
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Identify the disease in which the person's immune system no longer recognizes its own tissues or organs.
- A. Allergies
- B. Immunodeficiencies
- C. Autoimmune diseases
- D. Delayed hypersensitivity
Correct Answer: C
Rationale: The correct answer is C: Autoimmune diseases. This is because autoimmune diseases occur when the immune system mistakenly attacks the body's own tissues or organs. In this condition, the immune system fails to recognize self from non-self, leading to inflammation and tissue damage.
A: Allergies involve an exaggerated immune response to harmless substances, not attacking self-tissues.
B: Immunodeficiencies result in a weakened immune system, making it less effective at fighting infections, not attacking self-tissues.
D: Delayed hypersensitivity is a type of immune response that occurs hours to days after exposure to an allergen, not involving the immune system attacking self-tissues.
In summary, autoimmune diseases are characterized by the immune system targeting the body's own tissues or organs, distinguishing them from allergies, immunodeficiencies, and delayed hypersensitivity.
A patient with a pH of 7.29 has metabolic acidosis. Which value is useful in determining whether the cause of the acidosis is an acid gain or a bicarbonate loss?
- A. PaCO2
- B. Anion gap
- C. Serum Na+ level
- D. Bicarbonate level
Correct Answer: D
Rationale: Bicarbonate levels help differentiate between acid gain (low bicarbonate) and bicarbonate loss (normal or high anion gap).
T-cell receptors or antibodies react with antigens
- A. because both are made by lymphocytes
- B. because of complementary of molecular fit of both with antigen
- C. because both have light chain and heavy chain polypeptides
- D. cause histamine release
Correct Answer: B
Rationale: The correct answer is B because T-cell receptors and antibodies recognize antigens through complementary molecular fit. This interaction is based on the specific shape of the antigen-binding site on the receptor or antibody matching the shape of the antigen. This molecular complementarity allows for strong and specific binding between the antigen and the receptor/antibody. Choices A and C are incorrect as the presence of lymphocytes or specific polypeptide chains alone does not explain the mechanism of antigen recognition. Choice D is incorrect because histamine release is not directly related to the interaction between T-cell receptors or antibodies with antigens.
When a B cell undergoes class switching it allows the cell to:
- A. Differentiate into a memory cell
- B. Make two or more antibody classes at the same time
- C. Stop making one class of antibody and begin to make another
- D. Receive costimulatory signals from any T helper cell subset
Correct Answer: C
Rationale: Rationale:
1. Class switching in B cells involves changing the class of antibody produced.
2. This allows the B cell to stop making one class of antibody and start making another.
3. This process enhances the immune response by generating antibodies with different functions.
4. Differentiating into a memory cell (choice A) is a separate process from class switching.
5. Making two or more antibody classes simultaneously (choice B) is not a characteristic of class switching.
6. Costimulatory signals from T helper cells (choice D) are important for B cell activation but not directly related to class switching.
Epithelial cells at mucosal sites have barrier functions exerted through several mechanisms. These mechanisms do not include:
- A. Secretion of mucins
- B. Secretion of antimicrobial peptides
- C. Phagocytosis of microbes
- D. Tight junctions
Correct Answer: C
Rationale: The correct answer is C: Phagocytosis of microbes. Epithelial cells primarily act as a physical barrier to prevent the entry of microbes. Phagocytosis is a function of immune cells, not epithelial cells. A: Secretion of mucins helps trap pathogens. B: Secretion of antimicrobial peptides aids in defense. D: Tight junctions form a physical barrier between cells. Therefore, phagocytosis is not a direct mechanism exerted by epithelial cells at mucosal sites.