Overlapping endothelial cells in lymphatic capillaries act as one-way flaps that let interstitial fluid enter.
Correct Answer
True
True. The loosely overlapping endothelial cells of lymphatic capillaries open when interstitial fluid pressure rises and close to keep lymph from leaking back out. This makes lymphatic capillaries highly permeable to fluid and even large particles.
Category: Lymphatic Anatomy
Question 2
Lymph enters a lymph node through efferent vessels and leaves through afferent vessels.
Correct Answer
False
False. Lymph enters a node through several afferent vessels and leaves through efferent vessels at the hilum. Along the way it passes through sinuses where macrophages and lymphocytes screen it for antigens.
Category: Lymphatic Anatomy
Question 3
The red bone marrow and the thymus are classified as primary lymphoid organs.
Correct Answer
True
True. Primary lymphoid organs are where lymphocytes develop and mature: B cells in the bone marrow and T cells in the thymus. Lymph nodes, the spleen and lymphoid nodules are secondary organs where mature lymphocytes respond to antigens.
Category: Lymphatic Anatomy
Question 4
Peyer's patches are clusters of lymphoid follicles in the wall of the stomach.
Correct Answer
False
False. Peyer's patches are mucosa-associated lymphoid tissue in the wall of the small intestine, mainly the ileum. Their M cells sample material from the intestinal lumen and pass it to immune cells beneath.
Category: Lymphatic Anatomy
Question 5
Lysozyme in saliva and tears kills bacteria by digesting their cell walls.
Correct Answer
True
True. Lysozyme is an enzyme in body secretions that breaks down the peptidoglycan of bacterial cell walls. It is one of the chemical barrier defenses of innate immunity.
Category: Innate Defenses
Question 6
Natural killer cells belong to the adaptive immune system.
Correct Answer
False
False. Natural killer cells are lymphocytes of the innate immune system. They kill virus-infected and some cancer cells without prior exposure or antigen-specific receptors.
Category: Innate Defenses
Question 7
The redness and heat of an inflamed area result from dilation of local blood vessels.
Correct Answer
True
True. Mediators such as histamine and prostaglandins dilate local vessels, bringing more warm blood to the area. Increased capillary permeability adds swelling, and pain completes the classic signs.
Category: Innate Defenses
Question 8
Complement proteins C5 through C9 assemble into a membrane attack complex that punches pores in bacterial membranes.
Correct Answer
True
True. The membrane attack complex inserts into the pathogen's membrane and disrupts its osmotic balance, causing lysis. It is especially effective against many bacteria.
Category: Innate Defenses
Question 9
The secondary immune response is slower and weaker than the primary immune response.
Correct Answer
False
False. The secondary response is faster and stronger because memory cells formed during the first exposure respond quickly. It often clears the pathogen before symptoms appear.
Category: Adaptive Immunity
Question 10
Each T cell produces receptors of only one antigen specificity.
Correct Answer
True
True. All the T cell receptors on a given T cell are identical and bind the same epitope. The enormous diversity of the T cell population comes from many different clones, each with its own receptor.
Category: Adaptive Immunity
Question 11
MHC class II molecules are found on nearly all nucleated cells of the body.
Correct Answer
False
False. MHC class II molecules are found mainly on antigen-presenting immune cells such as macrophages, dendritic cells and B cells. MHC class I is the type found on nearly all nucleated cells.
Category: Adaptive Immunity
Question 12
Dendritic cells, macrophages and B cells function as professional antigen-presenting cells.
Correct Answer
True
True. These three cell types take up antigen, process it and display it on MHC class II molecules to helper T cells. Dendritic cells are especially important for activating naive T cells.
Category: Adaptive Immunity
Question 13
A typical antibody molecule is made of two identical heavy chains and two identical light chains.
Correct Answer
True
True. The four chains form a Y-shaped molecule with two identical antigen-binding sites at the tips of the arms. The stem, formed only by heavy chains, binds Fc receptors on immune cells.
Category: Antibodies
Question 14
During class switching, a B cell changes the antigen specificity of the antibody it secretes.
Correct Answer
False
False. Class switching changes the antibody class, for example from IgM to IgG, while the antigen-binding sites and specificity stay the same. Only the heavy chain constant region is changed.
Category: Antibodies
Question 15
Vaccination produces artificial passive immunity.
Correct Answer
False
False. A vaccine stimulates the person's own immune system to make antibodies and memory cells, which is artificial active immunity. Artificial passive immunity comes from injecting preformed antibodies, which protect only temporarily.
Category: Antibodies
Question 16
Antibodies can enter infected host cells to destroy viruses replicating in the cytoplasm.
Correct Answer
False
False. Antibodies cannot cross the plasma membrane, so they act on viruses before they enter cells. Once a virus is inside a cell, cytotoxic T cells and natural killer cells must destroy the infected cell.
Category: Pathogen Responses
Question 17
Virus-infected cells that reduce the MHC class I molecules on their surface become targets for natural killer cells.
Correct Answer
True
True. Many viruses lower MHC class I expression to hide from cytotoxic T cells. Natural killer cells detect this missing MHC class I and kill the cell, closing the escape route.
Category: Pathogen Responses
Question 18
The tuberculin skin test reaction is an example of type I hypersensitivity.
Correct Answer
False
False. The tuberculin reaction is a type IV, delayed, cell-mediated hypersensitivity. T cells release cytokines that recruit macrophages, producing firm swelling that develops over 24 to 72 hours after the test.
Category: Immune Disorders
Question 19
Severe combined immunodeficiency disease impairs both B cell and T cell responses.
Correct Answer
True
True. SCID is a group of inherited defects that cripple both arms of adaptive immunity. Without treatment such as a bone marrow transplant, affected infants usually die of opportunistic infections early in life.
Category: Immune Disorders
Question 20
Graft-versus-host disease occurs when the recipient's lymphocytes attack transplanted donor bone marrow.
Correct Answer
False
False. In graft-versus-host disease, mature T cells from the donor marrow attack the recipient's tissues, such as the skin, liver and intestinal lining. Removing mature T cells from donor marrow lowers this risk.
Category: Transplant and Cancer