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The thymus is the only lymphoid organ that __________.

• does not directly fight antigens

• contains both B cells and T cells

• becomes increasingly functional with advancing age

Memory lymphocytes __________.

• are the basis of acquired immunity; wait within lymphoid tissues until the body encounters a specific antigen, then proliferate rapidly

• stimulate the various cells of the immune system by secreting chemicals called cytokines

• cause people to get the same sickness multiple times

Functions of the spleen include __________.

• removal of blood borne antigens and removal of aged or defective blood cells

• removal of aged or defective blood cells; it is also the site of hematopoiesis throughout life

• storage of platelets throughout life; it is also the site where immature lymphocytes develop into T lymphocytes

Clusters of lymphoid follicles in the walls of the distal part of the small intestine, the ileum, are called __________.

• aggregated lymphoid nodules

• lymphoid follicles

• lymphatic sacs

The lymphatic vessels function in __________.

• all of the listed responses are correct

• returning leaked proteins to the blood

• returning excess tissue fluid to the bloodstream

• returning excess tissue fluid to the bloodstream and returning leaked proteins to the blood

Helper (CD4+) T cells __________.

• stimulate the various cells of the immune system by secreting chemicals called cytokines

• do not recognize specific antigens, but act when they detect a lack of "self" cell surface molecules or the presence of certain sugars on a target cell

• differentiate into plasma cells that secrete antibodies

Which of the following is the definition of Hassall's corpuscles?

• Thought to be collections of deteriorating epithelial reticular cells

• Cells that do not recognize specific antigens but, instead, act when they detect a lack of "self" cell surface molecules or the presence of certain carbohydrates on a target cell

• Short-lived cells that respond immediately to a pathogen and then die

Within the spaces of the reticular fiber network reside which of the following cells?

• T lymphocytes and B lymphocytes

• T lymphocytes, B lymphocytes, and macrophages

• T lymphocytes

B cells (B lymphocytes) __________.

• differentiate into plasma cells that secrete antibodies and flag cells for destruction by macrophages

• attack foreign cells directly

• bind to an antigen-bearing cell, secreting proteins that perforate the foreign cell's membrane and signal the cell to undergo apoptosis

Where does external respiration take place?

• Between oxygen in alveoli and the capillaries in the lungs

• In each respiratory structure from the trachea through the terminal bronchioles

• Within blood vessels traveling to organs