MCAT Biology - Problem Drill 16: The Lymphatic and Immune Systems

Transcription

1 MCAT Biology - Problem Drill 16: The Lymphatic and Immune Systems Question No. 1 of Which of the following statements about pathogens is true? Question #01 (A) Both viruses and bacteria need to infect a cell to survive and replicate. (B) Viruses can have DNA or RNA as their genetic material and have envelope proteins, which facilitate uptake into cells. (C) Bacteria are abnormal host proteins that can exist outside the body. (D) Prions are proteinaceous infection particles that can easily be broken down by host enzymes or heat. Bacteria can replicate without invading a host cell. B. Correct! Viruses can have DNA or RNA as their genetic material and have envelope proteins, which facilitate uptake into cells. Prions are abnormal host proteins. Prions are very resistant to breakdown by host enzymes or heat. Pathogens are infectious agents that cause illness or disease to its host. Viruses can have genetic material (RNA or DNA) inside a protective protein capsid, have envelope proteins, which facilitate cellular binding and uptake, and they must enter the cell to replicate. Bacteria release toxins or break down surrounding tissue. Due to the bacterial cell cycle, they can divide without invading a host cell. Parasites can survive inside or outside of human cells. The can be transmitted by insects or invade a host through the skin or mucous membranes. Prions are proteinaceous infection particles, which are abnormally structured host proteins. They are transmissible by ingestion and are very resistant to breakdown by host enzymes or heat. The correct answer is (B).

2 Question No. 2 of B cells perform which of the following functions as part of the immune system? Question #02 (A) B cells interact with T cells to produce an immune response and produce antibodies against a particular antigen. (B) B cells interact with B cells during positive selection in the thymus. (C) B cells undergo both positive and negative selection in the thymus and produce antibodies against a particular antigen. (D) B cells mature in the thymus and produce antibodies against a particular antigen. A. Correct! B cells interact with T cells to produce an immune response and produce antibodies against a particular antigen. T cells undergo positive and negative selection in the thymus. T cells undergo positive and negative selection in the thymus. T cells mature in the thymus. B cells develop in the bone marrow and become antibody-producing plasma cells. B cells bind antigens to surface-bound antibodies and are involved in antigen presentation to T cells, leading to activated immune response. The correct answer is (A).

3 Question No. 3 of Which of the following statements about T cells is correct? Question #03 (A) T cells are produced in the bone marrow, develop in the spleen and can differentiate into T-helper cells or T-cytotoxic cells. (B) T-helper cells induce B cell differentiation, antibody production and induce inflammation. (C) T-cytotoxic cells are produced in the spleen, develop in the thymus and kill target cells by granule exocytosis or the Fas cell death system. (D) B cells induce T cells to produce antibodies in response to antigen stimulation. T cells are produced in the bone marrow and develop in the thymus. B. Correct! T-helper cells induce B cell differentiation, antibody production and induce inflammation. T cells are produced in the bone marrow and develop in the thymus. T cells induce B cells to produce antibodies in response to antigen stimulation. T cells are produced in the bone marrow and develop in the thymus. T cells differentiate into T-helper cells or T-cytotoxic cells. T-helper cells induce B cell differentiation, antibody production and induce inflammation. T-cytotoxic cells are sensitive against a specific antigen, and kill target cells by granule exocytosis or the Fas cell death system. The correct answer is (B).

4 Question No. 4 of The structure of antibodies includes. Question #04 (A) Heavy and light chains linked together by disulfide bridges, an antigenbinding site made up of 1 heavy chain variable region and 1 heavy chain constant region. (B) Classification into 1 of 5 isotypes, and an antigen-binding site made up of 1 heavy chain variable region and 1 light chain variable region. (C) Classification into 1 of 4 isotypes, and 2 heavy chains and 2 light chains linked together by disulfide bridges. (D) The ability to bind antigens only when they are bound to the surface of B cells. The antigen binding site of an antibody is made up of 1 heavy chain and 1 light chain variable regions. B. Correct! Classification into 1 of 5 isotypes, and an antigen-binding site made up of 1 heavy chain variable region and 1 light chain variable region. There are 5 types (isotypes) of antibodies: IgA, IgD, IgE, IgG and IgM. Antibodies can bind antigens when they are bound to the surface of B cells as well as unbound in the circulation. Antibodies are soluble proteins that are bound to the surface of cells, as well as unbound in the circulation. There are 5 types (isotypes) of antibodies: (1) IgA: protects mucosal surfaces, (2) IgD: B cell antigen receptor, (3) IgE: involved in allergy, (4) IgG: majority of antibody-based immunity, and (5) IgM: key to B cell immunity. Antibody diversity is due to various combinations of heavy and light chain variable regions. The correct answer is (B).

5 Question No. 5 of Which of the following statements about humoral immunity is correct? Question #05 (A) When T cells bind to antigens, they produce specific antibodies. (B) During the primary response: (1) plasma cells produce antibodies, and (2) memory B cells are produced. (C) During the secondary response: (1) plasma cells produce antibodies, and (2) memory B cells are produced. (D) During the secondary response, killer T cells attack and destroy infected cells. During the primary response, plasma cells produce antibodies. B. Correct! During the primary response: (1) plasma cells produce antibodies, and (2) memory B cells are produced. Memory B cells are produced during the primary response and facilitate a stronger immune response upon re-exposure. Killer T cells attack and destroy infected cells during cell-mediated immunity. Humoral immunity is made up of a primary response and a secondary response. During the primary response plasma cells produce antibodies to kill the pathogen. Memory B cells remember how to kill the antigen. Upon re-exposure to the same antigen (secondary response) a stronger immune response is triggered, because the system is already prepared via memory B cells. The correct answer is (B).

6 Question No. 6 of Bone marrow produces. Question #06 (A) B cells and memory T cells that circulate to other lymphoid organs to be stimulated by antigens. (B) Hematopoietic stem cells, which differentiate into lymphoid progenitor and myeloid progenitor cells in the lymph node and spleen. (C) Myeloid progenitor cells, which differentiate into B cells and T cells. (D) B cells and T cells that circulate to other lymphoid organs to be stimulated by antigens. Bone marrow produces B cells and T cells that circulate to other lymphoid organs to be stimulated by antigens; not memory T cells. Hematopoietic stem cells differentiate into lymphoid progenitor and myeloid progenitor cells in the bone marrow, not in the lymph node and spleen. Lymphoid, not myeloid progenitor cells differentiate into B cells and T cells. D. Correct! B cells and T cells circulate to other lymphoid organs to be stimulated by antigens. Within the bone marrow exists hematopoietic stem cells, which are the starting point for all blood cells. These cells differentiate into mult-ipotential stem cells. Multi-potential stem cells differentiate into (1) myeloid progenitor cells, which differentiate into RBCs, granulocytes and platelets, and (2) lymphoid progenitor cells, which differentiate into NK cells, B cells and T cells. The correct answer is (D).

7 Question No. 7 of Which of the following statements about the spleen is correct? Question #07 (A) The spleen is a lymphoid organ, which is not involved in immune responses. (B) The spleen contains 2 functional areas: (1) red pulp, which is rich in T cells responsible for fighting infection, and (2) white pulp, which is made of blood filled sinuses and is responsible for removing damaged or worn out red blood cells from the circulation. (C) The spleen contains 2 functional areas: (1) red pulp, which is made of blood filled sinuses and is responsible for removing damaged or worn out red blood cells from the circulation, and (2) white pulp, which is rich in T cells responsible for fighting infection. (D) White pulp is rich in T cells only. The spleen is a lymphoid organ, which is involved in immune responses through activated B cells and T cells. The red pulp is made of blood filled sinuses and is responsible for removing damaged or worn out red blood cells from the circulation. C. Correct! The spleen contains 2 functional areas: (1) red pulp, which is made of blood filled sinuses and is responsible for removing damaged or worn out red blood cells from the circulation, and (2) white pulp, which is rich in T cells responsible for fighting infection. White pulp is rich in B cells and T cells. The spleen is made up of masses of lymphoid tissue, which are located around terminal branches in the circulation. The spleen contains 2 functional areas: (1) red pulp that is made up of blood-filled sinuses and is responsible for removing wornout or damaged red blood cells from the circulation, and (2) white pulp that is made up of follicles rich in B cells and periarteriolar lymphoid sheaths (PALS), which are rich in T cells. Lymphocytes in the white pulp help fight infection. The correct answer is (C).

8 Question No. 8 of The thymus is made up of two lateral lobes filled with smaller lobules. What is the function of the thymus? Question #08 (A) Lymphocyte precursors mature into T cells, and then must undergo positive and negative selection in order to be released into the circulation. (B) Lymphocyte precursors mature into B cells, and then must undergo positive and negative selection in order to be released into the circulation. (C) Positive selection involves the elimination of T cells that are autoreactive, and negative selection involves testing the reactivity and specificity of the T cell. (D) Negative selection is intended to permit autoreactive T cells to enter the circulation. A. Correct! Lymphocyte precursors mature into T cells, and then must undergo positive and negative selection in order to be released into the circulation. In the thymus lymphocyte precursors mature into T cells. Positive selection involves testing the reactivity and specificity of the T cell. Negative selection involves the elimination of T cells that are autoreactive. Negative selection is intended to eliminate autoreactive T cells and prevent them from entering the circulation. The thymus is made up of 2 lateral lobes, which are enclosed in a capsule. Each lateral lobe is made up of many smaller lobules. Inside the thymus, lymphocyte precursors mature into T cells. To be released into the circulation, the T cells must undergo both positive and negative selection. Positive selection involves testing the reactivity and specificity of the T cell. Negative selection involves the elimination of T cells that are autoreactive. The correct answer is (A).

9 Question No. 9 of Which of the following statements about the lymph nodes is correct? Question #09 (A) Lymph nodes are located throughout the body and serve as filters for tissue fluid. (B) When an antigen enters the lymph node, plasma cells develop in the paracortical area and are then disseminated throughout the body. (C) When an antigen enters the lymph node, sensitized T cells develop in the lymph vessel and are then disseminated throughout the body. (D) Plasma cells develop in the paracortical area and then undergo negative selection. A. Correct! Lymph nodes are located throughout the body and serve as filters for tissue fluid. When an antigen enters the lymph node, sensitized T cells develop in the paracortical area and are then disseminated throughout the body. When an antigen enters the lymph node, sensitized T cells develop in the paracortical area. Plasma cells differentiate in the germinal centers and secrete specific antibodies. Lymph nodes are located throughout the body and serve as filters for tissue fluid. When antigen enters a lymph node: (1) B cells and T cells are activated, causing the formation of germinal centers. Plasma cells differentiate and secrete specific antibodies, and (2) sensitized T cells also develop in the paracortical area of the lymph node and are disseminated throughout the body. The correct answer is (A).

10 Question No. 10 of What is the function of the lymphatic system? Question #10 (A) It equalizes fluid distribution, produces specific antibodies and sensitized lymphocytes, and transports lymph using pressure in the tissue. (B) It transports tissue fluid (originally lymph) back to the systemic circulation. (C) It transports lymph fluid containing many red blood cells and just a few lymphocytes. (D) It includes the following organs: spleen, lymph nodes, tonsils and the retina. A. Correct! The lymphatic system equalizes fluid distribution, produces specific antibodies and sensitized lymphocytes, and transports lymph using pressure in the tissue. The lymphatic system transports lymph (originally tissue fluid) back to the systemic circulation; it does not transport tissue fluid. The lymphatic system transports lymph containing a few red blood cells and many lymphocytes. The lymphatic system includes the following organs: primary bone marrow and thymus, and secondary - spleen, lymph nodes, Peyer s patches and tonsils. It does not include the retina. The lymphatic system returns fluid to the body s circulation system and is involved in defending the body against pathogens. Primary organs include bone marrow and the thymus. Secondary organs include the spleen, lymph nodes, Peyer s patches and tonsils. The lymphatic system has three main functions: (1) equalizes fluid distribution, (2) returns materials to the blood, and (3) production of specific antibodies and sensitized lymphocytes. The correct answer is (A).