MCAT Biology : Lymphoid Organs

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #8 : Immune And Lymphatic Systems

Which of the following is NOT a part of the lymphatic system?

Possible Answers:

Liver

Thymus and spleen

Adenoids and tonsils

Bone marrow

Correct answer:

Liver

Explanation:

All of the following are parts of the lymphatic system, except the liver. The liver is considered to be primarily a part of the digestive system. 

Example Question #1 : Lymphoid Organs

Which of the following are you most likely to find in the medulla of a lymph node?

Possible Answers:

B-cells

T-cells

Stromal cells

Dendritic cells

Correct answer:

T-cells

Explanation:

In the lymph node, the B-cells are located in the cortex and the T-cells are located in the medulla. The stromal cells are structural cells that are not particular to an area of the lymph node. Dendritic cells will move through the lymph node to present antigens to the adaptive immune system cells.

Example Question #10 : Immune And Lymphatic Systems

Which of the following is a primary lymphoid structure?

I. Thymus

II. Spleen

III. Lymph node

Possible Answers:

III only

I, II, and III

II and III

I only

Correct answer:

I only

Explanation:

Primary lymphoid tissues refer to the tissues where lymphoid cells are generated, while secondary lymphoid tissues are the functional organs of the lymphatic system.

Lymphocytes are generated and developed in the bone marrow and thymus only. The spleen and lymph nodes are examples of secondary lymphatic organs.

Example Question #2 : Lymphoid Organs

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

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Antibodies and antigens interact in secondary lymphoid tissue, such as the spleen. In addition to its role in promoting this interaction, what is the primary function of the spleen?

Possible Answers:

Secrete systemic hormones

Filter senescent red blood cells

Synthesize new white blood cells

Secrete digestive enzymes

Synthesize most serum proteins

Correct answer:

Filter senescent red blood cells

Explanation:

The spleen has two main functions. The first main function is immunological, while its second function is to filter unhealthy (senescent) red blood cells.

Most digestive enzymes are secreted by the pancreas into the small intestine. Systemic hormones come from a variety of glands throughout the body; the spleen does not have an endocrine function. White blood cells are synthesized in bone marrow and mature in the marrow and thymus. Serum proteins are synthesized in the liver.

Example Question #1 : Lymphoid Organs

Which of these is a lymphoid organ that is active in young children, but decreases in size and importance in adulthood?

Possible Answers:

Tonsils

Lymph nodes

Spleen

Thymus

Adenoids

Correct answer:

Thymus

Explanation:

The thymus is a lymphoid organ located in the mediastinal space. The thymus is the site of T-lymphocyte differentiation. The mature T-cells leave the thymus and migrate to the spleen, lymph nodes, and other lymphoid tissues where they control cell-mediated immune responses. The thymus grows from birth to puberty, at which point it begins to shrink. The reason for this involution may be that the organ has produced enough T-cells and is no longer necessary.

The spleen is another lymphocyte-producing organ. The spleen filters blood, exposing it to lymphocytes that destroy foreign particles. The size of the spleen remains constant, except in cases of infections such as mononucleosis. The tonsils are a patch of lymphoid tissue that contain lymphocytes located in the pharynx. The tonsils and adenoids form a ring of immunologically active tissue. These tissues remain at a constant size except when infected by bacteria. Lymph nodes receive lymph from a single organ or region of the body. An increase in size, known as lymphadenopathy, could result from combating infection or cancer. 

Example Question #4 : Lymphoid Organs

Which lymphoid organ is the site of erythrocyte, leukocyte, and lymphocyte production?

Possible Answers:

Lymph nodes

Thymus

Adenoids

Spleen

Tonsils

Correct answer:

Spleen

Explanation:

The spleen forms erythrocytes (red blood cells), and leukocytes (white blood cells, including lymphocytes) during the embryonic stage. After birth, only lymphocytes are produced.

The tonsils and adenoids are patches of lymphoid tissue located in the pharynx that filter pathogens that enter the body through the mouth and nose. Lymph nodes produce lymphocytes in response to infections by pathogens. The thymus is an organ that produces lymphocytes in infants and young children. 

Example Question #5 : Lymphoid Organs

The surface of which lymphoid organ is covered with stratified squamous epithelium and located at the entrance to the oropharynx?

Possible Answers:

Thymus

Spleen

Tonsils

Adenoids

Lymph nodes

Correct answer:

Tonsils

Explanation:

The surface of each tonsil is covered with stratified squamous epithelium, which forms deep crypts that detect and respond to pathogens entering the body. The tonsils are located on either side of the throat at the back of the tongue.

Adenoids are lymphoid tissue located in the nasopharynx, in the midline at the back of the throat. The spleen is in the upper left quadrant of the abdomen. The spleen has a smooth surface, as it is covered by an outer capsule of connective tissue. The thymus is in the mediastinum between the lungs. The thymus is composed of two lobes containing multiple lobules divided into an outer cortex and an inner medulla. The thymus is the site of T-cell differentiation. Lymph nodes filter lymph and remove foreign particles. Lymph nodes are located throughout the body, and are concentrated in the neck, axilla, and groin. 

Example Question #6 : Lymphoid Organs

What lymphoid organ is one of the primary sites of cancer metastasis?

Possible Answers:

Spleen

Tonsils

Lymph nodes

Adenoids

Thymus

Correct answer:

Lymph nodes

Explanation:

Lymph nodes function to drain lymph. As lymph carries interstitial fluid, it also carries pathogens and cancer cells. Malignant cells may spread through the lymphatic circulation.

Tonsils and adenoids are collections of lymphoid tissue in the pharynx that filter microbes that enter through the mouth and nose. They enlarge during infectious processes. The spleen filters blood, exposing it to macrophages and lymphocytes that destroy foreign particles and aged blood cells. The thymus is the primary site for T-cell differentiation. The mature T-cells leave the thymus and travel to the spleen, lymph nodes, and other lymphoid tissue where they control cell-mediated immune responses. 

Example Question #7 : Lymphoid Organs

The lymphoid tissues are responsible for creating, storing, and processing lymphocytes, which are essentially the effector cells of the immune system. Which of the following is a lymphoid structure that is also responsible for recycling old red blood cells? 

Possible Answers:

Bone marrow

Thymus 

Liver

Spleen

Appendix

Correct answer:

Spleen

Explanation:

The spleen is a lymphoid structure that contains resident lymphocytes that produce antiobodies, as well as T-cells that are released into the bloodstream. It also contains resident macrophages, which are responsible for removing and degrading microbes and worn-out red blood cells. 

Example Question #2 : Lymphoid Organs

Destruction of the lymph nodes would most likely affect the immune system in which way?

Possible Answers:

Inability to produce killer T cells

Inability to carry out a second response to an antigen significantly shorter in duration than the first

Inability to initiate and sustain an inflammatory response at the site of infection

Inability to bind antibodies to an antigen

Correct answer:

Inability to carry out a second response to an antigen significantly shorter in duration than the first

Explanation:

The secondary response of the immune system is significantly shorter in duration due to the storage of memory cells after the initial infection has been combated. During the primary infection, a B-cell will bind with an antigen. Once this occurs, the B-cells will begin to divide rapidly into plasma cells and memory cells. Plasma cells release high quantities of antibodies, which are integral in combating the infection. Memory cells are stored in lymph nodes so that if the same antigen is ever encountered again, it can be quickly dealt with by a fast-responding production of the correct form of plasma cell. If lymph nodes were destroyed, memory cells would not be able to mount this quick secondary response.

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