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Question
Which of the following has germinal centers in the lymph node?
Which of the following has germinal centers in the lymph node?
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Solution
The correct option is B Secondary follicle
Lymphoid organs are specialized tissues that provide the microenvironment for the functional maturity (primary lymphoid organs) or activation (secondary lymphoid organs) of lymphocytes.
Lymph nodes are secondary lymphoid organs. Lymph nodes consist of lymphoid and nonlymphoid cell aggregates surrounded by a network of lymphatic capillaries and these structures are called lymphoid follicles.
Morphologically a lymph node is divided into three concentric regions as follows :
- Cortex (outermost region) - Populated mainly by B-cells, thus it is called the thymus-independent region.
- Paracortex (middle region) - Enriched largely by T-cells. Thus it is referred to as the thymus-dependent region.
- Medulla (inner region) - It is a B dependent region and contains large blood vessels, sinuses, and medullary cords.
A lymphoid follicle is known as a primary follicle until it is not challenged by an antigen. The primary follicle consists of resting B-cells along with other cells.
Once a primary follicle is challenged by an antigen, it becomes enlarged and known as a secondary follicle. It consists of actively dividing B-cells at the center known as the germinal center surrounded by a ring of B-lymphocytes. So the germinal center is present in the secondary follicle. Hence option b is correct.
Tertiary and quaternary follicles are not present in lymph nodes.
Figure : Structure of lymph node
Lymphoid organs are specialized tissues that provide the microenvironment for the functional maturity (primary lymphoid organs) or activation (secondary lymphoid organs) of lymphocytes.
Lymph nodes are secondary lymphoid organs. Lymph nodes consist of lymphoid and nonlymphoid cell aggregates surrounded by a network of lymphatic capillaries and these structures are called lymphoid follicles.
Morphologically a lymph node is divided into three concentric regions as follows :
- Cortex (outermost region) - Populated mainly by B-cells, thus it is called the thymus-independent region.
- Paracortex (middle region) - Enriched largely by T-cells. Thus it is referred to as the thymus-dependent region.
- Medulla (inner region) - It is a B dependent region and contains large blood vessels, sinuses, and medullary cords.
Once a primary follicle is challenged by an antigen, it becomes enlarged and known as a secondary follicle. It consists of actively dividing B-cells at the center known as the germinal center surrounded by a ring of B-lymphocytes. So the germinal center is present in the secondary follicle. Hence option b is correct.
Tertiary and quaternary follicles are not present in lymph nodes.
Figure : Structure of lymph node Suggest Corrections
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