Organs of Immunity Flashcards
What is one of the main functions of the lymphoid system?
2
To enable lymphocytes to encounter antigens
It is here that adaptive immune responses are initiated
What does the lymphoid system consist of?
3
Primary lymphoid organs
Secondary lymphoid organs
Lymphatic vessels
List the parts of the primary lymphoid organs.
2
Bone marrow
The thymus
What is a primary lymphoid organ?
A location where cells of the immune system are generated or mature
How is bone marrow a primary lymphoid organ?
2
B and T lymphocytes are produced from stem cells in the bone marrow
B lymphocytes mature in the bone marrow
How is the thymus a primary lymphoid organ?
T lymphocytes mature in the thymus
What happens to B and T lymphocytes after they mature?
They accumulate in secondary lymphoid organs
List the secondary lymphoid organs.
Lymph nodes
Tonsils
Appendix
Spleen
Peyer’s patches
What is a secondary lymphoid organ?
A location in the body where immune responses can be initiated and organised
What do all secondary lymphoid organs contain?
4
Germinal centres
T-cells
B-cells
Antigen presenting cells
What are germinal centres
This is where mature B cells are activated/become plasma cells
What connects the secondary lymphoid organs to the rest of the body?
A vast network of lymphatic vessels
Where are peyer’s patches found?
They are found in the small intestine
What are developing cells in the thymus called?
Thymocytes
Describe the structure of the thymus.
4
It is an encapsulated organ
It consists of two lobes of glandular tissue
The lobes are divided into lobules by septae
Each lobule consists of a densely cellular cortex and a less cellular medulla
How many lobes does a thymus have?
Two
What divides the thymus lobes into lobules?
Connective tissue called septae
Which part of the lobule is densely cellular?
The cortex which is on the outside
Which part of the lobule is not densely cellular?
The medulla which is in the middle
What can be found in the medulla of the thymus?
Hassall’s corpuscles
What do Hassall’s corpuscles look like?
Rings in the medulla
Describe the pathway of cells in the thymus.
3
Arterial vessels bring the undifferentiated lymphocytes to the cortex
The cells then migrate to the medulla while differentiating into mature T cells
T cells leave for the systemic circulation or the lymph nodes (by lymphatic vessels)
What happens to 98% of thymocytes?
They are killed as they are either useless or potentially dangerous
What happens to the thymus as a person gets older?
It becomes involuted
what is involution?
The infiltration of the thymus by adipose tissue
What do lymph nodes do?
They act as filters
How do lymph nodes act as filters?
They contain a honeycomb structure of connective tissue filled with lymphocytes that destroy bacteria and viruses
What happens to the lymph nodes when there is an infection?
They swell due to increasing numbers of lymphocytes
How many lymph nodes does a person have?
Approximately 500-600
Give five places where there are clusters of lymph nodes.
Underarms
Groin
neck
Chest
Abdomen
How are lymph nodes shaped?
They are bean shaped
What is a lymph node surrounded by?
A capsule
What is found inside the capsule of a lymph node?
The fibrous capsule extends to form trabeculae
What is the concave side of the lymph node called?
Hilum
What attaches at the hilum of a lymph node?
The artery and vein
What is the lymph node divided into?
3
The outer cortex (B-cell zone)
A paracortex (T cell zone)
An inner medulla
What is the B cell zone of the lymph node?
The cortex
What is the T cell zone of the lymph node?
A paracortex
How does lymph travel to a lymph node?
Via afferent lymphatic vessels
Where does lymph drain into the lymph node?
In a space beneath the capsule called the subcapsular sinus
How does lymph leave the lymph node?
Via the efferent lymphatic vessels
What is found in the cortex of lymph nodes?
Lymphoid follicles
What occurs in the lymphoid follicles?
Plasma cell activation and antibody production
List the parts of a lymph node
8
Cortex
Paracortex
Medulla
Lymphoid follicles
Hilum
Capsule
Subcapsular sinus
Trabeculae
