Structure and function of lymph node and spleen Flashcards
Describe the origin and maturation of lympoid cells
- Lymphocytes originate from haematopoietic stem cells which are present in the fetal liver/postnatal bone marrow
- Through differentiation and proliferation precursor lymphoid cells are formed from these stem cells
- T cell lymphoid precursors originate in the bone marrow and then go to the thymus gland where they mature into mature T cells
- B cells originate and mature in the bone marrow
- Mature B and T cells then travel to the secondary lymphoid organs
What are the 2 primary lymphoid organs and what is there function ?
Bone marrow and thymus - Primary lymphatic organs are where lymphocytes are formed and mature
What are the different secondary lymphoid tissues and what is there function?
- Lymph nodes
- Spleen
- Tonsils (Waldeyer’s ring)
- Epithelio-lymphoid tissues also called mucosa associated lymhoid tissue (MALT)
- Bone marrow
Lymph nodes and the spleen are the 2 main secondary lymphoid tissues
Secondary/peripheral lymphoid organs, maintain mature naive lymphocytes and initiate an adaptive immune response. The peripheral lymphoid organs are the sites of lymphocyte activation by antigens. Activation leads to clonal expansion and affinity maturation.
What are the 2 main functions of lymphoid tissues ?
- Filtration of circulatory fluids
- Location for cells of the immune system
What is the term given for lymph node enlargement and how can it be categorised ?
Termed as lymphadenopathy
Can be categorised as:
- Localised, more wide-spread or generalised
- Peripheral or Central (internal)
What is the term given to splenic enlargement and how is it categorised
- Splenomegaly
- Categorised as Slight, moderate or massive
Define splenic atrophy
Decreased size of the spleen
Give an overview of the lymphatic system
The lymphatic system carries a fluid called ‘lymph’ around the body in lymph vessels (these vessels have valves to ensure the correct flow of lymph). The fluid passes through lymph nodes (glands), which are spread throughout your body.
The lymphatic system also includes organs and tissues that are places where immune system cells collect. These include the parts of the body that make cells for the immune system (the primary and secondary organs previously mentioned)
What are the functions of the lymphatic system ?
The lymphatic system defends your body against disease by removing germs (bacteria, viruses and parasites) and toxins (poisons). It also helps to destroy cells that are old, damaged or have become abnormal by:
- Houses cells of the innate immune system
- Traffic of APCs links innate and adaptive immune responses
- Seat of the adaptive immune response
As a drainage system, it removes excess fluid and waste from your tissues and returns it to your bloodstream ==> maintaining fluid homeostasis by returning the lymph to the circulation and also prevents excessive accumulation of fluid in the tissues – oedema
The whole of the lymphatic system helps to protect us against infection. Any part of it can be affected by lymphoma.
Describe what mucosa associated lymphoid tissue is
- Mucosa-associated lymphoid tissue (MALT) is an area in the mucosa where lymphocytes and other immune system cells collect together. MALT can be found in the wall of the bowel (where it is known as ‘Peyer’s patches’) and in other organs, such as the lungs, eyes, nose and the thyroid gland.
- MALT helps protect the body from infections and toxins entering through a part of the body lined by mucosa.
What is the function of the tonsils ?
They contain lots of immune system cells that help protect your body against infections that enter through the mouth and nose.
Describe what lymph is and its general route in the lymphatic system
Lymph is a clear fluid that flows around the body in the lymphatic system. It is formed from plasma. Plasma is carried around your body in your blood vessels. It leaks out of the blood vessels and bathes your tissues and supplies the cells of your body with nutrients. Most of this plasma then drains back into the blood vessels. A small amount is left behind, together with:
- waste products from the cells
- fat that is broken down in the bowel and needs to be carried to larger blood vessels
- things that have got into the body and might be harmful, such as germs and toxins
- damaged or abnormal cells, including cancer cells.
This all drains into tiny lymph vessels. Lymph vessels in the small intestine also absorb fats and fat-soluble vitamins.
When it is in lymph vessels, the fluid is known as ‘lymph’.
What is the normal macroscopic appearance of lymph nodes and where are they located ?
- Small (upto 2.5cm) oval shaped
- Located along the course of lymphatic vessels
What cells are contained within lymph nodes and what are there functions ?
Lymphocytes:
B cells - Cells that produce antibodies
- Associated with follicles and germinal centres
- Interfollicular
- Plasma cells – mainly in the medulla
T cells
- T helper cells - Cells with T cell receptors that activate macrophages and that help B cells develop their response
- T cytotoxic cells - Cells with T cell receptors that kill virally infected cells and certain cancer cells
Natural killer cells - Cells that kill virally infected cells (part of the innate not adaptive immune response)
Macrophages, antigen presenting cells, and dendritic cells (Collect antigen out in the tissues and carry it to ymph nodes in order to start an adaptive (specific) immune respons)
Endothelial cells
Describe the drainage of lymph after leaving the lymph node through the efferent lymphatic vessels
After transversing one or more lymph nodes, lymph enters larger lymphatic vessels called lymphatic trunks, which unite to form either the R lymphatic or the thoracic duct
- The R lymphatic duct drains lymph from the bodys R upper quadrant (R side of head, neck, thorax and upper limb). This duct ends in the R subclavian vein at its angle of junction with the internal jugular vein called the R venous angle
- The thoracic duct drains lymph from the rest of the body, This duct begins in the abdomen as a sac (cisterna chyli) and ascends through the thorax and enters the junction of the L internal jugular and L subclavain veins called the left venous angle
Describe the structure of a lymph node
- Lymph flows into a node through afferent lymphatic vessels that enter the convex side of a node draining through the capsule into the peripheral sinus
- Lymph then filters through the node parenchyma and leaves via efferent lymphatic vessels from the hilum
Whilst in the node parenchyma Interactions between cells in the node and cells or substances contained within the lymph fluid occurs
Arterial and venous vessels serving the node enter/exit at the hilum
What do you need to remember when exammining regional lymphadenopathy ?
- Examine the territory that drains to that group of nodes.
- In cases of superficial infection may see red lines extending from an inflamed lesion - lymphangitis
Where are the different cells in a lymph node located ?
Mainly talking about B&T cells and dendritic cells
- The outer layer (Cortex) contains the B-cell areas, or follicles.
- The middle layer (Paracortex) is mostly populated by T cells and dendritic cells
What are the 2 markers to look at B and T cells in lymph nodes ?
- CD20 - B cell marker
- CD3 - T cell marker
In the pics the cells are indicated by the darkish colour
