Lymphatic System

Question 1

What does the lymphatic system consist of?

Answer 1

1) Fluid - lymph
2) Vessels - lymphatic
3) Cells - lymphocytes (B, T NK), Supporting cells e.g. Follicular dendritic cells and macrophages
4) Tissues
5) Organs

Question 2

What propels lymph along along lymphatic vessels?

Answer 2

Skeletal muscle movement, pressure changes in the thorax during breathing and the pulsation of adjacent arteries
Increased physical activity

Question 3

What direction is lymphatic flow?

Answer 3

Superficial to deep

Question 4

What do lymphatic lie adjacent to?

Answer 4

Arteries and veins

Question 5

What do lymphatic pass through?

Answer 5

Muscles - muscle contraction within deep compartments is critical to lymph circulation

Question 6

What do larger lymphatics (e.g. In a dome and thorax) contain in their walls?

Answer 6

Smooth muscle - contraction of this smooth muscle is an important contributor to lymph flow

Question 7

Are there lymphatics in the CNS

Answer 7

No

Question 8

What does the lymphatic system consist of?

Answer 8

Tissues

• Diffuse, mucosal associated lymphatic tissue (MALT) including gut-associated (GALT) and bronchus-associated (BALT)
• Lymphatic nodules

Organs

• Lymph nodes
• Thymus
• Spleen

Question 9

Is there bacteria in the small bowel?

Answer 9

Shouldn’t be

Question 10

Is there bacteria in the colon?

Answer 10

Always normally have bacteria in the colon
Not in small bowel
These need to stay in colon
Illea-caecal valve and lymph nodes prevent bactera from getting into the digestive system

Question 11

What is the function of lymph nodes?

Answer 11

Serve as filters as lymph percolates on its way to the vascular system

Question 12

How many lymph nodes in the human body?

Answer 12

700

Question 13

Describe the lymphatics flow to and away from the lymph nodes

Answer 13

Each node has afferent lymphatic vessels that enter via the convex surface and efferent lymphatics that leave via the hilum

Question 14

Describe the blood supply to the lymph nodes

Answer 14

Each lymph node has a feeding artery and draining vein that enter and leave via the hilum
Good blood supply

Question 15

What are follicular dendritic cells?

Answer 15

Located in the germinal centres
Antigen antibody complexes adhere to their dendritic processes and the cell can retain antigen for months Follicular dendritic cells cause proliferation of B cells, in particular
memory B cells

Question 16

What are professional APCs?

Answer 16

Unlike B cells, T cells fail to recognize antigens in the absence of antigen presentation

Most cells are capable of presenting antigens and activating the
adaptive response. Some cells, however, are specially equipped
to acquire and present antigen, and prime naive T cells. B cells
and macrophages play a major role in the innate response, also
acting as professional antigen-presenting cells (APC). These
professional APCs are equipped with special immunostimulatory
receptors that allow for enhanced activation of T cells

Question 17

What is inflammation

Answer 17

The initial reaction of the body to an antigen is an inflammatory response. Mediated mainly by neutrophils and/or macrophages.
Degradation of the antigen may lead to presentation of a portion of the antigen to elicit a specific immune response

Question 18

What is the specific immune response?

Answer 18

The specific immune response is usually a mixture of humoral and cell-mediated.

Question 19

Briefly describe humoral immunity

Answer 19

Humoral immunity is B lymphocyte mediated and involves antibody production by B lymphocytes that transform into plasma cells that synthetise and secrete a specific antibody

Question 20

Describe cell-mediated immunity

Answer 20

Cell-mediated immunity is T cell mediated. T cells need antigen presenting cells (macrophages, B lymphocytes) to recognise antigen.

Cell-mediated immunity is important in defence against:
– viral, fungal and mycobacterial infections
– tumour cells
– transplant rejection

Question 21

What are 2 functions of lymph nodes?

Answer 21

Serve as filters as lymph percolates on its way to the vascular system, traps antigen, processes antigen and presents processed antigen to T cells

Is a repository of macrophages, B cells and T cells that work together to produce an inflammatory (macrophages, neutrophils) response followed by an immune response (B cells, T cells)

Question 22

Where do lymphocytes enter and leave lymph nodes?

Answer 22

The majority of lymphocytes enter lymph nodes via the feeding artery (a few in lymph) and the majority leave in the efferent lymphatics

Question 23

When do lymph nodes enlarge?

Answer 23

As lymph nodes fight infection the germinal centres fill with increasing numbers of lymphocytes causing the lymph nodes to swell can this can also cause some pain

Cancers can metastasise to lymph nodes vie the afferent lymphatics

Lymphoma often presents with lymphadenopathy

Question 24

What is the spleen?

Answer 24

Largest lymphatic organ, very rich blood supply

Question 25

What are the immune functions of the spleen?

Answer 25

Immune functions
– Antigen presentation by APCs
– Activation and proliferation of B and T lymphocytes, production of antibodies
– Removal of macromolecular antigen from blood (macrophages do this)

Question 26

What are the haemopoietic functions of the spleen?

Answer 26

Removal and destruction of old, damaged and abnormal erythrocytes and platelets
Retrieval of iron from erythrocyte haemoglobin

Question 27

Why do surgeons often remove the spleen and what consequences does this have?

Answer 27

Surgeons often remove the spleen (e.g trauma)
– The liver and bone marrow can take over the removal and destruction of ageing red cells
– Splenectomy increases the risk of infection by encapsulated bacteria
(e.g the meningococcus) and malaria
– Splenectomy increases the risk of DVT and pulmonary embolism
threefold (partly due to increased platelet count?)

Question 28

When may the spleen enlarge?

Answer 28

In the same way that lymph nodes enlarge in response to infection (usually localised), the spleen may enlarge in response to systemic infection (glandular fever, malaria, septicemia)

Question 29

What is the function of the thymus?

Answer 29

Its role is the maturation of bone marrow derived stem cells into immunocompetent T cells. This is called thymic cell education

Question 30

Where is the thymus located

Answer 30

It is located in the superior mediastinum, is fully formed and functional at birth, it involutes after puberty and by the late teens is mostly fat