Lecture 23 - The Lymphatic System

Question 1

What are the 4 components of the lymphatic system?

Answer 1

1) Lymph (the fluid)
2) Lymphatic vessels
3) Lymphoid tissues and vessels
4) Cells within tissues and organs (mainly lymphocytes)

Question 2

What is lymph?
What is the lymph that arises in the GI tract?
How much lymph is produced and recycled each day?

Answer 2

• Lymph is a thin fluid that resembles plasma (pH 7.4) with low amounts of protein.
• Chyle - white cloudy substance due to presence of chylomicrons.
• 3-5 Litres

Question 3

What is arrangement of lymphatic vessels through which lymph flows?
How are these vessels arranged?
What do the larger lymphatic vessels contain?

Answer 3

• Capillaries > Trunks > Ducts > Veins
• Lymphatic vessels are arranged into superficial and deep vessels (flow is superficial to deep)
• Ducts + Trunks (larger vessels) contain smooth muscle which aids in lymph flow.

Question 4

Once fluid is lost from the capillaries what happens to it?

Answer 4

This fluid is given up into the lymphatic system before the lymphatics return most/if not all of the fluid into the venous system.

Question 5

Describe 2 similarities and 1 difference between the lymphatic and venous system.
What is the role of the lymphangion?

Answer 5

• both low pressure systems, both have valves present, but the lymphatic system normally has no cells.
• The lymphangion is a functional unit of the lymphatics system which is compressed by veins and arteries to help propel the lymph.

Question 6

What does the upper right quadrant of the lymphatics system drain into?
Where does lymph from the rest of the body drain into?

Answer 6

Upper right quadrant = Right subclavian/internal jugular vein

Rest of the body = Left subclavian/internal jugular vein

Question 7

How many lymph nodes are there in the body?

Which are the most important ones clinically?

Answer 7

• 600-700

- Neck (cervical), groin (inguinal) & armpit (axillae)

Question 8

Describe the structure of a typical lymph node

Answer 8

Shaped like a kidney, each node has multiple afferent lymphatic vessels which enter via the convex surface, and 1 singular efferent lymphatic vessel which leaves via the hilum. Also has a feeding artery and draining vein which also enter and leave via the hilum.

Within the node, there are multiple follicles with nodules containing immune cells. And a lot of reticulin (collagen lll) connective tissue.

Question 9

What is the function of lymph nodes?
Where are follicular dendritic cells found and what is their function?
Can T or B cells recognise antigens?

Answer 9

• To filter lymph on its way to the vascular system (trap antigens, and present processed antigens to T-cells)
• The germinal centres of lymph nodes, they cause proliferation of memory B-cells which provides the basis for immunity.
• B-cells can, T-cells cannot and need to be presented to the antigen directly.

Question 10

What is lymphadenopathy and how can it be caused?

Answer 10

Swelling of lymph nodes as germinal centres fill with lymphocytes to fight infection. Can also occur in cancers when they metastasise to lymph nodes and cause lymphoma.

Question 11

What are the 6 lymphatic organs and where are they found?

Answer 11

1) Thymus - in the mediastinum
2) Bone marrow - red marrow within bone
3) Spleen - left side of abdomen
4) Tonsils - In the oropharynx and nasopharynx
5) Appendix - Lower right quadrant of abdomen
6) Payer’s patches - under mucosal membrane of SI

Question 12

Describe the location, structure and function of the thymus.

Answer 12

Location = Superior mediastinum (functional at birth)
Structure = Similar to lymph nodes, but no hilum 
Function = Where bone marrow stem cells are matured into T-cells (thymic cell education).

Question 13

Describe the location, structure and functions of the spleen.

Answer 13

Location = inferior to diaphragm (on left), posterior to stomach.

Structure = Similar to lymph node but separated into red and white pulp.

Function = Filters blood, presents antigens via APC’s, activated and proliferates T+B lymphocytes, removes damages/old erythrocytes and platelets, retrieves iron from Hb and serves as an erythrocyte storage site.

Question 14

What takes over the role of destruction of red blood cells after a splenectomy?
When does splenomegaly occur?

Answer 14

• The liver and bone marrow

- Localised infection (e.g.: of lymph nodes) and in response to systemic infection (over x10 the size normally)

Question 15

Describe the location, structure and function of the tonsils

Answer 15

Location = Oro and nasopharynx

Structure = nodules reside inferior to surface crypts. Surface epithelia have numerous microfolds (M-cells) which present antigens to underlying T+B cells (this is why tonsils become inflamed - proliferation of T+B cells)

Function = Prevents pathogen ingress through oral, nasal and aural (ear) routes. Crypts also increase surface area.

Question 16

Describe the location, structure and function of the vermiform appendix.

Answer 16

Location = Inferior to caecum (ascending colon).

Structure = Nodules inferior to crypts, many M-cells on inferior surface

Functions = prevent pathogen ingress through GI routes, and anything arriving from ileum.

Question 17

Describe the location, structure and function of Payer’s patches.

Answer 17

Location = Inferior and attached to side of ileum

Structure = Nodules inferior to surface domes, many M-cells on epithelial surface

Function = Prevents pathogen ingress through digestion

Question 18

Summarise the 4 main functions of the lymphatic system

Answer 18

1) Fluid balance - returns interstitial fluid to circulation
2) Transport of fats/fat-soluble vitamins - from digestive system to venous circulation
3) Defence against invading pathogen and disease - in lymph nodes
4) Storage + destruction of ages erythrocytes - Spleen responsible for this

Question 19

Why is the sentinel lymph node important in cancer detection?

Answer 19

The sentinel lymph nodes are the first to swell during cancer - during metastatic cancer, cells travel through lymph. Fluorography can be used to detect cancer (blue dye injected into lymph node) - often lymph nodes are removed (the ones that stain blue).

Question 20

What is the difference between primary and secondary lymphedema?

Answer 20

Primary = usually congenital 
Secondary = Usually due to surgical intervention or caused by immobility, occasionally due to parasites or infections

Treatment = Lympha press system which can reduce fluid accumulation but there is no known cure, just management of symptoms.