17 - The Lymphatic System

Question 1

What is lymph?

Answer 1

Thin fluid that resembles plasma but with lower amounts of protein. Travels within lymphatic vessels.

Question 2

What is chyle? How is it different from lymph?

Answer 2

Lymph fluid that arises in the GI tract

White, cloudy substance that contains lots of fats and dissolved lipids (+ fat-soluble vitamins)

Question 3

Where do lymph vessels drain?

Answer 3

Into lymphatic ducts and then into systemic veins

Question 4

Describe the structure of a lymphatic vessel

Answer 4

• Overlapping endothelial cells, fluid can pass through due to gap junctions opened by pressure (not fenestrations or sinusoids)
• Contain valves for unidirectional flow
• Reticulin fibres anchor the vessels in place (only type of collagen present in lymphatics)

Question 5

What processes aid the flow of lymph fluid?

Answer 5

• Muscle contraction for deep lymph vessels
• Pressure changes in breathing
• Pulsations of adjacent arteries
• Larger lymph vessels contain smooth muscle in their walls

Question 6

Where in the body are no lymphatics found?

Answer 6

The central nervous system

Question 7

What different types of lymph vessel does lymph pass through to get from tissue fluid to vein?

Answer 7

1. lymphatic capillary
2. lymphatic vessel
3. lymph node
4. lymphatic trunk
5. lymphatic duct

Question 8

What is a lymphangion?

Answer 8

• Functional unit of lymph vessel flow
• Section of vessel with a valve at either end, when compressed the fluid moves into the next lymphangion and backflow is prevented by closure of the valve

Question 9

What is the cisterna chyli?

Answer 9

Receives lymph drainage from the GI tract, contains chyle

Question 10

The upper right quadrant lymphatics of the body drain into …………………………….

The rest of the lymphatics of the body drain into …………………………….

Answer 10

Upper right - Right subclavian/internal jugular veins

Rest of body - Left subclavian/internal jugular veins

Question 11

How many lymph nodes are there in the body? Which are the most important clinically?

Answer 11

600-700

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

Question 12

What does a lymph node do?

Answer 12

• Filters the lymph as it percolates to the vascular system

- Contain immune cells to coordinate an immune response to pathogens

Question 13

What vessels enter and leave a lymph node?

Answer 13

• Multiple afferent lymph vessels enter the convex surface
• Single efferent lymph vessel leaves the concave hilium
• Feeding artery and draining vein enter and leave at the hilium

Question 14

A lymph node has nodules of immune cells. What immune cells are present?

Answer 14

Macrophages, dendritic cells, B cells and T cells

Question 15

What happens to lymph nodes when they are fighting infection?

Answer 15

The germinal centres fill with increasing numbers of lymphocytes causing the lymph nodes to swell, which can cause pain.

Question 16

Other than infection, what else may cause enlarged lymph nodes?

Answer 16

• Cancers elsewhere in the body can metastasise to the lymph nodes via afferent lymphatics
• Lymphoma (malignancy of the lymphoid tissue itself) –> Hodgkin’s and non-Hodgkin’s

Question 17

What is the technical term for enlarged lymph nodes?

Answer 17

Lymphadenopathy

Question 18

What is the thymus and what does it do?

Answer 18

Lymphatic organ in the superior mediastinum. Similar structure to a lymph node but without an afferent vessel (straight into blood).

Matures bone marrow derived stem cells into T cells (‘thymic cell education’).

Question 19

Where is the spleen found, what is it’s structure and what does it do?

Answer 19

Inferior to the diaphragm, posterior to the stomach

Similar to a lymph node in structure but has white pulp (immune) and red pulp (haemopoietic)

• Filters blood to remove debris and initiate immune responses
• Immune and haemopoietic functions

Question 20

What are the immune functions of the spleen?

Answer 20

• Antigen presentation by APCs
• Activation and proliferation of B and T lymphocytes
• Removal of macromolecular antigens from blood by macrophages

Question 21

What are the haemopoietic functions of the spleen?

Answer 21

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

Question 22

If the spleen is removed (splenectomy), how is its role taken over?

Answer 22

• Liver and bone marrow take over the removal and destruction of ageing red blood cells
• Increases risk of infection by encapsulated bacteria (e.g. meningococcus) and malaria as only the spleen can detect these

Question 23

What is splenomegaly and what causes it?

Answer 23

An enlarged spleen

• Enlarges in response to local infection, same as lymph nodes
• Also enlarges in response to systemic infection (e.g. malaria or septicaemia) - can enlarge 10x normal size

Question 24

Where are the tonsils found and what is their function?

Answer 24

• Oropharynx and nasopharynx
• Prevent pathogen ingress through oral and nasal and aural routes
• Crypts increase surface area

Question 25

What are the three types of tonsil?

Answer 25

• Pharyngeal tonsil (adenoid) - nasal cavity
• Palatine tonsils - either side of oral cavity
• Lingual tonsil - back of the tongue

Question 26

Where is the vermiform appendix and what is its function?

Answer 26

• Inferior and attached to caecum (ascending colon)
• Prevent pathogen ingress through GI routes
• Prevent pathogen ingress from ilium
• Crypts increase surface area

Question 27

Where are Payer’s patches found and what do they do?

Answer 27

Inferior and attached to side of the ilium (run along one side of the ilium)

• Prevent pathogen ingress through digestion

Question 28

What are the primary functions of the lymphatic system?

Answer 28

1. Fluid balance - ISF returned to circulation
2. Transport of fats and fat-soluble vitamins to venous circulation
3. Defence against invading pathogens and disease
4. Storage and destruction of aged erythrocytes (spleen)

Question 29

How can cancer cells travel in the body when they metastasise?

Answer 29

• Through newly produced vasculature (make their own vessels by angiogenesis)
• Through the interstitial space
• Through lymph

Question 30

What happens to cancer cells when they enter the lymphatic system?

Answer 30

Either:

• Destroyed
• Start making tumour ECM and proliferate

Question 31

In breast cancer, what are the first lymph nodes to be affected (sentinel lymph nodes)?

Answer 31

Axilla or pectoral nodes

Question 32

During surgery, by what method does a surgeon know whether a lymph node is affected with malignant cells?

Answer 32

Fluorography

• Blue dye containing fluoro-18-glucose is injected
• Taken up quickly by highly active cancer cells
• Remove anything stained blue in surgery

Question 33

What conditions cause primary lymphoedema?

Answer 33

• Milroy’s disease (congenital)
• Meige’s disease (early onset)
• Late onset

Question 34

What are some possible causes of secondary lymphoedema?

Answer 34

• Neoplasia (abnormal growth) in pelvic region or infiltrating a lymph node
• Surgery - accidental infiltration of lymph node
• Radiotherapy - nodal fibrosis
• Autoimmune disease - RA or eczema
• Infections - cellulitis (vessel obstruction) or filariasis (parasitic worm that invades lymph vessels)