Lymphatics (M2 20/11)

Question 1

• Describe the gross anatomical organisation of the lymphatic system
• Describe the microanatomical structure of the lymphatic system

Answer 1

These are the LO’s dodo brain.

Question 2

Which conditions are caused by lymphatic dysfunction?

Answer 2

1. Metastasis:

this is the development of secondary malignant growths at a distance from a primary site of cancer. The lymphatic route most common for metastasis to happen and spread of cancer can be predicted based on direction of lymph flow

2. Lymphoedema: localised retention of fluid caused by lymphatic dysfunction
3. Chylothorax: accumulation of lymphatic fluid (chyle) in the pleural cavity (appears white on x-ray).
4. Lymphadenopathy: inflammation of lymph vessels and nodes.

Question 3

What are the functions of the lymphatic system?

Answer 3

1. To drain interstitial fluid from the extracellular space. This refers to when hydrostatic pressure forces water and nutrients out of the blood, not all this tissue fluid is reabsorbed at the venous end by osmosis. The remaining fluid has to be drained by the lymphatic system.
2. Transports dietary lipids in lacteals. Lacteals are a type of lymphatic capillary inside the villi of the small intestine. Lacteals absorb lymph and carry them in the lymph fluid as chylomicrons. They are then transported to the liver using the blood circulation.
3. Is a defence mechanism against foreign particles. Lymph nodes are small bean-shaped organs localised at specific sites in the body. They act as a phagocytic filter by preventing unwanted particles from entering blood circulation. Lymph nodes provide a site for lymphocytes to come into contact with antigens, this increases the immune response through lymphocyte proliferation (rapid increase).

Question 4

Describe the organisation of the lymph system

Answer 4

• Organ plexuses (branching networks) drain into lymphatic vessels
• Lymph then passes through lymph nodes
• Most lymph drains through the thoracic duct (AKA left lymphatic duct AKA the largest of the two lymphatic ducts of the body)
• Lymph drains back into the venous system at the left venous angle mostly, even though there is a right lymphatic duct, because the lymph system is assymetrical. The thoracic duct drains lymph from the whole body apart from the right arm and head. See slide 14.

Lymphatic vessels have valves.

*watch youtube video on this

Question 5

Name the lymphoid organs

Answer 5

• Thymus: T-cell development and maturation
• Spleen: filters and site of immune response, destroys erythrocytes
• Tonsils, Adenoids, Appendix: contain lymphoid follicles, sites where lymphocytes reside and can proliferate (rapidly increase in no.)

Bone marrow: produces B-cells, T-cells and macrophages

•Lymph nodes

Question 6

Describe the structure of a lymph node

Answer 6

• similar to a kidney
• afferent lymphatic vessels
• see slide 23
  *

Question 7

Describe the thoracic lymph nodes/ drainage system

Answer 7

The main lymphatic vessel that drains the lymph of the lungs is the left bronchomediastinal trunk.

Subclavian trunk (L) also drains into the thoracic trunk.

The right subclavian trunk drains into the right lymphatic duct.

Question 8

Name the lymph nodes
of the neck

Answer 8

.

Question 9

Name the abdominal lymph nodes

Answer 9

.

Question 10

How does lymph flow without a pump?

Answer 10

• Lymphatic flow aided by peristalsis of surrounding intestinal wall (no smooth muscle in initial lymphatic walls)
• So lymph flow requires valves
• Lymphatic flow is maintained by hydrostatic pressure between interstitial fluid and lymph
• Hydrostatic pressure regulates expansion phase and compression phase

Question 11

What happens in the expansion and compression phases of lymph flow?

Answer 11

• The micro-valves on the walls of the lmyhatic vessel open, when the hydrostatic pressure in the interstitium exceeds that in the lymphatic vessel, so lymph can enter the vessel.
• The secondary valves inside the vessel close when the lymph has entered the vessel, because the hydrostatic pressure in the lymphatic vessel rises. This also causes the secondary valves to open, and lymph flows downstream.