The Lymphatic system

Question 1

What is the lymphatic system?

Answer 1

The lymphatic system absorbs dietary fat from the intestine, protects the body from foreign invaders, and maintains ECF volume by returning excess tissue fluid to the blood.

It consists of lymph, lymphocytes, lymphatic plexuses and vessels, lymph nodes and other lymphoid organs.

Question 2

Describe the journey of lymph through the lymphatic system

Answer 2

The lymphatic capillaries carry the lymph first through lymphatic plexuses, to lymphatic vessels, then to lymphatic trunks and finally drains into the venous system through the thoracic duct and the right lymphatic duct.

The lymph nodes are scattered throughout the body, and filter the lymph as it travels to the venous system.

Question 3

What does this image show?

Answer 3

Valves are the denser green sections. The lymphatic capillaries communicate w the deep collecting vessels

Question 4

What is lymph?

Answer 4

Lymph is formed from interstitial (tissue) fluid

Interstitial fluid originates as a plasma filtrate

Lymph contains salts, proteins, fat and cells (the cells are mainly lymphocytes but also dendritic cells and macrophages)

Question 5

What are lymph nodes/glands?

Answer 5

Lymph travels from lymphatic capillaries to collecting vessels, into lymph nodes

Lymph nodes filter the lymph (they filter particulates and organic matter) and check to see if there are any foreign invaders the body needs to attack using B and T lymphocytes

Question 6

Label this lymph gland

Answer 6

Question 7

Why is the lymphatic system so important in immunity?

Answer 7

Lymph vessels absorb the microbes responsible for an infection and transport them to lymph glands for acquired immunity.

Secondary Lymphoid Organs are filters where foreign invaders are captured, and lymphocytes are activated. SLOs inc:

• Lymph nodes
• Mucosa-associated lymphoid tissue (MALT) e.g. tonsils, Peyer’s patches of the small bowel
• Spleen

Question 8

How does the lymphatic system respond to an infection like Covid?

Answer 8

The lymphatic vessels bring info about the infection in the lymph to the lymph node. This enables lymphocytes in the lymph node to develop to fight the infection.

B cells produce antibody and T cells develop the ability to kill other infected cells. Lymphocytes leave the lymph glands to kill off the infection. Ongoing information will refine and strengthen the capability of the lymphocytes to fight the infection

Question 9

What is tissue fluid homeostasis?

Answer 9

Tissue fluid is formed from plasma escaping through the blood vessel wall

Tissue (interstitial) fluid drains predominantly as lymph and not by venous reabsorption

Question 10

Using starling’s principle of fluid exchange, explain why pulmonary oedema occurs in left sided heart failure

Answer 10

• The lung generates lymph even though pulmonary capillary pa(10mmHg)< plasma osmotic pa (25mmHg).
• Pulmonary capillaries are in a filtration state because pulmonary interstitial protein conc is high. So, the osmotic pa gradient is lower than the Hydraulic pa gradient.
• Left sided heart failure increases pulmonary capillary pressure, increasing filtration. Unless lymph drainage increases accordingly, oedema occurs in lung parenchyma.
• Interstitial fluid can overflow into alveoli and impair O2 exchange

Question 11

How is the lymphatic system related to cancer?

Answer 11

Cancer spreads during metastasis, preferentially by the lymphatic system. In the lymphatic system, they may be killed off by our immune cells in the lymph

Sentinel lymph node biopsy (taking an axila lymph node to look for cancer cells) is the recommended staging investigation for breast cancer. Helps inform treatment plans

Question 12

What is pitting oedema?

Answer 12

Indicates an excess of interstitial fluid. Results from:

• too much fluid filtration from blood vessels, overwhelming lymph drainage
• or too little lymph drainage

Question 13

What is venous oedema?

Answer 13

Varicose veins or venous engorgement e.g. heart failure, creates high venous pa. This increases microvascular fluid filtration into tissues.

If lymph drainage is adequate then oedema can be avoided

Question 14

What is lymphoedema?

Answer 14

Lymphoedema occurs when hay a failure of lymph drainage with no increase in capillary filtration (normal lymph load)

• e.g. breast cancer related lymphoedema- lymph gland has been removed or radiation damaged the lymph drainage pathway
• Elephantiasis- a worm infection transmitted by mosquitoes which blocks lymph vessels
• Primary lymphoedema is due to an inborn, presumed genetic, fault in lymph drainage

Question 15

What is cellulitis?

Answer 15

Cellulitis is a common complication of impaired lymph drainage and is often recurrent.

Impaired immune cell trafficking causes a failure to eradicate the infection- causing serious inflammation.

Question 16

How is the lymphatic system involved in fat transport?

Answer 16

• The mucosa of the small intestine is covered w fingerlike projections called villi.
• Special lymph capillaries called lacteals in the center of each villus absorb the fats from the intestine.
• The lymph capillaries merge to form collecting vessels, which lead to the lymph nodes. These filter the lymph before it enters the blood.
• The lymph eventually empties into the subclavian veins that feed blood back to the heart. The lymphatic system absorbs fat, and lymph flows back very slowly to venous circulation.

So fat level never rises sharply in blood and it helps in maintaining the health of arterial walls.

Question 17

What can disordered lymphatic fat transport can lead to?

Answer 17

Intestinal lymphactasia= fat malabsorption- eating fat rich food causes diarrohea and abdonminal pain. Due to abnormal lymphatics of the gut.

Lymph drainage is important for peripheral fat transport- impaired lymph drainage and lymphoedema causes increased peripheral tissue fat deposition

Could lead to obesity?- Obesity itself also impairs lymph drainage which results in more peripheral fat being deposited- vicious cycle