Ch. 18 - The Lymphatic System

Question 1

Identify the major components of the Lymphatic system.

Answer 1

The Lymphatic system consists of many vessels including:

• Lymphatic Pathways
• Lymphatic Capillaries
• Lymph Nodes
• Lymphatic Trunks
• Collecting Ducts
• Tonsils
• Appendix
• Peyer’s Patches(small intestine/ileum)

Lymphatic system transports a fluid called Lymph which is filtered in a variety of ways:

• Lymph Nodes-structures important in the filtering of Lymph
• Spleen-important in the filtering of the blood

Lymph is drained from the body via:

• Thoracic Duct-drains mostly from left side of the body
• Right Lymphatic Duct-drains mostly from the right side of the body

Question 2

Describe the structure of lymphoid tissues, vessels and organs.

Answer 2

Except for the Thymus, all Lymphoid organs consist mostly of Lymphoid tissue, which is mostly made up of loose, reticular connective tissue.

Lymphatic vessels are similar to veins, having 3 tunics, but the layers are thinner

Lymphatic capillaries consist of a single layer of squamous epithelium that allows tissue fluid to enter

Like veins, lymphatic vessels have valves that prevent backflow of lymph, but there are more of them

Anastamoses also exist within the lymphatic system, but occur more frequently

Question 3

Describe the major functions of the lymphatic system.

Answer 3

Structural basis of the immune system.

Primary function of the system is the production(lymphopoiesis), maintenance and distribution of lymphocytes.

The Lymphatic system transports Lymph and other fluids so interstitial fluid does not accumulate in tissue spaces(up to 3ltrs per day).

It absorbs digested fats and sends them to the venous circulation.

It coordinates the destruction of infectious micro-organisms and viruses, pathogens, toxins and cancer cells.

It produce lymphocytes, which defend the body by producing antibodies for its defense

Question 4

Describe the organisation of the lymphatic system

Answer 4

Lymphatic capillaries extend into interstitial spaces in complex networks

Fluid inside the capillaries is called Lymph

Lymphatic capillaries form tiny tubes called lymphatic pathways, which merge to form larger vessels, eventually uniting with veins in the thorax

The larger Lymphatic vessel valves prevent backflow, meaning lymph only flows through them toward the heart

Lymphatic vessels lead to specialised organs known as lymph nodes, then continue on to form larger lymphatic trunks

Skin lymphatics are routed alongside superficial veins, but in the trunk and digestive viscera the deeper lymphatic vessels are found alongside the deep arteries

The major lymphatic trunks of the body are paired:

• lumbar trunks
• bronchomediastinal trunks
• subclavian trunks
• jugular trunks

and the single - intestinal trunk

The lymph from the lympahtic vessels drains when they meet 1 of the 2 collecting ducts - Right Lymphatic Duct & the Thoracic Duct

Right Lymphatic Duct:

• lymph drainage from R upper limb, and Right side of the head, neck and thorax
• empties into the right subclavian vein near the right jugular vein

Thoracic Duct:

• larger and longer
• lymph drainage from lower limbs, abdomen, left upper limb, left side of head, neck and thorax
• empties into the left subclavian vein near the left jugular vein
• arises anteriorly to the first 2 lumbar vertebrae as the Cisterna Chyli, an enlarged sac, collecting lymph from the lumbar trunks and the intestinal trunk
• the superior portion of the thoracic duct recieves lymph from the left upper limb and the left side of the head, neck and thorax

Lymph moves from the 2 collecting ducts into the venous system, becoming part of the plasma, just before the blood is returned to the right atrium

as the lymphatic system has no organ to ‘pump’ the Lymph, it’s movement is controlled in the same way as the blood through the venous system, relying on skeletal and respiratory pumps