2.20 Lymphatic System of Man

The lymphatic system is a network of tissues, vessels, and organs that work together to return excess interstitial fluid to the blood, absorb fats from the digestive system, and provide immune defense. It includes lymph, lymphocytes, lymphatic vessels, lymph nodes, tonsils, spleen, and thymus gland.

Definition

• Returns excess interstitial fluid to the blood
• Absorbs fats and fat-soluble vitamins from the digestive system
• Provides immune defense against pathogens

Lymph: Lymph is the fluid that enters the lymphatic capillaries. It is derived from blood plasma and interstitial fluid.

Main Idea

• Returns fluid to the blood
• Absorbs fats from the digestive system (as chyle)
• Defends the body against infection
• Filters blood and lymph
• Produces lymphocytes

Core Concept

• Lymphatic capillaries = microscopic, closed-ended tubes
• Lymphatic vessels = formed by merging capillaries; have valves
• Lymphatic trunks = drain larger portions of the body
• Collecting ducts = thoracic duct and right lymphatic duct
• Lymph nodes = filter lymph; contain lymphocytes and macrophages
• Spleen = filters blood; stores blood and iron; produces lymphocytes
• Thymus = produces T lymphocytes
• Tonsils = lymphoid tissue in the throat

Detailed Explanation

Lymphatic Capillaries

• Lymphatic pathways begin as lymphatic capillaries.
• These are microscopic, closed-ended tubes.
• They extend into the spaces within interstitial spaces.
• They form complex networks that parallel the networks of blood capillaries.
• The walls of the lymphatic capillaries, like those of blood capillaries, consist of a single layer of squamous epithelial cells.
• This thin wall makes it possible for interstitial fluid from interstitial spaces to enter the lymphatic capillary.
• Once the fluid is inside a lymphatic capillary, it is called lymph.
• Each villus contains a lymph capillary called a lacteal.
• The lacteal absorbs fats and other substances from the digestive tract.

Lymphatic Vessels

• Lymphatic vessels are formed by merging of lymphatic capillaries.
• They have walls similar to those of veins.
• Like veins, lymphatic vessels have flap-like valves.
• Valves help to prevent the backflow of lymph.
• Typically, the lymphatic vessels lead to specialized organs called lymph nodes.
• After leaving these structures, the vessels merge to form still larger lymphatic trunks.

Lymphatic Trunks

• Lymphatic trunks drain lymph from relatively larger portions of the body.
• They are named for the region they serve.
• The lymphatic trunks then join one of two collecting ducts:
• Thoracic duct
• Right lymphatic duct

• The larger and longer of the two collecting ducts.
• Receives lymph from:
• Lower body regions
• Left side
• Left side of the head and neck
• Empties into the left subclavian vein near the junction of the left jugular vein.

• Receives lymph from:
• Right side of the head and neck
• Right arm
• Right thorax
• Empties into the subclavian vein near the junction of the right and jugular vein.

Lymph Nodes

- The lymph nodes are structures located along the lymphatic pathways.

• Contain a large number of lymphocytes.
• Act against foreign particles, such as bacteria and viruses.
• Contain macrophages, which engulf and destroy foreign substances, damaged cells, and cellular debris.

Spleen

• Helps get rid of germs.
• Contains white blood cells called lymphocytes and macrophages.
• These cells work to attack and destroy germs and remove them from the blood that passes through the spleen.
• Filters blood by removing cellular waste and getting rid of old or damaged blood cells.
• Stores blood and iron for future use.
• Makes white blood cells and antibodies that help to fight infection.
• Maintains the levels of fluid in your body.

Tonsils

• Tonsils are lymphoid tissue located in the throat.
• They help protect against infection.

Thymus

• The thymus is a lymphoid organ located in the upper chest.
• It produces T lymphocytes.
• It is most active during childhood.

Intermediate Level

Lymphatic System Components

Lymphatic Vessels and Valves

Lymph Nodes

Spleen

Thymus

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Lymphatic system returns excess fluid to the blood.
• 2. Lymphatic capillaries are microscopic, closed-ended tubes.
• 3. Lymphatic vessels have valves to prevent backflow.
• 4. Lymphatic trunks drain larger portions of the body.
• 5. Thoracic duct is the larger collecting duct.
• 6. Right lymphatic duct is the smaller collecting duct.
• 7. Thoracic duct drains lower body and left side.
• 8. Right lymphatic duct drains right upper body.
• 9. Lymph nodes filter lymph.
• 10. Lymph nodes contain lymphocytes and macrophages.
• 11. Spleen filters blood.
• 12. Spleen stores blood and iron.
• 13. Spleen produces lymphocytes and antibodies.
• 14. Thymus produces T lymphocytes.
• 15. Tonsils protect against infection.

Remember

• - Lymphatic system = returns fluid; absorbs fats; defends body
• - Lymphatic capillaries = microscopic, closed-ended
• - Lymphatic vessels = have valves
• - Lymphatic trunks = drain larger portions
• - Thoracic duct = larger; lower body, left side
• - Right lymphatic duct = smaller; right upper body
• - Lymph nodes = filter lymph
• - Spleen = filters blood; stores blood and iron
• - Thymus = produces T lymphocytes
• - Tonsils = protect against infection
• - Lacteal = lymph capillary in villus
• - Chyle = lymph from digestive system

Common Mistakes

• 1. Confusing lymphatic capillaries and blood capillaries — Lymphatic capillaries are closed-ended; blood capillaries are not.
• 2. Thinking lymph flows toward the heart — Lymph flows toward the heart, but it is not pumped by the heart.
• 3. Forgetting the role of valves — Valves prevent backflow in lymphatic vessels.
• 4. Mixing up the collecting ducts — Thoracic duct is larger; right lymphatic duct is smaller.
• 5. Confusing the drainage areas — Thoracic duct drains lower body and left side; right lymphatic duct drains right upper body.
• 6. Thinking the spleen only filters blood — The spleen also stores blood and iron, and produces lymphocytes.
• 7. Forgetting the role of the thymus — The thymus produces T lymphocytes.
• 8. Mixing up lymph nodes and tonsils — Lymph nodes are along lymphatic pathways; tonsils are in the throat.
• 9. Believing lymph is the same as blood — Lymph is a clear fluid; blood contains red blood cells.
• 10. Thinking the lymphatic system has a pump — It does not have a pump; lymph is moved by skeletal muscle contraction and respiratory movements.

Quick Revision

The lymphatic system is a network of tissues, vessels, and organs that work together to return excess interstitial fluid to the blood, absorb fats from the digestive system, and provide immune defense. It includes lymph, lymphocytes, lymphatic vessels, lymph nodes, tonsils, spleen, and thymus gland. Lymphatic capillaries are microscopic, closed-ended tubes that collect interstitial fluid. Lymphatic vessels have valves to prevent backflow. Lymphatic trunks drain larger portions of the body. The thoracic duct is the larger collecting duct; it drains the lower body and left side. The right lymphatic duct drains the right upper body. Lymph nodes filter lymph and contain lymphocytes and macrophages. The spleen filters blood, stores blood and iron, and produces lymphocytes and antibodies. The thymus produces T lymphocytes. Tonsils protect against infection.

60-Second Revision

• Lymphatic system = returns fluid; absorbs fats; defends body
• Lymphatic capillaries = microscopic, closed-ended
• Lymphatic vessels = have valves
• Lymphatic trunks = drain larger portions
• Thoracic duct = larger; lower body, left side
• Right lymphatic duct = smaller; right upper body
• Lymph nodes = filter lymph
• Spleen = filters blood; stores blood and iron
• Thymus = produces T lymphocytes
• Tonsils = protect against infection
• Lacteal = lymph capillary in villus
• Warning: Lymphatic system has no pump; lymph moves by skeletal muscle contraction and respiratory movements

CHAPTER COMPLETED

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• 2. Blood Circulatory System of Man

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• 3. Respiratory System of Man

• First Topic:
• 3.1 PROPERTIES OF RESPIRATORY SURFACE

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