6.4

The Lymphatic System

• The lymphatic system is a separate network of vessels that runs alongside the circulatory system.
• It's a network of lymphatic vessels, lymph nodes, lymphoid organs, and lymphatic tissue.
• Its purpose is to provide immunity to fight illness and foreign invaders.
• The fluid in the lymphatic system is called lymph.
• Lymph is composed of extra fluid that drains from cells, and proteins, lipids, and damaged cells, not absorbed by capillaries.
• Excess fluid rejoins the circulatory system at the subclavian veins.
• Lacteals, which absorb lipid digestion products, drain into lymphatic vessels before reaching the subclavian veins.
• Lymph contains white blood cells (lymphocytes) specialized to fight infection.

Lymphatic Structures

• Lymph Vessels: Similar to veins, ensuring one-way flow. Contain valves to prevent backflow.
• Lymph Nodes: Small, round clusters of tissue throughout the body. Connected to lymph vessels. Filter large particles from lymph fluid. Trap bacteria and cancer cells for destruction.
• Lymph nodes can also produce lymphocytes. When debris is trapped, lymphocytes fight bacteria causing nodes to swell and become inflamed (pain). This swelling can be an indicator of immune system activity. Long-term swelling may indicate a serious illness.
• Lacteals: Part of the digestive system; blind sacs in the villi of the small intestine. Absorb fat digestion products (glycerol + fatty acids) which enter the circulatory system at the subclavian veins.

Spleen

• The spleen is the body's largest lump of lymphatic tissue, located in the left abdomen, above the stomach.
• It produces lymphocytes.
• It stores excess blood.
• It regulates blood pressure. If blood pressure is high, the spleen stores excess blood. If low, releases blood into circulatory system.

Thymus Gland

• The thymus is a bi-lobed structure between the lungs.
• It produces special lymphocytes (T cells).
• It's a site for lymphocyte maturation (like a college or university).
• Its size decreases with age, which can affect the body's ability to fight infection.

Tonsils and Appendix

• Located on the sides of the pharynx.
• Contain lymphoid tissue.
• Thought to help remove invading organisms (bacteria).

How the Immune Response Works

• Step 1: Lymphocytes produce antibodies to identify and bind to specific antigens.
• Antibody binding to antigen forms an inactive complex, incapacitating the bacteria and alerting other lymphocytes.
• Step 2: Lymphocytes attack the bacteria through phagocytosis.
• Cells including white blood cells die during this process, often forming pus.

Capillary Fluid Exchange

• Water, gases, nutrients, and wastes are exchanged between blood and body tissues by diffusion and filtration through capillary walls.
• Processes:
  • Hydrostatic pressure: Blood pressure within a vessel.
  • Osmotic pressure: Pressure to stop the flow of solutes across a membrane. Produced by the high concentration of salts and plasma proteins in the blood.
• Blood pressure forces fluid from the capillary into tissue.
• At the middle of the capillary, blood pressure equals osmotic pressure. Gases, nutrients and wastes are exchanged here.
• On the Venule end of the capillary bed, osmotic pressure is higher than blood pressure and fluid moves into capillaries, and waste is filtered out.