Lymphatic System and Capillary Function

Lymphatics

• The lymphatic system is a network of vessels, tissues, and organs that help maintain fluid balance and fight infection.
• Capillaries have thin walls that decrease diffusion distance and are numerous and highly branched to increase the surface area for exchange.

Capillary Structure and Function

• Capillary walls are thin, which minimizes the diffusion distance.
• Numerous and highly branched capillaries provide a large surface area for exchange.
• The lumen is narrow, squeezing RBCs against the capillary wall, reducing diffusion distance.
• Spaces between the endothelial cells enable white blood cells to pass through.

Capillary Microcirculation

• Blood flow from the arterial side to venous end.
• Hydrostatic pressure forces fluid out of the capillary.
• Osmotic pressure draws fluid back into the capillary.
• Interstitial fluid is the fluid outside the capillaries.

Lymphatic System - Conducting System and Lymphoid Tissue

• The conducting system consists of lymphatic capillaries, lymph vessels, and thoracic ducts.
• The conducting system carries lymph.
• Lymphatic tissue consists of lymphocytes and other white blood cells in connective tissue.
• Lymphatic tissue is primarily involved in immune responses.
• Lymphoid tissue can be primary, secondary, or tertiary.

Lymphatic Capillaries

• Lymphatic capillaries are blind-ended, bulbous tubes.
• Their walls are composed of endothelial cells.
• They are permeable to fluids, proteins, and bacteria.
• They prevent the backflow of fluids into the tissues.
• They merge with collecting lymphatics.
• Lymph vessels contain smooth muscle and unidirectional valves.

Lymphatic System Organization

• Blood capillaries filter fluid into interstitial spaces.
• Lymph capillaries collect fluid, proteins, and bacteria from tissues.
• Lymph flows through lymph vessels.
• Lymph nodes filter lymph.
• Lymph returns to the bloodstream via veins.

Lymphoid Tissue

• Tonsils and adenoids
• Lymph nodes
• Spleen
• Peyer's patches
• Appendix
• Bone marrow

Primary Lymphoid Organs

• Thymus and bone marrow
• These organs produce and early select lymphocytes.
• They generate lymphocytes from immature cells

Secondary Lymphoid Organs

• Lymph nodes, spleen, Peyer's patches, adenoids, and tonsils.
• They maintain mature naïve lymphocytes and initiate an acquired immune response.
• They are sites of lymphocyte activation.

Oedema

• Oedema is swelling in tissues due to excess interstitial fluid.
• Occurs when lymphatic drainage is insufficient to remove excess fluid.

Elephantiasis

• A condition characterized by severe swelling in the limbs.
• Caused by a parasitic nematode worm blocking lymphatic vessels.

Why Might Filtration Be Increased?

• The net flow of water across capillary walls is determined by the balance between osmotic pressure and capillary hydrostatic pressure.
• Increased filtration can occur if osmotic pressure decreases or capillary hydrostatic pressure increases.

Low Plasma Protein - Kwashiorkor

• A disease resulting from insufficient protein intake.
• Leads to reduced plasma protein levels, potentially impacting osmotic pressure and fluid balance.

Brief Recap

• Filtration occurs at the capillaries, resulting in interstitial fluid.
• Lymph formation occurs by interstitial fluid entering lymphatic capillaries.
• Lymphatic vessels transport lymph through the body.
• Lymphoid tissue filters and processes lymph.
• Primary and secondary lymph organs are sites of production and activation.
• Oedema results from impaired lymphatic drainage.