Lymphatics and Capillary Structure

Lymphatics

• Lymphatics is a system for fluid transport, consisting of capillaries, vessels, and nodes.
• Capillaries have thin walls, increasing the surface area for exchange.
• Capillaries' narrow lumen forces RBCs against the walls.
• Spaces between the capillary lining allow white blood cells to pass.
• Lymph is formed from tissue fluid (interstitial fluid).
• Tissue fluid is formed from blood plasma at the arterial end of capillaries.
• Lymph is then transported via lymphatic vessels.
• Lymphatic vessels transport lymph throughout the body.

Intended Learning Outcomes

• Describe the structure of a capillary and how it relates to its function. Key aspects include thin walls, large surface area for exchange, and narrow lumen.
• Describe interstitial fluid and how it's formed. Formation involves hydrostatic pressure forcing fluid from the capillaries.
• Describe how lymph is formed and its content. Lymph is formed when interstitial fluid enters lymphatic capillaries.
• Describe the lymphatic system (conducting system and lymphoid tissue). This includes the path lymph takes from capillaries to the venous system.
• Briefly describe the roles of primary and secondary lymphatic organs. This involves naming and identifying roles.
• Describe the structure of a lymphatic capillary. It includes the characteristics relevant to its function like blind-ended bulbous tubes to allow fluid entry and smooth muscles for unidirectional transport.
• Define oedema and describe two physiological situations associated with oedema. Oedema is swelling due to excess interstitial fluid. Examples include Elephantiasis (nematode worms in lymphatic vessels) and low plasma protein (Kwashiorkor).

Capillary Structure and Function

• Thin walls decrease diffusion distance
• Numerous/highly branched increases surface area for exchange
• Narrow lumen squashes RBCs against sides, reducing diffusion distance
• Spaces between the endothelial lining let white blood cells pass.

Capillary Microcirculation

• Blood flow moves into the capillary.
• Hydrostatic pressure forces fluid out.
• Osmotic pressure draws fluid back into the capillary from the interstitial fluid.

Lymphatic System- Conducting System and Lymphoid Tissue

• The lymphatic system's conducting system comprises lymphatic capillaries, vessels, and thoracic ducts. It collects fluid and returns it to the bloodstream.
• The conducting system collects lymph throughout the body and returns it to the venous system.

Lymphatic Capillaries

• Blind-ended, bulbous tubes.
• Endothelial cells form walls, allowing fluid/protein/bacteria entry but preventing exit.
• Collects fluid into lymphatic vessels.
• Contains unidirectional valves to prevent backflow.

Lymphoid Tissue

• Involved in immune responses, containing lymphocytes and other white blood cells within connective tissue.
• Tissues include tonsils, adenoids, lymph nodes, thymus, spleen, Peyer's patches, appendix, and bone marrow
• Lymphocytes and other cells are enmeshed in the connective tissue through which lymph passes.

Primary Lymphoid Organs

• Thymus and bone marrow
• Production of lymphocytes, early selection of lymphocytes
• Generate lymphocytes from immature cells

Secondary Lymphoid Organs

• Lymph nodes, spleen, Peyer's patches, tonsils (and adenoids)
• Maintain mature naïve lymphocytes, initiate an acquired immune response
• Sites of lymphocyte activation

Oedema

• Swelling due to excess interstitial fluid
• Caused by increased filtration exceeding lymphatic drainage or dysfunction.
• Causes include Elephantiasis (nematode worms in lymph vessels) and low plasma protein

Why Might Filtration Be Increased?

• Net water flow depends on balance between osmotic (related to protein content in capillary) and hydrostatic (artery/vein pressures) pressures.

This quiz explores the lymphatic system and the structure of capillaries. You will learn about the formation of tissue fluid, how lymph is transported through vessels, and the functional aspects of capillary anatomy. Test your understanding of these critical concepts in fluid transport and immune function.