Lymphatic System: Third Purpose and Review

Third Purpose of the Lymphatic System: Transport

  • The lymphatic system has a third purpose: to transport substances into the blood that don't originate from it.

Absorption in the Small Intestine

  • The small intestine absorbs nutrients like glucose and fats.
  • Glucose is absorbed into intestinal cells and then pumped out into the surrounding space, where it diffuses into nearby capillaries.
  • Once in the capillaries, glucose spreads throughout the body to feed various cells.

Fat Absorption and Chylomicrons

  • Fatty acids are also absorbed by intestinal cells.
  • Once processed, they are packaged into large spherical objects called chylomicrons.
  • Chylomicrons consist of a carboxylic acid group attached to a long chain of carbons.
    • They are useful for holding a lot of fats together.
  • Because of their size, chylomicrons cannot diffuse into capillaries.

Role of Lymphatic Vessels (Lacteals)

  • Lymphatic vessels, specifically lacteals in the small intestine, provide an alternative route for chylomicron transport.
  • Chylomicrons diffuse into lacteals and are transported through the lymphatic system.
  • They eventually empty into the blood circulation, allowing fats to be distributed throughout the body.

Generalizing the Transport Function

  • The lymphatic system transports substances that don't come directly from the blood.
  • Example: Cells produce hormones or waste products.
  • These substances may have difficulty entering capillaries directly.
  • Lymphatic vessels provide a secondary route to get these substances into the blood.
Examples of Substances Transported
  • Hormones: Need to travel throughout the body to affect target tissues.
  • Waste Products: Need to get to the liver for breakdown or the kidneys for excretion.

Review of the Lymphatic System's Purposes

  • Three main purposes of the lymphatic system:
1. Fluid Recovery
  • Collects fluid forced out of capillaries due to high blood pressure.
  • Returns fluid (containing small plasma proteins) back into blood circulation.
  • Prevents excessive fluid accumulation in tissues.
2. Immune System Support
  • Transports bacteria and pathogens from infected tissues to lymph nodes.
  • Lymph nodes contain B cells and T cells, which initiate immune responses.
3. Transport of Non-Blood Substances
  • Transports substances like chylomicrons, hormones, and waste products into the blood.
  • Provides an alternative route for substances that cannot directly enter capillaries.