C.A.B.M. | 2024
1
The Lymphatic System and Body Defenses
Part I: The Lymphatic System
Structure and Components
• Two parts:
1. Lymphatic Vessels: Transport lymph
(fluid) back to the blood.
2. Lymphoid Tissues and Organs: House
cells for body defense and fluid balance.
Functions
1. Fluid Balance:
o Returns ~3L of fluid/day from tissues to
the blood.
o Lymph consists of:
▪ Water, solutes from blood
plasma (ions, nutrients, gases,
proteins), and cell waste
products.
2. Lipid Absorption:
o Lipids and substances absorbed via
lacteals in the small intestine.
o Lymph appears white due to lipid
content (chyle).
3. Defense:
o Filters pathogens from lymph (by
lymph nodes) and blood (spleen).
o Plays essential roles in body defense
and resistance to disease
Lymphatic Vessels
• Lymph consists of excess tissue fluid and plasma
proteins carried by lymphatic vessels
• If fluids are not picked up, edema occurs as fluid
accumulates in tissues
• Lymphatic vessels (lymphatics) pick up excess fluid
(lymph) and return it to the blood
• Structure:
o One-way system; lymph flows toward
the heart.
o Thin-walled with valves to prevent
backflow; larger vessels have valves
o Low-pressure, pumpless system;
transport aided by:
▪ Skeletal muscle contraction.
▪ Thoracic pressure changes
during breathing.
▪ Smooth muscle contraction in
vessel walls.
• Pathway:
o Lymph Capillaries: Weave between
tissue cells and blood capillaries,
allowing fluid entry through flaplike
minivalves; fluid leaks.
▪ Capillaries are anchored to
connective tissue by filaments
▪ Higher pressure on the inside
closes minivalves
▪ Fluid is forced along the vessel
o Lymphatic Collecting Vessels: Transport
lymph to and away from lymph nodes.
▪ Collect lymph from lymph
capillaries
o Lymphatic Ducts:
▪ Return fluid to circulatory veins
near the heart
▪ Right Lymphatic Duct:
Drains lymph from the
right upper body.
▪ Thoracic Duct: Drains
lymph from the rest of
the body.
