The lymphatic system is part of the circulatory and immune systems. It is made up of lymphatic vessels, ducts, and nodes that transport lymph fluid throughout the body. Interstitial fluid is formed from blood in capillaries and carries nutrients to cells, before 10% drains into lymphatic capillaries as lymph. Lymph is moved through the lymphatic system by muscle movement and flows into the subclavian veins. The lymphatic system includes lymph nodes that help fight infection.

1. BIOLOGY FORM 5

2. L YM P H A T IC S YS T E M

3. L E A R N IN G
O U TC O M E S
1. Describe the formation of interstitial
fluid
2. State the composition of interstitial
fluid
3. State the importance of interstitial
fluid
4. Describe the fate of interstitial fluid
5. Describe the structure of the
lymphatic system

4. THE LYMPHATIC SYSTEM
• Part of the circulatory system & immune system.
• A closed system  consist of a network of lymphatic
vessels, ducts & nodes.
• No pump, the fluid (lymph) id squeeze along the
lymphatic vessels by pressure associated with
movements of skeletal muscles, intestinal movements
& breathing.
• Thymus & spleen are important organs of lymphatic
system.

7. F O R M A T IO N O F
IN T E R S T IT IA L
F L U ID
• Blood flows from arteries 
capillaries, there is a higher
hydrostatic pressure at the arterial
end of the capillaries

9. LYMPHATIC FLUID
• Oxygenated blood @ arterial end of the
capillaries  high pressure  force water &
dissolved substances out  capillary wall 
interstitial spaces (spaces between cells) 
interstitial fluid/ tissue fluid/ extracellular fluid.
• Erythrocytes & plasma protein are too large to
pass through  remain in the capillary.

10. COMPOSITION OF INTERSTITIAL
FLUID
• Contains water + dissolved oxygen + amino acids +
glucose + fatty acids + glycerol + vitamins + minerals +
hormones.
• An adult has ~11 litres of interstitial fluid providing the
cells of the body with nutrients & a means of waste
removal.
• At the venous end of the capillary  90% absorbs by
blood consists of water, minerals & waste products.
• The rest  passes back into the BCS as lymph via the
LYMPHATIC SYSTEM.

11. The Importance of Interstitial
Fluid
• Carries dissolved substances (O2,
amino acids, glucose, fatty acids,
glycerol, vitamins, minerals &
hormones) to cells for exchange.
• Carries waste products (CO2, urea,
etc.) into BCS.

12. THE FATE OF INTERSTITIAL
FLUID
• 10% of interstitial fluid  drains into the
lymphatic capillaries forming lymph.
• Move due to the contraction & relaxation of
skeletal muscles  backflow is prevented by
semilunar valves.
• Lymph in the right lymphatic duct & the
thoracic duct  flows into the right & left
subclavian veins of the BCS, respectively.

15. THE STRUCTURE OF THE LYMPHATIC
SYSTEM
• Starts from the minute blind-ended tubes
including lacteals (in the ileum) & lymphatic
capillaries in other tissues.
• Lymphatic capillaries  form larger
lymphatic vessels  lymphatics.
• Semilunar valves are present along the
lymphatics.
• Lymphatics from all parts of the body  two
large ducts  the right lymphatic duct, the
thoracic duct.

16. THE STRUCTURE OF THE
LYMPHATIC SYSTEM
• Situated at intervals along the lymphatics
are the oval-shaped structures  lymph
nodes (neck, armpits & groin).
• Lymphocytes are found in the lymph nodes
 produce antibodies & play an important
role in the body’s immune system.
• Phagocytes in the lymph nodes help to
remove bacteria.