The lymphatic system complements the circulatory system by draining 10% of interstitial fluid into lymphatic capillaries to form lymph. Lymph moves through lymphatic vessels via muscle contraction and enters the circulatory system through the right and left subclavian veins. While blood, interstitial fluid, and lymph are all liquid transports, they differ in their protein, oxygen, and lipid contents. If interstitial fluid fails to return to the circulatory system, it can accumulate and cause edema in tissues. The lymphatic system works with the circulatory system to transport interstitial fluid back to the heart.

1. BIOLOGY FORM 5

2. L E A R N IN G
O U TC O M E S
• Explain how the lymphatic system
complements the circulatory system;
• Compare the content of blood,
interstitial fluid & lymph;
• Predict what will happen if interstitial
fluid fails to return to the circulatory
system;
• Conceptualise the relationship
between the lymphatic system &
circulatory system.

4. THE LYMPHATIC SYSTEM
COMPLEMENT THE CIRCULATORY
SYSTEM
• 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.

5. COMPARE THE CONTENT OF BLOOD,
INTERSTITIAL FLUID
& LYMPH
BLOOD INTERSTITIAL LYMPH
FLUID
SIMILARITIES
• Watery
liquid
•Transport gases, nutrients &
waste products.

6. COMPARE THE CONTENT OF BLOOD,
INTERSTITIAL FLUID & LYMPH
BLOOD INTERSTITIAL FLUID LYMPH
DIFFERENCES
Inside blood vessel In the intercellular Inside the lymphatic
spaces vessels
More protein than Less protein than More protein than
interstitial fluid & blood & lymph interstitial fluid but less
lymph than blood
Oxygenated Oxygenated Deoxygenated
Erythrocytes, Only leucocytes Only leucocytes
leucocytes & platelets present present
present
Low lipid content Low lipid content High lipid content

8. If In t e r s t it ia l F lu id F a ils
to R e turn to th
C ir c u la t o r y S y s t e m
• It accumulates in the organs &
tissues  the organs & tissues
swell up  oedema.
• Interstitial fluid should return to
the CS at the same rate as it is
produced.

10. THE RELATIONSHIP BETWEEN
LYMPHATIC SYSTEM & BLOOD
CIRCULATORY SYSTEM
• LS & BCS transport interstitial fluid back
to the heart.
• The LS joins the BCS when the right
lymphatic duct opens into the right
subclavian vein & the thoracic duct opens
into the left subclavian veins.