Lymph lacks Red Blood Cells (RBCs) primarily because RBCs do not normally leave the bloodstream to enter the extracellular fluid (ECF).
Understanding Lymph and Blood Circulation
Before diving into why lymph lacks RBCs, let's understand the basics:
- Blood: Circulates within a closed system of vessels, including arteries, veins, and capillaries. It carries oxygen, nutrients, and other vital substances.
- Lymph: A fluid that circulates through the lymphatic system, collecting waste products, cellular debris, and pathogens from the body's tissues.
- Extracellular Fluid (ECF): The fluid surrounding cells in the body's tissues.
Why RBCs Stay Out of Lymph
The key reason why lymph doesn't contain RBCs is that under normal conditions, red blood cells are confined to the blood vessels.
| Feature | Blood | Lymph |
|---|---|---|
| Primary Contents | RBCs, plasma, platelets, WBCs | Plasma, WBCs, Waste Products, Pathogens |
| Circulation System | Closed system of blood vessels | Open system of lymphatic vessels |
| Contains RBCs | Yes | No |
As the reference states, "Red Blood Cells do not enter the extra cellular space except when the capillaries are damaged. Since RBC's do not enter the ECF, RBC do not appear in the lymphatic fluid."
This means:
- Intact Capillaries: Red blood cells are large and cannot pass through the walls of healthy capillaries into the ECF.
- ECF Origin of Lymph: Lymph is essentially ECF that has entered the lymphatic system. Since RBCs do not typically enter the ECF, they will not be found in the lymph.
Exception to the Rule
While lymph typically doesn't have RBCs, there are exceptions. For example, during an injury or trauma, blood vessels, including capillaries, may be damaged. In these cases:
- RBC Leakage: Red blood cells can leak out of damaged blood vessels and enter the ECF. If this ECF finds its way into the lymphatic system, the lymph may temporarily contain RBCs.
Summary
In summary, lymph lacks red blood cells because RBCs are primarily confined to the blood vessels and do not typically pass into the extracellular fluid, which is the source of lymph. Only when there is damage to blood vessels do RBCs make their way into ECF, and consequently the lymphatic system.
