Sinusoids are characterised by

Options

A. Irregular lumen
B. Absence of endothelium
C. Mixing of blood and lymph
D. Both B and C.

Answer

To answer the question "Sinusoids are characterized by," we will analyze the characteristics of sinusoids step by step.

### Step-by-Step Solution:

1. **Definition of Sinusoids**:
Sinusoids are specialized types of blood vessels that are wider than capillaries and have a discontinuous endothelium. They allow for the passage of larger molecules and cells.

2. **Irregular Lumen**:
One of the main characteristics of sinusoids is their irregular lumen. Unlike the uniform shape of capillaries, sinusoids have a variable and often irregular shape, which facilitates the mixing of blood and the exchange of substances.

3. **Absence of Endothelium**:
This statement is incorrect. Sinusoids do have a lining, but it is not a continuous layer of endothelial cells as seen in typical blood vessels. Instead, they have a reticular endothelium that is discontinuous.

4. **Mixing of Blood and Lymph**:
Sinusoids are primarily involved in the circulation of blood. They do not mix blood and lymph; rather, they are involved in the filtration and exchange processes within organs like the liver and spleen.

5. **Conclusion**:
Based on the characteristics discussed, the correct answer to the question is that sinusoids are characterized by an irregular lumen.

### Final Answer:
Sinusoids are characterized by an irregular lumen.