Red Corpuscles

I need to create hundreds of red corpuscles floating in a vein. I assume you know that, but in case you don’t - they behave like a rigid bodies. They hit vein’s faces, they bounce and so on. To create such effect I used Particle effect and enabled Deflection for my vein. The result was more than just poor. Red Corpuscles were floating out of my vein, even after encreasing the number of Keys, number of Faces for the vein, or Extruding a vein couple a times. Is there a way I can solve this problem?

Sorry for all the mistakes I made in this subject; English is not my native language, you know…

Z góry dziękuję za wszelkie odpowiedzi!!