Two biology questions

[scissorrunner22]

Hello everyone!

Could someone please clarify the following two things for me:
1. Why does blood travel the slowest in capillaries? I thought that blood flow velocity is lowest in veins based on a diagram that I saw in Campbell Biology
2. What is a blood clot made of? I read that it consists of platelets and fibrin fibers, but DAT Destroyer said it is red blood cells instead of platelets

Thank you so much in advance!

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[510586]

1. Because it has the largest cross sectional area. Pressure is lowest in veins but speed is lowest in the capillaries. blood velocity is inversely proportional to total cross-sectional area. BP is highest in aorta then goes lowest from there.
2. Platelets are at the open wound, contacting collagen, so they release thromboplastin. Then thromboplastin converts prothrombin to thrombin which converts inactive fibrinogen into fibrin. The fibrin coats red damaged area and trap red blood cells to form a clot.