I understand that drinking blood can be seriously unhealthy, but is the human digestive system capable of digesting blood?

Yes it can..: Blood composes of red + white cells, platelets, and proteins/minerals. The cells are basically proteins/lipids + some fluid/minerals, and the red cells contain heme/iron giving it the red appearance. Red/raw meats contain blood and your gut can digest it fine. Carnivores consume meats/blood and digest it fine as well. I not sure if this is the answer you are looking for. Consult doc. Good luck.

Yes if not too much: Small amounts of blood are digested. Large amounts, such as would be there if you were bleeding internally, are passed in your bms. A large amount of blood can make your bms black and tarry, but other things that are not serious can also cause black bms. They can be tested for blood. If you are bleeding into your digestive system, get checked.