Internal Bleeding
Internal bleeding is extremely serious. You can determine if you have internal bleeding by the color of the blood.
Bright red blood means the blood cells were exposed to oxygen before they died. The function of the blood cells is to bind to oxygen molecules within the lungs and transport oxygen throughout the body. When the cells bind with oxygen, they appear the bright red color we all expect from blood.
For example, when you have a cut the blood is bright red. As the blood emerges from the wound, the cells are still alive. They continue to perform their duty and bind to oxygen in the air has they emerge from the wound. For pooping blood, this means the bleeding occurred as you had a bowel movement. The most likely cause is a hemorrhoid.
Dark or black blood is a sign of internal bleeding. This means either the blood cells died, or the blood is lacking oxygen. The dead cells no longer bind oxygen molecules. If you had internal bleeding in the digestive track, the environment lacked oxygen. In addition, the blood may have spent enough time in the intestine that the cells died.
If you see dark or black blood, seek medical help as soon as possible and explain the symptoms to them.