Blood is sometimes obvious when it appears in the stools but it can also be undetectable to the human eye. Bright red blood suggests the source is in the lower digestive tract including the colon, anus and rectal areas. Dark black fecal matter suggests the bleeding is from the upper parts of the digestive tract like the throat, esophagus, stomach and small intestines. Blood due to certain disorders or ailments can appear with mucus or take on a jelly-like form. Medical treatment is important for nearly any presence of blood in the stools to rule out serious digestive problems.
Bloody Diarrhea from Bacteria
A bacterial infection is the most common of the causes of blood in the stools, according to MIlton S. Hershey Medical Center College of Medicine. When bacteria enters any part of the digestive tract it can cause inflammation and irritation. The body's response to this is to attempt to expel the foreign agent by contracting. Increased contractions in the digestive tract, such as in the intestines, results in the rapid processing of foods. When foods are processed this quickly they are more liquid than normal. This intense action can irritate the digestive tract causing some bleeding and mucus as the body attempts to soothe itself. When examining the stools in this situation the blood will likely be bright red or brownish-red and may be accompanied by mucus. Salmonella, a food borne bacteria, is the most likely to result in bloody stools. Other examples of organisms that lead to a digestive infection and sometimes blood in the stools include viruses and parasites like rotavirus and Giardia lamblia.
Blood from Bowel Diseases and Disorders
Inflammatory bowel disease is a name given to a group of disorders that are characterized by intestinal inflammation. These diseases usually flare up and last through a person's lifetime. Such bowel disorders occur when the intestines and other components of the digestive tract are inflamed resulting in various uncomfortable symptoms including abdominal cramps, diarrhea, weight loss and bleeding from the intestines. No permanent cure exists for inflammatory bowel diseases but many respond favorably to medications and diet changes.
Bleeding associated with an inflammatory bowel disease can be bright red, jelly-like or it can cause darkened stools suggesting the blood has passed from the upper digestive tract regions before exiting. Crohn's disease and ulcerative colitis are just two of the several specific disorders found classified as inflammatory bowel diseases. These two diseases are very similar with the exception of the location of the inflammation. Crohn's disease is characterized by open sores called ulcers in the small and large intestines. Ulcerative colitis is the same except the sores are found in the lower part of the large intestine including the rectum. Food, stress and various other triggers can cause a flare up of symptoms and blood in the stools.
Any form of bowel obstruction can cause both bright red blood in the stools and darkened fecal matter depending on the location of the mass or blockage. Common obstructions include diverticulosis, hemorrhoids, colon polyps and tumors. Diverticulosis occurs when abnormal pockets form in the colon and make the surrounding areas more sensitive. Hemorrhoids are swollen veins found near the anus and in the rectum. Colon polyps and tumors are found during a colonoscopy or other invasive procedure that allows a specialist to view inside the colon and intestines. The blood associated with bowel obstructions is often bright red but it can also be full of mucus. Hemorrhoids are common can produce blood during a bowel movement or on a tissue when wiping the anus. Similarly, an anal fissure, or a small cut in the anus or lower rectal area, can produce a great deal of blood when irritated by the passing of stools.
FamilyDoctor.org: Inflammatory Bowel Disease https://familydoctor.org/online/famdocen/home/common/digestive/disorders/252.html
MayoClinic.com: Ulcerative Colitis https://www.mayoclinic.com/health/ulcerative-colitis/DS00598/DSECTION=symptoms
MedlinePlus: Bloody or Tarry Stools https://www.nlm.nih.gov/medlineplus/ency/article/003130.htm
Milton S. Hershey Medical Center College of Medicine: Diarrhea https://www.hmc.psu.edu/healthinfo/d/diarrhea.htm
National Digestive Diseases Information Clearinghouse: Viral Gastroenteritis https://digestive.niddk.nih.gov/ddiseases/pubs/viralgastroenteritis/#1
National Digestive Diseases Information Clearinghouse: Diarrhea https://digestive.niddk.nih.gov/ddiseases/pubs/diarrhea/
National Digestive Diseases Information Clearinghouse: Bleeding in the Digestive Tract https://digestive.niddk.nih.gov/ddiseases/pubs/bleeding/#diagnosed