Final answer:
Black, tarry stool is often a sign of upper gastrointestinal bleeding, with stomach ulcers being a common cause. It is important to seek medical attention for a proper diagnosis and treatment, which may include blood tests, a colonoscopy, or medications.
Step-by-step explanation:
Black, tarry stools, medically known as melena, is typically a sign of bleeding in the upper gastrointestinal tract, which includes the esophagus, stomach, and the first part of the small intestine. The dark color is due to the blood being digested and interacting with the stomach's digestive enzymes and acid, giving the stool its distinct black and tarry appearance. In particular, conditions such as stomach ulcers can cause such bleeding, often resulting from bacterial infections or irritation due to certain medications, alcohol, or stress.
Screening for fecal occult blood tests and a colonoscopy can help diagnose potential causes of bleeding, such as colorectal cancer, which sometimes presents with bleeding from the rectum that may not be visually apparent but can be detected in stool tests.
It is critical for a person experiencing black, tarry stools to seek medical attention to diagnose the underlying cause and receive appropriate treatment such as antibiotics for infections or medication to neutralize stomach acid in the case of ulcers.