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Biology LibreTexts

34.3C: Elimination

  • Page ID
    13852
  • Undigested food enters the colon where water is reabsorbed into the body and excess waste is eliminated from the anus.

    Learning Objectives

    • Describe the process of elimination and problems that can occur

    Key Points

    • Water is reabsorbed in the colon after undigested food enters it from the small intestine.
    • Waste is moved through the colon by peristaltic movements of the muscle and is stored in the rectum.
    • The rectum expands in response to the storage of fecal matter; neural signals are triggered, and the waste is eliminated from the anus by peristaltic movements of the rectum.
    • Constipation is a condition where the feces are hardened because of excess water removal in the colon.
    • Diarrhea results when large amounts of water are not removed from the feces.
    • Emesis, or vomiting, is elimination of food by forceful expulsion through the mouth caused by the strong contractions produced by the stomach muscles.

    Key Terms

    • emesis: the act or process of vomiting
    • intestinal flora: the bacterial colonies that normally live in the digestive tract of animals
    • constipation: condition where the feces are hardened because of excess water removal in the colon

    Elimination

    The final step in digestion is the elimination of undigested food content and waste products. After food passes through the small intestine, the undigested food material enters the colon, where most of the water is reabsorbed. Recall that the colon is also home to the microflora called “intestinal flora” that aid in the digestion process. The semi-solid waste is moved through the colon by peristaltic movements of the muscle and is stored in the rectum. As the rectum expands in response to storage of fecal matter, it triggers the neural signals required to set up the urge to eliminate. The solid waste is eliminated through the anus using peristaltic movements of the rectum.

    image

    Intestinal flora: Escherichia coli is one of the many species of bacteria present in the human gut.

    Common Problems with Elimination

    Diarrhea and constipation are some of the most common health concerns that affect digestion. Constipation is a condition where the feces are hardened because of excess water removal in the colon. In contrast, if not enough water is removed from the feces, it results in diarrhea. Many bacteria, including the ones that cause cholera, affect the proteins involved in water reabsorption in the colon and result in excessive diarrhea.

    Emesis

    Emesis, or vomiting, is elimination of food by forceful expulsion through the mouth. It is often in response to an irritant that affects the digestive tract, including, but not limited to, viruses, bacteria, emotions, trauma, and food poisoning. This forceful expulsion of the food is due to the strong contractions produced by the stomach muscles. The process of emesis is regulated by the medulla.

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