The bowels, also known as the intestines, are a long, tube-shaped organ located in the abdomen. They play a central role in the digestive system, completing the process of digestion and preparing waste for elimination from the body.
Anatomy and Role of the Bowels
The bowels are divided into two primary sections: the small intestine and the large intestine. The small intestine, despite its name, is the longer of the two, measuring about 18 to 25 feet (5.5 to 7.6 meters) in length in adults, though its diameter is narrower than the large intestine.
The small intestine is further divided into three segments: the duodenum, jejunum, and ileum. The duodenum is the initial segment, about 10 inches long, where partially digested food from the stomach, called chyme, mixes with digestive juices from the pancreas and bile from the gallbladder. This mixing facilitates the breakdown of carbohydrates, fats, and proteins into smaller molecules.
Following the duodenum, the jejunum, 8 feet (2.5 meters) long, is the primary site for nutrient absorption. Its inner lining features numerous folds, finger-like projections called villi, and even smaller projections called microvilli, which collectively increase the surface area for absorption. Sugars, amino acids, and fatty acids, the end products of digestion, are absorbed here into the bloodstream.
The final section, the ileum, extends for 9.8 feet (3 meters). Its main function involves absorbing remaining nutrients not absorbed in the jejunum, particularly vitamin B12 and bile salts. The ileum then transitions the remaining undigested material to the large intestine.
The large intestine is shorter but wider than the small intestine, measuring 5 to 6 feet (1.5 to 1.8 meters) in length. It begins in the lower right abdomen and extends upwards, across, and then downwards, ending at the anus. Its main role is to absorb water and electrolytes from indigestible food matter and to form and store feces.
The large intestine consists of the cecum, colon (ascending, transverse, descending, and sigmoid parts), rectum, and anal canal. As the liquid chyme residue enters the large intestine, water is absorbed through osmosis, driven by the absorption of electrolytes like sodium. This process converts the liquid waste into solid stool.
Beyond water absorption, the large intestine also houses a community of beneficial bacteria, known as the gut microbiota. These bacteria ferment remaining dietary fiber and polysaccharides, producing short-chain fatty acids and certain vitamins, which are then absorbed by the body. The final waste material, consisting of indigestible food, bacteria, and unabsorbed substances, is compacted and stored in the rectum before being eliminated from the body.
Common Bowel Conditions
Various conditions can affect the bowels, leading to uncomfortable symptoms. Constipation is a common issue characterized by infrequent or difficult bowel movements, often due to slow movement of waste through the large intestine, leading to harder stools. Diarrhea, conversely, involves frequent, loose, or watery stools, resulting from rapid passage of contents through the intestines or reduced water absorption.
Irritable Bowel Syndrome (IBS) is a common functional gastrointestinal disorder affecting an estimated 12% of people in the United States. It involves a group of symptoms including abdominal pain, cramping, bloating, and changes in bowel habits, which can manifest as constipation, diarrhea, or a mix of both. IBS does not cause inflammation or permanent damage to the intestines.
Inflammatory Bowel Disease (IBD) encompasses conditions like Crohn’s disease and ulcerative colitis, which involve chronic inflammation of the digestive tract. Unlike IBS, IBD can lead to severe abdominal pain, cramps, diarrhea, and can affect nutrient absorption. Crohn’s disease can impact any part of the digestive tract, while ulcerative colitis specifically affects the large intestine and rectum. These conditions can have serious implications if left untreated, potentially leading to malnutrition or anemia.
If persistent or severe symptoms such as abdominal pain, significant changes in bowel habits, unexplained weight loss, or blood in stool occur, seeking medical attention is advisable. A healthcare professional can accurately diagnose the condition and recommend appropriate management or treatment strategies.