- The intestine is a long, tubular structure in the digestive system that plays a critical role in digesting food, absorbing nutrients, and eliminating waste.
- It is typically divided into two main parts: the small intestine and the large intestine, each with distinct anatomical and functional characteristics. The entire intestine extends from the stomach to the anus, forming a continuous passage that processes food after it leaves the stomach.
- The small intestine is the longer of the two, measuring approximately 6 to 7 meters in adults, and is primarily responsible for the digestion and absorption of nutrients. It consists of three segments: the duodenum, jejunum, and ileum. The duodenum is the first part, where acidic chyme from the stomach is mixed with bile from the liver and digestive enzymes from the pancreas. The jejunum and ileum are specialized for nutrient absorption, with the inner lining containing villi and microvilli, which dramatically increase the surface area for absorption. Through these structures, essential nutrients such as amino acids, simple sugars, fatty acids, vitamins, and minerals enter the bloodstream.
- Following the small intestine is the large intestine, which measures about 1.5 meters in length and is wider in diameter. It includes the cecum, colon, rectum, and anal canal. The main functions of the large intestine are to absorb water and electrolytes from the remaining indigestible food matter and to form and expel feces. The colon is further divided into the ascending, transverse, descending, and sigmoid colon. In the large intestine, bacteria play a key role in breaking down some substances and synthesizing certain vitamins, like vitamin K and biotin, which are absorbed by the host.
- The intestine is richly supplied with blood vessels, nerves, and lymphatic tissues, enabling it to interact closely with the body’s circulatory and immune systems. The enteric nervous system, often referred to as the “second brain,” regulates many of the intestine’s functions independently of the central nervous system, including motility, secretion, and blood flow. Moreover, the intestine is a major site of immune surveillance and home to the gut-associated lymphoid tissue (GALT), which helps defend the body from pathogens that enter with food.
- A complex community of microorganisms known as the gut microbiota also resides in the intestine, particularly in the large intestine. These microbes assist in digestion, protect against harmful bacteria, and influence systemic immunity and even mood and cognition. Disruptions in this microbial balance have been linked to a range of health issues, including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), obesity, and mental health disorders.
- Diseases and disorders of the intestine can significantly impair health and quality of life. Common conditions include Crohn’s disease, ulcerative colitis, celiac disease, colon cancer, intestinal obstruction, and gastroenteritis. Diagnosis often involves procedures such as colonoscopy, endoscopy, or imaging studies, and treatment depends on the underlying cause.
