Small Intestine

The small intestine is a vital part of the digestive system, located between the stomach and the large intestine. It is where most of the digestion and absorption of nutrients from food occurs. Despite its name, the small intestine is actually the longest part of the digestive tract in humans, measuring around 20 feet (6 meters) in length.

• Three Segments: The small intestine is divided into three main segments: the duodenum, the jejunum, and the ileum. The duodenum is the shortest segment and is primarily responsible for receiving partially digested food from the stomach, as well as digestive juices from the pancreas and bile from the liver. The jejunum and ileum make up the remaining length of the small intestine and are primarily involved in nutrient absorption.
• Intestinal Villi and Microvilli: The lining of the small intestine is covered in tiny finger-like projections called villi, which greatly increase the surface area available for absorption. Each villus contains even smaller projections called microvilli, further increasing the absorptive surface area. Together, the villi and microvilli provide an extensive surface area for the absorption of nutrients such as carbohydrates, proteins, fats, vitamins, and minerals into the bloodstream.
• Digestive Enzymes: The small intestine secretes various enzymes and digestive juices to further break down food molecules into smaller components that can be absorbed. Enzymes produced by the pancreas, such as amylase, lipase, and proteases, help digest carbohydrates, fats, and proteins, respectively. Bile, produced by the liver and stored in the gallbladder, aids in the digestion and absorption of fats.
• Peristalsis: Like the rest of the digestive tract, the small intestine undergoes rhythmic contractions known as peristalsis, which propel food and chyme (partially digested food) through its length. Peristalsis helps mix the chyme with digestive juices and facilitates nutrient absorption.
• Absorption of Nutrients: The small intestine is the primary site of nutrient absorption in the digestive system. Nutrients are absorbed across the epithelial cells lining the intestinal villi and are then transported into the bloodstream or lymphatic system for distribution to cells throughout the body.
• Water Absorption: In addition to nutrient absorption, the small intestine also plays a role in absorbing water and electrolytes from the digestive tract, helping to maintain fluid balance in the body.