Digestion in the Small Intestine

After the digestion process occurs in the stomach and the food is mixed with digestive juices, the food enters as chyme into the small intestine. Small intestine, also called, small bowel is approximately 17 feet and is the longest section of digestive system. The parts of small intestine are – duodenum, jejunum and ileum, each one with a specific digestive function.

Small Intestine Function

Most of the chemical digestion occurs in small intestine.

  • Carbohydrates are broken down into simple sugars such as glucose
  • Fats (lipids) are broken down into fatty acids and glycerol
  • Complex protein molecules (peptides) are broken down into amino acids

The chyme is mixed with digestive enzymes such as bile, pancreatic juices and amylase and with intestinal enzymes such as sucrose, lactase and maltase. Thus the digestion process enhances with these enzymes and nutrient absorption occurs. The chyme changes to a thin watery mixture along the way of small intestine.

The absorbed nutrients flow into the liver along with the bloodstream. Here they are stored and later sent to other parts of the body.

Digestive Function of Duodenum

Duodenum is the first part of digestive system that continues the digestion process from stomach. It is horse-shoe shaped and finger-like. It has four segments namely superior, descending, horizontal and ascending duodenum. In duodenum, the chyme is mixed with bile juices secreted by gallbladder and pancreatic juices secreted by pancreas. Bile converts the fats into smaller droplets and pancreatic juices convert fats into fatty acids and glycerol. Pancreas also secrete sodium bicarbonate that helps in neutralizing stomach acids.

Digestive Function of Jejunum

Jejunum is the second part of small intestine where the chemical digestion completes. The enzymes of jejunum along with the pancreatic juices completely digest the chyme.

Digestive Function of Ileum

Ileum is the final part of small intestine that continues into large intestine through a junction called ileocecal valve. Ileum absorbs the nutrients from the digested food that are sent along the bloodstream to liver. The excess bile is also absorbed and returned to liver.

The unabsorbed watery mixture from the ileum is sent to large intestine. Here final digestion process occurs where the water is removed and the solid matter is eliminated from the body.

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