What happens in the first part of small intestine?

The first part of the small intestine is called the duodenum. It is here that the majority of digestion and absorption of nutrients occurs. The duodenum is a C-shaped organ that is about 25 centimeters long. It begins at the pyloric sphincter, which is a muscle that controls the passage of food from the stomach into the duodenum. The duodenum ends at the ligament of Treitz, which is a fold of peritoneum that suspends the jejunum and ileum from the duodenum.

The duodenum is lined with a mucous membrane that contains numerous villi and microvilli. Villi are small, finger-like projections that increase the surface area of the duodenum and help to absorb nutrients. Micrvilli are even smaller projections that cover the villi and also help to absorb nutrients.

The duodenum also contains several glands that secrete digestive enzymes and mucus. The most important digestive enzymes secreted by the duodenum are:

* Amylase: This enzyme breaks down carbohydrates into simple sugars.

* Lipase: This enzyme breaks down fats into fatty acids and glycerol.

* Protease: This enzyme breaks down proteins into amino acids.

In addition to digestive enzymes, the duodenum also secretes mucus. Mucus is a slippery substance that helps to protect the lining of the duodenum from the acidic contents of the stomach.

The duodenum is responsible for mixing the food that is swallowed with the digestive enzymes and mucus that are secreted. This mixture is then churned and moved along the duodenum by peristalsis, which is a series of involuntary muscle contractions.

The digested food is then absorbed into the bloodstream through the villi and microvilli. The absorbed nutrients are then transported to the liver, where they are used to provide energy or stored for later use.