An overview of intestinal absorptive and secretory processes

Although digestion of proteins, carbohydrates, and lipids may begin in the stomach, it is completed in the intestine. The absorption of nutrients, water, and electrolytes from food and drink also occurs in the intestine. The intestines can be divided into two structurally distinct organs—the small and large intestines.
Small Intestines
The small intestine is an ~7 meter-long tube with an inner diameter of just 2.5 cm. Since most nutrients are absorbed here, the inner lining of the small...

The small intestine exhibits a unique histological structure that significantly enhances its function in digestion and nutrient absorption. These structures include circular folds, villi, and various specialized cells that collectively facilitate the digestion of food.
The intestinal lining features transverse folds called circular folds, each housing fingerlike projections known as intestinal villi. These villi are covered by a layer of simple columnar epithelium, also referred to as...

Electrolytes are essential minerals and ions primarily obtained from the diet and absorbed through the gastrointestinal tract. Most electrolytes are absorbed in the small intestine. While the absorption of iron and calcium primarily occurs in the duodenum, calcium is also absorbed in the jejunum and ileum. In these regions, passive diffusion contributes to its absorption alongside active transport mechanisms in the duodenum. These ions can exit the enterocytes through specialized active...

The gastrointestinal (GI) tract, extending from the mouth to the anus, plays a pivotal role in the digestion and absorption of nutrients. This process involves both mechanical and chemical actions facilitated by various enzymes.
Digestion begins in the mouth, where food undergoes mechanical breakdown by chewing and combines with saliva. Salivary amylase, an enzyme in saliva, starts the breakdown of starches into maltose. The food then travels down the esophagus to the stomach.
In the stomach, a...

Drug absorption involves the movement of drugs from the point of administration into the systemic circulation. Initially, Gastrointestinal (GI) motility propels the drug through the digestive tract and into the stomach. However, the stomach's high acidity and limited surface area restrict its role in drug absorption for most drugs. The drug then moves from the stomach to the small intestine via gastric emptying, which can be slowed by various factors, including interactions with other...

Absorption refers to taking dietary nutrients from the intestinal lumen for transportation throughout the body. After digestion in the small intestine, carbohydrates, proteins, and fats are broken down into simpler forms. These essential macronutrients and other vital substances, such as vitamins, minerals, and water, are then prepared for absorption into the bloodstream.
Enterocytes, which are specialized polar epithelial cells, line the mucosa of the small intestinal walls. These cells...