intestinal absorption

Definition

Target type: biologicalprocess

A process in which nutrients are taken up from the contents of the intestine. [GOC:ai, GOC:dph]

Intestinal absorption is a complex process by which nutrients, water, and electrolytes from digested food are transported across the intestinal epithelium and into the bloodstream. It is a vital process for maintaining bodily functions and occurs primarily in the small intestine, with some absorption occurring in the stomach and large intestine.

The process begins with the breakdown of food in the mouth and stomach, where mechanical and chemical digestion occur. The resulting smaller molecules, along with water and electrolytes, then enter the small intestine. The small intestine is lined with specialized epithelial cells called enterocytes that play a key role in absorption.

Here's a detailed description of the process:

1. **Passive Diffusion:** Some substances, like water and small, lipid-soluble molecules (e.g., fatty acids, vitamins A, D, E, and K) can move directly across the epithelial cell membrane by simple diffusion, following their concentration gradient.

2. **Facilitated Diffusion:** Other substances, like glucose and amino acids, require the assistance of carrier proteins embedded in the cell membrane to move across the membrane. These carriers bind to the specific molecules and facilitate their movement down their concentration gradient.

3. **Active Transport:** Active transport involves moving substances against their concentration gradient, requiring energy expenditure. This is essential for absorbing nutrients that are present at low concentrations in the intestinal lumen but are needed in higher concentrations in the bloodstream. Examples include sodium, potassium, calcium, and iron.

4. **Pinocytosis and Phagocytosis:** Large molecules, such as proteins and fats, are absorbed through these processes. Pinocytosis involves the engulfment of fluids, while phagocytosis involves the engulfment of solid particles. Both processes rely on the formation of vesicles that pinch off from the cell membrane.

5. **Absorption of Specific Nutrients:**
* **Carbohydrates:** The primary site of carbohydrate absorption is the small intestine. Disaccharides like sucrose, lactose, and maltose are broken down into monosaccharides like glucose, fructose, and galactose. These monosaccharides are then absorbed by active transport mechanisms and enter the bloodstream.
* **Proteins:** Dietary proteins are digested into amino acids by enzymes. These amino acids are absorbed through active transport mechanisms and enter the bloodstream.
* **Fats:** Fats are broken down into fatty acids and glycerol. These molecules are then absorbed by passive diffusion across the epithelial cell membrane and enter the lymphatic system before reaching the bloodstream.
* **Water:** Water is absorbed by osmosis, moving from areas of high water concentration to areas of low water concentration. The majority of water absorption occurs in the small intestine.
* **Electrolytes:** Electrolytes, such as sodium, potassium, chloride, and bicarbonate, are absorbed through various mechanisms, including passive diffusion and active transport.

6. **Role of the Large Intestine:** Although the majority of absorption occurs in the small intestine, the large intestine plays a role in absorbing water, electrolytes, and some vitamins (vitamin K and some B vitamins) produced by gut bacteria.

The efficiency of intestinal absorption is influenced by various factors including the health of the intestinal lining, the presence of digestive enzymes, and the overall health of the individual. Conditions such as malabsorption syndromes, celiac disease, and inflammatory bowel disease can impair the absorption process, leading to nutrient deficiencies and other health problems.
'
"

Proteins (4)

Compounds (294)