Glucose, a simple sugar, is absorbed primarily in the small intestine through a sophisticated process. This process isn't a simple diffusion; it involves specialized transporters working in concert.
The Role of SGLT-1
The primary mechanism for glucose absorption involves a protein called the sodium-glucose linked transporter 1 (SGLT-1). Located on the apical membrane (the surface facing the intestinal lumen) of intestinal cells, SGLT-1 facilitates the co-transport of glucose and sodium ions (Na⁺) into the cells. This co-transport is driven by the pre-existing sodium gradient, meaning the movement of sodium into the cell powers the uptake of glucose. [As stated in multiple sources, including ScienceDirect Topics and JoVE, SGLT-1 is the key player in intestinal glucose absorption].
The Role of GLUT2
Once inside the intestinal cells, glucose then moves across the basolateral membrane (the side facing the bloodstream) via another transporter, GLUT2. GLUT2 is a glucose transporter that moves glucose passively down its concentration gradient, from the cell into the bloodstream. [This two-step process is described in the abstract provided]. [The PNAS article confirms that GLUT2 is not necessary for transepithelial glucose transport, however, this passive transport across the basolateral membrane is the common consensus].
Electrogenic Transport
It's important to note that glucose absorption is considered electrogenic; the movement of glucose across the intestinal epithelium affects the electrical potential difference across the cell membrane. [This is detailed in an article on the regulation of intestinal glucose absorption by ion channels and transporters].
Summary of the Glucose Absorption Process:
- Dietary carbohydrates are broken down into monosaccharides (simple sugars), including glucose, in the digestive system.
- Glucose enters intestinal cells via SGLT-1 co-transport with sodium.
- Glucose exits intestinal cells into the bloodstream via GLUT2 facilitated diffusion.
- Glucose is transported via the bloodstream to be used for energy or stored.
Glucose Absorption in Disease
Conditions such as glucose-galactose malabsorption (GGM) demonstrate the crucial role of proper glucose absorption. In GGM, a genetic defect prevents the efficient absorption of glucose and galactose, leading to diarrhea and malnutrition. [This condition is highlighted by Boston Children's Hospital's information on GGM.] The efficiency of glucose absorption can also be affected by various metabolic diseases, as discussed in several research articles.
