What Type of Absorption is Glucose Absorbed Via?

November 18, 2025 •

2 min read

Over 80% of glucose filtered by the kidneys is reabsorbed via SGLT2, illustrating the body's high-capacity absorption methods. In the small intestine, glucose is absorbed through a combination of secondary active transport and facilitated diffusion, depending on the concentration of glucose in the intestinal lumen. This dual-mechanism process ensures efficient and rapid uptake of dietary sugars into the bloodstream after a meal.

Quick Summary

The primary methods for glucose absorption in the small intestine are secondary active transport, mainly mediated by SGLT1, and facilitated diffusion, primarily involving GLUT2. The specific mechanism used depends on luminal glucose concentration, with SGLT1 dominating at low concentrations and GLUT2 contributing significantly at high concentrations to maximize uptake.

Key Points

Dual Transport System: Glucose absorption utilizes both secondary active transport and facilitated diffusion, with different transporters dominating based on luminal glucose concentration.
SGLT1 for Low Concentration: At low glucose levels, SGLT1 uses the sodium gradient to actively transport glucose against its concentration gradient.
GLUT2 for High Concentration: At high glucose levels, GLUT2 is recruited to the apical membrane, significantly increasing the rate of absorption via facilitated diffusion.
Basolateral Exit: Regardless of the entry method, glucose exits the enterocyte into the bloodstream through GLUT2 on the basolateral membrane.
Energy and Gradient: Secondary active transport by SGLT1 requires energy indirectly (via a sodium pump), while facilitated diffusion by GLUT2 is a passive process driven by the glucose concentration gradient.
Hormonal Regulation: Hormones like GLP-1, released in response to meals, help regulate the activity and expression of these glucose transporters.

The absorption of glucose in the human body is a complex and highly regulated process involving multiple transport systems in the small intestine. The two main mechanisms are secondary active transport, which relies on an ion gradient, and facilitated diffusion, which moves glucose down its concentration gradient. Together, these pathways ensure that glucose is efficiently moved from the intestinal lumen into the bloodstream to supply the body's energy needs.

The Role of SGLT1: Secondary Active Transport

At lower concentrations of glucose, such as during fasting or between meals, the primary transporter responsible for glucose absorption is the sodium-glucose cotransporter 1 (SGLT1). This process is known as secondary active transport because it uses the electrochemical gradient of sodium ions ($Na^+$) to move glucose against its own concentration gradient.

How SGLT1 Works

SGLT1, located on the apical membrane, binds to two $Na^+$ ions and one glucose molecule. As $Na^+$ moves down its concentration gradient into the cell (driven by the Na+/K+-ATPase pump on the basolateral membrane that maintains low intracellular $Na^+$), it pulls glucose with it against the glucose gradient.

The Role of GLUT2: Facilitated Diffusion

When luminal glucose concentration is high after a high-carbohydrate meal, the GLUT2 transporter, usually on the basolateral membrane, is recruited to the apical membrane. GLUT2 facilitates the diffusion of glucose down its concentration gradient into the cell, significantly increasing absorption capacity beyond what SGLT1 can handle alone.

The Exit Strategy: Basolateral Membrane Transport

Glucose exits the enterocyte into the bloodstream via the GLUT2 transporter located on the basolateral membrane. This is a facilitated diffusion process, moving glucose down its gradient into the capillaries.

Comparative Analysis of Glucose Absorption Mechanisms


Feature	Secondary Active Transport (via SGLT1)	Facilitated Diffusion (via GLUT2)
Energy Requirement	Indirect energy via $Na^+$ gradient	None (passive)
Concentration Gradient	Against glucose gradient	Down glucose gradient
Luminal Concentration	Dominant at low	Recruited at high
Transport Capacity	Low capacity	High capacity
Location	Apical membrane	Apical (high conc.) & Basolateral
Coupling	Coupled with two $Na^+$	Uncoupled
Regulation	$Na^+$ gradient, diet, hormones	Luminal glucose, hormones

Factors Influencing Glucose Absorption

Factors influencing glucose absorption include dietary carbohydrate content, hormonal signals like GLP-1, circadian rhythms, and conditions such as diabetes which can alter transporter expression and activity.

The Two-Step Transcellular Journey

Glucose absorption is a two-step process: uptake from the lumen into the enterocyte via SGLT1 (low concentration) or SGLT1 and GLUT2 (high concentration), followed by exit into the bloodstream via basolateral GLUT2.

Conclusion

Glucose is absorbed via a sophisticated system using both secondary active transport (SGLT1) and facilitated diffusion (GLUT2). SGLT1 is key for efficient uptake when glucose is scarce, while GLUT2 provides high-capacity transport when glucose is abundant after a meal. This dual approach, coupled with GLUT2-mediated exit into the bloodstream, ensures the body efficiently manages its energy supply. For further details on the intricate mechanisms and their regulation, exploring academic sources like the MDPI article on glucose transport regulation provides an excellent resource.

Frequently Asked Questions

At low glucose concentrations, the primary absorption method is secondary active transport via the SGLT1 protein. This transporter uses the sodium gradient to pull glucose into the intestinal cells, even against a glucose concentration gradient.

GLUT2, which typically resides on the basolateral membrane, is recruited to the apical (lumen-facing) membrane when luminal glucose concentrations are high, such as after a meal. This allows for a massive influx of glucose via facilitated diffusion to maximize absorption capacity.

Yes, indirectly. SGLT1-mediated transport is considered active because it depends on the sodium gradient maintained by the energy-consuming Na+/K+-ATPase pump. GLUT2-mediated transport, however, is a passive form of transport (facilitated diffusion) that does not directly consume energy.

Active transport moves substances against their concentration gradient, requiring energy (either directly or indirectly). Facilitated diffusion moves substances down their concentration gradient with the help of a carrier protein but requires no direct energy input.

The dual mechanism of using both SGLT1 and GLUT2 allows the body to efficiently absorb glucose under a wide range of dietary conditions. SGLT1 is crucial for absorbing all available glucose when concentrations are low, while GLUT2 provides high-capacity absorption when concentrations are high after a large meal.

Defects in glucose absorption, such as in glucose-galactose malabsorption, can lead to severe gastrointestinal issues like diarrhea and dehydration because unabsorbed glucose and galactose draw water into the intestinal lumen. In conditions like diabetes, the transporters can be upregulated, contributing to hyperglycemia.

While some paracellular transport (between cells) can occur, especially at high glucose concentrations, it is generally considered a minor mechanism in glucose absorption compared to the transcellular transport mediated by SGLT1 and GLUT2.