Glucose Uptake and Transport Mechanisms

Glucose Uptake to Tissues

• Glucose uptake to tissues occurs through two major mechanisms: facilitated passive diffusion and secondary active transport (cotransport)
• Facilitated passive diffusion involves GLUTs (Glucose Transporters)
• Secondary active transport involves SGLT (Sodium-Dependent Glucose Transport) in specific tissues

Glucose Transporters (GLUTs)

• GLUT 1: found in erythrocyte, brain, kidney, and placenta; has the lowest Km value
• GLUT 2: found in liver, pancreas, β-cells, small intestine, and kidney; has a high Km value for quick catch of glucose from blood
• GLUT 3: found in brain, placenta, and testis; has a low Km value
• GLUT 4: found in adipose tissue, heart, and skeletal muscle; induced with insulin
• GLUT 5: found in small intestine and testis; helps with fructose absorption

Sodium-Dependent Glucose Transport (SGLT)

• SGLT-1: found in small intestine and renal tubules; involved in Na+ dependent glucose absorption in small intestine
• SGLT-2: found in renal tubules; involved in glucose absorption against the concentration gradient in proximal tubule

Blood Glucose Levels

• Normal blood glucose levels: 70-99 mg/dL (3.9-5.5 mmol/L)
• Slightly hyperglycemic: 100-125 mg/dL (5.6-6.7 mmol/L)
• Hyperglycemic: ≥126 mg/dL (≥6.7 mmol/L)
• Slightly hypoglycemic: 60-69 mg/dL (3.3-3.8 mmol/L)