Question

At low [blood glucose], what is your prediction about transport of glucose into adipose cells and braincells? Explain your rationale.

At high [blood glucose], what is your prediction about transport of glucose into adipose cells and brain cells? Explain your rationale.

Answer 1

The low blood-sugar level leads to decreased secretion of insulin and increased secretion of glucagon.

Glucose cannot be replaced as an energy source but it can be supplemented, as during strenuous physical activity when blood lactate levels are elevated or during prolonged starvation during which time brain can use ketone as energy source. Because the brain needs glucose continually, humans have developed an exquisitely precise regulatory system to ensure that adequate amounts of glucose are always present within a narrow concentration range in the bloodstream. Extremely low levels of glucose levels in brain can lead to brain seizures or coma. Glucose is transported into brain cells by the glucose transporter GLUT3,. With decreased insulin levels glucose is not transported to adipose cells.

At high levels of glucose, insulin secretion is increased and glucagon secretion is decreased

When glucose levels are high, brain unlike liver, skeletal muscles and adipose cells do not have the ablity to store glucose, in case of brain there are two type of transporters which carry glucose , Sodium dependent glucose transporters (SGLTs) which transport glucose against its concentration gradient and Sodium independent glucose transporters (GLUTs), which transport glucose by facilitative diffusion in its concentration gradient.. In case of adipose cells, insulin mediates glucose uptake into adipose tissue through GLUT4 glucose transporters. Vesicles containing GLUT4 glucose transporters are mobilized to the plasma membrane by insulin stimulation, thereby effecting glucose transport into the cell