Level of glucose transpoers are reduced after overnight fast in which of the following cells?
**Core Concept:** Glucose transporters are proteins that facilitate the movement of glucose across cellular membranes. In the context of the question, we are discussing the effect of fasting on glucose transporters in specific cells.
**Why the Correct Answer is Right:** After an overnight fast, the body enters a state of ketosis where glucose levels are low. To conserve glucose, the liver and muscle cells reduce the expression and activity of GLUT4 (a type of glucose transporter) to decrease glucose uptake. This occurs as a survival mechanism to conserve glucose for essential functions such as brain function.
**Why Each Wrong Option is Incorrect:**
A. Liver cells (hepatocytes): Liver cells are capable of gluconeogenesis, which is the synthesis of glucose from non-carbohydrate sources. Therefore, GLUT4 reduction in liver cells is not the primary response to fasting, as gluconeogenesis compensates for reduced glucose uptake.
B. Kidney cells (nephrons): Kidneys primarily filter the blood and maintain electrolyte and fluid balance. Although they can reabsorb glucose, the reduction in GLUT4 is not the primary response to fasting, as glucose reabsorption is not directly related to glucose conservation.
C. Fat cells (adipocytes): Although adipocytes may reduce glucose uptake, the primary response to fasting is the reduction of GLUT4 in liver and muscle cells, as these cells directly contribute to glucose conservation.
D. Brain cells (neurons): Glucose is the primary energy source for the brain, and reducing GLUT4 would lead to cerebral hypoglycemia. Therefore, the primary response to fasting is not reducing GLUT4 in brain cells, as this would compromise brain function.
**Clinical Pearl:** A correct understanding of glucose homeostasis and the body's response to fasting is crucial for healthcare professionals, as it helps in managing patients with diabetes and other glucose-related disorders appropriately.
**Correct Answer:** D. Brain cells (neurons): Following fasting, the body reduces the expression and activity of GLUT4 in neurons to conserve glucose for essential functions like brain function and avoid cerebral hypoglycemia.