A strain of mice remains healthy as long as they are fed regularly. After they eat, their blood glucose level rises slightly and then declines to a homeostatic level. However, when these mice fast or exercise, their blood glucose drops dangerously. Which hypothesis best explains their problem? (Explain your choice.) a. The mice have insulin-dependent diabetes. b. The mice lack insulin receptors on their cells. c. The mice lack glucagon receptors on their cells. d. The mice cannot synthesize glycogen from glucose.

Verified step by step guidance

1. Understand the role of insulin and glucagon in blood glucose regulation. Insulin lowers blood glucose levels by promoting the uptake of glucose into cells and conversion into glycogen. Glucagon raises blood glucose levels by promoting the breakdown of glycogen back into glucose.
2. Analyze the symptoms: The mice's blood glucose level rises after eating and declines to a normal level, indicating that insulin is functioning properly to reduce the high glucose levels post-meal.
3. Consider the effect of fasting or exercise, which typically lowers blood glucose levels. Normally, glucagon would counteract this by promoting glycogen breakdown to release glucose into the blood.
4. Evaluate the options based on the symptoms and normal hormonal functions: Option 'c' suggests that the mice lack glucagon receptors on their cells, which would mean that glucagon cannot effectively signal the liver to break down glycogen into glucose, leading to dangerously low glucose levels during fasting or exercise.
5. Conclude that the most likely hypothesis is that the mice lack glucagon receptors on their cells, as this would explain why their blood glucose levels cannot be maintained during fasting or exercise, despite normal function after meals.

Key Concepts

Homeostasis

Homeostasis refers to the body's ability to maintain stable internal conditions despite external changes. In the context of blood glucose levels, homeostasis involves the regulation of glucose through hormones like insulin and glucagon, ensuring that levels remain within a narrow range. Disruptions in this balance can lead to conditions such as diabetes or hypoglycemia.

Insulin and Glucagon

Insulin and glucagon are two key hormones produced by the pancreas that regulate blood glucose levels. Insulin lowers blood glucose by facilitating its uptake into cells, while glucagon raises blood glucose by promoting the release of glucose from glycogen stores in the liver. A deficiency or insensitivity to these hormones can lead to significant metabolic issues.

Glycogen Synthesis and Breakdown

Glycogen is a stored form of glucose found primarily in the liver and muscles. The synthesis of glycogen from glucose (glycogenesis) and its breakdown back into glucose (glycogenolysis) are crucial processes for maintaining energy levels. Impairments in these processes can lead to inadequate glucose availability during fasting or exercise, resulting in dangerously low blood sugar levels.