Question

Adipose tissue responds to low insulin:glucagon ratio by A. dephosphorylating the interconvertible enzymes. B. stimulating the deposition of fat. C. increasing the amount of pyruvate kinase. D. activation of hormone-sensitive lipase. E. releasing glutamine.

Short answer

Answer: Adipose tissue responds to a low insulin:glucagon ratio by activating hormone-sensitive lipase, leading to the breakdown of stored fat into free fatty acids and glycerol.

Step-by-step solution

Understand the functions of insulin and glucagon

Insulin and glucagon are hormones released by the pancreas that regulate sugar metabolism. In general, insulin promotes glucose uptake and storage, while glucagon stimulates glucose release into the bloodstream.

Analyze the options

A. Dephosphorylating the interconvertible enzymes: Interconvertible enzymes are enzymes that can be converted from an inactive form to an active form through phosphorylation/dephosphorylation. Dephosphorylating these enzymes would be a catabolic process, breaking down molecules for the release of energy. B. Stimulating the deposition of fat: Insulin promotes the storage of energy in the form of fat. Therefore, a low insulin:glucagon ratio would not favor the deposition of fat. C. Increasing the amount of pyruvate kinase: Pyruvate kinase is an enzyme involved in glycolysis, the process of breaking down glucose. A low insulin:glucagon ratio would favor gluconeogenesis (production of glucose), not glycolysis. D. Activation of hormone-sensitive lipase: Hormone-sensitive lipase is an enzyme involved in the breakdown of stored triglycerides in adipose tissue into free fatty acids and glycerol. This process would be in line with a low insulin:glucagon ratio. E. Releasing glutamine: Glutamine is an amino acid that is not directly involved in the insulin and glucagon pathways.

Choose the correct option

Based on the analysis, option D (activation of hormone-sensitive lipase) is the most accurate response to the question. Adipose tissue would respond to a low insulin:glucagon ratio by activating hormone-sensitive lipase, leading to the breakdown of stored fat into free fatty acids and glycerol.

Key concepts

Adipose Tissue Response

The body's adipose tissue, or fat tissue, is critically involved in maintaining energy balance. When the insulin:glucagon ratio is low, typically during fasting or heavy exercise, adipose tissue shifts its role from storing fat to mobilizing fat. This response includes the activation of certain enzymes that lead to the breakdown of stored triglycerides. These triglycerides are then released into the bloodstream as fatty acids and glycerol, which can be used by other tissues as an energy source.

It's important to understand that while glucose serves as a primary energy source under normal conditions, during periods of low insulin:glucagon ratio, the body needs to access its stored energy reserves. Adipose tissue is a primary site for this energy storage, and its responsive adaptation to hormonal cues is crucial for energy homeostasis in the human body.

Hormone-Sensitive Lipase Activation

Central to the mobilization of fat stores in adipose tissue is hormone-sensitive lipase (HSL), an enzyme that responds to hormonal signals. Under low insulin conditions, glucagon triggers the phosphorylation and thus activation of HSL. Once activated, HSL breaks down the triglycerides stored in fat cells into their constituent fatty acids and glycerol.

Understanding the mechanism of HSL is important as it plays a direct role in how the body toggles between energy storage and energy utilization. The regulation of HSL is an excellent example of the body's metabolic flexibility, ensuring that energy is available during periods of calorie restriction or increased energy demand. This process is critical for maintaining blood glucose levels and overall energy balance.

Glucose Metabolism Regulation

Regulation of glucose metabolism is a complex process that ensures that our body's cells receive a steady energy supply. Insulin and glucagon, hormones produced by the pancreas, play a pivotal role in this regulation. While insulin facilitates the uptake and storage of glucose by cells, glucagon promotes the release of glucose from stored glycogen in the liver.

During periods of fasting or between meals, when blood sugar levels drop, glucagon levels rise, resulting in increased glucose production and release by the liver, ensuring that cells continue to receive the energy they need. Conversely, after a meal, elevated insulin levels promote the storage of excess glucose, preventing hyperglycemia. This delicate balance maintains homeostasis within the body's metabolic systems.

Energy Storage and Mobilization

Energy storage and mobilization are two sides of the same coin in the body's metabolism. Energy is stored primarily in the form of glycogen in the liver and muscle tissue, and as triglycerides in adipose tissues. In response to hormonal signals, these stored forms of energy are mobilized to ensure a consistent supply during times of increased demand or when food intake is not sufficient.

Insulin promotes the synthesis of glycogen and triglycerides, which is why after eating, our body shifts to storage mode. On the flip side, during fasting or physical activity, glucagon and epinephrine stimulate the breakdown of these stores, liberating glucose and fatty acids into the bloodstream. Thus, the body is equipped with a dynamic system to either tuck away or unleash energy as needed to meet its metabolic demands.