Question

Which of the following tissues is most dependent on insulin? (A) Active skeletal muscle (B) Resting skeletal muscle (C) Cardiac muscle (D) Smooth muscle

Short answer

Resting skeletal muscle.

Step-by-step solution

- Understand Insulin's Role

Insulin is a hormone that helps cells absorb glucose from the bloodstream. Consider which tissues rely heavily on glucose uptake facilitated by insulin.

- Analyze Active Skeletal Muscle

Active skeletal muscle utilizes glucose during exercise but relies on immediate glucose uptake from the bloodstream, largely dependent on insulin.

- Analyze Resting Skeletal Muscle

Resting skeletal muscle also needs glucose but is less active in glucose uptake compared to when muscles are active. It relies more on insulin for glucose uptake during periods of rest.

- Analyze Cardiac Muscle

Cardiac muscle has a constant energy demand; however, it primarily relies on fatty acids and lactate for energy rather than glucose.

- Analyze Smooth Muscle

Smooth muscle is found in the walls of hollow organs and uses a combination of different energy sources including glucose, but it is less dependent on insulin compared to skeletal muscle.

- Conclusion

Resting skeletal muscle has a greater dependency on insulin for glucose uptake compared to active skeletal muscle, cardiac muscle, and smooth muscle. This is because it primarily uses glucose during periods of low activity.

Key concepts

Skeletal Muscle

Skeletal muscle is the type of muscle tissue that is connected to bones and helps in voluntary movements, like walking, running, or lifting objects. It plays a crucial role in locomotion and overall physical activity. When it comes to energy usage, skeletal muscle can use glucose and fatty acids. During physical activity, such as exercise, active skeletal muscles require a high amount of glucose for energy. Insulin facilitates glucose uptake specifically during periods of rest, making resting skeletal muscle more dependent on insulin. This means insulin is vital for moving glucose from the bloodstream into the muscle cells, especially when the muscles are not actively engaged in intense physical activities.

Cardiac Muscle

Cardiac muscle is the muscle tissue found in the heart. Unlike skeletal muscle, it works involuntarily to pump blood throughout the body. Cardiac muscle has a consistent energy demand as it constantly needs to contract and relax to maintain blood circulation. The primary energy sources for cardiac muscle are fatty acids and lactate, rather than glucose. While it can use glucose, cardiac muscle is less dependent on insulin for glucose uptake because it has alternative energy sources. This reduces its reliance on insulin compared to tissues like resting skeletal muscle. The heart's continuous activity and its preference for different energy fuels make its metabolic requirements distinct.

Glucose Uptake

Glucose uptake is the process by which cells absorb glucose from the bloodstream. This is essential for providing energy to cells. Insulin plays a significant role in this process by binding to insulin receptors on the cell surface, which signals the cells to take in glucose. Certain tissues, like resting skeletal muscles, are more reliant on insulin for their glucose uptake. During periods of low physical activity, these muscles primarily use glucose for energy. Therefore, insulin is crucial in helping these muscles absorb the necessary glucose from the blood. Conversely, other tissues like cardiac muscle and smooth muscle may use different mechanisms and energy sources.

Hormone Function

Hormones are chemical messengers that regulate various physiological processes in the body. Insulin, a hormone produced by the pancreas, plays a key role in regulating blood sugar levels. When you eat, your blood sugar levels rise, and insulin is released to help cells, particularly muscle and fat cells, absorb glucose from the bloodstream. This helps to lower blood sugar levels and provide energy to cells. Insulin is specifically important for tissues that have a high glucose demand but are unable to uptake glucose without the hormone's assistance. This is especially evident in resting skeletal muscles. Understanding insulin’s function helps in comprehending metabolic disorders like diabetes, where insulin production or function is impaired.