What is the main function of the Na-K pump at the cellular level?

Choice A Reason:

Norepinephrine is a key neurotransmitter released by the sympathetic nervous system during the “fight-or-flight” response. It plays a crucial role in preparing the body to respond to stress by increasing heart rate, blood pressure, and blood flow to muscles, as well as dilating the airways. These physiological changes are essential for coping with acute stress.

Choice B Reason:

Cortisol is a hormone released by the adrenal glands in response to stress, but it is primarily associated with the hypothalamic-pituitary-adrenal (HPA) axis rather than the sympathetic nervous system. While cortisol contributes to the body’s overall stress response by increasing blood sugar levels and suppressing the immune system, it is not the primary mediator of the acute “fight-or-flight” response.

Choice C Reason:

ACTH (adrenocorticotropic hormone) is a hormone produced by the pituitary gland that stimulates the adrenal glands to release cortisol. It is part of the HPA axis and plays a role in the body’s long-term stress response, but it is not directly involved in the immediate activation of the sympathetic nervous system.

Choice D Reason:

Glucagon is a hormone produced by the pancreas that raises blood glucose levels by promoting the breakdown of glycogen to glucose in the liver. While it can be involved in the body’s response to stress by ensuring an adequate supply of glucose, it is not a primary mediator of the acute stress response mediated by the sympathetic nervous system.

Choice A: Size

Muscular hypertrophy refers to the increase in the size of muscle cells12. This process typically occurs as a result of strength training, where the muscles are subjected to stress and damage, leading to the repair and growth of muscle fibers. The increase in muscle cell size enhances muscle strength and mass, making it a key goal for athletes and bodybuilders.

Choice B: Vacuoles

Vacuoles are membrane-bound organelles found in cells, primarily involved in storage and transport of substances3. While vacuoles play important roles in cellular function, they are not directly related to muscular hypertrophy. The primary change in muscular hypertrophy is the increase in muscle cell size, not the number or size of vacuoles.

Choice C: Types

Muscle cells can be categorized into different types, such as slow-twitch (Type I) and fast-twitch (Type II) fibers4. However, muscular hypertrophy does not involve a change in the types of muscle cells. Instead, it focuses on the growth and enlargement of existing muscle fibers, regardless of their type.

Choice D: Number

An increase in the number of muscle cells is referred to as hyperplasia, which is different from hypertrophy. Hyperplasia involves the formation of new muscle cells, whereas hypertrophy involves the enlargement of existing muscle cells. Current evidence suggests that hypertrophy, rather than hyperplasia, is the primary mechanism for muscle growth in response to strength training.