What structural feature allows skeletal muscles to contract efficiently?

A. Hormonal secretion: While bone tissue does secrete certain hormones like osteocalcin, hormonal secretion is not its primary function. The main roles of bones are structural support, movement, and protection.

B. Digestive enzyme production: Digestive enzymes are produced by organs such as the pancreas and stomach. Bone tissue does not contribute to digestion or enzyme production.

C. Oxygen transport: Oxygen transport is carried out by red blood cells in the bloodstream. Bone tissue provides a site for blood cell production in the marrow but does not directly transport oxygen.

D. Protection of internal organs: One of the primary functions of bone tissue is to protect vital internal organs. For example, the skull shields the brain, and the ribcage protects the heart and lungs, while bones also provide structural support and enable movement.

A. Insulin: Insulin is produced by the beta cells of the pancreas and regulates blood glucose levels. It promotes the uptake of glucose into cells and its storage as glycogen, playing a central role in energy metabolism.

B. Epinephrine: Epinephrine is synthesized in the adrenal medulla and functions in the fight-or-flight response. It increases heart rate, blood pressure, and blood glucose levels to prepare the body for rapid activity.

C. Growth hormone (GH): Growth hormone is secreted by the anterior pituitary gland. It stimulates growth of bones and tissues, promotes protein synthesis, and regulates metabolism, affecting multiple organ systems throughout the body.

D. Cortisol: Cortisol is produced by the adrenal cortex in response to ACTH from the anterior pituitary. It regulates metabolism, supports the stress response, and influences immune and anti-inflammatory functions.