Which of the following glands synthesizes antidiuretic hormone?

The hypothalamus is a region of the brain that synthesizes antidiuretic hormone (ADH), also known as vasopressin.

ADH is then transported to the posterior pituitary gland via neurohypophysial capillaries, where it is stored until it is ready to be secreted into the circulation.

Choice A. Pineal gland is not correct because it is a small endocrine gland located in the brain that secretes the hormone melatonin, which regulates sleep-wake cycles, but it does not synthesize ADH.

Choice B. Thymus is not correct because it is a gland located in the chest that produces hormones involved in immune system development, but it does not synthesize ADH.

Choice D. Pancreas is not correct because it is a gland located behind the stomach that secretes hormones such as insulin and glucagon, which regulate blood sugar levels, but it does not synthesize ADH.

Calcium ions play a crucial role in initiating muscle contraction.

When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.

Some of this calcium attaches to troponin, which causes it to change shape. This shape change exposes binding sites for myosin on the actin filaments.

Myosin’s binding to actin causes cross-bridge formation, and muscle contraction begins.

The other ions mentioned in the question do not have this specific role in muscle contraction.

Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.

Phosphorus ions are important for energy metabolism but do not bind to the troponin complex.

Sodium ions are important for generating action potentials but do not bind to the troponin complex.