Which of the following is a normal skin change associated with aging?

A. Cushing's syndrome is most commonly caused by the hypersecretion of cortisol from the adrenal glands. It can also result from excess production of adrenocorticotropic hormone (ACTH) from the pituitary gland, but the primary issue is often adrenal hypersecretion.

B. While the pituitary gland can contribute to Cushing's syndrome by secreting too much ACTH (which stimulates the adrenal glands), it is the adrenal glands that primarily cause the symptoms of the condition.

C. The parathyroid glands are responsible for regulating calcium levels in the blood, not for the production of cortisol.

D. The thymus plays a role in immune system development, but it is not involved in Cushing's syndrome.

A. Cardiac index is a measurement of cardiac output adjusted for body surface area. It provides a more individualized assessment of heart function, but it does not describe the amount of blood ejected during each contraction.

B. Cardiac output refers to the total amount of blood the heart pumps in one minute, which is the product of stroke volume and heart rate. However, it describes the overall volume pumped by the heart, not the blood ejected per contraction.

C. Stroke volume is the term used to describe the amount of blood ejected from the left ventricle during each contraction. It is a key indicator of cardiac function.

D. Ejection fraction is the percentage of blood in the left ventricle that is pumped out with each contraction, representing the efficiency of the heart. It is related to stroke volume but is not the same as the volume ejected per contraction.