Which of the following is secreted by the pituitary gland continuously throughout the life span?

Thyroxine (T4) is produced by the thyroid gland, not the pituitary gland. Its secretion is regulated by thyroid-stimulating hormone (TSH) released from the pituitary, creating a feedback loop rather than continuous secretion. While thyroxine levels fluctuate based on metabolic needs, it is not secreted continuously throughout life.

Melatonin is secreted by the pineal gland, primarily in response to darkness, and its levels vary significantly throughout the day-night cycle. It is involved in regulating sleep-wake cycles and is not continuously secreted, making it an inappropriate choice for this question.

Oxytocin, produced by the hypothalamus and released by the posterior pituitary, is involved in childbirth and lactation and is secreted in response to specific stimuli rather than continuously. Its release is episodic and varies based on physiological and emotional factors.

Cortisol is produced by the adrenal glands, regulated by adrenocorticotropic hormone (ACTH) from the pituitary gland. Although cortisol levels can fluctuate throughout the day, particularly in response to stress, it is not secreted continuously and has a diurnal rhythm.