The thyroid gland is under the control of the pituitary glan…

The thyroid gland is under the control of the pituitary gland. When the level of thyroid hormones (T3 and T4) drop the pituitary gland produces thyroid stimulating hormone (TSH), which stimulates the thyroid to produce more hormones. Under the influence of TSH, the thyroid will manufacture and secrete more T3 and T4, thus raising blood levels of thyroid hormones. The pituitary gland senses this and will decrease TSH production. This cycle is an example of a(n):

The human body obtains vitamin D either from the diet or sun…

The human body obtains vitamin D either from the diet or sun exposure. Darker-skinned individuals require more sunlight to create adequate vitamin D stores as the increased melanin in their skin acts like sunscreen; thus, it blocks the necessary UV required for vitamin D synthesis. Therefore, if these individuals spend inadequate time in the light, dietary sources of vitamin D are necessary. What form of vitamin D requires sunlight for its formation?