Question

multiple choice 2 points
which of the following is not a function of parathyroid hormone (pth)?
inhibit osteoblast activity
stimulate osteoclast activity
lower blood calcium
promote calcium reabsorption by the kidneys
promote calcitriol synthesis

Explanation:

Identify the core function of parathyroid hormone

Parathyroid hormone (PTH) is secreted by the parathyroid glands in response to low blood calcium levels. Its primary physiological goal is to increase blood calcium levels back to homeostasis.

Analyze the effects of PTH on bone cells

To raise blood calcium, PTH acts on bone tissue. It stimulates osteoclasts (bone-resorbing cells) to break down bone matrix and release calcium into the blood. It also inhibits osteoblasts (bone-building cells) to prevent them from depositing calcium into the bone matrix. Thus, inhibiting osteoblast activity and stimulating osteoclast activity are both true functions of PTH. This relates to our understanding of Bone Cell Types.

Analyze the effects of PTH on the kidneys

PTH acts on the kidneys to increase the reabsorption of calcium from the urine back into the blood, preventing calcium loss. Additionally, PTH stimulates the kidneys to activate vitamin D into calcitriol (active vitamin D), which in turn increases calcium absorption in the intestines. Therefore, promoting calcium reabsorption by the kidneys and promoting calcitriol synthesis are both true functions of PTH.

Identify the incorrect function

Since the primary purpose of PTH is to raise blood calcium levels, the statement "Lower blood calcium" is directly opposite to its actual function. Therefore, lowering blood calcium is not a function of parathyroid hormone.

Answer:

• Inhibit osteoblast activity
• Stimulate osteoclast activity
• Lower blood calcium (Correct answer)
• Promote calcium reabsorption by the kidneys
• Promote calcitriol synthesis