Parathyroid hormone:
a. Increases bone formation and lowers blood calcium levels
b. Increases calcium excretion from the body
c. Decreases calcium absorption from the gut
d. Demineralizes bone and raises blood calcium levels

Guida verificata passo dopo passo

Step 1: Understand the role of parathyroid hormone (PTH) in calcium homeostasis. PTH is secreted by the parathyroid glands and primarily functions to increase blood calcium levels when they are low.

Step 2: Recall that PTH acts on bones by stimulating osteoclasts, which break down bone tissue, releasing calcium into the bloodstream. This process is called bone demineralization.

Step 3: Recognize that PTH also acts on the kidneys to reduce calcium excretion, meaning it helps the body retain calcium rather than lose it through urine.

Step 4: Note that PTH indirectly increases calcium absorption from the gut by stimulating the production of active vitamin D (calcitriol), which enhances calcium uptake from food.

Step 5: Based on these actions, identify the correct description of PTH's effect: it demineralizes bone and raises blood calcium levels.

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Parathyroid Hormone (PTH) Function

Parathyroid hormone is a key regulator of calcium homeostasis in the body. It primarily acts to increase blood calcium levels by stimulating bone resorption, enhancing calcium reabsorption in the kidneys, and promoting calcium absorption in the intestines indirectly through activation of vitamin D.

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Bone Remodeling and Calcium Mobilization

Bone remodeling involves the balance between bone formation and resorption. PTH promotes bone resorption by activating osteoclasts, which break down bone tissue, releasing calcium into the bloodstream, thus increasing blood calcium levels.

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Calcium Absorption and Excretion

Calcium absorption occurs mainly in the intestines and is enhanced by active vitamin D, which is stimulated by PTH. PTH also reduces calcium excretion by the kidneys, conserving calcium in the body and contributing to elevated blood calcium levels.

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