Multiple Choice
The effects of epinephrine are typically observed within which of the following time frames after its release into the bloodstream?
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16. The Endocrine System
Introduction to the Endocrine System
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Which organs are primarily involved in the synthesis of calcitriol, the active form of vitamin D?
A
Pancreas, thyroid, and adrenal glands
B
Skin, liver, and kidneys
C
Stomach, small intestine, and colon
D
Heart, lungs, and spleen
Verified step by step guidance1
Understand that calcitriol is the active form of vitamin D, which plays a crucial role in calcium and phosphate homeostasis in the body.
Recognize that the synthesis of calcitriol involves multiple organs working sequentially: the skin, liver, and kidneys.
Step 1: In the skin, ultraviolet (UV) radiation converts 7-dehydrocholesterol into cholecalciferol (vitamin D3). This is the first step in the synthesis process.
Step 2: In the liver, cholecalciferol is hydroxylated at the 25th carbon position by the enzyme 25-hydroxylase, forming 25-hydroxyvitamin D (calcidiol).
Step 3: In the kidneys, calcidiol undergoes a second hydroxylation at the 1st carbon position by the enzyme 1-alpha-hydroxylase, forming calcitriol, the biologically active form of vitamin D.
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