1. Parathyroid Hormone (PTH) causes the kidneys to retain Ca2+. That means the kidneys keep calcium in the blood rather than let it go out into the urine. The target cells here are cells lining kidney tubules, which make urine.
Calcitriol causes the small intestine to absorb more calcium from your food. (think about what that means- you don't always absorb all of the calcium from your food- if you have plenty, some of it stays in the digestive tract and goes out with the feces!) The target cells here are cells lining the small intestine, which are responsible for moving nutrients from the lumen of the intestine into the blood. Both hormones exert their effect by causing their target cells to insert more calcium transporters into their membranes. The water-soluble hormone uses cAMP as a second-messenger.
Incidentally, PTH also causes cells of the kidneys to activate more calcitriol, and tells cells of the bone to release some stored calcium to the blood.
a. Are these hormones both water-soluble or fat-soluble, or is there one of each?
b. What chemical class does each belong to?
c. Draw a picture comparing and contrasting how each might cause its target cell to do this. Don't look it up! You have all the information you need from the notes to come up with a reasonable, logical hypothesis.
d. If somebody develops hyperparathyroidism (the parathyroid glands produce too much PTH), do you expect that person's blood levels of calcium to be too high or too low as a result? Explain.
e. If somebody develops hyperparathyroidism, will their bones gain or lose density?
Hi! As you have posted multiple questions, I will be answering the first two subparts for you. If you need help with the other questions, kindly repost them separately.
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