Calcitonin

[dmission]

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I was hoping someone could clarify this for me. Does calcitonin lower blood calcium levels by depositing them into bone, thereby making bones stronger? Otherwise I'm very confused.. thanks! (Whereas PTH would do the opposite?)

 

[muhali3]

Well, I'm not exactly sure calcium deposition onto bone would make it stronger by any significant amount. The strength of bone is due to its complex matrix, consisting of many proteins, not just minerals.

But all you need to know for the MCAT is calcitonin lowers blood calcium.

 

[dmission]

Ok, thanks. And since this is about hormones, I was reading that PTH directly impacts renal calcium reabsorption, and I'm just wondering if calcitonin does the same thing?

 

[muhali3]

Yeah, it does, it lowers renal absorption of calcium and phosphate.

 

[dmission]

Yeah, it does, it lowers renal absorption of calcium and phosphate.

So would it lower the absorption so more can be sent to the bone then, since it doesn't go to the blood?

 

[muhali3]

No, it just goes out in the urine.

http://en.wikipedia.org/wiki/Calcitonin#Effects

 

[muhali3]

Actually, I'll take back that it doesn't make bones stronger, because it is used as a treatment for osteoporosis.

As you can see, I'm getting all this from Wikipedia.

But still, for the MCAT: calcitionin decreases blood calcium concentrations.

 

[MT Headed]

EK Audio Osmosis has an awesome mnemonic for calcitonin:

"calcitonin tones the bone" (and then they play a little "ding")

While the purpose of calcitonin is to lower blood calcium levels via multiple methods (don't absorb calcium into the blood from the intestines, excrete calcium through the kidneys, use calcium to build bone), this little mnemonic helps you remember that calcitonin removes blood calcium, and therefore its opposite (parathyroid hormone, or PTH) increases blood calcium levels.

*ding*

 

[muhali3]

EK Audio Osmosis has an awesome mnemonic for calcitonin:

"calcitonin tones the bone" (and then they play a little "ding")

From that you can think about all the things a body would need to do to build up bone, i.e. collect calcium from the digestive system, don't throw away calcium in the urinary system, and deposit said calcium on the bones to tone them up.

*ding*

I use the same mnemonic too.

But...

Namely, calcitonin:

• Inhibits phosphate reabsorption by the kidney tubules[9]
• Calcitonin decreases tubular reabsorption of Ca2+, leading to increased rates of its loss in urine.[10]

and

Calcitonin lowers blood Ca2+ levels in two ways:

• Inhibits Ca2+ absorption by the intestines[7]
• Inhibits osteoclast activity in bones[8]
• Vitamin D regulation

So, the function of calcitonin is to primarily lower blood calcium and not to build up bone. The fact that it builds up bone in order to lower blood calcium is just a coincidence. It also inhibits absorption of calcium in the intestines and kidneys, so the function of calcitonin is not to build bone.

 

[MT Headed]

Yeah, my bad. Don't listen to me. I took the MCAT on friday, amazing how quickly this knowledge evaporates. I'm gonna edit my response a little... 😳

 

[muhali3]

it's ok...i say wrong stuff on here too.

 

[notbobtrustme]

CalcitonIN puts calcium IN urine/bone. To get IN to urine/bone, it has to come out of blood.

ParathyRoID hormone RIDs the bone of calcium. The only place calcium can go is into the blood.

That's how I remember it.

 

[dmission]

CalcitonIN puts calcium IN urine/bone. To get IN to urine/bone, it has to come out of blood.

ParathyRoID hormone RIDs the bone of calcium. The only place calcium can go is into the blood.

That's how I remember it.

Good one 👍 Thanks.

My only question though; is it important to also know about the absorption/phosphate?

 

[muhali3]

No.

MCAT Bio is very simple, if you've taken any of the AAMCs yet.

 

[notbobtrustme]

Good one 👍 Thanks.

My only question though; is it important to also know about the absorption/phosphate?

I'm sure it's important to know, but at the same time, calcitonin/PTH is likely to show up in a passage about bones in general, not in kidney function (unless it's explained). There's only so many answer choices that can be made, so I highly doubt the phosphate secretion/absorbion is absolutely necessary. I certainly don't have it memorized.

 

[salim271]

Both calcitonin and PTH work indirectly to affect blood cal levels by either stimulating or limiting osteoclast activity, they dont directly cause the bone to uptake or release calcium.