Pathophysiology Calcium Question

Question

Explain how malabsorption of calcium from the intestine would affect serum calcium and serum PTH.

Any help on this question would be greatly appreciated, thanks!

Answer 1

Parathyroid hormone control calcium levels in the blood when low by mobilizing calcium from bones. Vitamin D is the major controller of serum calcium and it absorbs calcium from the intestine through active and passive absorption pathways. Malabsorption from the intestine cause decreased serum levels and then PTH mobilizes calcium from bones to maintain the calcium homeostasis, but if the condition continues then aftereffects of this excessive calcium removal show effects in the form of pathological fractures of bones. so low calcium levels cause raised PTH and raised PTH to raise the level of calcium in serum.

Answer 2

If the intestines are unable to absorb calcium, this would likely mean that serum calcium levels are low. If serum calcium levels are low then that means serum PTH will be high. When PTH is high, this will increase the levels of serum calcium back to normal levels. Once calcium levels are returned to normal, PTH will slowly lower in the blood.

Remember the modes of action of PTH

1. BONES: PTH stimulates the release of calcium from reservoirs stored in bones. This hormone also releases calcium through an indirect process of stimulating osteoclasts to reabsorb bone. Many of the nitty gritty details involved in this process are largely unknown still but just know that PTH can release calcium from bones.
2. KIDNEYS: PTH can suppress the loss of calcium from urine. This happens by stimulating tubular reabsorption of calcium. The kidneys also produce the active form of vitamin D in response to PTH which can assist in the next process.
3. SMALL INTESTINES: Since your question says malabsorption in intestines I think this still applies. The generation of active vitamin D from the kidneys induces the synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates the absorption of calcium in the blood. Again since the question states malabsorption, this may be omitted and you can just go with the bone reabsorption.

I like to think of these two calcium hormones this way

Calcitonin tones the bones

Parathyroid VOIDS the bones of calcium

I hope this helps, if you need any more specifics or have any other questions, be sure to contact me!