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1. Two endogenous hormones increase serum calcium level: 1,25-(0H) 2 -vitamin D and parathyroid hormone (PTH).

2. Vitamin D is made in the skin after a reaction with sunlight but is inert until it is sequentially hydroxylated, first in the liver (to form 25-0H-D), and then again in the kidney (1,25-(OH) 2 D).

3. 1,25-(OH) 2 D, in tum, increases Ca 2+ and phosphorus absorption from the gut.

4. PTH increases calcium in the blood through the following:
- Stimulates release of bone calcium stores by indirect stimulation of osteoclasts ( c = chew bone)
- Increases renal tubular Ca2+ resorption and renal tubular phosphorus excretion
- Increases the production of 1,25-(OH) 2 D by increasing activity of kidney hydroxylase

5. Calcitonin - PTH antagonist. Decreases osteoclast activity + increases renal calcium clearance.

6. Estrogen - similar to calcitonin, decreases bone resorption + increases osteoblastic activity.


1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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