CALCIUM-METABOLISM

SUMMARY

1. Two endogenous hormones increase serum calcium level: 1,25-(OH)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 in the kidney (1,25-(OH)₂D).

3. 1,25-(OH)₂D, in turn, increases Ca²⁺ 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)₂D 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.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].