Physiology
Endocrine
What is the effect of activated vitamin D on the renal handling of calcium:
Answer:
Activated Vitamin D acts to increase renal calcium reabsorption (in the distal tubule via activation of a basolateral Ca2+ ATPase pump) and increase renal phosphate reabsorption.Vitamin D
Physiology / Endocrine / Calcium and Bone
Last Updated: 21st April 2019
Vitamin D2 (ergocalciferol), derived from plants and yeasts and Vitamin D3 (cholecalciferol), derived from animal (particularly dairy) products, are obtained in the diet and absorbed in the small intestine. Vitamin D3 can also be manufactured from cholesterol within the body, via a reaction that is enabled by ultraviolet irradiation of the skin.
Production of Activated Vitamin D
The D vitamins are converted to calcifediol (25-hydroxycholecalciferol) by vitamin D 25-hydroxylase in the liver.
This is further converted to activated vitamin D (calcitriol or 1, 25 - dihydroxycholecalciferol) by 1-alpha-hydroxylase in the cells of the renal proximal tubule. This final reaction is the slowest step in the process and therefore regulates the speed of the entire chain of reactions.
The enzyme 1-alpha-hydroxylase is stimulated by parathyroid hormone (PTH) and thus this final step is regulated by PTH.
Activation of Vitamin D. (Image modified by FRCEM Success. Original by SportEx Medicine via www.flickr.com)
Effects of Activated Vitamin D
Activated vitamin D acts to:
- GUT:
- increase calcium and phosphate absorption in the small intestine (the main action)
- KIDNEYS:
- increase renal calcium reabsorption (in the distal tubule via activation of a basolateral Ca2+ ATPase pump)
- increase renal phosphate reabsorption
- inhibit 1-alpha-hydroxylase activity in the kidneys (negative feedback)
- PARATHYROID GLANDS:
- inhibit PTH secretion from the parathyroid glands
Effects of Activated Vitamin D. (Image by SportEx Medicine via www.flickr.com)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
