Physiology
Renal
Regarding phosphate, which of the following statements is CORRECT:
Answer:
Phosphate is abundant in the body and is an important intracellular and extracellular anion (but is predominantly intracellular). About 65% of dietary phosphate is absorbed, mainly in the duodenum and jejunum by a transcellular process which is enhanced by vitamin D. Ca2+ and PO43- precipitate to form insoluble calcium phosphate and their concentrations in the blood are close to the saturation point at which calcium phosphate complexes precipitate out of solution onto the bone matrix. Therefore an increase in one of the ions results in the precipitation of some calcium phosphate and thus some of the other ion is removed from the solution; Ca2+ and PO43- concentrations are thus inversely proportional. Unbound PO43- is filtered freely at the glomerulus and there is reabsorption along the nephron.Phosphate Handling
Physiology / Endocrine / Calcium and Bone / Renal / Calcium Balance
Last Updated: 21st April 2019
Phosphate is abundant in the body and is an important intracellular and extracellular anion (but is predominantly intracellular). About 65% of dietary phosphate is absorbed, mainly in the duodenum and jejunum by a transcellular process which is enhanced by vitamin D.
Ca2+ and PO43- precipitate to form insoluble calcium phosphate and their concentrations in the blood are close to the saturation point at which calcium phosphate complexes precipitate out of solution onto the bone matrix. Therefore an increase in one of the ions results in the precipitation of some calcium phosphate and thus some of the other ion is removed from the solution; Ca2+ and PO43- concentrations are thus inversely proportional.
Renal Phosphate Handling
Unbound PO43- is filtered freely at the glomerulus and there is reabsorption along the nephron. The maximum rate of reabsorption is limited and and excess filtered phosphate above a threshold level is excreted. Of filtered phosphate, 80% is reabsorbed in the proximal tubule by a transcellular process. The distal tubules reabsorb a further 10% of the filtered phosphate and the collecting ducts a further 2 - 3%.
PO43- renal excretion is regulated by:
- PTH (increases excretion by inhibiting reabsorption in the proximal tubule)
- activated vitamin D (decreases excretion by increasing reabsorption in the distal tubule)
- acidosis (increases excretion)
- glucocorticoids (increases excretion)
- calcitonin (increases excretion)
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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 |
