Phosphorus

Overview

Phosphorus is the third most abundent intracellular ion:

1. Potassium

2. Magnesium

3. Phosphorus (as Phosphate)

Within the body it is found as Phosphate ions, or Phosphate within bone. The majority (~95%) is combined with Calcium in bone, forming Hydroxyapatite. Less than 1% is found in the extracelullar fluid.

Homeostasis

Serum concentrations of phosphorus are maintained by dietary sources. It is absorbed across the intestine via Passive diffusion and Vitamin D mediated active transport.

Phosphorus is excreted in the urine or saliva (particularly in ruminants).

Hormonal Regulation

PTH

• Mobilises phosphorus from bone, acting to increase plasma concentration of P
• Increases phosphorus loss in the urine and saliva, acting to decrease plasma concentration

So ultimately, PTH acts to remove phosphorus from the body entirely.

Calcitriol

• Increases phosphorus absorbtion from the intestines

Pathology

Diseases relating to phosphorus homeostasis include:

• Primary and Secondary Hyperparathyroidism
• Hyperphosphataemia
• Hypophosphatemia

Test yourself with the Phosphorus Homeostasis Flashcards

Phosphorus Homeostasis Flashcards