Phosphorus

Learning Objectives Dietary sources Daily Requirements Metabolism Important functions and Deficiency diseases

Phosphorous P At. No. 15 Atomic Mass: 30.77

PHOSPHORUS

Dietary Source Present in all foods, Dietary deficiency is therefore unknown. Distribution is similar to Ca++ . Adequate, intake of one ensures that of the other. Best sources (Milk and milk products) Lean meat is also a good source.

Recommended Dietary Allowance Infants Up to 6 months 240 mg 6 m – 1.0 year 360 mg Children 1 – 3 800 mg 4 – 6 800 mg 7 – 10 800 mg

Recommended Dietary Allowance Adults (Male/Females) 11 – 14 1200 mg 15 – 18 1200 mg 19 – 22 800 mg 23 – 50 800 mg 51+ 800 mg Pregnant and lactating women should take an additional 400 mg.

Absorption and Metabolism Normally about 70% of dietary P is absorbed (For calcium 10 – 30%) Mid jejunum is the main site of absorption for free PO4 . In ileum absorption occurs via active process.

Absorption and Metabolism Most of phosphorus in food is in combined form, absorption requires splitting off of PO4 by intestinal enzymes (Phosphatases) is hydrolyzed in GIT by Pancreatic & intestinal enzymes.

Absorption and Metabolism Inorganic phosphorus is released and absorbed Its absorption decreases during period of increased utilization of carbohydrate

Factors affecting absorption Similar to Calcium like: Enhancement by Vit D and Inhibition by binding agents i.e. Iron and Aluminium. Ca : P ratio in diet. Excess of one causes, an increased excretion of other.

Ratio of P : Ca Ideal 1 : 1 , Specially during the period of rapid growth (childhood), pregnancy and lactation. Ratio in other age groups if different, have no serious adverse effect

In Infants Care should be exercised as kidneys can’t handle high phosphate load. For Prevention of hypocalcemic tetany Ca : P ratio be 1.5 : 1 Ratio should be reduced to 1:1 by age 1 yr

Distribution Phosphorus accounts for about 1% of TBW. ¼th of total body mineral matter 80 – 90% joined with Ca++ in bones and teeth (Ratio 2:1) as a component of calcium phosphate and is being constantly deposited and liberated from bone structure. 10 – 20% present in all cells as phosphate ion (PO=4)

Functions Component of many compounds involved in many metabolic reactions. Sugar – PO4 linkage in DNA and RNA Phospholipids  Transport of fat in blood Phospholipids  cell membrane control transport of substances into and out of cell

Functions Phosphorylation Necessary for glucose absorption from intestine Glucose uptake by individual cells Resorption of glucose by kidney

Functions Monosaccharides are Phosphorylated several times during metabolic break down to yield energy. Involved in storage and release of Energy through high energy phosphate bond of ATP and ADP.

Functions Essential part of body’s delicate buffer system Many B vitamins becomes active only when combine with phosphate.

Hypo-Phosphatemia Diminished Supply: Starvation Malnutrition Vit D – Deficiency Increased excretion / loss Hyperparathyroidism Hyper thyroidism Renal defects

Hypo-Phosphatemia Intracellular shift of phosphorus Glucose induced Insulin induced Respiratory alkalosis Electrolytes administration Hypercalcaemia Hypomagnesimia

Hyper-Phosphatemia Endocrine disease 2. Renal Diseases Increased growth hormones (acromegaly) Hypo parathyroidism low calcium Pseudo hypo parathyroidism 2. Renal Diseases Chronic renal insufficiency Acute renal failure

Hyper-Phosphatemia 3. Catabolic states Excess intake or Absorption Stress or injury Chemotherapy for malignant disease Excess intake or Absorption Laxatives or Enemas containing phosphate Hyper vitaminosis – D

Excretion Phosphate level is regulated by urinary excretion 2 mg / dl is the renal thresh hold 500 mg / day is excreted in urine

Excretion General factors affecting intestinal absorption Plasma concentration and Hydrolysis of PO4 esters by phosphatases in the kidney. Decrease Ca++ intake will increase urinary PO4 excretion

Clinical Importance