Phosphorus Flashcards
Phosphorus food sources
Protein
Poultry, fish, meat
~15mg P/g Protein
Some in dairy products
Other sources: Nuts legumes cereal grains chocolate Soft drinks (dark soft drinks)
How is Phosphrous found in food?
Usually not found in the free form in nature
Typically in the organic form - bound to proteins, lipids, sugars
Phytates (Phytic Acid)
- Found in cereal grains, wheat, rice, corn
- Beans, legumes, nuts
How bioavailable is Phytate?
Less bioavailable then Phosphorus because when consumed it will bind to other minerals such as Ca, Zn, Fe, Mg making the Phosphorus in Phytate unavailable
What enhances P absorption?
Vitamin D
What inhibits P absorption?
Phytate Excessive intakes of: Mg Ca Al
Food Processing does what to food?
Adds more phosphorus in order to preserve shelf life
Foods high in Phosphorus Food Additives
Restructured meats Processed and spreadable cheeses Instant products Refrigerator bakery products Beverages
Which foods would the body absorb more P from?
Processed foods because it is more bioavailable
Someone with chronic kidney disease should stay away from which foods?
Processed foods because the phosphorus is absorbed more.
How is P absorbed?
By facilitated diffusion
Active transport only when intake is low or demand increased
Active transport of P is controlled by what?
Vitamin D
What is NPT2b?
A transporter for P uptake into the small intestine located on the apical membrane
Where is P found in the body?
Mainly in bone
Extracellular fluid
Soft tissues like muscle
What are hydroxyapatite crystals?
Constant ratio of calcium to phosphate 2:1
How does phosphorus move in and out of bone mineral?
Ionic exchange (another ion will substitute the bone) and active bone resorption
P Excretion
Most of it is excreted in urine by kidney
Little in the feces
What is chronic kidney disease?
They cannot excrete phosphorus. hence why they are on phosphorus restricted diets
What is a major regulator of blood phosphorus?
Renal excretion
Reabsorption and excretion of P vary because of
Blood P level
How are phosphorus levels regulated in the blood?
By hormonal changes
PTH along with Calcitriol (Vitamin D) triggers release of Ca from bone along with P
Which is more tightly regulated: Serum Ca or Serum P?
Serum Ca
Serum p ranges
3-4.5 mg/dl
Phosphorus Functions
Regualtions of acid/base balance (buffer) DNA/RNA Minerilization of bone and teeth Phospholipid structure ATP Regulation of enzyme activity
P Status Assessment
Serum P
What is the problem with using Serum P as assessment?
May not reflect body P stores
Only directly related to what is absorbed
Wide diurnal variations: circadian rhythm
P Def
Hypophosphatemia
Cause of P Def
Low absorption increased excretion hyperparathyroidism phosphorus imbalances malabsorptive diseases alcoholism large doses of antacids refeeding syndrome
RDA
700mg/d
Toxicity
Can cause hypocalcemia
UL 4000mg
