Final - Phosphorus Flashcards
What are the sources of phosphorus?
The sources are widely distributed in meat, poultry, fish, eggs and milk
Animal products are superior sources of available P
How is Phosphorus found in plants?
80% of P in plants is found as phytate
This limits the bioavailability to 50%
WHat inhibits phosphorus absorption?
Phytate, excessive intakes of magnesium, calcium and aluminum
What enhances phosphorus absorption?
Vitamin D
Why is phytate absorption inhibited?
mammalian digestive system lacks phytase
-Yeast and bacteria can hydrolyze some phytates to generate free P
How is phosphorus usually found?
Both organic and inorganic forms of phosphorus are not usually found free
How is organic P found?
Organic P is bound to proteins, sugars & lipids and it requires hydrolysis
How is phosphorus absorbed?
Phosphorus is absorbed in its inorganic form
What enzymes free organically bound P (that are not bound to Phytate)?
Phospholipase C
Alkaline phosphatase
Pepsin/Trypsin - releases protein bound P
What are the two processes that Phosphorus is absorbed by?
A saturable carrier mediated active transport system that is dependent on sodium (transported in vesicles) (Na-phosphate co transporter)
A concentration dependent diffusion process
How is most of the P found the blood?
Most P in blood is organic
What biological processes is Phosphorus involved in?
Energy transfer/storage Cell membrane structure Nucleic acid formation Intracellular second messenger Acid-base balance Bone mineralization
How does P function in Energy storage and transfer?
It functions via high energy phosphate bonds (ATP - adenosine triphosphate)
Creatine phosphate
Uridine phosphate (UTP) - activates UDP-glucose in glycogen synthesis
Coenzymes TPP NADP
How does P function in cell membrane structures?
It is an important component of DNA and RNA
The phospholipids in cell membranes
How does P function as an intracellular second messenger?
It is a structural component of cAMP (activates protein kinase) Inositol triphosphate (I3P) triggers Ca release
How does P function in acid base balance?
Phosphate is the main intracellular buffer
Role of phosphoproteins
Phosphorylation of different molecules regulate metabolism
Changes cellular activity of different proteins (enzymes)
Phosphorylation vs. dephosphorylation
How is P important in skeletal tissue?
Amphorus calcium phosphate and crystalline forms (hydroxyapatite -the chief structural element of bone)
What hormones influence P metabolism?
PTH, calcitriol and calcitonin influences P metabolism
How does PTH effect P?
PTH - stimulates reabsorption of phosphate from bone and stimulates the excretion of P in urine
How does Calcitriol effect P?
Calcitriol stimulates P reabsorption in the kidney and absorption of alkaline phosphatase in the gut
How does calcitonin effect P?
Calcitonin promotes bone mineralization (decreases plasma P)
how is phosphorus excreted?
The kidneys retain about 80% of the P filtered by the glomerulus
The PTH decreases the reabsorption by the proximal tubular cells
What is the deficiency of phosphorus?
Hypophosphatemia
Who gets hypophosphatemia?
Phosphate deficiency - It is rare It is common in hospital patients who are seriously ill -Leukemia & lymphoma -High bilirubin -Respiratory alkalosis, sepsis Heat stroke, gout (uric acid)
X-linked hypophosphatemina & dents syndrome - with out total body phosphorus deficit
What are the symptoms of Hypophosphatemia
It impairs growth
- early P deficiency is associated with losses of K, Mg and N
- Leads to abnormalities of cellular iron transport
Osteomalcia will occur in long standing P deficiency
Other symptoms: profound muscle weakness Myopathy and cardiopathy Respiratory insufficiency Erythrocyte, leukocyte and platelet dysfunction Metabolic acidosis
What might reduce plasma P and cause hypophosphatemia other that being seriously ill?
Decreased intake/intestinal absorption Vitamin D Deficiency Malabsorption Excessive vomiting Phosphate binding antacids Hyperparathyroidism Renal tube deficits Nervous system dysfunction
