Phosphorus Disorders Flashcards
What are the roles of phosphorus?
constituent of structural phospholipids in
cell membranes
- hydroxyapatite in bone
- an integral component of nucleic acids
- phosphoproteins involved in mitochondrial oxidative phosphorylation.
- Energy for essential metabolic processes
(e.g., muscle contraction, neuronal impulse conduction, epithelial transport) is stored ATP.
- 2,3-diphosphoglycerate (2,3-DPG) decreases the affinity of hemoglobin for oxygen and facilitates the delivery of oxygen to tissues.
- Cyclic adenosine monophosphate
(cAMP) is an intracellular second messenger for many polypeptide hormones.
- also an important urinary buffer, and urinary phosphate constitutes the
majority of titratable acidity
- Phosphorus is important in the intermediary metabolism
of protein, fat, and carbohydrate and as a component
of glycogen.
What is organic vs inorganic phosphorus?
organic (phospholipids and phosphate
esters)andinorganic(orthophosphoricandpyrophosphoric
acids) forms in the body
Almost all serum phosphorus is
in the form of orthophosphate.
How many mg in one millimole of phosphorus
31mg per mmol of elemental phos
At a pH of 7.4 how many mEq is 1 mmol of phos
1.8mEq
how much inorganic phosphorus is protein bound?
Approx 10-20%
How much inorganic phos is in bone?
80-85%
What is the normal serum phos of a dog/
2.5-6.0mg/dL - higher in younger dogs
What causes an increased phos in younger animals?
Bone growth and an increase in renal tubular reabsorption of phosphorus mediated by growth hormone
Why does feeding carbohydrates cause a decrease in serum phos?
bc phos shifts intracellularly as a result of glycolysis and formation of phosphorylated glycolytic intermediates in muscle, liver and adipose.
Why does a resp alkalosis cause a decrease in phos?
stimulates glycolysis
(by activating phosphofructokinase) and decreases
serum phosphorus concentration
What may result in inaccurate phos meausrements?
Hyperlipidemia
hyperproteinemia
Thrombocytosis
monoclonal gammopathy
Mannitol and other drugs
Icterus
hemolysis
What % of oral phosphate is absorbed?
60-70% absorbed in a linear function
What are the two mechanisms that result in intestinal phosphate absorption
- Passive diffusion is the principle route - paracellular. All segments
- Active -> mucosal transport is sodium dependent. Is saturable. Calictriol inhances absorption. Duodenum
What occurs during phosphate deprivation?
Renal - decrease phos excretion to almost 0 in 3 days
GI - continues to loss phos but gradually reduces over 3 weeks
This may result in a negative phos balance
Normally how much of the filtered phos load is resorbed by the kidneys?
80-90%
How is phos resorbed in the proximal tubule?
brush border sodium-phos cotransporters. translocates 3Na and 1 divalent phos
Luminal entry is the rate limiting step