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
What is the most common regulator of renal phos?
PTH - it decreases the tubular transport
What effect does growth hormone have on renal phos?
It increases resorption - partially accounts for high phos in young animals.
What effects does high doses of glucocorticoids have on renal phos.
Decreases absorption
What effects does acid base status have on phos resorbtion
Metabolic acidosis - Acute : Nil, chronic: Decreased
Resp acidosis - decrease
Resp alk - increase
What are phosphatonins?
substances that increase renal loss
- fibroblast growth factor
- secreted frizzled-related protein
- matrix extracellular phosphoglycoprotein
Hypophosphataemia
What detrimental effects may be seen with hypophosphataemia ?
decreased RBC ATP –> haemolysis
impaired red cell 2,3-DPG –> impair O2 delivery
impaired leukocyte function
Impaired platelet function
Muscle weakness and pain - rhado
GI signs and illeus
Neuro signs
Decreased cardiac contractility
Causes of hypophosphataemia
What are broad causes of hypophos?
translocation of
phosphate from extracellular to intracellular fluid (maldistribution),
increased loss (decreased renal reabsorption of
phosphate), or decreased intake (decreased intestinal
absorption of phosphate).
What are causes of translocation?
DKA treatment
Carb loading
Resp alkalosis
TPN
Hypothermia
Causes of increased Loss?
primary hyperPTH
renal tubular disease - fanconis
renal transplant
proximally acting diuretics
eclampsia
hyperA
Causes of decreased intake
GI signs,
Malabsorptive disease
Vit D deficiency
Phos binders
Why does Vit D deficiency cause hypophos?
because hypocalcemia increases PTH secretion, which
increases renal phosphate excretion. Decreased intestinal
phosphate absorption presumably also plays a role in this
setting.
What are the risks of parenterally administered phos?
hypocalcemia, tetany, soft tissue mineralization,
renal failure, or hyperphosphatemia
if very cautious (e.g., 0.01 to 0.06
mmol/kg/hr in dogs and cats with measurement
of serum phosphorus concentration every 6 to
8 hours)
HyperPhos
What are the major clinical consequences of hyperphos?
hypocalcaemia and tissue mineralisation
What is the main cause of hyperphosphataemia in small animals?
Decreased renal excretion
What are causes related to translocation?
Tumor cell lysis
* Tissue trauma or rhabdomyolysis
* Hemolysis
* Metabolic acidosis
What are causes related to increased intake
Gastrointestinal
○ Phosphate enemas
○ Vitamin D intoxication (e.g., cholecalciferol containing rodenticides, calcipotriene)
Parenteral
○ Intravenous phosphate
What are causes relating to decreased excretion?
Acute or chronic renal failure
* Uroabdomen or urethral obstruction
* Hypoparathyroidism
* Acromegaly (?)*
* Hyperthyroidism
Why does CKD cause hyperphos
As GFR decreases filtered load of phos decreases, intake remains constant = hyperphos
Treatment of hyperphos?
Saline volume expansion - natriuresis impairs phos resorption and GFR increase causes larger filtered load.
insulin glucose - rarely if ever used
reduce phos intake
never give them calcium lol
How do phos binders work?
Phosphate binders work because
the cation in the binder combines with dietary phosphate,
producing insoluble, nonabsorbable phosphate
compounds
May phosphate binders be helpful in inappetent animals?
YES! WHO KNEW - KNNNNNN!!!
In one study, calcium acetate reduced intestinal
absorption of phosphate best when ingested just before
or after a meal but was much less effective if given 2 hours
after eating.150 Approximately one third as much phosphate
was removed from the body when calcium acetate
was given during fasting compared with when it was given
with a meal. The endogenous phosphate removed probably
originated from basal intestinal secretions or passive
diffusion into the intestine.
