Phosphorus Disorders

Question 1

What are the roles of phosphorus?

Answer 1

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.

Question 2

What is organic vs inorganic phosphorus?

Answer 2

organic (phospholipids and phosphate
esters)andinorganic(orthophosphoricandpyrophosphoric
acids) forms in the body
Almost all serum phosphorus is
in the form of orthophosphate.

Question 3

How many mg in one millimole of phosphorus

Answer 3

31mg per mmol of elemental phos

Question 4

At a pH of 7.4 how many mEq is 1 mmol of phos

Answer 4

1.8mEq

Question 5

how much inorganic phosphorus is protein bound?

Answer 5

Approx 10-20%

Question 6

How much inorganic phos is in bone?

Answer 6

80-85%

Question 7

What is the normal serum phos of a dog/

Answer 7

2.5-6.0mg/dL - higher in younger dogs

Question 8

What causes an increased phos in younger animals?

Answer 8

Bone growth and an increase in renal tubular reabsorption of phosphorus mediated by growth hormone

Question 9

Why does feeding carbohydrates cause a decrease in serum phos?

Answer 9

bc phos shifts intracellularly as a result of glycolysis and formation of phosphorylated glycolytic intermediates in muscle, liver and adipose.

Question 10

Why does a resp alkalosis cause a decrease in phos?

Answer 10

stimulates glycolysis
(by activating phosphofructokinase) and decreases
serum phosphorus concentration

Question 11

What may result in inaccurate phos meausrements?

Answer 11

Hyperlipidemia
hyperproteinemia
Thrombocytosis
monoclonal gammopathy
Mannitol and other drugs
Icterus
hemolysis

Question 12

What % of oral phosphate is absorbed?

Answer 12

60-70% absorbed in a linear function

Question 13

What are the two mechanisms that result in intestinal phosphate absorption

Answer 13

1. Passive diffusion is the principle route - paracellular. All segments
2. Active -> mucosal transport is sodium dependent. Is saturable. Calictriol inhances absorption. Duodenum

Question 14

What occurs during phosphate deprivation?

Answer 14

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

Question 15

Normally how much of the filtered phos load is resorbed by the kidneys?

Answer 15

80-90%

Question 16

How is phos resorbed in the proximal tubule?

Answer 16

brush border sodium-phos cotransporters. translocates 3Na and 1 divalent phos
Luminal entry is the rate limiting step

Question 17

What is the most common regulator of renal phos?

Answer 17

PTH - it decreases the tubular transport

Question 18

What effect does growth hormone have on renal phos?

Answer 18

It increases resorption - partially accounts for high phos in young animals.

Question 19

What effects does high doses of glucocorticoids have on renal phos.

Answer 19

Decreases absorption

Question 20

What effects does acid base status have on phos resorbtion

Answer 20

Metabolic acidosis - Acute : Nil, chronic: Decreased
Resp acidosis - decrease
Resp alk - increase

Question 21

What are phosphatonins?

Answer 21

substances that increase renal loss
- fibroblast growth factor
- secreted frizzled-related protein
- matrix extracellular phosphoglycoprotein

Question 22

Hypophosphataemia

Question 23

What detrimental effects may be seen with hypophosphataemia ?

Answer 23

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

Question 24

Causes of hypophosphataemia

Question 25

What are broad causes of hypophos?

Answer 25

translocation of phosphate from extracellular to intracellular fluid (maldistribution), increased loss (decreased renal reabsorption of phosphate), or decreased intake (decreased intestinal absorption of phosphate).

Question 26

What are causes of translocation?

Answer 26

DKA treatment Carb loading Resp alkalosis TPN Hypothermia

Question 27

Causes of increased Loss?

Answer 27

primary hyperPTH renal tubular disease - fanconis renal transplant proximally acting diuretics eclampsia hyperA

Question 28

Causes of decreased intake

Answer 28

GI signs, Malabsorptive disease Vit D deficiency Phos binders

Question 29

Why does Vit D deficiency cause hypophos?

Answer 29

because hypocalcemia increases PTH secretion, which increases renal phosphate excretion. Decreased intestinal phosphate absorption presumably also plays a role in this setting.

Question 30

What are the risks of parenterally administered phos?

Answer 30

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)

Question 31

HyperPhos

Question 32

What are the major clinical consequences of hyperphos?

Answer 32

hypocalcaemia and tissue mineralisation

Question 33

What is the main cause of hyperphosphataemia in small animals?

Answer 33

Decreased renal excretion

Question 34

What are causes related to translocation?

Answer 34

Tumor cell lysis * Tissue trauma or rhabdomyolysis * Hemolysis * Metabolic acidosis

Question 35

What are causes related to increased intake

Answer 35

Gastrointestinal ○ Phosphate enemas ○ Vitamin D intoxication (e.g., cholecalciferol containing rodenticides, calcipotriene) Parenteral ○ Intravenous phosphate

Question 36

What are causes relating to decreased excretion?

Answer 36

Acute or chronic renal failure * Uroabdomen or urethral obstruction * Hypoparathyroidism * Acromegaly (?)* * Hyperthyroidism

Question 37

Why does CKD cause hyperphos

Answer 37

As GFR decreases filtered load of phos decreases, intake remains constant = hyperphos

Question 38

Treatment of hyperphos?

Answer 38

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

Question 39

How do phos binders work?

Answer 39

Phosphate binders work because the cation in the binder combines with dietary phosphate, producing insoluble, nonabsorbable phosphate compounds

Question 40

May phosphate binders be helpful in inappetent animals?

Answer 40

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.