Phosphorus and Phosphate Regulation Quiz

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Questions and Answers

What is the primary role of phosphorus in the body?

To facilitate oxygen transport in red blood cells

To serve as the major intracellular anion involved in energy metabolism (correct)

To regulate blood glucose levels

To act as a catalyst for protein synthesis

What percentage of phosphate is primarily stored in the bone matrix?

80% to 85% (correct)

50% to 60%

Less than 1%

14% to 15%

Which of the following hormones increases intestinal phosphate absorption?

Parathyroid hormone

Insulin

Calcitonin

Calcitriol (correct)

What condition results from abnormally low phosphate levels in the body?

Hypophosphatemia Signup and view all the answers

Why is measuring serum phosphate not reflective of total body stores?

Phosphate is mostly stored intracellularly Signup and view all the answers

In addition to managing phosphate derangements, what is an essential step in treating related conditions in dogs and cats?

Addressing the underlying cause of the derangement Signup and view all the answers

Which enzyme is regulated by phosphate in the body?

1a-hydroxylase Signup and view all the answers

What is the significance of phosphate in relation to dental health?

It is vital to normal dentition and osseous matrix Signup and view all the answers

What is the primary action of fibroblast growth factor-23 (FGF-23)?

Promote phosphate excretion in urine Signup and view all the answers

What percentage of ingested phosphorus is typically absorbed in the small intestine?

60% to 70% Signup and view all the answers

In patients with which condition is serum phosphate monitoring essential?

Patients with chronic kidney disease Signup and view all the answers

What is the normal range of serum phosphate concentration for dogs and cats?

2.5 to 6.0 mg/dL Signup and view all the answers

After how many hours post-meal do transient peaks in serum phosphate typically occur?

6 to 8 hours Signup and view all the answers

What is the consequence of severe hypophosphatemia below 1 mg/dL?

Whole-body phosphate depletion leading to hemolysis or rhabdomyolysis Signup and view all the answers

Which of the following substances increases renal tubular phosphate reabsorption?

Growth hormone Signup and view all the answers

What factor may cause a variation in serum phosphate values in dogs and cats?

The age of the patient Signup and view all the answers

What is a potential consequence of severe hyperphosphatemia?

Acute kidney injury Signup and view all the answers

Which factor would most likely lead to spurious hyperphosphatemia?

Hemolysis Signup and view all the answers

What type of intervention can cause phosphate to shift intracellularly?

Bicarbonate administration Signup and view all the answers

Severe hypophosphatemia might manifest with which of the following clinical signs?

Seizures Signup and view all the answers

Which condition is NOT a cause of hypophosphatemia?

Chronic hypocalcemia Signup and view all the answers

Which of the following substances can interfere with the gastrointestinal absorption of phosphate?

Phosphate-binding antacids Signup and view all the answers

What clinical signs could be expected with mild hypophosphatemia?

Generalized weakness Signup and view all the answers

A phosphate increase of 1 mg/dL is expected to decrease bicarbonate levels by how much?

0.55 mEq/L Signup and view all the answers

Study Notes

Phosphorus: The Body’s Intracellular Anion

Phosphorus, also known as phosphate, is the primary intracellular anion involved in cellular energy, membrane integrity, and metabolism.
While the two terms are often used interchangeably, it’s important to remember that phosphorus is an element, and phosphate is a molecular anion.
Phosphate is vital for normal dentition, osseous matrix, tissue oxygenation, and various enzymatic processes.
Despite its importance, serum phosphate levels only reflect a small percentage of total body stores as 80-85% of phosphate is found in bone, 14-15% in soft tissues, and less than 1% in the extracellular space.

Phosphate Regulation

Phosphate regulation involves a complex interplay of hormones and other substances:
- Parathyroid hormone ([ release of phosphate from bone, [ renal phosphate excretion)
- Calcitriol ([ intestinal phosphate absorption)
- Calcitonin ([ renal phosphate excretion)
- Phosphatonins, such as fibroblast growth factor-23 (FGF-23)
- FGF-23 primarily functions to increase phosphate excretion.
Gastrointestinal absorption of phosphorus is directly related to dietary intake, with 60-70% of ingested phosphorus being absorbed in the small intestine.
The kidneys play a crucial role in phosphate regulation, reabsorbing 60-100% of filtered phosphate in the proximal convoluted tubule.
Hormonal influences:
- Growth hormone, insulin, insulin-like growth factor 1, and thyroxine all increase renal tubular phosphate reabsorption.

Indications for Serum Phosphate Measurement

Serum phosphate is commonly measured as part of systemic disease investigations and in many chemistry panels.
It should be regularly monitored in patients with:
- Acute kidney injury or chronic kidney disease
- Oral phosphate binder use
- Chemotherapy with a high tumor burden
- Refeeding syndrome after severe malnutrition
- Diabetes mellitus or hyperosmolar conditions
- Concurrent hypercalcemic conditions
- Acute or chronic anorexia, vomiting, or diarrhea

Interpreting Serum Phosphate Levels

Serum phosphate levels don't accurately reflect total body phosphate due to its primarily intracellular location and rapid transcellular shifts.
Normal serum phosphate range for dogs and cats is 2.5 mg/dL to 6 mg/dL (0.8–1.9 mmol/L).
Notably, normal healthy puppies can have serum phosphate concentrations up to 10 mg/dL.
Transient peaks in serum phosphate are expected 6-8 hours after a meal, making it ideal to collect blood samples after a 12-hour fast.

Danger Values and Artifacts

Severe hypophosphatemia (below 1 mg/dL or 0.31 mmol/L) is typically associated with whole-body phosphate depletion and carries significant risks:
- Hemolysis
- Rhabdomyolysis
Severe hyperphosphatemia can lead to various complications:
- Tetany due to hypocalcemia
- Soft tissue mineralization, especially if the calcium-phosphate product is above 60-70
- Metabolic acidosis
- Acute kidney injury, particularly in cases of acute hyperphosphatemia without coexisting hypercalcemia, as seen in phosphate enema toxicity.
- Artifacts that affect serum phosphate measurement: -Mannitol (25 mmol/L) can interfere with DuPont Automatic Clinical Analyzer colorimetric tests, leading to false hypophosphatemia. -Hemolysis, hypertriglyceridemia, hyperbilirubinemia, and monoclonal gammopathy can lead to spurious hyperphosphatemia.

Drug Effects on Phosphate

Phosphate-binding antacids interfere with intestinal phosphate absorption.
Mannitol's diuretic effects can lead to phosphate wasting.
Insulin, dextrose, and bicarbonate cause phosphate to shift intracellularly, potentially leading to hypophosphatemia.

Hypophosphatemia

Potential causes (Box 1):
- Decreased gastrointestinal absorption (anorexia, diarrhea, vomiting, malabsorption)
- Transcellular shifts (metabolic or iatrogenic alkalosis, refeeding syndrome, insulin therapy)
- Increased renal excretion (conditions with diuresis, such as diabetic ketoacidosis, diuretics, fluid overload, postobstructive diuresis)
Clinical signs:
- Mild hypophosphatemia (1–2.5 mg/dL) can present with non-specific signs: generalized weakness, tremors, muscle pain, ataxia, anorexia, nausea, functional ileus, vomiting.
- Severe hypophosphatemia (

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Description

Test your knowledge on the role of phosphorus in the body and its regulation mechanisms. This quiz covers essential concepts such as phosphate's importance in cellular metabolism, its various physiological roles, and the hormones that regulate its levels. Perfect for students studying biochemistry or physiology.