Pathology: Electrolytes

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Questions and Answers

Two-thirds of the body's water is contained within the extracellular fluid compartment.

False

What role does the vascular endothelium play in relation to electrolytes?

It is freely permeable to ionic solutes (electrolytes).

Changes in electrolyte or water excretion usually occur through the __________ and kidneys.

GIT

Match the electrolyte with its primary regulation process:

Sodium = Tightly regulated with higher concentrations outside the cells Potassium = Mainly affected by translocation across cell membranes Chloride = Influenced by changes in free water Calcium = Regulated by bone metabolism Signup and view all the answers

What is the primary impact of sodium loss or gain?

Has minimal impact on potassium Signup and view all the answers

The intracellular fluid and extracellular fluid compartments have similar electrolyte concentrations.

False Signup and view all the answers

What are the primary routes for electrolyte or water loss from the body?

GIT, kidneys, respiratory system, and skin. Signup and view all the answers

What is the primary role of sodium in the body?

Maintaining osmolality of extracellular fluid Signup and view all the answers

Hypernatraemia typically occurs when sodium loss exceeds water loss.

False Signup and view all the answers

What is a potential cause of hyponatraemia related to the adrenal glands?

Hypoadrenocorticism Signup and view all the answers

The ______ is the major intracellular cation in the body.

potassium Signup and view all the answers

Match the following conditions with their respective electrolyte disturbance:

Vomiting = Hyponatraemia Salt poisoning = Hypernatraemia Hypoadrenocorticism = Hyperkalaemia Diabetes mellitus (osmotic diuresis) = Hypernatraemia Signup and view all the answers

Which hormone acts to increase sodium reabsorption in the kidneys?

Aldosterone Signup and view all the answers

Bladder rupture can cause hyponatraemia due to the movement of sodium from the ECF into the urine in the abdomen.

True Signup and view all the answers

What is the most important electrolyte imbalance that can result from acute renal failure?

Hyperkalaemia Signup and view all the answers

Hyponatraemia can result from excessive water gain combined with severe liver disease or congestive heart failure, leading to ______.

oedema Signup and view all the answers

Match the following terms with their definitions:

Hyponatraemia = Low sodium concentration in the blood Hyperkalaemia = High potassium concentration in the blood Oliguria = Reduced urine output Diuresis = Increased urine production Signup and view all the answers

Which of the following is a common cause of hyperkalaemia?

Bladder rupture Signup and view all the answers

Potassium levels in animals can be artificially elevated due to leakage from red blood cells.

True Signup and view all the answers

What are two conditions that can lead to excessive fluid retention?

Oliguria, anuria Signup and view all the answers

A significant cause of ______ is the excessive loss of sodium due to gastrointestinal loss from vomiting and diarrhea.

hyponatraemia Signup and view all the answers

Match the following conditions with their electrolyte imbalance:

Cirrhosis = Hyponatraemia Dehydration = Hypernatraemia Renal failure = Hyperkalaemia Diabetes mellitus = Hypernatraemia Signup and view all the answers

What can cause hyperkalaemia?

Oliguria Signup and view all the answers

Hypokalaemia can occur after administration of potassium-rich fluids.

False Signup and view all the answers

What is the main consequence of decreased renal potassium excretion?

Hyperkalaemia Signup and view all the answers

Increased renal potassium excretion due to polyuria can lead to __________.

hypokalaemia Signup and view all the answers

Match the following conditions with their associated potassium balance alterations:

Diabetes mellitus = Hyperkalaemia Diarrhea = Hypokalaemia Metabolic acidosis = Hyperkalaemia Post-obstructive diuresis = Hypokalaemia Signup and view all the answers

What mechanism contributes to hypokalaemia during metabolic alkalosis?

Potassium moves from ECF to ICF Signup and view all the answers

Acidosis always leads to hyperkalaemia.

False Signup and view all the answers

Name one condition that may cause hypokalaemia due to increased loss?

Diarrhea Signup and view all the answers

The primary anion in ECF that parallels sodium levels is __________.

chloride Signup and view all the answers

Match the ions with their associated alterations:

Hyperkalaemia = Urethral obstruction Hypokalaemia = Increased loss from GIT Hypochloraemia = Diarrhoea and/or vomiting Hyperchloraemia = Accompanies hypernatraemia Signup and view all the answers

Which of the following conditions is associated with hypomagnesaemia?

Post-partum in cattle Signup and view all the answers

Increased excretion of bicarbonate in alkalosis can lead to an increase in potassium excretion.

True Signup and view all the answers

What is a common cause of hypochloraemia?

Vomiting Signup and view all the answers

Acute renal failure commonly leads to ___________________.

hyperkalaemia Signup and view all the answers

What is one of the consequences of severe muscle damage?

Increase in potassium levels Signup and view all the answers

What is the primary function of parathyroid hormone (PTH)?

Increase plasma ionised calcium concentration Signup and view all the answers

An increase in plasma phosphate concentration leads to an increase in plasma ionised calcium concentration.

False Signup and view all the answers

Name the hormone that is primarily responsible for lowering plasma calcium levels.

calcitonin Signup and view all the answers

The ionised fraction of calcium, which is physiologically active, is referred to as __________.

Ca2+ Signup and view all the answers

Match the following hormones to their functions:

Parathyroid hormone = Increases plasma ionised calcium 1,25-dihydroxyvitamin D = Increases intestinal absorption of calcium and phosphorus Fibroblast growth factor 23 = Decreases plasma phosphate concentration Calcitonin = Decreases plasma ionised calcium Signup and view all the answers

What effect does parathyroid hormone have on phosphorus levels in the body?

Decreases phosphorus reabsorption Signup and view all the answers

Plasma phosphorus concentration is more tightly regulated than plasma calcium concentration.

False Signup and view all the answers

What is the effect of parathyroid hormone on vitamin D?

It stimulates the conversion of vitamin D to its active form. Signup and view all the answers

What is the primary function of 1,25-dihydroxyvitamin D?

Increase plasma ionised calcium and phosphorus concentrations Signup and view all the answers

Calcitonin acts to increase the release of calcium from the bones.

False Signup and view all the answers

What is a common cause of hypocalcaemia in cattle during calving?

Milk fever Signup and view all the answers

Fibroblast growth factor 23 primarily controls _______ homeostasis.

phosphorus Signup and view all the answers

Match the following conditions with their associated causes of hypocalcaemia:

Hypoalbuminaemia = Decreased protein binding of calcium Pregnancy and lactation = Increased demand for calcium Renal secondary hyperparathyroidism = Impaired phosphate excretion Nutritional secondary hyperparathyroidism = Skewed calcium to phosphorus ratio in diet Signup and view all the answers

Which of the following hormones inhibits the secretion of PTH?

FGF23 Signup and view all the answers

Vitamin D toxicity can lead to hypocalcaemia.

False Signup and view all the answers

What is a common effect of hypomagnesaemia on calcium levels in the body?

Hypoparathyroidism Signup and view all the answers

The first step in vitamin D activation forms ______.

25OHD Signup and view all the answers

Which of the following is a true cause of hypercalcaemia?

Humoral hypercalcaemia of malignancy Signup and view all the answers

Hypercalcaemia occurs more frequently in young animals than adults.

True Signup and view all the answers

What is one of the primary regulators of plasma phosphorus levels?

Fibroblast growth factor 23 (FGF23) Signup and view all the answers

The primary biological function of calcitonin is to inhibit _______ bone resorption.

osteoclastic Signup and view all the answers

Match the following conditions with their related effects on serum calcium levels:

Hypocalcaemia = Low serum calcium Hypercalcaemia = High serum calcium Pregnancy and lactation = Increased calcium demand Nutritional secondary hyperparathyroidism = Increased PTH leading to bone resorption Signup and view all the answers

What is the most common cause of hypercalcaemia in dogs?

Neoplasia Signup and view all the answers

Hypocalcaemia is more common than hypercalcaemia in dogs and cats.

True Signup and view all the answers

Name one uncommon cause of hypercalcaemia.

Hypervitaminosis D Signup and view all the answers

One potential cause of hypophosphataemia is increased urinary P excretion due to prolonged ______.

diuresis Signup and view all the answers

Which diagnostic measure is NOT commonly used to test for magnesium status?

Saliva magnesium concentration Signup and view all the answers

The most common cause of idiopathic hypercalcaemia in cats is chronic kidney disease.

False Signup and view all the answers

What should be done before interpreting serum calcium and magnesium test results?

Samples should be collected before treatment. Signup and view all the answers

Hypocalcaemia can occur in dairy cows due to the loss of calcium into ______.

milk Signup and view all the answers

Which condition is associated with hypomagnesaemia in dairy cows?

Grass staggers Signup and view all the answers

In grazing cattle, hypomagnesaemia is less likely to occur during winter.

False Signup and view all the answers

What must be tested in a group of animals to better assess magnesium status?

Serum magnesium concentration or urine magnesium:creatinine ratio Signup and view all the answers

Calcium balance alterations can occur due to factors such as ______, malignancy, and hyperparathyroidism.

chronic renal failure Signup and view all the answers

Which of the following is a common cause of hypoclecemia?

Hypoalbuminaemia Signup and view all the answers

Match the following conditions with their associated electrolyte imbalance:

Chronic renal failure = Hypocalcaemia Neoplasia = Hypercalcaemia Hypoadrenocorticism = Hypercalcaemia Vitamin D deficiency = Hypophosphataemia Signup and view all the answers

Study Notes

Overview of Electrolytes

Electrolytes are substances that produce ions when dissolved in water, including sodium, potassium, chloride, calcium, magnesium, and phosphate.
Sodium, potassium, and chloride are primary focus areas, with calcium, magnesium, and phosphate discussed in another context.
The animal body consists of approximately 60% water, with two-thirds (67%) in the intracellular fluid (ICF) and one-third in the extracellular fluid (ECF).

Body Water Compartments

ECF is divided into interstitial fluid (25% of total body water) and intravascular fluid (8% of total body water).
The endothelium is permeable to ionic solutes; interstitial and intravascular fluids have similar ion concentrations.
ICF and ECF maintain specific ion concentrations using cellular pumps, leading to differences in their electrolyte profiles.

Mechanisms of Electrolyte Changes

Electrolyte concentration changes can result from:
- Free water loss or gain, affecting sodium and chloride levels.
- Intake of electrolytes, particularly potassium.
- Translocation of electrolytes between ICF and ECF, mainly affecting potassium.
- Excretion/loss of electrolytes through gastrointestinal tract, kidneys, or respiratory system.

Clinical Situations for Electrolyte Assessment

Assess electrolytes in cases of excessive fluid loss (vomiting, diarrhea), retention (oliguria/anuria), major muscle weakness, acute renal failure, fluid shifts (diabetes mellitus), and excessive fluid/electrolyte gain (salt poisoning).

Sodium (Na)

Sodium is the major extracellular cation essential for maintaining ECF osmolality and water retention.
Serum sodium concentration must be understood in the context of hydration status.
Sodium balance is regulated via the renin-angiotensin-aldosterone system (RAAS) and affected by atrial natriuretic peptide (ANP).
Hyponatraemia occurs with sodium loss exceeding water depletion; hypernatraemia arises when water loss exceeds sodium.
Complex cases include hypoadrenocorticism (Addison’s disease) and bladder rupture affecting sodium levels.

Causes of Altered Sodium Balance

Hyponatraemia can result from:
- Water retention from conditions like liver disease, heart failure, or kidney issues.
- Excessive sodium loss through GIT or renal loss.
Hypernatraemia can result from water deficits, renal loss, or sodium gain (e.g., salt poisoning).

Potassium (K)

Primarily found inside cells; serum potassium levels can indicate severe imbalances but not total body potassium.
Both hypokalaemia and hyperkalaemia can lead to life-threatening conditions affecting muscle function.
Potassium regulation involves aldosterone, insulin, and adrenaline, with renal excretion being crucial.
Hyperkalaemia may result from potassium shifts from ICF to ECF, decreased renal excretion, or tissue necrosis.
Hypokalaemia occurs due to shifts to ICF, loss from GIT, skin, or kidneys, or decreased dietary intake.

Causes of Altered Potassium Balance

Hyperkalaemia causes include:
- Renal failure, urethral obstruction, metabolic acidosis, and severe muscle damage.
Hypokalaemia causes include:
- Increased utilization or loss from vomiting, diarrhea, renal issues, and metabolic alkalosis.

Chloride (Cl-)

Chloride is the major anion in ECF; its alterations often mirror those of sodium.
Hypochloraemia typically arises from gastrointestinal losses or sweating, while hyperchloraemia usually accompanies hypernatraemia.

Magnesium (Mg2+)

Hypomagnesaemia is common in postpartum cattle and correlates with decreased intake or increased loss.
Can also present in horses and critically ill small animals, with supplementation helping reduce morbidity and mortality.

Calcium and Phosphorus Homeostasis

Calcium and phosphorus are essential for bodily functions beyond skeletal development.
The skeleton serves as a storage site for these minerals, providing them when dietary levels are low.
Ionised calcium (Ca2+) is the active form, regulated by parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, and calcitonin affecting intestines, skeleton, and kidneys.
Plasma phosphorus control is less precise than calcium, influenced by fibroblast growth factor 23 (FGF23), diet, age, sex, pH, and hormones.
An inverse relationship exists between ionised phosphate and ionised calcium; increased phosphate lowers calcium levels.

Parathyroid Hormone (PTH)

Produced by chief cells of the parathyroid gland, which have calcium-sensing receptors.
Functions of PTH include:
- Increasing calcium reabsorption in kidney's distal convoluted tubules.
- Decreasing phosphorus reabsorption in kidney's proximal tubules.
- Stimulating osteoclastic bone resorption to release calcium and phosphorus into the bloodstream.
- Enhancing conversion of vitamin D to its active form (1,25-dihydroxyvitamin D3) for increased intestinal absorption of calcium and phosphorus.
PTH increases plasma ionised calcium and decreases plasma phosphorus concentrations.

Vitamin D

Obtained from diet or synthesized in skin via sunlight, requiring two hydroxyl groups to become active.
The unregulated formation of 25OHD indicates dietary or sunlight-derived vitamin D levels.
The action of 1,25-dihydroxyvitamin D includes:
- Enhancing calcium and phosphate absorption from the small intestine.
- Stimulating calcium and phosphate release from bone.
- Increasing phosphate reabsorption in kidneys.
Overall, 1,25(OH)2D3 raises plasma levels of calcium and phosphorus.

Calcitonin

Acts as a counterbalance to vitamin D and PTH by inhibiting osteoclastic bone resorption.
Reduces release of calcium from bone, helping maintain normal plasma calcium levels.

Fibroblast Growth Factor 23 (FGF23)

Primary regulator of phosphorus homeostasis.
Functions:
- Decreases active vitamin D formation, leading to reduced calcium and phosphorus absorption from the intestine.
- Stimulates phosphorus excretion from kidneys (phosphaturia).
- Inhibits PTH secretion, decreasing renal calcium reabsorption.
Ultimately lowers both plasma phosphorus and calcium concentrations.

Laboratory Diagnosis of Calcium and Phosphorus Disorders

Total serum calcium consists of:
- 50% free or ionised form (tightly regulated).
- 40-45% protein-bound (mainly to albumin).
- 5-10% bound to anions (e.g., citrate, phosphate).

Hypocalcaemia

Rare in animals except post-partum; common in cattle (milk fever) and small breed dogs (eclampsia).
Hypocalcaemia can result from:
- Hypoalbuminaemia, causing mild-moderate hypocalcaemia.
- High calcium demands during pregnancy and lactation.
- Contamination of serum samples with EDTA, which chelates calcium.
- Hypomagnesaemia, leading to low serum calcium.
- Renal secondary hyperparathyroidism due to impaired phosphate excretion.
- Nutritional secondary hyperparathyroidism in young puppies/kittens on all-meat diets.
- Oxalate toxicity in horses and ruminants, as well as ethylene glycol toxicity in dogs.

Hypercalcaemia

Commonly observed in lab results but true hypercalcaemia is rare.
Potential causes include:
- Non-pathologic: dehydration causing hyperproteinaemia, lipaemia, and elevated calcium in young animals.
- Pathological:
  - Tumors producing parathyroid hormone-related peptide (PTHrP).
  - Primary hyperparathyroidism.
  - Chronic renal failure leading to calcium retention.
  - Vitamin D toxicity.

Hypophosphataemia

Caused by:
- Increased urinary phosphorus excretion (prolonged diuresis or increased PTH).
- Decreased intestinal absorption (anorexia or vitamin D deficiency).
- Defective mobilization from bone (milk fever, eclampsia).
- Equine renal failure (variable finding).

Hyperphosphataemia

Possible causes include:
- Decreased urinary phosphorus excretion due to chronic kidney disease.
- Increased intestinal absorption from vitamin D toxicity or phosphate enemas.
- Myopathies releasing phosphorus from damaged muscle fibers.

Ruminant Considerations

Hypocalcaemia mainly affects mature dairy cows around calving, losing calcium through milk.
Hypomagnesaemia in cattle can lead to tetany (grass staggers) due to low magnesium intake from pastures.
Routine monitoring of serum calcium and magnesium concentrations before calving aids in diagnosing deficiencies.
Consideration of environmental factors, dietary supplementation, and herd status is crucial in management decisions.

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Test your understanding of electrolytes and their roles in the human body. This quiz covers the types of electrolytes, their distribution in body fluids, and the mechanisms that regulate their concentrations. Perfect for students in health sciences or nursing.