Patho: Chapter 8 (Electrolyte Balance)

What is intracellular fluid (ICF)?

Fluid found inside the cells

What is extracellular fluid (ECF) found?

Fluid found in the interstitial (tissue) spaces, plasma, (vascular) compartment, and cerebrospinal fluid (CSF).

What are the 2 major physiologic mechanisms of regulating body levels of water?

• Thirst, which triggers increased water intake

• Antidiuretic hormone (ADH) release

What does thirst lead to?

Increased water intake

What does the release of Antidiuretic hormone (ADH) lead to?

Water reabsorption from urine

How is thirst controlled?

Via the thirst center, osmoreceptors located in the hypothalamus detect changes in osmolarity and help regulate thirst.

What is hypodipsia?

A decrease in the ability to sense thirst.

What causes hypodipsia?

• Damaged hypothalamus

• Less responsive hypothalamus

Is hypodipsia common in the elderly?

Yes

What happens when someone has a damaged or less responsive hypothalamus?

They have a decreased or impaired ability to sense thirst (hypodipsia)

What can damage the hypothalamus?

• Head trauma

• Meningiomas

• Subarachnoid hemorrhage

When can abnormal synthesis and release of ADH occur?

• Diabetes Insipidus (DI)

• Syndrome of inappropriate ADH (SIADH)

What is the effect of nicotine on ADH?

It increases ADH release/levels

What is the effect of alcohol on ADH?

It decreases ADH release/levels

What is Diabetes Insipidus (DI)?

A disorder in which a person is unable to concentrate urine and excretes large volumes of urine.

What causes Diabetes Insipidus (DI)?

• Defect in ADH synthesis or release (Neurogenic DI)

• Kidneys do not respond to ADH (Nephrogenic DI)

What are the characteristics/manifestations of Diabetes Insipidus (DI)?

• Inability to concentrate urine

• Large volumes of urine

• Excessive thirst

• Risk for hypertonic dehydration

• Increased serum osmolality

What are the two types of Diabetes Insipidus (DI)?

• Neurogenic DI

• Nephrogenic DI

What is Neurogenic Diabetes Insipidus?

Diabetes insipidus due to a defect in the synthesis or release of ADH

What causes Neurogenic Diabetes Insipidus?

• Defect in ADH synthesis or release

• Head trauma damaging the hypothalamus

What is Nephrogenic Diabetes insipidus?

Diabetes indipidus due to the kidneys not responding to ADH

What causes Nephrogenic Diabetes insipidus?

• Lithium use

• Potassium depletion

• Chronic hypercalcemia

What is Syndrome of Inappropriate ADH (SIADH)?

A disorder characterized by excessive ADH secretion despite decreased serum omolarity.

What causes Syndrome of Inappropriate ADH (SIADH)?

Failure of the negative feedback system that regulates the release and inhibition of ADH

What are the characteristics/manifestations of Syndrome of Inappropriate ADH (SIADH)?

• Excessive ADH secretion

• Water retention

• Dilutional hyponatremia

• Decreased serum osmolarity.

What is hyponatremia?

A plasma sodium concentration below 135 mEq/L (135 mmol/L)

What are the types of hyponatremia?

• Hypertonic hyponatremia

• Hypervolemiic (hypotonic) hyponatremia

What is hypertonic hyponatremia?

A type of hyponatremia caused by an osmotic shift of water from the ICF to the ECF, diluting the sodium in the ECF

What causes hypertonic hyponatremia?

• Osmotic shift of water from ICF to ECF

• hyperglycemia

What is an example of hypertonic hyponatremia?

Elevated glucose causes water to move out of cells, diluting sodium in the ECF (hyperglycemia).

What is hypovolemic (hypotonic) hyponatremia?

A type of hyponatremia that occurs when water is used to replace lost body fluids and electrolytes

What causes hypovolemic (hypotonic) hyponatremia?

• Replacement of fluid losses with water alone

• Loss of electrolytes followed by water replacement

What is an example of hypovolemic (hypotonic) hyponatremia?

Replacing electrolytes lost through sweating with water alone during exercise.

What is hypernatremia?

An elevated plasma sodium concentration

What causes hypernatremia?

• Inadequate water intake

• Excessive water loss

• Acute renal failure

• Chronic renal failure

• Excessive sodium administration

Who is more likely to suffer from hypernatremia?

Older adults

Why are older adults more likely to develop hypernatremia?

They often have impaired thirst perception and may be unable to adequately replace water losses

Can acute renal failure or chronic renal failure cause hypernatremia?

Yes

What also causes hypernatremia?

Excessive sodium administration

What are the functions of potassium?

• Maintains intracellular osmolarity

• Controls resting membrane potential (RMP)

• Needed for the Na+/K+ pump

• Exchanged for H+ to buffer changes in blood pH

What are the normal serum potassium levels?

3.5 - 5.0 mEq/L

What is hypokalemia?

A serum potassium level below 3.5 mEq/L

What causes hypokalemia?

• Inadequate dietary intake of potassium

• Excessive GI, renal, or skin losses

• Diuretic therapy

• Trauma

• Increased aldosterone levels

• Redistribution of potassium from ECF to ICF

What is hyperkalemia?

A serum potassium level above 5.0 mEq/L

What causes hyperkalemia?

• Decreased renal elimination (CKD)

• Shift of potassium from the ICF to the ECF (burns)

• Excessive or rapid potassium administration

What is the most serious effect of hyperkalemia?

Its effect on the heart

How does hyperkalemia affect the heart?

• Decreases membrane excitability

• Delays atrial and ventricular depolarization

• Increase the rate of ventricular repolarization

What are the earliest ECG changes seen in hyperkalemia?

• Peaked, narrow T waves

• Shortened QT interval

What effect does a potassium level of 7.5 mEq/L have on resting membrane potential?

The RMP becomes less negative and moves closer to threshold, making cells easier to stimulate

What effect does hyperkalemia have on cell excitability?

A weaker stimulus is needed for the cell to fire because the resting membrane potential is closer to threshold.

What are the functions of calcium?

• Provides bone strength and stability

• Helps regulate membrane potential and cellular excitability

• Enables contraction of all muscle types

• Participates in blotting

• Facilitates hormone and neurotransmitter activity

What are the normal serum calcium levels?

8.5 - 10.5 mg/dL

What is hypocalcemia?

A serum calcium level below 8.5 mg/dL

What causes hypcalcemia?

• Impaired ability to mobilize calcium from bone due to hypoparathyroidism

• Abnormal loss of calcium by the kidneys (renal failure)

• Hyperphosphatemia

• Vitamin D deficiency

What effect does hypocalcemia have on nerve firing?

Nerves fire more easily

What is hypercalcemia?

A serum calcium level above 10.5 mg/dL

What cause hypercalcemia?

• Increased bone resorption

• Increased PTH due to neoplasm

• Hyperparathyroidism

• Inability of the kidneys to remove calcium

What effect does hypercalcemia have on nerve firing?

Nerves are less likely to fire

What are the functions of phosphorus?

• Supports bone formation

• Helps produce ATP

• Supports glucose, fat, and protein metabolism

• Contributes to DNA, RNA, and phospholipid synthesis

• Acts as an acid-base buffer

• Supports RBC, WBC, and platelet function

What are the normal serum phosphorus levels?

2.5 - 4.5 mg/dL

What is hypophosphatemia?

A serum phophorus level below 2.5 mg/dL

What causes hypophosphatemia?

• Insufficient intestinal absorption

• Increased renal loss

What is hyperphosphatemia?

A serum potassium level above 4.5 mg/dL

What causes hyperphosphatemia?

• Kidneys failure with impaired phosphorus elimination

• High phosphorus intake

What are the functions of magnesium?

• Serves as a cofactor in enzymatic reactions

• Helps generate ATP

• Supports DNA replication

• Supports protein translation

• Blocks potassium exit from cardiac cells

• Acts as a smooth muscle relaxant

What are the normal serum magnesium levels?

1.8 - 2.6 mg/dL

What is hypomagnesemia?

A serum magnesium level below 1.8 mg/dL

What causes hypomagnesemia?

• Insufficient magnesium intake

• Excess magnesium losses

• Starvation

• Diarrhea

• Decreased intestinal absorption

• Chronic alcoholism

What is hypermangesemia?

A serum magnesium level above 2.6 mg/dL

What causes hypermangesemia?

• Excessive magnesium intake

• Decreased magnesium excretion

What is the normal blood pH?

7.35 - 7.45

What is acidosis?

A blood pH below 7.35

What is alkalosis?

A blood pH above 7.45

How is blood pH regulated by the body?

• Chemical buffer systems regulate pH immediately

• The lungs eliminate CO₂

• The kidneys eliminate H⁺ and reabsorb/generate HCO₃^-

How do the lungs regulate blood pH in the body?

• Increased CO₂ → decreased pH (more acidic)

• Decreased CO₂ → increased pH (more alkaline)

How do the kidneys regulate blood pH in the body?

• Excrete H⁺ → increase pH

• Reabsorb or generate HCO₃^- → increase pH

What is respiratory acidosis?

Acidosis characterized by a decrease in pH and an increase in pCO₂ due to decreased ventilation

What causes respiratory acidosis?

• Acute respiratory failure

• Drug overdose

• Lung disease

• Chest injury

• Airway obstruction

What is respiratory alkalosis?

Alkalosis characterized by an increase in pH and a decrease in arterial pCO₂ due to increased ventilation

What causes respiratory alkalosis?

• Hyperventilation syndrome

• Pregnancy

• Septic shock

• Systemic Inflammatory Response Syndrome (SIRS)

What is metabolic acidosis?

Acidosis characterized by a decrease in pH and serum bicarbonate (HCO₃^-) concentration

What causes metabolic acidosis?

• Increased ketoacids

• Increased lactic acid

• Chronic kidney disease (CKD)

What is metabolic alkalosis?

Alkalosis characterized by an increase in pH and bicarbonate (HCO₃^-) levels

What causes metabolic alkalosis?

• Loss of stomach acids through vomiting

• Hyperaldosteronism

• Cushing disease

Which of the following can cause metabolic alkalosis?

Both a and b

Respiratory alkalosis can be caused by a respiratory rate in excess of that which maintains a normal plasma PCO₂ levels. What is a common cause of respiratory alkalosis?

Hyperventilation