Section 26.3: Electrolyte Balance and Fluid Movement

Sodium Balance & Fluid Shifts: What is the primary electrolyte that directs fluid movement in the body?

Sodium (Na⁺)—it has strong osmotic power, so water follows sodium.

Sodium Balance & Fluid Shifts: What are four functions of sodium in the body?

Fluid shifts between compartments

Membrane excitability

Depolarization/repolarization

Membrane permeability

Sodium Balance & Fluid Shifts: How does sodium enter and leave the body?

- Enters through food and small amounts from metabolism

- Exits through urine, sweat, feces, and occasionally vomiting

Sodium Balance & Fluid Shifts: What is hyponatremia, and what are its effects?

Too little sodium → low blood volume, low BP, poor fluid distribution

Sodium Balance & Fluid Shifts: How is hyponatremia treated?

- Increase sodium intake (diet, salt pills, electrolyte drinks)

- Severe cases may need sodium therapy

Sodium Balance & Fluid Shifts: What happens if sodium levels are too high?

Causes fluid retention and may increase blood pressure.

Sodium Balance & Fluid Shifts: How does sodium affect blood pressure?

Low sodium → less water in blood → low BP

High sodium → more water retained → high BP

Sodium Balance & Fluid Shifts: What is POTS?

Postural Orthostatic Tachycardia Syndrome—autonomic dysfunction affecting BP regulation when standing up.

Sodium Balance & Fluid Shifts: What happens during POTS?

Heart rate spikes, BP drops → symptoms include dizziness, fainting, arrhythmia.

Sodium Balance & Fluid Shifts: What POTS treatments overlap with sodium imbalance treatment?

Increase salt, hydrate well, and avoid rapid position changes.

Hormonal Control of Sodium: How does estrogen influence sodium levels?

Increases sodium reabsorption, making tubules more permeable → water retention and bloating (common during ovulation and early pregnancy).

Hormonal Control of Sodium: How does progesterone affect sodium levels?

Decreases sodium reabsorption, resulting in less water retention—not typically linked to bloating.

Hormonal Control of Sodium: What do glucocorticoids do to sodium balance?

Mimic estrogen by increasing sodium reabsorption → can cause swelling or edema if used long-term.

Blood Volume Feedback: Baroreceptors: What do baroreceptors detect?

Stretch in blood vessel walls, which reflects blood volume and pressure.

Blood Volume Feedback: Baroreceptors: How do baroreceptors regulate sodium and water?

Increased stretch → sodium excreted → water follows → volume decreases

Decreased stretch → sodium retained → water follows → volume increases

Potassium and Cardiac Function: What role does potassium play in heart function?

Works with sodium to maintain membrane potential in cardiac cells.

Potassium and Cardiac Function: What is potassium essential for?

Depolarization (contraction)

Repolarization (relaxation)

Potassium and Cardiac Function: What happens when potassium levels are too low?

The heart can’t reset properly → risk of arrhythmias.

EKG Changes from Electrolyte Imbalance: What does an EKG measure?

The electrical activity of the heart.

EKG Changes from Electrolyte Imbalance: How do electrolytes affect EKG waveforms?

Low calcium → distinct pattern

Low/high potassium → unique waveforms

High sodium → rhythm changes

EKG Changes from Electrolyte Imbalance: What are the consequences of severe electrolyte imbalance?

Can lead to arrhythmias, cardiac arrest, or death.

Clinical Application – CPR & Electrolytes: What happened to the 42-year-old woman at Carowinds?

She collapsed from electrolyte depletion after sweating all day and not hydrating.