Fluid and Electrolyte Balance Overview

What is the average daily sodium intake for an American?

9g of NaCl per day (155 mOsm)

What is the effect of adding 9g of NaCl without adding fluid to the ECF?

It would raise ECF osmolarity to 307 mOsM.

How does the body initially handle excess sodium?

By increasing ECF volume.

What hormone increases sodium reabsorption in the kidneys?

Aldosterone.

What triggers the production of aldosterone?

Increased potassium in ECF and decreased blood pressure.

What is the role of aldosterone in sodium balance?

It increases Na reabsorption by P cells in distal tubules and collecting ducts.

Describe the process by which aldosterone functions at the cellular level.

Aldosterone combines with a cytoplasmic receptor, forming a hormone-receptor complex that initiates transcription in the nucleus, leading to protein synthesis of new channels and pumps.

What is the renin-angiotensin system (RAS) stimulated by?

Decreased blood pressure, decreased NaCl transport in tubule, and increased sympathetic activity.

What are natriuretic peptides and what is their function?

They are RAS antagonists that help decrease blood pressure.

What is the normal range for potassium levels in ECF?

3.5-5.5 mM.

What happens to potassium levels when there is excess potassium in the body?

Aldosterone triggers increased secretion of potassium.

What are the pH levels for arterial blood, venous blood, and intracellular fluid (ICF)?

Arterial blood: 7.40, Venous blood and ISF: 7.35, ICF: 7.00.

What defines alkalosis and acidosis in terms of arterial pH?

Alkalosis: arterial pH > 7.45; Acidosis: arterial pH < 7.35.

What is the primary source of hydrogen ions (H+) in the body?

The body produces up to 12,500 mmol of H+ each day.

What is a buffer and how does it function in pH regulation?

A buffer moderates changes in pH by binding to H+ when pH decreases and releasing H+ when pH increases.

What are some examples of intracellular buffers?

Proteins, phosphate ions, and hemoglobin.

Which buffer system is the most important in extracellular fluid (ECF)?

The bicarbonate buffer system.

How do renal mechanisms regulate pH?

NHE secretes H+, which combines with filtered HCO to form CO2; CO2 combines with water to form H+ and HCO, which is reabsorbed with Na.

What role do intercalated cells in the collecting duct play in acid-base balance?

They fine-tune pH balance by secreting or reabsorbing H+, HCO3, and K.

What distinguishes Type A and Type B intercalated cells in terms of their function?

Type A cells secrete H+ and reabsorb HCO3 and K during acidosis; Type B cells secrete HCO3 and K and reabsorb H during alkalosis.

What are the two types of acid-base disturbances?

Respiratory and metabolic.