chapter 26 Electrolytes, water, and acid base balance

ADH, by itself, cannot reduce an increase in osmolality in body fluids. Why not? What other mechanism is required?

ADH cannot add water—it can only conserve what is already there. In order to reduce an increase in osmolality of body fluids, the thirst mechanism is required.

Define acidemia

Acidemia is an arterial pH below 7.3

Define alkalemia.

alkalemia is a pH above 7.45.

antacid

an agent that counteracts acidity, such as sodium bicarbonate, aluminum hydroxide gel, and magnesium trisilicate. Commonly used to manage heartburn

Hyperaldosteronism

excessive output of aldosterone from the adrenal gland, leading to increased sodium and water retention and loss of potassium

What are the body's three major chemical buffer systems?

he three major chemical buffer systems of the body are the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system.

For each of the following, state whether it might result in dehydration, hypotonic hydration, or edema (discussed in Chapter 19): (a) decreased synthesis of plasma proteins due to liver failure; (b) copious sweating; (c) using ecstasy (MDMA), which promotes ADH secretion.

(a) A decrease in plasma proteins causes edema. (b) Copious sweating causes dehydration. (c) Using ecstasy (together with drinking lots of fluids) could cause hypotonic hydration because ecstasy promotes ADH secretion, which interferes with the body's ability to get rid of extra water.

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

A group of disorders associated with excessive ADH secretion in the absence of appropriate (osmotic or nonosmotic) stimuli. Characterized by hypotonic hydration (hyponatremia, fluid retention, and weight gain) and concentrated urine. Usual causes are ectopic secretion of ADH by cancer cells (e.g., small cell lung cancers) and brain disorders or trauma affecting the ADH-secreting hypothalamic neurons. Temporary management involves restricting water intake.

Renal tubular acidosis

A metabolic acidosis resulting from impaired renal reabsorption of bicarbonate; the urine is alkaline.

What change in plasma is most important for triggering thirst? Where is that change sensed?

An increase in osmolality of the plasma is most important for triggering thirst. This change is sensed by osmoreceptors in the hypothalamus.

You eat salty pretzels without drinking. What happens to the volume of your extracellular fluid? Explain.

If you eat salty pretzels, your extracellular fluid volume will expand even if you don't ingest fluids. This is because water will flow by osmosis from the intracellular fluid to the extracellular fluid.

Renal tubule cells acidify the urine and parietal cells acidify the stomach contents (see Chapter 23, p. 891). In each case (a) which intracellular enzyme is key, and (b) blood concentration of which ion increases?

In both renal tubule cells and parietal cells, (a) the enzyme carbonic anhydrase is key, (b) blood concentration of HCO3− increases.

Nathan has Addison's disease (insufficient aldosterone release). How does this affect his plasma Na+ and K+ levels? How does this affect his blood pressure? Explain.

Insufficient aldosterone would cause Nathan's plasma Na+ to be decreased and his plasma K+ to be elevated. The decrease in plasma Na+ would cause a decrease in blood pressure, because plasma Na+ is directly related to blood volume, which is a major determinant of blood pressure.

Joanne, a diabetic patient, is at the emergency department with acidosis due to the production of ketone bodies (p. 632). Would you expect her ventilation to be increased or decreased? Why?

Joanne's ventilation would be increased. The acidosis caused by the accumulated ketone bodies will stimulate the peripheral chemoreceptors, and this will cause more CO2 to be "blown off" in an attempt to restore pH to normal.

Which two abnormalities in plasma are key features of an uncompensated metabolic alkalosis? An uncompensated respiratory acidosis?

Key features of an uncompensated metabolic alkalosis are an increase in blood pH and an increase in blood HCO3−. Key features of an uncompensated respiratory acidosis are a decrease in blood pH and an increase in blood PCO2.

What is the major cation in the ECF? In ICF? What are the intracellular anion counterparts of ECF's chloride ions?

Na+ is the major cation in the ECF and K+ is the major cation in the ICF. The intracellular counterparts to extracellular Cl− are HPO42− and protein anions.

How do the kidneys compensate for respiratory acidosis?

The kidneys compensate for respiratory acidosis by excreting more H+ and generating new HCO3− to buffer the acidosis.

Which hormone is the major regulator of Ca2+ in the blood? What are the effects of hypercalcemia? Hypocalcemia?

The major regulator of calcium in the blood is parathyroid hormone. Hypercalcemia decreases excitability of neurons and muscle cells and may cause life-threatening cardiac arrhythmias. Hypocalcemia increases excitability and causes muscle tetany.

What is the most important buffer inside cells?

The most important intracellular buffer is the protein buffer system.

What is the most important urinary buffer of H+?

The most important urinary buffer of H+ is the phosphate buffer system.

List the two mechanisms by which tubule and collecting duct cells generate new HCO3−.

The tubule and collecting duct cells generate new HCO3− either by excreting ammonium ions (NH4+) or by excreting buffered H+ ion

Which do you have more of, extracellular or intracellular fluid? Plasma or interstitial fluid?

You have more intracellular than extracellular fluid and more interstitial fluid than plasma

in what direction does the largest fraction of Ca2+ moves? Which arrow represents hormonally regulated movement of Na+? Which arrow represents hormonally regulated movement of K+?

the proximal convoluted tubule shows the site where most Ca2+ is reabsorbed. Arrow 5 corresponds to Na+ reabsorption in the collecting duct, which is regulated by aldosterone. Arrow 4 corresponds to K+ secretion in the collecting duct, which is regulated by aldosterone.