Review Questions for Chapter 27 Fluid, Electrolyte, and Acid-Base Balance for Anatomy and Physiology

What are the three major buffer systems in body fluids? How does each system work?

(1) *protein buffer systems*: These depend on the ability of amino acids to respond to changes in pH by accepting or releasing hydrogen ions. If the pH rises, the carboxyl group of the amino acid dissociates to release a hydrogen ion; if the pH drops, the amino group accepts an additional hydrogen ion to form an amino group ion (NH3+) and the carboxylate ion can accept a hydrogen ion to form a carboxyl group. Plasma proteins contribute to the buffering capabilities of blood; inside cells, protein buffer systems stabilize the pH of the ECF by absorbing extracellular hydrogen ions or exchanging intracellular hydrogen ions for extracellular potassium. (2) *carbonic acid-bicarbonate system*: Most carbon dioxide generated in tissues is converted to carbonic acid, which dissociates into a hydrogen ion and a bicabonate ion. Hydrogen ions released by dissociation of organic or fixed acids combine with bicarbonate ions, elevating the PCO2; additional CO2 is lost at the lungs. (3) *phosphate buffer system*: This buffer system plays of H2PO4, a weak acid that, in solution, reversibly dissociates into a hydrogen ion and HPO4 2-. The phosphate buffer system plays a relatively small role in regulating the pH of the ECE, because the ECF contains far higher concentrations of bicarbonte ions than phosphate ions; however, it is important in buffering the pH of the ICF.

Define and give an example of (a) a volatile acid (b) a fixed acid (c) an organic acid. Which represents the greatest threat to acid-based balance? Why?

(a) acids that can leave solution and enter the atmosphere, such as carbonic acid, are *volatile acids*. (b) Acids that do not leave solution, such as sulfuric acid, are *fixed acids*. (c) Acids produced during metabolism, such as lactic acid, are *organic acids*. Volatile acids are the greatest threat because of the large amounts generated by normal cellular processes.

Changes in the pH of body fluids are compensated for by all of the following *except* (a) an increase in urine output (b) the carbonic acid-bicarbonate buffer system (c) the phosphate buffer system (d) changes in the rate and depth of breathing (e) protein buffers

(a) an increase in urine output

Metabolic alkalosis occurs when (a) bicarbonate ion concentrations become elevated (b) a severe bicarbonate loss occurs (c) the kidneys fail to excrete hydrogen ions (d) ketone bodies are generated in abnormally large quantities

(a) bicarbonate ion concentrations become elevated

Write the missing names and molecular formulas for the following reactions between the carbonic acid-bicarbonate buffer system and the bicarbonate reserve. ( figure 27-12 a; p 1015)

(a) carbonic acid (H2Co3) (b) bicarbonate ion (HCO3-) (c) sodium bicarbonate (NaHCO3)

Dan has been lost in the desert for 2 days with very little water. As a result of this exposure, you would expect to observe which of the following? (a) elevated ADH levels (b) decreased blood osmolarity (c) normal urine production (d) increased blood volume (e) cells enlarged with fluid

(a) elevated ADH (antidiuretic hormone) levels

The osmotic concentration of the ECF decreases if an individual gains water without a corresponding (a) gain of electrolytes (b) loss of water (c) fluid shift from ECF to the ICF (d) a, b, and c

(a) gain of electrolytes

The principal anions in the intracellular fluid are (a) phosphate and proteins (Pr-) (b) phosphate and bircarbonate (c) sodium and chloride (d) sodium and potassium

(a) phosphate and proteins (Pr-)

Respiratory acidosis develops when the plasma pH is (a) elevated due to an decreased plasma PCO2 level (b) decreased due to an elevated plasma PCO2 level (c) elevated due to an elevated plasma PCO2 level (d) decreased due to a decreased plasma PCO2 level

(b) decreased due to an elevated plasma PCO2 level

In a protein buffer system, if the pH rises, (a) the protein acquires a hydrogen ion from carbonic acid (b) hydrogen ions are buffered by hemoglobin molecules (c) a hydrogen ion is released and a carboxyl ion is formed (d) a chloride shift occurs

(c) a hydrogen ion is released and carboxyl ion is formed

The primary components of the extracellular fluid are (a) lymph and cerebrospinal fluid (b) plasma and serous fluids (c)interstitial fluid and plasma (d) all of these

(c) interstitial fluid and plasma

Osmoreceptors in the hypothalamus monitor the osmotic concentration of the extracellular and secrete _____ in response to higher osmotic concentrations (a) BNP (Natriuretic Peptides) (b) ANP (Natriuretic Peptides) (c) aldosterone (d) ADH (Antidiuretic Hormone)

(d) ADH (Antidiuretic Hormone)

Calcium homeostasis primarily reflects (a) a balance between absorption in the gut and excretion by the kidneys (b) careful regulation of blood calcium levels by the kidneys (c) an interplay between parathormone and aldosterone (d) an interplay among reserves in the bones, the rate of absorption, and the rate of excretion (e) hormonal control of calcium reserves in the bones

(d) an interplay among reserves in the bones, the rate of absorption, and the rate of excretion

When the pH of body fluids begins to fall, free amino acids and proteins will (a) release a hydrogen from the carboxyl group (b) release a hydrogen from the amino group (c) release a hydrogen at the carboxyl group (d) bind a hydrogen at the amino group

(d) bind a hydrogen at the amino group

The *most* important factor affecting the pH of body tissues is the concentration of (a) lactic acid (b) ketone bodies (c) organic acids (d) carbon dioxide (e) hydrochloric acid

(d) carbon dioxide

Drinking a hypotonic solution causes the extracellular fluid to (a) increase in volume and become hypertonic with respect to the ICF (b) decrease in volume and become hypertonic with respect to the ICF (c) decrease in volume and become hypotonic with respect to the ICF (d) increase in volume and become hypotonic with respect to the ICF

(d) increase in volume and become hypotonic

Differentiate among fluid balance, electrolyte balance, and acid-base balance, and explain why each is important to homeostasis.

*Fluid balance* is a state in which the amount of water gained each day is equal to the amount lost to the environment. It is vital that the water content of the body remain stable, because water is an essential ingredient of cytoplasm and accounts for about 99 percent of ECF volume. *Electrolyte balance* exists when there is neither a net gain nor a net loss of any ion in body fluids. It is important that the ionic concentrations in body water remain within normal limits; if levels of calcium or potassium become too high, for instance, cardiac arrhythmias can develop. *Acid-base balance* exists when the production of hydrogen ions precisely offsets their loss. The pH of body fluids must remain within a relatively narrow range, variations outside this range can be life threatening.

What is the difference between metabolic acidosis and respiratory acidosis? What can cause these conditions?

*Respiratory acidosis*, which results from an abnormally high level of carbon dioxide (hypercapnia), is usually caused by hyperventilation. *Metabolic acidosis*, which occurs when bicarbonate ion levels falls, can result from overproduction of fixed or organic acids, impaired ability to secrete H+ ions at the kidney, or severe bicarbonate loss.

Differentiate between respiratory compensation and renal compensation.

*Respiratory compensation* is a change in the respiratory rate that help stabilize the pH of the ECF. Increasing or decreasing the rate of respiration alters pH by lowering or raising the PCO2. When the PCO2 declines, the pH rises, when the PCO2, increases the pH decreases. * Renal compensaton* is a change in the rates of hydrogen and bicarbonate ion secretion or reabsorption in response to changes in plasma pH. Tubular hydrogen ion secretion results in the diffusion of bicarbonate ions into the ECF.

Distinguish between respiratory and metabolic disorders that disturb acid-base balance.

*Respiratory disorders* result from abnormal CO2 levels in the ECF. An imbalance exists between the rate of CO2 removal at the lungs and its generation in other tissues. *Metabolic disorders* are caused by the generation of organic or fixed acids or by conditions affecting the concentration of bicarbonate ions in the ECF.

Identify four hormones that mediate major physiological adjustments affecting fluid and electrolyte balance. What are the primary effects of each hormone?

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While visiting a foreign country, Milly inadvertently drinks some water, even through she had been advised not to. She contracts an intestinal disease that causes severe diarrhea, How would you expect her condition to affect her blood pH, urine pH, and pattern of ventilation?

Digestive secretions contain high levels of bicarbonate, so individuals with diarrhea can lose significant amounts of this important ion, leading to acidosis. We would expect Milly's blood pH to be lower than 7.35, and that of her urine to be low (due to increased renal excretion of hydrogen ions). We would also expect an increase in the rate and depth of breathing as the respiratory system tries to compensate by eliminating carbon dioxide.

The most recent advice from medical and nutritional experts is to monitor one's intake of salt so that it does not exceed the amount needed to maintain a constant ECF volume. What effect does excessive salt ingestion have on blood pressure?

Excessive salt intake causes an increase in total blood volume and blood pressure due to an obligatory increase in water absorption across the intestinal lining and recall of fluid from the ICF.

What are fluid shifts? What is their function, and what factors can cause them?

Fluid shifts are rapid water movements between the ECF and the ICF that occur in response to increases or decreases in the osmotic concentration of the ECF. Such water movements dampen extreme shifts in electrolyte balance.

Why should a person with a fever drink plenty of fluids?

Individuals with a fever should increase fluid intake because for each degree (Celsius) the body temperature rises above normal, daily water loss increases by 200 mL.

Refer to the diagnostic flowchart in Figure 27-18. Use information from the blood test results in the accompanying table to categorize the suspected acid-base disorders of the patients represented in the table.

Patient has compensated respiratory alkalosis. Patient 2 has acute metabolic acidosis due to the generation or retention of organic or fixed acids. Patient 3 has acute respiratory acidosis. Patient 4 has metabolic alkalosis.

How do respiratory and renal mechanisms support the buffer systems?

Respiratory and renal mechanisms support buffer systems by secreting or absorbing hydrogen ions, by controlling the excretion of acids and bases, and be generating additional buffers.

Exercise physiologists recommend that adequate amounts of fluid be ingested before, during, and after exercise. Why is fluid replacement during extensive sweating important?

Since sweat is usually hypotonic, the loss of a large volume of sweat causes hypertonicity in body fluids. The loss of fluid volume is primarily from the interstitial space, which leads to a reduction in plasma volume and an increase in the hematocrit. Severe dehydration can cause the blood viscosity to increase substantially, resulting in an increased workload on the heart, ultimately increasing the probability of heart failure.

Yuka is dehydrated, so her physician prescribes intravenous fluids. The attending nurse becomes distracted and erroneously gives Yuka a hypertonic glucose solution instead of normal saline. What effect will this mistake have on Yuka's plasma ADH levels and urine volume?

The hypertonic solution will cause fluid to move from the ICF to the ECF, further aggravating Yuka's dehydration. The slight increase in pressure and osmolarity of blood should lead to an increase in ADH, even though ADH levels are probably quite high already. Despite the high ADH levels, urine volume would probably increase, because the kidneys could not reabsorb much of the glucose. The remaining glucose would increase the osmolarity of the tubular filtrate, decreasing water reabsorption and increasing urine volume.

After falling into an abandoned stone quarry filled with water and nearly drowning, a young boy is rescued. In assessing his condition, rescuers find that his body fluids, have high PCO2 and lactate levels, and low PO2 levels. Identify the underlying problem and recommend the necessary treatment to restore homeostatic conditions.

The young boy has metabolic and respiratory acidosis. The metabolic acidosis resulted primarily from the large amounts of lactic acid generated by the boy's muscles as he struggled in the water. (The dissociation of lactic acid releases hydrogen ions and lactate ions.) Sustained hypoventilation during drowning contributed to both tissue hypoxia and respiratory acidosis. Respiratory acidosis developed as the PCO2 increased in the ECF increasing the production of carbonic acid and its dissociation into H+ and HCO3-. Prompt emergency treatment is essential. The usual procedure involves some form of artificial or mechanical respiratory assistance (to increase the respiratory rate and decrease PCO2 in the ECF) couple with the intravenous infusion of a buffered isotonic solution containing sodium lactate, sodium gluconate, or sodium bicarbonate that would absorb the H+ in the ECF and increase body fluid pH.

Mary. a nursing student, has been caring for burn patients. She notices that they consistently show elevated levels of potassium in the urine and wonders why. What would you tell her.

When tissues are burned, cells are destroyed and their cytoplasmic contents leak into the interstitial fluid and then move into the plasma. Since potassium ions are normally found within the cell, damage to a large number of cells release relatively large amounts of potassium ions into the blood. The elevated potassium level stimulates cells of the adrenal cortex to produce aldosterone and cells of the juxtaglomerular complex to produce renin. The renin activates the angiotensin mechanism. Ultimately, angiotensin II stimulates increased aldosterone secretion, which promotes sodium retention and potassium secretion by the kidneys, thereby accounting for the elevated potassium levels in the patient's urine.