Review Questions - Fluid, Electrolyte, and Acid-Base Balance

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1

Body water content is greatest in

A)Infants
B)Young adults
C)Elderly adults

A)Infants

2

Potassium, magnesium, phosphate ions are predominate electrolytes in

A)Plasma
B)Interstitial fluid
C)Intercellular fluid

C)Intercellular fluid

3

Sodium balance is regulated primarily by control of amounts

A)Ingested
B)Excreted in urine
C)Lost in perspiration
D)Lost in feces

B)Excreted in urine

4

Water balance is regulated by control ammounts

A)Ingested
B)Excreted in urine
C)Lost in perspiration
D)Lost in feces

A)Ingested
B)Excreted in urine

5

Two main substances regulated by the influence of aldosterone

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

H)Potassium
I)Sodium

6

Two main substances regulated by parathyroid hormone

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

C)Calcium
G)Phosphate

7

Two Substances secreted into the proximal convoluted tubules in exchange for sodium ions

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

A)Ammonium ions
E)Hydrogen ions

8

Part of an important chemical buffer system in plasma

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

B)Bicarbonate

9

Two ions produced during catabolism of glutamine

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

A)Ammonium ions
B)Bicarbonate

10

Substances regulated by ADH’s effects on the renal tubules

A)Ammonium ions
B)Bicarbonate
C)Calcium
D)Chloride
E)Hydrogen ions
F)Magnesium
G)Phosphate
H)Potassium
I)Sodium
J)Water

J)Water

11

Which of the following factors will enhance ADH release?

A)Increase in ECF volume
B)decrease in ECF volume
C)Increase in ECF osmolality
D)decrease in ECF osmolality

B)decrease in ECF volume
D)decrease in ECF osmolality

12

The Ph of the blood varies directly with

A)HCO3-
B)Pco2
C)H+
D)None of the above

A)HCO3-

13

in an individual with metabolic acidosis, a clue that the respiratory system is compensating is provided by

A)High blood bicarbonate levels
B)Low blood bicarbonate levels
C)Rapid deep breathing
D)Slow, shallow breathing

C)Rapid deep breathing

14

Name the body fluid compartments, noting their locations and the approximate fluid volume in each.

The body fluid compartments include the intracellular fluid compartment, located inside the cells with fluid volume of approximately 25 liters, and the extracellular fluid compartment (plasma and interstitial fluid), located in the external environment of each cell with fluid volume of approximately 15 liters.

15

Describe the thirst mechanism, indicating how it is triggered and terminated.

A decrease in plasma volume of 10–15% and/or an increase in plasma osmolality of 2–3% results in a dry mouth and excites the hypothalamic thirst or drinking center. Hypothalamic stimulation occurs because the osmoreceptors in the thirst center become irritable and depolarize as water, driven by the hypertonic ECF, moves out of them by osmosis. Collectively, these events cause a subjective sensation of thirst. The quenching of thirst begins as the mucosa of the mouth and throat are moistened and continues as stretch receptors in the stomach and intestine are activated, providing feedback signals that inhibit the hypothalamic thirst center.

16

Explain why and how ECF osmolality is maintained.

It is important to control the extracellular fluid (ECF) osmolality because the ECF determines the ICF volume and underlies the control of the fluid balance in the body. The ECF is maintained by both thirst and the antidiuretic hormone (ADH). A rise in plasma osmolality triggers thirst and the release of ADH; a drop in plasma osmolality inhibits thirst and ADH.

17

Explain why and how sodium balance, ECF volume, and blood pressure are jointly regulated.

Sodium is pivotal to fluid and electrolyte balance and to the homeostasis of all body systems because it is the principal extracellular ion. While the sodium content of the body may be altered, its concentration in the ECF remains stable because of immediate adjustments in water volume. The regulation of the sodium-water balance is inseparably linked to blood pressure and entails a variety of neural and hormonal controls: (1) aldosterone—increases the reabsorption of sodium from the filtrate; water follows passively by osmosis, increasing blood volume (and pressure). The renin-angiotensin mechanism is an important control of aldosterone release; the juxtaglomerular apparatus responds to: (a) decreased stretch (due to decreased blood pressure), (b) decreased filtrate osmolality, or (c) sympathetic nervous system stimulation, resulting ultimately in aldosterone release from the adrenal cortex. (2) ADH—osmoreceptors in the hypothalamus sense solute concentration in the ECF: increases in sodium content stimulate ADH release, resulting in increased water retention by the kidney (and increasing blood pressure). (3) Atrial natriuretic peptide—released by cells in the atria during high-pressure situations, it has potent diuretic and natriuretic (sodium-excreting) effects; the kidneys do not reabsorb as much sodium (therefore water) and blood pressure drops.

18

Describe the role of the respiratory system in controling acid-base balance

Respiratory system regulation of acid-base balance provides a physiological buffering system. Falling pH, due to rising hydrogen ion concentration or PCO2 in plasma, excites the respiratory center (directly or indirectly) to stimulate deeper, more rapid respirations. When pH begins to fall, the respiratory center is inhibited.

19

Explain how the chemical buffer systems resist changes in pH.

Chemical acid-base buffers prevent pronounced changes in H+ concentration by binding to hydrogen ions whenever the pH of body fluids drops and releasing them when pH rises.

20

Explain the relationship of the following to renal secretions and excretion of hydrogen ions:

A)Plasma carbon dioxide levels
B)Phosphates
C)Sodium bicarbonate

A)Plasma carbon dioxide levels - The rate of H+ secretion rises and falls directly with CO2 levels in the ECF. The higher the content of CO2 in the peritubular capillary blood, the faster the rate of H+ secretion.

B)Phosphates - Type A intercalated cells secrete H+ actively via a H+-ATPase pump and via a K+-H+ antiporter. The secreted H+ combines with HPO42–, forming H2PO4–, which then flows out in urine.

C)Sodium bicarbonate - The dissociation of carbonic acid in the tubule cells liberates HCO3– as well as H+. HCO3– is shunted into the peritubular capillary blood. The rate of reabsorption of bicarbonate depends on the rate of secretion or excretion of H+ in the filtrate.

21

List several factor that place new born babies at risk for acid-base imbalance

Factors that place newborn babies at risk for acid-base imbalances include very low residual volume of infant lungs, high rate of fluid intake and output, relatively high metabolic rate, high rate of insensible water loss, and inefficiency of the kidneys.

22

Critical Thinking

Mr. Jessup, a 55-year old man, is operated on for a cerebral tumor. About a month later, he appears at his physician's office complaining of excessive thirst. He claims to have been drinking about 20 liters of water daily for the past week and that he has been voiding nearly continuously. A urine sample is collected and its specific gravity is reported as 1.001.
a. What is your diagnosis of Mr. Jessup's condition?
b. What connection might exist between his previous surgery and his present problem?

This patient has diabetes insipidus caused by insufficient production of ADH by the hypothalamus. The operation for the removal of the cerebral tumor has damaged the hypothalamus or the hypothalamohypophyseal tract leading to the posterior pituitary. Because of the lack of ADH, the collecting tubules and possibly the convoluted part of the distal convoluted tubule are not absorbing water from the glomerular filtrate. The large volume of very dilute urine voided by this man and the intense thirst that he experiences are the result.

23

Critical Thinking

For each of the following sets of blood values, name the acid-base imbalance, determine its cause (metabolic or respiratory), decide whether the condition is being compensated, and cite at least one possible cause for the imbalance.
Problem 1: pH 7.63; Pco2 19mm Hg; HCO3- 19.5 mEq/L
Problem 2: pH 7.22; Pco2 30mm Hg; HCO3- 12.0 mEq/L

Problem 1: pH 7.63, PCO2 19 mm Hg, HCO3– 19.5 m Eq/L
1. The pH is elevated = alkalosis.
2. The PCO2 is low and is the cause of the alkalosis.
3. The HCO3– is also low = compensating. This is a respiratory alkalosis, possibly due to hyperventilation, being compensated by metabolic acidosis.

Problem 2: pH = 7.22, PCO2 30 mm Hg, HCO3– 12.0 mEq/L
1. The pH is below normal = acidosis.
2. The PCO2 is low, therefore not the cause of the acidosis, but is compensating.
3. The HCO3– is very low and is the cause of the acidosis. This is a metabolic acidosis. Possible causes include ingestion of too much acid (drinking too much alcohol), excessive loss of bicarbonate ion (diarrhea), accumulation of lactic acid during exercise, or shock, or by the ketosis that occurs in diabetic crises or starvati

24

Critical Thinking

Explain how emphysema and congestive heart failure can lead to acid-base imbalance.

Emphysema impairs gas exchange or lung ventilation, leading to retention of carbon dioxide and respiratory acidosis. Congestive heart failure produces oxygenation problems as well as edema and causes metabolic acidosis due to an increase in lactic acid

25

Critical Thinking

Mrs. Bush, a 70 year old woman is admitted to the hospital. Her history states that she has been suffering from diarrhea for three weeks. On admission, she complains of severe fatigue and muscle weakness. A blood chemistry reveals the following lab values: Sodium is 142 mEq/L, potassium is 1.5mEq/L; chloride: 92 mEq/L; PC02 is 32 mmHg. Which electrolytes are within normal limits? Which are so abnormal that the patient has a medical emergency? Which of the following represents the greatest danger to Mrs. Bush
a. fall due to her muscular weakness
b. edema,
c. cardiac arrhythmias and cardiac arrest

The patient has a normal sodium ion concentration; CO2 is slightly low, as is Cl–. The potassium ion concentration is so abnormal that the patient has a medical emergency. The greatest danger is (c) cardiac arrhythmia and cardiac arrest.

26

Critical Thinking

During a routine medical checkup, Candace, a 26-year-old physiotherapy student, is surprised to hear that her blood pressure is 180/110. She also has a rumbling systolic and diastolic abdominal bruit (murmur) that is loudest at the mid-epigastric area. Her physician suspects renal artery stenosis (narrowing). She orders an abdominal ultrasound and renal artery arteriography, which confirms that Candace has a small right kidney, and that the distal part of her right renal artery is narrowed by more than 70%. Her physician prescribes diuretics and calcium channel blockers as temporary measures, and refers Candace to a cardiovascular surgeon. Explain the connection between Candace’s renal artery stenosis and her hypertension. Why is her right kidney smaller than her left? What would you expect Candace’s blood levels of potassium, sodium, aldosterone, angiotensin II, and renin to be?

Candace’s right kidney is smaller due to decreased blood flow from the narrowing of her right renal artery. The right kidney’s reduced blood flow is decreasing the glomerular filtration rate of the kidney, which is responding by signaling to the body to increase blood pressure to increase blood flow to the kidney. You would expect to find her potassium levels low, and the levels of sodium, aldosterone, angiotensin II, and renin to all be high.