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Chapter 27 : Fluid, Electrolyte, and Acid-Base Balance
Terms in this set (31)
The primary components of the extracellular fluid are
The principal anions in the ICF are
phosphate and proteins (Pr-)
Osmoreceptors in the hypothalamus monitor the osmotic concentration of the ECF and secrete ____________ in response to higher osmotic concentrations.
Write the missing names and molecule formulas for the following reactions between the carbonic acid-bicarbonate buffer system and the bicarbonate reserve.
(Carbomic Acid-Bicarbonate Buffer System) CO2 + H2O --> carbonic acid (H2CO3-) --> H+ + bicarbonate ion (HCO3-) --> (Bicarbonate Reserve) Na+ & HCO3- --> sodium bicarbonate (NaHCO3)
Calcium homeostasis primarily reflects
an interplay among reserves in the bones, the rate of absorption, and the rate of excretion.
The most important factor affecting the pH of body tissues is the concentration of
Changes in the pH of body fluids are compensated for by
the carbonic acid-bicarbonate buffer system, the phosphate buffer system, changes in the rate of depth and breathing, protein buffers but NOT an increase in urine output.
Respiratory acidosis develops when the blood pH is
decreased due to an increased blood PCO2 levels.
Metabolic alkalosis occurs when
bicarbonate ion concentrations become elevated.
Identify four (4) hormones that mediate major physiological adjustments affecting fluid and electrolyte balance. What are the primary effects of each hormone?
Four (4) major hormones involved in fluid and electrolyte balance are (1) antidiuretic hormone (ADH): stimulates water conservation by the kidneys and stimulates thirst center; (2) aldosterone: determines the rate of sodium reabsorption and potassium secretions along the DCT and collecting system of the kidney; and (3) ANP and (4) BNP; reduce thirst, promote the loss of Na+ and water by the kidneys, and block the release of ADH and aldosterone.
Drinking a solution hypotonic to the ECF causes the ECF to
increase in volume and become hypotonic to the ICF.
The osmotic concentration of the ECF decreases if an individual gains water without a corresponding
gain of electrolytes
When the pH of the body fluids begins to decrease, free amino acids and proteins will
bind a hydrogen at the amino group
In a protein buffer system, if the pH increases
a hydrogen ion is released and a carboxylate ion is formed.
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.
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?
A person with a fever should increase fluid intake because for each degree (Celsius) the body temperature increases above normal, daily water loss increases by 200 mL.
Define and give an example of (a) volatile acid, (b) a fixed acid, and (c) an organic acid. Which represents the greatest threat to acid-base balance? Why?
(a) Acids that can leave solution and enter the atmosphere, such as carbonic acid, are volatile acids. (b) Acids that do no leave solution, such as sulfuric acids, are fixed acids. (c) Acids produced during metabolism, such as lactic acid and ketones, are organic acids. Volatile acids are the greatest threat because of the large amounts generated by normal cellular processes.
What are the three (3) major buffer systems in body fluids? How does each system work?
(1) phosphate buffer system: This buffer system consists of H2PO4-, a weak acid that, in solution, reversibly dissociates into a hydrogen ion and HPO(4)2-. The phosphate buffer system plays a relatively small role in regulating the pH of the ECF, because the ECF contains far higher concentrations of bicarbonate ions than phosphate ions; however, it is important in buffering the pH of the ICF. (2) 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 acids dissociates to release a hydrogen ion; if the pH drops, the amino group accepts an additional hyfrogen ion to form an amino ion (NH3+) and the carboxylate ion can accept a hydrogen ion to form a carboxyl group. Plasma proteins contribute to the buffering capabilities of the 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. (3) carbonic acid-bicarbonate system: Most carbon dioxide generated in tissues is converted to carbonic acid, which dissociates into a hydrogen ion and a bicarbonate ion. Hydrogen ions released by dissociation of organic or fixed acids combine with bicarbonate ions, elevating PCO2; additional CO2 is lost at the lungs.
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 by generating additional buffers.
Differentiate between respiratory compensation and renal compensation.
Respiratory compensation is a change in the respiratory rate that helps stabilize the pH of the ECF. Increasing or decreasing the rate of respiration alters pH by decreasing or increasing the PCO2. When the PCO2 decreases, the pH increases; when the PCO2 increases, the pH decreases. Renal compensation is a change in the rates of hydrogen and bicarbonate ion secretion or reabsorption in response to changes in plasma pH. Tubular hydrogen secretion results in the diffusion or 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 by 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.
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 hypoventilation. Metabolic acidosis, which occurs when bicarbonate ion levels decrease, can result from overproduction of fixed or organic acids, impaired ability to secrete H+ ions by the kidney, or severe bicarbonate loss.
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 volcume, 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.
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 decrease 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.
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 POC2 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 PCO3 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) coupled with the intravenous infusion of buffered isotonic solution containing sodium lactate, sodium gluconate, or sodium bicarbonate that would absorb the H+ in the ECF and increase body fluid pH.
Dan has born lost in the desert for two days with very little water. As a result of this exposure, what would you expect to observe?
increased ADH levels
Mary, a nursing student, has been caring for burn patients. She notices that they consistently show elevated levels of potassium in their urine and wonders why. What would you tell her?
When tissues are burned, cells are destroyed and their cytoplasmic content 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 releases 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-aldosterone system. Ultimately, angiotensin II stimulates increased aldosterone secretion, which promotes sodium retention and potassium secretion by the kidneys, thereby accounting for the elevated potassium level's in the patient's urine.
While visiting a foreign country, Milly inadvertently drinks some water, even tho 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 pf 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.
Yuka is dehydrated, so her physical 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 the 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 mich of the glucose. The remaining glucose would increase the osmolarity of tubular filtrate, decreasing water reabsorption and increasing urine volume.
Refer to the diagnostic flowchart in Spotlight 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 1 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 acidosos. Patient 4 has metabolic alkalosis.
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