CHAPTER 20. Quick Check and Active Learning Answer Keys QUICK CHECK

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1 CHAPTER 20 QUICK CHECK Page Renal cortex and renal medulla 2. The nephron is composed of two principal components: the renal corpuscle and renal tubule. The renal corpuscle can be subdivided into the renal Bowman capsule and the glomerulus. The renal tubule can be subdivided into the proximal convoluted tubule, Henle loop, distal convoluting tubule, and the collecting duct. 3. The kidneys form urine by filtering the blood of its nitrogenous wastes. Normally, the kidneys balance the amount of many substances entering and leaving the blood. By eliminating wastes and adjusting fluid balance, the kidneys play an essential part in maintaining homeostasis. The kidneys also play a key role in regulating levels of many chemical substances in the blood, such as chloride, sodium, potassium, and bicarbonate. They also regulate water and salt content. In addition, specialized cells of the juxtaglomerular apparatus regulate blood volume and blood pressure. Finally, the kidneys secrete the hormone erythropoietin that stimulates the production of additional red blood cells. 4. When erythropoietin is released from the kidneys into the blood stream, it travels to the red bone marrow and stimulates the production of additional erythrocytes (red blood cells). Page Ureters 2. Elastic fibers and involuntary muscle fibers in the wall of the urinary bladder make it well suited for expanding to hold variable amounts of urine and then contracting to empty itself. 3. Urethra 4. The internal urethral sphincter is involuntary and the external urethral sphincter is composed of striated muscle and is under voluntary control. 5. Incontinence refers to involuntary voiding or loss of urine in an older child or adult. Page Filtration, reabsorption, and secretion 2. The countercurrent mechanisms maintain hypertonic conditions in the medulla, which enable the kidney to concentrate the urine by reabsorbing more water than otherwise possible. 3. ADH decreases the amount of urine and aldosterone stimulates the kidney tubules to reabsorb sodium and water, thereby reducing urine volume. Both ADH and aldosterone reduce urine volume. 4. When blood volume and pressure drop below normal, this is sensed by the cells in the juxtaglomerular apparatus (JG). JG cells then release an enzyme called renin that initiates the reninangiotensin-aldosterone system (RAAS). The RAAS eventually produces constriction of blood vessels and thus raises blood pressure. The RAAS also triggers adrenal gland secretion of aldosterone, which promotes water retention and thus increases total blood volume. 5. Anuria is the absence of urine. Polyuria is an unusually large amount of urine. Page Renal calculi develop when calcium and other minerals, such as uric acid, crystallize on the renal papillae and break off into the urine. 2. Nephrotic syndrome is a collection of signs and symptoms that accompany various glomerular disorders. These include proteinuria, hypoalbuminemia, and edema. 3. Acute renal failure is an abrupt reduction in kidney function characterized by oliguria and a sharp rise in nitrogenous compounds in the blood. It is assessed by the blood-urea-nitrogen (BUN) test, which measures the concentration of nitrogenous wastes in the blood. Page 1 of 10

2 ACTIVE LEARNING Review Questions 1. The kidneys lie just above the waistline. The right kidney is usually a little lower than the left. They are located under the muscles of the back and behind the parietal peritoneum. A heavy cushion of fat normally encases each kidney, helping to hold it in place. 2. The internal structures of the kidney are composed of the following. Cortex - the outer layer of each kidney. Medulla - the inner portion of the kidney. Pyramids - the triangular divisions of the medulla of the kidney. Papilla - the narrow innermost end of a pyramid Pelvis - an expansion of the upper end of a ureter, which lies inside the kidney. Calyx - a division of the renal pelvis. 3. Ureters are narrow tubes less than 6 mm wide and cm long with thick, muscular walls. Mucous membranes line both ureters and each renal pelvis. Contractions of the muscles produce peristaltictype movements that assist in moving urine down the ureters into the bladder. The lining membrane of the ureters is richly supplied with nerve endings. 4. Chemical analysis of urine usually provides information about ph, urea concentrations, and the presence of abnormal chemicals, such as glucose, acetone, protein, or bile. 5. Casts are small particles formed by deposits of minerals or cells on the walls of the renal tubules that break off into the urine. A large number of casts may indicate several types of kidney disorders. 6. The wall of the urinary bladder contains elastic fibers and involuntary muscle fibers that make it wellsuited for expanding to hold variable amounts of urine. A mucous membrane lines the urinary bladder and the lining is loosely attached to the deeper muscular layer so that the bladder is wrinkled and lies in folds called rugae when it is empty. When the bladder is filled, its inner surface is smooth. One triangular area on the back surface of the bladder, called the trigone, is free of rugae and is always smooth. The trigone extends between the openings of the two ureters above and the point of exit of the urethra below. 7. The urethra is the lowest point of the urinary tract. The same sheet of mucous membrane that lines each renal pelvis, ureters, and the bladder extends down into the urethra. The urethra is a narrow tube that is 4 cm long in women and 20 cm long in men. 8. Two sphincters guard the pathway leading from the bladder. The internal urethral sphincter is located at the bladder exit. The external urethral sphincter circles the urethra just below the neck of the bladder. When contracted, both sphincters seal off the bladder and allow urine to accumulate. As the bladder wall is stretched, nervous impulses are transmitted to the second, third, and fourth sacral segments of the spinal cord, which initiates the emptying reflex. The reflex causes the contraction of the muscle of the bladder wall and relaxation of the internal sphincter. Urine enters the urethra. If the external sphincter, which is under voluntary control, is relaxed, micturition occurs. Contraction of the external sphincter abruptly terminates urination voluntarily. 9. Urinary retention is a condition in which no urine is voided. The kidneys produce urine, but the bladder is unable to empty itself. Urinary suppression occurs when the kidneys do not produce urine, but the bladder retains the ability to empty itself. 10. Incontinence is a condition in which the individual voids urine involuntarily. It frequently occurs in people who have suffered a stroke or spinal cord injury. If the sacral segments of the spinal cord are injured, some loss of bladder function always occurs. 11. Filtration is the movement of water and dissolved substances out of the blood in the glomeruli into the Bowman capsule. Reabsorption is the movement of water and dissolved substances out of the kidney tubules back into the blood. Secretion is the movement of hydrogen ions, potassium ions, ammonia, and certain drugs out of the blood and into the urine from the distal and collecting tubules. Page 2 of 10

3 Page 3 of 10 Quick Check and Active Learning 12. Blood flowing through the glomeruli exerts pressure that is high enough to push water and dissolved substances out of the glomeruli into the Bowman capsule. Water, glucose, other nutrients, sodium, and other ions are reabsorbed. Reabsorption begins in the proximal convoluted tubules and continues in the Henle loop, distal convoluted tubules, and collecting tubules. Secretion of substances into the urine occurs in the distal and collecting tubules. Substances secreted are hydrogen ions, potassium ions, certain drugs, and ammonia. The processes of filtration, reabsorption, and secretion occurring in successive portions of the nephron accomplish the function of urine formation. 13. Water, glucose, hydrogen ions, potassium ions, sodium ions, ammonia, and certain drugs are some of the substances eliminated or regulated by the kidney. 14. The juxtaglomerular apparatus functions in blood pressure regulation. When blood pressure is low, these cells secrete a hormone that initiates constriction of blood vessels and raises blood pressure. 15. The three hormones that regulate urine volume are antidiuretic hormone (ADH), aldosterone, and atrial natriuretic hormone (ANH). 16. A bladder infection is the most common urinary disorder. 17. Hydronephrosis occurs when urine backs up into the kidney, causing swelling of the renal pelvis and calyces. 18. Another term for renal calculi is kidney stones. Renal calculi are usually made of calcium or uric acid. 19. Urethritis is an inflammation of the urethra. Cystitis is an inflammation of the bladder. Pyelonephritis is an inflammation of the renal pelvis and connective tissue of the kidney. 20. Proteinuria is the presence of proteins, especially albumin, in the urine. Hypoalbuminemia is a low albumin concentration in the blood, resulting from the loss of albumin from the blood through damaged glomeruli. 21. In stage one of chronic renal failure, some nephrons are lost but the remaining healthy nephrons compensate by enlarging and taking over the functions of the lost nephrons. In stage two, the kidney can no longer adapt to the loss of nephrons. The remaining healthy nephrons cannot handle the urea load and the blood urea nitrogen (BUN) level begins to rise dramatically. Stage three is the final stage in chronic renal failure. The BUN level of the blood becomes very high because of the loss of kidney function. Edema and hypertension can also develop because of the retention of body fluids. Critical Thinking 22. ADH decreases the amount of urine by making the collecting tubules permeable to water. If no ADH is present, the tubules are practically impermeable to water, so little or no water is reabsorbed by the blood. When ADH is present, the collecting tubules are permeable to water and water is reabsorbed from them. As a result, less water is lost from the body as urine. Aldosterone plays an important part in controlling the kidney tubules reabsorption of salt. It stimulates the tubules to reabsorb sodium salts at a faster rate. Secondarily, aldosterone also increases water reabsorption as water follows salt. 23. Blood pressure is necessary to generate enough force to push the water and dissolved substances out of the glomerulus into the Bowman capsule. Without this process, the kidneys would be unable to function. 24. There would be a great deal of ADH in the blood. This person would be losing water and the body would be trying to retain as much water as possible. ADH allows water to be reabsorbed from the kidney tubules rather than having it lost in the urine. Chapter Test Bowman capsule, glomerulus 3. Henle loop or nephron loop, collecting duct 4. proximal convoluted tubule, distal convoluted tubule 5. urinalysis 6. casts

4 7. internal urethral sphincter 8. Suppression 9. Incontinence 10. Retention 11. filtration, reabsorption, and secretion 12. Countercurrent 13. diuretic 14. ADH 15. Aldosterone 16. renin-angiotensin-aldosterone 17. g. outer part of the kidney 18. a. inner layer of the kidney 19. k. triangular division in the medulla of the kidney 20. b. expansion of the ureter in the kidney 21. d. tube leading from the bladder to outside of the body 22. f. saclike structure used to hold urine until its voided 23. j. tube connecting the kidney and bladder Quick Check and Active Learning 24. h. an area of the bladder that has openings for the two ureters and the urethra 25. c. cup-shaped part of the nephron that catches filtrate 26. e. network of capillaries nestled within the Bowman capsule 27. i. the part of the renal tubules that is located between the proximal and distal convoluted tubules 28. d. condition caused by urine backing up into the kidney, causing swelling of the renal pelvis and calyces 29. b. another term for a kidney stone 30. a. an inflammation of the urethra that commonly results from a bacterial infection 31. e. an inflammation of the bladder 32. g. inflammation of the renal pelvis and connective tissue of the kidney 33. f. low albumin in the blood due to loss of albumin through damaged glomeruli 34. c. protein, especially albumin, in the urine Case Studies 1. The loss of the fatty pad that surrounds and supports the kidneys may cause them to drop from their normal positions, a condition called nephroptosis. In nephroptosis, the ureters may become kinked and cause urine to backflow into the kidneys and thereby produce hydronephrosis. Hydronephrosis, in turn, may prevent normal filtration of fluids into nephrons and thus cause kidney failure. 2. Thiazide diuretics lower blood pressure by inhibiting water reabsorption in the kidney, thus reducing the amount of water retained by the blood. As you may recall from Chapter 15, such a reduction in blood volume reduces the overall blood pressure. Because the water is prevented from re-entering the blood stream, it remains as urine, greatly increasing the volume of urine output. The term diuretic is applied to any agent that increases the volume of urine output. 3. The fluid used in CAPD is isotonic to normal body fluids, including blood plasma. If the fluid is significantly hypertonic to plasma, it will draw water osmotically from the blood and cause dehydration of the body. If the fluid is significantly hypotonic to plasma, it will lose water osmotically to the blood, causing the blood cells to swell and burst. The dialyzing fluid is isotonic to plasma, but contains a different mixture of solutes than plasma, a mixture devoid of metabolic wastes such as urea. Page 4 of 10

5 CHAPTER 21 QUICK CHECK Page Electrolytes are substances, such as salts, that dissolve or break apart in water solution to form electrically charged atoms (or groups of atoms) called ions. 2. Extracellular and intracellular 3. Fluid balance means that both the total volume and distribution of water in the body remain normal and relatively constant. Page Fluid output 2. Water vapor lost when we exhale; sweat that evaporates from the skin; urine output by the kidney; and water lost in the feces 3. The body maintains fluid balance mainly by changing the volume of urine excreted to match changes in the volume of fluid intake. 4. The hormones that regulate urine volume are antidiuretic hormone (ADH), aldosterone, and atrial natriuretic hormone (ANH). 5. When dehydration starts to develop, changes occur in the extracellular fluid. The extracellular fluid volume decreases and the solute concentration of the extracellular fluid increases. Sensory receptors in the brain and elsewhere in the body detect the change in the volume and concentration of extracellular fluids. They relay this information to the thirst center of the hypothalamus. Signals from the hypothalamus cause a decrease in salivary secretion, which produces a dry mouth feeling that enhances a feeling of thirst. Page If capillary pressure increases, more fluid is pushed or filtered out of blood into the IF. 2. Plasma proteins contribute to osmotic pressure and thereby act as a water-pulling or water-holding force. 3. Hot weather, exercise, or prolonged diarrhea or vomiting Page Electrolytes are compounds that have molecular bonds that permit them to dissociate in water solution into separate particles. Nonelectrolytes are compounds that do not dissociate in water. 2. Many ions are major trace elements in the body (i.e., iron, iodine). They are also required for many cellular activities, such as nerve conduction and muscle contraction. 3. Electrolytes have important nutrient or regulatory roles in the body and influence the movement of water among the three fluid compartments of the body. Page Hypernatremia may result from overuse of salt tablets, dehydration, or prolonged diarrhea. Hyponatremia may be caused by excessive salt loss resulting from burns or diuretics. 2. Hypokalemia (low potassium level) may cause skeletal muscle weakness, cardiac problems, and smooth muscle dysfunction in the gastrointestinal tract. 3. Calcium serves as a basic structural building block in bone and teeth. In addition, it is essential for the maintenance of a normal heartbeat, functioning of nerves and muscles, metabolism, blood coagulation, and in many other enzymatic reactions. Page 5 of 10

6 ACTIVE LEARNING Review Questions 1. The three fluid compartments of the body are (1) intracellular fluid inside the cells, (2) interstitial fluid in the microscopic spaces between the cells, and (3) plasma, the liquid part of the blood. Interstitial fluid and plasma make up extracellular fluid. 2. The following factors influence the percent of water in the body. Total body weight - the more the person weighs, the more water the body contains. Fat content of the body - the more fat, the less water. Gender - the proportion of body weight represented by water is about 10% less in women than in men. Age - in newborns, water may account for 80% of total body weight. 3. The three sources of water in the human body are liquids we drink, water in the food we eat, and water that is produced as a result of the catabolism of foods. 4. Regulating fluid output and exchanging fluids between compartments and from place to place within the body are the main mechanisms balancing these fluid volumes. 5. Fluid output occurs through the kidneys, lungs, skin, and intestines. 6. Aldosterone increases the reabsorption of sodium by the kidney tubules. Because there is an increase in sodium in the blood, water is drawn into the blood by diffusion. This moves water out of the kidney tubules and into the blood. 7. There is some fluid loss that occurs as long as life continues. Beyond the body s control, water is lost through the skin by diffusion and from the lungs with expired air. 8. Capillary blood pressure is a water-pushing force. It pushes fluid out of the blood capillaries into the interstitial fluid. If capillary blood pressure increases, more fluid is filtered into the interstitial fluid. If capillary blood pressure is decreased, less fluid is filtered into the interstitial fluid. 9. Plasma proteins act as a water-pulling or water-holding force. Plasma proteins keep water in the blood and pull it into the blood from the interstitial fluid. If the concentration of plasma proteins decreases appreciably, less water moves from the interstitial fluid to the blood and fluid collects in the tissues. 10. Dehydration is a decrease of water in the body; interstitial fluid is lost first. If the dehydration continues, plasma volume and intracellular fluid can also decrease below normal levels. Too little fluid intake, too much fluid loss, vomiting, or diarrhea can cause dehydration. 11. Overhydration is an increase of body fluid. One cause is giving intravenous fluids too rapidly. This can put too heavy a burden on the heart. 12. An electrolyte dissociates into ions in solution. A nonelectrolyte may dissolve in solution, but will not dissociate into ions. 13. Chloride, bicarbonate, and phosphate ions are named in the textbook. Any three important negative ions would be correct. 14. Sodium, calcium, potassium, and magnesium are named in the textbook. Any three important positive ions would be correct. 15. Many of the clinical manifestations of hyperkalemia are related to muscle malfunction. Severe hyperkalemia results in cardiac arrest. Critical Thinking 16. Any loss of skin increases the loss of water, so dehydration would be a serious problem. In addition, large amounts of tissue destruction result in ICF being released. Because ICF has a high concentration of K+, hyperkalemia also could occur. 17. Water would be absorbed into the blood and as a result, the (colloid) osmotic pressure of the blood would decrease. Water would diffuse out of the blood, resulting in decreased (colloid) osmotic Page 6 of 10

7 pressure in the interstitial and other extracellular fluids. In turn, water would diffuse from the interstitial fluid into the cells, increasing the volume of ICF. Chapter Test 1. interstitial fluid, plasma 2. Intracellular 3. fluid output 4. water from catabolism 5. kidneys, skin, lungs, intestines 6. aldosterone; atrial natriuretic hormone 7. ions 8. chloride 9. sodium 10. false 11. false 12. false 13. b. sodium is moved from the kidney tubules to the blood 14. c. an increase in ECF 15. b. moves fluid from the plasma to the interstitial fluid 16. a. move interstitial fluid into the plasma Case Studies 1. Tom s body can deal with an excessive input of sodium by excreting an increased amount of sodium in the urine. The specific mechanism involves decreased reabsorption of sodium ions in the kidney tubules (see Chapter 20). 2. If Jo has consumed a large amount of distilled water, especially without also consuming salts, she is likely to produce an excessive amount of urine. This occurs because the body attempts to maintain its homeostasis of fluid volume (so it gets rid of excess fluid), electrolytes, and water concentration (so it gets rid of excess water to maintain the normal osmotic balance). A urinalysis might reveal decreased specific gravity (density), perhaps one that is closer to the density of pure water (1.000). Because of the increased water content in Jo s urine, the remaining components (solutes) will be diluted. Thus, the color may appear lighter than usual and the concentration of each solute will be less than normal. 3. Until and unless the body can reverse overhydration by increasing urinary output (see answer #2 above), the presence of excess water in the internal environment makes the blood volume greater than normal. Increased blood volume means increased blood pressure. If peripheral blood pressure increases, the heart must pump harder to exceed that pressure and thus maintain blood flow. (Recall from Chapter 15 that the heart must generate a pressure higher than peripheral vessels to maintain the pressure gradient that allows blood to flow through the circulatory system.) Page 7 of 10

8 CHAPTER 22 QUICK CHECK Page Buffer mechanism, respiratory mechanism, and urinary mechanism 2. Carbon dioxide 3. Buffers are chemical substances that prevent a sharp change in the ph of a fluid when an acid or base is added to it. Page When an individual exhales, carbon dioxide and water leave the body. The carbon dioxide has diffused out of the venous blood as it moves through lung capillaries. The decrease in carbon dioxide in the blood means that there is less available for combining with water to form carbonic acid. Hence, after expiration, the arterial blood contains less carbonic acid and fewer hydrogen ions and has a higher ph (7.45) than does the venous blood (ph 7.35). If a person retains the carbon dioxide (holding breath), then the blood content of carbon dioxide increases. This would increase the amount of carbonic acid, thus decreasing blood ph. 2. The kidneys change the ph of the blood through two mechanisms: acidification of urine and conservation of base by the distal renal tubule secretion of hydrogen ions, and the acidification of urine by tubule secretion of ammonia. Page Acidosis is when the blood ph falls as hydrogen ion concentration increases. In chemical medicine, the term acidosis is used to describe an arterial blood ph of less than Alkalosis occurs when the blood ph is higher than normal. In chemical medicine, the term alkalosis is used to describe an arterial blood ph greater than Metabolic acidosis (bicarbonate deficit) and metabolic alkalosis (bicarbonate excess) 3. Respiratory acidosis (carbonic acid excess) and respiratory alkalosis (carbonic acid deficit) 4. Vomiting causes a loss of acid-containing gastric fluids. This loss of acid upsets the acid-base balance. ACTIVE LEARNING Review Questions 1. As the concentration of hydrogen ions increases in a solution, the solution becomes more acid and the ph value decreases. As the concentration of hydroxide ions increases in a solution, the ph value also increases and the solution becomes more basic or alkaline. 2. The chemical reaction that converts carbon dioxide and water to carbonic acid is: CO 2 + H 2 O = H 2 CO 3. This reaction is catalyzed by carbonic anhydrase. 3. A buffer is a chemical substance that prevents a sharp change in the ph of a solution when an acid or base is added to it. 4. In the buffer pair NaHCO 3 -H 2 CO 3, an addition of hydrogen ions would cause the formation of more of the weak carbonic acid. The hydrogen ion would replace the sodium in the sodium bicarbonate. Because carbonic acid is weak, it would not dissociate as much as a strong acid and the number of hydrogen ions in the solution would be reduced, increasing the ph value. 5. In the buffer pair NaHCO 3 -H 2 CO 3, an addition of hydroxide ions would cause one of the hydrogens from the carbonic acid to be attracted to the hydroxide ion, forming water. There would be fewer hydroxide ions in the solution and because water is neutral, the ph value would decrease. Page 8 of 10

9 6. The changes that occur in blood as a result of buffering fixed acids are (1) the amount of H 2 CO 3 in blood increases slightly because an acid, such as lactic acid, is converted to H 2 CO 3 ; (2) the amount of bicarbonate in blood, mainly NaHCO 3, decreases because bicarbonate ions become part of the newly formed H 2 CO 3 ; (3) the hydroxide ion concentration of blood increases slightly; and (4) blood ph decreases slightly below arterial levels. 7. The lungs remove most of the carbon dioxide from the blood. The amount of carbon dioxide in the blood is directly related to the amount of carbonic acid that can be formed. The more carbon dioxide, the more carbonic acid; the more carbonic acid in the blood, the lower the ph. The amount of carbon dioxide removed from the blood by the lungs impacts the ph of the blood. 8. Respiratory rate has a direct effect on blood ph. If breathing is impaired for any length of time, CO 2 would not be expired and blood CO 2 would increase. This would then increase the amount of H 2 CO 3 and hydrogen ion concentration in blood and decrease blood ph. 9. The distal tubules of the kidneys rid the blood of excess acid and at the same time conserve the base present in it. Carbon dioxide leaves the blood and enters into cells that form the wall of the distal kidney tubule. Carbon dioxide then combines with water to form carbonic acid with the aid of carbonic anhydrase, an enzyme. As soon as carbonic acid forms, some of it dissociates to yield hydrogen ions and bicarbonate ions. Hydrogen ions diffuse out of the tubule cells into urine. Here they replace sodium ions in a salt (Na 2 HPO 4 ) to form another salt (NaH 2 PO 4 ), which leaves the body in urine. 10. Acidosis is a decrease in blood ph caused by an increase in acid or a loss of base. Alkalosis is an increase in blood ph caused by a loss of acid or an increase in base. 11. Metabolic disturbances affect the amount of bicarbonate in the buffer pair. Bicarbonate deficit can cause metabolic acidosis. This can occur because of renal disease, uncontrolled diabetes, prolonged diarrhea, or the ingestion of toxic chemicals. Bicarbonate excess can cause metabolic alkalosis. This can occur because of loss of acid-containing gastric fluid caused by vomiting or suction, diuretic therapy, or certain diseases. 12. Respiratory disturbances affect the amount of carbonic acid in the buffer pair. Carbonic acid deficit can cause respiratory alkalosis. This can occur as a result of hyperventilation. Carbonic acid excess can cause respiratory acidosis and can be the result of slow breathing caused by depression of the respiratory center due to drugs, anesthesia, or pulmonary disease. Critical Thinking 13. The ph scale indicates the acidity or alkalinity of a solution. A ph less than 7 indicates an acid solution, which contains more hydrogen ions than hydroxide ions. A ph more than 7 indicates a basic solution, which contains more hydroxide ions than hydrogen ions. A solution with a ph of exactly 7 indicates a neutral solution, which contains equal numbers of hydrogen and hydroxide ions. A solution with a ph of 4 would have a hydrogen ion concentration of 1 x 10-4 ; a solution with a ph of 6 would have a hydrogen ion concentration of 1 x Vomiting is one of the most frequent causes of metabolic alkalosis. The bicarbonate excess of metabolic alkalosis results because of the massive loss of chloride ions from the stomach as HCl. The loss of chloride causes an increase of bicarbonate ions in the extracellular fluid, resulting in metabolic alkalosis. Normal saline contains chloride ions, which replace the bicarbonate ions and thus help relieve the bicarbonate excess. 15. The proper ratio of NaHCO 3 to H 2 CO 3 is 20:1. A person suffering from untreated diabetes has abnormally large amounts of acid entering the blood. The normal 20:1 ratio is altered as the NaHCO 3 component of the buffer pair reacts with the acids in the blood. The ratio can drop to as low as 10:1. This condition is called uncompensated metabolic acidosis. The body attempts to correct or compensate for the acidosis by altering the ratio. This can be accomplished by rapid breathing, which can blow off carbon dioxide, resulting in less carbonic acid in the blood. A new compensated ratio of perhaps 10:0.5 may result, causing the blood ph to return to normal. Page 9 of 10

10 Chapter Test 1. carbonic anhydrase 2. Buffers 3. H 2 CO 3 4. NaHCO 3 5. distal tubule 6. NaH 2 PO 4 7. NH 4 Cl 8. base 9. alkalosis 10. acidosis NaHCO alkalosis 15. b. a ph less than a. a ph greater than b. A solution with a ph of 9 is a base. 18. b. arterial blood is slightly more alkaline than venous blood 19. decreases 20. increases 21. increases 22. decreases 23. increase 24. decrease 13. H 2 CO 3 Case Studies 1. Chronic obstruction of the airways, as in chronic bronchitis, may reduce the respiratory system s rate of CO 2 excretion. This elevates the concentration of carbonic acid (H 2 CO 3 ) in the blood and thus decreases ph, causing respiratory acidosis. In such chronic disorders, the body compensates for this ph imbalance by increasing sodium bicarbonate (NaHCO 3 ) levels to increase the ph to normal levels. One would expect to see blood ph within the normal range (because this is compensated acidosis), but an elevated level of H 2 CO 3 and NaHCO There is indeed a connection because Larry s body is attempting to compensate for the reduced blood ph characteristic of metabolic acidosis. By hyperventilating, Larry is increasing the rate of CO 2 excretion by the lungs and, thus, reducing his blood CO 2 level. This in turn decreases his blood H 2 CO 3 level. This sequence of events thus lowers the acid content of Larry s blood and increases blood ph toward the normal range. 3. If aldosterone increases secretion of H + into kidney tubules (i.e., into the urine) from the blood, then the urine is acidified (gaining H + ) and the blood becomes less acid (losing H + ). Thus, the blood ph increases. In hypersecretion of aldosterone, the blood ph may rise dramatically. In hyposecretion, there is less aldosterone present and thus the blood will retain the H + it would have otherwise lost, decreasing the blood ph. Page 10 of 10