Physiology - Questions - Block 3 - BRS - Renal
16. Which of the following substances must be further digested before it can be absorbed by specific carriers in intestinal cells? (a) Fructose (B) Sucrose (c) Alanine (d) Dipeptides (e) Tripeptides
16. The answer is B [V A, B; Table 6-4]. Only monosaccharides can be absorbed by intestinal epithelial cells. Disaccharides, such as sucrose, must be digested to monosaccharides before they are absorbed. On the other hand, proteins are hydrolyzed to amino acids, dipeptides, or tripeptides, and all three forms are transported into intestinal cells for absorption.
17. Slow waves in small intestinal smooth muscle cells are (A) action potentials (B) phasic contractions (C) tonic contractions (D) oscillating resting membrane potentials (E) oscillating release of cholecystokinin (CCK)
17. The answer is D [III A; Figure 6-3]. Slow waves are oscillating resting membrane potentials of the gastrointestinal (GI) smooth muscle. The slow waves bring the membrane potential toward or to threshold, but are not themselves action potentials. If the membrane potential is brought to threshold by a slow wave, then action potentials occur, followed by contraction.
At which nephron site is the tubular fluid glucose concentration highest? (A) Site A (B) Site B (C) Site C (D) Site D (E) Site E (see diagram)
The answer is A Glucose is extensively reabsorbed in the early proximal tubule by the Na+ -glucose cotransporter. The glucose concentration in tubular fluid is highest in Bowman space before any reabsorption has occurred.
Which of the following substances has the highest renal clearance? (A) Para-aminohippuric acid (PAH) (B) Inulin (C) Glucose (D) Na+ (E) Cl-
The answer is A Para-aminohippuric acid (PAH) has the greatest clearance of all of the substances because it is both filtered and secreted. Inulin is only filtered. The other substances are filtered and subsequently reabsorbed; therefore, they will have clearances that are lower than the inulin clearance.
At which nephron site is the tubular fluid inulin concentration lowest? (A) Site A (B) Site B (C) Site C (D) Site D (E) Site E (see diagram)
The answer is A The tubular fluid inulin concentration depends on the amount of water present. As water reabsorption occurs along the nephron, the inulin concentration progressively increases. Thus, the tubular fluid inulin concentration is lowest in Bowman space, prior to any water reabsorption.
Which of the following substances is secreted in response to an oral glucose load? (a) Secretin (B) Gastrin (c) Cholecystokinin (CCK) (d) Vasoactive intestinal peptide (VIP) (e) Glucose-dependent insulinotropic peptide (GIP)
The answer is E [II A 4; Table 6.4]. Glucose-dependent insulinotropic peptide (GIP) is the only gastrointestinal (GI) hormone that is released in response to all three categories of nutrients—fat, protein, and carbohydrate. Oral glucose releases GIP, which, in turn, causes the release of insulin from the endocrine pancreas. This action of GIP explains why oral glucose is more effective than intravenous glucose in releasing insulin.
Compared with a person who ingests 2 L of distilled water, a person with water deprivation will have a (A) higher free-water clearance CH O2 ( ) (B) lower plasma osmolarity (C) lower circulating level of antidiuretic hormone (ADH) (D) higher tubular fluid/plasma (TF/P) osmolarity in the proximal tubule (E) higher rate of H2O reabsorption in the collecting ducts
The answer is E. The person with water deprivation will have a higher plasma osmolarity and higher circulating levels of antidiuretic hormone (ADH). These effects will increase the rate of H2O reabsorption in the collecting ducts and create a negative free-water clearance (-CH2O). Tubular fluid/plasma (TF/P) osmolarity in the proximal tubule is not affected by ADH.
A patient with uncontrolled hypertension is placed on a new diuretic targeted to act on the Na+ reabsorption site from the basolateral surface of the renal epithelial cells. Which of the following transport processes is the new drug affecting? a. Facilitated diffusion b. Na+/H+ exchange c. Na+-glucose cotransport d. Na+ -K+ pump e. Solvent drag
The answer is d. Na+ is pumped out of renal epithelial cells by the Na+ -K +pump located on the basolateral surface of the cells. The Na+/H+ exchanger and the Na+ -glucose cotrans-porter are located on the apical surface of the epithelial cells. Na+ is transported from the peritubular spaces to the capillaries by solvent drag.
A 57-year-old woman undergoes resection of the terminal ileum as part of treatment for her chronic inflammatory bowel disease. Removal of the terminal ileum will most likely result in which of the following? a. Decreased glucose absorption b. Decreased water content of the feces c. Increased bile acid concentration in the enterohepatic circulation d. Increased excretion of fatty acids e. Increased iron absorption
The answer is d. (Barrett, pp 465-466, 479, 484-485.) Removal of the terminal ileum can lead to diarrhea and steatorrhea. The terminal ileum contains specialized cells responsible for the absorption of primary and secondary bile salts by active transport. Bile salts are necessary for adequate digestion and absorption of fat. In the absence of the terminal ileum, there will be an increase in the amounts of bile acids and fatty acids delivered to the colon (choice d). Fats and bile salts in the colon increase the water content of the feces by promoting the influx (secretion) of water into the lumen of the colon (not decrease, choice b). Essentially all glucose is absorbed across the wall of the small intestine before the remains of a meal reach the terminal ileum (choice a). Iron is primarily absorbed in the duodenum (choice e). The majority of the bile acid pool circulates between the small intestine and the liver; most bile acids are absorbed in their conjugated forms from the terminal ileum, so removal of the terminal ileum would decrease, not increase (choice c), bile acid concentration in the enterohepatic circulation.
Secretion of which of the following substances is inhibited by low pH? (a) Secretin (B) Gastrin (c) Cholecystokinin (CCK) (d) Vasoactive intestinal peptide (VIP) (e) Gastric inhibitory peptide (GIP)
the answer is B [II A 1; Table 6.1]. Gastrin's principal physiologic action is to increase H+ secretion. H+ secretion decreases the pH of the stomach contents. The decreased pH, in turn, inhibits further secretion of gastrin—a classic example of negative feedback.
10. Which of the following is the site of secretion of gastrin? (a) Gastric antrum (B) Gastric fundus (c) Duodenum (d) Ileum (e) Colon
the answer is a [II A 1 b; Table 6.3; Figure 6.7]. Gastrin is secreted by the G cells of the gastric antrum. HCl and intrinsic factor are secreted by the fundus.
Cholecystokinin (CCK) inhibits (a) gastric emptying (B) pancreatic HCO3− secretion (c) pancreatic enzyme secretion (d) contraction of the gallbladder (e) relaxation of the sphincter of Oddi
the answer is a [II A 2 a; Table 6.1]. Cholecystokinin (CCK) inhibits gastric emptying and therefore helps to slow the delivery of food from the stomach to the intestine during periods of high digestive activity. CCK stimulates both functions of the exocrine pancreas— HCO − secretion and digestive enzyme secretion. It also stimulates the delivery of bile from 3 the gallbladder to the small intestinal lumen by causing contraction of the gallbladder while relaxing the sphincter of Oddi.
Which of the following changes occurs during defecation? (a) Internal anal sphincter is relaxed (B) External anal sphincter is contracted (c) Rectal smooth muscle is relaxed (d) Intra-abdominal pressure is lower than when at rest (e) Segmentation contractions predominate
the answer is a [III E 3]. Both the internal and external anal sphincters must be relaxed to allow feces to be expelled from the body. Rectal smooth muscle contracts and intra- abdominal pressure is elevated by expiring against a closed glottis (Valsalva maneuver). Segmentation contractions are prominent in the small intestine during digestion and absorption.
Which of the following is characteristic of saliva? a) Hypotonicity relative to plasma (B) A lower HCO − concentration than plasma3 (c) The presence of proteases (d) Secretion rate that is increased by vagotomy (e) Modification by the salivary ductal cells involves reabsorption of K+ and HCO
the answer is a [IV A 2 a; Table 6.2]. Saliva is characterized by hypotonicity and a high HCO − concentration (relative to plasma) and by the presence of α-amylase and lingual 3 lipase (not proteases). The high HCO − concentration is achieved by secretion of HCO − 33 into saliva by the ductal cells (not reabsorption of HCO −). Because control of saliva 3 production is parasympathetic, it is abolished by vagotomy.
When parietal cells are stimulated, they secrete (a) HCl and intrinsic factor (B) HCl and pepsinogen (c) HCl and HCO − 3 (d) HCO − and intrinsic factor 3 (e) mucus and pepsinogen
the answer is a [IV B I; Table 6.3]. The gastric parietal cells secrete HCl and intrinsic factor. The chief cells secrete pepsinogen.
20. Which of the following substances inhibits gastric emptying? (a) Secretin (B) Gastrin (c) Cholecystokinin (CCK) (d) Vasoactive intestinal peptide (VIP) (e) Gastric inhibitory peptide (GIP)
the answer is c [II A 2 a; Table 6.1]. Cholecystokinin (CCK) is the most important hormone for digestion and absorption of dietary fat. In addition to causing contraction of the gallbladder, it inhibits gastric emptying. As a result, chyme moves more slowly from the stomach to the small intestine, thus allowing more time for fat digestion and absorption.
8. Which of the following abolishes "receptive relaxation" of the stomach? (a) Parasympathetic stimulation (B) Sympathetic stimulation (c) Vagotomy (d) Administration of gastrin (e) Administration of vasoactive intestinal peptide (VIP) (f) Administration of cholecystokinin (CCK)
the answer is c [III C 1]. "Receptive relaxation" of the orad region of the stomach is initiated when food enters the stomach from the esophagus. This parasympathetic (vagovagal) reflex is abolished by vagotomy
Which of the following is true about the secretion from the exocrine pancreas? (a) It has a higher Cl− concentration than does plasma (B) It is stimulated by the presence of HCO − in the duodenum 3 (c) Pancreatic HCO − secretion is increased by gastrin 3 (d) Pancreatic enzyme secretion is increased by cholecystokinin (CCK) (e) It is hypotonic
the answer is d [II A 2, 3; Table 6.2]. The major anion in pancreatic secretions is HCO − 3 (which is found in higher concentration than in plasma), and the Cl− concentration is lower than in plasma. Pancreatic secretion is stimulated by the presence of fatty acids in the duodenum. Secretin (not gastrin) stimulates pancreatic HCO3 secretion, and cholecystokinin (CCK) stimulates pancreatic enzyme secretion. Pancreatic secretions are always isotonic, regardless of flow rate.
Which of the following substances is released from neurons in the GI tract and produces smooth muscle relaxation? (a) Secretin (B) Gastrin (c) Cholecystokinin (CCK) (d) Vasoactive intestinal peptide (VIP) (e) Gastric inhibitory peptide (GIP)
the answer is d [II C 1]. Vasoactive intestinal peptide (VIP) is a gastrointestinal (GI) neurocrine that causes relaxation of GI smooth muscle. For example, VIP mediates the relaxation response of the lower esophageal sphincter when a bolus of food approaches it, allowing passage of the bolus into the stomach.
Which of the following causes hyperkalemia? (A) Exercise (B) Alkalosis (C) Insulin injection (D) Decreased serum osmolarity (E) Treatment with β-agonists
The answer is A Exercise causes a shift of K+ from cells into blood. The result is hyperkalemia. Hyposmolarity, insulin, β-agonists, and alkalosis cause a shift of K+ from blood into cells. The result is hypokalemia.
Which of the following would produce an increase in the reabsorption of isosmotic fluid in the proximal tubule? (A) Increased filtration fraction (B) Extracellular fluid (ECF) volume expansion (C) Decreased peritubular capillary protein concentration (D) Increased peritubular capillary hydrostatic pressure (E) Oxygen deprivation
The answer is A Increasing filtration fraction means that a larger portion of the renal plasma flow (RPF) is filtered across the glomerular capillaries. This increased flow causes an increase in the protein concentration and oncotic pressure of the blood leaving the glomerular capillaries. This blood becomes the peritubular capillary blood supply. The increased oncotic pressure in the peritubular capillary blood is a driving force favoring reabsorption in the proximal tubule. Extracellular fluid (ECF) volume expansion, decreased peritubular capillary protein concentration, and increased peritubular capillary hydrostatic pressure all inhibit proximal reabsorption. Oxygen deprivation would also inhibit reabsorption by stopping the Na+ -K+ pump in the basolateral membranes.
Which of the following is an action of parathyroid hormone (PTH) on the renal tubule? (A) Stimulation of adenylate cyclase (B) Inhibition of distal tubule K+ secretion (C) Inhibition of distal tubule Ca2+ reabsorption (D) Stimulation of proximal tubule phosphate reabsorption (E) Inhibition of production of 1,25-dihydroxycholecalciferol
The answer is A Parathyroid hormone (PTH) acts on the renal tubule by stimulating adenyl cyclase and generating cyclic adenosine monophosphate (cAMP). The major actions of the hormone are inhibition of phosphate reabsorption in the proximal tubule, stimulation of Ca2+ reabsorption in the distal tubule, and stimulation of 1,25-dihydroxycholecalciferol production. PTH does not alter the renal handling of K+.
To maintain normal H+ balance, total daily excretion of H+ should equal the daily (A) fixed acid production plus fixed acid ingestion (B) HCO3- excretion (C) HCO3- filtered load (D) titratable acid excretion (E) filtered load of H+
The answer is A Total daily production of fixed H+ from catabolism of proteins and phospholipids (plus any additional fixed H+ that is ingested) must be matched by the sum of excretion of H+ as titratable acid plus NH4+ to maintain acid-base balance.
The following information was obtained in a 20-year-old college student who was participating in a research study in the Clinical Research Unit: Plasma Urine [Inulin] = 1 mg/mL [Inulin] = 150 mg/mL [X] = 2 mg/mL [X] = 100 mg/mL Urine flow rate = 1 mL/min Assuming that X is freely filtered, which of the following statements is most correct? (A) There is net secretion of X (B) There is net reabsorption of X (C) There is both reabsorption and secretion of X (D) The clearance of X could be used to measure the glomerular filtration rate (GFR) (E) The clearance of X is greater than the clearance of inulin
The answer is B To answer this question, calculate the glomerular filtration rate (GFR) and CX. GFR = 150 mg/mL × 1 mL/min ÷ 1 mg/mL = 150 mL/min. CX = 100 mg/mL × 1 mL/min ÷ 2 mg/mL = 50 mL/min. Because the clearance of X is less than the clearance of inulin (or GFR), net reabsorption of X must have occurred. Clearance data alone cannot determine whether there has also been secretion of X. Because GFR cannot be measured with a substance that is reabsorbed, X would not be suitable.
A woman has a plasma osmolarity of 300 mOsm/L and a urine osmolarity of 1200 mOsm/L. The correct diagnosis is (A) syndrome of inappropriate antidiuretic hormone (SIADH) (B) water deprivation (C) central diabetes insipidus (D) nephrogenic diabetes insipidus (E) drinking large volumes of distilled water
The answer is B This patient's plasma and urine osmolarity, taken together, are consistent with water deprivation. The plasma osmolarity is on the high side of normal, stimulating the posterior pituitary to secrete antidiuretic hormone (ADH). Secretion of ADH, in turn, acts on the collecting ducts to increase water reabsorption and produce hyperosmotic urine. Syndrome of inappropriate antidiuretic hormone (SIADH) would also produce hyperosmotic urine, but the plasma osmolarity would be lower than normal because of the excessive water retention. Central and nephrogenic diabetes insipidus and excessive water intake would all result in hyposmotic urine.
Which of the following is the site of secretion of intrinsic factor? (a) Gastric antrum (B) Gastric fundus (c) Duodenum (d) Ileum (e) Colon
The answer is B [IV B 1; Table 6.3; Figure 6.7]. Intrinsic factor is secreted by the parietal cells of the gastric fundus (as is HCl). It is absorbed, with vitamin B12, in the ileum.
Which of the following would best distinguish an otherwise healthy person with severe water deprivation from a person with the syndrome of inappropriate antidiuretic hormone (SIADH)? (A) Free-water clearance CH O2 ( ) (B) Urine osmolarity (C) Plasma osmolarity (D) Circulating levels of antidiuretic hormone (ADH) (E) Corticopapillary osmotic gradient
The answer is C Both individuals will have hyperosmotic urine, a negative free-water clearance (−CH O2 ), a normal corticopapillary gradient, and high circulating levels of antidiuretic hormone (ADH). The person with water deprivation will have a high plasma osmolarity, and the person with syndrome of inappropriate antidiuretic hormone (SIADH) will have a low plasma osmolarity (because of dilution by the inappropriate water reabsorption).
Which curve describes the inulin profile along the nephron? (A) Curve A (B) Curve B (C) Curve C (D) Curve D (See graph)
The answer is C Once inulin is filtered, it is neither reabsorbed nor secreted. Thus, 100% of the filtered inulin remains in tubular fluid at each nephron site and in the final urine.
The reabsorption of filtered HCO3 - (A) results in reabsorption of less than 50% of the filtered load when the plasma concentration of HCO3- is 24 mEq/L (B) acidifies tubular fluid to a pH of 4.4 (C) is directly linked to excretion of H+ as NH4+ (D) is inhibited by decreases in arterial Pco2 (E) can proceed normally in the presence of a renal carbonic anhydrase inhibitor
The answer is D Decreases in arterial Pco2 cause a decrease in the reabsorption of filtered HCO3- by diminishing the supply of H+ in the cell for secretion into the lumen. Reabsorption of filtered HCO3- is nearly 100% of the filtered load and requires carbonic anhydrase in the brush border to convert filtered HCO3- to CO2 to proceed normally. This process causes little acidification of the urine and is not linked to net excretion of H+ as titratable acid or NH4+
17. Which of the following would cause an increase in both glomerular filtration rate (GFR) and renal plasma flow (RPF)? (A) Hyperproteinemia (B) A ureteral stone (C) Dilation of the afferent arteriole (D) Dilation of the efferent arteriole (E) Constriction of the efferent arteriole
The answer is C Dilation of the afferent arteriole will increase both renal plasma flow (RPF) (because renal vascular resistance is decreased) and glomerular filtration rate (GFR) (because glomerular capillary hydrostatic pressure is increased). Dilation of the efferent arteriole will increase RPF but decrease GFR. Constriction of the efferent arteriole will decrease RPF (due to increased renal vascular resistance) and increase GFR. Both hyperproteinemia (↑ π in the glomerular capillaries) and a ureteral stone (↑ hydrostatic pressure in Bowman space) will oppose filtration and decrease GFR.
One gram of mannitol was injected into a woman. After equilibration, a plasma sample had a mannitol concentration of 0.08 g/L. During the equilibration period, 20% of the injected mannitol was excreted in the urine. The woman's (A) extracellular fluid (ECF) volume is 1 L (B) intracellular fluid (ICF) volume is 1 L (C) ECF volume is 10 L (D) ICF volume is 10 L (E) interstitial volume is 12.5 L
The answer is C Mannitol is a marker substance for the extracellular fluid (ECF) volume. ECF volume = amount of mannitol/concentration of mannitol = 1 g - 0.2 g/0.08 g/L = 10 L.
Use the values below to answer the following question: Glomerular capillary hydrostatic pressure = 47 mm Hg Bowman space hydrostatic pressure = 10 mm Hg Bowman space oncotic pressure = 0 mm Hg At what value of glomerular capillary oncotic pressure would glomerular filtration stop? (A) 57 mm Hg (B) 47 mm Hg (C) 37 mm Hg (D) 10 mm Hg (E) 0 mm Hg
The answer is C Glomerular filtration will stop when the net ultrafiltration pressure across the glomerular capillary is zero; that is, when the force that favors filtration (47 mm Hg) exactly equals the forces that oppose filtration (10 mm Hg + 37 mm Hg).
A 58-year-old man is given a glucose tolerance test. In the test, the plasma glucose concentration is increased and glucose reabsorption and excretion are measured. When the plasma glucose concentration is higher than occurs at transport maximum (Tm), the (A) clearance of glucose is zero (B) excretion rate of glucose equals the filtration rate of glucose (C) reabsorption rate of glucose equals the filtration rate of glucose (D) excretion rate of glucose increases with increasing plasma glucose concentrations (E) renal vein glucose concentration equals the renal artery glucose concentration
The answer is D At concentrations greater than at the transport maximum (Tm) for glucose, the carriers are saturated so that the reabsorption rate no longer matches the filtration rate. The difference is excreted in the urine. As the plasma glucose concentration increases, the excretion of glucose increases. When it is greater than the Tm, the renal vein glucose concentration will be less than the renal artery concentration because some glucose is being excreted in urine and therefore is not returned to the blood. The clearance of glucose is zero at concentrations lower than at Tm (or lower than threshold) when all of the filtered glucose is reabsorbed but is greater than zero at concentrations greater than Tm.
A woman runs a marathon in 90°F weather and replaces all volume lost in sweat by drinking distilled water. After the marathon, she will have (A) decreased total body water (TBW) (B) decreased hematocrit (C) decreased intracellular fluid (ICF) volume (D) decreased plasma osmolarity (E) increased intracellular osmolarity
The answer is D By sweating and then replacing all volume by drinking H2O, the woman has a net loss of NaCl without a net loss of H2O. Therefore, her extracellular and plasma osmolarity will be decreased, and as a result, water will flow from extracellular fluid (ECF) to intracellular fluid (ICF). The intracellular osmolarity will also be decreased after the shift of water. Total body water (TBW) will be unchanged because the woman replaced all volume lost in sweat by drinking water. Hematocrit will be increased because of the shift of water from ECF to ICF and the shift of water into the red blood cells (RBCs), which causes their volume to increase.
1. Secretion of K+ by the distal tubule will be decreased by (A) metabolic alkalosis (B) a high-K+ diet (C) hyperaldosteronism (D) spironolactone administration (E) thiazide diuretic administration
The answer is D Distal K+secretion is decreased by factors that decrease the driving force for passive diffusion of K+ across the luminal membrane. Because spironolactone is an aldosterone antagonist, it reduces K+ secretion. Alkalosis, a diet high in K+, and hyperaldosteronism all increase [K+] in the distal cells and thereby increase K+ secretion. Thiazide diuretics increase flow through the distal tubule and dilute the luminal [K+] so that the driving force for K+ secretion is increased.
Cholecystokinin (CCK) has some gastrin- like properties because both CCK and gastrin (a) are released from G cells in the stomach (B) are released from I cells in the duodenum (c) are members of the secretin-homologous family (d) have five identical C-terminal amino acids (e) have 90% homology of their amino acids
The answer is D [IIA2].The two hormones have five identical amino acids at the C terminus. Biologic activity of cholecystokinin (CCK) is associated with the seven C-terminal amino acids, and biologic activity of gastrin is associated with the four C-terminal amino acids. Because this CCK heptapeptide contains the five common amino acids, it is logical that CCK should have some gastrin-like properties. G cells secrete gastrin. I cells secrete CCK. The secretin family includes glucagon.
Which of the following is transported in intestinal epithelial cells by a Na+-dependent cotransport process? (a) Fatty acids (B) Triglycerides (c) Fructose (d) Alanine (e) Oligopeptides
The answer is D [V A-C; Table 6.4]. Fructose is the only monosaccharide that is not absorbed by Na+-dependent cotransport; it is transported by facilitated diffusion. Amino acids are absorbed by Na+-dependent cotransport, but oligopeptides (larger peptide units) are not. Triglycerides are not absorbed without further digestion. The products of lipid digestion, such as fatty acids, are absorbed by simple diffusion.
At which nephron site is the tubular fluid/plasma (TF/P) osmolarity lowest in a person who has been deprived of water? (A) Site A (B) Site B (C) Site C (D) Site D (E) Site E (see diagram)
The answer is D. A person who is deprived of water will have high circulating levels of antidiuretic hormone (ADH). The tubular fluid/plasma (TF/P) osmolarity is 1.0 throughout the proximal tubule, regardless of ADH status. In antidiuresis, TF/P osmolarity is greater than 1.0 at site C because of equilibration of the tubular fluid with the large corticopapillary osmotic gradient. At site E, TF/P osmolarity is greater than 1.0 because of water reabsorption out of the collecting ducts and equilibration with the corticopapillary gradient. At site D, the tubular fluid is diluted because NaCl is reabsorbed in the thick ascending limb without water, making TF/P osmolarity less than 1.0.
2. Jared and Adam both weigh 70 kg. Jared drinks 2 L of distilled water, and Adam drinks 2 L of isotonic NaCl. As a result of these ingestions, Adam will have a (A) greater change in intracellular fluid (ICF) volume (B) higher positive free-water clearance CH O2 ( ) (C) greater change in plasma osmolarity (D) higher urine osmolarity (E) higher urine flow rate
The answer is D. After drinking distilled water, Jared will have an increase in intracellular fluid (ICF) and extracellular fluid (ECF) volumes, a decrease in plasma osmolarity, a suppression of antidiuretic hormone (ADH) secretion, and a positive free-water clearance (CH O2 ), and will produce dilute urine with a high flow rate. Adam, after drinking the same volume of isotonic NaCl, will have an increase in ECF volume only and no change in plasma osmolarity. Because Adam's ADH will not be suppressed, he will have a higher urine osmolarity, a lower urine flow rate, and a lower CH O2 than Jared.
Which of the following is a cause of metabolic alkalosis? (A) Diarrhea (B) Chronic renal failure (C) Ethylene glycol ingestion (D) Treatment with acetazolamide (E) Hyperaldosteronism (F) Salicylate poisoning
The answer is E A cause of metabolic alkalosis is hyperaldosteronism; increased aldosterone levels cause increased H+ secretion by the distal tubule and increased reabsorption of "new" HCO3-. Diarrhea causes loss of HCO3- from the gastrointestinal (GI) tract and acetazolamide causes loss of HCO3- in the urine, both resulting in hyperchloremic metabolic acidosis with normal anion gap. Ingestion of ethylene glycol and salicylate poisoning leads to metabolic acidosis with increased anion gap.
At which nephron site is the tubular fluid inulin concentration highest during antidiuresis? (A) Site A (B) Site B (C) Site C (D) Site D (E) Site E (See diagram)
The answer is E Because inulin, once filtered, is neither reabsorbed nor secreted, its concentration in tubular fluid reflects the amount of water remaining in the tubule. In antidiuresis, water is reabsorbed throughout the nephron (except in the thick ascending limb and cortical diluting segment). Thus, inulin concentration in the tubular fluid progressively rises along the nephron as water is reabsorbed, and will be highest in the final urine.
A 63-year-old hospitalized woman becomes oliguric and confused. A blood sample is drawn to measure her glucose concentration, which is found to be 35 mg/dL. An IV access is obtained and an ampule of 50% dextrose is given followed by a continuous infusion of 10% dextrose. Most of the glucose that is filtered through the glomerulus undergoes reabsorption in which of the following areas of the nephron? a. Proximal tubule b. Descending limb of the loop of Henle c. Ascending limb of the loop of Henle d. Distal tubule e. Collecting duct
The answer is a. Glucose is reabsorbed along with Na+ in the early portion of the proximal tubule via a secondary active transport process. Normally, essentially all filtered glucose is reabsorbed. In diabetes mellitus, hyperglycemia results in a tubular filtration load that exceeds and glycosuria ensues. The renal threshold for glucose is the plasma level at which glucose first appears in the urine. The predicted renal threshold is approximately 300 mg/dL, that is, the transport maximum (Tmax) for glucose of 375 mg/min divided by the GFR (normally ~125 mL/min). However, the actual renal threshold is only approximately 200 mg/dL because the Tmax for glucose is not identical in all tubules.
A 54-year-old man with small cell lung cancer presents with lethargy, confusion, and muscle cramps. Blood work shows an increase in plasma levels of antidiuretic hormone (ADH). In patients with the syndrome of inappropriate antidiuretic hormone (SIADH), which of the following will increase? a. Intracellular volume b. Plasma oncotic pressure c. Plasma osmolarity d. Plasma sodium concentration e. Urine flow
The answer is a. SIADH can occur as a paraneoplastic process in patients diagnosed with small cell lung cancer. The increased secretion of ADH increases the permeability of the distal nephron to water and therefore increases the reabsorption of water from the kidney. The excessive reabsorption of water dilutes the extracellular fluid, producing a decrease in plasma sodium (choice d), osmolarity (choice c), and oncotic pressure (choice b). The decreased extracellular osmolarity causes water to flow from the extracellular fluid compartment into the intracellular fluid compartment, increasing intracellular volume (choice a). Because more water is being reabsorbed, less is excreted and urine flow (choice e) is decreased.
A 37-year-old man with AIDS presents with a fever, anorexia, weight loss, and GI bleeding. Physical examination reveals a palpable abdominal mass. Endoscopy and biopsy reveal a proximal small-bowel malignancy requiring surgical resection. Removal of proximal segments of the small intestine would most likely result in a decrease in which of the following? a. Basal acid output b. Maximal acid output c. Gastric emptying of liquids d. Gastric emptying of solids e. Pancreatic enzyme secretion
The answer is a. (Barrett, pp 502-504. Le, pp 325, 327, 577, 580. Longo, p 2402. Widmaier, pp 533-538, 542-543.) Increases in intragastric volume normally are not associated with large increases in intragastric pressure because of receptive relaxation, also known as the accommodation reflex, which is vagally mediated. The reflex, which is abolished by vagotomy, is a property of the orad stomach only and counterbalances the stretch-induced myogenic contraction of the gastric smooth muscle. Peristalsis, trituration (grinding), and retropulsion (mixing) are terms referring to the contractile activity and functions of the caudad stomach. Segmental contractions are the primary contractile pattern of the small intestine during the digestive period.
A 43-year-old woman presents with dysphagia to solids and liquids, bland regurgitation, and diffuse chest pain of 2 months duration. During this time, she has lost about 20 pounds. The patient is scheduled for esophageal imaging and motility testing. The esophagogram during a barium swallow shows a dilated esophagus with an area of distal stenosis and esophageal manometry tracings during a wet swallow shows a high lower esophageal sphincter (LES) opening pressure and uncoordinated peristalsis. These findings are consistent with which of the following diagnoses? a. Achalasia b. Diffuse esophageal spasm c. GERD d. Schatzki ring e. Zenker diverticulum
The answer is a. Achalasia is a neurogenic disorder of esophageal motility with the absence of normal peristalsis and impaired relaxation of the LES in response to deglutition. The barium esophagogram demonstrates a dilated esophagus with a sharply tapered "birds beak" narrowing of the terminal esophagus. Esophageal manometry shows normal to increased pressure in the LES with no relaxation in response to swallowing. The etiology is unknown, but achalasia is thought to arise from scarring (nerve damage) in Auerbach plexus. An association with viral infections and autoantibodies against myenteric plexus has been reported, but the causal relationship remains unclear. Endoscopy should be done to rule out malignancy as a cause of the achalasia. Treatment is strictly palliative with excellent palliation available in over 90% of patients. Current pharmacological (nitroglycerin, endoscopic injection of botulinum toxin) and surgical (balloon dilation, myotomy) therapeutic options are aimed at reducing LES pressure and promoting esophageal emptying of retained food and liquids. Primary achalasia "is a rare disease with an annual incidence of approximately 1/100,000 and a prevalence rate of 10/100,000, but frequent enough to be encountered at least once by every gastroenterologist." (Farrokhi and Vaezi, p 38.) Diffuse esophageal spasm (choice b) is another esophageal motility disorder characterized by frequent nonperistaltic contractions. The barium esophagogram has a classic "corkscrew" pattern and esophageal manometry shows high amplitude in the esophagus, sometimes including the proximal esophagus. GERD may be caused by decreased esophageal motility and a relaxed or incompetent LES, but is not associated with aperistalsis. In GERD, acidic gastric contents enter the esophagus in contrast to neutral regurgitation in achalasia. Schatzki ring (choice d) is a narrow lower esophageal ring-like growth at the gastroesophageal junction associated with dysphagia to solids only. Zenker diverticulum (choice e) is a pharyngeal or esophageal pouch due to a defect in the muscular wall of the posterior hypopharynx. The outpouching of the esophagus can be seen on a barium swallow. The clinical signs and symptoms include sensation of food getting "stuck on the way down," regurgitation/vomiting of food days after it was eaten, frequent aspiration, and halitosis.
A 46-year-old man presents to his physician with a 12-week history of frontal headaches. CT of the brain shows a mass in the posterior pituitary, and the posterior pituitary "bright spot" is absent on MRI. The patient also complains of increased thirst and waking up frequently during the night. Which of the following best describes his urine? a. A higher-than-normal flow of hypertonic urine b. A higher-than-normal flow of hypotonic urine c. A lower-than-normal flow of hypertonic urine d. A lower-than-normal flow of hypotonic urine e. A normal flow of hypertonic urine
The answer is b. - The presence of a mass in the posterior pituitary, coupled with the presentation of thirst and nocturia, suggests that the patient has a central diabetes insipidus with inadequate pituitary secretion of ADH. As a result of decreased ADH, the urine will have a low tonicity. A patient with diabetes insipidus often presents with polyuria, polydipsia, and dehydration. Due to the inability to reabsorb water, the patient may also have serum hyperosmolarity due to hypernatremia. On MRI, the absence of the normal bright spot in the region of the posterior pituitary further supports the diagnosis.
27-year-old female medical student with irritable bowel syndrome (IBS) has an alteration in intestinal motility resulting in fluctuating constipation and diarrhea. Her condition has worsened in the last month as the date she has scheduled for her licensure examination approaches. Which of the following best describes small intestinal motility? a. Contractile activity is initiated in response to bowel wall distention. b. Contractile frequency is constant from duodenum to terminal ileum. c. Migratingmotor complexes (MMCs) occur duringthe digestive period. d. Peristalsis is the only contractile activity that occurs during feeding. e. Vagotomy abolishes contractile activity during the digestive period.
The answer is a. Contractile activity in the small intestine is initiated in response to distention of the bowel wall. Three types of smooth muscle contractions contribute to small intestinal motility—peristalsis, segmental contractions, and tonic contractions. A fourth type of contraction, peristaltic rushes, is very intense peristaltic waves that may occur in intestinal obstruction. The basal electrical rhythm (BER) is the spontaneous rhythmic fluctuation in membrane potential in the smooth muscle along the GI tract. The BER itself rarely causes muscle contraction; contractions occur only during the depolarizing phase of BERs, which function to coordinate the various types of contractile activity. The BER is initiated by the interstitial cells of Cajal, which, in the small intestine, are located in the outer circular muscle layer near the myenteric plexus. There are an average of approximately 12 BER cycles per minute in the duodenum and proximal jejunum and 8 cycles per minute in the distal ileum. During fasting between periods of digestion,cyclesofmotoractivity,calledmigratingmotorcomplexes(MMCs),migratefromthestomachtothedistalileum.TheMMCsimmediately stop with ingestion of food. After vagotomy, contractile activity becomes irregular and chaotic.
A 37-year-old man presents with dehydration and hypokalemic metabolic acidosis. This acid-base and electrolyte disorder can occur with excess fluid loss from which of the following organs? a. Colon b. Duodenum c. Liver d. Pancreas e. Stomach
The answer is a. Excessive loss of fluid from the GI tract can lead to dehydration and electrolyte and acid- base disturbances that depend on the origin of the fluid loss. Because the pancreas, liver, ileum, and colon secrete bicarbonate, excessive loss of fluids from these organs 2++++ leads to metabolic acidosis. Generally, plasma K increases in metabolic acidosis due to H -K excess fluid loss from the colon is accompanied by hypokalemia. Intestinal loss of K infectious diarrheal disease. Noninfectious GI processes such as celiac disease, ileostomy, and chronic laxative abuse can also lead to significant hypokalemic, metabolic acidosis, as can colonic pseudo-obstruction (Ogilvie syndrome), which is associated with a secretory diarrhea with abnormally high potassium content caused by marked activation of colonic K secretion. Loss of gastric juice results in hypokalemic, metabolic alkalosis. The hydrogen ion and potassium ion concentration of gastric juice exceeds that of the plasma. As a result, excess gastric fluid loss leads to metabolic alkalosis accompanied by hypokalemia.
A 23-year-old woman presents with burning epigastric pain. A careful history reveals that the burning is exacerbated by fasting and improved with meals. The woman is prescribed the H2-receptor antagonist, cimeti-dine, for suspected peptic ulcer disease. Cimetidine may also have an adverse effect on proximal tubular function. Which of the following substances is more concentrated at the end of the proximal tubule than at the beginning of the proximal tubule? a. Bicarbonate b. Creatinine c. Glucose d. Phosphate e. Sodium
The answer is b. Because creatinine is not reabsorbed from the tubule, its concentration rises as water is reabsorbed. The H2 receptor antagonist, cimetidine, competes with creatinine for proximal tubule transport by the organic cation pathways. This may elevate serum creatinine levels, but this change does not reflect changes in GFR. Phosphate (choice d) is almost completely reabsorbed in the proximal tubule, so its concentration decreases along the length of the tubule. The concentrations of glucose (choice c) and bicarbonate (choice a) are also less at the end of the proximal tubule than at the beginning. Sodium is isosmotically reabsorbed from the proximal tubule; that is, when sodium is reabsorbed, water flows out of the proximal tubule to maintain a constant osmolarity; thus, the concentration of sodium (choice e) does not normally change as the filtrate flows through the proximal tubule.
A 16-year-old girl presents for her annual high school athletic physical. She states that she seems more tired than usual, she has been having muscle cramps in her calves, and her legs get very weak and sore after running and playing soccer. Her blood pressure is 160/100 mm Hg, and her ECG shows a prolonged QT interval and the presence of a U wave. Blood analysis shows hypokalemia, metabolic alkalosis, and decreases in plasma renin activity and aldosterone concentration. Her clinical condition is reversed after she is placed on the diuretic amiloride. Based on this finding, which of the following renal transport processes is the major defect causing her metabolic disorder? a. Greater than normal sodium reabsorption by the proximal tubules b. Greater than normal sodium reabsorption by the cortical collecting ducts c. Inability of the distal nephron to secrete hydrogen d. Inability of the distal nephron to secrete potassium ion e. Inability to concentrate urine
The answer is b. The patient is treated with amiloride, a potassium sparing diuretic, which blocks sodium channels in the principal cells of the cortical collecting ducts thus limiting sodium reabsorption. Sodium reabsorption in the cortical collecting ducts is normally under the control of aldosterone. In patients with Liddle syndrome, the cortical collecting ducts reabsorb excess Na+ despite low levels of aldosterone and renin in the plasma, because of a mutation in the genes for the renal ENaCs, which increases ENaC activity and sodium retention. Metabolic alkalosis, hypokalemia, and hypertension are also present secondary to the increased sodium (and water) reabsorption. An inability of the distal nephron to secrete hydrogen (choice d) would cause RTA type I. An inability to concentrate urine (choice e) occurs when patients are treated with loop diuretics like furosemide, which prevents the kidney from developing medullary hypertonicity, thus limiting the reabsorption of water and the production of concentrated urine. The amount of sodium reabsorbed in the proximal tubules is relatively constant (choice a) at roughly 60% of the filtered amount, primarily as a result of Na+/H+ exchange. The inability of the distal nephron to secrete potassium ion (choice c) would result in hyperkalemia, not hypokalemia as described in the case presentation.
A 14-year-old girl with polycystic kidney disease has a decrease in both GFR and RBF. The nephrologist wants to administer a drug that will increase both GFR and RBF. Both GFR and RBF would increase if which of the following occurred? a. The efferent and afferent arterioles are both constricted. b. The efferent and afferent arterioles are both dilated. c. Only the afferent arteriole is constricted. d. Only the efferent arteriole is constricted. e. The afferent arteriole is constricted and the efferent arteriole is dilated.
The answer is b. The renal artery pressure and the resistance of the renal vascular bed determine renal blood flow (RBF). Decreasing the resistance of either the afferent or efferent arterioles could increase RBF. Alternatively, if the resistance of one of these vessels decreased more than the resistance of the other one increased, RBF would also increase. GFR will increase if glomerular capillary pressure increases. This can occur if the afferent arteriolar resistance decreases or if the efferent arteriolar resistance increases.
A 52-year-old man with diabetes mellitus type 1 has persistent nausea and vomiting due to gastroparesis with gastroesophageal reflux disease (GERD). Which of the following best describes the function of gastric emptying? a. Acidification of the antrum increases gastric emptying. b. Hyperosmolality of duodenal contents initiates a decrease in gastric emptying. c. Meals containingfat empty faster than carbohydrate-rich food. d. Solids empty more rapidly than liquids. e. Vagal stimulation decreases receptive relaxation in the upper portion of the stomach.
The answer is b. Gastroparesis is delayed emptying of food from the stomach, and is a common cause of GERD. The rate of gastric emptying depends upon neural (enterogastric reflex) and hormonal inhibitory feedback from the proximal small bowel. Gastroparesis is common in diabetes mellitus because hyperosmolality of the duodenum initiates a decrease in gastric emptying, which is probably neural in origin and is sensed by duodenal osmoreceptors. Because solids must be liquefied prior to emptying from the stomach, the gastric emptying of liquids begins before the emptying of solids. Emptying is fastest with a carbohydrate meal and slowest after a fatty meal. Acid in the antrum inhibits gastrin secretion, which may inhibit gastric motility. The vagus mediates receptive relaxation, the process in which the fundus and upper portion of the body of the stomach relax in response to movement in the pharynx and esophagus in order to accommodate food that enters the stomach.
An 85-year-old woman presents with a fever and hypovolemic hypotension. To assess her renal function, the filtration fraction is determined using a freely filterable substance that is neither reabsorbed nor secreted. The infusate yields a renal artery concentration of 12 mg/mL and a renal vein concentration of 9 mg/mL. Which of the following is her filtration fraction? a. 0.05 b. 0.15 c. 0.25 d. 0.35 e. 0.45
The answer is c Because the amount of fluid excreted by the kidney is only a small fraction of the renal plasma flow, the volume of fluid in the vein is essentially equal to that in the artery. Thus, the difference between the arterial and venous concentrations is due to the loss of solute. Because the material is neither reabsorbed nor secreted, its removal from the plasma must have been by glomerular filtration. Therefore, the filtered solute equals (12 mg/mL - 9 mg/mL), and the percentage of the arterial concentration that is filtered (and, therefore, the fraction of plasma filtered) 3mg/mL / 12mg/mL = .25 Filtration fraction is normally 0.16 to 0.20. When there is a fall in systemic blood pressure, the GFR falls less than the RPF because of efferent arteriolar constriction, and thus the filtration fraction rises.
A 36-year-old African American man presents with low renin essential hypertension. Renin release from the juxtaglomerular apparatus is normally inhibited by which of the following? a. Aldosterone b. β-Adrenergic agonists c. Increased pressure within the afferent arterioles d. Prostaglandins e. Stimulation of the macula densa
The answer is c. Juxtaglomerular cells are sensitive to changes in afferent arterial intraluminal pressure. Increased pressure within the afferent arteriole leads to a decrease in renin release, whereas decreased pressure tends to increase renin release. Angiotensin appears to inhibit renin release by initiating the flow of calcium into the juxtaglomerular cells. Renin release is increased in response to increased activity in the sympathetic neurons innervating the kidney. Prostaglandins, particularly PGI2 and PGE2, stimulate renin release. Stimulation of the macula densa leads to an increase in renin release, and although the mechanism is not fully understood, it appears that increased delivery of NaCl to the distal nephron is responsible for stimulating the macula densa. Aldosterone does not appear to have any direct effect on renin release.
A 92-year-old man presents with dehydration following 4 days of persistent diarrhea. Under this circumstance, hypotonic fluid would be expected in which of the following? a. Glomerular filtrate b. Proximal tubule c. Ascending limb of the loop of Henle d. Cortical collecting tubule e. Distal collecting duct
The answer is c. When a person is dehydrated, the decrease in extracellular fluid volume is sensed by stretch receptors in the low pressure receptors in the great veins, right and left atria, and pulmonary vessels, leading to an increase in vasopressin (ADH) secretion from the posterior pituitary. The ascending limb of the loop of Henle is not affected by ADH and remains impermeable to water; thus, as sodium and other electrolytes are reabsorbed from the ascending limb, its filtrate becomes hypotonic. The glomerular filtrate and proximal tubular fluid remain isotonic to plasma, which in the case of dehydration is higher than normal. In the presence of ADH, the cortical and medullary collecting tubules become permeable to water due to the insertion of aquaporin channels in the luminal membrane, and the filtrate within these portions of the nephron reaches osmotic equilibrium with the interstitial fluid surrounding them.
A 47-year-old woman presents for her annual physical examination. A year ago, the patient started a diet and exercise regimen when her blood pressure was 130/85 mm Hg. She has lost 10 lb and reduced her BMI to 25 kg/m 2, but her blood pressure on this visit is found to be 145/98 mm Hg. The patient is started on a combination of a low dose of hydrochlorothiazide with the K+ -sparing diuretic, triamterene. The amount of potassium excreted by the kidney will decrease if which of the following occurs? a. Circulating aldosterone levels increase. b. Dietary intake of potassium increases. c. Distal tubular flow increases. d. Na+ reabsorption by the distal nephron decreases. e. The excretion of organic ions decreases.
The answer is d. The amount of potassium excreted is controlled by the amount of potassium secreted by the distal tubule. Potassium secretion is a passive process that depends on the electrochemical gradient between the distal tubular cells and the tubular lumen and the permeability of the luminal cells to potassium. By inhibiting Na+ reabsorption, the intraluminal potential becomes less negative and K+ secretion is reduced. K + -sparing diuretics such as amiloride act in this fashion. Aldosterone increases the intracellular potassium concentration by augmenting the activity of the Na-K pump and increasing the potassium permeability of the luminal membrane. Increasing dietary intake increases the plasma potassium concentration, which in turn stimulates aldosterone production. Increasing the rate of distal tubular flow increases the rate of K+ secretion. The high flow maintains a low tubular K+ concentration and therefore increases the electrochemical gradient for K+ secretion. Low-dose thiazide diuretics, such as hydrochlorothiazide, are often used as first- line antihypertensive agents, and are often combined with a potassium-sparing diuretic to prevent hypokalemia. Health-promoting lifestyle modifications are recommended for individuals with prehypertension and as an adjunct to therapy in hypertensive individuals.
A 32-year-old man complaining of fatigue and muscle weakness is seen by his physician. Blood tests reveal a serum glucose level of 325 mg/dL and serum creatinine of 0.8 mg/dL. Results of a 24-hour urine analysis are as follows: Total volume = 5L Total glucose = 375 g Total creatinine = 2.4 g The patient's GFR is approximately which of the following? a. 75 mL/min b. 100 mL/min c. 125 mL/min d. 200 mL/min e. 275 mL/min
The answer is d. GFR is approximately equal to the clearance of creatinine. In this case, Creatine clearence= creatine excreted/plasma creatine concentration 2.4/.8 d= 300L/day After conversion= 200 mL/min
A 35-year-old male smoker presents with burning epigastric pain that is most pronounced on an empty stomach. In addition to peptic ulcer disease and gastric acid hypersecretion, the patient has a paroxysmal rise in serum gastrin in response to intravenous (IV) secretin. Normally, basal acid output is increased by which of the following? a. Acidification of the antrum b. Acidification of the duodenum c. Administration of an H2-receptor antagonist d. Alkalinization of the antrum e. Vagotomy
The answer is d. Alkalinization of the antrum releases the gastrin-containing cells from the inhibitory influences of somatostatin and increases acid secretion. Acidification of the antrum promotes the release of somatostatin from cells in the GI mucosa, which inhibits gastrin release and gastric acid secretion. Acidification of the duodenum elicits inhibitory neural and hormonal reflexes that also inhibit acid output. Administration of a histamine antagonist, PPI, and vagotomy all reduce acid secretion. ZES has a triad of peptic ulcer disease, gastric acid hypersecretion, and an elevated gastrin level. In ZES, a pancreatic acinar cell adenoma (gastrinoma) is the site for the synthesis and secretion of large amount of gastrin. Unlike gastrin released from the antrum in response to normal physiological stimuli, the pancreatic release of gastrin from the pancreas is not under physiological control, that is, intestinal feedback and gastric pH. ZE can be part of a multiple endocrine neoplasia type I (MEN I). PPIs (omeprazole, lansoprazole) are the treatment of choice for peptic ulcer disease in ZE, and have decreased the need for total gastrectomy
An 18-year-old man with pernicious anemia lacks intrinsic factor, which is necessary for the absorption of cyanocobalamin. Vitamin B12 is absorbed primarily in which portion of the gastrointestinal (GI) tract? a. Stomach b. Duodenum c. Jejunum d. Ileum e. Colon
The answer is d. Most vitamins are absorbed in the upper small intestine, but active absorption of vitamin B12 (cobalamin) occurs primarily in the terminal ileum. Vitamin B12 binds with intrinsic factor, a glycoprotein secreted by the parietal cells of the gastric mucosa. The vitamin B12-intrinsic factor complex is propelled along the small intestine to the terminal ileum, where specific active transporters located on the enterocyte microvilli bind the vitamin B12-intrinsic factor complex and the complex is absorbed across the ileal mucosa. Pernicious anemia is a disease in which there is autoimmune destruction of the parietal cells, leading to lack of intrinsic factor. Other causes of vitamin B12 deficiency include malabsorption (sprue, enteritis, Diphyllobrothium latum), removal of the intrinsic factor-secreting tissue (gastrectomy, gastric bypass surgery), or by diseases/absence of the terminal ileum + (Crohn's disease). Binding of the vitamin B12-intrinsic factor complex requires Ca . Although vitamin B12 and folate absorption is Na independent, all seven of the +other water-soluble vitamins are absorbed by carriers that are Na cotransporters. A second mechanism for cobalamin absorption is passive, occurring equally through buccal, duodenal, and ileal mucosa; this process is rapid but extremely inefficient, with <1% of an oral dose being absorbed by this process.
A 67-year-old man with a history of alcohol abuse presents to the emergency room with severe epigastric pain, hypotension, abdominal distension, and diarrhea with steatorrhea. Serum amylase and lipase are found to be greater than normal, leading to a diagnosis of pancreatitis. The steatorrhea can be accounted for by a decrease in the intraluminal concentration of which of the following pancreatic enzymes? a. Amylase b. Chymotrypsin c. Colipase d. Lipase e. Trypsin
The answer is d. The process of fat digestion begins in the stomach and is completed in the proximal small intestine, predominately by enzymes synthesized and secreted by the pancreatic acinar cells. The major lipolytic pancreatic enzyme is the carboxylic esterase, known as lipase (choice d). Lipase is secreted as an active enzyme but full activity of lipase requires the protein cofactor colipase, as well as an alkaline pH, bile salts, and fatty acids. Colipase (choice c) is secreted in an inactive proform and is activated in the intestinal lumen by trypsin (choice e), which, along with chymotrypsin (choice b), is endopeptidase involved in protein digestion. Amylase (choice a) is involved in the digestion of carbohydrates.
A 52-year-old man presents to his internist for a 6-month checkup following diuretic therapy and recommended diet changes for his essential hypertension. His blood pressure is 145/95 mm Hg and serum aldosterone levels are increased. Aldosterone secretion is increased when there is a decrease in the plasma concentration of which of the following? a. Adrenocorticotropic hormone (ACTH) b. Angiotensin II c. Potassium d. Renin e. Sodium
The answer is e. A decrease in plasma sodium increases aldosterone secretion. Aldosterone secretion increases in response to an increase in all of the other answer choices. The effects of sodium on aldosterone secretion are mediated via the renin-angiotensin system. Hyponatremia, as may occur with a low-sodium diet, is associated with a decrease in extracellular volume, which increases renin secretion, probably due to a reflex increase in renal sympathetic nerve activity. Increased renin leads to increased production of angiotensin II, which binds to AT1 receptors in the zona glomerulosa, which act via a G protein to activate phospholipase C. The resultant increase in protein kinase C fosters the conversion of cholesterol to pregnenolone and facilitates the action of aldosterone synthase, resulting in the conversion of deoxycorticosterone to aldosterone. Increased potassium concentration directly stimulates aldosterone secretion. Like angiotensin II, K+ stimulates the conversion of cholesterol to\ pregnenolone and the conversion of deoxycorticosterone to aldosterone by aldosterone synthase. Potassium exerts effect on aldosterone secretion by depolarizing the zona glomerulosa cells, which opens voltage-gated Ca 2+ channels, increasing intracellular Ca2+. ACTH stimulates aldosterone synthesis and secretion via increases in cAMP and protein kinase A. The stimulatory effect of ACTH on aldosterone secretion is usually transient, declining in 1 to 2 days, but persists in patients with glucocorticoid-remediable aldosteronism, an autosomal dominant disorder in which the 5′ regulatory region of the 11β-hydroxylase gene is fused to the coding region of aldosterone synthase gene, producing an ACTH-sensitive aldosterone synthase.
A 69-year-old man presents with symptoms of thirst and dizziness, and physical evidence of orthostatic hypotension and tachycardia, decreased skin turgor, dry mucous membranes, reduced axillary sweating, and reduced jugular venous pressure. He was recently placed on an angiotensin-converting enzyme (ACE) inhibitor for his hypertension. Urinalysis reveals a reduction in the fractional excretion of sodium and the presence of acellular hyaline casts. The internist suspects acute renal failure of prerenal origin associated with increased renin secretion by the kidney. A stimulus for increasing renal renin secretion is an increase in which of the following? a. Angiotensin II b. Atrial natriuretic peptide (ANP) c. GFR d. Mean blood pressure e. Sympathetic nerve activity
The answer is e. (Barrett, pp 644, 705-706. Le, p 485. Widmaier, pp 497-499.) Renin secretion is stimulated by the sympathetic nerves innervating the juxtaglomerular apparatus. Sympathetic nerve activity increases when baroreceptors sense low blood pressure. Increasing mean blood pressure (choice d) decreases sympathetic activity, thereby decreasing renin secretion. Angiotensin II (choice a) decreases renin release through a negative feedback loop by binding to AT1 receptors on the juxtaglomerular cells to increase intracellular Ca2+ concentration, which inhibits renin secretion. ANP (choice b) also decreases renin release. Increases in GFR (choice c) sensed by the macula densa lead to the secretion of a mediator, perhaps adenosine or ATP, which contracts the afferent arteriole (tubuloglomerular feedback) and decreases renin release. Decreases in GFR lead to an increase in renin release.
A 63-year-old woman has an intractable duodenal ulcer failing all previous treatments. After consultation with a surgeon, a laparoscopic vagotomy is performed. Subsequently, the patient experiences nausea and vomiting after ingestion of a mixed meal. Which of the following best explains her symptoms? a. Decreased gastric emptying of liquids b. Decreased gastric emptying of solids c. Increased gastric emptying of liquids d. Increased gastric emptying of solids e. Increased gastric emptying of solids and liquid
The answer is e. Inflammation or removal of the upper small intestine leads to a decrease in pancreatic and hepatobiliary function. The proximal small intestine contains a number of receptors that monitor the physical (volume) and chemical (pH, fat content, caloric density, and osmolality) composition of the chyme emptied from the stomach. Stimulation of these receptors releases secretin, which acts on pancreatic ductal cells to increase HCO − secretion, as well as cholecystokinin, which acts on pancreatic acinar cells to increase pancreatic 3 enzyme secretion (lipases, amylases, and proteases). Stimulation of proximal small intestine receptors also activates neural reflexes, which initiate pancreatic enzyme and bicarbonate secretion, stimulate gallbladder emptying, and provide feedback for inhibitory regulation of gastric function. Removal of these reflexes decreases pancreatic secretion and gallbladder emptying and increases gastric emptying and acid output.
Which of the following causes relaxation of the lower esophageal sphincter (LES) in response to swallowing? a. Circulating gastrin b. Inhibitory sympathetic nerve input to the LES c. Intrinsic myogenic tone of circular smooth muscle d. Release of acetylcholine from the myenteric plexus e. Release of vasoactive intestinal peptide and nitric oxide from inhibitory ganglionic neurons
The answer is e. Unlike the rest of the esophagus, the muscle of the gastroesophageal junction (LES) is tonically active (contracted) at rest and relaxes on swallowing. In contrast to the proximal esophagus, which consists of striated muscle directly innervated by lower motor neurons of the vagus nerve, the distal esophagus and LES are composed of smooth muscle and are controlled by excitatory and inhibitory neurons within the esophageal myenteric plexus. The inhibitory ganglionic neurotransmitters causing relaxation are vasoactive intestinal peptide and nitric oxide. Contraction is produced by neurotransmitters of the excitatory ganglionic neurons, namely, acetylcholine and substance P. The tonic activity of the LES is associated with a high pressure that limits reflux of gastric contents into the esophageal body. Intrinsic (myogenic) properties of the circular smooth muscle of the LES contribute to the resting tone. The normal esophageal manometry findings, along with the finding that the chest and epigastric pain do not respond to PPI, suggest that etiologies other than GERD should be considered. Cardiac disease would be the most concerning, and should be ruled out first.
A 24-year-old male graduate student participates in a clinical research study on intestinal motility. Peristalsis of the small intestine (a) mixes the food bolus (B) is coordinated by the central nervous system (CNS) (c) involves contraction of circular smooth muscle behind and in front of the food bolus (d) involves contraction of circular smooth muscle behind the food bolus and relaxation of circular smooth muscle in front of the bolus (e) involves relaxation of circular and longitudinal smooth muscle simultaneously throughout the small intestine
the answer is d [III D 2]. Peristalsis is contractile activity that is coordinated by the enteric nervous system (not the central nervous system [CNS]) and propels the intestinal contents forward. Normally, it takes place after sufficient mixing, digestion, and absorption have occurred. To propel the food bolus forward, the circular smooth muscle must simultaneously contract behind the bolus and relax in front of the bolus; at the same time, longitudinal smooth muscle relaxes (lengthens) behind the bolus and contracts (shortens) in front of the bolus.
Which of the following is the site of Na+-bile acid cotransport? (a) Gastric antrum (B) Gastric fundus (c) Duodenum (d) Ileum (e) Colon
the answer is d [IV D 4]. Bile salts are recirculated to the liver in the enterohepatic circulation via a Na+-bile acid cotransporter located in the ileum of the small intestine.