GI Midterm Review Flashcards
A newborn becomes lethargic and drowsy 24 h after birth. Blood analysis shows hyperammonemia, coupled with orotic aciduria. This individual has an enzyme deficiency that leads to an inability to directly produce which of the following?
A. Carbamoyl phosphate
B. Ornithine
C. Citrulline
D. Argininosuccinate
E. Arginine
C. Citrulline
Given these symptoms, the defect is in the urea cycle and the elevated orotate suggests deficiency of ornithine transcarbamoylase.
A newborn becomes lethargic and drowsy 24 h after birth. Blood analysis shows hyperammonemia, coupled with orotic aciduria. Considering the patient in question above, orotic acid levels are high in this patient due to which of the following?
A. Elevated ammonia
B. Elevated glutamine
C. Increased pyrimidine synthesis
D. Increased purine synthesis
E. Inhibition of carbamoyl phosphate synthetase I (CPS-I)
C. Increased pyrimidine synthesis
Given these symptoms, the defect is in the urea cycle and the elevated orotate suggests deficiency of ornithine transcarbamoylase.
In an OTC deficiency, the carbamoyl phosphate produced in the mitochondria leaks into the cytoplasm, leading to orotic acid synthesis as the regulated step of the pyrimidine synthesis pathway (CPSII step) is being bypassed.
A newborn becomes lethargic and drowsy 24 h after birth. Blood analysis shows hyperammonemia, coupled with orotic aciduria. A potential treatment for
the patient is supplementation with which of the following?
A. Arginine and glutamine
B. Lysine and glutamine
C. Arginine and benzoate
D. Lysine and benzoate
E. Glutamine and phenylbutyrate
C. Arginine and benzoate
Given these symptoms, the defect is in the urea cycle and the elevated orotate suggests deficiency of ornithine transcarbamoylase (OTC).
Whenever there is a urea cycle defect, arginine becomes an essential amino acid (as its route of synthesis is the urea cycle). Benzoate, along with phenylbutyrate, is given to patients with urea cycle defects to conjugate with a nitrogen carrying molecule (benzoate conjugates with glycine while phenylbutyrate, after activation to phenylacetate, conjugates with glutamine), which is then excreted
A 49-year-old male with a rare recessive condition is at high risk for deep vein thrombosis and stroke and has had replacement of ectopic lenses. He has a normal hematocrit and no evidence of megaloblastic anemia. He responds positively to pyridoxine administration. A mutation in the gene encoding which of the following is most likely to cause this disease?
A. Cystathionine b-synthase
B. Methionine Synthase
C. Fibrillin
D. Homogentisate oxidase
E. Branched chain α-ketoacid dehydrogenase
F. Methylmalonyl-CoA mutase
A. Cystathionine b-synthase
Homocysteine, the substrate for the enzyme, accumulates increasing the risk of deep vein thrombosis and ectopic lenses. Deficiency of Methionine Synthase would cause
homocystinuria, but would also predispose to megaloblastic anemia
Methionine would also be elevated in case of CBS deficiency
A 12-year-old boy is brought to the pediatrician because of behavioral problems noted by the parents. Upon examination, the physician notices brittle and coarse hair, long, thin arms and legs (reminiscent of Marfan syndrome patients), scoliosis, pectus excavatum, displaced lens, and muscular hypotonia. Blood work is likely to show an elevation of which of the following metabolites?
A. Tyrosine
B. Phenylpyruvate
C. Cysteine
D. Orotate
E. Homocystine
E. Homocystine
The symptoms suggest homocystinuria, commonly caused by a mutation in CBS (cystathionine B-synthase) which presents with high levels of homocysteine and methionine
An individual has been shown to have a deficiency in an intestinal epithelial cell amino acid transport system for leucine. However, the individual shows no symptoms of amino acid deficiency. This could be due to which of the following?
A. The body synthesizes leucine to compensate for the transport defect.
B. The kidney reabsorbs leucine and sends it to other tissues.
C. There are multiple transport systems for leucine.
D. Isoleucine takes the place of leucine in proteins.
E. Leucine is not necessary for bulk protein synthesis.
C. There are multiple transport systems for leucine.
A strict vegan who has not consumed meat products for about 5 years slowly develops tiredness and lethargy and also occasional tingling of feet and lower extremities. An analysis of total folate indicate normal amounts. In which form will the folate be mostly found?
A. DHF
B. THF
C. Methyl-folate
D. Methylene-folate
E. Formyl-folate
C. Methyl-folate
People on a vegan diet may develop a Vitamin B12 deficiency because of paucity of this nutrient in vegan foods. A B12 deficiency may result in the “folate trap,” where much of the folate is “stuck” in the methyl folate form. This occurs because the B12-dependent reaction
that converts homocysteine to methionine is impaired
A nutritional deficiency in which of the following may result in propionic acid accumulation?
A. Vitamin B6
B. Biotin
C. Folate
D. Vitamin B1
E. Vitamin B2
B. Biotin
Like the other carboxylases discussed (pyruvate carboxylase and acetyl CoA carboxylase) Propionic CoA carboxylase is a biotin-dependent enzyme
A 6-month-old boy is brought to the office by his mother over concerns of a developmental delay and foul-smelling wet diapers. Pregnancy and birth history are unremarkable. The baby and his mother immigrated to the United States one month ago. On physical examination the patient has a social smile but does not hold his head up on his own or make babbling noises. Brisk reflexes are noted in the upper and lower extremities. Plasma tyrosine levels are low while ammonia levels are normal. Which of the following enzymes is most likely deficient in this patient?
A. Cystathionine β-synthase
B. Dihydrobiopterin reductase
C. Homogentisate oxidase
D. Tyrosinase
E. Methylmalonyl CoA mutase
B. Dihydrobiopterin reductase
The symptoms align with PKU. Classic PKU is caused by a deficiency in PAH, while variant form is caused by a deficiency in DHPR
The co-factor, pyridoxal phosphate, promotes two distinct enzymatic reactions. Which combination is CORRECT?
A. Transamination reactions, and in the conversion of homocysteine to cysteine.
B. Oxidative deamination by glutamate dehydrogenase, and conversion of homocysteine to methionine.
C. Activation of carbamoyl phosphate synthase I and in the conversion of homocysteine to cysteine.
D. In the ATP-dependent conversion of glutamate to glutamine, and by phenylalanine hydroxylase in the conversion of phenylalanine to tyrosine.
E. Activation of S-adenosyl methionine synthase, and in carbon transfer reactions mediated by methyl tetrahydrofolate
A. Transamination reactions, and in the conversion of homocysteine to cysteine.
The nitrogens in urea are most directly derived from which of the following compounds (choose best answer)?
A. Ornithine and carbamoyl phosphate
B. Ornithine and aspartate
C. Ornithine and glutamate
D. Carbamoyl phosphate and aspartate
E. Carbamoyl phosphate and alanine
F. Aspartate and glutamine
D. Carbamoyl phosphate and aspartate
Your 56-year-old male patient presents with intense redness, heat, and pain over his right great toe at the metatarsophalangeal joint. Fluid from this joint shows bifringent crystals. This disease is caused by the degradation of an excessive amount of which of the following?
A. Adenine
B. Thymine
C. Uracil
D. Cytosine
E. Ribose-5-phosphate
A. Adenine. Gout is caused by uric acid crystallization into a joint and an intense inflammatory reaction to those crystals. Uric acid is an insoluble breakdown product of purines (adenine, hypoxanthine, or guanine).
Pyrimidines (thymine, uracil, and cytosine) breakdown to different water-soluble products that do not crystallize. Ribose-5-phosphate is also degraded to very water-soluble product
A 6-month-old infant is seen by the pediatrician for developmental delay. Blood work shows megaloblastic anemia, although measurements of B12 and folate are in the high normal range. Urinalysis demonstrates, upon standing, the formation of a crystalline substance. Supplementation of the child’s diet with uridine reversed virtually all of the clinical problems. The crystalline substance was most likely composed of which of the following?
A. Uracil
B. Thymine
C. Orotate
D. Aspartate
E. Cytosine
C. Orotate. The child has hereditary orotic aciduria, a mutation in the UMP synthase that leads to orotic acid accumulation in the urine.
Treatment with uridine bypasses the block and allows UTP, CTP, and dTTP synthesis. Uridine treatment also has the beneficial effect of blocking further orotate production, as UTP inhibits carbamoyl phosphate synthetase II, the rate-determining step of pyrimidine production. As CPS-II is inhibited, less orotate is produced.
The megaloblastic anemia is the result of inadequate DNA synthesis in the red cell precursors due to the lack of dTTP and dCTP. The crystals are made of orotate, as that is the compound that is accumulating.
Which ONE of the following statements about ribonucleotide reductase is CORRECT?
A. The amount of the enzyme in cells varies with the cell cycle.
B. It is postulated that the immunodeficiency observed with ADA results fromhigh levels of
dGTP shutting off the reduction of all ribonucleotides.
C. The enzyme requires NADH for regeneration.
D. The enzyme is critical for the reduction of the rings in the formation of purines.
E. The 3’OH of the ribose ring is reduced by this enzyme.
A. The amount of the enzyme in cells varies with the cell cycle.
The level of the enzyme corresponds with the need for DNA synthesis during S phase. ADA results in high levels of dATP. The enzyme uses NADPH for regeneration, not NADH. The enzyme has nothing to do with ring formation in purine biosynthesis, but reduces the 2’OH of the ribose
Which ONE of the following statements about pyrimidine biosynthesis is CORRECT?
A. The level of purines in cells affects the rate of pyrimidine synthesis.
B. The committed step is the synthesis of 5’ phosphoribosylamine.
C. The final step in the pathway is the transfer of the ribose-5-P from PRPP.
D. Synthesis occurs solely in the cytoplasm.
E. IMP is the parent compound for UMP and CMP
A. The level of purines in cells affects the rate of pyrimidine synthesis.
ATP, a purine, does regulate pyrimidine synthesis. Formation of 5’phosphoribosylamine occurs in purine biosynthesis. Transfer of PRPP occurs onto an intermediate in the pathway. One enzyme in the pathway is in the outer face of the inner mitochondrial membrane
The mucosal layer of the jejunum…
A. exhibits Brunner’s glands.
B. differs from that of the duodenum because it has a stratified squamous epithelium.
C. lacks a lamina propria.
D. lacks goblet cells.
E. exhibits a muscularis mucosae
E. exhibits a muscularis mucosae
The lamina propria
A. lacks capillaries.
B. contains nerve fibers.
C. contains the cell bodies of the myenteric plexus.
D. lacks lymphocytes.
E. has all of the above features
B. contains nerve fibers.
Paneth cells
A. are found throughout the stomach.
B. are found in the epithelium of villi of the small intestine.
C. produce lysozyme.
D. are restricted to the anal-rectal junction.
E. function as macrophages.
C. produce lysozyme.
A young male patient has self-medicated by taking substantial quantities of over-the-counter medications. You have concerns about the effect of the drugs on his liver. Which statement is the most true and relevant?
A. The liver is exposed to the highest level of toxins because it is the first organ to receive blood from the intestine.
B. A liver biopsy would show that cells in the centrolobular zone (zone 3) would be the most damaged.
C. The fixed hepatic macrophages would contain large numbers of phagosomes, evidence of their role in detoxification.
D. The drugs would be converted into bile salts and excreted.
E. The hepatic stellate cells (lipocytes) would be depleted of vitamin A and have few
lipid droplets.
B. A liver biopsy would show that cells in the centrolobular zone (zone 3) would be the most damaged.
Which statement about hepatocyte function is correct?
A. In a well-fed individual, the perilobular/periportal region (zone 3) would have the highest amount of glycogen.
B. In a starved individual, the centrolobular zone (zone 1) would be the most active in glycolysis.
C. The cells in zone 1 are exposed to the highest concentrations of oxygen and nutrients in the blood coming from the intestine.
D. The bile flows in the bile ductules in the direction from zone 1 to zone 3.
E. The venous and arterial blood flow in opposite directions between zones 1 and 3.
C. The cells in zone 1 are exposed to the highest concentrations of oxygen and nutrients in the blood coming from the intestine.
In relating the ultrastructure of the hepatocyte to cellular function…
A. Abundant rough endoplasmic reticulum is consistent with the hepatocyte being the major site of enzymes involved in lipid biosynthesis.
B. Abundant mitochondria are the sites of fatty acid and glucose metabolism.
C. Apolipoprotein synthesis is consistent with an extensive smooth endoplasmic reticulum.
D. The presence of peroxisomes is an indicator of the phagocytic activity of the hepatocyte.
E. The heterochromatic nucleus is indicative of the limited transcriptional activity by the hepatocyte.
B. Abundant mitochondria are the sites of fatty acid and glucose metabolism.
Which of the following illustrates the liver’s function as an endocrine gland?
A. Secretion of bile
B. Receptor mediated endocytosis of HDL-cholesterol
C. Secretion of VLDL
D. Storage of vitamin A
E. Synthesis of albumin
C. Secretion of VLDL
During an evaluation for swallowing problems, changes in pressure due to muscle contractions were recorded from the pharynx to the stomach. The results show strong contractions in the pharynx followed by a strong esophageal peristaltic wave over the entire length of the esophagus. This observation would most likely be described as a(n)…
A. abnormal primary esophageal wave.
B. normal primary esophageal wave.
C. abnormal secondary esophageal wave.
D. normal secondary esophageal wave.
E. inadequate evidence to make an evaluation
B. normal primary esophageal wave.
The normal primary esophageal (peristaltic) wave starts from the top to the end of the esophagus, and is strong.
The loss of GI motility in a patient after an open abdominal surgery to remove gallbladder cancer is because of the activation of…
A. Colono-colonic reflex
B. Colonic-intestinal reflex
C. Ileal-gastric reflex
D. Intestino-intestinal reflex
E. Peritoneo-intestinal reflex
E. Peritoneo-intestinal reflex
Peritoneo-intestinal reflex, also called adynamic ileus, is activated by abdominal surgery or peritoneal irrigation
Extensive loss of saliva may cause which of the following to be too low in the plasma?
A. Na+
B. K+
C. Cl-
D. Ca2+
B. K+
Saliva is rich in potassium, but low in sodium and chloride
During a meal, pancreatic enzyme secretion is most likely mediated by…
A. acetylcholine
B. gastrin
C. GIP
D. secretin
E. Somatostatin
A. acetylcholine
Cephalic stimuli can activate the parasympathetic system, which controls pancreatic enzyme secretion. CCK would be the other major inducer, although not listed as an answer.
Which of the following is mainly responsible for the secretion of a large volume of fluid from the pancreas 3 hours after a meal?
A. Acetylcholine
B. CCK
C. Gastrin
D. GRP
E. Secretin
E. Secretin
During the intestinal phase, in response to H+ from the stomach, secretin is produced during the intestinal phase to induce ductular secretion
Cholecystokinin acts in an endocrine manner by:
A. Promoting gastric distension
B. Crossing the blood brain barrier to induce satiety
C. Stimulating pancreatic enzyme secretion
D. Inhibiting pancreatic bicarbonate secretion
E. Being stimulated by carbohydrate digestion product
C. Stimulating pancreatic enzyme secretion
Which of the following GI peptides is secreted in response to the presence of the digestive products of all three macronutrients (carbohydrates, fats and proteins) in the duodenum and jejunum, and leads to an increase in insulin secretion?
A. CCK
B. Gastrin
C. GIP
D. Motilin
E. Secretin
C. GIP
Inhibition of sodium transport has the least effect on absorption of which of the following?
A. Monoglycerides
B. Galactose
C. Glucose
D. Dipeptides
E. Vitamin C (ascorbic acid)
Monoglycerides are absorbed by diffusion whereas all the rest are transported in a Na-dependent manner.
In the normal individual, most of the water absorption occurs in the…
A. stomach.
B. lumen
C. colon
D. small intestine.
E. pancreas
D. small intestine.
Absorption of water is osmotically induced. Osmotically active particles are absorbed mainly throughout the small intestine.
One of the many important roles cholesterol plays in the body is as the precursor to the bile acids and salts. A number of structural modifications are carried out in their synthesis in the liver and during their function in the intestine. Which ONE of the following statements CORRECTLY describes one of these changes?
A. To improve the amphipathicity of the bile acids, the liver adds the amino acids glycine or phenylalanine to the four-ring structure derived from cholesterol.
B. Bile acid synthesis includes the addition of hydroxyl groups at some positions on the parent cholesterol molecule while carbon atoms are removed elsewhere.
C. Conversion of primary bile acids and salts into secondary bile acids and salts takes place in the bile duct.
D. Bile salts are converted into bile acids by enzymes in the portal vein.
E. Primary bile acids are synthesized from endogenous cholesterol while secondary bile acids are synthesized from dietary cholesterol
B. Bile acid synthesis includes the addition of hydroxyl groups at some positions on the parent cholesterol molecule while carbon atoms are removed elsewhere.
Conversion of cholesterol to the amphipathic bile acids involves the addition of one or two hydroxyl groups and the shortening of the so-called hydrocarbon “tail” by three carbon atoms. The amino acids that are added to the bile acids are glycine and taurine.
The conversion of primaries to secondaries occurs in the intestine, via bacterial enzyme action. No distinction is made in the synthesis of the bile acids as to the endogenous or dietary source of the cholesterol precursor.
Which of the following would be MOST likely be the result of resection of the ileum?
A. Increased absorption of Vitamin A
B. Decreased solubility of cholesterol in bile
C. Increased digestion of lipids
D. Decreased water content of the feces
B. Decreased solubility of cholesterol in bile
Ileal resection leads to decreased enterohepatic circulation of bile salts. As a result, the concentration of bile salts in the bile is also reduced, decreasing cholesterol solubility in bile
Which ONE of the following statements about de novo cholesterol synthesis is CORRECT?
A. The HMG CoA synthase isozyme that is used to synthesize the HMG CoA that serves as a precursor to cholesterol is located in the mitochondria.
B. NADH is the source of the reducing equivalents required for cholesterol synthesis.
C. Compared to a diet containing 150 mg cholesterol per day, consumption of 1500 mg cholesterol per day will lead to a decrease in HMG CoA reductase activity.
D. ATP is not required for the production of cholesterol.
C. Compared to a diet containing 150 mg cholesterol per day, consumption of 1500 mg cholesterol per day will lead to a decrease in HMG CoA reductase activity.
Chylomicron remnants (containing dietary cholesterol) internalized by liver cells, and low density lipoproteins internalized by cells of the liver and peripheral tissues, provide cholesterol, which causes a decrease in transcription of the HMG CoA reductase gene, leading to a decrease in de novo cholesterol synthesis.
HMG CoA reductase is the regulatory enzyme in the pathway of cholesterol biosynthesis. Which ONE of the following statements regarding this enzyme is INCORRECT?
A. Cholic acid is an inhibitor of this enzyme.
B. Insulin signaling stimulates the activity of this enzyme by means of a phosphatase.
C. The statin class of drugs are competitive inhibitors of the enzyme
D. Cholesterol levels influence the rate of HMG CoA reductase mRNA synthesis.
A. Cholic acid is an inhibitor of this enzyme.
Cholic acid (a precursor to the bile salts) is an inhibitor of the 7-alpha hydroxylase involved in bile acid synthesis, but has no allosteric effects on HMG CoA reductase
A feature of the process of heme degradation is the lack of solubility this molecule has in aqueous solutions. Which ONE of the following statements CORRECTLY describes one of the means by which the system of organs, cells and enzymes that is responsible for heme degradation and excretion manages this low solubility in a healthy individual?
A. Covalent attachment to CoA groups enhances the solubility of heme breakdown intermediates.
B. Bilirubin is converted to its diglucuronide form by intestinal bacteria.
C. Bilirubin diglucuronide is transported in the blood stream in association with albumin.
D. Acidic derivatives of glucose are covalently attached to bilirubin prior to its export in the bile.
E. Biliverdin is bound to albumin while it is being covalently modified in cells of the liver.
D. Acidic derivatives of glucose are covalently attached to bilirubin prior to its export in the bile.
Which ONE of the following statements regarding the first steps in the breakdown of red blood cell components, in cells of the reticuloendothelial (RE) system of a healthy individual, is CORRECT?
A. At an early stage in the degradation of the globin tetramer, the heme ring is released intact into the circulation, with the iron quickly changing to the Fe+3 state.
B. The first chemical change in heme ring breakdown is the opening of the ring structure, with the conversion of Fe+2 to Fe+3.
C. Macrophages covalently attach a pair of glucuronic acid residues to the newly linearized porphyrin ring structure.
D. Biliverdin is transported to the liver via attachment to albumin.
E. The amino acids derived from globin tetramer protein degradation are secreted in the urine.
B. The first chemical change in heme ring breakdown is the opening of the ring structure, with the conversion of Fe+2 to Fe+3.
Complete the following sentence so that it is CORRECT: “The catabolism of hemoglobin…”
A. occurs in red blood cells.
B. involves the complete oxidative breakdown of the porphyrin ring to CO2, H20 and NH3.
C. results in the liberation of carbon monoxide.
D. results in the formation of protoporphyrinogen.
E. is inhibited by hemin.
C. results in the liberation of carbon monoxide.
During the process of heme degradation, urobilinogen is formed in the:
A. Spleen
B. Liver
C. Urinary tract
D. Bowel
E. Kidney
D. Bowel
Which ONE of the following is an INCORRECT statement about the bile acids and salts?
A. Bile salts facilitate the absorption of fat-soluble vitamins from the intestine.
B. Bile salts are converted to bile acids by the addition of glycine or taurine.
C. A deficiency of bile salts can lead to cholelithiasis (gall bladder disease).
D. Bacteria in the intestine can convert cholic acid into deoxycholic acid, and chenodeoxycholic acid into lithocholic acid.
E. Bile is stored and concentrated in the gall bladder.
B. Bile salts are converted to bile acids by the addition of glycine or taurine.
Bile acids are converted into bile salts by the addition of glycine or taurine
A 50 year old patient who had ileal resection mentioned that she can eat some eggs and bacon for breakfast and feels fine but other than breakfast, she has diarrhea after lunch and dinner. What could explain this?
A. carbohydrate maldigestion and malabsorption
B. protein maldigestion and malabsorption
C. lipid maldigestion and malabsorption
D. pancreatic insufficiency
C. lipid maldigestion and malabsorption
Bile salt synthesis during the night (interdigestive period) results in sufficient bile to be made and stored in the gallbladder to aid in the digestion of the lipids consumed in the breakfast. However, because of the ileal resection, reabsorption of bile is impaired, and so bile available for digestion/absorption of meals later in the day is deficient, causing the diarrhea.
An individual has overdosed on his heart medicine (digitalis intoxication) and the GI tract is being affected as evidenced by watery diarrhea. This poisoning of the Na+K+ ATPase most likely leads to a reduction in the absorption of which of the following?
A. Free fatty acids
B. Glucose
C. Iron
D. Cl-
B. Glucose
Glucose is co-transported with Na+ via SGLT1. The Na+K+ ATPase provides the engine that drives the absorption of Na+-dependent transporters.
