Biochem step 1 contd

Question 1

Increased bone growth is not a symptom of ?

Answer 1

hypothyroidism, which would occur? if the patient stops taking levothyroxine.

Question 2

Increased gluconeogenesis would not be likely to occur if the patient stops taking levothyroxine. Because thyroid hormone promotes?

Answer 2

gluconeogenesis, the patient would be at risk for decreased gluconeogenesis if she discontinues thyroid hormone replacement.

Question 3

Increased serum calcium is a feature of ?

Answer 3

hyperparathyroidism, which can result from injury to the parathyroid. Because there is no indication that the parathyroid was damaged during surgery, increased serum calcium is unlikely to occur if the patient stops taking levothyroxine.

Question 4

This patient has neurologic symptoms of gait problems and impaired light touch and vibration sense. She has fatigue and tachycardia, and lab findings of macrocytic RBCs (mean corpuscular volume >100 fL) and hypersegmented neutrophils (seen in the vignette photo). Put together, all of these signs and symptoms are consistent with? .

2. In pernicious anemia, cytotoxic autoantibodies are directed against ? .

Answer 4

vitamin B12 deficiency due to anemia

2. gastric parietal cells, decreasing the production of intrinsic factor. Without intrinsic factor, vitamin B12 cannot be absorbed in the terminal ileum, resulting in a megaloblastic anemia

Question 5

A patient with alcoholism, liver cirrhosis, and esophageal varices who is producing bloody emesis most likely has a variceal hemorrhage. Esophageal vessels can spontaneously rupture after prolonged portal hypertension secondary to impaired blood flow through a cirrhotic (fibrotic) liver. Patients with hemorrhage should be stabilized hemodynamically and administered a medication to reduce portal venous hypertension. There are several medications available for this purpose; however, they are all analogs of ?

Answer 5

Either somatostatin (octreotide) or vasopressin/antidiuretic hormone (ADH) (terlipressin). Both somatostatin and ADH act on G-protein–coupled receptors (GPCRs).
Of all the answer choices, only calcitonin also binds with GPCRs. The calcitonin receptor is a Gs-protein–coupled receptor that activates adenylyl cyclase, causing increased intracellular cAMP concentrations in target cells.

Question 6

Epidermal growth factor,
Insulin
and Platelet-derived growth factor acts on a ?

Answer 6

tyrosine kinase receptor.

Question 7

Estrogen is an?

Answer 7

intracellular steroid hormone receptor.

Question 8

This is a 40-year-old patient with a history of hyperlipidemia, BMI of 35, and acanthosis nigricans on exam, which is indicative of insulin resistance and is associated with type 2 diabetes mellitus. Long-term exercise has been shown to?

Answer 8

both upregulate the expression of GLUT-4 protein and increase the translocation of GLUT4 from intracellular stores to the cell surface.

Question 9

Exercise does not decrease ?

Answer 9

glucose uptake nor does it increase insulin production. While exercise does increase lipid metabolism, this is likely not the mechanism for reduced incidence of type 2 diabetes mellitus. Exercise does not increase translocation of GLUT1 to the cell surface, but does increase translocation of GLUT4 to the surface of cells. Exercise does not augment the activity of SGLT-1 or SGLT-2.

Question 10

This child presents with a constellation of abdominal issues, including abdominal pain, vomiting, and constipation. He also shows signs of emotional lability (eg, irritability) and developmental regression. Taken together, these signs and symptoms suggest? l

Answer 10

Lead poisoning.The mechanism of lead toxicity involves the inhibition of several enzymes involved in heme synthesis, including aminolevulinic acid dehydratase located in the cytoplasm

Question 11

β-Glucocerebrosidase deficiency causes? .

Answer 11

Gaucher disease, a lysosomal storage disease. Clinically, these patients present with organomegaly and bone pain

Question 12

Depletion of glutathione stores results from ? .

Answer 12

ingestion of toxins such as acetaminophen. Early signs (24–48 hours) of acetaminophen toxicity include anorexia, nausea, and vomiting. However, this patient’s symptoms have a more insidious onset, over the past 6 months, making accidental acetaminophen ingestion less likely

Question 13

Glucose-6-phosphatase deficiency results in ?

Answer 13

von Gierke disease, which manifests with severe hypoglycemia in the first few months of life. It is an unlikely diagnosis for this 3-year-old boy.

Question 14

Hexosaminidase A deficiency results in ?

Answer 14

Tay-Sachs disease, which manifests with neurologic (ataxia, seizures) and ophthalmologic (cherry-red spot on macula) dysfunction. This patient’s neurologic findings are more behavioral, however.

Question 15

This patient’s symptoms of calf pain and leg swelling in the setting of venous stasis (a long airplane flight) are most consistent with a ?

2. Thromboxane A2 also acts as ?

Answer 15

deep vein thrombosis (DVT). Patients with one or more elements of the Virchow triad (local trauma to the vessel wall, stasis, and hypercoagulability) are at increased risk for developing DVT. Thromboxane A2, produced by platelets, stimulates platelet aggregation and vasoconstriction and is elevated at the site of a forming clot.

2.an amplification signal for more potent platelet agonists, such as thrombin. Elevation of thromboxane A2 levels is a step in the signaling cascade that results in formation of a clot, such as with this patient’s DVT

Question 16

This patient presents with irregular menstrual cycles, hirsutism, and possible diabetes. She is most likely suffering from ?

Answer 16

polycystic ovarian syndrome (PCOS), one of the most common endocrinopathies in women. In addition to hirsutism, PCOS is associated with infertility (secondary to oligo-ovulation), insulin resistance, hyperandrogenism, and obesity.

Question 17

Multiple therapies are often required. Of note, oral contraceptive pills (OCPs) are the first-line treatment for PCOS. If treatment with OCPs yields unacceptable cosmetic results after six months, an antiandrogen, such as ?

Answer 17

spironolactone, is added to treat hirsutism. Spironolactone acts by blocking androgen receptors and inhibiting androgen biosynthesis; it is also a diuretic. Additional drugs for PCOS include gonadotropin analogs and clomiphene.

Question 18

Ganirelix is a GnRH antagonist which would cause?

2. Furosemide is a diuretic drug that would have no efficacy against this ?
3. Minoxidil would cause an ?.
4. Estrogen would not help this patient, whose ?

Answer 18

ovarian suppression.

2. patient’s hirsutism
3. increase in hair growth
4. estrogen levels are most likely already elevated due to her condition.

Question 19

This neonate’s skeletal abnormalities (ie, bilateral hip dislocation), restricted joint movement, and coarse facial features (ie, bulging, scaphocephalic head with a flat, short nose and bulging neck veins), and corneal clouding are most suggestive of ?

Answer 19

I-cell disease, an inherited lysosomal storage disease. The mechanism of this disease is a defect in N-acetylglucosaminyl-1-phosphotransferase, which plays an important role in cell trafficking by phosphorylating mannose to generate mannose-6-phosphate in the Golgi apparatus.

Question 20

This baby is genotypically female (karyotype 46,XX) but presents with virilization of her external genitalia (resulting in an ambiguous appearance) and hypotension. Both are due to ?

Answer 20

congenital adrenal hyperplasia (CAH). CAH is caused by deficiencies in enzymes required for adrenocortical steroid synthesis, such as 21-hydroxylase and 11β-hydroxylase.
This infant’s symptoms are most consistent with 21-hydroxylase deficiency, which results in an inability to synthesize aldosterone and cortisol. Intermediates in aldosterone/cortisol synthesis are diverted to the synthesis of androgens, and elevated androgen levels lead to masculinization/virilization in genotypically female neonates and precocious puberty in both sexes. In addition, the lack of aldosterone leads to inefficient reabsorption of sodium ions in the kidneys, resulting in hypovolemia and hypotension.

Question 21

11β-Hydroxylase deficiency also presents?

Answer 21

with masculinization and prevents synthesis of cortisol and aldosterone, but at a later step in the pathway. This results in accumulation of 11-deoxycorticosterone, a very powerful mineralocorticoid, which causes increased salt retention, hypertension, and hypervolemia. The finding of hypotension in this patient rules out 11β-hydroxylase deficiency.

Question 22

17α-Hydroxylase deficiency results in a ?

Answer 22

phenotypically female newborn and is associated with production of excess aldosterone, resulting in hypertension and hypokalemia. The findings of hypotension and ambiguous genitalia in this patient are inconsistent with 7α-hydroxylase deficiency.

Question 23

5α-Reductase deficiency only occurs in?

Answer 23

46,XY individuals, who are born with male internal reproductive organs and female external genitalia. This patient has a 46,XX karyotype and hypotension, findings that are not consistent with 5α-reductase deficiency.

A possible memory aid for enzyme deficiencies in CAH is the mnemonic phrase “One, Up!”: if the CAH deficiency starts with a 1 (eg, 11 or 17), then it causes HYPERtension) and if it ends with a 1 (eg, 11 or 21), then it causes virilization in females.

Question 24

Complete androgen insensitivity syndrome (AIS) is a result of a?

Answer 24

mutation in the androgen receptor gene. Individuals with AIS have a 46,XY karyotype and testes that are undescended or located in the labia majora. However, they have external female genitalia including a vagina. This patient has a 46,XX karyotype and ambiguous external genitalia.

Question 25

This patient’s amenorrhea, hypertension, impaired development of secondary sexual characteristics, and presence of normal uterus and ovaries, suggest a diagnosis of?

2. 17-α-Hydroxylase deficiency decreases levels of both cortisol and androgens, but increases levels of ?

Answer 25

17-α-hydroxylase deficiency, a rare cause (<1% of cases) of congenital adrenal hyperplasia. The 17-α-hydroxylase enzyme is active in both the adrenal gland and the gonads, where it catalyzes steps in the generation of corticosteroids (produced in the zona fasciculata) and androgens (produced in the zona reticularis). It does not play a role in the pathway that produces mineralocorticoids.

2. 11-deoxycorticosterone, which increases both renal sodium reabsorption and potassium secretion. Patients typically present with hypogonadism, hypokalemia, and hypertension.

Question 26

A 65-year-old African American man presents to his physician because of jaundice. He says that in the past few months he has not had much of an appetite and has lost 13.6 kg (30 lb). Physical examination is notable for a palpable, nontender gallbladder.

Answer 26

The patient most likely has adenocarcinoma at the head of the pancreas, leading to obstruction of the common bile duct. Weight loss, jaundice, and a palpable gallbladder (Courvoisier sign) can occur in pancreatic cancer. The obstruction from the growing tumor results in hyperbilirubinemia and increased urine bilirubin levels. The majority of bilirubin results from the breakdown of heme groups in senescent RBCs. After cellular release, bilirubin binds to albumin and is taken up by the liver. Hepatocellular uptake and glucuronidation in the endoplasmic reticulum generate conjugated bilirubin, which is water soluble and excreted in the bile. The urine bilirubin level is elevated secondary to the increased plasma concentration of direct (conjugated) bilirubin, which is water-soluble and undergoes renal excretion.

Question 27

Congenital adrenal hyperplasia occurs when one of the numerous enzymes required to convert cholesterol to cortisol is deficient or defective and the question asks which compound is the primary reducing equivalent used in tissues that synthesize steroids.?

Answer 27

All nicotinamides and flavin nucleotides are activated electron carriers, but only NADPH can be used in anabolic (energy-requiring) reactions like steroid synthesis. NADP+, NADH, NAD+, FAD, and FADH2 do not supply reducing equivalents for steroid synthesis.

Question 28

FAD (flavin adenine dinucleotide) is an important redox cofactor. It is the oxidizing agent used to make double bonds, such as the production of ?

Answer 28

fumarate from succinate in the tricarboxylic cycle (also known as Krebs or citric acid cycle).

Question 29

FADH2 (reduced form of flavin adenine dinucleotide) is derived from vitamin B2 (riboflavin) and is another electron carrier that participates in?

Answer 29

the electron transport chain. It is generated during the oxidation of succinate to fumarate.

Question 30

This mouse model has a defect in the GLUT family of glucose transporters (GLUT 1–5). These transporters are responsible for ?

Answer 30

cellular uptake in many cell types. Enterocytes and nephrons, in addition to GLUT transporters, utilize SGLT glucose transporters that acquire glucose through cotransport with sodium ions. Since all GLUT transport proteins (1-5) are knocked out, only enterocytes and nephrons will have the ability to continue to take up glucose normally due to the presence of functional SGLT glucose transporters.