Deck 2: Physiology of Cells and Molecules

Question 1

Your patient has been diagnosed with malignant hyperthermia after a surgical procedure. The most common cause of malignant hyperthermia in humans is an
Abnormal response to general anesthetics involving the:

A) Na⁺-Ca²⁺ exchanger
B) Sarcoplasmic reticulum Ca²⁺ release channel
C) IP₃ receptor
D) Na⁺K⁺-ATPase
E) Central nervous system (CNS)

Answer 1

Sarcoplasmic reticulum Ca²⁺ release channel

Question 2

Consider a patient with pH = 7.33; [HCO₃^-] = 36 mEq/L; PCO₂ = 70 mmHg. What is the acid-base status of the patient?

A) Compensated metabolic alkalosis
B) Compensated metabolic acidosis
C) Compensated respiratory alkalosis
D) Compensated respiratory acidosis
E) Uncompensated respiratory alkalosis

Answer 2

Compensated respiratory acidosis

Question 3

Which of the following is correct for male sex differentiation?

A) The male phenotype is determined by the presence of either X or Y chromosomes.
B) Stimulation and development of the indifferent gonad is initiated by the sex-determining region of the Y chromosome (SRY) gene.
C) The müllerian ducts develop into the male reproductive tract.
D) Sertoli cells are stimulated to produce testosterone.
E) Testes have descended into the scrotum by 9 weeks' gestation.

Answer 3

Stimulation and development of the indifferent gonad is initiated by the sex-determining region of the Y chromosome (SRY) gene.

Question 4

In aging, if osteoclast activity is constant, but osteoblast activity progressively decreases, which disease will likely develop?

A) Osteoclastoma
B) Osteomalacia
C) Paget's disease
D) Osteoporosis
E) Scurvy

Question 5

A patient complains of excessive urine output and constant thirst. Laboratory tests show an elevated plasma sodium concentration (151 mEq/L) and elevated plasma osmolality (320 mOsm/L). The urine osmolality is only 75 mOsm/L. Which of the following could explain the patient's problem?

A) Defective epithelial sodium channel (ENaC)
B) Defective ROMK proteins
C) Defective V₂ receptor proteins
D) Excessive antidiuretic hormone (ADH) secretion
E) Defective atrial natriuretic peptide (ANP) secretion

Question 6

A 58-year-old woman develops a fever and dyspnea approximately 24 h after undergoing a laparoscopic cholecystectomy. Physical examination shows decreased percussion, increased tactile fremitus, and decreased breath sounds in the right lower lobe. Which of the following is the most likely diagnosis?

A) Atelectasis
B) Lobar pneumonia
C) Lung abscess
D) Pulmonary infarction
E) Spontaneous pneumothorax

Question 7

Which of the following when administered to a normal individual produces effects similar to that observed in patients with myasthenia gravis?

A) Black widow spider toxin
B) Neostigmine
C) Curare
D) 'Nerve gas'
E) Edrophonium

Question 8

The primary source of estriol (E₃) during pregnancy is the:

A) Maternal ovary
B) Fetal ovary
C) Fetal adrenal and placenta
D) Endometrium
E) Corpus luteum

Question 9

A 45-year-old woman arrives at the clinic and exhibits athetoid movements. She probably has a:

A) Cerebellar lesion
B) Lesion in the basal ganglia
C) Thalamic lesion
D) Frontal eye field lesion
E) Lesion in the cerebral cortex

Question 10

In a patient recovering from cholera, pH = 7.35; [HCO₃^-] = 16 mEq/L; PCO₂ = 30 mmHg. What is the acid-base status of the patient?

A) Compensated metabolic alkalosis
B) Compensated metabolic acidosis
C) Compensated respiratory alkalosis
D) Compensated respiratory acidosis
E) Uncompensated respiratory alkalosis

Question 11

A 1-day-old neonate with acute respiratory distress syndrome (ARDS) has moderately severe hypoxemia. Physical examination reveals, dry inspiratory crackles in the lungs and a continuous harsh murmur heard over the entire precordium. Which of the following sets of oxygen saturation (SaO₂) values in the cardiac chambers and vessels most likely match those of this patient? $$\begin{array} { | l | l | } \hline \text { Right atrium (RA) } & \text { Normal } \mathrm { SaO } _ { 2 } ( \% ) \\\hline \text { Right ventricle (RV) } & 75 \\\hline \text { Pulmonary artery (PA) } & 75 \\\hline \text { Pulmonary veir (PV) } & 75 \\\hline \text { Left ventricle (LV) } & 95 \\\hline \text { Aorta } ( \mathrm { A } ) & 95 \\\hline\end{array}$$ $$\begin{array} { l l l l l l l } & \text { RA } & \text { RV } & \text { PA } & \text { PV } & \text { LV } & \text { A } \\& ( \% ) & ( \% ) & ( \% ) & ( \% ) & ( \% ) & ( \% ) \\\hline \text { A } & 75 & 80 & 80 & 95 & 95 & 95 \\\text { B } & 80 & 80 & 80 & 95 & 95 & 95 \\\text { C } & 75 & 75 & 80 & 95 & 95 & 95 \\\text { D } & 75 & 75 & 75 & 95 & 80 & 80 \\\text { E } & 75 & 75 & 75 & 95 & 95 & 95\end{array}$$

A) $\begin{array} { l l l l l l } 75 & 80 & 80 & 95 & 95 & 95\end{array}$
B) $\begin{array} { l l l l l l } 80 & 80 & 80 & 95 & 95 & 95\end{array}$
C) $\begin{array} { l l l l l l } 75 & 75 & 80 & 95 & 95 & 95\end{array}$
D) $\begin{array} { l l l l l l } 75 & 75 & 75 & 95 & 80 & 80\end{array}$
E) $\begin{array} { l l l l l l } 75 & 75 & 75 & 95 & 95 & 95\end{array}$

Question 12

A 56-year-old right-handed woman states that her right hand shakes when she tries to open a door. Her physician does not observe a tremor when the patient's hands are resting in her lap. She further states that she falls frequently, usually to the right side. The most likely cause of these findings is a lesion in the:

A) Left internal capsule
B) Left precentral gyrus
C) Right caudal medulla
D) Right cerebellum
E) Right lateral corticospinal tract

Question 13

A 30-year-old female patient with hypercapnia that is not the result of compensation for an acid-base disturbance is seen in the clinic. Thus, this patient is suffering from:

A) Nothing, the patient has normal acid-base balance.
B) Respiratory acidosis
C) Respiratory alkalosis
D) Metabolic acidosis
E) Metabolic alkalosis

Question 14

You determine that your 1-year-old male patient has cryptorchidism. Cryptorchidism is the term used to describe non-descent of the testes. Which of the following statements is correct in connection with this process?

A) Fertility is unaffected in males with undescended testes.
B) Hormone treatment is not effective to induce descent.
C) Leydig cell function is reduced in boys with undescended testes.
D) There is an increased rate of testicular malignant change in cryptorchidism.
E) Klinefelter's syndrome may be responsible for testicular non-descent.

Question 15

Suppose the plasma membrane of a particular mammalian cell is much more permeable to water and urea than to any other solute. The water permeability is higher than the urea permeability. The cell is initially in a normal physiological saline solution and then is suddenly moved into a solution consisting of 600 mM urea as the only solute. The cell will:

A) Swell initially and continue to swell until lysis
B) Swell initially until it reaches osmotic equilibrium with the medium
C) Shrink initially and then swell until lysis
D) Shrink initially and stay shrunken
E) Swell initially and then shrink back to normal volume

Question 16

A medical student complains of severe vomiting and diarrhea for 2 days since eating at the Roadkill Café. His blood pressure is 120/70 mmHg supine and 90/50 mmHg standing. His skin and mucous membranes are dry. Which of the following laboratory finding would you expect to find?

A) Low serum aldosterone concentration
B) High atrial natriuretic peptide (ANP) levels
C) Low plasma renin activity
D) Low urinary sodium concentration
E) High urine volume

Question 17

Which one of the following statements is correct regarding salivary secretion?

A) The secretion of saliva is essential for the complete digestion of starch.
B) It is primarily under hormonal control.
C) It does not prevent decalcification of the teeth.
D) It is an acidic solution that begins the digestion of protein in the mouth.
E) It is the only hypotonic gastrointestinal secretion.

Question 18

Insulin binding to its receptor tyrosine kinase leads to:

A) Activation of Janus kinase-signal transducer and activator of transcription (JAK-STAT)
B) Mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (ERK) activation
C) Insulin-receptor binding to the MAPK promoter
D) G_s activation and substrate phosphorylation by PKA
E) G_i activation of phosphodiesterase (PDE)

Question 19

Which of the following statements best describes ARDS (acute respiratory distress syndrome)?

A) It occurs only in adults.
B) It is best described as a diffuse pulmonary process with decreased thickness of the pulmonary membrane.
C) A direct pulmonary insult is required for ARDS to develop.
D) Hypercarbia is the most common finding in the early stages of ARDS.
E) Mortality rate has been decreasing over the past 5 years.

Question 20

Two people have the same total body mass (70 kg) but one has a much higher percentage of body fat than the other. They both habitually ingest 2.5 L of water per day.
The individual with the higher percentage of fat will have a:

A) Higher extracellular fluid (ECF) volume than the other individual
B) Lower rate of water turnover than the other individual
C) Higher rate of water turnover than the other individual
D) Positive water balance
E) Negative water balance

Question 21

A 16-year-old boy has become totally deaf in his left ear after a motor vehicle accident even though hearing in his right ear is normal. A lesion at which of the following sites is the most likely cause of this finding?

A) Left dorsal and ventral cochlear nuclei
B) Left inferior colliculus
C) Left superior colliculus
D) Right medial geniculate nucleus
E) Right temporal lobe

Question 22

A 45-year-old woman experiences blurred vision and difficulty swallowing after eating some home-canned vegetables. These symptoms are followed by respiratory distress and flaccid paralysis. The symptoms of her illness are most associated with which of the following?

A) Black widow spider toxin
B) Botulinum toxin
C) Organophosphate poisoning
D) Benzodiazepine ingestion
E) ( $\alpha$ )-Bungarotoxins

Question 23

A 50-year-old homeless man with a 30-year history of alcoholism complains of painful lesions on the mucous membranes of his mouth and tongue and has pigmented keratotic scaling lesions on his face and hands. In addition, he is weak, forgetful, and has burning sensations in various parts of the body and diarrhea. A deficiency of which of the following is most likely to account for these findings?

A) Biotin
B) Folic acid
C) Niacin
D) Riboflavin
E) Vitamin C

Question 24

A healthy 16-year-old man experiences severe hemorrhaging following an automobile accident. He is conscious and aware upon arrival at the emergency department, but hypotensive, and tachypneic. Which of the following is associated with the hemodynamic response to hemorrhage?

A) Decreased coronary blood flow
B) Decreased sympathetic tone to the venous system
C) Increased blood flow to the skin, intestines, and kidneys
D) Increased cholinergic vasoconstrictor tone of skeletal muscle arterioles
E) Normal cerebral blood flow

Question 25

An 8-year-old healthy boy is concerned about his very short stature. His growth hormone level is within normal limits despite the fact that his growth rate and bone age are below the norm for children of the same chronologic age. The level of which of the following hormones is most likely to be abnormal?

A) Fibroblast growth (FGF)
B) Insulin
C) Insulin-like growth factor I (IGF-I)
D) Somatostatin
E) Somatotropin

Question 26

A 5-year-old boy has a history of growth retardation, pulmonary infections, and bulky, oily, malodorous stools. Which of the following test results would be expected in this patient?

A) Abnormal sweat chloride test
B) Low C₃ complement level
C) Abnormal nitroblue tetrazolium (NBT) dye test
D) Positive wheal and flare reaction with antigen scratch testing
E) Sputum with Gram-positive diplococci

Question 27

The glomerular filtration rate (GFR) can be determined from:

A) Urinary flow rate (V), plasma P-aminohippuric acid (PAH) concentration (P_PAH) and urinary PAH concentration (U_PAH)
B) Urinary flow rate (V), plasma arginine vasopressin (AVP) concentration (P_AVP) and urinary AVP concentration (U_AVP)
C) Urinary flow rate (V), plasma creatinine concentration (P_creatinine) and urinary creatinine concentration (U_creatinine)
D) Urinary flow rate (V), plasma urea concentration (P_urea) and urinary urea concentration (U_urea)
E) Urinary flow rate (V), plasma insulin concentration (P_insulin) and urinary insulin concentration (U_insulin)

Question 28

A 24-year-old bicyclist severely injures his right leg after colliding with an automobile. He is hemorrhaging from the wound but is stabilized, with a blood pressure of 90/40 mmHg and a heart rate of 100/min. He was not wearing protective head gear at the time of the accident, but shows no evidence of head trauma. His breathing is rapid and shallow. Blood pressure and urine flow could best be improved in this patient by:

A) Oral administration of diuretic
B) Administration of physiologic saline solution
C) Blood transfusion
D) Indirect cardiac massage
E) Intravenous injection of norepinephrine

Question 29

A 70-year-old man complains of weakness in his right leg. Physical examination is notable for hyperactive muscle stretch reflexes, a positive Babinski sign, and diffuse areas of weakness in his right leg. Although he can accurately distinguish sharp and dull pain in the right leg he is unable to distinguish these types of pain in his left leg. The most likely cause of these findings is a lesion in the:

A) Cerebellum
B) Internal capsule, left anterior limb
C) Left lateral funiculus
D) Reticular formation
E) Right frontal lobe

Question 30

Which of the following causes of brain hypoxia would most strongly stimulate the aortic and carotid chemoreceptors?

A) Carbon monoxide poisoning
B) Severe anemia
C) Formation of methemoglobin
D) A marked decrease in pulmonary diffusing capacity
E) Acute respiratory alkalosis

Question 31

A tall, obese 14-year-old boy with long arms has bilateral gynecomastia, decreased testicular size for his age, and sparse axillary and pubic hair. A buccal smear preparation shows a single Barr body extending off the nuclear membrane of many squamous cells. Which of the following sets of laboratory studies would be expected in this patient?

A) $\text { High} \quad \text { High } \quad \text { Low}$

B) $\text {High } \quad \text { Normal } \quad \text { Normal }$
C) $\text {Low } \quad \text {Low } \quad \text { Low }$
D) $\text {Normal } \quad \text {High } \quad \text { Low }$

E) $\text {Low } \quad \text {Low } \quad \text { High}$

Question 32

A 58-year-old woman has left hemiparesis and right ptosis (droopy eyelids). She cannot adduct, elevate, or depress her right eye. The most likely cause of these findings is a lesion in which of the following sites?

A) Cavernous sinus
B) Cerebral cortex
C) Left genu of the internal capsule
D) Mesencephalon
E) Right occipital lobe

Question 33

A 74-year-old comatose man, exhibits flexion of the left upper extremity with passive movement of the head to the right, and flexion of the right upper extremity when the head is moved to the left. His legs are fixed in extension during all movements. Which of the following is the most likely explanation of these findings?

A) Alternating hemiplegia syndrome
B) Brown-Séquard syndrome
C) Decerebrate rigidity
D) Decorticate rigidity
E) Transection of the spinal cord below vertebra TV

Question 34

A 23-year-old woman, who complains of chronic cough, shortness of breath, and chest tightness is diagnosed with asthma. Which of the following is the best clinical indicator of significant pulmonary obstruction in patients with asthma?

A) Arterial hypoxemia
B) Dyspnea
C) Forced expiratory volume in 1 second (FEV₁)/forced vital capacity (FVC) ratio of less than 75%
D) Large anatomic dead space volume
E) Rapid respirations

Question 35

A 45-year-old woman is concerned by a history of episodes of confusion and fainting over the past year that occur either on first arising in the morning or after exercising. The episodes are preceded or accompanied by shaking, sweating, and palpitations. The woman's husband has noticed that eating can prevent the onset of symptoms. Which of the following is the most likely cause of this patient's symptoms?

A) Autonomic insufficiency leading to orthostatic hypotension
B) Benign insulin-secreting tumor causing periodic hypoglycemia
C) Glucagon-secreting tumor causing periodic hypoglycemia
D) Meningioma in the region of the frontal cortex
E) Norepinephrine-secreting tumor causing periodic hyperglycemia

Question 36

A 30-year-old woman in her first trimester of pregnancy complains of easy fatigability, heat intolerance, and palpitations. Physical examination shows a slightly enlarged, nontender thyroid gland. Thyroid function studies show an increased total serum thyroxine (T₄) level, but normal serum thyroid-stimulating hormone (TSH) levels. Which of the following best explains the results of these studies?

A) Decreased thyroid-binding globulin (TBG)
B) Increased synthesis of T₄
C) Increased synthesis of triiodothyronine (T₃)
D) Thyroiditis-induced release of T₄
E) Normal finding in pregnancy

Question 37

A 30-year-old man with a family history of sudden cardiac death has a systolic murmur that increases in intensity when he is sitting up. An echocardiogram shows abnormal movement of the anterior mitral valve leaflet against an asymmetrically thickened interventricular septum. The mechanism for sudden cardiac death in this patient's family is most closely attributed to which of the following conditions?

A) Acute myocardial infarction (MI)
B) Congenital bicuspid aortic valve
C) Conduction system defect
D) Dissecting aortic aneurysm
E) Mitral valve prolapse (MVP)

Question 38

A 32-year-old female undergoes an appendectomy without complications, but has markedly reduced bowel sounds and an absence of flatus or defecation during the immediate postoperative period. Which of the following mechanisms best explains this decrease in bowel sounds?

A) Decreased sympathetic activity to the gut
B) Increased activity of the gastrocolic reflex
C) Increased parasympathetic activity to the gut
D) Increased plasma acetylcholine concentration
E) Increased plasma norepinephrine concentration

Question 39

A 25-year-old woman complains of chronic constipation and progressive weight gain over the past 6 months despite maintaining a pure vegan diet. Physical examination reveals a fatigued woman with brittle hair, face and eyelid puffiness, a symmetrically enlarged, non-tender thyroid gland, prolonged relaxation phase of deep tendon reflexes, and proximal muscle weakness in her lower extremities. Which set of the following results of thyroid function studies shown below would you expect in this patient? $$\begin{array} { l l l l } & \begin{array} { l } \text { Serum } \\\text { thyroxine } \\\left( \mathrm { T } _ { 4 } \right)\end{array} & \begin{array} { l } \text { Serum } \\\text { thyroid- } \\\text { stimulating } \\\text { hormone } \\\text { (TSH) }\end{array} & \begin{array} { l } 131 \mathrm { I } \\\text { (radioactive } \\\text { iodine) } \\\text { uptake }\end{array} \\\hline \text { A } & \text { Low } & \text { Low } & \text { Low } \\\mathrm { B } & \text { Low } & \text { High } & \text { Nomal } \\\mathrm { C } & \text { High } & \text { Low } & \text { Low } \\\mathrm { D } & \text { High } & \text { Low } & \text { High } \\\mathrm { E } & \text { Normal } & \text { Normal } & \text { Normal }\end{array}$$

A) $\text {Low}$ $\quad$$\quad$$\text {Low}$$\quad$ $\quad$$\text {Low}$
B) $\begin{array}{llcc} \text {Low } & \text { High } & \text { Normal }\\\end{array}$

C) $\begin{array}{llcc} \text { High } & \text {Low } & \text { Low } \\\end{array}$

D) $\text { High } \quad \text { Low } \quad \text { High }$
E) $\text { Normal } \quad \text { Normal } \quad \text { Normal }$

Question 40

A 56-year-old obese woman suffering from heartburn and regurgitation of acid saliva after large meals is treated with cimetidine. During cimetidine treatment, her serum creatinine concentration increases significantly. The increase in serum creatinine with cimetidine treatment is most likely due to:

A) Being reabsorbed by the nephron in exchange for creatinine
B) Blocking synthesis of creatinine by skeletal muscle
C) Causing acute renal failure
D) Competing with creatinine for renal tubular secretion
E) Inhibiting uptake of creatinine ingested with food

Question 41

If a healthy 70 kg man loses 2 L of sweat while doing yard work and simultaneously drinks 2 L of pure water, which of the following body fluid changes would be expected?

A) An increase in extracellular osmolarity
B) An increase in extracellular fluid (ECF) volume
C) An increase in intracellular osmolarity
D) An increase in intracellular fluid (ICF) volume
E) An increase in plasma Na⁺ concentration

Question 42

A 30-year-old man complains of progressive muscle weakness and double vision (diplopia) and some difficulty in swallowing solid foods. Neurologic studies show a neuromuscular conduction defect, and diagnostic studies with an intravenous injection of edrophonium are found to rapidly increase his muscle strength. When the patient is treated with neostigmine, his status improves. The most probable target molecule in this treatment is:

A) Acetylcholinesterase
B) Choline acetyltransferase
C) Monoamine oxidase
D) Muscarinic acetylcholine (ACh) receptor
E) Nicotinic ACh receptor

Question 43

A newborn presents with somewhat ambiguous external genitalia. The genitalia appear as an enlarged clitoris and a scrotum-like structure that appears to result from labial fusion. An ultrasound reveals normal ovarian development. The karyotype is 46 XX. The findings are most likely due to a deficiency in which one of the following enzymes?

A) 11 $\beta$ -hydroxylase
B) 16 $\alpha$ -hydroxylase
C) 17 $\alpha$ -hydroxylase
D) 21 $\alpha$ -hydroxylase
E) 3 $\beta$ -hydroxysteroid dehydrogenase

Question 44

A 25-year-old woman has had secondary amenorrhea for the past 8 months. She plans to get married soon, and states that she has been trying to lose weight for her upcoming wedding. A urine pregnancy test is negative. The patient is given an intramuscular injection of progesterone. Ten days later she reports that she has had no withdrawal bleeding. Laboratory studies show the following serum levels: $\begin{array}{|l|l|l|}\hline&&\text { Normal range }\\\hline \text { Prolactin } & 10 \mathrm{ng} / \mathrm{mL} & 5-10 \mathrm{ng} / \mathrm{mL} \\\hline \text { Follicle-stimulating hormone (FSH) } & 3 \mathrm{mUJ} / \mathrm{mL} & 5-15 \mathrm{~mL} / \mathrm{mL} \\\hline \text { Luteinizing hormone }(\mathrm{LH}) & 2 \mathrm{mUU} / \mathrm{mL} & 5-22 \mathrm{mLU} / \mathrm{mL} \\\hline \text { Thyroid-stimulating hormone }(\mathrm{TSH}) & 4.1 \mu \mathrm{m} / \mathrm{mL} & 10 \mu \mathrm{mL} / \mathrm{mL} \\\hline \text { Estradiol } & 1 \mathrm{ng} / 24 \mathrm{~h} & 0-14 \mathrm{ng} / 24 \mathrm{~h} \\\hline \text { Cortisol (a.m.) } & 35 \mu \mathrm{gL} & 5-25 \mu \mathrm{dL} / \mathrm{dL} \\\hline \text { Growth hormone } & 10 \mathrm{ng} / \mathrm{mL} & <5 \mathrm{ng} / \mathrm{mL}\\\hline\end{array}$
Which of the following is the most likely diagnosis?

A) Acromegaly
B) Cushing's syndrome
C) Hypopituitarism
D) Primary ovarian disease
E) Weight loss syndrome

Question 45

A middle-aged woman has had asthma since childhood and has been a heavy smoker since her early teens. During the past few years, she has experienced progressive dyspnea (breathing difficulty) and somnolence (sleepiness). Physical examination reveals a cachectic (general ill health and malnutrition) female with shortness of breath, prolonged expirations, and frequent coughing. Laboratory data are as follows: arterial pH 7.35; arterial HCO₃^- 32 mEq/L; arterial PCO₂ 60 mmHg; and arterial PO₂, 60 mmHg. Which of the following is a likely diagnosis?

A) Acute metabolic acidosis with renal compensation
B) Acute respiratory acidosis without renal compensation
C) Chronic metabolic acidosis with considerable renal compensation
D) Chronic respiratory acidosis with considerable renal compensation
E) Respiratory acidosis with metabolic acidosis

Question 46

A 60-year-old man develops an acute onset of confusion, ataxia, nystagmus, and hypothermia shortly after the administration of an intravenous solution containing 5% glucose and normal saline. The pathogenesis of this patient's neurologic disorder is most closely related to which of the following conditions?

A) Central pontine myelinolysis
B) Purkinje cell atrophy
C) Thiamine deficiency
D) Viral encephalitis
E) Vitamin B₁₂ deficiency

Question 47

A 50-year-old woman has diminished sensation in the left part of her face and eyelid. She feels no pain in her left cornea and has no tearing in that eye. A lesion in which of the following areas is most likely to cause these findings?

A) Left frontal lobe
B) Left motor nucleus of the trigeminal nerve (CN V)
C) Left ventral posterolateral (VPL) nucleus of the thalamus
D) Ophthalmic division of the left trigeminal nerve
E) Right nucleus of the trigeminal nerve

Question 48

A 60-year-old man comes to your office complaining of dyspnea (difficult breathing). His laboratory values are as follows: $\begin{array}{|l|l|l|}\hline& \text {Breathing}& \text {Breathing \( 100 \% \)}\\& \text {air}& \text {\(\mathrm{O}_{2} \text { for } 7 \text { minutes }\)} \\\hline \text { Arterial } \mathrm{PO}_{2}(\mathrm{mmHg}) & 76 & 500 \\\hline \text { Arterial } \mathrm{PCO}_{2}(\mathrm{mmHg}) & 55 & 65 \\\hline \text { Arterial } \mathrm{Hb}(\mathrm{g} / 100 \mathrm{~mL}) & 18 & 18 \\\hline \text { Arterial } \mathrm{O}_{2} \text { saturation (\%) } & 85 & 100 \\\hline \text { Arterial } \mathrm{pH} & 7.35 & 7.20\\\hline\end{array}$
Which of the following diagnoses best explains the laboratory test findings?

A) Patent ductus arteriosus
B) Patent foramen ovale
C) Complete obstruction of the right bronchus
D) Thickened alveolar membrane impairing diffusion
E) Pulmonary fibrosis restricting lung movement

Question 49

A 46-year-old man complains of progressive muscle weakness. Laboratory studies show a serum pH of 7.6, HCO₃^- of 32 mEq/L, and an elevated plasma aldosterone concentration. The most likely cause of muscle weakness in this patient is:

A) Hyperchloremia
B) Hyperkalemia
C) Hypocalcemia
D) Hypokalemia
E) Hyponatremia

Question 50

A middle-aged man is evaluated for polydipsia and polyuria. His 24-hour urine volume is 7.0 L with a low osmolality, and is negative for red blood cells, leukocytes, protein, and glucose. His blood pressure and heart rate are both normal. Which of the following is a likely cause of polyuria in this patient?

A) Acute attack of diabetes mellitus without glucosuria
B) Acute renal failure with a severe decrease in glomerular filtration rate (GFR)
C) Cerebrovascular accident damaging the anterior pituitary gland
D) Renal supersensitivity to the effects of antidiuretic hormone (ADH)
E) Suppression of ADH secretion due to polydipsia