GEM Module 3 Mock

A 55-year-old man is diagnosed with lung cancer. During a surgical procedure, he suffers an injury to a nerve that hooks under the arch of the aorta. Which of the following findings is most likely on examination?

• Weakness of the trapezius muscle
• Hoarseness of voice and dysphagia
• Inability to shrug the shoulders
• Winged scapula
• Diaphragmatic paralysis

Answer explanation

The nerve that hooks under the arch of the aorta is the left recurrent laryngeal nerve, a branch of the vagus nerve. It hooks under the ligamentum arteriosum (the remnant of the ductus arteriosus, which was the left 6th aortic arch). Injury to this nerve paralyzes the ipsilateral vocal cord, leading to hoarseness, and can affect pharyngeal muscles, causing dysphagia.

A medical student is revising the embryological origins of heart structures. Which of the following adult structures is derived from the sinus venosus?

• Trabeculated part of the left ventricle
• Ascending aorta
• Mitral valve
• Smooth posterior wall of the right atrium
• Muscular interventricular septum

Answer explanation

The sinus venosus contributes to the smooth-walled parts of the atria, specifically the posterior walls. It also forms the coronary sinus and the sino-atrial (SA) node. The trabeculated ventricles come from the primitive ventricle and bulbus cordis, the ascending aorta from the truncus arteriosus, the valves from endocardial cushions, and the muscular septum from the primitive ventricle.

During a tutorial on aortic arch derivatives, a student is asked about the fate of the fourth pharyngeal arch artery. Which of the following is the correct paired derivative?

• Left: Arch of the aorta; Right: Proximal right subclavian artery
• Left: Ductus arteriosus; Right: Degenerates
• Left: Common carotid artery; Right: Common carotid artery
• Left: Degenerates; Right: Arch of the aorta
• Left: Proximal left subclavian; Right: Ductus arteriosus

Answer explanation

The 4th aortic arch pairs have asymmetric fates. On the left, it forms part of the arch of the aorta (between the left common carotid and left subclavian arteries). On the right, it forms the proximal part of the right subclavian artery. The ductus arteriosus is derived from the 6th arch.

A newborn is diagnosed with a post-ductal coarctation of the aorta. Which of the following classic signs is most likely to be found on physical examination?

• Cyanosis of the lower limbs
• Radio-femoral delay
• Loud, single second heart sound
• Mid-diastolic murmur
• Pansystolic murmur at the apex

Answer explanation

In post-ductal (adult-type) coarctation, the narrowing is just after the left subclavian artery origin. This results in higher blood pressure in the upper limbs (supplied by arteries proximal to the coarctation) compared to the lower limbs. This manifests as radio-femoral delay (a delayed and weaker femoral pulse compared to the radial pulse) and hypertension in the upper limbs.

Which of the following structures is the postnatal remnant of the umbilical vein?

• Ligamentum arteriosum
• Ligamentum venosum
• Medial umbilical ligaments
• Ligamentum teres
• Fossa ovalis

Answer explanation

The umbilical vein carries oxygenated blood from the placenta to the fetus. After birth, it degenerates into the ligamentum teres (round ligament), which is found in the free edge of the falciform ligament. The ligamentum arteriosum is from the ductus arteriosus, the ligamentum venosum is from the ductus venosus, the medial umbilical ligaments are from the umbilical arteries, and the fossa ovalis is from the foramen ovale.

A 25-year-old athlete has a resting heart rate of 45 bpm and a stroke volume of 120 mL. What is his approximate cardiac output?

• 4.0 L/min
• 5.4 L/min
• 6.0 L/min
• 6.8 L/min
• 7.2 L/min

Answer explanation

Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV). CO = 45 bpm × 0.120 L/beat = 5.4 L/min. This is within the normal range for cardiac output, which is typically around 5 L/min, and demonstrates the athlete's high stroke volume compensating for a low resting heart rate.

A patient with a history of hypertension has a blood pressure reading of 170/100 mmHg. What is his calculated mean arterial pressure (MAP)?

• 113 mmHg
• 123 mmHg
• 135 mmHg
• 140 mmHg
• 157 mmHg

Answer explanation

MAP = Diastolic BP + 1/3(Pulse Pressure). Pulse Pressure = Systolic - Diastolic = 170 - 100 = 70 mmHg. Therefore, MAP = 100 + (70/3) ≈ 100 + 23.3 = 123.3 mmHg.

A 60-year-old man with heart failure is found to have elevated levels of B-type natriuretic peptide (BNP). From which cardiac cells is BNP primarily secreted?

• Atrial myocytes
• Sino-atrial (SA) node cells
• Ventricular myocytes
• Coronary artery endothelial cells
• Purkinje fibres

Answer explanation

While atrial natriuretic peptide (ANP) is primarily secreted by the atria, B-type natriuretic peptide (BNP) is primarily secreted by the ventricular myocytes in response to ventricular wall stretch and volume overload, which is characteristic of heart failure.

Which of the following best describes the primary mechanism of increased coronary blood flow during exercise?

• Sympathetic alpha-adrenergic mediated vasoconstriction
• A sharp rise in diastolic blood pressure
• Metabolic hyperaemia due to local vasodilators
• A significant increase in systolic blood pressure
• Parasympathetic vasodilatory signals

Answer explanation

During exercise, the heart's oxygen demand increases. This leads to local metabolic factors such as hypoxia, adenosine, K+, H+, and CO2 which cause potent vasodilation of the coronary arteries. This metabolic hyperaemia overrides any sympathetic vasoconstriction.

According to the Starling forces, which of the following changes would most directly promote the formation of peripheral oedema?

• A decrease in interstitial hydrostatic pressure (Pi)
• An increase in plasma oncotic pressure (πc)
• A decrease in capillary hydrostatic pressure (Pc)
• An increase in capillary hydrostatic pressure (Pc)
• A decrease in interstitial oncotic pressure (πi)

Answer explanation

Net Filtration Pressure (NFP) = (Pc + πi) - (πc + Pi). An increase in Pc (capillary hydrostatic pressure) directly increases the outward driving force, favouring filtration of fluid into the interstitium and causing oedema. This is a key mechanism in right-sided heart failure.