Thorax Practice Questions

Q: Which structure does not pass through the aortic opening?

Vagus nerve. The diaphragm has three major openings, and remembering the structures passing through them is high-yield for NEET-PG. The **Aortic Opening** is located at the level of the **T12** vertebra. It is an osseo-aponeurotic opening (not a muscular one), meaning it does not constrict during inspiration. ### Why the Vagus Nerve is the Correct Answer The **Vagus nerve (CN X)** does not pass through the aortic opening. Instead, the left and right vagus nerves form the esophageal plexus and enter the abdomen as the anterior and posterior vagal trunks by passing through the **Esophageal Opening** at the level of **T10**. ### Analysis of Incorrect Options * **Aorta:** As the name suggests, the Aorta is the primary structure passing through this opening to become the abdominal aorta. * **Azygos vein:** This vein ascends through the aortic opening on the right side of the aorta. * **Thoracic duct:** This major lymphatic vessel ascends through the aortic opening, typically situated between the aorta and the azygos vein. ### High-Yield NEET-PG Pearls To remember the structures passing through the Aortic Opening (T12), use the mnemonic **"AAT"**: 1. **A**orta 2. **A**zygos vein 3. **T**horacic duct **Summary of Major Diaphragmatic Openings:** * **Vena Caval (T8):** Inferior Vena Cava, Right Phrenic nerve. * **Esophageal (T10):** Esophagus, Vagus nerves, Esophageal branches of left gastric vessels. * **Aortic (T12):** Aorta, Azygos vein, Thoracic duct. *Clinical Note:* Because the aortic opening is behind the diaphragm (posterior to the median arcuate ligament), blood flow in the aorta is not compromised during diaphragmatic contraction.

Q: The interior of the right atrium is partially divided into two parts by which structure?

Crista terminalis. The interior of the right atrium is embryologically and anatomically divided into two distinct parts by the **crista terminalis**, a vertical muscular ridge. [1] ### 1. Why Crista Terminalis is Correct The crista terminalis serves as the internal boundary separating: * **Sinus Venarum:** The smooth-walled posterior part derived from the embryonic sinus venosus. It receives the SVC, IVC, and coronary sinus. [1] * **Atrium Proper:** The rough-walled anterior part derived from the primitive atrium, characterized by musculi pectinati. Externally, this ridge corresponds to a shallow groove called the **sulcus terminalis**. ### 2. Why Other Options are Incorrect * **Musculi Pectinati:** These are the parallel muscular ridges found only in the anterior part (atrium proper) and the auricle. They do not divide the atrium into two parts. * **Fossa Ovalis:** This is an oval depression on the interatrial septum, representing the site of the fetal foramen ovale. It separates the right atrium from the left atrium, not the interior of the right atrium itself. * **Sinus Venarum Cavarum:** This is the name of the smooth posterior *part* itself, not the dividing structure. ### 3. High-Yield NEET-PG Pearls * **SA Node Location:** The Sinoatrial (SA) node is located in the upper part of the sulcus terminalis, just below the opening of the SVC. * **Valve of IVC (Eustachian Valve):** Directs oxygenated blood from the IVC toward the foramen ovale in fetal life. * **Triangle of Koch:** Located in the right atrium; its boundaries are the **Tendon of Todaro**, the septal leaflet of the tricuspid valve, and the orifice of the coronary sinus. It contains the **AV node**.

Q: Which of the following is the uppermost structure in the hilum of the right lung?

Bronchus. In the anatomy of the lung hilum, the arrangement of structures differs between the right and left sides, which is a high-yield topic for NEET-PG. **Why Bronchus is Correct:** On the **right side**, the principal bronchus divides into two before entering the hilum: the **Eparterial bronchus** and the **Hyparterial bronchus**. The Eparterial bronchus (so named because it lies *above* the pulmonary artery) is the **uppermost structure** in the right hilum. [1] **Analysis of Incorrect Options:** * **Superior pulmonary vein:** This is the most **anterior** structure in both the right and left hila, but not the highest on the right. * **Bronchial artery:** These are small nutritional vessels usually located on the posterior aspect of the bronchi; they do not occupy the superior-most position. [1] * **Inferior pulmonary vein:** This is consistently the most **inferior** structure in the hilum of both lungs. **High-Yield NEET-PG Pearls:** 1. **Mnemonic for Superior-to-Inferior arrangement:** * **Right Hilum:** **B-A-V** (Eparterial **B**ronchus → Pulmonary **A**rtery → Pulmonary **V**ein). * **Left Hilum:** **A-B-V** (Pulmonary **A**rtery → **B**ronchus → Pulmonary **V**ein). Note that the Pulmonary Artery is the highest structure on the left. 2. **Anterior-to-Posterior arrangement:** This is identical for both lungs: **V-A-B** (Pulmonary **V**ein → Pulmonary **A**rtery → **B**ronchus). 3. **Pulmonary Ligament:** A fold of pleura extending downwards from the hilum that allows for the expansion of pulmonary veins during increased venous return.

Q: Occlusion of the left anterior descending artery will lead to infarction of which area?

Anterior wall of the left ventricle. The **Left Anterior Descending (LAD) artery**, often called the "widow-maker," is a branch of the Left Main Coronary Artery. It travels in the anterior interventricular groove and is the most common site of coronary occlusion. **Why the correct answer is right:** The LAD provides the primary blood supply to the **anterior wall of the left ventricle** and the **apex** of the heart. Additionally, it supplies the **anterior 2/3rd of the interventricular septum** via its septal branches. Therefore, occlusion leads to an anteroseptal myocardial infarction (MI). **Analysis of Incorrect Options:** * **A. Posterior part of the interventricular septum:** This area (the posterior 1/3rd) is supplied by the **Posterior Interventricular Artery**, which usually arises from the Right Coronary Artery (RCA) in right-dominant hearts. * **C. Lateral part of the heart:** This region is primarily supplied by the **Left Circumflex Artery (LCX)**. * **D. Inferior surface of the right ventricle:** The inferior (diaphragmatic) surface of the heart is supplied by the **Right Coronary Artery (RCA)**. **NEET-PG High-Yield Pearls:** 1. **Artery of Sudden Death:** The LAD is the most frequently occluded artery in MI (approx. 40–50% of cases). 2. **ECG Correlation:** LAD occlusion typically shows ST-elevation in leads **V1 to V4** [1]. 3. **Conductive System:** The LAD supplies the **Right Bundle Branch** and the **Anterior Fascicle** of the Left Bundle Branch; occlusion can lead to bundle branch blocks. 4. **Coronary Dominance:** Determined by which artery gives rise to the Posterior Interventricular Artery (85% RCA = Right Dominant).

Q: Humans commonly become infected by M.tuberculosis by which route?

Inhalation. **Explanation:** **Mycobacterium tuberculosis (M.tb)** is primarily an airborne pathogen. The correct answer is **Inhalation** because the infection is transmitted via "droplet nuclei" (1–5 micrometers in diameter). These tiny particles are expelled when an infected person coughs, sneezes, or speaks. Due to their small size, they bypass the upper airway's mucociliary defenses and reach the terminal alveoli of the lungs, where the primary infection (Ghon focus) is established. **Analysis of Incorrect Options:** * **Ingestion:** Historically, *M. bovis* was transmitted via unpasteurized milk, causing intestinal TB. However, *M. tuberculosis* is rarely transmitted this way as it is highly sensitive to gastric acid. * **Contact:** Direct skin contact does not transmit TB. It is not a contagious skin disease, though rare cutaneous manifestations exist via other routes. * **Inoculation:** This refers to direct accidental entry through the skin (e.g., "Prosector’s wart" in pathologists). While possible in occupational settings, it is an extremely rare route for the general population. **Clinical Pearls for NEET-PG:** * **Ghon Complex:** Consists of a parenchymal subpleural lesion (Ghon focus) + draining lymphadenopathy. * **Ranke Complex:** A healed, calcified Ghon complex visible on X-ray. * **Location:** Primary TB typically affects the lower part of the upper lobe or upper part of the lower lobe. Secondary (Reactivation) TB favors the **apical segments** of the upper lobes due to higher oxygen tension ($P_{a}O_{2}$), which favors the obligate aerobe *M. tuberculosis*. * **Infectivity:** A single cough can release up to 3,000 droplet nuclei; only 10 bacilli are needed to initiate infection in a susceptible host.

Q: The hilum of the right lung is arched by which structure?

Azygos vein. ### Explanation The correct answer is **B. Azygos vein**. **1. Why the Azygos Vein is Correct:** The anatomical relations of the lung hila are high-yield topics for NEET-PG. On the **right side**, the azygos vein travels superiorly along the vertebral column and then arches anteriorly over the **root (hilum) of the right lung** to drain into the Superior Vena Cava (SVC) [1]. This arching occurs at the level of the 4th thoracic vertebra (T4). **2. Why the Other Options are Incorrect:** * **Recurrent laryngeal nerve:** The right recurrent laryngeal nerve loops under the right subclavian artery, while the left loops under the arch of the aorta [3]. Neither arches over the lung hilum. * **Thoracic duct:** This structure ascends in the posterior mediastinum between the azygos vein and the aorta. It arches over the apex of the left lung (not the hilum) to enter the junction of the left internal jugular and subclavian veins. * **Vagus nerve:** Both the right and left vagus nerves pass **posterior** to the lung roots to form the pulmonary plexuses; they do not "arch over" the hilum [2]. **3. Clinical Pearls & High-Yield Facts:** * **Left Lung Comparison:** The structure that arches over the **left lung hilum** is the **Arch of the Aorta** [3]. * **Azygos Lobe:** Occasionally, the azygos vein fails to migrate medially and instead cuts through the apex of the right lung, creating an accessory "Azygos Lobe" (visible on X-ray as the azygos fissure). * **Phrenic vs. Vagus:** A common exam trap—the **Phrenic nerve** passes **anterior** to the lung hilum, while the **Vagus nerve** passes **posterior** to it [2].

Q: Hassall's corpuscles are seen in which organ?

Thymus. **Explanation:** **Hassall’s corpuscles** (also known as thymic corpuscles) are the histological hallmark of the **Thymus**. They are located specifically in the **medulla** of the thymus. Structurally, they are spherical clusters of flattened epithelial reticular cells arranged concentrically, often showing central keratinization or calcification. Their primary function is the production of cytokines (like TSLP) that aid in the development of regulatory T-cells. **Analysis of Incorrect Options:** * **B. Thyroid:** The histological features of the thyroid include follicles lined by follicular cells and filled with colloid, along with parafollicular (C) cells [1]. * **C. Parathyroid:** This gland consists primarily of Chief cells (which secrete PTH) and Oxyphil cells. It does not contain concentric epithelial structures. * **D. Spleen:** The spleen is characterized by White pulp (containing PALS and Malpighian corpuscles) and Red pulp (containing splenic sinusoids and cords of Billroth) [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** The thymus develops from the **3rd pharyngeal pouch**. * **Blood-Thymus Barrier:** This exists only in the **cortex**, not the medulla; this is why Hassall’s corpuscles are found in the medulla where mature T-cells reside. * **Age Involution:** The thymus is most active in childhood and undergoes "fatty infiltration" or involution after puberty, though Hassall’s corpuscles persist throughout life [2]. * **DiGeorge Syndrome:** Characterized by the failure of the 3rd and 4th pouches to develop, leading to thymic aplasia and T-cell deficiency.

Q: What is the normal diameter of the tricuspid orifice?

4 cm. The **tricuspid orifice** is the largest of the four cardiac valves, located between the right atrium and the right ventricle. In a healthy adult, the normal diameter of the tricuspid valve is approximately **4 cm** (with a normal valve area of 7–9 cm²). **Why Option D is Correct:** The tricuspid valve is structurally larger than the mitral valve because the right-sided chambers handle higher volumes of blood at lower pressures compared to the left side [1]. A diameter of **4 cm** (or roughly the width of three fingers) is the standard anatomical measurement for a patent, non-stenotic tricuspid orifice. **Why Other Options are Incorrect:** * **Options A & B (2 cm & 2.5 cm):** These values are too small for a normal tricuspid valve. A diameter in this range would indicate significant **tricuspid stenosis**, which clinically manifests when the valve area drops below 2.0 cm². * **Option C (3 cm):** While 3 cm is closer to the diameter of the **mitral valve** (which is typically 3–3.5 cm), it is still undersized for the tricuspid valve. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of Thumb:** The tricuspid valve is the "three-finger valve," while the mitral valve is the "two-finger valve." * **Surface Anatomy:** The tricuspid valve is best auscultated at the **left 4th or 5th intercostal space** at the lower left sternal border. * **Clinical Sign:** Tricuspid stenosis is rare and usually rheumatic in origin; it is characterized by a mid-diastolic murmur that **increases with inspiration** (Carvallo’s sign), distinguishing it from mitral stenosis.

Question 1

Which structure does not pass through the aortic opening?

Accepted Answer

Vagus nerve

Answer

Aorta

Answer

Azygos vein

Answer

Thoracic duct

Question 2

The interior of the right atrium is partially divided into two parts by which structure?

Accepted Answer

Crista terminalis

Answer

Musculi pectinati

Answer

Fossa ovalis

Answer

Sinus venarum cavarum

Question 3

Which of the following is the uppermost structure in the hilum of the right lung?

Accepted Answer

Bronchus

Answer

Superior pulmonary vein

Answer

Bronchial artery

Answer

Inferior pulmonary vein

Question 4

Occlusion of the left anterior descending artery will lead to infarction of which area?

Accepted Answer

Anterior wall of the left ventricle

Answer

Posterior part of the interventricular septum

Answer

Lateral part of the heart

Answer

Inferior surface of the right ventricle

Question 5

Humans commonly become infected by M.tuberculosis by which route?

Accepted Answer

Inhalation

Answer

Ingestion

Answer

Contact

Answer

Inoculation

Question 6

At the level of the arch of the aorta, what is the anatomical relationship between the left vagus nerve and the left phrenic nerve?

Accepted Answer

Left phrenic nerve is anterior and the left vagus nerve is posterior.

Answer

Left phrenic nerve is posterior and the left vagus nerve is anterior.

Answer

Both nerves are in the same plane anteroposteriorly.

Answer

The relationship between the nerves is variable.

Question 7

The hilum of the right lung is arched by which structure?

Accepted Answer

Azygos vein

Answer

Recurrent laryngeal nerve

Answer

Thoracic duct

Answer

Vagus nerve

Question 8

Hassall's corpuscles are seen in which organ?

Accepted Answer

Thymus

Answer

Thyroid

Answer

Parathyroid

Answer

Spleen

Question 9

A 3-day-old newborn was born with ectopia cordis. Despite intensive care efforts, the infant died from cardiac failure and hypoxemia. Which of the following embryologic events is most likely responsible for the development of this condition?

Accepted Answer

Faulty development of the sternum and pericardium, secondary to incomplete fusion of the lateral folds

Answer

Interruption of third pharyngeal arch development

Answer

Interruption of fourth pharyngeal arch development

Answer

Interruption of fifth pharyngeal arch development

Question 10

What is the normal diameter of the tricuspid orifice?

Accepted Answer

4 cm

Answer

2 cm

Answer

2.5 cm

Answer

3 cm

Thorax — MCQs

Thorax — MCQs

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