Thorax — MCQs

Thorax Indian Medical PG Practice Questions and MCQs

Question 611: The incidence of a foreign body being aspirated into the right lung is higher than into the left lung. All of the following statements support this, EXCEPT?

A. Tracheal bifurcation directs the foreign body to the right lung
B. Right lung is shorter and wider than left lung (Correct Answer)
C. Right inferior lobar bronchus is in continuation with the right principal bronchus
D. Right principal bronchus is more vertical than the left bronchus

Explanation: ***Right lung is shorter and wider than left lung*** - This statement, while anatomically true, does **NOT directly explain** why foreign bodies preferentially enter the right lung - The dimensions of the **lung parenchyma itself** (shorter due to the diaphragm being pushed up by the liver, and wider) are unrelated to aspiration patterns - What determines aspiration is the **bronchial tree geometry** (angle, diameter, verticality), not the overall lung size - This is the EXCEPTION - it's a true anatomical fact but doesn't support the aspiration phenomenon *Incorrect - Tracheal bifurcation directs the foreign body to the right lung* - This statement DOES support higher right aspiration, so it cannot be the answer - The **carina angle** and bifurcation geometry favor the right side, directing foreign bodies preferentially to the right main bronchus - This is a key anatomical reason for the higher incidence *Incorrect - Right inferior lobar bronchus is in continuation with the right principal bronchus* - This statement DOES support higher right aspiration - After the right superior lobar bronchus branches off, the **intermediate bronchus** continues more directly toward the inferior lobe - This creates a straighter pathway from trachea → right main bronchus → intermediate bronchus → inferior lobar bronchus - Foreign bodies follow this direct path, often lodging in the right inferior lobe *Incorrect - Right principal bronchus is more vertical than the left bronchus* - This statement DOES support higher right aspiration - The right main bronchus diverges at approximately **25 degrees** from vertical, while the left diverges at **45 degrees** - This more vertical orientation makes the right bronchus a more direct continuation of the trachea - Gravity and airflow naturally direct aspirated material down this straighter path

Question 612: Left superior intercostal vein drains into?

A. Brachiocephalic vein (Correct Answer)
B. Hemiazygos vein
C. Internal thoracic vein
D. Azygos vein

Explanation: ***Brachiocephalic vein*** - The **left superior intercostal vein** is formed by the confluence of the **2nd and 3rd** left posterior intercostal veins. - It typically drains into the **left brachiocephalic vein**, which then contributes to the superior vena cava. *Hemiazygos vein* - The **hemiazygos vein** is on the left side of the vertebral column and primarily drains the lower left posterior intercostal veins (9th-11th). - It usually joins the **azygos vein** around the T8-T9 vertebral level, rather than directly receiving the left superior intercostal vein. *Internal thoracic vein* - The **internal thoracic veins** drain the anterior sensory chest wall and typically run alongside the sternum. - While they eventually drain into the brachiocephalic veins, they do not directly receive the posterior intercostal veins like the left superior intercostal vein. *Azygos vein* - The **azygos vein** is primarily on the right side of the vertebral column, draining the right posterior intercostal veins. - It usually receives the **hemiazygos** and **accessory hemiazygos veins** but not the left superior intercostal vein directly.

Question 613: Which of the following structures is NOT innervated by the phrenic nerve?

A. Diaphragm
B. Mediastinal pleura
C. Serratus anterior (Correct Answer)
D. Pericardium

Explanation: ***Serratus anterior*** - The **serratus anterior** muscle is innervated by the **long thoracic nerve (roots C5, C6, C7)**, not the phrenic nerve. - Its primary actions are to protract and rotate the scapula, and it is crucial for overhead arm movements. *Diaphragm* - The **diaphragm** is primarily innervated by the **phrenic nerve (C3, C4, C5)**, which is essential for its role in respiration [1]. - Sensory fibers from the phrenic nerve also supply the central part of the diaphragm. *Mediastinal pleura* - The **mediastinal pleura**, which lines the mediastinum, receives sensory innervation from the **phrenic nerve**. - Irritation of this pleura can cause referred pain to the shoulder, due to shared innervation origins. *Pericardium* - The **fibrous pericardium** and the **parietal layer of the serous pericardium** are innervated by the **phrenic nerves**. - This innervation accounts for referred pain to the shoulder in conditions affecting the pericardium.

Question 614: The pleura extends down to which rib at the midclavicular line?

A. 6th rib
B. 10th rib
C. 12th rib
D. 8th rib (Correct Answer)

Explanation: ***8th rib*** - The **parietal pleura** extends to the **8th rib** at the **midclavicular line**, marking the inferior border of the pleural cavity in this region. [1] - This creates the **costodiaphragmatic recess** below the lung border, which extends only to the 6th rib at the midclavicular line. [1] - Understanding these anatomical landmarks is crucial for procedures like **thoracentesis** to avoid lung injury while accessing the pleural space. [1] *6th rib* - The **lung** (not pleura) extends to the **6th rib** at the **midclavicular line**. - The pleura extends approximately **two rib spaces lower** than the lung to create the costodiaphragmatic recess. - This is an important distinction for safe needle placement during thoracentesis. *10th rib* - The **parietal pleura** extends to the **10th rib** at the **midaxillary line**, not the midclavicular line. - This represents a more lateral and inferior extension of the pleural cavity. *12th rib* - The **parietal pleura** extends to the **12th rib** at the **paravertebral (scapular) line**, which is the most posterior and inferior extension. - This is significantly lower and more posterior than the midclavicular line.

Question 615: Which of the following statements is true regarding the anatomy of the breast?

A. The superior medial quadrant has more tissue
B. The nipple is located at the level of the fourth intercostal space in most women
C. There are 15-20 lobules present
D. The axillary tail of Spence crosses the anterior axillary fold (Correct Answer)

Explanation: ***The axillary tail of Spence crosses the anterior axillary fold*** - The **axillary tail of Spence** is an extension of breast glandular tissue that passes superolaterally from the main breast body and often **penetrates the deep fascia** in the axilla [3]. - Its presence crossing the **anterior axillary fold** is relevant for physical examination and surgical considerations, as it can be a site for breast pathologies. *The superior medial quadrant has more tissue* - The **superior lateral quadrant** of the breast typically contains the **most glandular tissue** and lymphatics, making it the most common site for breast cancers. - This anatomical distribution is crucial for understanding the **etiology and metastasis** of breast malignancies. *The nipple is located at the level of the fourth intercostal space in most women* - The **nipple** typically lies at the level of the **fourth rib (not intercostal space)** in nulliparous women, but its position can vary significantly based on individual factors like breast size, age, and parity [1]. - Topographical landmarks such as the **midclavicular line** are often used for more consistent localization. *There are 15-20 lobules present* - Each breast typically contains **15-20 lobes**, not lobules, arranged radially around the nipple [1]. - Each **lobe** consists of numerous smaller **lobules**, which are the functional units of milk production, draining into ducts that converge at the nipple [2].

Question 616: Which heart chamber has the thickest wall?

A. Right atrium
B. Left atrium
C. Left ventricle (Correct Answer)
D. Right ventricle

Explanation: ***Left ventricle*** - The left ventricle is responsible for pumping **oxygenated blood** to the entire systemic circulation, requiring significant force. - Its muscular wall is the **thickest** to generate the high pressures needed to overcome systemic vascular resistance [1]. *Right atrium* - The right atrium receives deoxygenated blood from the body and pumps it to the right ventricle, which is a **low-pressure circuit** [2]. - Its walls are relatively thin compared to the ventricles, as it only needs to provide a small "kick" to fill the right ventricle. *Left atrium* - The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle, operating under **low pressure**. - Its walls are thin, similar to the right atrium, as it does not need to generate high pressures. *Right ventricle* - The right ventricle pumps deoxygenated blood to the **pulmonary circulation**, which is a **low-pressure system** [1]. - While thicker than the atria, its wall is thinner than the left ventricle because it faces less resistance and pumps against lower pressures to the lungs.

Question 617: Which muscle is involved in elevating the ribs during inspiration?

A. External intercostal muscles (Correct Answer)
B. Internal intercostal muscles
C. Transversus thoracis
D. Rectus abdominis

Explanation: ***External intercostal muscles*** - The **external intercostal muscles** contract during **inspiration**, pulling the ribs upwards and outwards [1]. - This action increases the **thoracic volume**, leading to a decrease in intrathoracic pressure and allowing air to flow into the lungs [1]. *Internal intercostal muscles* - The **internal intercostal muscles** are primarily active during **forced expiration**, pulling the ribs downwards and inwards. - Their contraction decreases the **thoracic volume**, helping to expel air from the lungs. *Transversus thoracis* - The **transversus thoracis** muscle is a thin muscle lying on the inside of the anterior chest wall. - It is involved in **forced expiration** by depressing the ribs. *Rectus abdominis* - The **rectus abdominis** is a major muscle of the anterior abdominal wall. - It is involved in **forced expiration** by pulling the rib cage downwards and compressing the abdominal contents, which in turn pushes the diaphragm upwards.

Question 618: Identify the muscle that assists in both breathing and changes in the volume of the thoracic cavity.

A. External oblique
B. Diaphragm (Correct Answer)
C. Rectus abdominis
D. Internal intercostal

Explanation: ***Diaphragm*** - The **diaphragm** is the primary muscle of inspiration, and its contraction causes it to flatten, increasing the **vertical diameter** of the thoracic cavity [1]. - This increase in thoracic volume leads to a decrease in intrapleural pressure, drawing air into the lungs [1]. *External oblique* - The **external oblique** is an abdominal muscle involved in forced expiration by compressing the abdominal contents and pushing the diaphragm upwards. - It does not directly affect the initial increase in thoracic volume during quiet breathing. *Rectus abdominis* - The **rectus abdominis** is an abdominal muscle that aids in forced expiration by pulling the sternum and rib cage downwards, thereby decreasing thoracic volume. - It is not a primary muscle involved in increasing thoracic volume for inspiration. *Internal intercostal* - The **internal intercostals** are primarily involved in forced expiration, pulling the ribs downwards and inwards to decrease the thoracic volume. - During quiet inspiration, the **external intercostals** elevate the ribs to increase thoracic volume, not the internal intercostals [1].

Question 619: Which nerve is primarily responsible for the motor supply to the diaphragm?

A. Phrenic nerve (Correct Answer)
B. Cervical spinal roots C3, C4, and C5
C. Accessory nerve
D. Intercostal nerves

Explanation: ***Phrenic nerve*** - The **phrenic nerve** is the sole **motor supply** for the diaphragm, originating from the **cervical spinal roots C3, C4, and C5** (primarily C4) [1], [2]. - Its stimulation causes the diaphragm to contract, which is essential for **inspiration** [1]. - The well-known mnemonic is **"C3, 4, 5 keeps the diaphragm alive"**. *Cervical spinal roots C3, C4, and C5* - This option describes the **origin** of the phrenic nerve, not the nerve itself. - The **phrenic nerve is formed** by fibers from these cervical spinal roots, but the question asks for the **nerve** that provides motor supply [2]. - These roots contribute to forming the nerve, but they are not the primary structure responsible for innervation. *Accessory nerve* - The **accessory nerve (Cranial Nerve XI)** primarily innervates the **sternocleidomastoid** and **trapezius muscles**. - It plays no direct role in the motor control of the diaphragm. *Intercostal nerves* - **Intercostal nerves** innervate the **intercostal muscles**, which contribute to breathing by moving the rib cage [2]. - They do not innervate the diaphragm; their function is distinct from the phrenic nerve.

Question 620: Which of the following passes posterior to the hilum of the lung?

A. Vagus (Correct Answer)
B. Phrenic nerve
C. SVC
D. Right atrium

Explanation: ***Vagus*** - The **vagus nerves** (cranial nerve X) descend through the neck and thorax, passing **posterior to the lung hila** as they contribute to the pulmonary plexus and then continue to the esophagus and abdominal viscera [2]. - They are primarily responsible for **parasympathetic innervation** to the thoracic and abdominal organs [1]. *Phrenic nerve* - The **phrenic nerves** (C3-C5) descend through the thorax, passing **anterior to the lung hila** and between the fibrous pericardium and the mediastinal pleura [2]. - They provide motor innervation to the **diaphragm** and sensory innervation to the central diaphragm, mediastinal pleura, and pericardium. *SVC* - The **superior vena cava (SVC)** is a large vein that drains blood from the upper body into the right atrium, situated in the superior mediastinum and passing **anterior to the right lung hilum** [2]. - Its position is medial and anterior to the structures of the hilum, not posterior. *Right atrium* - The **right atrium** is one of the four chambers of the heart, located in the middle mediastinum, **anterior to the lung hila** [2]. - It receives deoxygenated blood from the SVC, inferior vena cava (IVC), and coronary sinus.

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Thoracic Wall and Diaphragm

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Pleura and Lungs

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Mediastinum

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Heart and Pericardium

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Great Vessels and Azygos System

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Thoracic Duct and Lymphatics

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Autonomic Innervation

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Applied Anatomy and Clinical Correlations

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Thoracic Imaging and Cross-sectional Anatomy

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Embryological Development of Thoracic Structures

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