Respo – Anatomy

✅ Correct Answer: Phrenic nerve

Explanation:
The phrenic nerve (C3–C5) is the sole motor nerve supply to the diaphragm, the main muscle of inspiration.

• It originates mainly from the C4 spinal segment, with contributions from C3 and C5, remembered by the mnemonic “C3, 4, and 5 keep the diaphragm alive.”

• Injury to the phrenic nerve results in paralysis of the corresponding half of the diaphragm, which then moves upward (paradoxically) during inspiration due to unopposed pressure from the abdominal viscera.

• Such injury may occur during neck surgery, trauma, or mediastinal tumors compressing the nerve.

❌ Recurrent laryngeal nerve
A branch of the vagus nerve, it supplies the laryngeal muscles for phonation and airway protection — not the diaphragm.

❌ Supraclavicular nerve
A sensory nerve from the cervical plexus (C3–C4) that supplies skin over the shoulder and upper chest, not the diaphragm.

❌ Sympathetic trunk
Carries autonomic fibers controlling visceral and vascular tone, but has no role in diaphragm movement.

❌ Esophageal plexus
Formed by fibers of the vagus nerve, it supplies the esophagus and related structures, not the diaphragm’s motor control.

✅ Correct Answer: Sternal angle

Explanation:
The trachea bifurcates (divides into the right and left main bronchi) at the level of the sternal angle, which corresponds to the intervertebral disc between the T4 and T5 vertebrae.
At this point, an internal ridge called the carina marks the site of bifurcation — it is a sensitive area that triggers the cough reflex when irritated.

This anatomical landmark (the Angle of Louis) is important clinically and radiologically because it also corresponds to:

• The beginning and end of the aortic arch,

• The upper limit of the pericardium, and

• The division between the superior and inferior mediastinum.

❌ Gastroesophageal junction
Located much lower, around the T10–T11 level, where the esophagus enters the stomach — unrelated to tracheal anatomy.

❌ T4
Partially correct in reference, but the tracheal bifurcation is more precisely at the T4–T5 intervertebral disc, identified externally by the sternal angle.

❌ T6
Too low — this level is below the tracheal bifurcation, closer to the diaphragm.

❌ T3
Too high — the trachea lies higher in the neck and upper thorax at this level, not yet bifurcated.

✅ Correct Answer: Right bronchus

Explanation:
The right main bronchus is the most common site for foreign body aspiration because of its anatomical orientation:

• It is wider, shorter, and more vertical than the left bronchus.

• When a person inhales or accidentally aspirates an object, gravity and airflow dynamics favor entry into the right bronchial tree, particularly the right lower lobe bronchus in an upright person.

In children, this is clinically important because they frequently aspirate small objects such as coins, peanuts, or toy parts, leading to wheezing, coughing, or localized pneumonia if not promptly removed.

❌ Lobule of lung
Too distal — a large foreign body like a coin cannot reach this far into the lung parenchyma.

❌ Left bronchus
It is longer, narrower, and more horizontal, making foreign body entry less likely.

❌ Bronchioles
They are too small for a coin to pass into; only very small particles can reach this level.

❌ Trachea
A coin lodged in the trachea would cause immediate severe respiratory distress and stridor, not localized wheezing.

✅ Correct Answer: Has its own vein

Explanation:
A bronchopulmonary segment is the smallest functional and anatomical unit of the lung that can be surgically removed without affecting other segments.
Each segment is:

• Pyramidal in shape, with its apex facing the hilum and base toward the pleural surface.

• Supplied by its own segmental (tertiary) bronchus and segmental branch of the pulmonary artery — making it an independent functional unit for ventilation and perfusion.

However, pulmonary veins do not run within the segment. They lie in the connective tissue between adjacent segments and therefore drain more than one segment. This is why a bronchopulmonary segment does not have its own vein.

❌ Independent functional unit
True — each segment has its own airway and blood supply, functioning semi-independently.

❌ Segmental bronchus
True — each segment receives air through its own segmental bronchus branching from the lobar bronchus.

❌ Has its own artery
True — supplied by a segmental branch of the pulmonary artery accompanying the bronchus.

❌ Pyramidal in shape
True — the shape helps in surgical identification and removal during segmentectomy.

✅ Correct Answer: Above 1st rib

Explanation:
The apex of the lung extends into the root of the neck, above the level of the first rib and clavicle. It rises about 2.5 cm (1 inch) above the medial third of the clavicle, just posterior to the sternocleidomastoid muscle.
It is covered by a tough membrane called the suprapleural membrane (Sibson’s fascia), which protects it from injuries and maintains pleural integrity during respiration.

Clinically, this is important because penetrating injuries to the root of the neck (e.g., stab wounds or central line insertions) can damage the lung apex, causing pneumothorax.

❌ Below root of neck
The apex lies within the root of the neck, not below it.

❌ Below clavicle
It actually extends above the clavicle, not below it.

❌ Above 2nd rib
This is too low; the apex is above the 1st rib, not the 2nd.

❌ Below C1
The apex does not reach as high as the level of C1 vertebra; it’s closer to the neck of the 1st rib (around T1).

✅ Correct Answer: 1

Explanation:
The 1st rib is the shortest, broadest, and most curved of all ribs and has two distinct grooves on its superior surface separated by a small ridge called the scalene tubercle.

• The anterior groove transmits the subclavian vein, while

• The posterior groove transmits the subclavian artery and the lower trunk of the brachial plexus.

The scalenus anterior muscle inserts into the scalene tubercle between these grooves. This anatomical arrangement is crucial in understanding thoracic outlet anatomy, where compression of these structures can cause neurovascular symptoms.

❌ 2
The 2nd rib has a tuberosity for the serratus anterior muscle and is longer and thinner than the 1st rib. It does not have grooves for the subclavian vessels.

❌ 3
A typical rib, lacking any grooves for the subclavian artery or vein.

❌ 4
Also a typical rib; no special features for the subclavian artery.

❌ 6
A typical rib as well, with no grooves for subclavian structures.

✅ Correct answer: Mediastinal pleura

Explanation:

The phrenic nerve (C3–C5) provides somatic sensory innervation to the mediastinal pleura and the central part of the diaphragmatic pleura. These areas can transmit sharp, well-localized pain when irritated, such as in pleuritis.

• The costal pleura and peripheral diaphragmatic pleura are innervated by intercostal nerves.
• The visceral pleura is supplied by autonomic nerves (pulmonary plexus) and is relatively insensitive to pain.
• The cervical (cupola) pleura is innervated by the intercostal nerves of the first thoracic segment.

Why the other options are incorrect:

• Diaphragmatic pleura (peripheral part): ❌
  → Supplied by intercostal nerves, not phrenic.
• Visceral pleura: ❌
  → Supplied by autonomic fibers; insensitive to pain.
• Cervical part: ❌
  → Supplied by T1 intercostal nerves.
• Costal part: ❌
  → Supplied by intercostal nerves (T1–T11).

✅ Correct answer: Pectoralis major

Explanation:

Intercostal muscles — external, internal, and innermost intercostals — are directly innervated by the intercostal nerves (ventral rami of thoracic spinal nerves). They are primarily responsible for moving the ribs during respiration. Similarly, the subcostal muscles, being part of the inner thoracic musculature, are also innervated by intercostal nerves.

The pectoralis major, however, is innervated by the medial and lateral pectoral nerves, which originate from the brachial plexus, not the intercostal nerves. Therefore, pressure on intercostal nerves does not affect the pectoralis major.

Why the other options are incorrect:

• Innermost intercostal: ❌
  → Directly innervated by intercostal nerves; affected by compression.
• External intercostal: ❌
  → Directly innervated by intercostal nerves; affected.
• Internal intercostal: ❌
  → Directly innervated by intercostal nerves; affected.
• Subcostal: ❌
  → Considered part of intercostal musculature; innervated by intercostal nerves.

✅ Correct answer: Cervical rib

Explanation:

The lower trunk of the brachial plexus (formed by C8 and T1 nerve roots) passes between the anterior and middle scalene muscles and over the first rib. An extra cervical rib (a congenital anomaly arising from C7) can compress the lower trunk, leading to pain, paresthesia along the medial forearm and hand, and wasting of intrinsic hand muscles, a condition known as thoracic outlet syndrome.

Why the other options are incorrect:

• Second rib fracture: ❌
  → Usually does not affect the lower trunk; it’s located too inferiorly.
• First rib fracture: ❌
  → While it may affect the brachial plexus, a congenital cervical rib is the classic cause of lower trunk compression.
• Extra vertebrae: ❌
  → Unlikely to directly compress the brachial plexus trunks.
• Abdominal rib: ❌
  → Rare anomaly, not associated with brachial plexus compression.

✅ Correct answer: Internal and innermost intercostal muscles

Explanation:

The intercostal neurovascular bundle (intercostal vein, artery, and nerve — in that order from superior to inferior) runs in the costal groove of the rib, located between the internal intercostal and innermost intercostal muscles. This positioning protects the vessels and nerve and allows for safe passage along the rib cage.

Why the other options are incorrect:

• Innermost intercostal and transversus thoracic muscles: ❌
  → These are not the layers where the neurovascular bundle lies; the transversus thoracis is more internal and anterior.
• Innermost intercostal and subcostal muscles: ❌
  → Subcostal muscles are posterior and deeper, not associated with the typical intercostal neurovascular bundle pathway.
• Subcostal and transversus thoracic muscles: ❌
  → These are deeper thoracic muscles; vessels and nerves are not found between them.
• External and internal intercostal muscles: ❌
  → The external intercostals lie more superficial; the neurovascular bundle is deep to internal intercostals, not between external and internal.

The thoracic cage is connected by several types of joints — synovial, primary cartilaginous, and secondary cartilaginous — depending on their function and mobility.

• Second to seventh sternocostal joints are synovial plane joints, allowing slight gliding movement during respiration.

• Manubriosternal joint is a secondary cartilaginous (symphysis) joint, allowing limited movement during inspiration.

• Costochondral joints (between rib and costal cartilage) are primary cartilaginous (synchondroses) — immovable joints where hyaline cartilage directly unites bone and cartilage.

• Xiphisternal joint is also a primary cartilaginous joint that ossifies later in life.

• However, interchondral joints (between costal cartilages of ribs 6–9, sometimes 9–10) are synovial plane joints, not secondary cartilaginous.

Therefore, the statement pairing interchondral joints with secondary cartilaginous is incorrect.

❌ Why the Other Options Are Correct

• Second to seventh sternocostal joints → Synovial joints:
  ✅ True — they have synovial cavities permitting slight gliding movement.

• Manubriosternal joint → Secondary cartilaginous joint:
  ✅ True — a symphysis between manubrium and body of sternum.

• Costochondral joints → Primary cartilaginous joints:
  ✅ True — formed by direct union of rib and costal cartilage.

• Xiphisternal joint → Primary cartilaginous joint:
  ✅ True — a synchondrosis between xiphoid process and sternal body.

✅ Correct answer: Cardiac

Explanation:

The left lung has a deep cardiac notch on its anterior border to accommodate the heart, which lies more towards the left side of the thoracic cavity. This is especially visible on the lower part of the anterior border of the left lung.

Why other options are incorrect:

• Infrasternal:
  → Refers to the area below the sternum, not a feature of the lung.
• Suprasternal:
  → Refers to the jugular notch above the sternum, unrelated to lung anatomy.
• Pulmonary:
  → Not a specific notch; “pulmonary” simply refers to the lungs.
• Aortic:
  → The aortic impression is on the medial surface of the left lung, not the anterior border.

✅ Correct answer: Neurovascular bundle

Explanation:

When performing pleural tap (thoracocentesis) or intercostal drainage, the needle is inserted just above the upper border of the lower rib to avoid injury to the neurovascular bundle that runs along the lower border of the rib above.

Anatomical reasoning:

Each intercostal space contains a neurovascular bundle arranged in the following order (from top to bottom):

Vein – Artery – Nerve (VAN)

This bundle lies in the costal groove along the inferior border of each rib.

So, if you insert the needle below a rib, you risk puncturing:

• Intercostal vein
• Intercostal artery
• Intercostal nerve

Hence, the safe site for needle insertion is just above the upper border of the rib below, where the neurovascular bundle is absent or minimal.

✅ Correct answer: Lies to left of the esophagus in posterior mediastinum

Explanation:

The thoracic duct is the main lymphatic channel of the body — it collects lymph from most of the body (except the right upper quadrant).

Key anatomical facts about the thoracic duct:

• Origin:
  Begins at the cisterna chyli (level of L2 vertebra) in the abdomen.
• Course:
  • Enters the thorax through the aortic hiatus (not the vena caval opening).
  • In the posterior mediastinum, it ascends between the aorta (on left) and azygos vein (on right).
  • It lies to the right of the midline at lower thoracic levels,
    then crosses behind the esophagus to its left side (at about T5).
  • In the superior mediastinum, it ascends on the left side of the esophagus and terminates in the left venous angle (junction of left internal jugular and left subclavian veins).

✅ Lower lobe — Correct.
When the stethoscope is placed below the 5th intercostal space on the posterior chest wall, the lower lobe of the lung is being examined. The lower lobes occupy most of the posterior surface of both lungs and are best auscultated from the back, especially below the scapular line.

❌ Apical lobe — Heard high up near the supraclavicular or interscapular area.
❌ Lingula — Part of the left upper lobe, located anteriorly, not posteriorly.
❌ Middle lobe — Present only in the right lung, best heard anteriorly near the 4th–6th costal cartilages.
❌ Upper lobe — Found mainly above the 4th rib posteriorly, higher than the area described.

✅ 2nd intercostal nerve — Correct.
The 2nd intercostal nerve gives off the intercostobrachial nerve, which crosses the axilla to supply the floor of the axilla and the upper part of the medial side of the arm. It’s clinically important because it can cause referred pain from angina or myocardial infarction to the inner arm.

❌ 1st intercostal nerve — Mainly supplies muscles of the intercostal space; it doesn’t have a cutaneous branch to the arm.
❌ 3rd intercostal nerve — Gives a smaller lateral cutaneous branch but not the intercostobrachial nerve.
❌ 8th and 11th intercostal nerves — Supply the lower thoracic and abdominal walls, far from the axilla.

✅ Trachea — Correct.
The trachea passes through the superior mediastinum, just anterior to the esophagus and surrounded by lymph nodes. Enlarged mediastinal lymph nodes (especially from lung carcinoma) can compress the trachea, leading to cough, dyspnea, or stridor due to airway obstruction.

❌ Bronchi — Located in the middle mediastinum, below the level of the superior mediastinum.
❌ Heart — Lies in the middle mediastinum, enclosed within the pericardium — not affected by superior mediastinal nodes.
❌ Thyroid — Found in the neck, above the thoracic inlet, not in the mediastinum.
❌ Primary bronchus — Lies inferior to the tracheal bifurcation, within the middle mediastinum, not directly compressed by superior mediastinal nodes.

✅ Right primary bronchus — Correct.
The right main (primary) bronchus is wider, shorter, and more vertically oriented than the left. Because of this alignment with the trachea, foreign bodies like coins or peanuts are more likely to enter the right bronchial tree, especially lodging in the right lower lobe bronchus.

❌ Left primary bronchus — Longer, narrower, and more horizontal — foreign bodies rarely enter here.
❌ Secondary bronchus — Refers to lobar bronchi, which are reached later, after the main bronchus.
❌ Tertiary bronchus — Even smaller segmental branches, not the first site of entry.
❌ Respiratory bronchus — The finest airway near alveoli — a foreign body wouldn’t reach this far initially.

✅ Scalene tubercle is present on its inner concave border — Incorrect statement.
The scalene tubercle is located on the upper surface of the first rib, not on its inner concave border. It separates the grooves for the subclavian vein (in front) and subclavian artery (behind).

✔ Correct features of the first rib:

• It is the shortest and most curved rib.

• It has no costal groove on its inferior surface.

• The angle lies on its outer border.

• Its anterior end is larger and attaches to the manubrium of the sternum.

✅ Elastic recoil of lungs & thoracic cage — Correct.
During quiet expiration, there is no active muscular contraction. The process is passive, resulting from the elastic recoil of the stretched lungs and thoracic cage as they return to their resting position after inspiration.

❌ Serratus posterior — Assists in forced respiration, not in quiet breathing.
❌ Serratus anterior — Elevates the ribs during deep inspiration, not expiration.
❌ Pectoralis minor — Aids forced inspiration when the upper limb is fixed.
❌ Diaphragm — Active during inspiration, but relaxes during quiet expiration.

✅ External intercostal — Correct.
The external intercostal muscles elevate the ribs during inspiration, thereby increasing the anteroposterior and transverse diameters of the thoracic cavity. They are the primary muscles of active inhalation besides the diaphragm.

❌ Internal intercostal — Fibers run downward and backward; they act mainly during forced expiration, pulling the ribs down.
❌ Innermost intercostal — Assist the internal intercostals in expiration, not inspiration.
❌ Subcostalis — Also help in forced expiration by depressing ribs.
❌ Transversus thoracis — A thin muscle on the inner anterior chest wall that depresses costal cartilages during expiration.

✅ Esophagus — Correct.
On the mediastinal surface of the left lung, a shallow groove for the esophagus can often be seen posterior to the hilum, as the esophagus descends through the posterior mediastinum toward the diaphragm.

❌ Azygous vein — Lies on the right side, producing a groove on the right lung, not the left.
❌ Inferior vena cava — Related to the right lung and diaphragm, not the left lung.
❌ Ascending aorta — Found anterior and to the right of the midline, producing a groove on the right lung.
❌ Right lymphatic duct — Drains the right upper quadrant of the body; it does not leave any groove on the lungs.

✅ Subclavian artery — Correct.
In thoracic outlet syndrome, the subclavian artery (along with the brachial plexus and sometimes the subclavian vein) can be compressed as it passes between the anterior and middle scalene muscles, over the first rib, and beneath the clavicle. This leads to symptoms like arm pain, numbness, and diminished pulses.

❌ Brachiocephalic artery — Lies more medially in the thorax and is not part of the thoracic outlet passage.
❌ Internal carotid artery — Found in the neck, supplying the brain — not involved in thoracic outlet compression.
❌ Internal thoracic artery — Runs downward along the sternum, not through the thoracic outlet.
❌ External carotid artery — Supplies the face and neck, well above the thoracic outlet region.

✅ 11th and 12th ribs — Correct.
These are called floating ribs because their anterior ends are free; they do not connect to the sternum or to the costal cartilages of other ribs. They are short, have no neck or tubercle, and provide attachment for abdominal muscles.

❌ All atypical ribs — Includes 1st, 2nd, 10th, 11th, and 12th, but only the last two (11th and 12th) are floating.
❌ 1st and 2nd rib — Both are atypical, but they are attached to the sternum (directly or via cartilage).
❌ 9th and 10th rib — Usually false ribs, attached indirectly to the sternum through the 7th costal cartilage.
❌ 10th and 11th rib — The 10th is typically false, not floating.

✅ Middle mediastinum — Correct.
The heart, enclosed within the pericardium, occupies the middle mediastinum, which also contains the roots of the great vessels, phrenic nerves, and pericardiacophrenic vessels.

❌ Anterior mediastinum — Lies in front of the pericardium, containing loose connective tissue and thymic remnants.
❌ Inferior mediastinum — A broader subdivision that includes the anterior, middle, and posterior parts — the heart is specifically in the middle part of it.
❌ Posterior mediastinum — Lies behind the pericardium, housing structures like the esophagus, thoracic aorta, and thoracic duct.
❌ Superior mediastinum — Above the heart, containing the great vessels, trachea, and thymus.

✅ External intercostals — Correct.
These muscles run obliquely downward and forward between adjacent ribs. When they contract, they elevate the ribs, increasing the anteroposterior and transverse diameters of the thoracic cavity — essential for inspiration.

❌ Deltoid — Moves the shoulder, not involved in respiration.
❌ Pectoralis major — A chest muscle that moves the humerus; it only assists in forced inspiration when the arms are fixed.
❌ Rectus abdominis — Involved in forced expiration, not inspiration.
❌ Sternocleidomastoid — Assists in deep or forced inspiration by elevating the sternum, but not during quiet breathing like the external intercostals.

✅ Cardiac notch — Correct.
The left lung has a deep cardiac notch on the lower part of its anterior border, created by the heart’s left ventricle. This indentation gives the left lung its distinctive shape and contributes to the small lingula projection below it.

❌ Aortic notch — Found on the medial surface, not the anterior border, where the aortic arch lies.
❌ Infersternal — No such anatomical notch exists.
❌ Suprasternal — Refers to the jugular notch of the manubrium, not part of the lung.
❌ Pulmonary — Not a specific anatomical notch of the lung’s anterior border.

✅ Neurovascular bundle — Correct.
The intercostal vein, artery, and nerve (VAN) run together in the costal groove along the lower border of each rib. During pleural aspiration or intercostal drainage, the needle is inserted just above the upper border of the lower rib to avoid damaging this bundle.

❌ Long thoracic nerve — Lies on the lateral chest wall over the serratus anterior, not between ribs.
❌ Intercostal nerve — It’s part of the neurovascular bundle, not an isolated structure at risk when staying above the upper border.
❌ Intercostal artery — Also part of the bundle, not alone.
❌ Intercostal vein — Likewise, within the same bundle, which is why the whole neurovascular bundle is named as the structure to be avoided.

✅ Lies to the left of the esophagus in the posterior mediastinum — Correct.
This is the typical course of the thoracic duct after it crosses from right to left behind the esophagus and ascends toward the venous angle.

❌ Lies at 2nd lumbar vertebra — Incorrect. That’s where it originates (cisterna chyli), not where it lies in the thorax.

❌ Lies to left of esophagus in superior mediastinum — Incorrect. In the superior mediastinum, it’s crossing from right to left, not entirely left-sided yet.

❌ Receives right jugular lymph trunk — Incorrect. The right jugular trunk drains into the right lymphatic duct, not the thoracic duct.

❌ Passes through vena caval opening of diaphragm — Incorrect. It passes through the aortic opening (T12) along with the aorta and azygos vein.

✅ Correct answer: Ribs 7 to 10

Explanation:

The bucket handle movement refers to the elevation of the lateral portions of the ribs during inspiration — this increases the transverse (side-to-side) diameter of the thoracic cavity.

This movement occurs primarily in ribs 7–10, which are false ribs attached anteriorly to the costal cartilage of the rib above. Their orientation allows a swinging motion, much like a bucket handle being lifted.

🫁 Types of Rib Movements During Breathing:

• Pump handle movement → Ribs 1–6
  • Increases the anteroposterior diameter of the thorax.
  • Movement occurs at the costovertebral and costotransverse joints.
• ✅ Bucket handle movement → Ribs 7–10
  • Increases the transverse diameter of the thorax.
  • Lateral ends of ribs move upward and outward.
• Caliper movement → Ribs 11–12 (floating ribs)
  • Move slightly posteriorly and laterally like a caliper opening, due to their lack of anterior attachment.

The intercostal nerves (T1–T11) are the anterior rami of the thoracic spinal nerves.
They supply:

• The intercostal muscles (external, internal, and innermost)

• The subcostal muscles

• The skin of the thoracic wall

• The parietal pleura and peritoneum

If the intercostal nerves are compressed, the muscles they supply (intercostals and subcostals) may undergo pain, twitching, or spasms.

However, pectoralis major is not innervated by intercostal nerves — it receives its nerve supply from the brachial plexus.

🔹 Nerve Supply:

The intercostal nerve — the anterior ramus of a thoracic spinal nerve — runs forward in the costal groove on the inferior surface of each rib, accompanied by the intercostal artery and vein (arranged as VAN: vein, artery, nerve from superior to inferior).

As the nerve proceeds laterally, near the angle of the rib, it gives off a collateral branch:

• The collateral branch descends to run along the superior border of the rib below, within the same intercostal space.

• It accompanies a collateral artery and vein (often arranged NAV, opposite of the main bundle).

• This branch provides motor fibers to intercostal muscles and sensory fibers to the overlying skin and pleura — serving as a secondary neurovascular pathway.

Thus, the collateral branch originates near the rib angle, distinguishing it from other branches of the intercostal nerve.

❌ Incorrect Options Explained:

• Anterior cutaneous branch:
  Arises near the sternum, as the terminal branch of the intercostal nerve. It supplies the anterior chest wall and skin near the midline, not the rib angle.

• Rami communicantes:
  Originate close to the vertebral column, connecting the intercostal nerve with the sympathetic chain ganglion — far posterior to the rib’s angle.

• Muscular branches:
  Given off along the length of the intercostal nerve to supply intercostal and subcostal muscles; they do not arise specifically at the rib angle.

• Lateral cutaneous branch:
  Emerges midway along the intercostal space, much anterior to the rib angle, where it pierces the intercostal muscles to supply skin on the lateral thoracic wall.

✨ In summary:
The collateral branch of the intercostal nerve arises near the angle of the rib, runs along the superior margin of the rib below, and provides supplementary motor and sensory innervation to the intercostal space.

The human thoracic cage consists of 12 pairs of ribs, which are classified according to their anterior attachments:

🔹 Classification of Ribs:

1. True ribs (vertebrosternal ribs):

   • Ribs 1–7

   • Attach directly to the sternum via their own costal cartilages.

2. False ribs (vertebrochondral ribs):

   • Ribs 8–10

   • Do not attach directly to the sternum; instead, their costal cartilages join the cartilage of the rib above, forming a continuous costal margin.

3. Floating ribs (vertebral ribs):

   • Ribs 11 and 12

   • Have no anterior attachment — their cartilages end in the muscles of the abdominal wall.

❌ Why the Other Options Are Incorrect:

• 11 and 12:
  These are floating ribs (vertebral ribs) — they have no anterior attachment to the sternum or to other costal cartilages.

• 10 and 11:
  Rib 10 is a vertebrochondral rib, but rib 11 is a floating rib — this pair doesn’t belong to the same category.

• 1 till 7:
  These are true ribs (vertebrosternal ribs) — they attach directly to the sternum via their own cartilages.

• 2 till 7:
  All are true ribs, not vertebrochondral.

The first sternocostal joint is a primary cartilaginous joint, also known as a synchondrosis.

In contrast, the 2nd–7th sternocostal joints are synovial plane joints, allowing limited gliding movements essential for respiration.

❌ Why the Other Options Are Incorrect:

• Fourth sternocostal joint:
  Synovial plane joint — permits slight gliding movement during respiration.

• Second sternocostal joint:
  Synovial joint, not cartilaginous. It’s located at the sternal angle (Angle of Louis) and marks the level where the trachea bifurcates and the aortic arch begins and ends.

• Fifth sternocostal joint:
  Also a synovial plane joint; allows movement during breathing.

• Manubriosternal joint:
  Secondary cartilaginous joint (symphysis) — contains fibrocartilage, not hyaline, and allows limited movement.

  • Located between the manubrium and body of the sternum

  • Important clinical landmark (Angle of Louis)

The posterior intercostal arteries supply the intercostal spaces and thoracic wall, but their origin differs between the upper two and the remaining nine pairs.

🔹 1st and 2nd Posterior Intercostal Arteries

• Do not arise directly from the descending thoracic aorta.

• Instead, they originate from the superior intercostal artery, a branch of the costocervical trunk of the subclavian artery.

• These arteries descend to supply the upper two intercostal spaces.

🔹 3rd to 11th Posterior Intercostal Arteries

• Arise directly from the descending thoracic aorta.

• The subcostal arteries (below the 12th rib) are their continuations and run along the subcostal space.

This pattern reflects a gradual transition of blood supply from subclavian to aortic sources as you move inferiorly along the thoracic wall.

✅ Why the Other Statements Are Correct:

• Give mammary branches to the breast:
  ✔ Yes — especially the 2nd to 4th posterior intercostal arteries, which provide lateral mammary branches to the breast, contributing to its rich vascular supply.

• Eleven in number on each side:
  ✔ Correct — there are 11 intercostal spaces (and hence 11 posterior intercostal arteries) on each side, plus a subcostal artery below the 12th rib.

• Give right bronchial artery:
  ✔ Correct — the right bronchial artery often arises from the 3rd posterior intercostal artery or occasionally from a left superior bronchial artery.

• Content of costal groove:
  ✔ True — each posterior intercostal artery travels within the costal groove of the rib, accompanied by the intercostal vein and nerve, arranged from superior to inferior as:
  Vein – Artery – Nerve (V–A–N).

✨ In summary:
The 1st and 2nd posterior intercostal arteries are branches of the superior intercostal artery (from the costocervical trunk), while the 3rd–11th arise directly from the descending thoracic aorta.
All other described features — mammary branches, number, bronchial contribution, and costal groove positioning — are correct anatomical details.

The right main bronchus is:

• Wider

• Shorter

• More vertical (25° from the trachea)

Whereas the left main bronchus is:

• Narrower,

• Longer, and

• More horizontal (45° from the trachea)

Because of its more vertical orientation and wider diameter, the right bronchus provides a more direct continuation of the trachea, allowing foreign bodies to enter the right lung more easily.

❌ Why the Other Options Are Incorrect:

• Right bronchus is narrower than the left one:
  ❌The right bronchus is actually wider, not narrower, which facilitates the passage of foreign bodies.

• Right lung has one lobe more than left lung:
  ✅ The right lung does have three lobes, but this does not determine where aspirated objects go — the orientation of the bronchi does.

• Right lung is shorter than the left lung:
  ✅ True due to the higher position of the right hemidiaphragm (caused by the liver beneath), but this has no impact on aspiration pathways.

• Right lung is heavier than the left lung:
  ✅ The right lung is slightly heavier and larger, but this does not affect the direction of airflow or aspiration.

The anterior mediastinum contains loose connective tissue, lymph nodes, fat, and the thymus (or its remnants).
Therefore, tumors of the thymus (thymoma) are the most common cause of anterior mediastinal masses, particularly in adults.

Anterior Mediastinal Mass Mnemonic: “4 Ts”

1. Thymoma

2. Teratoma (germ cell tumor)

3. Thyroid mass (retrosternal goiter)

4. Terrible lymphoma

❌ Why the Other Options Are Incorrect:

• Diaphragmatic hernia:

  • Involves abdominal viscera herniating into the thoracic cavity through a defect in the diaphragm.

  • Most commonly seen posteriorly (Bochdalek) or anteriorly (Morgagni), but it appears lower than the anterior mediastinum on imaging.

  • Not a true mediastinal mass.

• Carcinoma of bronchi (Bronchogenic carcinoma):

  • Arises in the lung parenchyma or bronchi, typically in the middle mediastinum (near hilum) — not the anterior one.

• Esophageal tear (Boerhaave syndrome):

  • Affects the posterior mediastinum, since the esophagus runs there.

  • Leads to mediastinitis (inflammation), not a discrete mass.

• Fibroma:

  • Can theoretically occur anywhere but is rare in the anterior mediastinum.

  • Lacks the strong anatomical and clinical association that thymoma has with this region.

The pleural cavity is a potential space between the parietal pleura (lining the thoracic wall) and the visceral pleura (covering the lungs). Normally, it contains a thin layer of lubricating fluid, but in conditions like pleurisy or pleural effusion, excess fluid accumulates.

The site of fluid accumulation depends on gravity and the shape of the pleural reflections.

🔹 Costodiaphragmatic Recess:

• The deepest part of the pleural cavity, located between the costal pleura and diaphragmatic pleura.

• Extends from the 8th to the 10th rib in the midaxillary line (approximately).

• This recess represents the lowest area in the pleural cavity when a person is standing or sitting upright.

• During quiet respiration, the lungs do not fully expand into this recess — hence, it serves as a potential space where fluid accumulates first in pleural effusion.

🔹 Clinical Relevance:

• Pleural effusion (fluid), hemothorax (blood), or chylothorax (lymph) commonly collect here.

• Thoracocentesis (pleural tap):

  • Procedure performed to drain fluid from this recess.

  • Common site: Midaxillary line, 8th or 9th intercostal space, just above the upper border of a rib (to avoid the neurovascular bundle)

❌ Why the Other Options Are Incorrect:

• Costomediastinal recess:

  • Located between costal and mediastinal pleura along the anterior border of the lungs.

  • Shallow; accommodates the cardiac notch of the left lung — not the major site for fluid accumulation.

• Hilar reflection:

  • Area where visceral and parietal pleura are continuous around the lung root (hilum).

  • Serves as an attachment site for the pulmonary ligament, not a dependent space for fluid collection.

• Lingula:

  • A tongue-like projection of the left upper lobe of the lung corresponding to the middle lobe on the right.

  • It’s part of the lung, not a pleural recess; does not accumulate pleural fluid.

• Cupola (Cervical Pleura):

  • The dome-shaped apex of the pleural cavity extending into the root of the neck above the first rib.

  • It’s the highest part of the pleural cavity, not the lowest — air, not fluid, accumulates here (as in pneumothorax).

To better understand the organization of thoracic structures, the mediastinum is divided into parts.

🔹 Divisions of the Mediastinum:

1. Superior Mediastinum

2. Inferior Mediastinum, which is further divided into:

   • Anterior

   • Middle

   • Posterior

The plane dividing the superior and inferior mediastinum passes:

• Anteriorly: through the sternal angle (Angle of Louis)

• Posteriorly: to the intervertebral disc between T4 and T5 vertebrae

This plane is known as the transverse thoracic plane or plane of Ludwig.

🔹 Angle of Louis (Sternal Angle):

• Formed by the junction of the manubrium and the body of the sternum.

• Easily palpable at the level of the second costal cartilage.

• Serves as a key clinical and anatomical landmark because it marks several important transitions.

❌ Why the Other Options Are Incorrect:

• Costodiaphragmatic recess:

  • A potential space between the costal and diaphragmatic pleura.

  • Important for pleural effusion drainage but not related to mediastinal division.

• 12th thoracic vertebra:

  • Too low in position; corresponds roughly to the diaphragmatic level, not the mediastinal division.

• Foramen of Winslow (Epiploic foramen):

  • An opening in the peritoneal cavity (between greater and lesser sacs), not a thoracic structure.

• Thoracic inlet:

  • Marks the upper boundary of the thoracic cavity, but it does not divide the mediastinum; it forms its superior opening.

The rib described is the first rib, which has several atypical features compared to typical ribs:

• Single facet on head: articulates only with T1 vertebra

• No neck or only a rudimentary neck

• No prominent angle

• **Has a tuberosity on its superior surface for attachment of scalene muscles (serratus anterior tubercle is also present)

• Costal groove is shallow

Other options:

• Tubercle for serratus anterior → present but not unusual

• Single facet on head → normal for first rib

• Costal groove → present, though shallow

• Neck → present but rudimentary

The mediastinum is the central compartment of the thoracic cavity between the two pleural sacs. It is divided into superior and inferior parts by a plane passing through the sternal angle (T4–T5 level). The inferior mediastinum is further divided into anterior, middle, and posterior compartments.

The posterior mediastinum lies behind the pericardium and in front of the vertebral column (T5–T12). It contains several key structures:

• Esophagus

• Thoracic duct

• Descending thoracic aorta

• Azygos and hemiazygos veins

• Vagus nerves and sympathetic trunks

These structures are responsible for vital thoracic and abdominal communication pathways — for example, the thoracic duct drains lymph from most of the body into the left venous angle.

❌ Why the Other Options Are Incorrect

• Anterior mediastinum:
  Lies between the sternum and pericardium; contains fat, lymph nodes, and remnants of the thymus, but no esophagus or thoracic duct.

• Superior mediastinum:
  Contains thymus, great vessels (aortic arch and branches), trachea, esophagus (upper part), and thoracic duct, but the sympathetic chains are located posteriorly.

• Inferior mediastinum:
  A collective term — it includes anterior, middle, and posterior mediastina; not a specific compartment itself.

• Middle mediastinum:
  Contains the heart, pericardium, ascending aorta, pulmonary trunk, and phrenic nerves, but not the esophagus or sympathetic chains.

The twelfth rib (and also the 11th) is a “floating rib” with several distinctive features:

• Single facet on the head: articulates only with T12 vertebra

• No neck or tubercle: unlike typical ribs, which articulate with the transverse process

• No costal groove: unlike most other ribs, making neurovascular bundle less protected

• Floating: does not attach anteriorly to the sternum via costal cartilage

Other options:

• Angle, neck, costal groove, costal cartilage → either absent or underdeveloped in the 12th rib

Flail chest is a serious thoracic injury characterized by:

• Definition: A segment of the thoracic wall becomes detached from the rest of the chest wall

• Cause: Usually ≥3 consecutive ribs fractured in ≥2 places

• Clinical feature: Paradoxical movement of the flail segment during respiration:

  • Inward during inspiration

  • Outward during expiration

• Can lead to impaired ventilation and hypoxia

Other options:

• Single rib fracture / fracture at costal cartilage / first rib fracture → do not produce flail chest

• Multiple ribs fractured at one place → may cause pain but not flail segment

On the right lung, the arch of the azygos vein creates the most pronounced impression:

• Location: Posterior part of the superior lobe, near the hilum

• Other structures:

  • Right common carotid artery → does not leave a significant impression on the lung

  • Right phrenic nerve / right vagus nerve → minor grooves only

  • Thoracic aorta → impression is on the left lung, not right

• In the thorax, the esophagus changes its position relative to surrounding structures as it descends:

  • Upper thoracic esophagus: posterior to trachea, slightly right of midline

  • Middle thoracic esophagus: lies posterior to the trachea and left of the thoracic aorta

  • Lower thoracic esophagus (just before hiatus): lies medial to the aorta before entering the diaphragm

Other options:

• Anterior mediastinum / superior mediastinum / middle mediastinum / root of the neck → esophagus is posterior or lateral, not medial to the aorta

The larynx is the part of the upper respiratory tract that connects the pharynx to the trachea. It functions as both an air passageway and a phonatory organ, containing structures that allow voice production and airway protection.

🔹 Composition:

1. Cartilages:
   The larynx contains nine cartilages (three paired and three unpaired):

   • Unpaired: Thyroid, cricoid, epiglottic

   • Paired: Arytenoid, corniculate, cuneiform

   These cartilages provide rigid support and maintain the patency of the airway.

2. Muscles:

   • The intrinsic muscles of the larynx (e.g., cricothyroid, posterior cricoarytenoid, lateral cricoarytenoid, thyroarytenoid) are composed of skeletal (voluntary) muscle fibers.

   • These muscles control the tension, position, and length of the vocal cords, which are essential for phonation.

   • The extrinsic muscles (e.g., sternothyroid, thyrohyoid) move the entire larynx during swallowing and speech.

Because it contains cartilage (for structure) and skeletal muscles (for movement and sound modulation), the larynx is the respiratory organ that possesses both tissue types.

❌ Why the Other Options Are Incorrect:

• Respiratory bronchiole:
  Contains smooth muscle but no skeletal muscle or cartilage. It’s part of the respiratory zone where gas exchange begins.

• Terminal bronchiole:
  Has smooth muscle in its wall but lacks cartilage. It’s part of the conducting zone, not involved in phonation or voluntary movement.

• Alveoli:
  Composed of simple squamous epithelium for gas exchange — contain no cartilage or muscle (only some elastic fibers and contractile cells).

• Trachea:
  Contains C-shaped hyaline cartilage rings and smooth muscle (trachealis) but no skeletal muscle. Its movements are involuntary and regulated by the autonomic nervous system.

The organ described — the thymus — is a primary lymphoid organ crucial for T-lymphocyte maturation during childhood. It is relatively large at birth and continues to grow until puberty, after which it undergoes involution, being gradually replaced by adipose tissue.

🔹 Anatomical Location:

• The thymus lies in the superior mediastinum and partly extends into the anterior part of the inferior mediastinum.

• It is located posterior to the manubrium sterni and anterior to the pericardium and great vessels (such as the arch of the aorta and its branches).

❌ Why the Other Options Are Incorrect:

• Posterior mediastinum:
  Lies behind the pericardium; contains the esophagus, thoracic aorta, azygos vein, thoracic duct, and sympathetic trunks, not the thymus.

• Inferior mediastinum:
  A broad term that includes anterior, middle, and posterior parts. The thymus is not classified as being primarily in the inferior mediastinum, though it may slightly extend into its anterior part in children.

• Anterior mediastinum:
  Lies in front of the pericardium and behind the sternum; in adults, this space contains fat, lymph nodes, and connective tissue, but not the active thymus.

• Middle mediastinum:
  Contains the heart, pericardium, and roots of great vessels, not the thymus.

The first rib is closely related to the subclavian artery, which arches over it. The subclavian artery passes posterior to the anterior scalene muscle and superior to the first rib as it travels laterally toward the axilla, where it continues as the axillary artery.

Because of this intimate anatomical relationship, a fracture of the first rib poses a significant risk of injuring the subclavian artery, potentially leading to hemorrhage, hematoma formation, or ischemia in the upper limb.

❌ Why the Other Options Are Incorrect:

• Internal thoracic artery:
  A branch of the subclavian artery that runs downward along the inner surface of the anterior thoracic wall, parallel to the sternum. It is not directly related to the first rib but to the costal cartilages of the upper ribs.

• Perforating arteries:
  Small branches of the internal thoracic artery that pierce the intercostal spaces to supply the skin and pectoral muscles. They are not in contact with the first rib.

• Intercostal arteries:
  Run below each rib in the costal groove. The first intercostal artery arises from the highest intercostal branch of the costocervical trunk, which itself is a branch of the subclavian artery — but the first rib fracture endangers the main subclavian artery, not its distal intercostal branches.

• Carotid artery:
  Found in the neck, ascending toward the head — far removed from the thoracic inlet and unrelated to the first rib.

The left recurrent laryngeal nerve, a branch of the vagus nerve (cranial nerve X), descends into the thorax and loops around the arch of the aorta near the ligamentum arteriosum, before ascending back up in the tracheoesophageal groove to reach the larynx.

It supplies all intrinsic muscles of the larynx except the cricothyroid, and it also provides sensory innervation below the vocal cords.

When the left recurrent laryngeal nerve is damaged, the ipsilateral vocal cord becomes paralyzed, leading to:

• Hoarseness (due to inability of the vocal cord to adduct properly),

• Low-pitched voice (loss of tension control), and

• Stridor or noisy breathing (air passing through a partially closed glottis).

This type of nerve injury can result from aortic aneurysm, left atrial enlargement, or surgery in the mediastinum.

❌ Why the Other Options Are Incorrect:

• Internal laryngeal nerve:
  A sensory branch of the superior laryngeal nerve; provides sensation above the vocal cords and taste to the epiglottis. It doesn’t supply any muscles, so it cannot cause hoarseness or vocal cord paralysis.

• External laryngeal nerve:
  Supplies only the cricothyroid muscle, which tenses the vocal cords. Damage here leads to difficulty in producing high-pitched sounds — not hoarseness or stridor.

• Vagus nerve:
  While the recurrent laryngeal is a branch of the vagus, complete vagus nerve injury would cause broader effects, including loss of gag reflex and palate drooping, not just isolated vocal cord paralysis.

• Intercostal nerve:
  Supplies intercostal muscles and skin over the thoracic wall; it has no relation to phonation or the larynx.

The bronchial arteries provide nutritional (systemic) blood supply to the lungs, bronchi, and connective tissue of the lung root.

• Left bronchial arteries: Usually two in number — both arise directly from the thoracic aorta.

• Right bronchial artery: Usually one, and it most commonly arises from the third posterior intercostal artery, though sometimes it may originate from the upper left bronchial artery.

❌ Why the Other Options Are Incorrect

• Posterior surface of the thoracic aorta: The left, not the right, bronchial arteries arise directly from the thoracic aorta.

• Anterior surface of the thoracic aorta: No bronchial arteries arise from here.

• Upper left bronchial artery: Rare anatomical variant; not the usual origin.

• Second intercostal artery: Too high — the right bronchial artery usually comes from the third, not the second, posterior intercostal artery.

Each intercostal space contains a neurovascular bundle located along the inferior border of the rib above, within the costal groove.
This bundle is arranged from superior to inferior as:
Vein → Artery → Nerve (VAN).

The intercostal nerve lies lowest and most exposed, making it the most likely structure to be injured if a needle is inserted too close to the lower border of a rib.

To avoid this, the needle is introduced just above the upper border of the rib below, thereby minimizing the risk of damaging the intercostal nerve (and accompanying vessels).

❌ Why Other Options Are Incorrect

• Neurovascular bundle:
  Although the nerve is part of this bundle, the question asks for the specific structure at risk — that is, the intercostal nerve itself.

• Intercostal artery / Intercostal vein:
  These lie above the nerve within the same bundle and are less likely to be injured if the needle is inserted just above the rib below.

• Long thoracic nerve:
  Lies on the lateral thoracic wall, outside the intercostal spaces — not relevant here.

The right main bronchus differs anatomically from the left in several key ways:

Because of its more vertical orientation and wider lumen, the right main bronchus is more in line with the trachea, making it the most common site for aspirated foreign bodies (especially in children).

❌ Why Other Options Are Incorrect

• Right main bronchus passes anterior to esophagus:

  • True for the trachea, not relevant to aspiration mechanics.

• Right main bronchus is horizontal:

  • Incorrect — it is more vertical, not horizontal.

• Right main bronchus is narrower:

  • It is actually wider, which further facilitates entry of foreign bodies.

• Right main bronchus is longer:

  • It is shorter than the left.

The internal thoracic artery (ITA) is an important vessel that supplies the anterior chest wall, diaphragm, and breasts.

It begins in the root of the neck as a branch of the first part of the subclavian artery. From there, it descends posterior to the first six costal cartilages, about 1 cm lateral to the sternum, accompanied by paired veins.

It provides anterior intercostal arteries to the upper six intercostal spaces, pericardiophrenic and perforating branches, and then divides into its two terminal branches:

• Musculophrenic artery (to diaphragm and lower intercostal spaces)

• Superior epigastric artery (to anterior abdominal wall)

The ITA is often used in coronary artery bypass grafting because of its consistent structure and long-term patency.

❌ Why the Other Options Are Incorrect

• Musculophrenic artery arises from the internal thoracic artery as its terminal branch:
  ✅ True — one of the ITA’s terminal branches.

• It runs posterior to upper six costal cartilages:
  ✅ True — this protects it from trauma.

• It gives rise to anterior intercostal arteries:
  ✅ True — these supply the anterior thoracic wall.

• It runs superficial to the vagus nerve:
  ✅ True — the vagus nerve lies deeper in the mediastinum, not along the chest wall.

Sympathetic ganglia include:

• Paravertebral (chain) ganglia

• Prevertebral (collateral) ganglia like celiac, superior mesenteric, inferior mesenteric

• Ganglion impar → the terminal ganglion of the sympathetic chain located anterior to the coccyx

Other options:

• Dorsal vagus nucleus → parasympathetic nucleus

• Dorsal root ganglion → sensory (afferent) neurons

• Ciliary ganglion / Otic ganglion → parasympathetic ganglia

The trachea bifurcates at the level of the sternal angle (Angle of Louis), which corresponds to the T4–T5 intervertebral disc posteriorly.

• Right and left primary bronchi arise here.

• The carina (ridge inside the trachea at the bifurcation) is a key landmark in bronchoscopy.

Other options:

• T1/T2 → upper thoracic vertebrae, trachea still intact.

• T6/T7 → lower than the bifurcation, already within the lungs.

The thoracic duct drains lymph from most of the body, including:

• Both lower limbs

• Left side of thorax and upper limb

• Left bronchomediastinal trunk

• Left intercostal nodes

The right intercostal nodes drain into the right lymphatic duct (or directly into the right venous angle), not the thoracic duct.

Key features of the right main bronchus:

• More vertical than the left bronchus → why aspirated objects often enter the right lung

• About 6 cm in length

• Azygos vein arches superiorly and posteriorly to it

• Bifurcation (carina) at T4/T5 vertebral level

It does NOT lie posterior to the aortic arch — that is a feature of the left main bronchus, which passes under the aortic arch and anterior to the esophagus and thoracic aorta.

The posterior mediastinum lies behind the pericardium and in front of the vertebral column. It contains several vital structures, including:

• Thoracic duct

• Esophagus

• Sympathetic trunks

• Descending thoracic aorta

• Azygos and hemiazygos veins

Other options:

• Superior mediastinum → contains great vessels, trachea, thymus, and vagus/phrenic nerves.

• Middle mediastinum → contains heart, pericardium, and roots of great vessels.

• Anterior mediastinum → mostly fat, lymph nodes, and thymic remnants.

• Inferior mediastinum → divided into anterior, middle, and posterior parts; “posterior” is the one with these structures.

The angle of the rib is the most common site of rib fracture because it’s the most curved and weakest part, located a few centimeters lateral to the tubercle.
This area bears the brunt of bending stress during trauma.

Other options:

• Costal groove – protects intercostal vessels and nerves (rarely fractures here).

• Facet of head – articulates with vertebral bodies, less exposed.

• Tubercle – articulates with transverse process, protected by muscles.

• Neck – stronger, near vertebra.

The descending thoracic aorta gives off several visceral and parietal branches, but coronary arteries are not among them.
Instead, the coronary arteries arise directly from the ascending aorta, just above the aortic valve at the aortic sinuses.

⚙️ Branches of the Descending Thoracic Aorta:

🔹 Visceral branches (to organs):

• Bronchial arteries

• Esophageal arteries

• Pericardial arteries

• Mediastinal arteries

🔹 Parietal branches (to body wall):

• Posterior intercostal arteries (3rd–11th)

• Subcostal arteries

• Superior phrenic arteries

⚖️ Why the Other Options Are Correct Branches:

The thoracic duct is the main lymphatic channel of the body. It drains all lymph except from the right upper quadrant, which includes:

• Right side of head and neck

• Right upper limb

• Right side of thorax

These regions instead drain into the right lymphatic duct, not the thoracic duct.

⚙️ Thoracic Duct Drainage Summary:

Thus, if the thoracic duct is ligated, lymph from the right upper quadrant — including the right intercostal nodes — remains unaffected, since it never drained into the thoracic duct in the first place.

⚖️ Reasoning for Incorrect Options:

• Left brachiomediastinal trunk: ✔️ Drains into thoracic duct → affected

• Left parasternal nodes: ✔️ Drain via thoracic duct → affected

• Diaphragmatic nodes: ✔️ Inferior ones drain into cisterna chyli → affected

• Left jugular trunk: ✔️ Drains into thoracic duct → affected

The mediastinum is divided into four parts for descriptive anatomy:

1. Superior mediastinum – above the sternal angle (contains great vessels, trachea, esophagus, etc.)

2. Inferior mediastinum, which is subdivided into:

   • Anterior mediastinum – between sternum and pericardium

   • Middle mediastinum – contains the heart, pericardium, roots of great vessels, and phrenic nerves

   • Posterior mediastinum – behind the pericardium (contains thoracic aorta, azygos vein, esophagus, etc.)

Thus, the heart and pericardial sac are located in the middle mediastinum, a part of the inferior mediastinum.

Contents of superior mediastinum (from anterior to posterior):

• Thymus or its remnants

• Veins: Right and left brachiocephalic veins and upper part of SVC

• Arteries: Arch of aorta and its three branches

  • Brachiocephalic trunk

  • Left common carotid artery

  • Left subclavian artery

• Nerves: Vagus, phrenic, and left recurrent laryngeal nerve

• Trachea, esophagus, and thoracic duct

❌ Why other options are incorrect

• Brachiocephalic veins: Present — drain into the superior vena cava within the superior mediastinum.

• Arch of azygos vein: Curves over the root of the right lung to drain into the superior vena cava. 

• Left common carotid: Present — arises directly from the arch of the aorta in the superior mediastinum.

• Arch of aorta: Present — a defining feature of the superior mediastinum.

Inspiration involves the active enlargement of the thoracic cavity, allowing air to enter the lungs due to negative intrathoracic pressure.

🔹 Muscles Involved in Inspiration:

1. Primary Muscle:

   • Diaphragm — main inspiratory muscle (contracts → flattens → increases thoracic volume).

2. Accessory Muscles (during deep or labored breathing):

   • External intercostals → elevate ribs and expand thoracic cavity.

   • Sternocleidomastoid → elevates sternum.

   • Scalenus anterior (and medius, posterior) → elevate the first two ribs.

   • Serratus anterior → assists in elevating ribs when scapula is fixed.

These muscles aid inspiration by increasing the anteroposterior and lateral diameters of the thorax.

❌ Muscle Not Involved in Inspiration:

• Internal intercostal muscles (except intercartilaginous part)
  → Mainly active during forced expiration, pulling ribs downward and inward, reducing thoracic volume.

Only the intercartilaginous (parasternal) part may assist slightly in inspiration — but overall, the internal intercostals as a group are expiratory.

Each intercostal space contains an intercostal neurovascular bundle, composed of:

• V → Intercostal vein

• A → Intercostal artery

• N → Intercostal nerve

These structures run in the costal groove along the inferior border of each rib, sandwiched between the internal intercostal and innermost intercostal muscles.

Therefore, when performing a thoracentesis (pleural effusion drainage) or inserting any needle into an intercostal space, the correct and safe approach is to insert the needle just above the upper border of the lower rib — i.e., above the superior border of the rib below the intended intercostal space.

This avoids injuring the intercostal vein, artery, and nerve, which lie inferior to the rib above.

❌ Why Other Options Are Incorrect:

• Parietal pleura:
  → The parietal pleura may be penetrated intentionally during pleural fluid drainage to access the pleural cavity — avoiding it is not the goal.

• Visceral pleura:
  → Lies directly on the lung surface and is not encountered during thoracentesis unless the lung is accidentally punctured (a complication).

• Pericardium:
  → Lies deeper and more medially, not at risk in the 3rd intercostal space lateral to the sternum.

• Lungs:
  → The lung may be injured if the needle goes too deep, but this is avoided by careful depth control, not by inserting the needle above the rib.

Innervation of diaphragm:

• The phrenic nerve (C3, C4, C5) provides motor innervation to the diaphragm.

• It also provides sensory innervation to:

  • The central part of the diaphragm

  • The mediastinal and diaphragmatic pleura

  • The pericardium

🩸 Mnemonic:
“C3, 4, 5 keep the diaphragm alive.”

❌ Why Other Options Are Incorrect:

• Iliohypogastric nerve:
  → Arises from L1; supplies abdominal wall muscles and skin, not the diaphragm.

• Intercostal nerves:
  → Supply intercostal muscles and sensory innervation to the peripheral part of the diaphragm, but not the main motor supply.

• Subcostal nerve:
  → The 12th thoracic nerve — supplies abdominal wall muscles, not the diaphragm.

• Vagus nerve:
  → Provides parasympathetic innervation to thoracic and abdominal organs — not the diaphragm.

🩸 Components of the anterior thoracic wall:

1. Sternum, consisting of:

   • Manubrium (upper part)

   • Body of sternum (middle, largest portion)

   • Xiphoid process (small, inferior portion)

2. Costal cartilages connecting ribs to the sternum.

3. Intercostal muscles lie between ribs but do not form the main bony structure.

Hence, when viewing an X-ray of the anterior thoracic wall, the sternum (manubrium + body + xiphoid process) is the key structure visualized in the midline.

❌ Why Other Options Are Incorrect:

• Intervertebral discs:
  → Found posteriorly between thoracic vertebrae, not in the anterior wall.

• Intercostal muscles:
  → They fill spaces between ribs but are not bony structures forming the anterior wall itself.

• Thoracic vertebrae:
  → Form the posterior wall of the thoracic cage.

• Ribs:
  → Contribute to lateral walls, not the anterior midline structure visualized in front.

Unlike the parietal pleura, which is pain-sensitive, the visceral pleura is insensitive to pain, temperature, or touch because it is innervated by autonomic (vasomotor) nerves derived from the pulmonary plexus.

✳️ Innervation details:

• Visceral pleura:

  • Supplied by autonomic nerves (both sympathetic and parasympathetic fibers) from the pulmonary plexus.

  • These fibers regulate vasomotor tone (blood flow) and glandular secretion, not somatic sensation.

  • Pain sensations from visceral pleura are not well localized and are often referred vaguely to the thoracic or upper abdominal region.

• Parietal pleura:

  • Costal pleura → intercostal nerves

  • Mediastinal pleura → phrenic nerve

  • Diaphragmatic pleura → lower intercostal nerves (peripherally) and phrenic nerve (centrally)

  • Highly sensitive to pain

❌ Why Other Options Are Incorrect:

• Collateral intercostal nerve / Only intercostal nerves:
  → These innervate parietal pleura (costal part), not visceral pleura.

• Somatic nervous system:
  → Supplies skeletal muscles and body wall structures; visceral pleura is under autonomic control, not somatic.

• Phrenic nerve:
  → Innervates mediastinal and central diaphragmatic pleura, not visceral pleura.

The mediastinal surface of the left lung faces the heart and great vessels, and it bears several grooves and impressions formed by adjacent thoracic structures.

On the left lung, the key relationships are:

• Arch of aorta: Forms a superior curved groove over the hilum of the left lung.

• Descending thoracic aorta: Leaves a vertical groove posterior to the hilum.

• Left subclavian artery and left common carotid artery: Leave smaller impressions above the aortic arch groove.

• Heart (left ventricle and left atrium): Form the cardiac impression, which is deeper on the left lung.

Therefore, the arch of the aorta specifically produces the prominent curved groove on the mediastinal surface of the left lung, differentiating it from the right lung (which has a groove for the arch of the azygos vein).

❌ Why Other Options Are Incorrect:

• Arch of azygos vein: Related to the right lung, not the left; it arches over the right lung root to drain into the superior vena cava.

• Superior vena cava: Also related to the right lung; it lies anterior and to the right of the trachea.

• Ascending aorta: Lies more central and anterior in the mediastinum, making no direct groove on the left lung.

• Thoracic duct: Runs posterior to the esophagus and does not form a visible surface groove on the lung.

Course of the thoracic duct:

• Begins at the cisterna chyli (around T12) in the abdomen.

• Enters the thorax through the aortic hiatus (also at T12).

• Ascends through the posterior mediastinum, behind the esophagus, and between the aorta and azygos vein.

• At around T5, it crosses from the right side to the left, entering the superior mediastinum.

• Continues upward to terminate at the venous angle.

Therefore, the thoracic duct exits the posterior mediastinum at T5, marking its transition into the superior mediastinum.

❌ Why Other Options Are Incorrect:

• T12: This is the level where the thoracic duct begins (cisterna chyli and aortic hiatus), not where it exits the posterior mediastinum.

• T10: This is the esophageal hiatus level, still within the posterior mediastinum.

• T8: This is the caval opening level — associated with the inferior vena cava, not the thoracic duct.

• T2: Too high — by this point, the thoracic duct has already entered the superior mediastinum and is ascending toward the neck.

https://www.researchgate.net/figure/Drawing-of-a-transverse-section-through-the-thorax-at-the-level-of-the-aortic-arch-shows_fig1_7851907

The transverse plane through the sternal angle (T4–T5) includes several classic landmarks:

• Arch of azygos vein draining into the SVC ✅

• Bifurcation of the trachea (carina) ✅

• Beginning and end of the aortic arch (hence nearby great vessels)

• Left common carotid artery (arising from the aortic arch) ✅

However, the right brachiocephalic trunk (innominate artery) does not lie at this plane. It originates from the aortic arch but then ascends and bifurcates behind the right sternoclavicular joint into:

• Right common carotid

• Right subclavian

That bifurcation is above the sternal angle, at the root of the neck, not at T4–T5.

❌ Why the others are in the vicinity

• Azygos vein drains into SVC → occurs at the T4–T5 level as it arches over the right lung root.

• Right common carotid artery → its proximal part (from brachiocephalic trunk) lies near this plane.

• Left common carotid → arises directly from the aortic arch at this level.

• Bifurcation of trachea → the carina is a classic T4–T5 landmark.

✅ Correct Answer: T12

Explanation of Correct Option:

• The thoracic duct enters the posterior mediastinum through the aortic hiatus of the diaphragm at the level of T12.
• It travels upward between the aorta (on its left) and the azygos vein (on its right), posterior to the esophagus.
• This duct is the largest lymphatic vessel in the body, carrying lymph from most of the body (except the right upper quadrant) into the left venous angle (junction of the left subclavian and internal jugular veins).

Explanation of Incorrect Options:

❌ T10

• This is the level of the esophageal hiatus, through which the esophagus and vagal trunks pass — not the thoracic duct.

❌ L1

• The thoracic duct begins as the cisterna chyli around L1–L2, but it does not enter the thoracic cavity here.

❌ L2

• The cisterna chyli, the origin of the thoracic duct, is typically located at L2, below the diaphragm.

❌ T8

• This is the level of the caval opening in the diaphragm for the inferior vena cava, not related to the thoracic duct.

✅ Correct Answer: 2nd costal cartilage

Explanation of Correct Option:

• The pulmonary trunk arises from the right ventricle and carries deoxygenated blood toward the lungs.
• It runs upward, backward, and slightly to the left, and at the level of the 2nd costal cartilage, just below the sternal angle (T4/T5 vertebral level), it bifurcates into the right and left pulmonary arteries.
• This level corresponds roughly to the plane of Ludwig’s angle, which is a key anatomical landmark separating the superior and inferior mediastinum.

Explanation of Incorrect Options:

❌ 3rd intercostal space

• Lies below the actual level of bifurcation; by this point, the pulmonary trunk has already divided into pulmonary arteries.

❌ 1st intercostal space

• Too high; this space lies near the origin of the pulmonary trunk but not its bifurcation.

❌ 3rd costal cartilage

• Also too low; the bifurcation occurs above this level.

❌ 1st costal cartilage

• This level corresponds roughly to the origin of the pulmonary trunk from the right ventricle, not its division.

Pump Handle Movement

• Ribs involved: 2–6
• Axis: Transverse (through costovertebral and costotransverse joints)
• Movement: Upward and forward rotation of ribs
• Effect: Increases the anteroposterior diameter of the thoracic cavity
• Example: Sternum moves like a pump handle during inspiration

Bucket Handle Movement

• Ribs involved: 7–10
• Axis: Anteroposterior
• Movement: Upward and outward elevation of ribs
• Effect: Increases the transverse diameter of the thoracic cavity
• Example: Ribs move like the handle of a bucket

Caliper Movement

• Ribs involved: 11–12
• Axis: Vertical (near vertebral ends)
• Movement: Outward and backward (swinging open like calipers)
• Effect: Increases the lateral dimensions of the lower thorax
• Example: Floating ribs widen the lower thoracic aperture

✅ Correct Answer: Mediastinal pleura

Explanation:

The phrenic nerve (C3–C5) provides sensory innervation to the central part of the diaphragm, mediastinal pleura, and diaphragmatic pleura (central portion).

Therefore, injury to the phrenic nerve will denervate the mediastinal pleura, leading to loss of sensation in that area. The pain from this pleura normally refers to the shoulder (C3–C5 dermatome) because of the same spinal segments.

❌ Lateral diaphragmatic pleura:

This is supplied by intercostal nerves, not the phrenic nerve.

❌ Cervical pleura (cupula):

Innervated by the first intercostal nerve, not the phrenic nerve.

❌ Costal pleura:

Supplied by intercostal nerves, corresponding to the thoracic wall segments.

❌ Apical pleura:

This is another term for cervical pleura, also innervated by intercostal nerves, not the phrenic.