📚 Question Bank

The Merkel cells act as touch receptors. They are present in the basal layer of the epidermis and outer root sheath of some big hair follicles and their functions are as follows:

• Act as slowly adapting mechanoreceptors in the skin that convey touch sensation.
• Detects the directional deformation of the epidermis and hair movement.
• Sense sustained pressure and edges of applied objects on the skin.

Meissner corpuscles are present in the dermal papillae (upper dermis).

They are primarily present in the dermal papillae of all parts of the hand and foot, the lips, the anterior aspect of the forearm, palpebral conjunctiva and mucous membrane of the apical part of the tongue. They are highly concentrated in the finger pads.

Meissner’s corpuscles are rapidly adapting mechanoreceptors that are sensitive to shape and textural changes during exploratory and discriminatory touch. Their high sensitivity provides the neurological basis for sensing the Braille text.

The muscle responsible for goosebumps (image) is the arrector pili muscle which is a smooth muscle supplied by the sympathetic nerves. It connects the dermal sheath of the hair follicles to the papillary layer of the dermis.

Contraction of these muscles makes the hair more vertical (piloerection), elevates the epidermis around the hair (goosebump), and dimples the skin surface where the muscle is inserted.

The image given below shows the arrector pili muscle attached to the hair follicles:

Apocrine sweat glands produce secretions that undergo bacterial decomposition to generate odour.

Sweat glands are classified as follows:

• Eccrine sweat glands - The majority of sweat glands in the body are eccrine and open via rounded pores to the skin surface.
• Apocrine sweat glands - They are present in the axillae, perianal area, areolae, periumbilical skin, and genitalia.

The white opaque crescent present in the proximal part of the nail is known as the lunula. Parts of the nail:

• Root - It is the proximal hidden part, buried into the nail groove and is overlapped by the nail fold of the skin.
• Free border - It is the distal part of the nail that is free from the skin.
• Body - It is the exposed part of the nail that is adherent to the underlying skin.

The non-fibrous element of the extracellular matrix in the connective tissue is formed by the ground substance.

Connective tissue consists of cells and extracellular matrix:

• The cells include fibroblasts, macrophages, plasma cells, mast cells, fat cells, and pigment
• cells.
• The extracellular matrix contains fibrous and non-fibrous elements.
• The fibrous element has three types of fibres - collagen, elastin and reticulin
• The non-fibrous element is formed by the ground substance

The statement 'ligaments are devoid of nerve supply' is false.

Ligaments have a rich nerve supply. This helps them function as sense organs and participate

in reflex mechanisms important for monitoring the position and movements of the joint. Intrinsic ligaments surround the joint, whereas extrinsic ligaments are away and independent of the joint.

The majority of ligaments are made up of collagen fibres predominantly. These are inelastic and not stretchable. Ligamentum flavum and ligaments of auditory ossicles are exceptions, as

they predominantly have elastin fibres that make them elastic and stretchable.

The structure marked X in the image is the interosseous membrane which is a modified form of deep fascia. It is present in the forearm and leg.

The interosseous membrane helps in:

• Maintaining optimum distance between bones
• Increasing surface area for attachment of muscles
• Transmission of weight from one bone to another

The following image shows the graphical illustration of interosseous membrane of the Leg:

The linear fibrous band formed by interdigitation of the tendinous or aponeurotic ends of the muscles is known as raphe.

Unlike most ligaments, the raphe are stretchable. Examples of raphe include:

• linea alba
• pterygomandibular raphe
• mylohyoid raphe
• median pharyngeal raphe
• anococcygeal raphe

The heart enclosed in the pericardium occupies the middle mediastinum.

The middle mediastinum is the broadest part of the inferior mediastinum and contains the pericardium, heart, tracheal bifurcation, and corresponding vessels and nerves.

Option B: The thymus or its remnants are present in the superior and anterior mediastinum. Option C: The posterior mediastinum is bounded:

• Anteriorly by
• Tracheal bifurcation
• Pericardium
• Pulmonary vessels
• Posteriorly by
• Bodies of T5-T12 vertebrae
• Anteroinferiorly by
• Arched posterior 1/3rd of the central portion of the diaphragm

Option D: The lower border of the posterior mediastinum extends more inferiorly as compared to the anterior mediastinum.

The left recurrent laryngeal nerve will not be visualized in this section, as it is not present in the middle mediastinum. It is located in the superior mediastinum.

The right recurrent laryngeal nerve does not pass through the superior thoracic aperture, but the left recurrent laryngeal nerve does. The right recurrent laryngeal nerve hooks around the right subclavian artery in the neck region and ascends up in the tracheoesophageal groove to supply the larynx.

Structures passing through the superior thoracic aperture/thoracic inlet are:

• Viscera:
• Esophagus
• Trachea
• Lung apices with pleura
• Thymic remnants
• Large vessels:
• Brachiocephalic artery
• Right and left brachiocephalic vein
• Left common carotid artery
• Small vessels:
• Right and left internal thoracic arteries
• Right and left superior intercostal arteries
• Right and left first intercostal veins
• Inferior thyroid veins
• Nerves:
• Left recurrent laryngeal nerve
• Right and left phrenic nerves
• Right and left vagus nerves
• Right and left sympathetic trunks
• Right and left first thoracic nerves
• Muscles:
• Sternohyoid
• Sternothyroid
• Longus colli
• Thoracic duct

The given clinical scenario is suggestive of obstruction of the superior vena cava. It does not pierce the pericardium at the level of 3rd costal cartilage.

The superior vena cava pierces the pericardium opposite 2nd costal cartilage (angle of Louis/sternal angle), at the level of T4-T5 intervertebral disc. It also receives the azygous vein about 2 cm below the sternal plane at the level of T5 vertebra.

It enters the right atrium at the level of the 4th intercostal space.

Superior vena cava syndrome:

Obstruction of superior vena cava due to metastatic cancers (eg. lung cancer, breast cancer, etc.) can result in reduced venous return from head and neck and upper extremities. It presents with swelling of the neck and face, dyspnea, headache, dizziness, and hemoptysis. Symptoms are aggravated by bending forwards.

On examination, the following may be seen

• Dilated neck veins
• Proptosis
• Papilledema
• Increased collateral veins on the anterior chest wall - flow is completely downward

CT-chest shows an absence or reduction of the opacification of the central veins and the presence of prominent collateral venous circulation.

The thoracic duct usually originates at the level of the L1 vertebra.

The thoracic duct usually originates anterior to L1 or L2 vertebra. It is formed when the intestinal and two lumbar lymph trunks join to form cisterna chyli which continues as the thoracic duct.

Course: It passes through the aortic hiatus of the diaphragm and enters the posterior mediastinum lying to the right between the aorta and the azygos vein up till T4-T5 vertebra. It then crosses over to the left side posterior to the esophagus. It continues upwards in the superior mediastinum and arches over the subclavian artery and descends anteriorly to drain into the confluence of the left jugular vein and left subclavian vein.

It receives lymph from both halves of the body below the diaphragm and only the left half of the head and neck, upper limb, and thorax.

The thoracic duct does not receive a tributary from the right bronchomediastinal trunk. It receives a tributary from the left bronchomediastinal trunk.

The right lymphatic duct receives lymphatic drainage from the right half of the body above the diaphragm from:

• The right half of head and neck via the jugular trunk
• The right half of thoracic cavity via right bronchomediastinal trunk
• Right upper limb via subclavian trunk
• Clinical relevance:

Chylothorax refers to the condition in which, there is an accumulation of lymphatic fluid in the pleural cavity. Depending on whether the obstruction of the thoracic duct is below or above the level of the fifth thoracic vertebra the pleural effusion is either right or left-sided, respectively.

The structure affected in this case is the thoracic duct. It drains into the junction of the left jugular and left subclavian veins.

The given image shows chyle, and the case scenario is suggestive of chylothorax secondary to obstruction of the thoracic duct by Virchow's node.

Clinical note:

In gastric cancer, metastasis to the left supraclavicular lymph node causes its enlargement, and it is known as Virchow's node. The Virchow's node is closely related to the thoracic duct at the site where it drains into the venous system, therefore its enlargement can mechanically obstruct the thoracic duct.

The cross-section shown in the image is at the level of T3-T4.

The cross-section shows a large vascular opening of the arch of the aorta, along with three small openings corresponding to the brachiocephalic trunk, left common carotid artery and left subclavian artery. This suggests that the section was taken at the level between T3 and T4.

Options A, B: In cross-sections at the levels of T1-T2 and T2-T3, only the small vascular openings of the branches arising from the arch of aorta would be visible.

Option D: In cross-section at the level of T4-T5, where, the arch of the aorta begins and ends, bifurcation of the pulmonary trunk is visible.

The diaphragm is not supplied by the middle phrenic artery The blood supply of diaphragm is via (Mnemonic - Simple):

• Superior phrenic arteries
• Inferior phrenic arteries
• Musculophrenic arteries
• Pericardiophrenic arteries
• Lower 5 intercostal and subcostal arteries

The area marked A represents the medial arcuate ligament. The thoracic sympathetic trunk passes posterior to it and becomes the lumbar sympathetic trunk.

The esophageal hiatus is located at the level of the T10 vertebra, and it forms a normal constriction of the esophagus. It transmits the following:

• Esophagus
• Vagal trunks
• Gastric nerves
• Esophageal branches of the left gastric vessels and
• Some lymphatic vessels

Clinical significance:

Anatomical constrictions of the esophagus are important landmarks in esophagoscopy. These are 4 in number and located at a distance from the upper incisors as follows:

• 15cm - Cricopharyngeus muscle
• 22.5cm - Aortic arch
• 27.5cm - Left bronchus
• 37.5cm - Diaphragmatic opening

The azygous vein and the thoracic duct are present at the aortic hiatus. These are transmitted along with the thoracic aorta.

Clinical significance:

Aortic dissection occurs when there's an intimal tear in the aorta. It presents with tearing interscapular pain and extension of dissection into the abdominal aorta can present with abdominal pain. CT/MRI are the investigations of choice. Aortic dissections are classified using the DeBakey and Stanford systems. Depending on the classification, aortic dissections are managed with aggressive antihypertensive therapy or immediate surgical intervention (open/endovascular).

The structure marked A is the aortic opening of the diaphragm.

The vagal trunk does not pass through the aortic opening of the diaphragm. It passes through the esophageal opening at the level of T10 vertebra.

The left phrenic nerve is unlikely to be injured as does not pass through any specific opening in the diaphragm. It passes through the muscular part of the diaphragm anterior to the central tendon, just lateral to the left cardiac surface and more anterior than the right phrenic nerve.

Structures passing through the esophageal hiatus are:

• Esophagus
• Vagal trunks
• Gastric nerves
• Esophageal branches of the left gastric vessels
• Some lymphatic vessels
• Clinical significance:

In carcinoma esophagus involving the lower third, the Orringer approach or transhiatal esophagectomy is done. The stomach and lower part of esophagus are mobilised via laparotomy and the upper part is mobilized via the left side of the neck. Blunt dissection is done at the hiatus to approach the thorax from the abdomen. Other alternatives to this procedure are robotic and thoracoscopic techniques

The greater splanchnic nerve usually pierces through the crus of the diaphragm to enter the thorax and does not pass posterior to the crus of the diaphragm.

The aortic hiatus is present posterior to the crus of the diaphragm, hence the following structures are likely to be damaged-

• Aorta
• Thoracic duct
• Azygous vein

The surface marking of aortic valve is beside the sternum in the left third intercostal space.