2. Thorax

What shape is the thorax and what are its two openings?

Cylinder-shaped with a superior thoracic aperture at the top and an inferior thoracic aperture at the bottom

Why is the superior thoracic aperture open?

To allow vessels and structures to pass to and from the neck

What closes the inferior thoracic aperture?

The diaphragm

What three compartments does the thorax enclose?

Two pleural cavities (containing the lungs) and the mediastinum

What structures make up the thoracic cage?

Thoracic vertebrae (TI-TXII) and intervertebral discs, sternum, and ribs (I-XII)

Which ribs are true ribs?

Ribs I-VII

Which ribs are false ribs?

Ribs VIII-XII

Which ribs are floating ribs?

Ribs XI and XII

What are the boundaries of the superior thoracic aperture?

TI vertebra posteriorly, manubrium of sternum anteriorly, and rib I on either side

What are the boundaries of the inferior thoracic aperture?

TXII vertebra posteriorly, rib XII and distal end of rib XI laterally, costal margin (ribs VII-X) anterolaterally, and xiphisternum anteriorly

Which structures pass through the diaphragm?

Oesophagus and inferior vena cava

Which structure passes posteriorly to the diaphragm?

Aorta

Name the chest wall muscles

Pectoralis major, pectoralis minor, subclavius, and intercostal muscles (external, internal, innermost)

What are the main vessels exiting the heart?

Aorta and pulmonary arteries

What are the branches of the aorta in the thorax?

Left carotid artery, left subclavian artery, and brachiocephalic trunk

What supplies blood to the rib cage?

Anterior and posterior intercostal arteries

What does the internal thoracic artery divide into?

Musculophrenic and superior epigastric arteries

What are the main vessels entering the heart?

Superior and inferior vena cava

What makes up the azygos network?

Azygos vein (right), hemiazygos vein (lower left), and accessory hemiazygos vein (upper left)

Where is the mediastinum located?

Medially between the two pleural cavities, from the manubrium of the sternum anteriorly to the thoracic vertebrae posteriorly

How is the mediastinum divided?

Into superior and inferior regions; the inferior is further divided into anterior, middle (pericardium and heart), and posterior

What does the mediastinum contain?

Thymus gland, pericardial sac, heart, trachea, major arteries and veins, oesophagus, thoracic duct, and nervous system components

What is the function of the thymus?

It is an essential immune organ primarily responsible for the production and maturation of T lymphocytes

What happens to the thymus with age?

It becomes less active and regresses, with its tissue replaced by adipose tissue

What are the clinical landmarks at the vertebral plane TIV/TV?

Rib II, superior/inferior mediastinum border, arch of aorta, entrance of superior vena cava to heart, bifurcation of trachea, and upper limit of pulmonary trunk

What are the two layers of pleura?

Visceral pleura (next to lungs) and parietal pleura (next to ribs)

What is a pneumothorax?

A collection of gas or air in the pleural cavity causing the lung to collapse

What is a tension pneumothorax?

When air accumulates and pushes the mediastinum to one side — a clinical emergency

At what level does the trachea bifurcate?

At TIV/TV, into the left and right primary bronchi at the carina

Why are inhaled objects more likely to lodge in the right primary bronchus?

Because it is more vertical and wider than the left

What is the order of bronchial divisions?

Primary bronchus → secondary (lobar) bronchus → tertiary (segmental) bronchus → bronchioles

What is the pericardium?

A fibro-serous sac surrounding the heart, made up of the fibrous pericardium (outer) and serous pericardium (inner)

What forms the right border of the heart on a PA chest X-ray?

Superior vena cava, right atrium, and inferior vena cava

What forms the left border of the heart on a PA chest X-ray?

Arch of the aorta, pulmonary trunk, left auricle, and left ventricle

Describe the circulation of blood through the right side of the heart

Superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → lungs

Describe the circulation of blood through the left side of the heart

Pulmonary veins → left atrium → mitral (bicuspid) valve → left ventricle → aortic valve → ascending aorta → body

What drains blood from the body into the right atrium?

Superior and inferior vena cava

What does the pulmonary trunk divide into?

Left and right pulmonary arteries, which enter the lungs at the hilum

How many pulmonary veins are there and where do they drain?

Four — superior and inferior on left and right — they drain into the left atrium

What are the branches of the aortic arch?

Left common carotid artery, left subclavian artery, and brachiocephalic trunk

Which vertebra does Rib I articulate with?

TI

Which vertebrae does Rib II articulate between?

Between TI and TII

Which vertebra does Rib X articulate with?

TX only

Which vertebrae do Ribs XI and XII articulate with?

Their own corresponding vertebrae only (XI with TXI, XII with TXII)

What structures make up the lung root attaching the pleural cavity to the mediastinum?

Bronchus, blood vessels, lymphatics, and nerves

What veins drain parasternally into the internal thoracic vein?

Musculophrenic and superior epigastric veins