Thorax and lungs

Describe the bones of the thoracic cage (ribs, thoracic vertebrae and sternum).

• 12 pairs of ribs (true, false, floating, typical, atypical)

• 12 thoracic vertebrae (T1–T12) - heart-shaped body, long downward sloping spinous process + costal facets for ribs

• Sternum (manubrium, body, xiphoid process)

What does the manubrium of the sternum articulate with? Which notches does it contain?

jugular notch, clavicular notches, articulation with rib 1

What does the body of the sternum articulate with?

ribs 2-7

What does the xiphoid process of the sternum delimit? 

lower end marking the midline at T9

Recall the arrangement and location of structures within the intercostal spaces + their function

Located between adjacent ribs (11 pairs)

Contents (from superficial → deep):

• External intercostal muscle

• Internal intercostal muscle

• Innermost intercostal muscle

• Neurovascular bundle (in costal groove):

  • Vein (superior)

  • Artery (middle)

  • Nerve (inferior) → mnemonic: VAN

• Collateral branches below rib

Function:

• Maintain rigidity of thoracic wall; assist in respiration

Recognise the mediastinum, describing its divisions and contents.

Central thoracic compartment between pleural sacs

Divisions:

• Superior mediastinum (above sternal angle, T4–T5):

  • Thymus

  • Great vessels (arch of aorta, SVC, brachiocephalic veins)

  • Trachea, esophagus, thoracic duct

  • Vagus & phrenic nerves

• Inferior mediastinum (below T4–T5):

  • Anterior: connective tissue, lymph nodes

  • Middle: heart, pericardium, roots of great vessels, phrenic nerves

  • Posterior: descending aorta, esophagus, thoracic duct, azygos/hemiazygos veins, vagus nerves

Describe the morphology and anatomical relations of the lungs.

Right Lung:

• 3 lobes (superior, middle, inferior)

• 2 fissures (oblique, horizontal)

• Relations:

  • Heart (right atrium), SVC, azygos vein, esophagus

Left Lung:

• 2 lobes (superior, inferior)

• 1 fissure (oblique)

• Cardiac notch & lingula

• Relations:

  • Heart (left ventricle), aortic arch, descending aorta

Hilum contents:

• Pulmonary artery (superior), pulmonary veins (inferior), bronchus (posterior)

• “RALS” mnemonic: Right – artery anterior, Left – artery superior

What is a hilum?

specialised area on an organ where vessels, nerves, and lymphatic vessels enter or exit

Locate and describe the thoracic diaphragm and its key features.

Location: Dome-shaped muscle separating thorax & abdomen

Attachments:

• Sternal part: xiphoid process

• Costal part: lower 6 ribs

• Lumbar part: crura from L1–L3 vertebrae

• Central tendon: insertion point

Openings:

• Caval opening (T8): IVC, right phrenic nerve

• Esophageal hiatus (T10): esophagus, vagal trunks

• Aortic hiatus (T12): aorta, thoracic duct, azygos vein
  → Mnemonic: “I 8 10 Eggs At 12”

Function: Main muscle of inspiration

Locate and trace the phrenic and vagus nerves, describing their course through the thorax, and the structures that they innervate.

Phrenic Nerve (C3–C5):

• Course:

  • Descends anterior to scalene anterior

  • Enters thorax between subclavian artery & vein

  • Runs anterior to root of lung

  • Reaches diaphragm (motor supply)

• Innervation:

  • Motor: diaphragm

  • Sensory: pericardium, mediastinal pleura, diaphragmatic pleura/peritoneum

Vagus Nerve (CN X):

• Course:

  • Enters thorax posterior to sternoclavicular joint

  • Right: passes posterior to root of lung → forms posterior vagal trunk

  • Left: crosses aortic arch → posterior to root of lung → anterior vagal trunk

• Innervation:

  • Parasympathetic to thoracic & abdominal viscera

  • Branches: recurrent laryngeal, cardiac, pulmonary, esophageal plexuses

What is a cavity in anatomy? 

Space between and around structures 

Essentially, what key structures make up the thorax?

• thoracic wall : bones - thoracic cage + intercostal muscle, skin, fascia

• thoracic cavity: cavity containing heart, cavity containing lungs

• thoracic viscera/organs : trachea, lungs (including root and hilum), heart and nerves

Which key internal organs make up the thorax?

heart and lungs

What makes up the thoracic wall? What is its function?

thoracic cage (bones) + muscle + skin + fascia

enclosing part of the thorax

Which cavities constitute the thoracic cavity?

mediastinum + pleura and pleural cavity

Which three main structures make up the thoracic cage?

sternum, ribs and thoracic vertebra

What are the 3 main structures of the sternum?

manubrium, body, xiphoid process

What are the main structures of a rib?

head, neck, tubercle, shaft/body, costal groove

What defines a false rib? Which rib pairs are they?

ribs that attach indirectly to the sternum by connecting to the cartilage of the true rib above them

8th, 9th, and 10th ribs

What defines a true rib? Which ones are they?

ribs that attach directly to the sternum via their own cartilage

first seven pairs

What defines a floating rib? Which pairs of ribs are they?

ribs which do not attach to the sternum at all

11th and 12th

What distinguishes a typical from an atypical rib?

typical: ribs 3-9 - consist of a head, neck and body - head is wedge shaped with 2 articular facets

atypical: 1, 2 and 10 through 12 - shorter, single facet instead of two

What are the qualities due to the differing structures of typical and atypical ribs?

articulation - two facets on the head of a typical rib allow it to articulate with two adjacent vertebrae

flexibility - Ribs are flexible and move to allow for breathing, as they increase the size of the thoracic cavity

What are the main structures making up thoracic vertebrae?

body, pedicle, transverse process, lamina, and spinous process

Network of bones allowing structure and flexibility around the lungs and heart

thoracic cage

What are the 3 types of vertebrae?

cervical, thoracic, lumbar

What do intercostal muscles control the movement of? Which biological process does this allow?

thoracic cage

breathing

What differentiates intercostal muscles from superficial to deep?

superficial: external intercostal muscles running in upwards direction

deep: internal, running in downwards direction

Which bundle is found on the costal groove of intercostal muscles? Between which layers of intercostal muscles is it found?

neurovascular bundle

between internal and innermost intercostal muscles 

What vessels are found just under the intercostal groove of intercostal muscles from superior to inferior?

intercostal vein, artery then nerve (VAN)

What’s found at the very top of the thoracic cavity? What does it differentiate between?

superior thoracic aperture (inlet)

neck from thorax

Where is the superior thoracic aperture found?

at the level of sternum, 1st rib and 1st thoracic vertebrae

Where is the inferior thoracic aperture found?

at the level of the xiphisternal joint + costal cartilage 7th - 10th ribs + 11th to 12th ribs + 12th thoracic vertebrae

What does the inferior thoracic aperture act as? What does it separate?

an outlet

thorax from diaphragm

What is the biggest organ of the thorax?

diaphragm

What is the primary muscle of respiration? What innervates it?

diaphragm

phrenic nerve

How is the diaphragm attached within the thoracic cavity?

central tendon + R/L crura (finger like extensions)

What are the 3 passageways into the abdomen?

• caval opening

• oesophageal hiatus

• aortic hiatus

What is the mediastinum? Which organs does it contain? 

area between the lungs

heart, its large blood vessels, the trachea, oesophagus, thymus and lymph nodes 

Which pleura is in direct contact with the lungs?

visceral pleura

What are the 2 main parts of the mediastinum and further subcategories ?

• superior

• inferior

  • anterior

  • middle

  • posterior

Between which ribs does the mediastinum become the inferior mediastinum?

between IV and V, at very top of the heart

What is the role of fluid between the 2 layers of the pleura?

to reduce friction between layers

What does the pleural cavity contain?

small amount of serous fluid: lubricates the lung's surfaces = smooth mvt during breathing + generates surface tension to keep the lungs connected to the chest wall

What is the trachea?

cartilaginous tube from larynx to bronchi of the lungs

What is the trachea made up of?

tracheal cartilages, trachealis muscles and ligaments

At which point does the trachea bifurcate? Into what structures?

at carina - into right and left bronchi

What distinguishes the right bronchus from the left one?

right is shorter, wider and descends more vertically than left one

What distinguishes the structure of the right bronchus from the left one?

just like each lung, right divides into 3 lobar bronchi // left divides into 2 lobar bronchi - in both cases each lobar bronchi is divided into further segmental bronchi

If food were to enter the trachea, which bronchus would it go down, left or right and why?

into right because is more vertical

Why does it make sense for the trachea to be made up of carteal muscle and for it to be flexible? 

direct contact with oesophagus so extending or flexing allows bigger pieces of food to go down the oesophagus = avoids choking

What are the main structures of the lungs?

apex, base, lobes and fissures

How many lobes and fissures does the right lung have?

3 lobes (superior, middle and inferior) and 2 fissures (oblique and horizontal)

How many lobes and fissures does the left lung have? What special structures/imprints does it have and what are their roles?

2 lobes (superior and inferior) and 1 fissure (oblique)

lingula is a tongue like projection protecting the heart + cardiac notch is a space for the heart, slight imprint to make room for it and keep it close to lungs for oxygenation of blood

What do mediastinal surfaces have impressions for ?

heart, oesophagus and great vessels

When considering an organ, how can we determine which vessel is the artery based solely on relative position to other vessels?

artery is always most superior

What distinguishes the hilum of the lung from the root of the lung?

hilum is the area // root is the structures

Where does the bronchus of the lobe of the lung lie ? (anatomical position)

posteriorly

Where does the pulmonary artery lie relatively to the pulmonary vein?

superiorly

Which vessels are the most anterior and inferior in the lungs? (as opposed to artery eg)

superior and inferior pulmonary veins

Which two nerves innervate the thoracic viscera?

vagus and phrenic

Where does the vagus nerve (CNX) lie relatively to the lung’s root? 

posteriorly

What does the vagus nerve innervate?

thoracic viscera (heart/lungs) then penetrates the diaphragm with the oesophagus to supply abdominal viscera (liver/gallbladder/spleen/kidneys/pancreas…)

Where does the phrenic nerve lie relatively to the lung’s root?

anteriorly

What does the phrenic nerve innervate?

pericardium and diaphragm

If a nerve in the thorax is not innervating the diaphragm or the pericardium, which nerve can we be sure it is?

vagus 

Before entering the thorax, where do the phrenic and vagus nerve lie relatively? Why is this changed when entering the thorax?

phrenic is posterior and vagus A, they cross over when entering and therefore innervate A and P respectively in the thorax.

In the thorax, which nerve lies anteriorly?

phrenic, going to pericardium and diaphragm

What are the thoracic viscera?

internal organs within chest cavity ie heart, lungs, trachea, esophagus, thymus gland

Where do intercostal muscles lie and what do they surround?

lie within the intercostal space and surround the neurovascular bundle