Anatomy: Lungs and the Thorax

Question 1

What 2 distinct clinical and anatomical regions can the airway be split into?

Answer 1

The upper and lower airway

Question 2

What are the major structures of the upper airway?

Answer 2

Nasal cavity
Oral cavity
Nasopharynx
Oropharynx
Laryngopharynx
Larynx
(also the sinuses which cannot all be seen)

Question 3

What are the major structures of the lower airway?

Answer 3

Trachea
Left main bronchus
Right main bronchus
(and the smaller bronchi, bronchioles and alveoli which cannot be seen)

Question 4

What are the two entrances for air into the pharynx?

Answer 4

Nasal cavity

Oral cavity

Question 5

What are the three divisions of the pharynx?

Answer 5

The nasopharynx is most superior division, lying behind the nasal cavity.
The oropharynx lies posteriorly to the oral cavity.
The most inferior part of the pharynx is the laryngopharynx (also hypopharynx).

Question 6

Where does air exit the pharynx? What about food?

Answer 6

Air exits via the larynx

Food exits via the oesophagus

Question 7

What is the trachea and where is it situated?

Answer 7

The trachea (or windpipe) is a flexible tube arising from the inferior end of the larynx at the level of the 6th cervical vertebra (C6).
The trachea is approximately 10 cm long and ends at the level of the sternal angle (T4/5 intervertebral disc) where it divides into left and right main bronchi, one for each lung. This is the level of the transthoracic plane.

Question 8

What are the tracheal rings?

Answer 8

These are C-shaped rings of fibrocartilage which are deficient posteriorly where the trachea is adjacent to the oesophagus.

Question 9

What does the flexibility of the trachea allow for?

Answer 9

The flexibility of the trachea allows the upper end to move with the larynx, for example on swallowing. The lower end moves with the diaphragm as it is lowered and raised in respiration.

Question 10

What is located on either side of the trachea?

Answer 10

On either side of the trachea are the common carotid arteries taking blood to the head and, in front of it, lies the thyroid gland at the level of C5-T1.

Question 11

What main bronchus are aspirated foreign bodies most likely to end up in?

Answer 11

The right main bronchus is the site aspirated structures tend to lodge due to its wider and more vertical structure

Question 12

What are the features of the main bronchi?

Answer 12

Notice that the right main bronchus is wider and shorter (2.5cm) than the left (5cm) and passes directly to the hilum of the lung. Because it is wider and more vertical than the left main bronchus, foreign objects inhaled by small children lodge more frequently in the right main bronchus than the left.

Question 13

What are the lobar and segmental bronchi?

Answer 13

Within the lung the main bronchi divide into lobar bronchi each supplying one lobe of a lung with air. The left lung has two lobes while the right lung has three so there are two lobar bronchi on the left and three on the right. Each lobar bronchus divides into several segmental bronchi each going to one bronchopulmonary segment (see below). These airways then subdivide many times, the branches becoming smaller on each division.

Question 14

What are the bronchioles and what are their features?

Answer 14

The smallest branches are called bronchioles. These do not have any cartilage in their walls but do have large amounts of smooth muscle so that these airways, by constricting or relaxing, control the flow of air into the air sacs or alveoli, where gaseous exchange takes place.

Question 15

What structures have a complete ring of cartilage?

Answer 15

Cricoid

Question 16

What structures have a C-shaped ring of cartilage?

Answer 16

Trachea

Main bronchi

Question 17

What structures have plates or crescents of cartilage?

Answer 17

Small bronchi

Question 18

What structures have no cartilage?

Answer 18

Bronchioles

Question 19

What is the carina?

Answer 19

Where the trachea splits into the left and right bronchi

Question 20

What is the diaphragm? Which parts are muscular/fibrous? What is its function?

Answer 20

The diaphragm forms a partition between the abdomen and the thorax. The outer part is muscular while the inner part, the central tendon, is fibrous and is firmly attached to the pericardium, the fibrous sac containing the heart. The diaphragm is the main muscle of ventilation, descending into the abdomen on inspiration (breathing in).

Question 21

What are the three parts of the diaphragm that attach the bony skeleton of the thorax?

Answer 21

The sternal part is attached to the posterior aspect of the xiphoid process.
The costal part is attached to internal surfaces of the lower six ribs & costal cartilages.
The lumbar part attaches to the first 3 lumbar vertebrae posteriorly (around the aorta).

Question 22

How high up is the diaphragm in relation to the sternum?

Answer 22

The right dome of the diaphragm reaches as high as the upper border of the 5th rib, and the left dome reaches the lower border of the 5th rib (NB the height of the nipple is 4th intercostal space so domes of diaphragm just below this level). This is always higher than students think.

Question 23

At what vertebral levels do the oesophagus, aorta and inferior vena cava pass through the diaphragm?

Answer 23

IVC = T8
Oesophagus = T10
Aorta = T12

Question 24

What is the pleura

Answer 24

A serous 2-layered membrane covering each lung

Question 25

What is the visceral pleura, parietal pleura and pleural cavity?

Answer 25

The visceral pleura covers the surface of each lung. The outer layer is the parietal pleura which lines the inside of the thoracic cavity. Between the two layers is the pleural cavity, a potential space (i.e. usually shouldn't be a big space), which contains a very thin layer of fluid – the pleural fluid which allows the layers of pleura to slide smoothly over each other during respiration.

Question 26

What does the visceral pleura cover?

Answer 26

Just the lungs

Question 27

What can the parietal pleura be subdivided into (based on what it covers)?

Answer 27

The pleural lining extends above the first rib into the neck forming the cervical pleura. The mediastinal pleura cover the lateral surface of the mediastinum (in green). The diaphragmatic pleura cover the superior surface of the diaphragm on each side of the heart. The costal pleura covers the thoracic wall.

Question 28

Physiologically and pathologically, when might there be a pleural space?

Answer 28

The costal and diaphragmatic pleurae usually lie in opposition to (touching) the visceral pleura. However a (pleural) space may be generated between them: Physiologically: In deep inspiration, the diaphragm (and therefore the lung base) descends and the costal and diaphragmatic pleurae can separate. This lower area of the pleural cavity into which the lung expands is called the costodiaphragmatic recess – this is also known as the costophrenic recess. Pathologically: If fluid (transudate, pus, blood, chyle) or gas (air) collects in the space.

Question 29

What is the lowest point of the pleural cavity?

Answer 29

The costophrenic recess is the lowest point of the pleural cavity. If there is excess fluid in the pleural cavity (such as blood or pus) this is where it will collect.

Question 30

Where might the following substances collecting pathologically in the pleural cavity - blood, pus, serous fluid, urine, lymphatic fluid and air?

Answer 30

``` Blood = haemothorax Pus = pyothorax (empyema) Serous fluid = hydrothorax Urine = urinothorax Lymphatic fluid = chylothorax Air = pneumothorax ```

Question 31

What is the phrenic nerve, where is it located and what is its function?

Answer 31

The phrenic nerve arises from nerve roots C3,4,5 (keeps you alive!). Each phrenic nerve provides motor suply to one hemi-diaphragm. It also supplies sensation to the mediastinal pleura and pericardium, and to some of the parietal pleura covering the diaphragm. (The intercostal nerves provide the sensory innervation to the peripheral diaphragmatic parietal pleura, close to the costal margins)

Question 32

What structures are not controlled by the phrenic nerve?

Answer 32

Intercostal muscles | Visceral pleura

Question 33

What structures are the motor function of the phrenic nerve?

Answer 33

Diaphragm

Question 34

What structures are the sensory function of the phrenic nerve?

Answer 34

Diaphragmatic parietal pleura Mediastinal parietal pleura Pericardium

Question 35

Which lung is taller and thinner, and why?

Answer 35

The Liver is on the right, and pushes up the diaphragm making the right lung shorter, whilst the heart on the left makes the left lung thinner. So the left lung is taller and thinner than the right lung.

Question 36

How many lobes are in each lung? What are the lobes separated by?

Answer 36

There are three lobes in the right lung and two lobes in the left lung. These are separated by an oblique fissure on the left, and both oblique and horizontal fissures on the right.

Question 37

What structures are present in each lung?

Answer 37

Each lung has a base, an apex, costal and medial surfaces and a hilum (the area on the medial surface where vessels, nerves and bronchi enter and leave the lung).

Question 38

What can you see at the hilum of the right lung?

Answer 38

At the hilum of the right lung you can see the main bronchus and its branch going to the superior lobe. In front of these are the pulmonary artery and its main branch to the superior lobe and below these you will see the two pulmonary veins.

Question 39

How is the left lung distinguished from the right lung?

Answer 39

The left lung is distinguished from the right by the large cardiac notch which is the impression left by the heart to the left of the midline. The hilum of the left lung has two lobar bronchi lying posteriorly. The pulmonary artery lies above them and the two pulmonary veins lie below and in front.

Question 40

What is the contents of each structure in the hilum?

Answer 40

Bronchus = Air Pulmonary arteries = Deoxygenated blood Pulmonary veins = Oxygenated blood

Question 41

What can the lobes of the lungs be further divided into? What are these and how many are there per lung?

Answer 41

Lobes can be further divided into bronchopulmonary segments, of which there are 10 per lung. These are pyramidal shaped segments of lung with the apex of the segment at the lung root and its base on the surface. The segments are separated by connective tissue septa.

Question 42

What is each bronchopulmonary segment supplied by? Why is this useful for surgery?

Answer 42

Each bronchopulmonary segment is supplied by a segmental bronchus and a segmental branch of the pulmonary artery. In surgery, a segment containing a tumour can be removed without too much trauma to adjacent segments. You are not expected to know individual bronchopulmonary segments.

Question 43

What nerve innervates the mediastinal pleura and central diaphragmatic pleura and where?

Answer 43

The phrenic nerve arises from nerve roots C3,4,5 (keeps you alive!). Each phrenic nerve provides motor suply to one hemi-diaphragm. It also supplies sensation to the mediastinal pleura and pericardium, and to some of the parietal pleura covering the centre of the diaphragm.

Question 44

What nerve innervates the costal pleura and peripheral diaphragmatic pleura and where?

Answer 44

The intercostal nerves provide the sensory innervation to the peripheral diaphragmatic parietal pleura, and the costal parietal pleura (lining the inner chest wall). Remember general sensory innervation gives well localised sensation of all sensory modalities.

Question 45

What nerve innervates the visceral pleura and lung parenchyma and where?

Answer 45

At the root of each lung is a pulmonary plexus composed of efferent and afferent autonomic nerve fibres. The plexus is formed from branches of the sympathetic trunk (T1-T5) and receives parasympathetic fibres from the vagus nerve (X). Sympathetic simulus generally causes bronchodilation and vasoconstriction of large pulmonary arteries. Parasympathetic stimulation causes bronchoconstriction and vasodilation of large pulmonary arteries. (The tone of smaller, more peripheral arteries/arterioles is under the control of local factors - the von Euler-Liljestrand reflex). General visceral afferent fibres are also carried from the lungs and visceral pleural. These visceral afferent fibres mainly detect stretch and provide poorly localised sensation.

Question 46

How do the tissues of the pleura and lung receive oxygenated blood from the systemic circulation?

Answer 46

This is done via the intercostal vessels (parietal pleura) and bronchial vessels (lung and visceral pleura)

Question 47

Which arteries serve the different parts of the lungs?

Answer 47

Parietal pleura: Anterior and posterior intercostal arteries Visceral pleura and lung: Bronchial arteries. These small vessels arise from the thoracic aorta on the left (and may number 1-3) and on the right there is one whose origins may be: the aorta or an intercostal artery.

Question 48

Which veins serve the different parts of the lungs?

Answer 48

Visceral pleura and lung: Bronchial veins. These small vessels return blood from the lungs to the azygos vein on the right, while the left side drains into an intercostal vein or the accessory hemiazygos vein.

Question 49

Where do lymphatic vessels travel in the lungs?

Answer 49

LYMPHATICS Lymphatic vessels of the lung travel in parallel to the airways, through loose connective tissues of the parenchyma. They drain fluid and protein in the interstitium towards the hilum.

Question 50

What happens when the lungs are full of air?

Answer 50

As the lungs are full of air they take on the impressions of more solid structures which surround them. (e.g. aortic arch, oesophagus, etc)

Question 51

What are the two functions of the larynx?

Answer 51

The larynx has two functions: to act as a sphincter protecting the lower respiratory tract; and to produce phonation.

Question 52

Where is the larynx located relative to other parts of the airway?

Answer 52

It is continuous above with the lower part of the pharynx (the laryngopharynx), and below with the trachea.

Question 53

What is the larynx made of?

Answer 53

The larynx is made of a framework of cartilage and bone, with associated membranes, ligaments and muscles.

Question 54

What are the major components of the laryngeal skeleton?

Answer 54

The major components of the skeleton of the larynx are the: thyroid cartilage, cricoid cartilage and arytenoid cartilages, the epiglottis and the hyoid bone.

Question 55

What is the thyroid cartilage?

Answer 55

The thyroid cartilage is the larged part of the skeleton. It has two flat surfaces (laminae) joined anteriorly to form the laryngeal prominence (Adam’s apple).

Question 56

What is the epiglottis and how is it involved in swallowing?

Answer 56

The epiglottis, a leaf-shaped cartilage, is attached in the midline to the inner surface of the thyroid cartilage, and extends upwards and backwards behind the tongue. During swallowing, the epiglottis deflects downwards and covers the laryngeal inlet.

Question 57

What lies below the thyroid cartilage?

Answer 57

Below the thyroid cartilage lies the cricoid cartilage, a modified tracheal cartilage ring.

Question 58

What is the structure of the cricoid cartilage?

Answer 58

The cricoid cartilage is shaped like a signet ring, with a narrow anterior arch and a wide posterior lamina (“cricoid” = Greek for “ring-shaped”). Below the cricoid lies the trachea. The cricoid forms synovial joints with the thyroid cartilage. The lamina of the cricoid also articulates with two small pyramid-shaped arytenoid cartilages (“arytenoid” = Greek for “funnel-shaped”).

Question 59

What are the arytenoid cartilages?

Answer 59

The arytenoids are a pair of pyramidal cartilages that sit atop of the cricoid cartilages. One corner of this pyramid is attached to the posterior aspect of the vocal cord. They can slide and rotate on the cricoid, which causes movement in the vocal cord.

Question 60

What is the hyoid bone?

Answer 60

The hyoid bone is the uppermost skeletal part of the larynx. It consists of a body with greater and lesser horns.

Question 61

What are the laryngeal membranes?

Answer 61

The skeleton of the larynx is held together by anumber of membranes (which are often named by the structures they connect). - Between the cricoid and thyroid cartilages in the midline lies the cricothyroid membrane. - Between the arytenoid and thyroid cartilages lies the vocal fold. Above the vocal fold is the vestibular fold (sometimes called the false vocal cord). - The thyrohyoid membrane fills the space between the hyoid bone and the top of the thyroid cartilage.

Question 62

What are the two types of laryngeal muscles?

Answer 62

Extrinsic | Intrinsic

Question 63

What are the extrinsic laryngeal muscles?

Answer 63

The extrinsic muscles (divided into suprahyoid and infrahyoid groups) will not be covered here for simplicity. They control the position of the larynx within the neck, including moving it upwards during swallowing.

Question 64

What are the intrinsic laryngeal muscles and which ones should you know?

Answer 64

The intrinsic laryngeal muscles alter the position and tension of the vocal cords. This allows them to close tightly to act as a protective sphincter, assist coughing, open widely during deep inspiration and to modify sound. You do not need to know the names of all the intrinsic muscles at this stage, but you should be familiar with: Cricothyroid, between the cricoid and thyroid cartilages antero-laterally (the only intrinsic muscle visible on the anterior surface of the larynx). Posterior crico-arytenoids, between the lamina of the cricoid and the arytenoid cartilages which is the only muscle that actively opens the vocal cords. Vocalis, lies in the free edge of the vocal fold

Question 65

What do the vocalis, posterior cricoarytenoids, transverse arytenoids and cricothyroid muscles do?

Answer 65

Vocalis = Reduces tension on the vocal cords, reducing pitch of voice Posterior cricoarytenoids = Moves the arytenoids away from each other Transverse arytenoids = Moves the arytenoids towards each other Cricothyroid = Increases tension on the vocal cords, increasing pitch of voice

Question 66

What is the vasculature of the larynx?

Answer 66

The laryngeal branches of the superior and inferior thyroid arteries (from the external carotid); venous drainage via the thyroid veins into the internal jugular vein. (You will study the arrangement of blood vessels in the neck in more detail in Year 2 Metabolism).

Question 67

What is the neurology of the larynx?

Answer 67

The larynx is supplied by the left and right superior laryngeal nerves and the left and right recurrent laryngeal nerves, branches of the vagus nerve (CN X). The recurrent laryngeal nerves arise in the root of the neck and ascend between the oesophagus and trachea. Recurrent laryngeal: motor to all intrinsic muscles (except cricothyroid). The recurrent laryngeal nerves are the nerves of phonation. The superior laryngeal nerve divides to form the internal laryngeal nerve (sensory) and the external laryngeal nerve (motor). Internal laryngeal nerve: sensory to structures of the larynx and laryngopharynx above the vocal folds. (VERY important sensitive nerve - afferent branch of choking reflex) External laryngeal nerve: motor to cricothyroid – provides tone to voice

Question 68

What are the structures in the laryngeal skeleton?

Answer 68

Hyoid bone Thyroid cartilage Cricoid cartilage Epiglottis

Question 69

What are the structures in the laryngeal membranes and muscles?

Answer 69

Thyrohyoid membrane Cricothyroid membrane Vocal fold Cricothyroid muscle

Question 70

What arteries serve the larynx?

Answer 70

External carotid artery Subclavian artery Superior thyroid artery Inferior thyroid artery

Question 71

What veins serve the larynx?

Answer 71

Internal jugular Brachiocephalic veins Superior thyroid vein Inferior thyroid veins

Question 72

What nerves serve the larynx?

Answer 72

``` Vagus nerve Superior laryngeal nerve - internal branch - external branch Recurrent laryngeal nerve ```

Question 73

What separates the paired nasal cavities from the oral cavity and the cranium, and from each other?

Answer 73

The paired nasal cavities are separated from the oral cavity below by the palate, and from the cranium above by the cribiform plate of the ethmoid bone. In the midline is the nasal septum, which separates the two nasal cavities.

Question 74

What structures contribute to the nasal septum?

Answer 74

Septal cartilage Ethmoid Vomer

Question 75

What are the nasal conchae/turbinates?

Answer 75

Within each cavity, on the lateral walls are three shell-like projections, the superior, middle and inferior nasal conchae which project into the cavity from the lateral walls.

Question 76

What are the meatuses?

Answer 76

The spaces beneath the conchae are referred to as the superior, middle and inferior meatuses (singular: meatus). The nasolacrimal (tear) duct drains into the inferior meatus (which is why your nose runs when you cry).

Question 77

What are the paranasal air sinuses? What are they lined with? What happens when they get infected?

Answer 77

The paranasal air sinuses are spaces within the following facial bones ``` Frontal Sphenoid Maxilla Ethmoid The nasal cavity and the paranasal air sinuses are lined with mucous epithelium. The sinuses drain into the nasal cavity. ``` Infection of the air sinuses (sinusitis) causes thickening of the mucous membranes, which may block the openings.