Anatomy of the Thorax 2

Question 1

What is the chest cavity divided into?

Answer 1

o Median partition - mediastinum

o Lateral pleura & lungs

Question 2

Where does the mediastinum extend to?

Answer 2

o Root of neck above
o Diaphragm below
o Sternum anteriorly
o Vertebral column Posteriorly

Question 3

Label the subdivisions of the mediastinum

Answer 3

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Question 4

What does each lung consist of?

Answer 4

• Apex – The blunt superior end of the lung. It projects upwards, above the level of the 1st rib and into the floor of the neck.
• Base – The inferior surface of the lung, which sits on the diaphragm.
• Lobes (two or three) – These are separated by fissures within the lung.
• Surfaces (three) – These correspond to the area of the thorax that they face. They are named costal, mediastinal and diaphragmatic.
• Borders (three) – The edges of the lungs, named the anterior, inferior and posterior borders.

Question 5

Describe the lobes and fissures of the lungs

Answer 5

The right and left lungs do not have an identical lobular structure.

The right lung has three lobes; superior, middle and inferior. The lobes are divided from each other by two fissures:
• Oblique fissure – Runs from the inferior border of the lung in a superoposterior direction, until it meets the posterior lung border.
• Horizontal fissure– Runs horizontally from the sternum, at the level of the 4th rib, to meet the oblique fissure.

The left lung contains superior and inferior lobes, which are separated by a similar oblique fissure.

Question 6

What are the 3 surfaces of the lungs?

Answer 6

There are three lung surfaces, each corresponding to an area of the thorax.

The mediastinal surface of the lung faces the lateral aspect of the middle mediastinum. The lung hilum (where structures enter and leave the lung) is located on this surface.

The base of the lung is formed by the diaphragmatic surface. It rests on the dome of the diaphragm, and has a concave shape. This concavity is deeper in the right lung, due to the higher position of the right dome overlying the liver.

The costal surface is smooth and convex. It faces the internal surface of the chest wall. It is related to the costal pleura, which separates it from the ribs and innermost intercostal muscles.

Question 7

Describe the borders of the lungs

Answer 7

The anterior border of the lung is formed by the convergence of the mediastinal and costal surfaces. On the left lung, the anterior border is marked by a deep notch, created by the apex of the heart. It is known as the cardiac notch.

The inferior border separates the base of the lung from the costal and mediastinal surfaces.

The posterior border is smooth and rounded (in contrast to the anterior and inferior borders, which are sharp). It is formed by the costal and mediastinal surfaces meeting posteriorly.

The left ventricle projection is the reason for fewer lobes on the left lung and the formation of the cardiac notch.

Question 8

Label the borders and surfaces of the lung

Answer 8

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Question 9

Label the left and right lung prosected image

Answer 9

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Question 10

What are bronchopulmonary segments?

Answer 10

• The lobes of the lung can be divided into independently smaller functional units called bronchopulmonary segments – an area of lung which is supplied by (tertiary bronchus and accompanying pulmonary artery branch)
• Each bronchopulmonary segment is shaped like an irregular cone which narrows to an apex facing the lung root and a base at the pleural surface.

Question 11

Why are bronchopulmonary segments useful clinically?

Hint: connective tissue septum

What runs in this septum?

Answer 11

• These bronchopulmonary units are considered to be the smallest, functionally independent units of a lung that can be isolated and removed without affecting adjacent regions (clinical context). It can also can help to prevent spread of infection from one section to the other as they are separated by connective tissue septum (which separates and isolates). Running in this septum is the pulmonary vein tributaries

Question 12

Where does the pulmonary artery and veins run in relation to the bronchopulmonary segments?

How many pulmonary segments are in the left and right lung?

Answer 12

• The pulmonary artery runs in the bronchopulmonary segments and the veins run in the septa between the segments
• In the right lung there are 10 pulmonary segments, in the left there are 8-10 as some of the bronchopulmonary segments fuse together in the left lung.

Question 13

What is the hilum of the lung?

Answer 13

The hilum of the lung is a large triangular depression on the mediastinal surface of the lung.

Question 14

What does the hilum of the lung serve as?

Answer 14

It is housing the lung root, a collection of tubular structures that are entering and leaving the lung.

Question 15

What is the hilum surrounded by?

Answer 15

The hilum is surrounded by a sleeve of mediastinal pleural membrane that reflects onto the mediastinal surface of the lung.

Question 16

Label the hilum of the right lung

Answer 16

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Question 17

What are the bronchial vessels?

Answer 17

Bronchial vessels – small vessels which come from the systemic circulation, branches of the aorta which bring oxygenated blood to the lung tissue and supporting structures

Question 18

Describe the hilum of the left lung and label

How many pulmonary arteries are there in the left lung?

Can we see the mediastinal pleural membrane surrounding the root?

What does the mediastinal pleural membrane do and where does it extend from?

Where does the pulmonary ligament extend from and what does it do?

What nerves pass posterior and anterior to the lung root?

Answer 18

• There is 1 pulmonary artery that hasn’t branched yet.
• We can see the starting of the left main bronchus into the lobar bronchi
• We can also see the pulmonary veins
• We can also see the mediastinal pleura surrounding the lung root. There is also a sleeve of mediastinal pleura which extends down from the inferior surface. This will help support the lung root. It also allows for movement of the structures of the lung root without compression of the vessels during respiration. This extension of pleura prevents constriction of these structures. It also stabilises the inferior lobe. This sleeve of pleura is called the pulmonary ligament.
• We can also see the arch of the aorta moving into the descending thoracic aorta. This is a really notable depression on the mediastinal surface of the left lung
• We can also see the depression for the oesophagus
• We can also see depressions where branches of the aortic arch will pass over the superior thoracic aperture (subclavian vessels)

Question 19

Label the hila of the right and left lungs

Answer 19

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Question 20

What forms the tracheobronchial tree?

Where are they located?

Answer 20

The trachea, bronchi and bronchioles form the tracheobronchial tree – a system of airways that allow passage of air into the lungs, where gas exchange occurs. These airways are located in the neck and thorax.

Question 21

Describe the pathway of the trachea

Answer 21

• The trachea marks the beginning of the tracheal-bronchial tree
• It passes down through the neck from the continuation with the larynx (inferior cartilage of the larynx – cricoid cartilage)
• It moves down into the superior mediastinum by passing through the superior thoracic aperture (shown in red)
• It will the bifurcate at the level of the sternal angle into the left and right main bronchi

Question 22

Label the trachea 1

Answer 22

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Question 23

What is the the trachea held open by?

What are the rings of cartilage connected by?

Where does the trachea divide?

What is the point of division called?

How long is the trachea?

What are the posterior ends of the trachea completed by?

Answer 23

1. The trachea, like all of the larger respiratory airways, is held open by cartilage – here in C-shaped rings. The free ends of these rings are supported by the trachealis muscle.
2. The rings of cartilage in the trachea are connected my membranes (so it is a relatively mobile tube)
3. The trachea divides into the left and right bronchi at the sternal angle (T4-T5). The point of division is called the carina. It is a very sensitive area of the trachea.
4. The trachea is approximately 11cm long, 2.5 cm in diameter
5. Fibroelastic tube kept patent by U-shaped bars (rings) of hyaline cartilage
6. Posterior free ends connected by smooth muscle trachealis muscle, that runs down all the length
7. Complete cartilaginous rings of the trachea would not allow swallow, the oesophagus can expand to swallow.

Question 24

What is the internal surface of the trachea and bronchi lined by?

Answer 24

The trachea and bronchi are lined by ciliated pseudostratified columnar epithelium, interspersed by goblet cells, which produce mucus. The combination of sweeping movements by the cilia and mucus from the goblet cells forms the functional mucociliary escalator. This acts to trap inhaled particles and pathogens, moving them up out of the airways to be swallowed and destroyed.

Question 25

What type of cartilage lies at the bifurcation of the primary bronchi?

Answer 25

At the bifurcation of the primary bronchi, a ridge of cartilage called the carina runs anteroposteriorly between the openings of the two bronchi. This is the most sensitive area of the trachea for triggering the cough reflex, and can be seen on bronchoscopy.

Question 26

Label the trachea structure

Answer 26

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Question 27

Compare the right and left main bronchus

Answer 27

• Right main bronchus is wider and shorter (2.5cm length)

* Left main bronchus is narrower, longer and more horizontal (5cm length)

Question 28

Where is an inhaled object likely to pass?

Answer 28

• Inhalation of foreign bodies – more likely to enter right bronchus, passing into middle or lower lobe bronchi

Question 29

What direction does bifurcation of the trachea lie?

Answer 29

• Bifurcation of the trachea runs anteriorposteriorly

Question 30

What is a bronchoscopy?

Answer 30

o Experience permits view of lobar and even segmental bronchi
o Can be used for biopsy of mucous membrane and removal of inhaled foreign bodies

Question 31

What does the right bronchus and left bronchus divide into?

Answer 31

Within the lungs, the main (primary) bronchi branch into lobar (secondary) bronchi. Each secondary bronchi supplies a lobe of the lung, thus there are 3 right lobar bronchi and 2 left. The lobar bronchi then bifurcate into several segmental (tertiary) bronchi, each of which supplies a bronchopulmonary segment. Bronchopulmonary segments are subdivisions of the lung lobes, and act as the functional unit of the lungs. The structure of bronchi are very similar to that of the trachea, though differences are seen in the shape of their cartilage. In the main bronchi, cartilage rings completely encircle the lumen. However in the smaller lobar and segmental bronchi cartilage is found only in crescent shapes.

Question 32

What do the segmental bronchi branch into?

Label the bronchial tree

Answer 32

The segmental bronchi undergo further branching to form numerous smaller airways – the bronchioles.

Conducting bronchioles then eventually end as terminal bronchioles. These terminal bronchioles branch even further into respiratory bronchioles, which are distinguishable by the presence of alveoli extending from their lumens.

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Question 33

What are the pleura and what do they permit?

Answer 33

The pleurae refer to the serous membranes that line the lungs and thoracic cavity. They permit efficient and effortless respiration.

Question 34

Describe how the pleura spaces are formed

Answer 34

1. Smooth membrane which secretes serous fluid
2. Two membranes of epithelial cells
3. Line and enclose body cavities
4. One continuous layer in each cavity
5. Parietal (lines body walls) and Visceral (lines organs or ‘viscera’) layers
6. Reflections of serous membranes between organs and body wall which form ‘potential spaces’. Potential for build-up of fluid in that space.

Question 35

Describe the development of the pleura

Answer 35

Early on during embryonic development we have the laryngotracheal tube which will give rise to the trachea and tracheobronchial tree. At the distal end of the tube we have the beginning of the development of the lungs (lung buds).

These lung buds grow out laterally from the distal part of the laryngotracheal tube into coelomic cavity. One open cavity lined with mesothelium membrane. This lining the cavity will form the Parietal pleura. As the lung buds begin to develop into lungs as they pass laterally into the space they will acquire a layer of the mesothelium which will surround the lungs which will give rise to form the visceral pleura.

So when we have a fully developed lower respiratory tract we can see the lungs have filled a large proportion of the space on the lateral aspect which has now become thoracic cavity. The parietal pleura is lining the inner walls of the thoracic cavity but is continuous with the visceral pleura which is lining the lungs.

The space in between the two layers of pleura is pleural cavity/space. This a potential space which contains a small volume of serious fluid: lubricate the surface of the pleura to move over each other to slide and produce a surface tension which pulls the two layers of pleura together to ensure when the thorax expands and we contract our intercostal muscles and diaphragm the lungs also expand with them.

Question 36

Describe what the visceral and parietal pleura line

What is the visceral pleura continuous with?

Answer 36

The visceral pleura covers the outer surface of the lungs, and extends into the interlobar fissures. It is continuous with the parietal pleura at the hilum of each lung (this is where structures enter and leave the lung).

The parietal pleura covers the internal surface of the thoracic cavity

Question 37

What is the parietal pleura divided into?

Answer 37

• Mediastinal pleura – Covers the lateral aspect of the mediastinum (the central component of the thoracic cavity, containing a number of organ such as heart and great vessels).
• Cervical pleura – Lines the extension of the pleural cavity into the neck. This lines the extension of the pleural cavity up into the route of the neck over the first rib.
• Costal pleura – Covers the inner aspect of the ribs, costal cartilages, and intercostal muscles.
• Diaphragmatic pleura – Covers the thoracic (superior) surface of the diaphragm. This covers the superior surface of the diaphragm.

Question 38

What are the 2 recesses of the pleural cavity?

Answer 38

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Question 39

Describe the bronchial circulation

Answer 39

• Part of the circulatory system that supplies nutrients and oxygen to the bronchi, lung roots, visceral pleura and supporting lung tissue comes from the:
o Bronchial arteries
 Arise from the descending aorta
o Bronchial veins drain into the azygous vein (R) and accessory hemiazygous vein (L)
o Because of the dual blood supply to the lungs via the bronchial and pulmonary systems, the lungs are more resistant to infarction

Question 40

What do the bronchial arteries supply?

Where do they travel and branch?

What does every bronchopulmonary segment have?

How many bronchial arteries are there?

Where do they arise from?

Answer 40

• The bronchial arteries supply the bronchi and connective tissue.
• They travel and branch with the bronchi
• Every bronchopulmonary segment has a branch of the pulmonary tree and branch from the bronchial artery
• They will end at the level of the respiratory bronchioles
o X2 left lung (sup/inf)
o X1 right lung
• Left arise direct from aorta
• Right arise from 3rd posterior intercostal artery

Question 41

What do the bronchial veins drain?

What are the structures drained by?

Answer 41

• Return blood from larger bronchi and structures of the lung root. That carry a small proportion of blood flow
• Carrying waste products away from cells that constitute lung tissue
• Actually carry only 13% blood flow – rest is returned to the heart via the pulmonary veins
• Right side drains into azygous veins
• Left side drains into accessory hemiazygous vein

Question 42

Lymphatic vessels of the lung arise from 2 lymphatic plexuses which are?

What do they empty into?

Where do they pass and terminate?

Answer 42

o Superficial - drains the lung parenchyma
o Deep – drains the structures of the lung root

• Both empty into tracheobronchial nodes – located around the bifurcation of the trachea and main bronchi
• Then pass into the bronchomediastinal trunks and subsequently into the left hand side thoracic duct and right lymphatic duct into the cardiovascular system
• Dissemination of cancer cells is common because of this.