Anatomy of lower respiratory tract Flashcards
List the components of the lower respiratory tract
The lower respiratory tract
is comprised of:
- larynx - below the vocal cords
- trachea
- bronchi
- bronchioles
- lungs
Describe the location and components of the trachea
The trachea runs from C6 - cricoid cartilage to T4/sternal angle, or the tracheal bifucation.
Note that the carina actually referes to the internal ridge located at the tracheal bifurcation.
The trachea is made of smooth muscle, referred to as the trachealis, as well as U-shaped tracheal cartilages and annular ligaments.
Note the rigidity of the trachea, due to the presence of cartilage, as compared to the oesophagus, which is soft, and closed, unless a bolus of food is moving through. The respiratory system structures are typically rigid to ensure that they are patent and open. ^[potential exam question]
Note also the differences between left and right primary bronchus. The right primary bronchus is more vertical, wider, and shorter, as compared to the left, which is more lateral and longer.
As a result, if an object has been inhaled that shouldn’t, it will often be lodged in the right main bronchus.
Describe the blood supply of the lungs
The lungs are chiefly supplied by bronchial arteries and bronchial veins.
The left bronchial artery branches directly off the descending thoracic aorta to supply the left main bronchus. It will then divide further to supply the lobes and segments of the left lung.
The right bronchial artery branches off an intercostal artery to supply the branches of the right main bronchus, and divides further to supply the lobes and segments of the right lung.
As for drainage, the azygos, hemiazygos and accesssory hemiazygos veins are responsible, with azygos the main draingae for the thoracic cavity.
These vessels also divide to drain lobes and segments.
Note: some blood is also drained into pulmonary veins ^[clarify with Riemke on this], although the vast majority drains via bronchial veins, azygos vein and returns to superior vena cava.
segmental arrangement of arteries and veins, following the segmental arrangement of the bronchioles.
Describe the lung pleura
Recall that the pleura of the lung can be divided into parietal and visceral, with a potential space between them filled with pleural fluid.
The two pleura are separate and non-continuous, although they do “break” to form the hila.
There are four surfaces of the pleura:
- cervical
- diaphragmatic
- mediastinal
- costal
Describe the morphology of the right and left lungs
the left and right lung differ slightly in their morphology.
The left lung is slightly smaller in size due to the presence of the cardiac notch, where the apex of the heart sits, and has only two lobes, and one fissure.
The hilum is bordered by the free edge of the visceral pleura and contains:
- pulmonary artery
- left main bronchus
- closely followed by bronchial vessels
- pulmonary veins
- broncho-pulmonary lymph nodes
The right lung by contrast is larger, and contains three lobes and two fissures.
The right lung hilum contains:
- pulomary arteries
- bronchial vessels
- pulmonary veins
- superior lobar bronchus
- ingerior and middle lobar bronchus
- all three are contained within the right main bronchus
- bronchi-pulmonary lymph nodes
Note that the 1st division of the primary bronchus occurs in the hilum. Thus pulmonary arteries and veins also follow this division.
Describe the bronchopulmonary segments
Both left and right lung have the same number of segments, despite differing numbers of lobes.
There are 10 segments for each lung, and they constitute distinct anatomical, functional and surgical units.
As they stand alone, if a tumour grows within a single segment, it can be resected and the lung can continue to function.
Within the left lung there is an even split of the segments between the superior and inferior lobes.
Describe the bronchial tree
Bronchial tree begins at trachea, then divides into primary, lobar and segmental bronchi.
Note: there are three lobar bronchi as there are three lobes in the right lung.
Note that the bronchial tree can be divided into conduction and respiratory portions.
- the conduction portion is made up of the bronchi, bronchioles (terminal)
- the conduction portion is responsible for filtering (?), warming and humidifying air
- bronchi (segmental and subsegmental) have cartilage and smooth muscles, and continue for 10 generations
- bronchioles have smooth muscles, and go for 11-16 generations
- the respiratory portion is made up of respiratory bronchioles and alveoli, and these go for 17-23 generations
Note: terminal bronchioles lined with smooth muscle, but it is more distinct and classed separately from bronchioles
Describe the components of teh lung lobule
Lung lobules are made of structural and vascular compartments:
- a single terminal bronchiole, and its branches
- respiratory bronchioles
- alveolar ducts
- alveolar sacs
- alveoli
- associated blood vessels, including arterioles, capillaries and venules
Pulmonary artery enters lobules –> which divides until it reaches capillary plexus of alveolus, the site of gas exchange —> pulmonary vein (which exists on the periphery).
Note also: bronchiole capillaries and shunt connecting directly into pulmonary vein
Describe the lymphatic drainage of the lower respiratory tract
Understanding lymphatic drainage is important for flow of inflammation and metastases.
The thoracic duct is the major component of lymphatic drainage.
Tracheobronchial nodes receive most of the pulmonary drainage, which in turn drains into bronchomediastinal trunk and venous system.
Describe the innervation of the lungs
Innervation of lungs
via the pulmonary plexus, which contains the anterior and posterior pulmonary plexuses.
Parasympathetic innervation is supplied by the vagus nerve. Ganglia are located in the plexus. Parasympathetic innervation is responsible for bronchial constriction e.g. in asthma and emphysema.
Sympathetic innervation is supplied by the upper thoracic and cervical ganglia of the sympathetic trunk.
Sympathetic innervation is responsible for bronchial dilation, thus is stimulated and not inhibited by respiratory drugs (e.g. SABAs, LABAs, are agonists, not antagonists).
Describe the structures which facilitate breathing
Breathing
Muscles of inspiration:
- external intercostals
- diaphragm
- scalenes
- sternocleidomastoid
This enables a decrease in pressure in the pleural space which increases volume and draws air into alveoli.
Muscles of expiration: (only in forced expiration)
- internal intercostals
- external oblique, internal oblique, transversus abdominis, and rectus abdominis which increase abdominal pressure and helps to push diaphragm up, compressing alveoli
Note also the pump handle and bucket movements necessary for breathing:
- ribs increase and decrease in diameter, ribs move up and out = bucket handle
- sternum base flares out = pump handle
Describe the surface anatomy of the lung
The apices of the lung extend about three centimetres above the medial third of the clavicles then project inferolaterally to the junction of medial and middle thirds of clavicle. Anteriorly, the hila lie at the level of costal cartilages 3-4; this is vertebral level T5-7.
The inferior margins of the lung are:
T6 - mid-clavicular line
T8 - mid-axillary line
T10 - posteriorly At each point, the parietal pleural reflections sit inferiorly by approximately 2 ribs. However, this level varies with respiratory phase.
The anterior margins are different on each side and largely follow the lines of parietal pleural reflection:
on the right:
deep to the right side of the sternum between the second and fourth costal cartilages inferiolaterally to the level of
the deep surface of the sixth right intercostal cartilage
on the left:
deep to the sternum near the midline inferiorly between the levels of costal cartilages 2 and 4
displaced laterally and more obliquely than left side to a point about 3cm lateral to the left sternal edge at the upper margin of the sixth costal cartilage
the space created by the lateral deviation of pleura and lung on the left side is termed the cardiac notch
The surface markings of the fissures of the lungs are described in the submenu. A general point about the lobes produced by the fissures is that the great majority of the surface area:
anteriorly is covered by upper and middle lobes on the right and upper lobe alone on the left
posteriorly is covered by lower lobes on both sides
