Anatomy

1. LOWER RESPIRATORY TRACT
PRESENTED BY GROUP 7

2. • The major passages and structures of the lower
respiratory tract include the windpipe (trachea) and within
the lungs, the bronchi, bronchioles, and alveoli.
• Deep in the lungs, each bronchus divides into secondary
and tertiary bronchi, which continue to branch to smaller
airways called the bronchioles.

4. TRACHOBRONCHIAL TREE
The trachea, bronchi and bronchioles form
the tracheobronchial tree.
It is 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.

5. TRACHEA
Anatomical Position
The trachea marks the beginning of the tracheobronchial
tree. It arises at the lower border of cricoid cartilage in the
neck, as a continuation of the larynx.
It travels inferiorly into the superior mediastinum, bifurcating
at the level of the sternal angle (forming the right and left
main bronchi). As it descends, the trachea is located
anteriorly to the oesophagus, and inclines slightly to the
right.

6. STRUCTURE
• 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 tracheal muscle.
• 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

8. • 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.
NEUROVASCULAR SUPPLY
The trachea receives sensory innervation from
the recurrent laryngeal nerve.
Arterial supply comes from the tracheal branches of

9. BRONCHI
At the level of the sternal angle, the trachea bifurcates into
the right and left main bronchi. They undergo further
branching to produce the secondary bronchi. Each
secondary bronchi supplies a lobe of the lung, and gives
rise to several segmental bronchi.
Along with branches of the pulmonary artery and veins, the
main bronchi make up the roots of the lungs.

10. STRUCTURE
Right main bronchus – wider, shorter, and descends more
vertically than its left-sided counterpart. Clinically, this
results in a higher incidence of foreign body inhalation. The
right superior lobar bronchus arises before the left hilum.
Left main bronchus – passes inferiorly to the arch of the
aorta, and anteriorly to the thoracic aorta and oesophagus
in order to reach the hilum of the left lung.he right main
bronchus enters the hilum.

12. 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.

13. NEUROVASCULAR SUPPLY
The bronchi derive innervation from pulmonary branches of
the vagus nerve (CN X). Blood supply to the bronchi is from
branches of the bronchial arteries, while venous drainage is
into the bronchial veins.

14. BRONCHIOLES
The segmental bronchi undergo further branching to form
numerous smaller airways – the bronchioles.
STRUCTURE
The smallest airways, bronchioles do not contain any
cartilage or mucus-secreting goblet cells. Instead, club
cells produce a surfactant lipoprotein which is instrumental
in preventing the walls of the small airways sticking together
during expiration.

16. Initially there are many generations of conducting
bronchioles, which transport air but lack glands and are
not involved in gas exchange. 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.
Alveoli are tiny air-filled pockets with thin walls (simple
squamous epithelium), and are the sites of gaseous
exchange in the lungs. Altogether there are around 300
million alveoli in adult lungs, providing a large surface
area for adequate gas exchange.

17. ASTHMA
Asthma is a chronic inflammatory disorder of the airways,
characterised by hypersensitivity, reversible outflow
obstruction and bronchospasm.
There is remodelling of the small airways, causing
increased smooth muscle thickness around the
bronchioles, damaged epithelium and a thickened
basement membrane.

18. “Asthma attacks” are acute exacerbations of
the condition whereby a trigger (e.g.
allergens, exercise) causes sudden
inflammation and contraction of the smooth
muscle around bronchioles (bronchospasm).
This narrows the airways, causing difficulty in
breathing and wheezing, a characteristic
feature of asthma.

20. MEDIASTINUM
The mediastinum is the central compartment of the thoracic
cavity, located between the two pleural sacs. It contains
most of the thoracic organs, and acts as a conduit for
structures traversing the thorax on their way into the
abdomen.
Anatomically, the mediastinum is divided into two parts by
an imaginary line that runs from the sternal angle (the angle
formed by the junction of the sternal body and manubrium)
to the T4 vertebrae:

21. • Superior mediastinum – extends upwards, terminating
at the superior thoracic aperture.
• Inferior mediastinum – extends downwards, terminating
at the diaphragm. It is further subdivided into the
anterior mediastinum, middle mediastinum and
posterior mediastinum.

22. The Middle Mediastinum
Contents
The middle mediastinum is the largest subdivision of the inferior
mediastinum. It contains several important organs, vessels, nerves
and lymphatic structures.
Organs
The middle mediastinum contains the heart, and its protective
sheath, the pericardium. It also contains the tracheal bifurcation and
the left and right main bronchi.
Vessels
The middle mediastinum is associated with the origins of the great
vessels that run to and from the heart:

24. • Ascending aorta – the first part of the aorta, which arises from
the aortic orifice. It moves upwards, exiting the fibrous
pericardium and entering the superior mediastinum – where it
then becomes the aortic arch. The ascending aorta gives rise
to two branches; the left and right coronary arteries.
• Pulmonary trunk – gives rise to the left and right pulmonary
arteries. The trunk itself is relatively short and wide, allowing a
large volume of blood to pass through it.
• Superior vena cava – returns deoxygenated blood from the
upper half of the body. It is formed by the right and left
brachiocephalic veins.

26. NERVES
The cardiac plexus and the
phrenic nerves are both located
within the middle mediastinum.
• Cardiac plexus a network of
nerves located at the base of
the heart, containing
sympathetic and
parasympathetic fibres. The
sympathetic nerves are
derived from the T1-T4
segments of the spinal cord,
and the parasympathetic

27. • Phrenic nerves (left and right) – mixed nerves that provides motor
innervation to the diaphragm. They arise in the neck, and descend
through the middle mediastinum to reach the diaphragm.
Lymphatics
The tracheobronchial lymph nodes are located within the middle
mediastinum. They are a group of nodes associated with the trachea
and bronchi of the respiratory tract – and are characteristically
enlarged in certain lung pathologies. They form from the gathering of
bronchial nodes within the hila of the lungs. Individual groups of nodes
are connected via fine lymphatic channels.

28. Contents
The superior mediastinum contains neural, vascular
and respiratory structures passing from the adjacent
regions of the neck and abdomen (via the inferior
mediastinum.
GREAT VESSELS
The great systemic blood vessels of the heart lie
within the superior mediastinum and their main
branches arise before passing through the superior
thoracic aperture.

29. Arch of Aorta
The three major branches of the aortic arch arise
within the superior mediastinum:
• Brachiocephalic artery – supplying the right side of
the head & neck and the right upper limb.
• Left Common carotid artery – to the left side of the
head & neck.
• Left Subclavian artery – to the left upper limb.

30. The superior mediastinum is bordered by the following
thoracic structures:
• Superior – Thoracic inlet.
• Inferior – Continuous with the inferior mediastinum at
the level of the sternal angle.
• Anterior – Manubrium of the sternum.
• Posterior – Vertebral bodies of T1-4.
• Lateral – Pleurae of the lungs.

32. SUPERIOR VENA CAVA
The following tributaries of the superior vena cava are
located within the superior mediastinum:
• Brachiocephalic veins – draining blood from the upper
body.
• Left superior intercostal vein – collects blood from the left
2nd and 3rd intercostal vein. It drains into the left
brachiocephalic vein.
• Supreme intercostal vein – drains the vein from first
intercostal space directly into the brachiocephalic veins.
• Azygos vein – receiving blood from the right posterior
intercostal veins. The left intercostal veins drain first into

33. NERVE
Vagus Nerve
In the superior mediastinum, the vagus nerve has two distinctive paths:
• Right vagus nerve – runs parallel to the trachea and passes
posteriorly to the superior vena cava and the right primary bronchus.
• Left vagus nerve – enters the superior mediastinum between the left
common carotid and the left subclavian arteries. It descends
anteriorly to the aortic arch, before travelling posterior to the left
bronchus.
• The left recurrent laryngeal nerve arises from the left vagus nerve as
it passes the aortic arch. It loops under the arch, to the left
of ligamentum arteriosum, before continuing its journey to the larynx
in the tracheal-oesophageal groove.

35. Phrenic Nerve
From the anterior surface of the anterior scalene muscle, the phrenic nerves
(roots C3, C4 and C5) enter the superior mediastinum lateral to the great
vessels. They then descend anteriorly into the middle mediastinum, passing
anteriorly to the hilum of the lungs.
OTHER NERVES
Cardiac nerves – originate from the superior, middle and inferior cardiac
ganglion and form the superficial and deep cardiac plexuses in the superior
mediastinum. The superior plexus sits between the aortic arch and right
pulmonary artery. The deep plexus lies on the surface of the trachea at the
point of bifurcation.
Sympathetic trunk – runs bilaterally to the vertebral bodies along the entire
length of the vertebral column.

37. OTHER STRUCTURES IN THE SUPERIOR MEDIASTINUM
The thymus gland is the most anterior structure within the superior
mediastinum. It sits flush against the posterior surface of the sternum and
extends into the anterior mediastinum (Fig 4) and can often reach into the
neck.
The trachea bifurcates into the primary bronchi posterior to the ascending
aorta at the level of the sternal angle.
The oesophagus ascends towards the pharynx, which it joins at the level of
C6.
The thoracic duct passes to the left of the oesophagus on its path to the
junction of the left internal jugular and subclavian veins in the superior
mediastinum.

38. • The sternohyoid and sternothyroid muscles
originate from the posterior surface of the manubrium.
They are part of the infrahyoid muscle group of the
neck.
• The inferior aspect of the longus colli muscle also
originates within the superior mediastinum.

39. THE ANTERIOR MEDIASTINUM
The mediastinum is the central compartment of the thoracic cavity,
located between the two pleural sacs. It contains most of the thoracic
organs, and acts as a conduit for structures traversing the thorax on
their way into the abdomen.
Anatomically, the mediastinum is divided into two parts by an
imaginary line that runs from the sternal angle (the angle formed by
the junction of the sternal body and manubrium) to the T4 vertebrae:
Superior mediastinum – extends upwards, terminating at the superior
thoracic aperture.
Inferior mediastinum – extends downwards, terminating at the
diaphragm. It is further subdivided into the anterior mediastinum,
middle mediastinum and posterior mediastinum

41. Borders
• The anterior mediastinum is bordered by the following thoracic structures:
• Lateral borders: Mediastinal pleura (part of the parietal pleural membrane).
• Anterior border: Body of the sternum and the transversus thoracis muscles.
• Posterior border: Pericardium.
• Roof: Continuous with the superior mediastinum at the level of the sternal
angle.
• Floor: Diaphragm.

43. • The anterior mediastinum contains no major structures.
It accommodates loose connective tissue (including
the sternopericardial ligaments, which tether the
pericardium to the sternum), fat, some lymphatic
vessels, lymph nodes and branches of the internal
thoracic vessels.
• In infants and children, the thymus extends inferiorly
into the anterior mediastinum. However the thymus
recedes during puberty and is mostly replaced by
adipose tissue in the adult.

44. THE POSTERIOR MEDIASTINUM
The mediastinum is the central compartment of the thoracic cavity,
located between the two pleural sacs. It contains most of the thoracic
organs, and acts as a conduit for structures traversing the thorax on
their way into the abdomen.
Anatomically, the mediastinum is divided into two parts by an
imaginary line that runs from the sternal angle (the angle formed by
the junction of the sternal body and manubrium) to the T4 vertebrae:
• Superior mediastinum – extends upwards, terminating at the
superior thoracic aperture.
• Inferior mediastinum – extends downwards, terminating at the
diaphragm. It is further subdivided into the anterior mediastinum,
middle mediastinum and posterior mediastinum

46. Borders
• The posterior mediastinum is bordered by the following thoracic
structures:
• Lateral: Mediastinal pleura (part of the parietal pleural membrane).
• Anterior: Pericardium.
• Posterior: T5-T12 vertebrae.
• Roof: Imaginary line extending between the sternal angle (the angle
formed by the junction of the sternal body and manubrium) and the T4
vertebrae.
• Floor: Diaphragm.

47. The posterior mediastinum contains a number of major
organs, blood vessels and nerves. We shall now explore
the anatomy of these structures in more detail.
Thoracic Aorta
The thoracic (descending) aorta is a continuation of the
arch of the aorta, beginning at the lower edge of the T4
vertebra. It descends through the posterior mediastinum to
the left of the vertebrae, becoming more medially located
as it moves. At the inferior border of T12, the thoracic aorta
becomes the abdominal aorta, and passes through
the aortic hiatus of the diaphragm.

48. A number of branches arise from the thoracic aorta in the
posterior mediastinum. These tend to arise in three vascular
planes; unpaired branches to viscera extend anteriorly,
paired branches to viscera extend laterally, and paired
segmental parietal branches extend mostly posterolaterally.
The major branches are:

49. • Posterior intercostal arteries – Paired parietal branches. Nine such pairs
branch from the posterior aspect of the aorta, supplying the intercostal
spaces (except the first two). Pass posteriorly and laterally, in parallel with
the ribs.
• Bronchial arteries – Paired visceral branches, usually one or two. The left
bronchial arteries always arise directly from the thoracic aorta, while those on
the right usually branch indirectly from a right posterior intercostal artery.
They go on to supply the tracheobronchial tree.
• Oesophageal arteries – Unpaired visceral branches, arising from the anterior
aspect of the aorta. In most individuals there are two, but there can up to five.
As the name suggests, these branches go on to supply the oesophagus.
• Superior phrenic arteries – Arise from the anterior aspect of the thoracic aorta
at the aortic hiatus, varying in number. They supply the superior aspect of the
diaphragm.

50. THORACIC DUCT
The thoracic duct is the largest lymphatic vessel in the
body, allowing return of lymph from most of the body (all but
the right superior quadrant) into the venous system.
The duct originates from the cisterna chyli in the abdomen
and enters the mediastinum via the aortic hiatus. It ascends
to lie directly anterior to the T6-T12 vertebrae, before
deviating left as it ascends into the superior mediastinum.
While located in the posterior mediastinum, the thoracic
duct receives lymphatic drainage from the intercostal
spaces and neighbouring anatomical structures through a
number of branches.

51. Azygos System of Veins
This venous network drains blood from the body walls and
mediastinal viscera and empties into the superior vena cava.
It consists of three major veins:
• Azygos vein – Formed by the union of the right lumbar vein
and the right subcostal vein. It enters the mediastinum via
the aortic hiatus and drains into the superior vena cava.
The azygos venous network, which empties into the superior ven
a cava

52. • Hemiazygos vein – Formed by the union of the left
lumbar vein and left subcostal vein. It enters the
mediastinum through the left crus of the diaphragm,
ascending on the left side. At the level of T8, it turns to
the right and combines with the azygos vein.
• Accessory hemiazygos vein – Formed by the union of
the fourth to eighth intercostal veins. It drains into the
azygos vein at T7.

54. Oesophagus
• The oesophagus is a muscular tube that connects the pharynx to
the stomach; allowing swallowed food to pass into the digestive
system. It passes into the posterior mediastinum from the superior
mediastinum, descending posteriorly to the arch of the aorta and the
heart. Whilst initially positioned to the right, the oesophagus
deviates to the left as it moves downwards. It leaves the
mediastinum via the oesophageal hiatus of the diaphragm.
• The oesophageal plexus is a network of nerves surrounding the
oesophagus as it descends, comprising of branches from
the left and right vagus nerves. Immediately above the diaphragm,
the fibres of the plexus converge to form the anterior vagal trunk
and posterior vagal trunk, which travel along the surface of the
oesophagus as it exits the thorax.

55. Sympathetic Trunks
• The sympathetic trunks are paired bundles of nerves
that extend from the base of the skull to the coccyx. In
the thoracic region, these nerve bundles are known as
the thoracic sympathetic trunks. As they descend
through the thorax, they lie within the posterior
mediastinum.
• Arising from these trunks are the lower
thoracic splanchnic nerves – they continue inferiorly to
supply the viscera of the abdomen.

56. PLEURAE
The pleurae refer to
the serous membranes that
line the lungs and thoracic
cavity. They permit efficient
and effortless respiration.
This article will outline the
structure and function of
the pleurae, as well as
considering the clinical
correlations.

57. PARIETAL PLEURA
The parietal pleura covers the internal surface of
the thoracic cavity. It is thicker than the visceral
pleura, and can be subdivided according to the part
of the body that it is contact with:
• Mediastinal pleura – Covers the lateral aspect
of the mediastinum (the central component of
the thoracic cavity, containing a number of
organ).
• Cervical pleura – Lines the extension of the
pleural cavity into the neck.
• Costal pleura – Covers the inner aspect of the
ribs, costal cartilages, and intercostal muscles.
• Diaphragmatic pleura – Covers the thoracic
(superior) surface of the diaphragm.

58. VISCERAL PLEURA
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).
•

59. PLEURAL CAVITY

60. The pleural cavity is a potential space between the
parietal and visceral pleura. It contains a small volume of
serous fluid, which has two major functions.
It lubricates the surfaces of the pleurae, allowing them to
slide over each other. The serous fluid also produces a
surface tension, pulling the parietal and visceral pleura
together. This ensures that when the thorax expands, the
lung also expands, filling with air.
(Note: if air enters the pleural cavity, this surface tension
is lost – a condition known as pneumothorax).

61. PLEURAL RECESSES
Anteriorly and posteroinferiorly, the pleural cavity is not completely filled by the
lungs. This gives rise to recesses – where the opposing surfaces of the parietal
pleura touch.
There are two recesses present in each pleural cavity:
• Costodiaphragmatic – located between the costal pleurae and the
diaphragmatic pleura.
• Costomediastinal – located between the costal pleurae and the mediastinal
pleurae, behind the sternum.
These recesses are of clinical importance, as they provide a location where
fluid can collect (such as in a pleural effusion).

62. Neurovascular Supply
The two parts of the pleurae receive a different neurovascular supply:
 Parietal Pleura
The parietal pleura is sensitive to pressure, pain, and temperature. It produces a well localised
pain, and is innervated by the phrenic and intercostal nerves.
The blood supply is derived from the intercostal arteries.
 Visceral Pleura
The visceral pleura is not sensitive to pain, temperature or touch. Its sensory fibres only detect
stretch. It also receives autonomic innervation from the pulmonary plexus (a network of nerves
derived from the sympathetic trunk and vagus nerve).
Arterial supply is via the bronchial arteries (branches of the descending aorta), which also
supply the parenchyma of the lungs.

63. CLINICAL RELEVANCE: PNEUMOTHORAX
• A pneumothorax (commonly referred to a collapsed
lung) occurs when air or gas is present within the
pleural space. This removes the surface tension of the
serous fluid present in the space, reducing lung
extension.
• Clinical features include chest pain, and shortness of
breath, and asymmetrical chest expansion. Upon
percussion, the affected side may be hyper-
resonant (due to excess air within the chest).

64. There are two main classes of pneumothorax – spontaneous
and traumatic.
• Spontaneous: A spontaneous pneumothorax occurs
without a specific cause. It is sub-divided into primary (no
underlying respiratory disease) and secondary (underlying
respiratory disease present).
• Traumatic: A traumatic pneumothorax occurs as a result of
blunt or penetrating chest trauma, such as a rib fracture
(often seen in road traffic collisions).

65. RADIOGRAPHIC APPEARANCE OF THE LEFT
PNEUMOTHORAX

66. Treatment depends on identifying the underlying cause.
Primary pneumothoraces tend to be small and generally
require minimal intervention, whereas secondary and
traumatic pneumothoraces may require decompression
to remove the extra air/gas in order for the lung to
reinflate (this is achieved via the insertion of a chest
drain).

67. LUNGS
The lungs are the organs of respiration. They are located in
the thorax, either side of the mediastinum.
The function of the lungs is to oxygenate blood. They
achieve this by bringing inspired air into close contact with
oxygen-poor blood in the pulmonary capillaries.
In this article, we shall look at the anatomy of the lungs –
their anatomical relations, neurovascular supply and clinical
correlations.

68. • The lungs lie either side of the mediastinum, within the
thoracic cavity. Each lung is surrounded by a pleural
cavity, which is formed by the visceral and parietal pleura.
• They are suspended from the mediastinum by the lung
root – a collection of structures entering and leaving the
lungs. The medial surfaces of both lungs lie in close
proximity to several mediastinal structures:
Anatomical position of the lungs.

69. RIGHT LUNG
• Oesophagus
• Heart
• Inferior vena cava
• Superior vena cava
• Azygous vein
• Heart
• Arch of aorta
• Thoracic aorta
• Oesophagus

70. Structure of the lungs
Each lung consists of:
• 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.

71. • 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.

72. LOBES OF THE LUNGS
• Oblique fissure – Runs from the inferior border of the
lung in a superior-posterior 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.

74. SURFACES OF THE LUNG
• 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.

75. The Borders
• 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.

76. The lung root and Hilum
• The lung root is a collection of structures that suspends
the lung from the mediastinum. Each root contains a
bronchus, pulmonary artery, two pulmonary veins,
bronchial vessels, pulmonary plexus of nerves and
lymphatic vessels.
• All these structures enter or leave the lung via the hilum –
a wedge shaped area on its mediastinal surface.

77. Nerve Supply
The nerves of the lungs are derived from the pulmonary plexuses. They
feature sympathetic, parasympathetic and visceral afferent fibres:
• Parasympathetic – derived from the vagus nerve. They stimulate
secretion from the bronchial glands, contraction of the bronchial
smooth muscle, and vasodilation of the pulmonary vessels.
• Sympathetic – derived from the sympathetic trunks. They stimulate
relaxation of the bronchial smooth muscle, and vasoconstriction of the
pulmonary vessels.
• Visceral afferent – conduct pain impulses to the sensory ganglion of
the vagus nerve.

78. LYMPHATIC DRAINAGE
The lymphatic vessels of the lung arise from two lymphatic
plexuses:
• Superficial (subpleural) – drains the lung parenchyma.
• Deep – drains the structures of the lung root.
Both these plexuses empty into the trachebronchial nodes – located
around the bifurcation of the trachea and the main bronchi. From
here, lymph passes into the right and left bronchomediastinal trunks.

79. Vasculature
• The lungs are supplied with deoxygenated blood by the
paired pulmonary arteries. Once the blood has received
oxygenation, it leaves the lungs via four pulmonary
veins (two for each lung).
• The bronchi, lung roots, visceral pleura and supporting
lung tissues require an extra nutritive blood supply. This
is delivered by the bronchial arteries, which arise from
the descending aorta.

82. Clinical Relevance – Pulmonary Embolism
A pulmonary embolism refers to the obstruction of a pulmonary artery by a substance
that has travelled from elsewhere in the body. The most common emboli are:
• Thrombus – responsible for the majority of cases and usually arises in a distant
vein.
• Fat – following a bone fracture or orthopaedic surgery.
• Air – following cannulation in the neck.
The effect of a pulmonary embolism is a reduction in lung perfusion. This results in
decreased blood oxygenation, and the accumulation of blood in the right ventricle of the
heart. Clinical features include dyspnoea, chest pain, cough, haemoptysis and
tachypnoea. In clinical medicine, the Wells’ score is used to assess the probability of
PE.
Definitive treatment involves anticoagulation and thrombolytic therapy. This reduces
the size of the embolus, and prevents further clotting.

83. Breathing
• The process in which air moves in and out of the lungs is
known as breathing. This is carried out through various
respiratory organs. In other words, breathing is a simple
give and take process.
• In a day, a person breathes several times. One breath
comprises one inhalation and one exhalation. In a minute,
the number of times a person breathes is termed as
his/her breathing rate. By calculating the breathing rate,
we can know the number of times we breathed in a day.

84. • However, the breathing rate varies which is dependent
upon a person’s activity. It raises when a person is brisk
walking, running or after a heavy exercise; similarly,
decreases when a person is calm.
• The breathing rate of an adult is 15-18 times per minute.
However, during heavy exercise, the breathing rate
exceeds 25 times per minute.

85. Mechanism of Breathing
• The air that we breathe in and out of the lungs varies in its
pressure. So basically when there is a fall in air pressure
the alveolar spaces fall and the air enters the lungs
(inspiration) and as the pressure of the alveoli within
exceeds the atmospheric pressure, the air is blown from
the lungs (expiration). The flow rate of air is in proportion
to the magnitude of the pressure difference.
• The breathing mechanism involves two processes:
• Inspiration
• Expiration

86. Mechanism Of Inspiration
• The process of intake of atmospheric air is known as
inspiration. It is an active process.
• When the volume of the thoracic cavity increases and the
air pressure decreases, inspiration takes place.
• Contraction of external intercostal muscles increases the
volume of the thoracic cavity.
• Contraction of the diaphragm further increases the size of
the thoracic activity. Simultaneously, the lungs expand
• With the expansion of the lungs, the air pressure inside
the lungs decreases.
• The pressure equalizes and the atmospheric air rushes

87. Mechanism Of Expiration
• The process of exhaling carbon dioxide is called
expiration. It is a passive process.
• It occurs when the size of the thoracic activity decreases
and the air pressure outside increases.
• Now the external intercostal muscles relax and the
internal intercostal muscles contract.
• As a result, the ribs are pulled inwards and the size of the
thoracic cavity is reduced.
• The diaphragm is relaxed and the lungs get compressed.
• Consequently, the pressure increases and the air is
forced outside.

89. Mechanism of Respiration
• Mechanism of respiration involves the breathing
mechanism and exchange of gases.
• The gaseous exchange occurs by diffusion in the alveoli.
It depends upon the pressure differences between blood
and tissues, or atmospheric air and blood. The exchange
of gases takes place at the surface of the alveolus.
• The mechanism of breathing has already been explained
above. Let us have a look at the steps involved in the
exchange of gases.

90. Transport of Oxygen
• Oxygen in the blood is carried to the tissue in two forms-
Oxyhaemoglobin- chemical composition of oxygen with
haemoglobin, and solution of oxygen in the blood plasma.
• The oxygen in the blood combines with haemoglobin
when the concentration of oxygen is high in the blood.
• Oxyhemoglobin, being unstable, dissociates to release
oxygen. Low oxygen, low pH and high temperatures
stimulate the dissociation process.

91. Internal Respiration
• The gaseous exchange taking place in the tissues is
called internal respiration. Here, the oxygen carried in the
form of oxyhemoglobin gets dissociated to release
oxygen.
• This oxygen breaks down glucose to release carbon
dioxide, water, and energy. The energy is utilized by the
body, while the carbon dioxide is diffused from the
tissues.

92. Transport Of Carbon dioxide From Tissues To Lungs
• Carbon dioxide is transported by three mechanisms:
• Some carbon dioxide dissolves in the water of plasma to
form carbonic acid.
• Carbonic acid ionizes to form bicarbonate ions. The
hydrogen ions are catalyzed by the enzyme carbonic
anhydrase. Bicarbonate ions combine with sodium and
potassium to form sodium bicarbonate and potassium
bicarbonate.
• Some carbon dioxide combines with haemoglobin for the
formation of carbaminohemoglobin.
• It is finally carried to the lungs and released out of the

94. Intrapleural Breathing
• Intrapleural breathing is used to refer to the pressure that
is present in the space between the pleura and the lungs.
This space is referred to as the pleural cavity. The
pressure in this region is normally less than the
atmospheric pressure. This is the reason why pleural
pressure is termed as negative pressure.
• The lung movement is governed by the pressure gradient,
the transpulmonary pressure, which exists between the
pleura and the lungs. The difference in the pressures
between intrapulmonary and intrapleural pressures is
known as transpulmonary pressure.

95. • The pressure in the pleural cavity while breathing turns
negative while there is an increase in the transpulmonary
pressure causing the lungs to expand. While expiration,
the lungs recoil as a result of an increase in the pleural
pressure.
• The competing forces inside the thorax results in the
formation of negative intrapleural pressure, one of these
forces is associated with the lung’s elasticity. The lungs
have elastic tissues which cause it to be pulled inwards
off the thoracic wall. An inward pull of the lung tissue is
also generated by the surface tension of the alveolar fluid.
The inward tension generated from the lungs is opposed
by forces from the thoracic wall and the pleural fluid.

96. Respiratory Gas Transport
• After the gases have scattered in the lungs, causing the
blood to become oxygenated, leaving carbon dioxide, the
next phase of transportation of oxygen-rich blood to the
tissues takes place. Meanwhile, the next round of
deoxygenated blood needs to be brought to the lungs for
the cycle to continue.
• In the bloodstream, the transportation of gases occurs all
through the body which is contributed to the
cardiovascular system comprising the blood vessels and
the heart. The blood carrying oxygen leaves the lungs to
flow into the heart through the pulmonary veins, which are
pumped to the rest of the body from the left ventricle

97. NAMES OF GROUP MEMBERS
1. WILHELMINA SWANZY ESSILFIE
2. ANAKWAH EMELIET ESI
3. ASANTE ABIGAIL
4. AHMED BURHAN-DEEN TIJANI
5. MUSAH MARIAM
6. FAASE OSWELL
7. ABUGRI HARRISON
8. AYAMGA DOROTHY AWINSAKIYA
9. OBUOBI BRIGHT
10. TWUMWAA SIAW MAYFAIR
11. YENLI ELLISON SAANAALONG

98. THANK YOU