Anatomy Flashcards
(280 cards)
1
Q
Where does the sternum lie?
A
Anteriorly in the midline of the thoraic cage
2
Q
3 parts the sternum is composed of
A
The Manubrium
The body
the xiphoid process
3
Q
The manubrium
A
is the superior part of the sternum:
● the superior border has a notch in it – the suprasternal (jugular) notch
● laterally, it articulates with the clavicle (collarbone) at the sternoclavicular joint, and with the first rib
● inferiorly, it articulates with the body of the sternum at the manubriosternal joint, also known as the sternal angle (or the ‘angle of Louis’).
4
Q
The body
A
is inferior to the manubrium:
● it articulates with ribs 2 - 7
● the second rib articulates with the sternum at the sternal angle (i.e. with the inferior part of the manubrium and the superior part of the body).
● inferiorly, it articulates with the xiphoid process
5
Q
The xiphoid process (or xiphisternum)
A
is inferior to the body:
● it is small and variable in shape
● the seventh rib articulates with the inferior part of the body of the sternum and the superior part of the xiphoid process.
6
Q
How many ribs form the anterior, lateral, and posterior walls of the thoraic cage
A
12
7
Q
What are the anterior parts of the ribs made of?
A
costal cartilage
8
Q
Where do the ribs articulate with their costal cartilage?
A
at costochondral joints.
● The costal cartilages of ribs 1 - 7 articulate directly with the sternum at sternocostal joints – they are ‘true’ ribs.
● The costal cartilages of ribs 8 - 10 unite and join the seventh costal cartilage –they are ‘false’ ribs.
9
Q
What forms the costal margin, which is palpable?
A
The costal cartilages of ribs 7-10
10
Q
Ribs 11 and 12
A
are short and do not articulate with the sternum – they are
‘floating’ ribs
11
Q
The ribs articulate posteriorly with the thoracic vertebrae at costovertebral joints.
A
Adjacent ribs are connected to each other by intercostal muscles, which lie in the intercostal spaces.
12
Q
Typical ribs
A
look similar and share common anatomical features
Ribs 3 - 9 are typical ribs. They have a head, neck, tubercle, and body (shaft).
13
Q
Atypical ribs
A
look different to typical ribs and / or lack some of the features of typical ribs
Ribs 1, 2 and 10-12 are atypical, for various reasons. For example, ribs 1, 11 and 12 are much shorter than typical ribs.
14
Q
The vertebrae
A
Twelve thoracic vertebrae (T1 - T12) lie posteriorly in the midline of the thoracic cage
The spinous processes of the thoracic vertebrae are palpable in the midline of the back.
The thoracic vertebrae articulate with the posterior parts of the ribs at costovertebral joints.
Typically the head of the rib articulates with the vertebral body and the tubercle of the rib articulates with the transverse process of the vertebra.
15
Q
What forms the superior thoracic aperture?
A
The manubrium, the first ribs and the first thoracic vertebra form the boundary of the superior thoracic aperture
16
Q
What is the role of the superior thoracic aperture
A
The ‘passageway’ through which structures pass between the neck and the thorax
17
Q
Dermatome
A
an area of skin innervated by a single spinal nerve.
Each pair of thoracic spinal nerves supplies a ‘strip’ around the chest wall
18
Q
Axillary tail
A
The part of the breast where Breast tissue extends towards the anterior axilla (armpit)
19
Q
Contents of the breast
A
● Fat - variable amounts
● Glandular / secretory tissue arranged in lobules
● Ducts which converge on the nipple. The areola is the region of pigmented skin that surrounds the nipple
● Connective tissue and ligaments
● Blood vessels and lymphatics
20
Q
What branches is the breast primarily supllied by?
A
● internal thoracic artery (which arises from the subclavian artery)
● axillary artery
21
Q
internal thoracic artery
A
courses deep to the lateral edge of the sternum.
It gives rise to anterior intercostal arteries that supply the breast and the intercostal spaces
22
Q
How does blood return?
A
Venous blood returns to the axillary and internal thoracic veins.
23
Q
Somatic nerves and sympathetic fibres
A
The breast is supplied with somatic nerves and sympathetic fibres via the intercostal nerves.
Somatic sensory fibres innervate the skin of the breast.
Sympathetic fibres innervate smooth muscle in the blood vessel walls and nipple.
24
Q
There are 5 groups of lymph nodes in the axilla:
A
central
pectoral
humeral
subscapular
apical
25
Role of the nodes
● They drain the breast, upper limb, chest wall, scapular region, and the abdominal wall.
● The apical nodes (in the apex of the axilla) receive lymph from all other lymph nodes in the axilla. Because they drain most of the lymph from the breast, the axillary lymph nodes are often involved in the spread of breast cancer.
26
Intercostal muscles lie in the intercostal spaces between the ribs. Within each intercostal space, there are three layers of muscles:
● the external intercostal is most superficial
● the internal intercostal lies deep to the external intercostal
● the innermost intercostal lies deep to the internal intercostal.
27
Functions of intercostal muscles
Collectively they move the ribs and alter the dimensions of the thoracic cavity with inspiration (breathing in) and expiration (breathing out).
28
Pectoralis major
is the most superficial muscle of the anterior chest wall. It attaches to the upper humerus, the clavicle and the upper six ribs.
29
Pectoralis minor
is a smaller muscle that lies deep to pectoralis major. It attaches to the scapula (shoulder blade) and ribs 3-5.
30
Serratus anterior
is a superficial muscle that sweeps around the lateral aspect of the thoracic cage. It attaches to the scapula and the upper eight ribs.
31
Role of these muscles
The prime function of these muscles is to move the upper limb (pectoralis major adducts the humerus; pectoralis minor and serratus anterior protract the scapula).
However, they can also function as accessory muscles of breathing because they attach to the ribs and hence can move the ribs if the humerus and scapula are fixed.
In patients, use of these muscles is a sign of respiratory distress.
32
Intercostal Muscles
The muscles in the intercostal spaces attach to the rib above and rib below.
There are three layers of muscles in the intercostal spaces.
Their fibres run in different directions to each other and hence act on the ribs in different ways.
33
External intercostal is most superficial. Its fibres are orientated antero-inferiorly (down and inwards)
● Contraction of external intercostal muscles pulls the ribs superiorly, hence is it most active in inspiration.
● In the anterior part of the intercostal space, the muscle becomes membranous and forms the external intercostal membrane.
34
Internal intercostal lies deep to the external intercostal. Its fibres run perpendicular to those of the external intercostal, running in a postero-inferior direction (back and below)
● Contraction pulls the ribs inferiorly, hence is it most active in expiration.
● The internal intercostal becomes membranous in the posterior part of the intercostal space and forms the internal intercostal membrane.
35
The innermost intercostal lies in the posterior part of the intercostal space deep to the internal intercostal.
Its fibres are orientated in the same direction as those of the internal intercostal.
The endothoracic fascia lies deep to the innermost intercostal and superficial to the parietal pleura, which surrounds the lung.
36
Intercostal Neurovascular Bundle
The neurovascular bundle in each intercostal space lies in the plane between the internal and innermost intercostal muscle.
It supplies the intercostal muscles, the overlying skin, and the underlying parietal pleura
37
Location of the intercostal neurovascular bundle
The neurovascular bundle for each intercostal space lies along the inferior border of the rib superior to the space.
It lies in a shallow costal groove on the deep surface of the rib.
38
Anterior and posterior intercostal arteries supply the anterior and posterior parts of the intercostal space, respectively.
● The anterior intercostal arteries are branches of the internal thoracic artery (a branch of the subclavian artery).
● The posterior intercostal arteries are branches from the descending aorta in the posterior thorax
39
intercostal veins
Anterior intercostal veins drain into the internal thoracic vein
Posterior intercostal veins drain into the azygos system of veins
40
intercostal nerves
are somatic and contain motor and sensory fibres.
They innervate the intercostal muscles, the skin of the chest wall and the parietal pleura.
Intercostal nerves also carry sympathetic fibres.
41
Function of the two layers of membranes- pleurae
cover the lungs and the structures passing into and out of the lungs (the pulmonary blood vessels and the main bronchi)
● The parietal pleura lines the inside of the thorax
● The visceral pleura covers the surface of the lungs and extends into the fissures
The two layers of pleura are continuous with each othe
42
What lies between the parietal and visceral pleura
A very thin pleural cavity (or space)
43
Role of pleura and pleural fluid
The pleural cells produce a small amount of pleural fluid, which fills the pleural cavity.
The pleura and pleural fluid are integral to the mechanics of breathing.
44
The parts of the parietal pleura are named according to the structures they lie adjacent to.
● The cervical pleura covers the apex of the lung
● The costal pleura lies adjacent to the ribs
● The mediastinal pleura lies adjacent to the heart
● The diaphragmatic pleura lies adjacent to the diaphragm.
45
The costodiaphragmatic recess
is a ‘gutter’ around the periphery of the diaphragm, where the costal pleura becomes continuous with the diaphragmatic pleura.
46
smaller costomediastinal
A smaller costomediastinal recess lies at the junction of the costal and mediastinal pleura.
These are potential spaces that the lungs expand into during deep inspiration.
47
The two pleural layers are innervated by different nerves
hence we perceive painful sensations from the parietal and visceral pleura differently
48
The parietal pleura is innervated by the intercostal nerves that innervate the overlying skin of the chest wall.
Somatic sensory fibres in these nerves carry sensation to our consciousness.
Injury to the parietal pleura (e.g. tearing by a fractured rib) is typically very painful.
49
The visceral pleura is innervated by autonomic sensory nerves
Sensation from visceral afferents usually does not reach our conscious perception.
50
What is the most superior part of the lung?
Apex which projects into the root of the neck, above the clavicle.
The base of the lung ‘sits’ on the diaphragm.
51
Each lung is formed of lobes- the right lung has 3 lobes
a superior (upper), middle, and inferior (lower) lobe.
52
The left lung has 2 lobes
a superior and inferior lobe.
An anterior extension of the superior lobe – the lingula (Latin for ‘small tongue’) – extends over the heart.
53
Function of fissures
Seperate the lobes. Both lungs have an oblique fissure.
54
Role of oblique fissure In the left lung,
it separates the superior and inferior lobes.
55
Role of oblique fissure In the right lung,
it separates the superior and middle lobes from the inferior lobe
56
Role of HORIZONTAL fissure in RIGHT lung
It separates the superior lobe from the middle lobe.
57
The lungs are described in terms of surfaces
● Costal surface - adjacent to the ribs
● Mediastinal surface - adjacent to the heart
● Diaphragmatic surface - the inferior surface of the lung
The surfaces of the lungs bear indentations (impressions) created by adjacent structures.
Rib markings are seen on the costal surfaces of both lungs.
Indentations created by the left ventricle and the descending aorta are seen on the mediastinal surface of the left lung and indentations made by the superior vena cava and azygos vein are seen on the mediastinal surface of the right lung.
58
The lungs are described in terms of borders.
● Anterior border - sharp and tapered
● Posterior border – thick and rounded
● Inferior border - sharp and tapered
59
The root of each lung lies between the heart and the lung and comprises the pulmonary artery, pulmonary veins, and main bronchus.
Pleura encloses the root of the lung like a sleeve.
60
The hilum of the lung
is the region on the mediastinal surface of the lung where the pulmonary artery, pulmonary veins and main bronchus enter and exit the lung.
61
The positions of the pulmonary artery and main bronchus relative to each other at the hilum is slightly different between the right and left lungs.
● At the hilum of the right lung, the main bronchus lies anterior to the pulmonary artery
● At the hilum of the left lung, the main bronchus lies inferior to the pulmonary artery
At both the right and left hila, the two pulmonary veins are usually the most anterior and inferior vessels
62
The trachea bifurcates into the left and right main bronchi at the level of the sternal angle (T4/T5)
The right main bronchus is shorter, wider and descends more vertically than the left main bronchus thus a foreign body entering the trachea is more likely to enter the right main bronchus than the left.
63
The bronchial tree
is the branching system of tubes that conduct air into and out of the lungs.
64
Each main bronchus divides into lobar bronchi;
three in the right lung and two in the left lung (i.e. one lobar bronchus for each lobe).
65
Each lobar bronchus divides to give rise to segmental bronchi.
There are ten segmental bronchi in each lung
66
Each segmental bronchus supplies a functionally independent region of the lung called a bronchopulmonary segment;
there are ten segments in each lung.
Because they are supplied by their own segmental bronchus and blood vessels, a segment may be resected (surgically removed) without affecting the rest of the lung.
67
Segmental bronchi within each bronchopulmonary segment continue to divide into bronchioles.
Bronchioles become smaller with each division.
The very smallest bronchioles conduct air to and from the alveoli - the site of gas exchange within the lung
68
The walls of the trachea and bronchi contain smooth muscle and cartilage, but the walls of bronchioles only contain smooth muscle.
Contraction and relaxation of the smooth muscle is under autonomic control.
69
The pulmonary arteries carry deoxygenated blood to the lungs
Bronchial arteries from the descending aorta also supply the lungs
The pulmonary veins return oxygenated blood to the heart from the lungs.
Bronchial veins return blood to the azygos system of veins
Autonomic nerves innervate the lungs.
70
Parasympathetic fibres stimulate:
● constriction of bronchial smooth muscle (bronchoconstriction)
● secretion from the glands of the bronchial tree.
71
Sympathetic fibres:
● stimulate relaxation of bronchial smooth muscle (bronchodilation)
● inhibit secretion from the glands.
72
Visceral afferents (visceral sensory fibres)
accompany the sympathetic and parasympathetic nerves and relay sensory information from the lungs and visceral pleura to the CNS, but these sensations do not usually reach our conscious perception.
somatic sensory fibres carried in the intercostal nerves innervate the parietal pleura
73
Lymph from the lungs ultimately drains into the venous system via…
the thoracic duct or right lymphatic duct.
74
The surface markings of the inferior borders of the lungs and the inferior extent of the parietal pleura are different as the parietal pleura extends more inferiorly than the inferior border of the lung.
The space between them is the costodiaphragmatic recess.
75
Surface Anatomy of the Lungs and Pleura
The apex of each lung projects into the lower neck, just superior to the medial end of the clavicle.
76
The inferior border of the lungs lies at the level of the:
• 6th rib anteriorly (midclavicular line)
• 8th rib laterally (midaxillary line)
• 10th rib posteriorly (at the vertebral column)
77
The parietal pleura extends to the:
• 8th rib anteriorly (midclavicular line)
• 10th rib laterally (midaxillary line)
• 12th rib posteriorly (at the vertebral column)
78
Fissures of the left and right lungs
The oblique fissure of both the left and right lungs extends from the 4th rib posteriorly to the 6th costal cartilage anteriorly; the fissure runs deep to the 5th rib
The horizontal fissure of the right lung extends anteriorly from the 4th costal cartilage and intersects the oblique fissure.
79
What is the diaphragm?
a broad, thin, domed sheet of skeletal muscle.
80
Role of The Diaphragm
● It separates the thoracic and abdominal cavities from each other
● Its superior (thoracic) surface is adjacent to the parietal pleura
● Openings (apertures) in the diaphragm allow the passage of structures between the thorax and abdomen (e.g. the aorta, inferior vena cava, and oesophagus)
● Its function is integral to the mechanics of breathing (ventilation)
81
Attachments and Movements of The Diaphragm
The diaphragm is attached to the xiphoid process, costal margin (and to the tips of the 11th and 12th ribs) and the lumbar vertebrae.
82
The central tendon
The central part of the diaphragm is not muscular, but fibrous
83
When the diaphragm contracts during inspiration, the muscle fibres of the right and left domes are pulled towards their peripheral attachments, and the domes flatten.
This increases the intrathoracic volume for the lungs to expand.
84
During expiration, the diaphragm relaxes and domes superiorly.
This decreases the intrathoracic volume and drives expiration of air from the lungs.
85
The right and left phrenic nerves innervate the right and left sides of the diaphragm, respectively
They are somatic nerves, formed in the neck by fibres from the C3, C4 and C5 spinal nerves, and hence contain motor and sensory fibres.
86
Breathing mechanics:
● Muscles move the thoracic cage and change the dimensions of the thoracic cavity
● The dimensions of the thoracic cavity determine intrathoracic volume
● Changes in intrathoracic volume alter intrathoracic pressure
● Pressure changes inside the thorax drive inspiration and expiration
● Different muscles are involved in normal, vigorous, and forced ventilation.
87
During ventilation, the dimensions of the thoracic cavity change in three planes:
● Vertically - due to the contraction and relaxation of the diaphragm
● Laterally - due to contraction of the intercostal muscles which move the ribs
● Antero-posteriorly (AP) – due to movement of the sternum secondary to movement of the ribs
88
The pleurae and pleural fluid are integral to ventilation.
The pleural fluid creates surface tension between the parietal pleura lining the thoracic cavity and the visceral pleura on the surface of the lung
89
Role of surface tension
Surface tension keeps the lung and thoracic wall ‘together’, so when the thoracic cavity changes volume, the lung changes volume with it.
Surface tension between the two pleural membranes keeps them in contact with each other and prevents the lung from ‘collapsing’ away from the thoracic wall.
90
What happens if the surface tension is broken?
e.g. by a penetrating injury of the chest that punctures the parietal pleura and introduces air into the pleural cavity - pneumothorax
ventilation may become dysfunctional.
91
In inspiration:
● The diaphragm and external intercostal muscles contract, increasing the intrathoracic volume (the external intercostals pull the ribs superiorly and laterally, and the ribs pull the sternum superiorly and anteriorly, increasing the AP and lateral dimensions of the thoracic cavity)
● The lungs expand (increase in volume) with the thoracic wall (due to surface tension)
● The pressure in the lungs decreases below atmospheric pressure and air is drawn into the lungs.
92
In expiration:
● The diaphragm and external intercostal muscles relax, and the internal intercostals contract, decreasing the intrathoracic volume (the internal intercostals pull the ribs inferiorly, and the ribs pull the sternum inferiorly and posteriorly, decreasing the AP and lateral dimensions of the thoracic cavity)
● The lungs recoil (decrease in volume)
● The pressure in the lungs increases above atmospheric pressure and air is expelled from the lungs.
93
Muscles Involved in Breathing
● In normal, quiet breathing…
inspiration is active and is mainly driven by movement
of the diaphragm, but expiration is passive.
94
Muscles Involved in Breathing
● In vigorous breathing (e.g. exercise)
the intercostal muscles become important.
Active expiration uses the internal intercostal muscles
95
Muscles Involved in Breathing
● In very vigorous or forced breathing (e.g. in an exacerbation of asthma or COPD, or in strenuous exercise)
the accessory muscles of breathing (sternocleidomastoid, pectoralis major and minor, serratus anterior) contribute to movement of the ribs and aid ventilation.
96
Mediastinum
part of the thoracic cavity that lies between the lungs
contains all the thoracic viscera apart from the lungs
97
The mediastinum extends from the:
● superior thoracic aperture superiorly to the diaphragm inferiorly
● sternum anteriorly to the thoracic vertebrae posteriorly.
98
The mediastinum contains
● The heart and pericardium (the fibrous sac around the heart)
● The great vessels that enter and leave the heart
● The veins that drain the chest wall
● The trachea and main bronchi
● The oesophagus
● Nerves (somatic and autonomic)
● Lymphatics
● The thymus gland
99
the mediastinum is divided into a superior and inferior compartment
The ‘line’ between these compartments runs from the sternal angle anteriorly to the T4/T5 junction posteriorly
100
The inferior mediastinum is further divided into
anterior, middle, and posterior compartments
101
Anterior
The anterior mediastinum lies between the posterior aspect of the sternum and the anterior aspect of the pericardial sac.
It is a narrow space that contains the thymus gland in children and its remnant in adults.
102
Middle
The middle mediastinum contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta
103
Posterior
The posterior mediastinum lies between the posterior aspect of the pericardial sac and the vertebrae
104
The main contents of the superior mediastinum are the:
● arch of the aorta and its three branches
● superior vena cava and its tributaries - the left and right brachiocephalic veins
● trachea
● oesophagus
● phrenic nerves (left and right) and vagus nerves (left and right)
● thoracic duct
● thymus gland
105
The aorta leaves the left ventricle and carries oxygenated blood to the systemic circulation.
There are three ‘parts’ in the thorax:
The ascending aorta
The arch
The descending (thoraic) aorta
106
The ascending aorta
is the short, first part.
It gives rise to the coronary arteries, which supply the myocardium
Found in the middle mediastinum
107
The arch
The arch of the aorta curves posteriorly.
It lies in the superior mediastinum.
108
The descending (thoracic) aorta
descends through the posterior mediastinum
and into the abdomen posterior to the diaphragm.
109
The arch of the aorta in the superior mediastinum gives rise to three major branches that supply the upper body
● First, the brachiocephalic trunk. It bifurcates into the right common carotid artery which supplies the right side of the head and neck, including the brain, and the right subclavian artery which supplies the right upper limb
● Second, the left common carotid artery, which supplies the left side of the head, neck, and brain
● Third, the left subclavian artery, which supplies the left upper limb
110
The arch of the aorta contains the aortic bodies where chemoreceptors are located.
These receptors constantly monitor arterial oxygen and carbon dioxide.
This visceral sensory information travels back to the CNS along the path of the vagus nerve and results in reflex responses that regulate ventilation
111
Ligamentum arteriosum
The ligamentum arteriosum is a fibrous, cord-like connection between the pulmonary trunk and the arch of the aorta
It is the remnant of the ductus arteriosus, a foetal circulatory shunt. In the foetus, gas exchange occurs at the placenta, not in the lungs
112
The ductus arteriosus
The ductus arteriosus diverts most of the blood entering the pulmonary trunk directly to the aortic arch (only a small amount of blood circulates through the foetal lungs; enough for them to develop).
When a baby starts to use their lungs at birth, the ductus arteriosus closes, and blood in the pulmonary trunk enters the lungs.
113
Veins
Two large veins carrying deoxygenated blood enter the right atrium: the superior vena cava and the inferior vena cava
114
The superior vena cava (SVC)
returns blood to the heart from the head, neck,
and upper limbs. The SVC and its tributaries lie in the superior mediastinum
● The SVC is formed by the union of the left and right brachiocephalic veins (brachium = arm; cephalic = head)
● The union of the internal jugular vein (which drains the head and neck) and the subclavian vein (which drains the upper limb) forms each brachiocephalic vein.
115
The inferior vena cava (IVC)
returns blood to the heart from all regions inferior to the diaphragm (abdomen, pelvis, and lower limbs).
The thoracic part of the IVC is very short - as soon as it enters the thorax (the inferior mediastinum) through the diaphragm it enters the right atrium.
116
Structure of Trachea
● It extends from the larynx in the midline of the neck into the superior mediastinum and is palpable just superior to the suprasternal notch
● It terminates at the level of the sternal angle (and junction between the T4 and T5 vertebrae) by bifurcating into the left and right main bronchi
117
Oesophagus
The oesophagus is a muscular tube that extends from the pharynx in the midline of the neck to the stomach.
‘Waves’ of contractions of smooth muscle in the oesophageal wall move swallowed food and fluid distally (peristalsis)
118
In the superior mediastinum, the oesophagus…
…the oesophagus lies in the midline of the thorax, posterior to the trachea.
It descends into the posterior mediastinum
119
Phrenic nerves
They are somatic nerves and contain motor and sensory fibres.
120
Phrenic nerves are fomed from
The left and right phrenic nerves, formed by fibres from the C3, C4 and C5 spinal nerves, innervate the diaphragm
121
Where are phrenic nerves found
They descend through the neck and enter the thorax through the superior thoracic aperture.
They course over the pericardium and pierce the diaphragm.
122
Where di vagus nerves arise from?
The left and right vagus nerves (CN X) arise from the brainstem and contain somatic sensory, somatic motor and parasympathetic fibres.
123
What structures do vagus nerves innervate?
structures of the thorax and abdomen, in addition to the head and neck
124
Vagus nerves innervate…
● They descend through the neck alongside the internal carotid artery and internal jugular vein and enter the thorax via the superior thoracic aperture.
● They each give rise to a recurrent laryngeal nerve (RLN), which ascend back up into the neck to innervate the muscles of the larynx.
● The left recurrent laryngeal nerve loops under the arch of the aorta before ascending back up the left side of the neck (alongside the trachea) to the larynx.
● The right recurrent laryngeal nerve descends anterior to the right subclavian artery and then loops under the inferior border of the artery before ascending back up the right side of the neck (between the trachea and oesophagus) to the larynx
● The vagus nerves descend in the thorax posterior to the root of the lung
● They contribute parasympathetic fibres to the heart, lungs, and oesophagus
● They traverse the diaphragm and convey parasympathetic fibres to most of the
abdominal viscera.
125
What is the thoracic duct?
The thoracic duct is a major channel for lymphatic drainage from most regions of the body.
126
Where is the thoracic duct found?
It ascends through the posterior mediastinum and into the superior mediastinum, where it empties into the venous system at the union of the left internal jugular vein and left subclavian vein
127
What type of organ is the Thymus gland?
lymphoid organ
128
Where is the thymus gland found?
It lies anteriorly in the superior mediastinum
It is important in children, but atrophies with age, eventually becoming fatty
129
What is the pericardium?
The pericardium is a tough, fibrous sac that encloses the heart like a loose-fitting bag; it is loose to allow for the movement of the heart within it.
130
What 2 layers is the pericardium composed of?
● a tough, outer fibrous layer that is attached superiorly to the great vessels and inferiorly to the central tendon of the diaphragm
● a thin, inner serous layer which has two parts: the parietal layer lines the inner aspect of the fibrous pericardium, and the visceral layer covers the surface of the heart.
The two layers are continuous with each other
131
The pericardial cavity
The narrow space between the two layers of serous pericardium
132
Structure of the pericardium cavity
It contains a small amount of pericardial fluid that lubricates the serous membranes and allows them to slide over each other with movements of the heart.
The left and right phrenic nerves give rise to sensory branches that innervate the fibrous pericardium.
133
Position and Surfaces of the Heart
The heart is shaped roughly like a pyramid lying on one of its sides
134
The apex
The ‘point’ of the pyramid is the apex, which projects to the left of the sternum towards the left lung
The apex is formed by the left ventricle.
It lies at the left 5th intercostal space in the midclavicular line and the apex beat is palpable here
135
The surfaces of the heart are the:
● base – it ‘faces’ posteriorly, so is also called the posterior surface
● inferior surface – it lies on the central tendon of the diaphragm, so is also called the diaphragmatic surface
● anterior surface – it ‘faces’ the sternum and ribs, so is also called the sternocostal surface
● The left and right sides of the heart ‘face’ the lungs and are referred to as the pulmonary surfaces.
136
The surfaces correspond to specific parts of the heart
● Base / posterior surface = left atrium, part of the right atrium
● Inferior / diaphragmatic surface = left ventricle, part of the right ventricle
● Anterior / sternocostal surface = right ventricle
● Left pulmonary surface = left ventricle
● Right pulmonary surface = right atrium
137
Borders of the heart (edges).
The borders of the heart correspond to specific parts of the heart, which are:
● Right border = right atrium
● Left border = left ventricle
● Inferior border = right ventricle and part of the left ventricle.
138
Right border
lies lateral to the right sternal edge, from the right 3rd costal cartilage to the right 6th costal cartilag
139
Left border
extends from the left 2nd intercostal space to the left 5th intercostal space in the midclavicular line (i.e. the apex)
140
Superior border
lies along the line connecting the superior extents of the right and left borders (i.e. from the right 3rd costal cartilage to the left 2nd intercostal space)
141
Inferior border
lies along the line connecting the inferior end of the right border with the apex (mostly formed by the right ventricle).
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Auricles (auricular appendages)
they are outpouchings from the
walls of the right and left atria.
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The Coronary Circulation
The arteries and veins that supply the heart are visible on its external surface.
The major arteries lie in grooves on the external surface called sulci (singular = sulcus; Latin for groove or furrow)
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Right Coronary Artery (RCA)
The right coronary artery and its branches supply parts of the conducting system of the heart, the right atrium, right ventricle, part of the left ventricle, and part of the interventricular septum.
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Right Coronary Artery (RCA)
The right coronary artery and its branches supply parts of the conducting system of the heart, the right atrium, right ventricle, part of the left ventricle, and part of the interventricular septum.
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The main branches of the right coronary artery and the territories they supply are as follows
● Branches to the sinoatrial node and atrioventricular node supply these major
components of the electrical conducting system of the heart
● The right marginal artery supplies the inferior border of the heart
● The posterior interventricular artery (PIV) is the continuation of the right coronary artery on the inferior (diaphragmatic) surface of the heart. It runs in the posterior interventricular sulcus and supplies both ventricles.
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Left Coronary Artery (LCA)
The left coronary artery and its branches supply parts of the conducting system of the heart, the left atrium, most of the left ventricle, part of the right ventricle, and part of the interventricular septum.
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The two terminal branches of the left coronary artery are the:
● Anterior interventricular artery (or the left anterior descending; ‘LAD’)
● Circumflex artery (abbreviated to ‘Cx’)
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The main branches of the left coronary artery and the territories they supply are as follows.
● The anterior interventricular artery (LAD) runs in the anterior interventricular sulcus towards the apex. It supplies both ventricles
● One or two diagonal branches arise from the LAD
● The circumflex artery runs around the heart onto the inferior /diaphragmatic surface. It supplies the left atrium, part of the right ventricle and the left ventricle
● The left marginal artery arises from the circumflex and supplies the left ventricle
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posterior interventricular
The posterior interventricular artery, which supplies a significant portion of the left ventricle, may arise from the right or left coronary artery
30% of people the circumflex gives rise to the PIV artery
90% of people the right coronary artery gives rise to the PIV artery
So in 20% of people there are 2 PIV arteries.
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The origin of the posterior interventricular artery determines if an individual has a right dominant or a left dominant coronary circulation
● Most people have a right dominant circulation; the PIV arises from the right coronary. In these people, both the right and left coronary arteries supply the left ventricle
● In those with a left-dominant circulation, the PIV arises from the circumflex artery; the left coronary artery supplies the entire left ventricle
● This is important in clinical practice. In someone with a right-dominant circulation, occlusion of the left main stem would impair blood flow to part of, but not the entire left ventricle
In someone with a left-dominant coronary circulation, blockage of the left main stem occludes blood flow to the entire left ventricle
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Valves importance
Valves inside the heart ensure unidirectional flow of blood through the chambers of the heart
Embedded deep in the heart is its conducting system. We cannot see this with the naked eye
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Right atrium
The right atrium receives deoxygenated blood from the body via the superior and inferior venae cavae, and from the heart via the coronary sinus.
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Internally the main features of the right atrium are:
● interatrial septum which separates it from the left atrium
● fossa ovalis – a depression in the interatrial septum. It is the remnant of the
foetal foramen ovale. In the foetus the foramen ovale shunts oxygenated blood
from the right atrium to the left atrium, hence bypassing the lungs.
● crista terminalis (is the SA node)– a muscular ridge that separates the smooth-walled posterior part of the atrium from the anterior part, which has a ridged, muscular wall.
The ridges are pectinate muscles and extend into the right auricle. The parts of the right atrium on either side of the crista have different embryological origins.
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Blood flow
From the right atrium, blood flows into the right ventricle via the right atrioventricular valve, also called the tricuspid valve.
The flow of blood is mostly passive, but the right atrium does contract to empty fully
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Right ventricle
The right ventricle pumps the deoxygenated blood that it receives from the right atrium into the pulmonary trunk, which bifurcates into a left and right pulmonary artery
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Role of the pulmonary valve
The pulmonary valve at the entrance of the pulmonary trunk prevents backflow of blood into the right ventricle
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Difference between the right ventricle and right atrium
As contraction of the right ventricle propels blood into the pulmonary trunk, the wall of the right ventricle is thicker than that of the right atrium.
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Features of the right ventricle
● interventricular septum which separates it from the left ventricle
● trabeculae carneae – muscular ridges on the internal wall
● papillary muscles (cardiac muscle) – modified regions of trabeculae carneae, which project into the lumen of the ventricle
● chordae tendineae – fibrous cords which connect the tips of the papillary muscles to the tricuspid valve
● moderator band – a modified region of the trabeculae carneae which connects the interventricular septum to one of the papillary muscles. Carries purkynje fibre to the right ventricle
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Left atrium
The left atrium receives oxygenated blood from the lungs via the pulmonary veins (two from each lung).
Like the right atrium, it has a thinner wall compared to the ventricles and internally has a smooth-walled posterior part and an anterior part bearing pectinate muscles.
Again, this reflects the left atrium’s development from two different embryological structures.
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Blood flow in the left atrium
From the left atrium, blood flows into the left ventricle via the left atrioventricular valve, also called the mitral valve.
The flow of blood is mostly passive, but the left atrium does contract to empty fully.
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Left ventricle
The left ventricle pumps the oxygenated blood that it receives from the left atrium into the aorta.
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Structure of the left ventricle
The first branches from the aorta are the coronary arteries. The aortic valve at the entrance to the aorta prevents backflow of blood into the left ventricle.
Because contraction of the left ventricle propels blood into the systemic circulation, the wall of the left ventricle is thicker than that of the right ventricle.
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Like the right ventricle, the left ventricle contains:
● trabeculae carneae
● papillary muscles; two in the left ventricle
● chordae tendineae that connect the tips of the papillary muscles to the mitral
valve.
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Atrioventricular valves- during contraction/systole
When the ventricles contract (ventricular systole), pressure rises inside the ventricles.
This rise in pressure has the potential to force blood back into the atria.
The tricuspid and mitral valves close during ventricular contraction and prevent regurgitation of blood back into the atria, ensuring that blood can only flow out the ventricles via the great vessels (the pulmonary trunk and aorta).
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The papillary muscles and chordae tendineae
are crucial for normal functioning of the atrioventricular valves.
These structures do not close the valves, but instead allow the closed valves to resist the pressure generated inside the ventricles during contraction and prevent them from being forced open.
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As pressure rises in the ventricles…
the valve cusps, which project into the ventricle, start to close passively.
When the ventricles contract, the papillary muscles also contract.
The papillary muscles tense the cords, which in turn ‘pull’ on the valve cusps and prevent them everting into the atria.
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Semilunar valves
The aortic and pulmonary valves are called semilunar valves, as their cusps are semi-circular (half-moon) shaped.
They prevent the backflow of blood from the aorta and pulmonary trunk into the left and right ventricles, respectively, that would otherwise occur at the end of ventricular contraction.
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Cusps
Each semilunar valve has three semi-circular cusps
Each cusp is attached to the inner wall of the vessel, with a free edge that projects into the vessel lumen
Each cusp forms a pocket, or sinus, between its free edge and the vessel wall.
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Blood flow through valves
When blood is forcefully propelled from the ventricles during ventricular systole, the valve cusps are ‘flattened’ onto the vessel wall and blood flows through the valve unimpeded.
At the end of ventricular systole, pressure in the ventricles drops.
Once pressure in the ventricle is less than that in the vessel (aorta or pulmonary trunk), blood in the vessel starts to flow back towards the heart.
As it flows back, blood is immediately ‘caught’ in the valve cusps. The sinuses rapidly fill with blood and the cusps balloon out into the lumen.
The free edges of the three valve cusps contact each other in the lumen and close the valve orifice.
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Why do the coronary arteries fill during ventricular relaxation (diastole)
In the aorta, the right and left coronary arteries arise from two of the three aortic sinuses
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The ‘auscultatory areas’ for each valve are:
● Aortic valve = 2nd intercostal space, just to the right of the sternum
● Pulmonary valve = 2nd intercostal space, just to the left of the sternum
● Tricuspid valve = 5th intercostal space, just to the left of the sternum
● Mitral valve = left 5th intercostal space, midclavicular line.
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Specialised cells in the heart generate and conduct the electrical impulses that stimulate myocardial contraction.
● Cells in the sinoatrial (SA) node spontaneously generate electrical impulses; it is the ‘pacemaker’ of the heart. It is located at the superior end of the crista terminalis.
● The SA node generates impulses at a rate of approximately 70 per minute.
● Impulses from the SA node stimulate contraction of the atria.
● Impulses are conducted to the atrioventricular (AV) node, located at the inferior end of the interatrial septum.
● From the AV node, conducting fibres form the atrioventricular bundle (Bundle of His).
● The atrioventricular bundle divides into two groups of fibres - the right and left bundle branches.
● The left and right bundle branches give rise to Purkinje fibres that enter the myocardium of the left and right ventricles, respectively, and stimulate contraction.
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Anatomical Variation in Blood Supply to the Conducting System
● The SA node is supplied by the RCA in approximately 60% of people and by the LCA in approximately 40% of people
● The AV node is usually supplied by the posterior interventricular artery. In most people, the PIV arises from the RCA
● In most people, the LCA supplies the Bundle of His.
Occlusion of either coronary artery can therefore result in conduction abnormalities, in addition to myocardial ischaemia.
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Although the SA node generates the electrical impulses within the heart, the heart is innervated by sympathetic and parasympathetic fibres.
These fibres act upon the SA node and can change the rate and force of myocardial contraction.
● Sympathetic stimulation increases the heart rate and force of contraction
● Parasympathetic stimulation slows the heart rate and force of contraction.
The heart is also innervated by visceral afferent fibres
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Visceral afferent fibres convey sensory information from the heart back to the CNS.
Usually, this sensory information doesn’t reach our conscious perception.
However, if the myocardium is ischaemic, this visceral sensory information is relayed back to our conscious perception and may be perceived as pain, burning, tightness or pressure in the chest.
Typically, the pain cannot be pinpointed, but is felt generally in the chest, the left side of the neck and / or the left arm. This is called referred pain.
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The posterior mediastinum lies behind the heart and pericardium. It contains the:
● descending (thoracic) aorta
● azygos veins
● oesophagus
● thoracic duct
● sympathetic trunk and splanchnic nerves
● posterior intercostal vessels and nerves
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Descending (thoracic) Aorta
As the aorta descends through the posterior mediastinum it gives rise to several branches
● Posterior intercostal arteries which supply the intercostal spaces
● Bronchial arteries which supply the lungs
● Oesophageal branches which supply the oesophagus
● Pericardial branches which supply the pericardium
● Phrenic branches which supply the diaphragm.
The aorta passes through the diaphragm at the level of T12.
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Azygos Veins
The azygos system of veins arises in the abdomen at the level of L1 / L2 and traverses the diaphragm to enter the posterior mediastinum.
It drains blood from the posterior thoracic wall and returns it to the superior vena cava.
The azygos veins lie on the bodies of the thoracic vertebrae.
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There is variation in Azygos Veins course and connections, but the system typically comprises:
● an azygos vein on the right side of the vertebral bodies
● a smaller (shorter) hemiazygos vein on the left side of the vertebral bodies
● one or more veins connecting the above veins to each other
The azygos system receives blood from the posterior intercostal veins, oesophageal veins, and bronchial veins.
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Oesophagus
In the posterior mediastinum, the oesophagus lies to the right of the aorta.
It is supplied by oesophageal arteries from the descending aorta.
Oesophageal veins return venous blood to the azygos system. The smooth muscle in the wall of the oesophagus is under autonomic control.
The oesophagus passes through the oesophageal hiatus in the diaphragm at the level of T10. The most distal part of the oesophagus lies inferior to the diaphragm.
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Thoracic Duct
The thoracic duct returns most of the body’s lymph to the venous system. It lies between the azygos vein and the aorta.
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● Lymph from the lower limbs, pelvis and abdomen flows towards the cisterna chyli, a sac-like swelling that gives rise to the thoracic duct, which ascends into the thorax
● In the thorax, the duct receives lymph from the intercostal spaces and lymph nodes
● The duct ascends into the neck, receiving lymph from the left side of the head and neck and the left upper limb
● It terminates by opening into the venous system at the junction between the left internal jugular vein and the left subclavian vein
The right side of the head and neck and the right upper limb are drained by lymphatic ducts that enter the venous system at the junction of the right internal jugular and right subclavian veins.
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Sympathetic Trunks
The trunks lie on the posterior thoracic wall, either side of the vertebral column and posterior to the parietal pleura.
They are thin, longitudinal fibre tracts regularly interspersed with ganglia (singular = ganglion).
a ganglion is a collection of cell bodies outside the CNS.
The ganglia in the sympathetic trunks are sometimes referred to as ‘paravertebral ganglia’ as they lie alongside the vertebral column. The trunks extend from the skull base to the coccyx.
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The cell bodies of preganglionic sympathetic neurons
lie in the thoracic and upper lumbar spinal cord segments (T1 – L2/3).
Because sympathetic fibres are visceral motor fibres, they leave the spinal cord from its ventral aspect and enter spinal nerves T1 – L2/3 along with somatic motor nerves, whose cell bodies lie in the ventral grey horn.
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However, sympathetic fibres must reach all parts of the body
they are not distributed only to the territories of the T1 - L2/3 spinal nerves.
The sympathetic trunk allows the sympathetic fibres arising from T1 - L2/3 to be distributed to all parts of the body.
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Distribution
● Preganglionic sympathetic fibres exit the spinal cord in spinal nerves T1 - L2/3.
● Almost immediately, they separate from the spinal nerves and enter the sympathetic trunk via a short communicating / connecting branch (white ramus
communicans)
● Once in the sympathetic trunk, the preganglionic axon does one of the following:
1. synapses in the ganglion at its level of entry (see Figure 1)
2. ascends or descends in the trunk before synapsing in a ganglion (see Figure 2)
3. travels through a ganglion (and the trunk) without synapsing (see Figure 3).
Look at figures page 58-59
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The abdominopelvic splanchnic nerves are the:
● Greater splanchnic nerve (sympathetic preganglionic fibres originating from T5-T9 segments of the spinal cord)
● Lesser splanchnic nerve (from T10-11)
● Least splanchnic nerve (from T12)
● Lumbar splanchnic nerves (from L1–L2)
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The greater, lesser, and least splanchnic nerves are formed in the posterior mediastinum and traverse the diaphragm to enter the abdomen.
The preganglionic sympathetic fibres in these splanchnic nerves do ultimately synapse with second neurons in prevertebral ganglia that lie close to major blood vessels in the abdomen.
After synapsing, the postganglionic fibres innervate abdominal viscera
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Posterior Intercostal Spaces
With the parietal pleura removed from the posterior thoracic wall, we see the posterior intercostal spaces. The posterior intercostal space contains:
● intercostal muscles
● a posterior intercostal artery (a branch of the thoracic aorta)
● a posterior intercostal vein (which drains to the azygos system)
● a posterior intercostal nerve
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The thoracic viscera are innervated by both sympathetic and parasympathetic fibres that have coordinated, but generally opposing actions:
● The cardiopulmonary splanchnic nerves convey postganglionic sympathetic fibres to the thoracic viscera
● The vagus nerves convey parasympathetic fibres to the thoracic viscera.
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Autonomic plexuses
These sympathetic and parasympathetic fibres form autonomic plexuses around the thoracic viscera.
The word plexus comes from the Latin for braid or plait and is not specific to nerves but also describes networks of veins and arteries.
The autonomic nerve plexuses look like delicate, fine meshes or webs. In the thorax we find the:
● cardiac plexus
● pulmonary plexus
● oesophageal plexus
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The cardiac plexus
innervates the sinoatrial node of the heart.
Sympathetic fibres increase the heart rate and force of contraction, whilst parasympathetic fibres decrease the heart rate and force of contraction.
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The pulmonary plexus
innervates the bronchi.
Sympathetic stimulation relaxes the bronchi and parasympathetic stimulation constricts them
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The oesophageal plexus
overlies the anterior surface of the oesophagus.
Sympathetic fibres inhibit peristalsis and parasympathetic fibres stimulate peristalsis.
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Visceral afferents
relay sensory information from the thoracic viscera back to the CNS along the paths of the vagus and thoracic splanchnic nerves.
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Cardiac pain is typically (but not always) felt in the central chest, left side of the neck and left arm. This is an example of referred pain, where pain from one part of the body is felt in another region.
The heart is innervated by the cardiac plexus, composed of sympathetic and parasympathetic fibres.
The sympathetic fibres travel to the cardiac plexus and heart from spinal cord segments T1 -T5 via the cardiopulmonary splanchnic nerves.
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The heart is also innervated by visceral sensory nerves, which convey sensory information from the heart back to the CNS - this sensation normally does not reach our conscious perception
However, if the myocardium is ischaemic this sensation does reach our conscious perception, and is interpreted as pain, tightness, crushing pressure or burning, which may be severe.
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Because the visceral sensory nerves travel back to the CNS alongside the sympathetic fibres that innervate the heart, the visceral sensory information enters spinal cord segments T1 - T5.
However, somatic sensory information from the skin of the chest wall, neck and arm also returns to spinal cord segments T1 - T5
Therefore painful visceral sensory information from the heart and somatic sensory information from the chest wall both enter spinal cord segments T1 - T5.
For reasons that are not fully understood, the brain interprets the cardiac pain as coming from the chest, neck, and arm.
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Another example of referred pain is shoulder pain resulting from pathology of the diaphragm.
Cervical spinal cord segments 3-5 contribute spinal nerve fibres to the phrenic nerve.
Cord segments C3-5 also contribute to the nerves that innervate the skin of the neck and shoulder.
The brain interprets pain coming from the diaphragm as coming from the shoulder region.
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The neck is an anatomically and clinically important region, containing structures that pass between the head, thorax, and upper limbs.
The cervical spine is flexible, and the neck is slender to allow optimal positioning of the head.
However, this flexibility means the neck is prone to injury. In addition, many vital structures are packed into this small region with little protection.
Therefore the neck is an extremely vulnerable area and injuries are often severely debilitating or fatal.
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The neck contains
● structures of the respiratory tract - the pharynx, larynx, and trachea
● structures of the gastrointestinal tract - the pharynx and oesophagus
● glands - the thyroid and parathyroid glands
● arteries and veins that serve the neck and head, including the brain
● nerves that serve the head and neck, upper limbs, thoraco-abdominal viscera (via the vagus nerves) and the diaphragm (via the phenic nerves)
● several groups of muscles. These include muscles that move the head and neck, move the larynx in speech and swallowing and that form the floor of the mouth.
Platysma is a very thin subcutaneous muscle deep to the skin of the neck.
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The seven cervical vertebrae
are small and articulate with each other at facet joints that are orientated obliquely.
This allows for a good range of flexion and extension of the cervical spine, in comparison to the thoracic spine
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The hyoid bone
is a slender bone situated anteriorly in the upper neck, inferior to the mandible.
It helps to keep the pharynx open and provides an attachment point for several muscles in the neck and of the tongue.
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The larynx (‘voice box’)
is composed of a ‘skeleton’ of small cartilages connected by membranes and small joints.
It protects the airway.
Muscles attach to the laryngeal cartilages and move them, in turn moving the vocal cords and allowing phonation.
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The neck is described in terms of the anterior and posterior triangles which are separated from each other by the sternocleidomastoid muscle.
Sternocleidomastoid (SCM) is attached to the sternum, clavicle, and the mastoid process (part of the temporal bone).
It can act unilaterally or bilaterally (i.e. both the left and right muscles act together).
It is innervated by the accessory nerve (cranial nerve XI).
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The boundaries of the anterior triangle are:
● anteriorly: the midline of neck
● posteriorly: the anterior border of sternocleidomastoid
● superiorly: the lower border of the mandible
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The anterior triangle contains:
● the trachea and larynx
● the thyroid gland, parathyroid glands, and the submandibular salivary gland
● the suprahyoid muscles which connect the hyoid to the skull. They form the floor of the mouth and move the hyoid and larynx in speech and swallowing.
● the infrahyoid muscles. Also called the ‘strap’ muscles, they connect the hyoid to the sternum and scapula. They move the hyoid and larynx in speech and swallowing.
● the common carotid artery and its terminal branches (the external and internal carotid arteries)
● branches of the external carotid artery to the head and neck
● the internal jugular vein
● branches of the facial nerve (CN VII), the glossopharyngeal nerve (CN IX), the vagus nerve (CN X- runs in the groove between the internal jugular vein and internal carotid artery), the accessory nerve (CN XI) and the hypoglossal nerve (CN XII- running down the carotid artery and then turns 90 degrees into base of tongue).
● the ansa cervicalis comes off the hypoglossal artery (fibres from C1-C3 which innervate the infrahyoid muscles).
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The boundaries of the posterior triangle are:
● anteriorly: the posterior border of sternocleidomastoid
● posteriorly: the anterior border of trapezius
● inferiorly: the clavicle.
Superiorly, the apex of the triangle is formed by sternocleidomastoid and trapezius.
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The posterior triangle contains:
● muscles that move the head
● part of the subclavian artery and the subclavian vein
● the external jugular vein which drains the scalp and face
● the accessory nerve (CN XI)
● the roots of the brachial plexus (spinal nerves that supply the upper limb)
● the cervical plexus (fibres from C1-4)
● the phrenic nerve.
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The Suprahyoid Muscles
These four paired muscles (mylohyoid, geniohyoid, stylohyoid and digastric) lie superior to the hyoid bone and form the floor of the mouth.
When they contract, they raise the hyoid bone and larynx during speech and swallowing.
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The Infrahyoid Muscles
These four paired ‘strap’ muscles lie inferior to the hyoid bone just lateral to the anterior midline of the neck.
They draw the hyoid bone and larynx inferiorly during speech and swallowing.
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Sternohyoid and omohyoid lie superficially; they attach the hyoid to the sternum and scapula, respectively.
Sternothyroid and thyrohyoid lie deep; they attach the sternum to the thyroid cartilage and the thyroid cartilage to the hyoid, respectively.
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The Thyroid Gland
The thyroid gland is composed of right and left lobes that lie just lateral to the lower larynx and upper trachea.
Each lobe lies deep to the sternothyroid muscle.
The two lobes are joined by the isthmus, which lies anterior to the trachea.
The thyroid gland produces hormones which play an important role in the regulation of metabolic processes.
The pituitary gland regulates hormone secretion from the thyroid gland.
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The thyroid gland has a rich blood supply via the:
● left and right superior thyroid arteries - branches of the external carotid arteries
● left and right inferior thyroid arteries - branches of the thyrocervical trunks (which in turn are branches of the subclavian artery).
Some people have an additional thyroid ima artery. Superior, middle, and inferior thyroid veins drain the thyroid gland.
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The Parathyroid Glands
There are usually four parathyroid glands - right and left superior and inferior glands - located posterior to the thyroid gland.
They produce parathyroid hormone which plays a role in calcium regulation.
They are typically supplied by the inferior thyroid arteries.
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Vessels in the Neck
The common carotid arteries ascend in the right and left sides of the neck, respectively.
The pulsation of the internal carotid can be palpated immediately lateral to the larynx.
The common carotid arteries bifurcate into external and internal carotid arteries.
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The internal carotid artery does not give rise to any branches in the neck.
It enters the cranium and supplies the brain.
The external carotid artery gives rise to several branches that supply the head and neck, including the pharynx, scalp, thyroid gland, tongue, and the face.
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At the point of bifurcation of the common carotid artery there is a small swelling - the carotid sinus. Baroreceptors here constantly monitor arterial blood pressure.
This visceral sensory information is relayed back to the CNS via the glossopharyngeal nerve and results in reflex responses that regulate the blood pressure.
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The subclavian artery gives rise to several vessels.
A large branch, the thyrocervical trunk, gives rise to the inferior thyroid artery. The subclavian artery supplies the upper limb.
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The internal jugular vein is a major vein in the neck, which drains blood from the brain and part of the face.
● It unites with the subclavian vein, which returns blood from the upper limb, to form the brachiocephalic vein.
● The right and left brachiocephalic veins unite to form the superior vena cava.
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The external jugular vein
The external jugular vein drains blood from the scalp and face. It joins the subclavian vein.
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Nerves in the neck
● The facial nerve (CN VII)
● The glossopharyngeal nerve (CN IX)
● The vagus nerve (CN X)
● The accessory nerve (CN XI)
● The hypoglossal nerve (CN XII)
● The phrenic nerve
● sympathetic nerves
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The facial nerve (CN VII)
supplies platysma in the neck.
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The glossopharyngeal nerve (CN IX) supplies the:
● pharynx (sensory innervation)
● carotid sinus (visceral sensory fibres that return to the CNS via CN IX)
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The vagus nerve (CN X) is vital for normal speech and swallowing. It supplies:
● the muscles of the pharynx (motor innervation)
● the larynx (motor and sensory innervation)
In the neck, the vagus nerve runs between the internal jugular vein and the internal carotid artery (above its bifurcation) and between the internal jugular vein and common carotid artery (below its bifurcation).
The three structures run together in a fascial sleeve called the carotid sheath.
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The accessory nerve (CN XI) supplies
the sternocleidomastoid and trapezius muscles.
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The hypoglossal nerve (CN XII)
is motor to the muscles of the tongue.
It does not supply any structures in the neck but travels through it.
It lies lateral to the internal carotid artery and deep to the external jugular vein.
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The phrenic nerve
is formed by C3, C4 and C5 nerve fibres.
It descends through the neck to enter the thorax.
It innervates the diaphragm.
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The head and neck are richly innervated with sympathetic nerves.
The sympathetic trunk extends as far as the base of the skull.
The associated sympathetic ganglia in the neck are the superior, middle, and inferior cervical ganglia.
Postganglionic fibres from these ganglia innervate the head and neck.
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What is the pharynx?
The pharynx is a muscular tube which lies in the neck.
It forms part of the respiratory and gastrointestinal systems
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The pharynx is one continuous passageway composed of three parts:
● The nasopharynx is posterior to the nasal cavity
The nose and occipital bone are the limitations of the nasopharyx
● The oropharynx is posterior to the oral cavity
Upper limit is soft palate and lower is oral cavity
● The laryngopharynx is posterior to the larynx (sometimes called the hypopharynx)
Upper limit is oral cavity and lower limit is epiglottis
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What are the walls of the pharynx composed of?
An outer layer of circular muscle and an inner layer of longitudinal muscle
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The external circular muscle layer is composed of three constrictor muscles
the superior, middle, and inferior constrictors - that overlap each other.
They contract superior to inferior, so that swallowed food moves down the pharynx towards the oesophagus
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What happens during swallowing?
During swallowing, food in the oral cavity is pushed into the oropharynx by the tongue.
The soft palate rises and closes off the nasopharynx from the oropharynx
Food enters the laryngopharynx and constriction of the muscles of the pharyngeal wall move the food into the oesophagus.
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What is the role of the epipiglottis?
One of the cartilages of the larynx - closes off the laryngeal inlet and prevents food or liquids from entering the larynx
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What nerves are found in the pharynx?
The pharynx is innervated by sensory fibres from the glossopharyngeal nerve and motor fibres from the vagus nerve.
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Several nerves lie close to the posterior pharyngeal wall:
● The cervical part of the sympathetic trunk and superior cervical ganglion
● Superior laryngeal nerve
● Hypoglossal nerve
● Glossopharyngeal nerve
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Superior laryngeal nerve.
This branch of the vagus nerve descends over the
posterior aspect of the internal carotid artery.
It passes between the inferior and middle constrictors of the pharynx to the larynx.
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Hypoglossal nerve.
This lies close to the vagus nerve
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Glossopharyngeal nerve
From the posterior aspect, it lies deep to the internal
carotid artery
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What is the larynx?
The larynx is a complicated structure composed of several cartilages, membranes, and small muscles.
243
Role of the larynx
The larynx protects the airway and contributes to phonation / speech
244
How many cartilages is the larynx composed of?
9
Three are unpaired, and three are paired.
Membranes and very small joints connect the cartilages to each other.
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What are the 3 unpaired cartilages?
Epiglottis
Thyroid cartilage
Cricoid cartilage
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What are the 3 paired cartilages?
arytenoids
Cuneiforms
Corniculate cartilages
The three paired cartilages are much smaller than the unpaired cartilages.
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Thyroid Cartilage
composed of two flat cartilages (laminae) that meet in the anterior midline to form the laryngeal prominence, or ‘Adam’s apple’, which is usually visible in males
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The superior and inferior horns.
Posteriorly, the laminae form extensions that project superiorly and inferiorly
The superior horns attach to the hyoid bone
The inferior horns articulate with the cricoid cartilage below
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The cricothyroid membrane
connects the inferior border of the thyroid and superior border of the cricoid.
This membrane is pierced to create an emergency airway.
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The epiglottis
epiglottis is attached to the superior aspect of the thyroid cartilage, where the two thyroid laminae meet.
During swallowing, the epiglottis covers the entrance to the larynx (the laryngeal inlet) and protects the airway from the entry of liquid or food.
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The arytenoids
sit on the superior surface of the cricoid cartilage
They articulate with the cricoid cartilage at small joints
Although small, the arytenoids are vital for phonation, as the vocal cords attach to them.
Movements of the arytenoids move the vocal cords.
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2 groups of muscles act upon the larynx
Extrinsic and intrinsic
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Extrinsic muscles
The suprahyoid and infrahyoid muscles.
They do not move the individual cartilages, but rather move the larynx as one
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Intrinsic muscles
These small muscles move the individual cartilages of the larynx relative to each other.
By moving the cartilages, they move the vocal cords, and this in turn alters the quality of speech.
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Structures in the neck that are palpable on examination are the:
● hyoid bone inferior to the mandible
● thyroid cartilage in the midline of the neck (the ‘Adam’s apple’)
● cricoid cartilage in the midline, inferior to the thyroid cartilage
● first tracheal cartilage inferior to the cricoid cartilage
● cricothyroid membrane between the thyroid cartilage and cricoid cartilage – this can be punctured to create an emergency airway
● lobes of the thyroid gland either side of the upper trachea and inferior larynx
● carotid pulse – best palpated just anterior to sternocleidomastoid at the level of the thyroid cartilage.
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What are the tonsils?
The tonsils are collections of lymphoid tissue in the upper parts of the pharynx
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The pharyngeal and tubal tonsils are found in the nasopharynx
● The pharyngeal tonsil (adenoid) lies in the roof of the nasopharynx
● The tubal tonsil surrounds the opening of the auditory tube (which connects the nasopharynx to the middle ear)
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The palatine tonsil
lies next to the pharyngeal wall in the oropharynx.
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The lingual tonsil
is a collection of lymphoid tissue on the posterior aspect of the tongue.
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Waldeyer’s ring
Ring formed connecting all the tonsils
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The epiglottis protects the larynx and airway from the entry of fluid or food.
The internal aspect of the larynx is modified for phonation.
Intrinsic muscles of the larynx move the laryngeal cartilages which in turn move the vocal cords that lie inside the larynx.
Injury to the nerves that innervate the intrinsic laryngeal muscles therefore affect speech.
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Within the larynx there are two pairs of folds that project into the cavity
These are the vestibular folds (false vocal cords) superiorly and the vocal folds (true vocal cords) inferiorly
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What are the vestibular folds?
folds of mucous membrane that lie superior to the vocal folds
A narrow space separates the vestibular and vocal folds
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What are the vocal cords?
are folds of mucous membrane that cover and protect the vocal ligaments – together they form the true vocal cords.
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What are the vocal ligaments?
are attached anteriorly to the internal aspect of the
laryngeal prominence and posteriorly to the arytenoid cartilages.
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Rima glottidis
The space between the true vocal cords
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What happens during adduction of the true vocal cords?
Adduction of the true vocal cords closes the rima glottidis, whilst abduction of the
folds opens it
Phonation requires adduction of the cords and closure of the rima glottidis
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Abduction of the cords opens the rima glottidis:
● to a small degree in whispering
● partially in normal breathing
● fully in forced breathing.
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What do the intrinsic muscles do?
The intrinsic muscles of the larynx move the laryngeal skeleton which moves the vocal cords and opens and closes the rima glottidis.
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Several pairs of intrinsic muscles move the laryngeal cartilages and hence the vocal cords
Cricothyroid muscle
Posterior cricoarytenoids
Transverse arytenoids
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Cricothyroid muscle anteriorly (between the thyroid and cricoid cartilages).
This muscle tips the thyroid cartilage anteriorly and inferiorly, which places tension on the vocal cords
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Posterior cricoarytenoids on the posterior surface of the cricoid
They attach to the arytenoids.
These muscles abduct the vocal cords and open the rima glottidis.
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Transverse arytenoids on the posterior aspect of the larynx, connecting the two arytenoid cartilages
These muscles adduct the vocal folds and close the rima glottidis.
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The superior laryngeal nerve (from the vagus)
innervates the cricothyroid muscle and is sensory to the larynx above the vocal folds
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The recurrent laryngeal nerve (from the vagus)
innervates all the intrinsic muscles except for the cricothyroid and is sensory to the larynx below the vocal folds.
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What are the 3 pairs of salivary glands that secrete saliva into the oral cavity?
the parotid
submandibular
sublingual
Glandular secretion is stimulated by parasympathetic fibres.
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What is the parotid gland?
The parotid gland is the largest of the three paired salivary glands and overlies the posterior part of the mandible.
Saliva empties into the mouth via the parotid duct, which opens adjacent to the upper second molar tooth.
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The parotid gland is closely related to the facial nerve
After the nerve exits the skull, it enters the deep surface of the parotid gland.
Within the gland the facial nerve divides into five branches which emerge to innervate the muscles of facial expression.
The parotid gland is also closely related to the external carotid artery
Secretion from the parotid gland is stimulated by parasympathetic fibres in the glossopharyngeal nerve
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The submandibular glands are smaller than the parotid glands.
Part of the gland lies within the mouth, and part lies outside.
The submandibular duct opens into the floor of the mouth, under the tongue.
Secretion of saliva is stimulated by parasympathetic fibres in the facial nerve.
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Sublingual Glands
These are small and lie in the floor of the mouth.
They open via several small ducts into the floor of the mouth.
Secretion is stimulated by parasympathetic fibres in the facial nerve
