Mediastinum Flashcards
(88 cards)
1
Q
What structures lie in the plane of the sternal angle?
A
T4 Superior border of the pericardium Bifurcation of the trachea Arch of the aorta Bifurcation of the pulmonary trunk Left recurrent laryngeal nerve Anastomosis of azygous vein and SVC
2
Q
What are the two tributaries of the SVC?
A
Left and right brachiocephalic veins
3
Q
What is the ligamentum arteriosum?
A
An embryological remnant of the ductus arteriosus that serves to attach the arch of the aorta to the left pulmonary artery
4
Q
What lies directly posterior to the trachea?
A
Oesophagus
5
Q
What lies within the middle mediastinum?
A
Pericardium, heart, origins of the great vessels, various nerves, and smaller vessels
6
Q
What are the different layers of pericardium?
A
Fibrous pericardium - tough connective tissue
Serous pericardium - thin and consists of two parts:
1. parietal layer - lines the inner surface of the fibrous
2. visceral layer (epicardium) - adheres to the heart and forms its outer covering
7
Q
Between which layers of pericardium is the pericardial cavity?
A
Between the two layers of serous pericardium and it contains a small amount of fluid
8
Q
What is the fibrous pericardium continuous with?
A
The adventitia of the great vessels
9
Q
What is the pericardium innervated by?
A
Vagus nerves, the sympathetic trunks and the phrenic nerves
10
Q
What is the oblique pericardial sinus?
A
Layers of serous pericardium are continuous around the roots of great vessels. Posteriorly at the roots of the IVC, SVC and pulmonary veins the reflection of serous pericardium is J shaped and forms the oblique pericardial sinus posterior to the left atrium.
11
Q
What is the transverse pericardial sinus?
A
A passage between the two sites of reflected serous pericardium. It is posterior to the aorta and pulmonary trunk but anterior to the SVC and superior to the left atrium. During surgery, a finger placed in the sinus separates arteries from veins.
12
Q
Where might pain from the parietal pericardium be felt?
A
Somatic sensation (pain) is carried by somatic afferent fibres in the phrenic nerves. Pain may be referred to the supraclavicular region of the shoulder or lateral neck area (dermatomes for C3, C4, C5)
13
Q
How does blood enter the right atrium?
A
SVC, IVC and coronary sinus
14
Q
What valve separates the right atrium from the right ventricle and what direction does it lie in?
A
Tricuspid valve, faces forward and medially
15
Q
Externally, what indicates the division of the interior of the right atrium?
A
A shallow vertical groove, the sulcus terminalis. It extends from the right side of the opening of the SVC to the right side of the opening of the IVC.
16
Q
Internally, what indicates the division of the interior of the right atrium?
A
The crista terminalis, which is a smooth, muscular ridge that begins on the roof of the atrium just infront of the opening of the SVC and extends down the lateral wall to the anterior lip of the IVC.
17
Q
What is the space posterior to the crista terminalis called?
A
The sinus of venae cavae, which is derived embryologically from the right horn of the sinus venosus
18
Q
What is the internal structure of the sinus of venae cavae?
A
Smooth, thin walls where both venae cavae empty in to
19
Q
What is the space anterior to the crista terminalis called?
A
The atrium proper (including the right auricle) - terminology is based on its embryological origin from the primitive atrium
20
Q
What is the internal structure of the atrium proper?
A
Its walls are covered by pectinate muscles, which fan out from the crista like the ‘teeth of a comb’
21
Q
What structure opens in to the right atrium just medially to the IVC?
A
Coronary sinus, which receives blood from most of the cardiac veins
22
Q
Where is the fossa ovalis located, what surrounds it and what is it a remnant of?
A
Located in the interatrial septum, just above the orifice of the IVC. Its prominent margin is the limbus fossa ovalis. It is a remnant of the embryological foramen ovale.
23
Q
What is the purpose of the fibrous pericardium?
A
By attachments with the diaphragm and sternum, it helps to retain the heart in its position within the thorax. The sac also limits cardiac distension.
24
Q
As well as the IVC, SVC and coronary sinus, what else opens in to the right atrium?
A
Smallest cardiac veins (the foramina of the venae cordis minimae), their openings are scattered throughout the right atrium
25
What is the name of the outflow tract of the right ventricle that leads to the pulmonary trunk?
The infundibulum which has smooth walls
26
Describe the internal structure of the right ventricle
Trabeculae carnae, papillary muscles and a moderator band
27
How many papillary muscles are there in the right ventricle?
3. Anterior, posterior and septal papillary muscles.
Anterior is the largest and most constant and arises from the anterior wall of the ventricle. The posterior may consist of one, two or three structures with some chordae tendineae arising directly from the wall. The septal is the most inconsistent.
28
What is the function of papillary muscles and chordae tendineae?
Attach to the cusps of atrioventricular valves preventing them from prolapsing during ventricular contraction.
29
What is the moderator band and what is its function?
Located in the RV, it is a single specialised trabeculum which forms a bridge between lower portion of the interventricular septum and the base of the anterior papillary muscle. It carries a portion of the cardiac conduction system, the right bundle of the atrioventricular bundle, to the anterior wall of the RV.
30
Describe how the pulmonary valve closes after ventricular contraction
There are 3 semilunar cusps (left, right and anterior) that form pocket-like sinuses. The recoil of blood after ventricular contraction feels these pulmonary sinuses and forces the cusps closed. This prevents blood in the pulmonary trunk from refilling the RV.
31
Describe the internal structure of the left atrium
The posterior half, or inflow portion, receives the four pulmonary veins. It has smooth walls and derives from the proximal parts of the pulmonary veins that are incorporated into the left atrium during development. The anterior half is continuous with the left auricle. It contains pectinate muscles and derives from the embryonic primitive atrium. There is no distinct structure separating the two components. The interatrial septum is also part of the anterior wall of the atrium and is the valve of the foramen ovale.
32
What is the outflow tract of the left ventricle called?
The aortic vestibule - it is smooth walled
33
How many papillary muscles are usually present in the left ventricle?
2, the anterior and posterior papillary muscles due to the associated bicuspid valve. They are larger than those in the RV.
34
What are the two parts of the interventricular septum?
Muscular part - thick and forms the major part of the septum
Membranous part - thin, upper part of the septum
May be a third part of the septum between the right atrium and the left ventricle as it lies above the septal cusp of the tricuspid valve
35
What are the names of the three cusps of the aortic valve?
left, right and posterior
36
Where do the right and left coronary arteries originate from?
Between the semilunar cusps and the wall of the ascending aorta are the right, left and posterior sinuses. The right and left coronary arteries arise from the right and left aortic sinuses.
37
What are the anulus fibrosus?
The four rings of the cardiac skeleton that surround the two atrioventricular orifices, the aortic orifice and opening of the pulmonary trunk
38
What are the interconnecting areas of the anulus fibrosis called?
The left and right fibrous trigone
39
What is the purpose of the cardiac skeleton?
Helps maintain the integrity of the openings it surrounds and provides points of attachment for the cusps. It also separates the atrial musculature from the ventricular musculature. It also serves as a dense connective tissue partition that electrically isolates the atria from the ventricles
40
What is the single connection between the atrial and ventricular myocardium?
The atrioventricular bundle which passes through the anulus fibrosus
41
Briefly describe the course of the right coronary artery
Originates from the right aortic sinus, it passes anteriorly and to the right between the right auricle and the pulmonary trunk and then descends vertically in the coronary sulcus, between the right atrium and right ventricle. On reaching the inferior margin it turns posteriorly and continues in the sulcus on the diaphragmatic surface and base of the heart.
42
What is the first branch of the right coronary artery?
An early atrial branch passes in the groove between the right auricle and ascending aorta, it gives off the sinu-atrial nodal branch, which passes posteriorly around the SVC to supply the sinu-atrial node.
43
Where is the right marginal artery located?
A branch of the right coronary artery which runs along the inferior (acute) margin of the heart towards the apex
44
What is the final major branch of the right coronary artery?
The posterior interventricular artery which lies in the posterior interventricular sulcus
45
Which parts of the heart does the right coronary artery supply?
Right atrium, right ventricle, sinu-atrial node, atrioventricular node, interatrial septum, a portion of the left atrium, the posteroinferior third of the interventricular septum, and a portion of the posterior part of the left ventricle
46
Briefly describe the course of the left coronary artery
It originates from the left aortic sinus, it passes between the pulmonary trunk and the left auricle before entering the coronary sulcus. While still posterior to the pulmonary trunk, it divides into its two terminal branches, the anterior interventricular artery and the circumflex artery
47
Briefly describe the course of the anterior interventricular artery
Continues around the left side of the pulmonary trunk and descends obliquely in the anterior interventricular sulcus towards the apex of the heart. It may give off one or two large diagonal branches along the way that supply the anterior left ventricle.
48
Briefly describe the course of the circumflex branch of the LCA
It courses towards the left, in the coronary sulcus and onto the base/diaphragmatic surface of the heart, and usually ends before reaching the posterior interventricular sulcus. It gives off a large branch, the left marginal artery which runs along the obtuse margin of the heart.
49
Which parts of the heart does the left coronary artery supply?
Most of the left atrium and left ventricle, most of the interventricular septum, including the atrioventricular bundle and its branches
50
What does right dominance mean?
The right coronary artery gives off the posterior interventricular artery. This is the most common variation.
51
What does left dominance mean?
The left coronary artery (specifically circumflex artery), gives off the posterior interventricular artery. This is less common than right dominance.
52
What is co-dominance?
Both LCA and RCA give off the posterior interventricular artery.
53
What are the four major tributaries to the coronary sinus?
The great, middle, small and posterior cardiac veins
54
Briefly describe the path of the great cardiac vein
It begins at the apex of the heart and ascends in the anterior interventricular sulcus. As it reaches the coronary sulcus it turns left and continues on the base/diaphragmatic surface of the heart. As it continues along the coronary sulcus it gradually enlarges to form the coronary sinus.
55
Briefly describe the course of the middle cardiac vein
Begins near the apex of the heart and ascends towards the coronary sinus in the posterior interventricular sulcus
56
Briefly describe the course of the small cardiac vein
It begins in the lower anterior portion of the coronary sulcus between the right atrium and right ventricle. It continues in this groove on to the base/diaphragmatic surface of the heart where it enters the coronary sinus at its atrial end. It may also receive the right marginal vein (from the acute angle).
57
Briefly describe the course of the posterior cardiac vein
It lies on the posterior surface of the left ventricle just to the left of the middle cardiac vein. It either enters the coronary sinus or joins the great cardiac vein.
58
Which veins are the only veins which drain directly in to the right atrium?
The anterior veins of the right ventricle. They enter the anterior wall of the right atrium and drain the anterior portion of the RV
59
What are the venae cordis minimae?
Small cardiac veins that drain directly in to the cardiac chambers
60
Where is the sinu-atrial node located?
Superior end of the crista terminalis at the junction of the SVC and right atrium
61
Where is the atrioventricular node located?
Located near the opening of the coronary sinus, close to the attachment of the septal cusp of the tricuspid valve, and within the atrioventricular septum.
62
Briefly describe the cardiac conduction system
Impulse begins at SAN, travels through atria and stimulates the AVN, the atrioventricular bundle is a direct continuation of the AVN. It splits into right and left bundles. The right bundle branch continues towards the apex of the RV and passes through the moderator band to the base of the anterior papillary muscle. It then divides and is continuous with the Purkinje fibres. The left bundle branch descends to the apex of the LV, it gives off branches that eventually become continuous with Purkinje fibres.
63
What is the parasympathetic innervation of the heart?
Cardiac branches from the right and left vagus nerves
64
What does parasympathetic stimulation of the heart cause?
Decrease in heart rate
Reduces force of contraction
Constricts coronary vessels
65
What is the sympathetic innervation of the heart?
Preganglionic sympathetic nerve fibres from the upper four or five segments of the the thoracic spinal cord enter and move through the sympathetic trunk. They synapse in cervical or upper thoracic sympathetic ganglia, and postganglionic fibres proceed as bilateral branches from the sympathetic trunk to the cardiac plexus.
66
What does sympathetic innervation of the heart do?
Increases heart rate
| Increases force of contraction
67
Why is pain felt in the chest and arm during an MI?
Visceral afferents are stimulated by cadiac cell death. These visceral sensory fibres follow the course of sympathetic fibres that innervate the heart and enter the spinal cord between T1 and T4. At this level, somatic afferent fibres from spinal nerves T1-T4 also enter the spinal cord via posterior roots. Both types of afferents synapse with interneurons, which then synapse with second neurons whose fibres pass across the cord and then ascend to the somatosensory areas of the brain that represent the T1-T4 levels. The brain is unable to distinguish clearly between the visceral sensory distribution and the somatic sensory distribution (dermatomes T1-T4, chest and inner arm and forearm) and therefore pain is interpreted as arising from the somatic regions rather than the visceral organ.
68
What lies immediately anterior to the origins of the three branches of the arch of the aorta?
The left brachiocephalic vein
69
Briefly describe the course of the right vagus nerve
It enters the superior mediastinum and lies between the right brachicephalic vein and the brachiocephalic trunk. It descends in a posterior direction toward the trachea, crosses the lateral surface of the trachea and passes posteriorly to the to the root of the right lung to reach the oesophagus. Just before the oesophagus, it is crossed by the arch of the azygos vein.
70
Briefly describe the course of the left vagus nerve
It enters the superior mediastinum posterior to the left brachiocephalic vein and between the left common carotid and left subclavian arteries. It crosses the left side of the arch of the aorta and passes posterior to the root of the left lung to reach the oesophagus.
71
Briefly describe the course of the left recurrent laryngeal nerve
Arises from the left vagus nerve at the inferior margin of the arch of the aorta just lateral to the ligamentum arteriosum. It passes inferior to the arch of the aorta before ascending on its medial surface. It enters a groove between the trachea and oesophagus where it continues superiorly to enter the neck and terminate in the larynx.
72
What do the phrenic nerves supply?
Motor and sensory innervation to the diaphragm and its associated membranes. Also somatic afferent fibres to the mediastinal pleura, fibrous pericardium, and parietal layer of serous pericardium
73
Describe the course of the right phrenic nerve
Enters the superior mediastinum lateral to the right vagus nerve and lateral and slightly posterior to the beginning of the right brachiocephalic vein. It continues inferiorly along the right side of this vein and the right side of the SVC. It then descends along the right side of the pericardial sac, within the fibrous pericardium, anterior to the root of the right lung. The pericardiocophrenic vessels accompany it through most of its course in the thorax. It passes through the diaphragm with the IVC.
74
Describe the course of the left phrenic nerve
Similar to right phrenic but on the opposite side. Lateral and slightly posterior to the left brachiocephalic vein, descends along the left lateral surface of the arch of the aorta, passing superficially to the left vagus nerve. It follows the left side of the pericardial sac. It leaves the thorax by piercing the diaphragm near the apex of the heart.
75
What are the major structures in the posterior mediastinum?
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Oesophagus (and associated nerve plexus)
Thoracic aorta
Azgos system of veins
Thoracic duct and associated lymph nodes
Sympathetic trunks
Thoracic splanchnic nerves
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76
The oesophagus can be compressed or narrowed in 4 locations, what are they?
1. The junction of the oesophagus with the pharynx in the neck
2. In the superior mediastinum where the oesophagus is cross by the arch of the aorta
3. In the posterior mediastinum where the oesophagus is compressed by the left main bronchus
4. In the posterior mediastinum at the oesophageal hiatus in the diaphragm
77
Where are the vagal trunks located?
Anterior vagal trunk on the anterior surface of the oesophagus inferior to the left atrium part of the oesophagus - contains mainly fibres from left vagus nerve
Posterior vagal trunk on the posterior surface of the oesophagus in the same place - contains mainly fibres from right vagus nerve
78
What are the branches of the thoracic aorta?
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Pericardial branches
Bronchial branches
Oesophageal branches
Mediastinal branches
Posterior intercostal arteries
Superior phrenic arteries
Subcostal artery
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79
Briefly describe the course of the azygos vein
Arises opposite L1/L2 at the junction between the right ascending lumbar vein and the right subcostal vein. It enters the thorax through the aortic hiatus or through or posterior to the right crus of the diaphragm. It ascends through the posterior mediastinum. At approx T4 is arches anteriorly over the root of the right lung to join the SVC.
80
What are the tributaries of the azygos vein?
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The right superior intercostal vein (formed from the junction of the 2nd, 3rd and 4th intercostal veins)
Fifth to eleventh right posterior intercostal veins
The hemiazygos vein
The accessory hemiazygos vein
Oesophageal veins
Mediastinal veins
Pericardial veins
Right bronchial veins
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81
What is the cisterna chyli?
The beginning of the thoracic duct, it is a confluence of lymph trunks in the abdomen that form a saccular dilation.
82
Briefly describe the course of the thoracic duct
It extends from L2 to the root of the neck. Enters the thorax through the aortic hiatus, posterior to the aorta. Ascends to the right of the midline between thoracic aorta and azygos vein. It lies posterior to the oesophagus and anterior to the vertebral bodies. At T5 it moves to the left of the midline. It is joined by the left jugular trunk and the left subclavian trunk. It finally empties in to the junction between the left subclavian vein and the left internal jugular vein.
83
What parts of the body does the thoracic duct NOT drain lymph from?
Right head and neck and right upper limb
84
Which sympathetic ganglia give rise to the three thoracic splanchnic nerves?
Medial branches from the lower seven ganglia
85
How many sympathetic ganglia are there in the thorax?
12, one for each thoracic vertebral level
86
From which thoracic ganglia does the greater splanchnic nerve arise?
T5-T9
87
From which thoracic ganglia does the lesser splanchnic nerve arise?
T10 and T11
88
From which thoracic ganglia does the least splanchnic nerve arise?
T12
