Anatomy 3 & 4

Question 1

Where does the mediastinum extend from?

Answer 1

Superior thoracic aperture superiorly to the diaphragm inferiorly

Sternum anteriorly to the thoracic vertebrae posteriorly

Question 2

What does the mediastinum contain?

Answer 2

Heart and pericardium (the fibrous sac around the heart)
Great vessels that enter and leave the heart
Veins that drain the chest wall
Trachea and main bronchi
Oesophagus
Nerves (somatic and autonomic)
Lymphatics
Thymus gland

Question 3

Where does the line between the superior and inferior compartments in the mediastinum run from?

Answer 3

Run from the sternal angle anteriorly to the T4/T5 junction posteriorly

Question 4

What is the inferior mediastinum divided into?

Answer 4

● 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.

● The middle mediastinum contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta.

● The posterior mediastinum lies between the posterior aspect of the pericardial sac and the vertebrae.

Question 5

What are the main contents of the superior mediastinum?

Answer 5

● 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

Question 6

What are the 3 parts of the aorta?

Answer 6

● The ascending aorta is the short, first part. It gives rise to the coronary arteries, which supply the myocardium.

● The arch of the aorta curves posteriorly. It lies in the superior mediastinum.

● The descending (thoracic) aorta descends through the posterior mediastinum
and into the abdomen posterior to the diaphragm.

Question 7

What are the 3 major branches that the arch of the aorta give rise to?

Answer 7

● 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.

Question 8

What does the arch of the aorta contain?

Answer 8

Contains 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.

Question 9

What is the ligamentum arteriosum?

Answer 9

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.

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.

Question 10

What two veins carry deoxygenated blood to the right atrium?

Answer 10

● 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.

● 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.

Question 11

What does the trachea do?

Answer 11

The trachea conducts air to and from the left and right main bronchi. It is semi-rigid due to C-shaped, incomplete rings of cartilage in its walls.

Question 12

Where does the trachea extend from and terminate?

Answer 12

● 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.

Question 13

What is the oesophagus?

Answer 13

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).

Question 14

What is the position of the oesophagus?

Answer 14

In the superior mediastinum, the oesophagus lies in the midline of the thorax, posterior to the trachea.

It descends into the posterior mediastinum, and we will learn more about the oesophagus when we look at the posterior mediastinum.

Question 15

What are the phrenic nerves formed from?

Answer 15

The left and right phrenic nerves, formed by fibres from the C3, C4 and C5 spinal nerves, innervate the diaphragm.

Question 16

What are the phrenic nerves and where are they found?

Answer 16

They are somatic nerves and contain motor and sensory fibres.

They descend through the neck and enter the thorax through the superior thoracic aperture.

They course over the pericardium and pierce the diaphragm.

Question 17

What are the vagus nerves?

Answer 17

The left and right vagus nerves (CN X) arise from the brainstem and contain somatic sensory, somatic motor and parasympathetic fibres. They innervate structures of the thorax and abdomen, in addition to the head and neck.

Question 18

Where are the vagus nerves found?

Answer 18

They descend through the neck alongside the internal carotid artery and internal jugular vein and enter the thorax via the superior thoracic aperture.

Question 19

What do the vagus nerves give rise to?

Answer 19

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.

Question 20

Where do the vagus nerves descend into?

Answer 20

Into the thorax posterior to the root of the lung

Question 21

What do the vagus nerves contribute?

Answer 21

They contribute parasympathetic fibres to the heart, lungs, and oesophagus.

● They traverse the diaphragm and convey parasympathetic fibres to most of the
abdominal viscera.

Question 22

What is the thoracic duct?

Answer 22

The thoracic duct is a major channel for lymphatic drainage from most regions of the body.

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.

Question 23

What is the thymus gland?

Answer 23

The thymus is a lymphoid organ. It lies anteriorly in the superior mediastinum.

It is important in children, but atrophies with age, eventually becoming fatty.

We will not see the thymus in the cadavers.

Question 24

What is the pericardium?

Answer 24

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.

Question 25

What two layers is the pericardium composed of?

Answer 25

● 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.

Question 26

What is the narrow space between the two layers of serous pericardium?

Answer 26

Pericardial 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.

Question 27

What is the apex?

Answer 27

'Point' of the heart, which projects to the left of the sternum towards the left lung

Question 28

What are the surfaces of the heart?

Answer 28

● 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.

Question 29

What do the heart surfaces correspond to?

Answer 29

● 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

Question 30

What is the apex formed by?

Answer 30

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.

Question 31

What do the borders of the heart correspond to?

Answer 31

● Right border = right atrium ● Left border = left ventricle ● Inferior border = right ventricle and part of the left ventricle.

Question 32

Where are the borders of the heart located?

Answer 32

● Right border = lies lateral to the right sternal edge, from the right 3rd costal cartilage to the right 6th costal cartilage. ● Left border = extends from the left 2nd intercostal space to the left 5th intercostal space in the midclavicular line (i.e. the apex). ● 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). ● Inferior border = lies along the line connecting the inferior end of the right border with the apex (mostly formed by the right ventricle).

Question 33

What are auricles (auricular appendages)?

Answer 33

So named because of their ear-like appearance They are outpouchings from the walls of the right and left atria.

Question 34

What is coronary circulation?

Answer 34

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).

Question 35

What is Patent ductus arteriosus (PDA)?

Answer 35

The ductus arteriosus usually closes immediately after birth. In some infants, the ductus arteriosus does not close and remains open (patent). After birth, the pressure in the aorta exceeds the pressure in the pulmonary trunk, hence blood flows through a patent ductus arteriosus from the aorta into the pulmonary trunk. Over time, increased flow through the pulmonary vessels can lead to pulmonary hypertension (high pressure in the vessels of the lungs) which strains the right side of the heart.

Question 36

Explain the Clinical relevance of Hoarseness of the voice and lung cancer?

Answer 36

Cancer at the apex of the lung may involve the recurrent laryngeal nerve, which supplies most of the muscles of the larynx. Nerve injury results in weakness or paralysis of the ipsilateral intrinsic laryngeal muscles, which move the larynx and the vocal cords (we will look at the larynx in detail in sessions 7 and 8). Hoarseness results as the patient can no longer fully adduct their vocal cords.

Question 37

Explain the pathology of the pericardium?

Answer 37

The pericardial space allows the heart to move within the pericardial sac with each contraction. Pericardial effusion is an increase in fluid volume in the pericardial space. Pericardial effusion may result from inflammation of the pericardium (a condition called pericarditis) or an accumulation of blood (due to trauma). Rapid fluid accumulation in the pericardial space can be rapidly fatal because the fibrous pericardium cannot stretch and so the heart is compressed and unable to fill properly - a condition called cardiac tamponade

Question 38

Where do the coronary arteries arise from?

Answer 38

Ascending aorta

Question 39

Where do the cardiac veins return blood?

Answer 39

Return venous blood to the coronary sinus, which enters the right atrium

Question 40

What branches does the right coronary artery supply?

Answer 40

● 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.

Question 41

What are the two terminal branches of the left coronary artery?

Answer 41

● Anterior interventricular artery (or the left anterior descending; ‘LAD’). ● Circumflex artery (abbreviated to ‘Cx’).

Question 42

What territories do the main branches of the left coronary artery supply?

Answer 42

● 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.

Question 43

What does the origin of the posterior interventricular artery determine?

Answer 43

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.

Question 44

Why is the origin of posterior interventricular artery important in clinical practice?

Answer 44

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.

Question 45

What do the valves inside the heart ensure?

Answer 45

Ensure unidirectional flow of blood through the chambers of the heart

Question 46

Where does the atrium receive deoxygenated blood from?

Answer 46

Via the superior and inferior venae cavae, and from the heart via the coronary sinus

Question 47

What are the main features of the right atrium?

Answer 47

● 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 – 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.

Question 48

Where does blood flow into the right ventricle from?

Answer 48

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.

Question 49

Where does the right ventricle pump blood into?

Answer 49

Pulmonary trunk, which bifurcates into a left and right pulmonary artery

Question 50

What is the purpose of the pulmonary valve?

Answer 50

The pulmonary valve at the entrance of the pulmonary trunk prevents backflow of blood into the right ventricle.

Question 51

Why is the wall of the right ventricle thicker than that of the right atrium?

Answer 51

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.

Question 52

What are the internal features of the right ventricle?

Answer 52

● interventricular septum which separates it from the left ventricle ● trabeculae carneae – muscular ridges on the internal wall ● papillary muscles – 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.

Question 53

Where does the left atrium receive blood from?

Answer 53

Receives oxygenated blood from the lungs via the pulmonary veins (two from each lung)

Question 54

What structure do the walls of the left atrium have?

Answer 54

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.

Question 55

Where does blood flow into the left ventricle from?

Answer 55

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.

Question 56

Where does the left ventricle pump blood into?

Answer 56

Aorta

Question 57

What are the first branches from the aorta?

Answer 57

Coronary arteries

Question 58

What does the aortic value do?

Answer 58

The aortic valve at the entrance to the aorta prevents backflow of blood into the left ventricle.

Question 59

Why is the wall of the left ventricle thicker than the right ventricle?

Answer 59

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

Question 60

What is it called when the ventricles contract?

Answer 60

Ventricular systole

Question 61

What happens to the valves during ventricular contraction?

Answer 61

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).

Question 62

What do the papillary muscles and chordae tendineae do?

Answer 62

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.

Question 63

What happens to the valve cusps when pressure rises in the ventricles?

Answer 63

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.

Question 64

What are the semilunar values?

Answer 64

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.

Question 65

How many cusps does each semilunar valve have?

Answer 65

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.

Question 66

What happens to the valve cusps during ventricular systole?

Answer 66

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.

Question 67

In the aorta where do the coronary arteries arise from?

Answer 67

Two of the three aortic sinuses, hence the coronary arteries fill during ventricular relaxation (diastole).

Question 68

What are the auscultatory areas for each valve?

Answer 68

● 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.

Question 69

What is the ‘pacemaker’ of the heart?

Answer 69

Sinoatrial node (SA), spontaneously generates electrical impulses

Question 70

Where is the SA node found?

Answer 70

It is located at the superior end of the crista terminalis.

Question 71

What is the rate of impulses the SA node generates?

Answer 71

70 per minute approx

Question 72

What do impulses from the SA node stimulate?

Answer 72

Stimulates contraction of the atria Impulses are conducted to the atrioventricular (AV) node

Question 73

Where is the AV node located?

Answer 73

Inferior end of the interatrial septum

Question 74

What is the atrioventricular bundle (Bundle of His)?

Answer 74

Conducting fibres The atrioventricular bundle divides into two groups of fibres - the right and left bundle branches.

Question 75

What do the bundle branches give rise to?

Answer 75

Purkinje fibres that enter the myocardium of the left and right ventricles, respectively, and stimulate contraction.

Question 76

What is the SA node supplied by?

Answer 76

RCA in approximately 60% of people and by the LCA in approximately 40% of people.

Question 77

What is the AV node supplied by?

Answer 77

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.

Question 78

What can occlusion of the coronary arteries lead to?

Answer 78

Can result in conduction abnormalities, in addition to myocardial ischaemia.

Question 79

What is the heart innervated by?

Answer 79

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 fibre

Question 80

What are the visceral afferent fibres?

Answer 80

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.

Question 81

What is myocardial infarction?

Answer 81

This is the death of a region of myocardium secondary to occlusion (blockage) of the coronary vessel that supplies it. Most commonly, it is caused by atherosclerosis within the coronary arteries. A fatty plaque in a coronary artery may grow until it narrows the vessel lumen (stenosis) and severely restricts blood flowing through it. A fatty plaque may shear from the vessel wall, causing a clot to form in the lumen, which occludes blood flow.

Question 82

Explain valve dysfunction?

Answer 82

The AV and semilunar valves may become narrowed (stenosis) or incompetent. Incompetent valves allow regurgitation of blood back into the preceding chamber. Both result in turbulent blood flow that produce murmurs on auscultation. Valve dysfunction may be congenital (i.e. the patient is born with it) or acquired. For example, an AV valve may become dysfunctional if a myocardial infarct involves the associated papillary muscles.

Question 83

What is cardiomyopathy?

Answer 83

Cardiomyopathies are diseases of myocardium, and most are inherited. There are different types – some cause the myocardium to thin, whereas others result in the myocardium becoming thick and stiff. This affects the heart’s ability to pump efficiently and can lead to heart failure. Unfortunately, some cardiomyopathies have no obvious symptoms and are a cause of sudden cardiac death in otherwise healthy, young people.

Question 84

Explain conducting system abnormalities?

Answer 84

Myocardial infarction can cause conduction disturbances if the vessels that supply the conducting system are affected. Sometimes patients may have no symptoms and the abnormality is picked up on ECG. Some conducting system abnormalities are life-threatening, but can be managed if they are detected, for example, by fitting a pacemaker or an internal cardiac defibrillator (ICD).

Question 85

What is heart failure?

Answer 85

Heart failure occurs when the heart does not pump efficiently. There are many possible causes, including dysfunction of one or more of the heart valves, or an ability of the myocardium to contract properly (e.g. due to damage by myocardial infarction or cardiomyopathy). Signs and symptoms of heart failure include tiredness, shortness of breath and leg swelling.

Question 86

Explain cardiac arrest

Answer 86

Cardiac arrest is the cessation of cardiac contraction. Sometimes there is still detectable electrical activity, but the heart does not contract in response. Myocardial infarction and conducting system abnormalities are two causes of cardiac arrest, but there are many more.