Surface anatomy of mediastinum and heart

Question 1

What is the mediastinum?

Answer 1

• Central compartment or median septum between two pleural cavities within thoracic cavity
• Highly mobile region in living subjects because it consists of mainly hollow visceral structures (air or fl
• Extends from the superior thoracic aperture to diaphragm inferiorly

Question 2

Subdivisions of mediastinum

Answer 2

Superior and inferior (anterior, middle, posterior)

Question 3

Contents of mediastinum

Answer 3

Oesophagus, trachea, great vessels, heart, pericardium, nerves, sympathetic chain, lymphatic vessels, thoracic ducts, lymph nodes

Question 4

Why is thoracic duct vulnerable during thoracic oesophageal surgery?

Answer 4

Variable course and difficulty with identification

Question 5

What happens to thymus with age?

Answer 5

It shrinks

Question 6

What happens to thoracic contents in supine position?

Answer 6

• Arch of the aorta lies superior to transverse thoracic plane
• Bifurcation of trachea is transected by transverse thoracic plane
• Central tendon of diaphragm (diaphragmatic surface of heart) lies at level of xiphisternal junction and vertebra T9

Question 7

What happens to thoracic contents in standing position?

Answer 7

• Arch of aorta is transected by the transverse thoracic plane
• Tracheal bifurcation lies inferior to transverse thoracic plane
• Central tendon of diaphragm (diaphragmatic surface of heart) may fall to level of middle of xiphoid process and T9-T10 intervertebral discs

Question 8

Possible causes for widened mediastinum

Answer 8

• Haemorrhage into mediastinum from lacerated great vessels
• Enlargement of mediastinal lymph nodes due to malignant lymphoma
• Hypertrophy of heart due to congestive heart failure

Question 9

What is the pericardium?

Answer 9

• A fibrous membrane covering heart and parts of great vessels
• A closed sac made of fibrous and serous pericardium
• Serous pericardium is made of parietal and visceral layers

Question 10

What are the two pericardial sinuses?

Answer 10

Transverse and oblique

Question 11

Receiving chambers

Answer 11

Right atrium and auricle, left atrium and auricle

Question 12

Discharging chambers

Answer 12

Right and left ventricles

Question 13

What is wall of heart made from?

Answer 13

Endocardium, myocardium, epicardium (visceral pericardium)

Question 14

External features of heart

Answer 14

• Apex of heart formed by inferolateral part of L ventricle, lies in 5th intercostal space about 9 cm from median plane
• Base of heart: formed by L (mainly) and R atria, received pulmonary veins at left atrial portion, received superior and inferior venae cavae in its right atrial portion
• Four surfaces: anterior (sternocostal) - RV, diaphragmatic (inferior) - L/RV, right pulmonary - RA, left pulmonary - LV
• Four borders: right (RA, between SVC and IVC), inferior (right and left ventricle), left (LV and L auricle), superior (R and L atria and auricles)

Question 15

4 borders of heart

Answer 15

• Superior border: from inferior border of 2nd left costal cartilage to superior border of 3rd right costal cartilage, 1-2cm from margin of sternum on each side
• Right border: from 3rd right costal cartilage to 6th right costal cartilage - slightly convex to the right, 1-2cm from margin of sternum on each side
• Inferior border: from inferior end of right border to a point in the 5th intercostal space close to midclavicular line - apex of heart/apex beat
• Left border: line connects left ends of superior and inferior borders

Question 16

Benefits of fibrous skeleton in chest

Answer 16

• Collagen forms four rings around orifices of cardiac valves
• Structural foundation of heart valves - keeps patent and prevents overstretching
• Anchors myocardium
• Acts as electrical insulator between atria and ventricles

Question 17

Characteristics of right atrium

Answer 17

• Sinus venarum (smooth thin part, from right sinus horn, receives opening of SVC, IVC and coronary sinus)
• Rough part - pectinate muscles (from primitive atrium)
• Right atrioventricular orifice
• Crista terminalis (sulcus terminalis externally - separates between smooth and rough parts)
• Opening of coronary sinus
• Interatrial septum
• Oval fossa (fossa ovalis) - remnant of oval foramen

Question 18

Characteristics of right ventricle

Answer 18

• Conus arteriosus or cordis (infundibulum)
• Trabecular carneae - irregular muscular ridges from proximal bulbus cordis
• Supraventricular crest
• Separates the trabeculated and smooth wall parts, part of bulbus cordis
• Right atrioventricular (tricuspid) orifice
• Tricuspid valve - cusps of tricuspid valve (anterior, posterior and septal)
• Tendinous cords (chordae tendineae)
• Papillary muscles (anterior, posterior, septal)
• Interventricular septum
• Septomarginal trabecula (moderator band) - transverses right ventricular chamber, carries part of right branch of AV bundle of His
• Pulmonary valve - semilunar cusps (anterior, right, left)

Question 19

Autonomic innervation of heart

Answer 19

• Located in medulla oblongata are cardioacceleratory (pressor centre) - sympathetic and cardioinhibitory (depressor centre) - parasympathetic
• Sympathetic fibres through cardiac plexus to SA and AV nodes, cardiac muscles and coronary arteries, increases rate and force of contractions
• Parasympathetic fibres through carduac plexus to SA and AV nodes, cardiac muscles and coronary arteries - slows heart rate
• Afferent sympathetic fibres go to T1/2 - T4, referred pain across chest and upper limb
• Afferent parasympathetic fibres run with vagus nerve and are concerned with cardiac reflexes (baroreceptor, aortic arch and carotid sinus reflexes for BP homeostasis)

Question 20

Landmarks of valves and vessels

Answer 20

• Valves are located deep to sternum - sounds best heard superficial to chamber or vessel into which blood has passed and in direct line with the valve in the direction of blood flow
• Pulmonary area: sternal end of 1st or 2nd left intercostal space
• Aortic area: sternal end of 1st or 2nd right intercostal soace
• Mitral area: near apex of heart in 5th left intercostal space
• Tricuspid area: sternal edge at level of 4th or 5th intercostal space right or left of the sternum