The heart and mediastinum Flashcards
Describe pulmonary circulation
Low resistance
pressure 20/10mmHg
Describe the systemic circulation
High variable resistance
120/80mmHg
What are the 3 layers of the heart wall?
3 layers of the heart wall
Epicardium (also visceral/serous pericardium)
Muscular myocardium
Endocardium (monolayer endothelial cells)
What’s the function of pericardial cavity?
Heart sits in it and allows friction free contraction within chest
Two layers of pericardium?
Outer fibrous layer (continuous with central tendon of diaphragm)
Serous layer inside
What is the pericardial sac?
Double layered sac, sealed to diaphragm which surrounds heart apart from where great vessels enter/leave
What are some abnormalities that arise of the pericardium?
Pericarditis: inflammation of pericardium, people complain with chest pain due to friction (heart beats and it rubs)
Tamponade: effusion of pericardium (e.g. post viral infection or shot in heart ), fluid builds up between 2 pericardial layers and insults pumping action of the heart
What is meant by pericardial sinus?
Cavities produced by pericardium around the heart
Two types of pericardial sinuses?
Oblique sinus between heart and great vessels
Transverse sinus: around aorta and pulmonary trunk posterior to heart
How is transverse sinus formed?
Dorsal mesocardium breaks down
Describe orientation of heart in thorax
Lies obliquely, RV and RA face anteriorly, LV and LA posterior
Describe the surface borders of the heart
Superior border: line following 2nd left costal cartilage to 3rd right costal cartilage
Right border: 3-6 right intercostal cartilage
Apex (left border): in 5th intercostal space in mid clavicular line
What happens in situs inversus
Mirror image positioning of all organs (compatible with life)
What is situs solitus?
Normal
What is fibrous skeleton formed of?
Cartilaginous ring at level of membranous ventricular septum (connective tissue frame which functions to electrically isolate the atria from the ventricles)
What is the function of fibrous skeleton of heart?
Non conducting separation of atria and ventricles, electroinsulation so impulses must pass through AVN
Support for valves
What are the principal venous structures draining to heart?
SVC, IVC (drain into right atrium)
Pulmonary veins
Coronary sinus
What is the coronary sinus?
A collection of veins joined together to form a large vessel (coronary sinus) that empties blood into right atrium
Where does coronary sinus run and which veins does it receive?
Runs in AV groove
Receives, great, middle and small cardiac vein
What is the name of the right AV valve?
Tricuspid valve
What does fibrous skeleton contain?
AV, aortic and pulmonary valve orifices
What are 3 cusps of tricuspid valve attached to?
Fibrous ring surrounding AV orifice
Structure of pulmonary/aortic valves?
3 semi lunar cusps
What veins does the left atrium receive?
4 pulmonary veins (2 inferior, 2 superior 2)
Why does left atrium have smooth walled interior?
Formed by incorporation of primitive pulmonary veins in development
What is the left AV valve?
Mitral valve
Describe structure of mitral valve?
2 cusps and papillary muscles larger than counterparts on right side
What are aortic sinuses?
Formed behind cusp of each valve as a bulge in aortic wall
What do left, right posterior and anterior aortic sinuses supply?
Left Posterior - origin of left coronary artery
Right anterior: origin of right coronary artery
Right posterior: no artery
What happens to blood supply to ventricular wall in systole, why, therefore, when does most coronary perfusion occur?
High pressure generated shuts off coronary circulation
Most coronary perfusion in diastole
How does heart blood supply show end organ circulation?
Branches of coronary artery are functional end structures (anastomoses between LCA and RCA rare and inefficient) and sensitive to obstruction
In terms of coronary arteries, why can myocardial infarctions/angina be caused?
Occlusion of major coronary arteries and inefficienct anastomoses between RCAs and LCAs
Where does coronary circulation originate from?
RCA and LCA arise above aortic valve at left/right aortic sinuses
Which layers of heart do coronary arteries supply?
Myocardium and epicardium
What do LCA and RCA supply generally?
LCA: left ventricles, atria and IV septum
RCA: right ventricles, atira and septum
How does the RCA branch?
The right coronary artery passes from the right aortic sinus and branches to form the right marginal artery (RMA) anteriorly.
In individuals who have right dominant circulation (~80% of individuals), it also branches into the posterior descending/interventricular artery.
How does the LCA branch?
Emerges from the left coronary sinus, initially branches to yield the left anterior descending (LAD) artery.
It also gives off the left marginal artery (LMA) and the left circumflex artery.
In ~20 of individuals, the left circumflex artery contributes to the posterior descending artery, these individuals are left dominant.
What does marginal branch of RCA supply?
RV and apex
What does the RCA supply?
SAN and RA
How does blood pooling help close SL valves in diastole?
Turbulence of blood as aortic pressure decreases, blood pools in aortic sinuses (then can travel through coronary arteries)
Which is the more important coronary artery and why?
Left, has 3 main branches instead of 2.
What does the LAD supply?
LV and septum
What does the LCA supply?
LA and LV anterior 2/3 of the interventricular septum
What does the LMA supply?
LV
Where is the SAN?
In cristae terminalis (separates the smooth and rough walls of the RA)
What happens to the bundle of his?
Divides into posterior and anterior left and right bundle branches which transmit impulses to endocardial regions on left and right ventricles.
What do branches of left and right branches of Bundle of His do?
Transmit impulses to Purkinje fibres
Why do many fibres innervating cardiac plexus arise in the neck?
Heart develops in cervical region of embryo
Why is there referred pain to chest arm and neck in myocardial infarction?
Cardiac sensory pain fibers follow the sympathetic back to the spinal cord and have their cell bodies located in thoracic dorsal root ganglia 1-4.
The central nervous system (CNS) perceives pain from the heart as coming from the somatic supplied by the T1-4 (dermatomes arising from this dorsal root ganglia (T1-5) are in the upper limb and up to the neck).
What is the inner wall of the right atrium like?
Lateral rough walled part consisting of pectinate muscle.
Smooth walled part
Why is there a smooth and rough wall of the right atrium?
Different embryological origin
Rough wall from primitive atrium
Smooth wall from sinus venosus and interatrial septum
Why is the right ventricle wall much thinner than the left ventricle wall?
Less force is required to pump the blood to the lungs. Pulmonary circulation has 6x lower resistance so 6x lower pressure needed to produce the same flow.
What is the name to describe the rough muscular surface of the ventricle wall?
Trabeculae carneae
What is the left atrial appendage and why is it clinically significant?
Additional volume outside of main chamber, blood can pool here, act more turbulent and clot.
How can you diagnose aortic stenosis?
Ejection systolic murmur, as blood rushes out of aorta, hear the murmur
How do you diagnose atrial regurgitation?
Hear murmur in early diastole as blood pools back into aorta
Murmur decrescendos in ventricular systole
What can murmurs suggest?
Valve problems
What is the mediastinum and what does it consist of?
Central compartment of the thoracic cavity surrounded by loose connective tissue.
Contains the heart and its vessels, oesophagus, trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.
What are the borders of the superior mediastinum?
Superior thoracic aperture to the thoracic plane at the angle of louis (T4).
What are the borders of the inferior mediastinum?
Thoracic plane (T4) to diaphragm
What three regions is the inferior mediastinum divided into?
Anterior - infront of the pericardium
Middle - pericardium and its contents
Posterior - behind the pericardium
What is the superior mediastinum bounded by?
Superiorly by the thoracic inlet, the upper opening of the thorax
Inferiorly by the transverse thoracic plane (T4)
Laterally by the pleurae
Anteriorly by the manubrium of the sternum
Posteriorly by the first four thoracic vertebral bodies.
What is the anterior mediastinum bounded by?
Laterally by the pleurae
Posteriorly by the pericardium
Anteriorly by the sternum, the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages.
What is the middle mediastinum bounded by?
The pericardial sac
What is the posterior mediastinum bounded by?
Anteriorly by (from above downwards): bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
Inferiorly by the thoracic surface of the diaphragm (below);
Superiorly by the transverse thoracic plane;
Posteriorly by the bodies of the vertebral column from the lower border of the fifth to the twelfth thoracic vertebra (behind);
Laterally by the mediastinal pleura (on either side).
The component of the primitive heart tube that forms the smooth walled parts of the atria…
Sinus venosus
Which side is tricuspid and mitral on?
Mitral - left
Tricuspid - right
What does the atrio-ventricular bundle (of His) peirce?
Pierces the fibrous skeleton which separates the atria from the ventricles
What chamber forms most of the left radiographic margin of the heart?
Left ventricle
A direct consequence of tricuspid valve incompetence i.e. a failure of the valve to close completely during ventricular contraction…
Raised right atrial pressure
Anterior mediastinum contains
Thymus, internal thoracic vessels
Middle mediastinum contains
Heart, pericardum, tracheal bifurcation, ascending aorta, SVC, cardiac plexus, left and right phrenic nerves
Posterior mediastinum contains
Thoracic aorta, oesophagus, thoracic duct, Azygous veins, sympathetic trunks
Superior mediastinum contains
Arch of aorta, SVC, vagus nerve, phrenic nerve, cardiac nerves, sympathetic trunk, trachea, oesophagus, thoracic duct.
What is found at the thoracic plane?
RATPLANT
2nd rib aortic arch tracheal bifurcation pulmonary trunk ligamentum arteriosum azygous vein nerves thoracic duct
Vagus nerves enter the superior mediastinum via the
Carotid sheath
When does the right vagus become the right recurrent laryngeal?
As it crosses the subclavian artery
Right recurrent laryngeal loops beneath… and supplies…
Loops beneath the right subclavian artery and supplies the larynx
When does the left vagus become the left recurrent laryngeal?
As it crosses the aorta
Left recurrent laryngeal loops beneath… and supplies…
Loops beneath the ligamentum arteriosum and supplies the larynx
Sympathetic roots of heart
T1-T5
Phrenic roots
C3,4,5
Costophrenic recess
Sharp angles between the thoracic wall and diaphragmatic pleurae
Paralysis of half the diaphragm
Inspiration - paralysed hemidiaphragm rises due to push from abdominal viscera
Exhalation - paralysed hemidiaphragm descends due to positive pressure within the lungs
Distention of the aortic arch vagus
Compression of left recurrent laryngeal as loops round the ligamentum arteriosum
Hoarse voice and gastroparesis
What area is clamped during surgery
Transverse sinus
Locations of heart sounds
Tricuspid - 4th IC space
Mitral - apex
Aortic - right 2nd IC space
Pulmonary - left 2nd IC space
Three physiological shunts in foetal CV system
foramen ovale - RA to LA
ductus venosus - umbilical vein to the IVC
ductus arteriosis - pulmonary trunk to arch of aorta
Changes at birth to CV system?
FO shuts forming fossa ovalis
Ductus arteriosis constricts (ligamentum arteriosum) when blood PO2 rises
Umbilical vein constricts (ligamenum teres) and ductus venosus forms the ligamentum venosum
