Theme 1: Lecture 3 - The Middle Mediastinum Flashcards
What is the anterior border of the middle mediastinum?
Anterior pericardium
What is the posterior border of the middle mediastinum?
Posterior pericardium
What is the lateral border of the middle mediastinum?
Mediastinal pleura
What is the inferior border of the middle mediastinum?
Diaphragm
What is the superior border of the middle mediastinum?
Transverse thoracic plane or level T4/5 or sternal angle
What are the contents of the middle mediastinum?
- Heart and pericardium
- Ascending aorta
- Pulmonary trunk and arteries
- Pulmonary veins
- Nerves (cardiac plexus and phrenic nerves)
Atrioventricular groove
Groove on the surface of the heart between atria and ventricles
Interventricular groove
Groove on the surface of the heart that divides the two ventricles
What are the auricles?
Flap over the surface of the heart that allows for extra blood volume to enter the atria
Which part of the aorta is in the middle mediastinum?
The ascending aorta
Describe the pulmonary trunk
- Deoxygenated blood leaves the heart via the pulmonary trunk
- Branches into the left and right pulmonary arteries
- Enters the hilum/root of the lung
Describe the pulmonary veins
- Oxygenated blood from lungs to left atrium
- Two veins from each side, left and right, inferior and superior
Describe the vena cava
- Blood enters the heart via the right atrium
- Receives deoxygenated blood from the superior and inferior vena cava
What are the 2 regions of the right atrium?
- Sinus venarum
- Pectinate muscle
What is the sinus venarum?
- Smooth walled muscle in the inner surface of the atria
- Often lies where the inflow and outflow of blood is occurring as the smooth surfaces allow for better blood flow
What is pectinate muscle?
- Parallel muscular columns in the inner surface of the atria
- Aids with contraction
Deoxygenated blood flows into the right atrium from the:
- Superior vena cava
- Inferior vena cava
- Coronary sinus
What is the coronary sinus?
The main vein that drains blood supplying the blood itself
What is the Crista terminalis?
The boundary between the sinus venarum and pectinate muscle
What are the landmarks used to identify the sinoatrial node?
- Superior part of the crista terminalis
- Junction of the superior vena cava with the right atrium
Describe the left atrium of the heart
Predominantly smooth walled but there is some pectinate muscle in the auricle
Moderator band
- Runs from the interventricular septum to the margin and is therefore only in the right ventricle
- Sometimes called the septomarginal band
Papillary muscle
Projections coming up from the walls of the ventricles and attach to the chordae tendineae
Chordae tendineae
Tendons connecting the papillary muscles to the AV valves
Trabeculae carneae
- Walls of the ventricles are predominately rough and this is called trabeculae carneae (as apposed to pectinate in the artia)
- Prevents surface tension between the walls of the ventricles and aids in contraction
What are the cusps of the mitral (bicuspid) valve?
- Anterior cusp
- Posterior cusp
What are the cusps of the tricuspid valve?
- Anterior cusp
- Posterior cusp
- Septal cusp
Pulmonary valve cusps
- Left
- Right
- Anterior
Aortic valve cusps
- Left
- Right
- Posterior
Where does the right coronary artery arise from?
Right cusp of the aortic valve
Where does the left coronary artery arise from?
Left cusp of the aortic valve
Describe the pericardium
- 3 layered sac that the heart is suspended in
- Attached to great vessels superiorly and diaphragm inferiorly
- Influenced by movement of the great vessels, sternum, diaphragm and lungs
- Phrenic nerve travels over pericardium
Describe the functions of the pericardium
- Fibrous so protects heart from overfilling (cardiac distension)
- Retains heart in position (pericardio-sternal ligaments)
Name the layers of the pericardium from the inside out
- Visceral layer (also called the epicardium as it’s the outermost layer of the heart wall
- Parietal layer
- Fibrous pericardium
What make up the serous pericardium?
- Visceral layer
- Parietal layer
Pericardial cavity
- Located between the parietal and visceral pericardium
- Contains small amounts of serous fluid to allow for uninhibited movement
Pericardial sinuses
Where the layers of the parietal and visceral layers of the serous pericardium meet and reflections form 2 sinuses on the heart
Transverse pericardial sinus
Between the outflow and inflow vessels of the heart - can be used in surgery to clamp the outflow of blood from the heart
Oblique pericardial sinus
Located between the pulmonary veins
Which arteries branch off the right coronary artery?
- Sino-atrial nodal branch of right coronary artery
- Right marginal branch of right coronary artery
- Posterior interventricular branch of right coronary artery
Which arteries branch off the left coronary artery?
- Circumflex branch of left coronary artery
- Left marginal branch of circumflex branch
- Anterior interventricular branch of left coronary artery
- Diagonal branch of anterior interventricular branch
Where are coronary vessels located?
In the atrioventricular and interventricular grooves
Where do functional (potential) anastomoses exist between the coronary artery branches?
- End branches of the anterior interventricular artery and the posterior interventricular artery
- However these don’t maintain collateral circulation if major branch is suddenly occluded (can from functional anastomoses if progressive occlusion)
What is coronary artery dominance?
Dominance is defines as the artery which gives rise to the posterior interventricular artery
What are the cardiac veins?
- Great cardiac vein
- Posterior cardiac vein
- Middle cardiac vein
- Small cardiac vein
- Coronary sinus
Where is the SAN located?
Close to the crista terminalis at the junction between the superior vena cava and the right atrium
What does the SAN do?
Initiates contraction, impulses spread through atrial wall to AV node via internodal tracts
Where is the AV node located?
Interatrial septum close to coronary sinus opening
Where are impulses conducted after the AV node?
They continue into the AV bundle (bundle of His) and divide into the interventricular septum to travel to left and right ventricles to conduct the impulse to the left and right Purkinje fibres
When do the AV bundles turn into the Purkinje fibres?
When they penetrate into the ventricles in the subendothelial layer
What is the fibrous skeleton
- Framework of 4 fibrous rings of dense connective tissue
- Provides attachment for AV and semi lunar valves
- Forms an electrical insulator between the atria and ventricles
Which nervous system is the myocardium regulated by?
Autonomic nervous system
Where do nerves from the ANS destined for the heart enter?
Cardiac plexus
Parasympathetic NS to the heart
Fibres from the Vagus nerve enter the cardiac plexus and then travel to SAN
Sympathetic NS to the heart
Fibres from sympathetic trunk levels T1-5 enter the cardiac plexus and then travel to the SAN.
