The Heart and Pericardium Flashcards
Where is the Pericardium?
Heart and the great vessels roots are enclosed in a pericardial sac. This pericardium is continuous with the central tendon of the diaphragm. This serves to stop the diaphragm from descending upon inspiration.
–> The pericardial sac positioned in the middle mediastinum.
What are the cavities in the thorax?
The thorax is generally neatly arranged with three cavities:
- right lung in right pleural cavity
- left lung in left pleural cavity
- everything else between them in the mediastinum
How is the Mediastinum divided?
The mediastinum has quite a number of structures within it and so it is further organised around a plane (imaginary) that is taken backwards from the manubriosternal junction (the angulation of the manubrium on the sternum).
This imaginary plane is known as the plane of Louis intersects the vertebral column at the level of T4-T5. This imaginary plane divides the mediastinum into superior and inferior.
The superior appature is far smaller than the inferior apperture because of the divergent dimensions of the thorax.
The inferior mediastinum is further divided into anterior, middle and posterior mediastinum.
- The heart sits within the middle of the inferior mediastinum and so everything in front of the heart is the anterior inferior mediastinum and everything behind it is the posterior inferior mediastinum.
Anatomically, the heart is situated behind the sternum and in front of the thoracic vertebrae 5-8. These are the anatomical landmarks used in CPR.
What are the two layers of the pericardium?
The pericardium is a two layered structure: Outer Fibrous Pericardium and an envelope of inner serous pericardium (made up of visceral and parietal)
During development, the heart enters the serous pericardium from behind to give the two layers.
The fibrous layer is quite durable/substantial.
The parietal layer of serous pericardium lines the internal aspect of the fibrous pericardium and the visceral layer of the serous pericardium lines the surface of the heart. The layers of serous pericardium are continuous over the great vessels however there is a cavity between the two layers which is made up of a potential space with a few mLs of serous fluid to create a frictionless glide during contraction of the heart.
Describe the anterior landmarks of the heart proper.
During development, the right chambers of the heart come to lie in front of the left sided chambers due to rotation.
- The atria lie to the right and the ventricles lie to the left.
This means that the anterior surface of the heart is predominantly right sided chambers. The developmental rotation is not a full rotation and so some of the left ventricle is visible from the anterior aspect of the heart.
Ant: RA –> RV –> LV
- The right border of the heart is formed by the right atrium which is important radiologically.
- The left border of the heart and the apex are formed by the left ventricle. The apical beat of the apex is felt in the 5th intercostal space (below rib 5) on the left side in the midclavicular line.
The base of the heart is where the great vessels emerge –> diagonally opposite the apex.
Describe the posterior landmarks of the heart?
The posterior side of the heart is predominantly LA.
Post: LV –> LA –> RA
The atria have small ear shaped appendages called auricles that extend from the RA anteriorly and the LA posteriorly and they face the anterior surface of the heart and can be useful in identifying the orientation of the organ.
Describe the sulci of the external heart?
Sulci/Grooves delineate where the chambers end/begin. There are atrioventricular sulci between the atria and ventricles and interventricular sulci between the two ventricles.
- Anterior/Posterior Atrioventricular Groove/Sulcus (CORONARY SULCUS): Between RA and RV.
- Anterior/Posterior Interventricular Groove/Sulcus: Between RV and LV
These grooves have the coronary vessels running in them for the blood supply to the heart.
Describe the internal features of the Right Atrium.
The posterior surface of the RA is known as the interatrial septum.
In general, atria are thin walled.
The internal aspect of the anterior RA wall is lined by ridges called musculi pectinati. The posterior wall of the internal RA is smooth called sinus venarum. The region where the surfaces change is at a clear line called crista terminalis.
RA is the receiving chamber collecting systemic venous return, with the SVC (no valve) returning blood from the head, neck. upper limbs and thorax from above, and the IVC returning blood from the lower limb and abdomen from below. The ICV comes through the diaphragm at level T8 straight into the RA. The IVC as a rudimentary valve where it enters the RA. That valve will lead to the fossa ovalis, and serves the channel blood to the foramen ovalis during development.
The venous return from the heart itself has its own sinus which collects most of (but not all) of the venous drainage. It opens directly into the RA, between the rudimentary IVC valve and the tricuspid valve.
The fossa ovalis is an oval imprint on the smooth posterior wall of the RA, that served as a bypass of the pulmonary circulation during utero/fetal development. During this time, it is called the foramen ovalis. This is shut after birth with the first few breaths of life.
Describe the internal features of the Right Ventricle.
The ventricles are the pumps of the heart and so they have far thicker walls. They also have far greater numbers of muscular ridges called trabeculae carnae. The only part of the ventricle that is not ridged is near the outflow tract just before the ventricle ends and the pulmonary vessels/valve begins. This smooth region is called conus arteriosis/infundibulum.
There are three atypical trabeulae carnae which project into the ventricle called papillary muscles. They attach to chordae tendinae which connect from the apex of the papillar muscle to the cusps of the tricuspid valve.
Describe the internal features of the Left Atrium.
The left atrioventricular valve is the mitral valve/biscuspid valve and only has two cusps compared to the tricuspid with three.
The left atrium is simply a thin, smooth walled chamber with four openings for the pulmonary veins (2R;2L).
The auricle of the LA distends around to the anterior side of the heart and is actually ridges (musculi pectinati) on the interior surface due to it having a different embryological derivation.
Describe the internal features of the Left Ventricle.
The LV has the thickest wall of all because it is pumping into the systemic circulation which is the highest pressure circulation.
There are only two papillary muscles.
Explain the fibroskeleton of the heart. What is the function of the fibroskeleton?
The fibrous skeleton of the heart to which the muscle fibres of the heart are attached is comprised of four rings that each surround the orifices for the valves.
There are a pair of coronets that surround the pulmonary and aortic valves and a pair of rings surrounding the atrioventricular valves (tricuspid and mitral). These four ring structures are all attached to each other. Trigones refer to the entire skeleton as a whole.
The fibrous skeleton anchors the muscle masses and electrically isolates them as well as providing attachment for the base of each valve cusp. It means that an electrical impulse from the atria requires a second signal to transmit to the ventricles
Describe the A-V valves.
Tricuspid valve/Mitral Valve
The cusps of these valves are extensions of the tissue that lines the heart with a fibrous centre for structure. The tricuspid valve has and anterior, septal and posterior cusp.
The atrial surface of the cusps are smooth. The ventricular surface of the valve is rough and has the attachments of the chordae tendinae. The chorade tendinae are not each attached to a separate cusp but instead they pull two adjacent cusps together so as not to allow any leakage from the cusps.
The function of the valves is to allow for pressure gradients to build up in each chamber. The valves open due to pressure on one side being greater than the other, the muscles do not open these valves. During diastole, when the ventricles contract, the papillary muscles also contract and the chordae tendinae hold the cups of the valve closed so that there is no blood flowing back into the atrium.
Describe the semi-lunar valves.
Pulmonary valve/Aortic Valve
Semi lunar valves: three half moon cusps that are characterised by their bases being attached to the internal surace of the wall of the vessel and the apex of each of the cusps meets the others in the centre of the valve.
These valves open when the pressure in the ventricle exceeds the pressure in the great vessels. As the pressure gradient decreases, the semilunar cusps simply close again .
Aortic Valve
The aortic valve and the pulmonary valve have the same structure in that each leaflet has a small nodule in the centre which indicates where the three meet in the centre.
Immediately above the nodule/attachments of the three cusps in the aortic valve, on the interior surface of the aorta are where the coronary arteries arise.
What are the openings for the coronary arteries called?
Ostea
