Heart - Chambers Flashcards
Right atrium?
The right atrium receives deoxygenated blood from the superior and inferior vena cavae, and from the coronary veins. It pumps this blood through the right atrioventricular orifice (guarded by the tricuspid valve) in the right ventricle.
In the anatomical position, the right atrium form the right border of the heart. Extending from the anterio0medial portion of the chamber is the right auricle (right atrial appendage) - a muscular pouch that acts to increase the capacity of the atrium.
The interior surface of the right atrium can be divided into two parts, each with a distinct embryological origin. These two parts are separated by muscular ridge called the crista terminalis:
1) Sinus venarum - located posterior to the crista terminalis. This part receives blood the SVC and IVC. It has smooth walls and is derived from the embryonic sinus venosus.
2) Atrium proper - located anterior to the crista terminalis, and includes the right ventricle. It is derived from the primitive atrium, and has a rough, muscular walls formed by pectinate muscles.
The coronary sinus receives blood from the coronary veins. It open into the right atrium between the IVC orifice and the right atrioventricular orifice.
Interatrial septum?
The interatrial septum is a solid muscular wall the separates the right and left atria.
The septal wall in the right atrium is marked by a small oval-shaped depression called the fossa ovalis. This is the remnant of the foramen ovale in the fetal heart, which allows right to left shunting of blood to bypass the lungs. It closes once the newborn takes its first breath.
Clinical relevance - atrial septal defect?
This is abnormal opening in the interatrial septum, persistent after birth. The most common site is the foramen ovale, and this is known as a patent foramen ovale.
In the adult, left atrial pressure is usually greater than that of the right atrium, so blood is shunted though the opening from left to right. In large septal defects, this can cause right ventricular overload, leading to pulmonary hypertension, right ventricular hypertrophy and ultimately right heart failure.
Definitive treatment is closure of the defect by surgical or transcatheter closure.
Left atrium?
The left atrium receives oxygenated blood from the four pulmonary veins, and pumps it through the left atrioventricular orifice (guarded by the mitral valve) into the left ventricle.
In the anatomical position, the left atrium forms the posterior border (base) of the heart. The left auricle extends from the superior aspect of the chamber, overlapping the root of the pulmonary trunk.
The interior surface of the left atrium can be divided into two parts, each with a distinct embryological origin:
- Inflow portion - receives blood from the pulmonary veins. Its internal surface is smooth and it is derived from the embryonic atrium.
- Outflow portion - located anteriorly, and includes the left auricle. It is lined by pectinate muscles, and is derived from the embryonic atrium.
Right ventricle?
Receives deoxygenated blood from the right atrium, and pumps it through the pulmonary orifice (guarded by the pulmonary valve), into the pulmonary artery.
The right ventricle can be divided into an inflow and outflow portion, which are separated by a muscular ridge known as the supraventricular crest.
Inflow portion
The interior of the inflow part of the right ventricle is covered by a series of irregular muscular elevations, called trabeculae carnae. They give the ventricle a ‘sponge-like’ appearance, and can be grouped into three main types:
- Ridges - attached along their entire length on one side to form ridges along the interior surface of the ventricle.
- Bridges - attached to the ventricle at both ends, but free in the middle. The most important example of this type is the moderator band, which spans between the interventricular septum and the anterior wall of the right ventricle. It has an important conductive function, containing the right bundle branches.
- Pillars (papillary muscles) - anchored by their base to the ventricles. Their apices are attached to fibrous cord (chordae tendinae), which are in turn attached to the three tricuspid valve cusps. By contracting the papillary muscles ‘pull’ on the chordae tendinae to prevent prolapse of the valve leaflets during ventricular systole.
Outflow portion (Conus arteriosus)
The outflow portion (leading to the pulmonary artery) is located in the superior aspect of the ventricle. It is derived from teh embryonic bulbus cordis. It is visibly different from the rest of the right ventricle, with smooth walls and no trabeculae carnae.
Interventricular septum?
It is composed of a superior membranous part and an inferior muscular part.
The muscular part forms the majority of the septum and is the same thickness as the left ventricular wall. The membranous part is thinner, and part of the fibrous skeleton of the heart.
Left ventricle?
Receives oxygenated blood from the left atrium, and pumps it through the aortic orifice (guarded by the aortic valve) into the aorta.
Inflow portion
The walls of the inflow portion of the left ventricle are lined by trabeculae carnae, as described with the right ventricle. There are two papillary muscles present with attach to the cusps of the mitral valve.
Outflow portion
The outflow part of the left ventricle is known as the aortic vestibule. It is smooth-walled with no trabeculae carnae, and is a derivative of the embryonic bulbus cordis.
Clinical relevance - tetralogy of Fallot?
It is a cyanotic congenital heart disease, comprising four abnormalities as a result of a single development defect. The four abnormalities are:
- Ventricular septal defect
- Overriding aorta (this is where the aorta is positioned directly over the VSD)
- Pulmonary valve stenosis
- Right ventricular hypertrophy
Stenosis of the pulmonary valve increase the force needed to pump the blood through it, resulting in right ventricular hypertrophy. Eventually, the pressure in the right ventricle become higher than that of the left - and blood then shunts from right to left through the ventricular septal defect. The overriding aorta lies over the ventricular septal defect, resulting in deoxygenated blood passing into the aorta.
It is usually treated surgically in the first few months of life or in severe cases, soon after birth.
