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Septa of the Heart & the Cardiac Skeleton
Septa of the Heart & the Cardiac Skeleton
Includes labeled diagrams, downloadable notes, anatomy quizzes, and interactive learning tools
The heart is divided into four chambers by partitions called septa (singular: septum). These septa are formed primarily by cardiac muscle, or myocardium, and are lined internally by the endocardium. Their main function is to separate the chambers of the heart, prevent the mixing of oxygen-rich and oxygen-poor blood, and ensure that blood flows efficiently through the pulmonary and systemic circulations.
The heart contains three major septa: the interatrial septum, the interventricular septum, and the atrioventricular septum.
Interatrial Septum
The interatrial septum forms the wall between the right and left atria. In the adult heart, this septum contains a shallow oval depression known as the fossa ovalis.
The fossa ovalis is a remnant of the foramen ovale, an opening that exists in the fetal heart. Before birth, the lungs are not yet functioning, and oxygen is supplied by the placenta. The foramen ovale allows blood to pass directly from the right atrium to the left atrium, bypassing the pulmonary circulation.
Shortly after birth, when the lungs begin to function and blood starts flowing through them, a flap of tissue called the septum primum closes the foramen ovale. Over time, the opening seals permanently, leaving only the fossa ovalis as evidence of fetal circulation.
Compared with the septum separating the ventricles, the interatrial septum is relatively thin because the atria generate lower pressures during contraction.
Interventricular Septum
The interventricular septum separates the right and left ventricles. Its primary role is to prevent the mixing of oxygenated and deoxygenated blood while allowing each ventricle to pump blood into a different circulation.
Unlike the interatrial septum, the interventricular septum is normally complete at birth and remains intact throughout life. It is considerably thicker because the ventricles generate much greater pressure during contraction than the atria.
Most of the interventricular septum consists of thick cardiac muscle, although its uppermost portion remains thin and membranous. This region, known as the membranous septum, lies between the bases of the posterior and right cusps of the aortic valve.
The muscular fibers of the septum originate from both ventricles. In addition to separating the chambers, the interventricular septum contributes to the powerful contractions required to pump blood through the pulmonary and systemic circulations.
Atrioventricular Septum
The atrioventricular septum separates the atria from the ventricles. Unlike the other septa, it is interrupted by four openings that allow blood to move through the heart.
Two of these openings lie between the atria and ventricles and are guarded by the atrioventricular valves: the tricuspid valve on the right side and the mitral valve on the left side. The other two openings lead from the ventricles into the great arteries and contain the semilunar valves: the pulmonary valve and the aortic valve.
These valves ensure that blood flows in only one direction and prevent backflow during the cardiac cycle.
Because the presence of multiple openings and valves weakens the atrioventricular septum, this region is reinforced by a dense connective-tissue framework known as the cardiac skeleton.
Cardiac Skeleton
The cardiac skeleton, also called the skeleton of the heart, consists of dense fibrous connective tissue that surrounds the openings between the chambers and the great vessels. It forms four strong fibrous rings that support the tricuspid, mitral, pulmonary, and aortic valves.
The cardiac skeleton serves several important functions. It strengthens the atrioventricular region, provides attachment points for the heart valves and cardiac muscle fibers, and helps maintain the shape of the valve openings during contraction.
In addition to its structural role, the cardiac skeleton plays an important part in the electrical conduction system of the heart. It electrically separates the musculature of the atria from that of the ventricles, ensuring that impulses travel through specialized conducting pathways and allowing the chambers to contract in a coordinated manner.
Need a recap? Take a look at the heart septa anatomy notes notes here.
Need a recap? Take a look at the heart septa anatomy notes notes here.
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References
References
Gray, H. (1918). Anatomy of the human body (W. H. Lewis, Ed.; 20th ed.). Lea & Febiger.
Sobotta, J. (1906). Atlas and text-book of human anatomy (J. P. McMurrich, Ed.; W. H. Thomas, Trans.). Vol. 2. W.B. Saunders Company.
J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix. (2013, April 25). Anatomy and Physiology. OpenStax. https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy.
Based on OpenStax, Anatomy and Physiology (2013), licensed under CC BY 4.0.
Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.
Content paraphrased; adaptations were made.
Image Credis
Image Credis
Images used in this guide and games are by Dr. Johannes Sobotta. They are in the public domain; modifications have been made to the originals.
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