Vena cava systems
Venous blood from organs and tissues returns to the heart via two main pathways: the superior and inferior venae cavae.
- Superior vena cava (v. cava superior) is formed by the confluence of the brachiocephalic veins. It collects blood from the head (via the jugular veins), neck, upper extremities (via the subclavian and axillary veins), and the thoracic cage (system of the azygos and hemiazygos veins). The vein has no valves and empties into the right atrium.
- Inferior vena cava (v. cava inferior) drains blood from the lower half of the trunk, abdominal cavity, pelvis (iliac veins), and lower extremities. It receives the hepatic, renal, lumbar, and other veins.
Important caval-caval anastomoses exist between these two systems, providing collateral blood outflow (for example, via the epigastric veins of the anterior abdominal wall or the ascending lumbar veins).
External structure and chambers of the heart
The heart is cone-shaped, with its base (basis cordis) directed upward and backward, and its apex (apex cordis) directed downward and forward. Externally, the sternocostal (anterior) and diaphragmatic (inferior) surfaces are distinguished. The boundaries between the chambers are marked by sulci: the coronary sulcus and two interventricular sulci (anterior and posterior).
Internally, the organ is divided into four chambers:
- Right atrium (atrium dextrum) receives blood from both venae cavae and the coronary sinus. The internal surface is partially covered by pectinate muscles. The fossa ovalis is located on the interatrial septum.
- Right ventricle (ventriculus dexter) pumps blood into the pulmonary trunk. It is separated from the atrium by the tricuspid valve. It features muscular trabeculae and papillary muscles.
- Left atrium (atrium sinistrum) receives oxygenated blood from the four pulmonary veins.
- Left ventricle (ventriculus sinister) has the thickest wall because it pumps blood into the aorta (systemic circulation). The bicuspid (mitral) valve is located between it and the atrium.
Wall structure and blood supply
The heart wall consists of three layers: the inner endocardium (forming the valves), the thick muscular myocardium, and the outer epicardium (visceral layer of the pericardium). The atrial and ventricular myocardium are separated by fibrous rings, with communication between them occurring exclusively through the conduction system.
Blood supply to the heart itself is provided by the right and left coronary arteries (aa. coronariae dextra et sinistra), branching from the aortic bulb:
- Right coronary artery supplies the right heart, the posterior wall of the left ventricle, and part of the septa. Its major branch is the posterior interventricular branch.
- Left coronary artery is larger, dividing into the anterior interventricular and circumflex branches. It supplies the anterior walls of both ventricles, the apex, and the left heart.
Class and exam questions
Where is the fossa ovalis located and what is its significance?
The fossa ovalis is located on the interatrial septum on the right atrial side. It is a closed oval foramen that in the fetus allowed blood to flow from the right atrium to the left, bypassing the lungs.
What is the difference in the structure of the atrial and ventricular myocardium?
The atrial myocardium is thinner and consists of two layers (superficial and deep). The ventricular myocardium is thicker (especially the left) and has three layers (outer, middle circular, and deep).
What pathways of blood outflow exist in case of obstruction of one of the venae cavae?
Blood can drain via caval-caval anastomoses: along the anterior abdominal wall (epigastric veins), subcutaneously (thoracoepigastric vein), and through the lumbar region (ascending lumbar veins, continuing into the azygos and hemiazygos veins).
What else to study on this topic
- Conduction system of the heart: nodes and the bundle of His
- Detailed topography of the superior and inferior venae cavae
- Structure of cuspid and semilunar valves
- Coronary artery anastomoses
- Detailed relief of the internal surfaces of the chambers (trabeculae, pectinate muscles)
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