Vena Cava Systems
Venous blood from organs and tissues returns to the heart via two major trunks: the superior and inferior venae cavae.
- Superior vena cava (v. cava superior) is formed by the union of the brachiocephalic veins. It collects blood from the head (via the jugular veins), neck, upper limbs (via the subclavian and axillary veins), and thorax (azygos and hemiazygous venous systems). The vein has no valves and drains into the right atrium.
- Inferior vena cava (v. cava inferior) drains blood from the lower half of the trunk, abdomen, pelvis (iliac veins), and lower limbs. It receives the hepatic, renal, lumbar, and other veins.
Important caval-caval anastomoses exist between these two systems, providing collateral venous drainage (e.g., via the epigastric veins of the anterior abdominal wall or the ascending lumbar veins).
External Structure and Cardiac Chambers
The heart is cone-shaped, with its base (basis cordis) directed superiorly and posteriorly, and its apex (apex cordis) directed inferiorly and anteriorly. Externally, sternocostal (anterior) and diaphragmatic (inferior) surfaces are distinguished. The boundaries between 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 lined by pectinate muscles. The interatrial septum features the fossa ovalis.
- Right ventricle (ventriculus dexter) — ejects blood into the pulmonary trunk. Separated from the atrium by the tricuspid valve. Features muscular trabeculae and papillary muscles.
- Left atrium (atrium sinistrum) — receives oxygenated blood from four pulmonary veins.
- Left ventricle (ventriculus sinister) — possesses the thickest wall, as it pumps blood into the aorta (systemic circulation). The bicuspid (mitral) valve is located between this chamber and the left 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 (the visceral layer of the serous pericardium). The atrial and ventricular myocardium are separated by fibrous rings, with electrical connection between them occurring exclusively via the conduction system.
The heart is supplied by the right and left coronary arteries (aa. coronariae dextra et sinistra), which arise from the aortic sinuses (bulbus aortae):
- Right coronary artery supplies the right heart, the posterior wall of the left ventricle, and part of the septum. Its major branch is the posterior interventricular artery.
- Left coronary artery is larger, branching into the anterior interventricular (left anterior descending) and circumflex branches. It supplies the anterior walls of both ventricles, the apex, and the left heart.