Cardiovascular System Anatomy and Blood Circulation Mechanics

Composition of the Cardiovascular System

The cardiovascular system consists of a main body, the heart, and a series of tubes or blood vessels, including arteries, veins, and capillaries, through which blood circulates.

The Human Heart

The heart is a muscle roughly the size of a fist, located in the chest cavity between the lungs with its conical apex pointing downward. Externally, it features blood vessels and nerves.

Internal Heart Structure

The heart contains four cavities: two upper chambers called atria (left and right) and two lower chambers called ventricles (left and right). Each atrium communicates with its corresponding ventricle through a valve that prevents backflow:

• Tricuspid Valve: Located between the right atrium and right ventricle.
• Mitral (Bicuspid) Valve: Located between the left atrium and left ventricle.

Vascular Connections and Valves

The walls of the atria and ventricles contain openings where arteries (from ventricles) or veins (to atria) connect. The right atrium receives two major veins, while four pulmonary veins flow into the left atrium. The pulmonary artery exits the right ventricle, and the aorta exits the left ventricle. Sigmoid valves are located at the ventricular outputs to prevent blood backflow.

Arterial Anastomosis

Arterioles are connected by branches called anastomoses, which ensure adequate blood supply even if a vessel becomes obstructed. In rare cases, such as the retinal artery, there is no anastomosis; therefore, an occlusion can lead to blindness.

How Heart Valves Function

Blood always circulates in one direction. When blood approaches, the valves open to allow passage; if the blood attempts to reverse direction, the valves shut to prevent backflow.

Circulatory Facts

If all the capillaries, veins, and arteries in the human body were laid out in a row, they would span approximately 95,000 km.

Types of Circulation

• Systemic Circulation: Blood is pushed by the left side of the heart to the rest of the body.
• Pulmonary Circulation: Blood is pushed by the right side of the heart to the lungs.

The Portal System

Abdominal vessels have a unique arrangement. While veins from most abdominal structures lead directly to the heart, blood from the stomach and intestines enters the liver first. Here, a second set of capillaries filters the blood, allowing the liver to store and process nutrients absorbed from the digestive tract. This process is known as the portal system.