Anatomy of the cardiovascular system

The cardiovascular system is also called the circulatory system. The cardiovascular system brings oxygen (O2), nutrients, water, and other substances (e.g., salts and hormones) to the body’s cells. It also carries waste products away from the cells to be excreted. These waste products include metabolic waste and** carbon dioxide (CO2)**.

The cardiovascular system is a closed system that includes the following structures:

• Blood vessels, consisting of arteries, arterioles, capillaries, venules, and veins that act as pipes to carry the blood around the body
• A heart, which pumps the blood
• Blood, which contains the nutrients for the cells and the waste products to be excreted

Cellular injury and death of the cells will occur if the system malfunctions and critical substances are withheld from the cells.

Blood vessels

Blood vessels create a pipeline for blood to move out to the body and back to the heart. Blood vessels differ in their role, structure, and size:

• Arteries: Strong, stretchy, thick-walled vessels that carry blood from the heart. They are made to withstand the pressure of the blood being pumped out from the heart. Arteries are involved in maintaining blood pressure. • Arterioles: Smaller arteries that move blood to the capillaries and are also involved with maintaining blood pressure.
• Capillaries: Thin-walled vessels that allow for the exchange of oxygen, nutrients, waste products, and other substances between the blood and cells. The diameter of the capillaries is so thin that only one blood cell can pass through at a time.
• Venules: Vessels that collect blood from capillaries and begin the return journey to the heart.
• Veins: Vessels that collect blood from the venules and return blood to the heart. Medium to large veins have valves, which help keep blood moving in one direction. The skeletal muscle contractions help move the blood toward the heart. Vessel walls are thinner and less rigid than arteries. Veins hold about 70% of the blood supply at any one time.

The heart

The heart, which is the size of a fist, is a complex muscular organ that pumps blood around the body. It is located in the mediastinum of the thoracic cavity, slightly left of the midline. The apex (pointed tip) of the heart rests just above the diaphragm. The area of the chest wall anterior to the heart and lower thorax is referred to as the precordium.

Heart chambers

The heart has two sets of chambers. The two upper chambers are called atria. The atria are small chambers with thin walls. The right atrium receives blood from the body, and the left atrium receives blood from the lungs. The two larger, lower chambers with thick muscular walls are called the right and left** ventricles**. They pump blood to the body and the lungs.

The** septum** is the thick muscular wall that divides the heart into right and left sections. The interatrial septum separates the left and right atria, and the interventricular septum divides the right and left ventricles.

Heart wall

The heart wall is composed of three layers:

• Endocardium: The inner thin endothelial layer that lines the chambers and valves.
• Myocardium: The middle and thickest layer of the heart, composed of cardiac muscles.
• Epicardium or visceral pericardium: The outer layer that covers the heart.

A space separates the epicardium from the parietal pericardium, which loosely covers the heart like a sac. The two layers of pericardium are serous membranes. As the heart beats, the two layers rub against each other, and the moisture between the layers reduces the amount of friction.

Heart valves

The heart has valves between the chambers and the arteries. The valves allow the blood to flow in one direction. Valves are competent if they open and close properly, letting through or holding back an expected amount of blood. The heart has two sets of valves: atrioventricular (AV) valves and semilunar (SL) valves.

An AV valve is found between each atrium and ventricle. When opened, it allows blood to flow into the ventricle. When closed, it prevents the backflow of blood into the atrium. The AV valves open and close with the help of the papillary muscles. These muscles are attached to the valve by the chordae tendineae, cordlike tendons. The AV valves are located as follows:

• Bicuspid or mitral valve: Found between the left atrium and ventricle and made up of two cusp or flaps.
• Tricuspid valve: Found between the right atrium and ventricle and made up of three cusps.

The SL valves are found between the ventricles and the arteries leading out of the heart. The SL valves allow blood to flow out of the heart and prevent the backflow of blood into the ventricles. The valves are created by flaps from the pulmonary artery and aorta. The SL valves are located as follows:

• Pulmonary valve: Between the right ventricle and the pulmonary artery
• Aortic valve: Between the left ventricle and the aorta

Heartbeat

A provider listens to the heart sounds with a stethoscope. The normal sound is a lub dub. The lub sound occurs when the AV valves close as the ventricles contract. This is a lower pitch and a longer sound, which is followed by a pause. The dub sound occurs when the SL valves close. With incompetent valves, the provider might hear additional abnormal noises.

A complete heartbeat or cardiac cycle can be divided into the diastole and systole phases. During the diastole phase, the heart is at rest, and the atria fill with blood. The systole phase occurs when the heart is contracting.