The Cardiovascular System

The cardiovascular system is composed of the heart and all the body's blood vessels. The blood vessels can be further broken into arteries, veins and capillaries. Arteries carry blood from the heart to capillaries, where nutrients and waste products are exchanged with various tissues. Veins are responsible for transporting blood back to the heart. Pulmonary circulation consists of blood flow between the heart and lungs. Systemic circulation involves the transport of blood between the heart and the rest of the body. The following sections will examine each topic in further detail:

Anatomy and Blood Flow of the Heart

The heart, roughly the size of a fist, is composed of cardiac muscle tissue under control of the autonomic nervous system. It is separated into four chambers, the left and right atria and the left and right ventricles. The upper atria collect blood and pass it to the lower ventricles. The right ventricle is responsible for pumping blood to the lungs to be oxygenated while the left ventricle pumps blood to the rest of the body.

The heart is located slightly to the left of your mid-chest and beats about 70 bpm for the average person. Through cardio training, the cardiac muscle of the heart would thicken and be made more efficient to pump more blood with each beat.

The following list chronicles the sequence of blood flow through the heart's major parts, starting with the veins that deposit deoxygenated blood into the right atrium:

Diagram of the Human Heart
  • Superior and Inferior Vena Cava: respectively receiving deoxygenateddblood from the upper and lower body, the vena cava attaches to the right atrium of the heartblood from the upper and lower body, the vena cava attaches to the right atrium of the heart

  • Right Atrium: the deoxygenated blood flows through the tricuspid valve into the the right ventricle. Any blood remaining would be pumped into the right ventricle when the atrium contracts.

  • Right Ventricle: the deoxygenated blood is pumped through the pulmonary semilunar valve into the pulmonary artery.

  • Pulmonary Artery: this carries the blood into the lungs to become oxygenated and remove carbon dioxide waste.

  • Pulmonary Vein: this returns the oxygen-rich blood to the left atrium.

  • Left Atrium: passes the oxygenated blood through the bicuspid valve into the left ventricle. Any remaining blood is pumped into the ventricle when it contracts.

  • Left Ventricle: the contraction of the left ventricle pumps the blood into the aorta and is a significant contributor to the blood pressure that drives the blood through the systemic circuit.

  • Aorta: this is the largest artery in the body and carries the oxygenated blood to the rest of the body's tissues.

Pulmonary Circulation

As mentioned, the pulmonary circuit delivers deoxygenated blood from the right ventricle to the lungs. There, the blood is passed in the lung's alveoli, where the pulmonary capillaries are, and oxygen is picked up and carbon dioxide is deposited. The oxygen rich blood is then passed back into the heart through the left atrium.

Systemic Circulatory Components

  1. Aorta: this large artery connects from the left ventricle and branches out into smaller arteries.

  2. Arteries: these blood vessels are smaller in diameter than the aorta and are characterized by thick walls made of smooth muscle and elastic tissue that allow it to maintain a high blood pressure.

  3. Arterioles: Even smaller than arteries, arterioles branch out from arteries. Arterioles have valves and smooth muscles that allow the control of blood distribution. For instance, during exercise vasoconstriction of specific arterioles stems blood flow to the digestive system while vasodilation of other arterioles increase blood flow to the muscles under stress.

  4. Capillaries: these are the smallest blood vessels and branch from the arterioles. As a result, a large cross-sectional area is created and both blood pressure and flow speed would decrease. This is to facilitate the exchange of nutrients, oxygen and carbon dioxide between the blood and the working cells of the body.

  5. Veins: the capillaries reform to larger veins that carry the deoxygenated blood back to the heart. One-way valves and the contractions of surrounding skeletal muscle help push the blood forward after the large pressure drop in the capillaries.

  6. Superior / Inferior Vena Cava: the superior and inferior vena cava collects deoxygenated blood from the veins and passes it to the right atria. The superior vena cava receives blood from veins of the upper body (ex. head, shoulders and arms) and the inferior vena cava receives blood from veins of the lower body (ex. torso and legs).

Related Pages:

Testing Cardio Fitness - Use the 1.5 Mile Walk/Run Test to evaluate your current cardio fitness level and find out how you can improve.

Borg Rating of Perceived Exertion and Talk Test - Determine how hard you are training with this set of simple tests.

Cardiovascular Functions - Not a physiology major? No problem. Here's a VERY SIMPLE overview of your heart and lungs and how they function.