Cardiovascular Anatomy

• Because blood circulation is a closed-loop system, blood is contained within the heart or blood vessels at all times. 
• There are three types of blood vessels: arteries, veins, and capillaries. Arteries carry blood away from the heart, toward organs and tissues. Veins carry blood toward the heart, away from organs and tissues. Capillaries are tiny vessels that form a network around tissues.
• Arteries branch into smaller blood vessels called arterioles, which further divide into capillaries.
• The heart is a muscular organ located in the middle of the chest, behind, and slightly to the left of the breastbone (sternum). It is made up primarily of cardiac muscle and has four chambers: two upper chambers called atria and two lower chambers called ventricles. The septum is the muscular structure separating the atria from the ventricles. The heart wall has three layers that include the outer layer (pericardium), the middle layer (myocardium, where most of the cardiac muscle tissue is located), and the innermost layer (endocardium).
• In addition to the four chambers, the heart also has four valves: the tricuspid valve, the pulmonary valve, the mitral valve, and the aortic valve. These valves regulate blood flow in and out of the heart.
• • Tricuspid valve regulates blood flow between the right atrium and right ventricle.
  • Pulmonary valve regulates blood flow from the right ventricle into the pulmonary artery.
  • Mitral valve regulates blood flow from the left atrium into the left ventricle.
  • Aortic valve regulates blood flow from the left ventricle to the aorta. The aorta is the largest artery in the body.
• The aorta is the largest artery in the body.
• The heart:

  
• Capillaries have thin walls and a very large surface area. Because of the capillaries’ thin walls, blood flow slows to facilitate exchanges between blood and the body’s tissues.
• Blood flows continuously in one direction, starting from the heart and moving towards the arteries, arterioles, and capillaries. Once blood reaches the capillaries, it interacts with the tissues through exchange. After this exchange, the blood is collected into venules, which then connect to veins and eventually return to the heart's atrium. For blood circulation to begin, the heart must relax between two heartbeats.
• Two types of circulatory processes occur in the body: Systemic circulation and Pulmonary Circulation.
• In Systemic circulation:

  1. The pulmonary vein pushes oxygenated blood into the left atrium.
  2. As the atrium relaxes, oxygenated blood drains into the left ventricle through the mitral valve.
  3. The left ventricle pumps oxygenated blood to the aorta.
  4. Blood travels through the arteries and arterioles before reaching the capillaries that surround the tissues.
• Systemic circulation diagram:

  
• In Pulmonary circulation:

  1. It has two major veins, the Superior Vena Cava and the Inferior Vena Cava, which bring deoxygenated blood from the upper and lower halves of the body.
  2. Deoxygenated blood is pooled into the right atrium and then sent into the right ventricle through the tricuspid valve, which prevents blood from flowing backward.
  3. The right ventricle contracts, causing the blood to be pushed through the pulmonary valve into the pulmonary artery.
  4. Deoxygenated blood becomes oxygenated in the lungs.
  5. Oxygenated blood returns from the lungs to the left atrium through the pulmonary veins.
• Pulmonary Circulation diagram:

  
• Keep in mind: Blood pressure is regulated by the body and is directly proportional to blood volume. The higher the blood volume, the higher the blood pressure, and the lower the blood volume, the lower the blood pressure.
• The complete cycle beginning with atrial contraction and ending with ventricular contraction is called the cardiac cycle. When the heart contracts and pumps blood into systemic circulation, this is called systole. Diastole refers to the period of relaxation when the heart chambers fill with blood.
• Because the heart is a muscle, it transmits electrical impulses (courtesy of the nervous/neural tissue) that cause the heart to contract. This electrical activity can be recorded using an electrocardiogram, or EKG.
• An EKG is a graph that shows the heart’s rate and rhythm over a period of time, and waves in an EKG graph represent the electrical activity of the heart and have different meanings.

  
• P wave = atrial systole. QRS complex (the combination of Q, R, and S waves) = ventricular systole. T wave = ventricular diastole. ST segment = flat line between S and T wave.