A Survey of Major Cardiovascular System Structures for the EMT Exam

Familiarize yourself with the cardiovascular system for the EMT exam. The cardiovascular system is broken down into three broad areas: the heart, the vasculature, and the blood. They interact closely to be able to create enough pressure in the system to produce perfusion (more commonly known as circulation).

The heart is the sophisticated pump that powers the cardiovascular system. Its four chambers can be divided in two ways:

• Top and bottom, or the atria and ventricles, respectively

• Right and left, or pulmonary and peripheral circulation, respectively

  

  Credit: Illustration by Kathryn Born, MA

One-way valves separate the atria from the ventricles, and pulmonary circulation from peripheral circulation. This structure has the effect of forcing blood to move in one direction only, starting with blood entering the heart from the right atrium and exiting to the body through the left ventricle.

Blood is fluid that’s comprised primarily of plasma, which contains mostly water along with various salts, minerals, and proteins. Red blood cells (erythrocytes) carry most of the oxygen you need to live. White blood cells (leukocytes) fight off infection and are part of your immune system.

Platelets begin the coagulation, or clotting, process when a tear in the vasculature is detected. Carbon dioxide, nutrients such as glucose, and waste such as urea are carried in the plasma.

You’ve probably heard the phrase, “Blood is thicker than water.” Well, besides having to do with the relatives you’re born with, it is indeed true that blood has a consistency, or viscosity, that’s slightly heavier than water. The cardiovascular system relies on this viscosity to help create pressure within the vasculature.

The vasculature is the combination of pipes that the heart pumps blood into, creating pressure. The arterial side of the vasculature carries blood away from the heart, either to the lungs via the pulmonary artery to pick up oxygen or to the rest of the body via the aorta to deliver oxygen to the body in the peripheral circulation.

Arteries are made of smooth muscle and have the ability to stretch and snap back to their original shape, which helps tremendously with the flow of blood. They can also constrict and dilate, depending on the demands of the tissue for oxygen and nutrients.

Arteries divide into smaller vessels called arterioles, which divide again numerous times and finally terminate in capillary beds within the tissues. Gas exchange occurs at the capillary beds. Diffusion of CO₂ and oxygen occurs based on the concentration of each gas between the capillary and the tissue cells.

The heart itself has its own vasculature. Coronary arteries branch off right where the aorta exits the left ventricle, and they supply the heart tissue, or myocardium.

Helping to return blood back to the heart is the venous system. Blood leaves the venous side of the capillary beds, collecting in venules. They, in turn, collect into veins. The veins are much more rigid than the arteries, which helps to maintain blood pressure as blood returns to the heart. Inside the veins are one-way valves that again force blood to travel in one direction.

All together, these vessels create a closed system of pipes that, with the heart acting as a pump, creates a pressure within itself. You measure that pressure with a blood pressure cuff. By measuring the patient’s blood pressure early in your assessment, you can get a sense of how well the system is working.

Credit: Illustration by Kathryn Born, MA

The heart, blood and vasculature make up a perfusion triangle, where all three parts interact with each other to create circulation. In reality, you measure perfusion by assessing the patient’s blood pressure.