12.1: The Cardiovascular System

Activity: Your heart and breath

Before you begin this chapter, take a moment to feel your heart and your breathing.

• Take your pulse.
  • Count how many times your heart beats in one minute.
  • In your wrist:
    • hold out one of your hands, with your palm facing upwards
    • press the first (index) finger and middle finger of your other hand on the inside of your wrist, at the base of your thumb – don’t use your thumb as it has its own pulse
    • press your skin lightly until you can feel your pulse – if you can’t find it, try pressing a little harder or move your fingers around
  • In your neck:
    • press your first finger and middle finger to the side of your neck, just under your jaw and beside your windpipe – don’t use your thumb
    • press your skin lightly to feel your pulse – if you can’t find it, try pressing a bit harder or move your fingers around
• Measure your respiratory rate
  • Count how many times you inhale and exhale in one minute.
• Multiple your one minute pulse and your one minute count of breaths by 1,440 to see how many times your heart beats and how many times you inhale/exhale in one day

If your heart beats 75 times per minute, it would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Your heart is an amazing organ that works all day, everyday, to ensure all of the cells, tissues, and organs in your body get the oxygen and nutrients needed to survive, while also removing carbon dioxide and waste by pumping about 2,000 gallons of blood around your body. This is a lot of work for an organ about the size of your fist that weighs less than a pound.

The heart is the power, or the pumping force, behind the circulation of blood through the body. Every time your heart beats it is contracting in order to push blood, much like you would squeeze a plastic ketchup bottle and push out ketchup. The heart is just one part of the cardiovascular system, the other part are the vessels through which blood travels through the body. The heart and blood vessels are a closed-loop system, where blood moves in one direction to and from your heart.

The heart has two halves, each with atria and ventricles known as the right atrium, right ventricle, left atrium, and left ventricle. As a closed-loop system, blood moves through the heart in a precise pattern.

• Deoxygenated blood enters the heart through the largest vein of the body called the superior vena cava
• The deoxygenated blood first enter the heart through the right atrium.
• The blood is then pushed down into the right ventricle.
• The deoxygenated blood now leaves the heart to go to the lungs and pick up oxygen.
• Oxygenated blood then returns to the heart through the left atrium.
• The blood is pushed into the left ventricle.
• Lastly the oxygenated blood leaves the heart to go to the body through the largest artery of the body called the aorta.

Each side of the heart plays an important role in the circulation of blood. The right side of the heart is responsible for circulating the deoxygenated blood to the lungs to pick up oxygen, called pulmonary circulation, and the left side of the heart is responsible for circulating the blood to the rest of the body, called systemic circulation.

Figure \(\PageIndex{1}\): Position of the heart in the body

The three main types of blood vessels that transport blood throughout the body are the arteries, veins, and capillaries. In short, arteries are large blood vessels that carry blood away from the heart, veins are large blood vessels that carry blood to the heart, and capillaries are the small blood vessels that delivery oxygenated blood to organs and tissues and pick up deoxygenated blood from organs and tissues for the veins to take back to the heart. You might think of arteries and veins as big freeways or highways and the capillaries as the neighborhood streets, both working to provide a pathway to deliver food and take away waste.

In pictures of the circulatory system, arteries are typically represented by red blood vessels and veins are typically represented as blue blood vessels. Red is used for arteries because most arteries carry oxygenated blood, or red blood. Veins typically carry deoxygenated blood, or blue blood. The faster the heart beats, the more oxygen and nutrients are transported throughout the body.

Figure \(\PageIndex{2}\): Arteries, capillaries, and veins

Figure \(\PageIndex{3}\): Blood flow through the heart

Each beat of the heart helps to keep the blood moving within the closed system, however the heart has an additional feature that helps to keep the blood moving in one direction and these are called heart valves. Heart valves ensure unidirectional blood flow through the heart. Valves operate link french doors that open when the heart contracts and close when the heart is at rest. The four valves in the heart are the tricuspid valve, pulmonary valve, bicuspid valve, and aortic valve.

Figure \(\PageIndex{4}\): Circulation of blood through the heart

You do not tell you heart to beat, rather your heart beats automatically. For example, when your body needs more oxygen, such as when exercising, your bodies autonomic nervous system tells your heart to speed up to pump more blood throughout your body. The Autonomic nervous system specifically sends messages to a specialized group of cells located high in the right atrium, called the Sinoatrial Node, or SA node. The SA node is commonly referred to as the pacemaker of the heart and is responsible for normal cardiac rhythm by sending an electrical signal that makes the heart contract.

Figure \(\PageIndex{5}\): Conduction System of The Heart

The contraction of the heart is called systole and the relaxation of the heart is called diastole. Imagine clenching and relaxing your fist, when it is clenched that is representing systole and when it is relaxed that is diastole. When the heart contracts (systole) and pushes blood from the heart into the blood vessel (artery) it puts pressure on the blood vessel walls. When the heart relaxes (diastole) the pressure on the blood vessel walls lowers. By measuring the pressure in the blood vessel we can better understand the health of the heart and blood vessels. Measuring the pressure created in the blood vessel is known as your blood pressure. When you get your blood pressure tested they give you two numbers, the top number is the pressure created during systole and the bottom number is the pressure created during diastole. Thus, blood pressure readings are read as systolic over diastolic pressure. Average blood pressure is considered to be 120/80 (systolic/diastolic). If the pressure increases to 140/90 you are considered to have high blood pressure.

Manually pumping blood: CPR

If the heart stops beating, the blood can be manually pumped by using an emergency technique known as cardiopulmonary resuscitation (CPR). When performing CPR, repeated pressure is placed on the heart to push the blood through both the pulmonary and systemic circuits. This is particularly critical for the brain, as irreversible damage and death of neurons occur within minutes of loss of blood flow.

Trained first responders will perform both chest compressions and mouth-to-mouth breathing. However, bystanders should perform compression-only CPR.

1. Call 9-1-1 (or send someone to do that)
2. Push hard and fast in the center of the chest

Current standards call for compression of the chest at least 5 cm deep and at a rate of 100-120 compressions per minute, a rate equal to the beat in “Staying Alive,” recorded in 1977 by the Bee Gees.

Figure \(\PageIndex{6}\): CPR Hand Placement