The Circulatory System

What Does The Circulatory System Do?

Your circulatory system delivers oxygen, nutrients and hormones to the cells of your body and removes waste material that the cells produce, such as carbon dioxide.

Circulatory System

What Makes Up The Circulatory System?

The circulatory system consists of your heart, blood and blood vessels.


The Human HeartYour heart is a muscle about the size of your fist which is located in the center of your chest, slightly to the left.

Your heart’s main function is to propel blood throughout the body. To do this, it usually beats from 60 to 100 times per minute, about 100,000 times a day, more than 30 million times per year, and about 2.5 billion to 3 billion times in a 70-year lifetime. All involuntarily, without you having to even think about it.

Your heart has four chambers: left atria, right atria, left ventricle and right ventricle.

The left and right ventricles are located at the bottom of the heart and pump blood out of the heart. A wall called the interventricular septum divides the ventricles.

The left and right atria, located in the upper part of your heart, receive blood entering the heart. A wall called the interatrial septum divides the right and left atria, which are separated from the ventricles by the atrioventricular valves. The tricuspid valve separates the right atrium from the right ventricle, and the mitral valve separates the left atrium and the left ventricle.

There are two other cardiac valves which separate the ventricles and the large blood vessels that carry blood leaving the heart. The pulmonic valve separates the right ventricle from the pulmonary artery which leads to the lungs, and the aortic valve separates the left ventricle from the aorta, the body’s largest blood vessel. The purpose of these valves is to keep blood flowing in one direction and not to flow backwards.


5 Interesting Facts About The Circulatory System

  1. As an adult, you have about 5 quarts of blood.
  2. If connected end-to-end, your blood vessels would be about 60,000 miles long. That’s enough to circle the equator more than twice! (The circumference of the earth is 24,901 miles.)
  3. Over a 70-year lifetime, your heart will beat about 2 ½ to 3 billion times.
  4. About 1 to 2 gallons of blood are pumped through your heart every minute of the day.
  5. One drop of blood contains ½ drop of plasma, 5,000,000 red blood cells, 10,000 white blood cells and 250,000 platelets.

Your blood, which is constantly circulating through your body, has four components: red blood cells, white blood cells, platelets and plasma.

  • Red Blood Cells

    Red Blood Cells pick up oxygen in the lungs and transport it to all the body cells. After delivering the oxygen to the cells, Red Blood Cells gather up the carbon dioxide, a waste gas produced by our cells, and transport it back to the lungs where it is removed from the body when we exhale.

  • White Blood Cells

    White Blood Cells attack and destroy germs when they enter the body. When you have an infection, your body will produce more White Blood Cells to help fight an infection. When more germ fighting is necessary, your doctor may prescribe antibiotics which help your White Blood Cells fight infections.

  • Platelets

    Platelets help stop bleeding. When we cut ourselves, blood leaks out from the broken blood vessel(s). In order to plug the holes where the blood is leaking from, the platelets start to stick to the opening of the damaged blood vessels. As the platelets stick to the opening of the damaged vessel they attract more platelets, fibers and other blood cells to help form a plug to seal the broken blood vessel. When the platelet plug is completely formed the wound stops bleeding. What do we call these platelet plugs? Scabs.

  • Plasma

    Plasma is a yellowish liquid that is mostly water. But it also carries important nutrients, hormones, and proteins throughout the body. Nutrients are chemicals from the food you eat that give your body energy and other things your body’s cells need to do their work and keep you healthy.

    Hormones carry messages throughout your body, telling it what to do and when. An example of a hormone is growth hormone. It gets your bones and muscles to grow.

    Plasma also carries away cell waste — chemicals that the cell doesn’t want anymore.

    Nutrients, hormones, proteins, and waste are dissolved in the plasma — kind of like the cocoa mix that dissolves in a cup of hot water. What are the marshmallows? The blood cells — they float in the plasma.

    Where do these blood components come from? Well, Plasma is absorbed from the intestines, with the liver supplying important proteins. And Red Blood Cells, White Blood Cells and Platelets are made by the bone marrow, which is a soft tissue inside of our bones.

Blood Types. Although all blood is made of the same basic elements, not all blood is alike. There are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells. The four blood types are: A, B, AB and O. In addition, there is a third antigen, called Rh factor, which can be either present (+) or absent ( – ), making the total number of possible blood groups eight.


Blood Vessels

There are three types of blood vessels — arteries, capillaries and veins.

  • Arteries

    Arteries carry blood away from the heart. They are the thickest blood vessels, with muscular walls that contract to keep the blood moving away from the heart and through the body. In systemic circulation, oxygen-rich blood is pumped from the heart into the aorta. This huge artery curves up and back from the left ventricle, then heads down in front of the spinal column into the abdomen. Two coronary arteries branch off at the beginning of the aorta and divide into a network of smaller arteries that provide oxygen and nourishment to the muscles of the heart.

    Unlike the aorta, the body’s other main artery, the pulmonary artery, carries oxygen-poor blood. From the right ventricle, the pulmonary artery divides into right and left branches on the way to the lungs where blood picks up oxygen.

    Arterial walls have three layers:

    The endothelium is on the inside and provides a smooth lining for blood to flow over as it moves through the artery.

    The media is the middle part of the artery, made up of a layer of muscle and elastic tissue.

    The adventitia is the tough covering that protects the outside of the artery.

    As they get farther from the heart, the arteries branch out into arterioles, which are smaller and less elastic.

  • Capillaries

    Capillaries are tiny blood vessels as thin or thinner than the hairs on your head. (Well, not thinner than the hairs on my head. Nothing is thinner than the hairs on my head.) Though tiny, the capillaries are one of the most important parts of the circulatory system because it’s through them that nutrients and oxygen are delivered to the cells. In addition, waste products such as carbon dioxide are also removed by the capillaries.

  • Veins

    Veins carry blood back to the heart. They’re not as muscular as arteries, but they contain valves that prevent blood from flowing backward. Veins have the same three layers that arteries do, but are thinner and less flexible. The two largest veins are the superior (above the heart) and inferior (below the heart)) vena cavae.

How Does The Circulatory System Work?

Actually, there are three circulatory systems that work both independently and together: pulmonary circulation, heart circulation and systemic circulation.

Pulmonary Circulation

Pulmonary Circulation is the movement of blood from the heart to the lungs and back to the heart again.

The veins bring waste-rich and oxygen-poor blood back to the heart, entering the right atrium throughout two large veins called vena cavae. The right atrium fills with the waste-rich blood and then contracts, pushing the blood through a one-way valve into the right ventricle. The right ventricle fills and then contracts, pushing the blood into the pulmonary artery which leads to the lungs. In the lung capillaries, the exchange of carbon dioxide and oxygen takes place. The fresh, oxygen-rich blood enters the pulmonary veins for the return trip to the heart, re-entering through the left atrium. The oxygen-rich blood then passes through a one-way valve into the left ventricle where it will exit the heart through the main artery, called the aorta. The left ventricle’s contraction forces the blood into the aorta and the blood begins its journey through your body.

The one-way valves are important for preventing any backward flow of blood. The circulatory system is a network of one-way streets. If blood started flowing the wrong way, the blood gases (oxygen and carbon dioxide) might mix, causing a serious threat to your body.

Systemic Circulation

Systemic circulation supplies nourishment to all of the tissue located throughout your body, with the exception of the heart and lungs because they have their own systems. Systemic circulation is the major part of the overall circulatory system and it is what we normally think of when we refer to circulation.

The blood vessels (arteries, veins, and capillaries) are responsible for the delivery of oxygen and nutrients to the tissue. The forceful contraction of the heart’s left ventricle forces the blood into the aorta which then branches into many smaller arteries which run throughout the body. Because the inside layer of an artery is very smooth, the blood flows quickly. The outside layer of an artery is very strong, allowing the blood to flow forcefully. The oxygen-rich blood enters the capillaries where the oxygen and nutrients are released. The waste products are collected and the waste-rich blood flows into the veins in order to circulate back to the heart where pulmonary circulation will allow the exchange of gases in the lungs.

Coronary Circulation

What’s the third type of circulation? Let’s not forget that, just like all other cells, the heart needs nourishment, too. Coronary Circulation refers to the movement of blood through the tissues of the heart.

What Can Go Wrong With Your Circulatory System?

Problems with the Circulatory system are common — more than 64 million Americans of all ages have some type of cardiac problem.

These are some of the most common heart and circulatory problems . . .

Congenital Heart Defects

These abnormalities in the heart’s structure are present at birth. Approximately 8 out of every 1,000 newborns have congenital heart defects ranging from mild to severe. These defects occur while the fetus is developing in the mother’s uterus and it’s not usually known why they occur. What all congenital heart defects have in common, however, is that they involve abnormal or incomplete development of the heart.

A common sign of a congenital heart defect is a heart murmur — an abnormal sound (like a blowing or whooshing sound) that’s heard when listening to the heart.


Cardiac arrhythmias, also called dysrhythmias or rhythm disorders, are problems in the rhythm of the heartbeat. They may be caused by a congenital heart defect or they may be acquired later. An arrhythmia may cause the heart’s rhythm to be irregular, abnormally fast, or abnormally slow. Arrhythmias can occur at any age. Depending on the type of rhythm disorder, an arrhythmia may be treated with medication, surgery, or pacemakers.


This chronic disease causes the heart muscle (the myocardium) to become weakened. Usually, it first affects the lower chambers of the heart, the ventricles, and then progresses and damages the muscle cells and even the tissues surrounding the heart. In its most severe forms, it can lead to heart failure and even death.

Coronary Artery Disease

The most common heart disorder in adults, coronary artery disease, is caused by atherosclerosis. Deposits of fat, calcium, and dead cells, called atherosclerotic plaques, form on the inner walls of the coronary arteries and interfere with the smooth flow of blood. Blood flow to the heart muscle may even stop if a thrombus, or clot, forms in a coronary vessel, which may cause a heart attack. In a heart attack (or myocardial infarction), the heart muscle becomes damaged by lack of oxygen, and unless blood flow returns within minutes, muscle damage increases and the heart’s ability to pump blood is compromised.

Hypercholesterolemia (high cholesterol)

Cholesterol is a waxy substance that’s found in the body’s cells, in the blood, and in some foods. Having too much cholesterol in the blood, also known as hypercholesterolemia, is a major risk factor for heart disease and can lead to a heart attack.

Cholesterol is carried in the bloodstream by lipoproteins. Two kinds — low-density lipoproteins (LDL) and high-density lipoproteins (HDL) — are the most important. High levels of LDL cholesterol (the bad cholesterol) increase a person’s risk for heart disease and stroke, whereas high levels of HDL cholesterol (the good cholesterol) can protect against these.

A blood test can indicate if someone’s cholesterol is too high. A normal level of overall cholesterol is under 200 milligrams per deciliter.

Hypertension (High blood pressure)

Over time, high blood pressure can damage the heart, arteries, and other body organs. Symptoms can include headache, nosebleeds, dizziness, and lightheadedness.

What Is Blood Pressure? Blood pressure is the force of blood against the walls of arteries. Blood pressure is recorded as two numbers—the systolic pressure (as the heart beats) over the diastolic pressure (as the heart relaxes between beats). The measurement is written one above or before the other, with the systolic number on top and the diastolic number on the bottom. For example, a blood pressure measurement of 120/80 mmHg (millimeters of mercury) is expressed verbally as “120 over 80.” Normal blood pressure is less than 120 mmHg systolic and less than 80 mmHg diastolic



Strokes occur when the blood supply to the brain is cut off or when a blood vessel in the brain bursts and spills blood into an area of the brain causing damage to brain cells.

How Do Your Keep Your Circulatory System Healthy?

To keep your circulatory system healthy, follow these 3 rules . . .

  1. Exercise regularly. A sedentary (inactive) lifestyle is one of the top risk factors for heart disease. Fortunately, it’s a risk factor that you can do something about. Regular exercise, especially aerobic exercise, has many benefits. It can 1)Strengthen your heart and cardiovascular system, 2) Improve your circulation and help your body use oxygen better, 3) Improve your heart failure symptoms, 4) Increase energy levels so you can do more activities without becoming tired or short of breath, 5) Increase endurance, and 6) Lower blood pressure, among other benefits.

  2. Make healthy food choices most of the time. Avoid saturated fats and trans fats. When you do use fats, choose monounsaturated fats, such as olive oil or canola oil. Polyunsaturated fats, found in nuts and seeds, also are good choices for a heart-healthy diet.

  3. Don’t Smoke!

This article is part of a series called “Your Body: An Owner’s Manual” which explains how your body systems work and how to maintain them. The first article in the series included a picture of my wife, fitness coach Kathie Lamir, who exemplifies a healthy body. Pictures of Kathie were so well received that I have included one with each article in the series

Fitness Queen Kathie Lamir

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