The Franklin Institute, June 15, 2015
If you go inside the walls of a car factory, you’re likely to encounter many different teams doing many different things. One team might make steering wheels. Another team might make seats. Other teams may assemble different parts of the engine.
But even though each team is doing its own thing, they all share a common goal: to make cars.
Your body operates in much the same way. Different systems within your body are responsible for different jobs, yet they all share the common goal of keeping you alive.
At the center of all of this activity is the heart. You could say it acts as the factory “foreman” to set the pace and regulate all of the other body systems.
Can you guess which of the body’s systems do the following things in your factory/body?
A) Grow fingernails and toenails
B) Create the sound that doctors listen for with a stethoscope
C) Push blood throughout your entire body
D) “Feed” the heart muscle
Read about each system to check your answers.
If the heart is the foreman, the circulatory system is the second in command of your body. This system is actually in charge of three different sets of operations, all designed to constantly move your blood throughout your body.
The term “circulation” takes it roots from the word “circle.” In your body, the heart, the lungs, and the blood vessels work together to form a closed loop through which blood travels. The pulmonary circulatory system regulates the lungs, the coronary circulatory system regulates the heart, and the systemic circulatory system handles the other parts of your body.
Much like those car factory teams we talked about, each circulatory system must do its job independently in order for the circulatory system to function as a whole.
Pulmonary circulation system
Did you know that you can actually hear pulmonary circulation?
Pulmonary circulation is the movement of blood through the right side of the heart, to the lungs, and then back through the left side of the heart. The “lub dub” you hear when using a stethoscope is the sound of the ventricles contracting and the heart valves closing during this circulation process.
Blood takes a very precise route during pulmonary circulation. Two large veins called the vena cavae bring blood to the right atrium of the heart. The atrium fills with the waste-rich blood and then contracts, pushing the blood through a one-way valve down into the right ventricle.
The right ventricle fills and then contracts, pushing the blood out of the heart into the pulmonary artery, which leads to the lungs. In the lung capillaries, the exchange of carbon dioxide waste and oxygen takes place.
Fresh, oxygen-rich blood enters the pulmonary veins and then returns to the heart, re-entering the organ 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 contraction of the left ventricle forces the blood into the aorta, allowing the blood to begin its journey throughout the body.
It’s important to note that the one-way valves are important for preventing any backward flow of blood. If blood started flowing the wrong way, the blood gases (oxygen and carbon dioxide) might mix, causing a serious threat to your body.
Coronary circulation system
The heart’s job is to ensure the blood flow that provides oxygen and nutrients to the rest of the body, and that allows waste to be carried away. However, the heart also provides these important services for itself using the coronary circulation system.
When blood leaves the left ventricle of the heart through the aorta, some of that blood branches off to two coronary arteries. These narrow arteries transport oxygen-rich blood into the tissue of the heart muscle.
Cardiac veins then transport de-oxygenated blood out of the heart muscle.
From there, the blood is returned to the right atrium to move through the pulmonary circulation system again.
Systemic circulation system
The systemic circulation system supplies nourishment to all of the tissue located throughout every part of the body, minus the heart and lungs.
Blood vessels (including arteries, veins, and capillaries) are responsible for the delivery of oxygen and nutrients to the tissue. Oxygen-rich blood enters the blood vessels through the aorta. The aorta then branches into many smaller arteries that run throughout the body.
The oxygen-rich blood is transported to capillaries, where the oxygen and nutrients are released to body tissue. The capillaries also collect waste-rich blood and channel it back into the veins. The veins carry the blood back to the heart where the circulatory process begins again.
If you've ever broken a blister, you've seen lymph. It's a colorless, slightly sticky liquid produced by the lymphatic system.
The lymphatic system is a critical part of the circulatory system, helping the body to absorb nutrients and remove waste.
Lymph is made up largely of white blood cells. It is created when blood plasma escapes from the blood vessels and is absorbed into the surrounding tissue. The fluid collects in lymph tubes throughout the body. After passing through a lymph node to deposit waste, the fluid is returned to the blood.
Lymph nodes are the clumps of tissue that collect the waste deposits. Your tonsils and adenoids are two examples of lymph nodes. The lymph nodes also assist the spleen and the bones in producing new white blood cells.
Do you know what happens when you breathe?
Each respiration, or breath, allows the body to take in oxygen and expel carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.
Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose every time you breathe in. The oxygen then passes through the larynx (also known as your “voice box”) and then through the trachea to the chest cavity. The trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again, forming the bronchial tubes. The bronchial tubes lead directly into the lungs, where they divide into many smaller tubes that connect to tiny, spongy sacs called alveoli. (The average adult's lungs contain about 600 million alveoli.)
Inhaled oxygen passes into the alveoli and then diffuses through the surrounding capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.
The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. The diaphragm helps pump the carbon dioxide out of the lungs and pull the oxygen back into the lungs. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.
Believe it or not, your body is full of poison. But fear not, because your excretory system is your dedicated poison-fighting team.
Body waste that isn’t properly attended to can make you extremely ill. Your lungs, kidneys, and skin work together to ensure that waste is carried away.
During systemic circulation, blood passes through the kidneys. This phase of systemic circulation is known as renal circulation. During this phase, the kidneys filter much of the waste from the blood. Each day, your kidneys produce about 1.5 liters of waste, which is expelled from your body as urine.
Waste gases, such as carbon dioxide, are carried by blood to the lungs where respiration takes place.
Waste from dead cells and sweat are removed from the body through the skin.
The body's integumentary system supports the excretory system in the removal of waste through the skin.
The skin not only protects the body; it has another important job as well. It also provides for the removal of dead cells and sweat, which contains waste products.
Hair, fingernails, and toenails are actually accumulations of dead epidermal cells being expelled through the integumentary system. As more cells die and need to be removed, the hair and nails grow.