This next unit is all about the circulatory and respiratory system and how they work together to circulate blood and oxygen throughout the body. Air moves in and out of the lungs through the trachea, bronchi and bronchioles. Blood moves in and out of the lungs through the pulmonery arteries and veins that connect to the heart …let’s go into a bit more detail about this.


The cardiovascular system is comprised of the heart, blood vessels and blood and delivers nutrients and oxygen to all cells in the body.

The arteries carry blood away from the heart and the veins carry it back to the heart.

The system of blood vessels resembles a tree: The “trunk” – the main artery (aorta) – branches into large arteries, which lead to smaller and smaller vessels. The smallest arteries end in a network of tiny vessels known as the capillary network.

Blood flows continuously through your body’s blood vessels. Your heart is the pump that makes it all possible.

The heart works as a double circulatory system. This means two pumps that work at the same time to pump blood in two different directions.

Double circulation vector illustration. Labeled educational bloo
The right-hand side of the heart collects deoxygenated blood from the body and pumps it to the lungs (to collect more oxygen). This is called pulmonary circulation.
The left-hand side of the heart collects oxygenated blood from the heart and pumps it round the body, providing organs, tissues, and cells with blood so that they get oxygen and other vital substances.
This is called systemic circulation.


Your heart is about the size of your clenched fist. It lies in the front and middle of your chest, behind and slightly to the left of your breastbone. It’s a muscle that pumps blood to all parts of your body to provide it with the oxygen and nutrients it needs to function.

The pathway of blood flow through the heart illustration

The atria are the top two chambers of the heart that receive incoming blood from the body.  The right atrium receives deoxygenated blood through the superior and inferior vena cavas from the body and pumps it to the right ventricle through the tricuspid valve, which opens to allow the blood flow through and closes to prevent blood backing up the atrium. The left atrium receives oxygenated blood through the pulmonary veins from the lungs. It pumps the blood through the mitral valve to the left ventricle.

The ventricles are the two lower chambers of the heart, separated by a triangular wall of cardiac tissue called the Septum. The right ventricle receives oxygen-poor blood from the right atrium and pumps it through the pulmonary valve to the pulmonary artery and into the lungs to be filled with oxygen. On the other hand, the left ventricle receives oxygen-rich blood from the left atrium and pumps it through the aortic valve to the aorta to deliver the oxygen to the rest of the body.


The pulmonary arteries deliver oxygen-poor blood from the right ventricle of the heart to the lungs, while the pulmonary veins deliver oxygen-rich blood from the lungs to the left atrium of the heart.


So in a nutshell, the atria receive blood and sends it to the ventricles which are the force to push the blood to where it needs to go!

Have a look at this simple video explanation.

Let’s learn a bit more about the vessels that the blood travels through to get to its destination.


Blood vessels

The arteries carry oxygen and nutrients away from your heart to your body’s tissues.

  • Arteries begin with the aorta, the large artery leaving the heart.
  • They carry oxygen-rich blood away from the heart to all of the body’s tissues.
  • They branch several times, becoming smaller and smaller as they carry blood further from the heart.


  • Capillaries are small, thin blood vessels that connect the arteries and the veins.
  • While in the capillaries, blood gives off carbon dioxide through the capillary wall into the alveoli and takes up oxygen from air in the alveoli.


  • These are blood vessels that take oxygen-poor blood back to the heart.
  • Veins become larger and larger as they get closer to the heart.
  • The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.

Blood pressure is the force that moves blood through the circulatory system.

Blood Pressure

We have 2 types of pressure:

Systolic blood pressure (SBP) is the pressure exerted when the cardiac muscle is contracting and pumping blood .. this is the highest of your numbers.

Diastolic blood pressure (DBP) is the pressure exerted when the heart is in a relaxed state which is the time the chambers of the heart can fill with blood, and this will be your lower number.

Your blood pressure is measured in millimetres of mercury (mmHg)

The ideal blood pressure reading is around 120/80mmHg.

As a general guide:

  • ideal blood pressure is around 120/90mmHg.
  • high blood pressure is around 140/90mmHg or higher
  • low blood pressure is around 90/60mmHg or lower

Blood pressure chart

The body can direct the flow of blood to different parts of the body due to the smooth muscle found in the blood vessels.

These muscles can narrow (vasoconstrict) or widen (vasodilate)

What exactly is Blood?

Blood is the life-maintaining fluid that circulates through the entire body.

And it’s function?

Blood carries the following to the body tissues:

  • Nourishment
  • Electrolytes
  • Hormones
  • Vitamins
  • Antibodies
  • Heat
  • Oxygen
  • Immune cells (cells that fight infection)

Blood carries the following away from the body tissues:

  • Waste matter
  • Carbon dioxide

What are the components of blood? 

The components of human blood are:

Plasma – the liquid component of the blood.

Platelets (thrombocytes) – help in blood clotting.

White blood cells (leukocytes) –  help fight infections and aid in the immune process.

Red blood cells (erythrocytes) – carry oxygen from the lungs to the rest of the body, which leads us nicely to the Respiratory system …

The Respiratory System


Your respiratory system is the network of organs and tissues that help you breathe.

It includes your airways, lungs, and blood vessels. The muscles that power your lungs are also part of the respiratory system. These parts work together to move oxygen throughout the body and clean out waste gases like carbon dioxide.

What does the respiratory system do?

The respiratory system has many functions, besides helping you inhale and exhale it also:

  • Allows you to talk and smell.
  • Warms air to match your body temperature and moisturizes it to the humidity level your body needs.
  • Delivers oxygen to the cells in your body.
  • Removes waste gases, including carbon dioxide, from the body when you exhale.
  • Protects your airways from harmful substances and irritants.


What are the parts of the respiratory system?

The respiratory system has many different parts that work together to help you breathe.

The respiratory system, labeled

Your airways deliver air to your lungs. Your airways include your:

  • Mouth and nose.
  • Sinuses: Hollow areas between the bones in your head that help regulate the temperature and humidity of the air you inhale.
  • Pharynx (throat): Tube that delivers air from your mouth and nose to the trachea (windpipe).
  • Trachea: Passage connecting your throat and lungs.
  • Bronchial tubes: Tubes at the bottom of your windpipe that connect into each lung.
  • Lungs: Two organs that remove oxygen from the air and pass it into your blood.

Let’s take a closer look at the lungs

The Lungs

The lungs are located on either side of the breastbone in the chest cavity.  From your lungs, your bloodstream delivers oxygen to all your organs. When you breathe out, your blood carries carbon dioxide and other waste out of the body.

Human lungs anatomy, medically illustration
Air enters the body through the mouth or nose and quickly moves to the pharynx, or throat. From there, it passes through the larynx, or voice box, and enters the trachea.

Within the lungs, the trachea branches into a left and right bronchus. These further divide into smaller and smaller branches called bronchioles. The bronchioles lead to the alveoli, which is where the exchange of oxygen and carbon dioxide take place with the help of the capillaries. The capillaries are the blood vessels in the alveoli walls that move oxygen from the lungs to the blood stream and at the same time carbon dioxide passes from the blood to the lungs, this is known as GAS EXCHANGE.

Gas exchange allows the body to replenish the oxygen and eliminate the carbon dioxide. Doing both is necessary for survival.


The proper terminology to get the breath in and out of the body is Inspiration and Expiration. Inhale/ Exhale.

In general, two muscle groups are used during normal inspiration and these are the diaphragm and the external intercostal muscles.

Contraction of the external intercostal muscles moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity. The expiration is when the diaphragm muscles relaxes and rises, the intercostal muscles relax and this creates a positive pressure that pushes some of the air out of the lungs.

Obviously when you exercise you need more breath, and the intercostal muscles work harder on inspiration and they contract during expiration to remove more air from the lungs.

Three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs:

  • Ventilation is the process by which air moves in and out of the lungs.
  • Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the alveoli and the capillaries in the lungs.
  • Perfusion is the process by which the cardiovascular system pumps blood throughout the lungs.

Super Quick Summary

Oxygen in and Carbon Dioxide out

Oxygen from the lungs is carried by the red blood cells to the heart where it’s then pumped to the body and Carbon dioxide from the cells is carried by the red blood cells back to the heart and into the lungs


The life story of the Cardiovascular and Respiratory system


The cardiovascular and respiratory system, like everything else, grows in the early years and by the time you’re 3 your lungs and heart look like a mini version of an adults.

Your lungs mature by the time you are about 20-25 years old and when the lungs stop growing so does the size of all the major organs involved in the cardiorespiratory system. After about the age of 35, it is normal for your lung function to gradually decline. In fact as we get older, our arteries thicken, our aerobic capacity decreases, our bones get thinner and our diaphragm weakens … and this is why we need to exercise!

When you are physically active, your heart and lungs work harder to supply the additional oxygen your muscles demand. Just like regular exercise makes your muscles stronger, it also makes your lungs and heart stronger. As your physical fitness improves, your body becomes more efficient at getting oxygen into the bloodstream and transporting it to the working muscles.

Some types of exercises can be found in purestretch and yoga classes that can also strengthen the muscles of the neck and chest, including the diaphragm and the intercoastal muscles that work together to power inhaling and exhaling.

Short Term Effects of Exercise on the Cardiovascular System

Many short-term effects take place during physical activity, including:

  • Faster heart contractions. This leads to an increased heart rate and increased circulation, which gets oxygenated blood to your muscles quicker.
  • More forceful heart contractions with each heartbeat. This leads to a greater amount of blood being pumped throughout the body.

Long Term Effects of Exercise on the Cardiovascular System

A well-conditioned athlete can see long term cardiovascular effects from exercising in as little as two weeks. People who are just beginning to exercise will see effects in up to four weeks. These effects include:

  • The heart and lungs become more efficient as your cardiovascular training increases.
  • Decreased resting heart rate, which means your heart doesn’t have to beat as often to circulate blood.
  • Improved ability to draw in deeper and longer breaths and take fewer breaths.
  • Reduced risk of heart disease.

…… Exercise is a great thing!