Back to B2 Home
B2 I) Circulatory System – The Heart
B2 I) Circulatory System – The Heart
Humans have a double circulatory system. One circulatory system circulates blood to the lungs (the pulmonary system) and the second circulatory system circulates blood to the rest of the body (the systemic system). The heart is the pump for both of these circulatory systems. The heart pumps blood at different pressures and different rates depending on the body’s needs. For example, when we are sleeping our blood pressure and heart rate is quite low in comparison to when we are undertaking vigorous exercise. Usually when we are sitting down, our heart rate will be about 50-70 beats per minute.
The Structure of the Heart
The heart is a complex organ. There is a diagram of the heart below.
The heart is a complex organ. There is a diagram of the heart below.
Blood is pumped through the heart by a series of contractions and relaxations in the cardiac muscle walls of the four chambers. Cardiac muscle is unlike other muscles in our bodies because it never gets fatigued (tired).
We can split the heart into two separate sides; these are the left side and the right side. From looking at the diagram, you can see that the left and the right side of the heart are not the left and right side of the diagram. This is because the labels for the left and right side of the heart are for the person’s whose heart it is, so the right is the left on the diagram, and the left is the right on the diagram.
The heart is made up of four chambers; right atrium, right ventricle, left atrium and left ventricle. The right side has two chambers and the left side also has two chambers. The two chambers on the top are atria (right atrium and left atrium), and the two chambers on the bottom are ventricles (right ventricle and left ventricle).
There are also four valves in the heart; again, two on the right side and two on the left side. The valves ensure that blood travels in the correct direction through the heart; the valves prevent backflow.
We can split the heart into two separate sides; these are the left side and the right side. From looking at the diagram, you can see that the left and the right side of the heart are not the left and right side of the diagram. This is because the labels for the left and right side of the heart are for the person’s whose heart it is, so the right is the left on the diagram, and the left is the right on the diagram.
The heart is made up of four chambers; right atrium, right ventricle, left atrium and left ventricle. The right side has two chambers and the left side also has two chambers. The two chambers on the top are atria (right atrium and left atrium), and the two chambers on the bottom are ventricles (right ventricle and left ventricle).
There are also four valves in the heart; again, two on the right side and two on the left side. The valves ensure that blood travels in the correct direction through the heart; the valves prevent backflow.
Blood Vessels & The heart
There are 4 different blood vessels that enter or exit the heart. These are the vena cava, pulmonary artery, pulmonary vein and the aorta. The locations of these 4 blood vessels are shown below.
There are 4 different blood vessels that enter or exit the heart. These are the vena cava, pulmonary artery, pulmonary vein and the aorta. The locations of these 4 blood vessels are shown below.
Blood coming from the rest of the body comes into the heart through the vena cava, which is a vein. As the blood has come from the rest of the body, it will be deoxygenated blood (have a low concentration of oxygen and a high concentration of carbon dioxide). Blood then passes through the right atrium, the right ventricle and then out of the heart through the pulmonary artery to the lungs. At the lungs, oxygen diffuses from the alveoli into the bloodstream, and carbon dioxide diffuses out of the bloodstream into the alveoli, which results in blood becoming oxygenated blood (high in oxygen and low in carbon dioxide). The oxygenated blood then travels through the pulmonary vein to the left atrium in the heart. After entering the left atrium, the oxygenated blood passes onto the left ventricle and then out of the heart through the aorta; the aorta is an artery.
So, out of the 4 blood vessels for the heart, the two arteries are the pulmonary artery and the aorta. And, the two veins are the vena cava and the pulmonary vein. We will look at the differences between arteries and veins in the next section.
So, out of the 4 blood vessels for the heart, the two arteries are the pulmonary artery and the aorta. And, the two veins are the vena cava and the pulmonary vein. We will look at the differences between arteries and veins in the next section.
The Pumping Process
These are the steps in the pumping process:
These are the steps in the pumping process:
- Blood always enters the atrium of the heart through a vein. The blood enters the right atrium via the vena cava (from the rest of the body), and the blood enters the left atrium via the pulmonary vein (from the lungs).
- The walls of the atria on each side of the heart contract, which pushes blood into the ventricles of the heart (the bottom chambers of the heart).
- The walls of the ventricles then contract, which pushes blood out of the heart through arteries. The blood is pushed out of the right ventricle through the pulmonary artery (to the lungs), and out of the left ventricle through the aorta (to the rest of the body).
- The atria then fill again and the whole process repeats.
Additional Points about the Heart
Here are some additional points about the heart.
The left ventricle pumps blood around the body, and the right ventricle pumps blood to the lungs. The distance between the heart and the rest of the body is greater than the distance between the heart and the lungs. The left ventricle has a thicker wall compared to the right ventricle. This is so that the left ventricle can pump blood out of the heart with a greater force so that blood can travel this further distance.
Blood is supplied to the cardiac muscle in the walls of the heart through coronary arteries. These coronary arteries come off of the aorta, which means that they take oxygenated blood to the heart muscles. The coronary arteries then branch off into capillaries, which supply the heart muscles with everything that they need (oxygen and gluocse). The capillaries then join back up to form the coronary vein, which takes the now deoxygenated blood to the right atrium.
Here are some additional points about the heart.
The left ventricle pumps blood around the body, and the right ventricle pumps blood to the lungs. The distance between the heart and the rest of the body is greater than the distance between the heart and the lungs. The left ventricle has a thicker wall compared to the right ventricle. This is so that the left ventricle can pump blood out of the heart with a greater force so that blood can travel this further distance.
Blood is supplied to the cardiac muscle in the walls of the heart through coronary arteries. These coronary arteries come off of the aorta, which means that they take oxygenated blood to the heart muscles. The coronary arteries then branch off into capillaries, which supply the heart muscles with everything that they need (oxygen and gluocse). The capillaries then join back up to form the coronary vein, which takes the now deoxygenated blood to the right atrium.
Pacemaker
There are a group of cells located in the wall of the right atrium that act as a pacemaker (they control heart rate). These cells send out small electrical impulses to the muscle cells in the heart, which causes the muscle cells to contract
Sometimes these pacemaker cells do not work properly. This can cause an individual’s heart to beat too fast, too slow or in an irregular rhythm. If this is the case, doctors can insert an artificial pacemaker, which is a small battery-operated electrical device that sits under the skin. The device has wires that go to the heart. The artificial pacemaker sends electrical impulses along these wires to produce normal contractions in the heart. The inserting of artificial pacemakers is one of the most common heart surgeries in the UK.
There are a group of cells located in the wall of the right atrium that act as a pacemaker (they control heart rate). These cells send out small electrical impulses to the muscle cells in the heart, which causes the muscle cells to contract
Sometimes these pacemaker cells do not work properly. This can cause an individual’s heart to beat too fast, too slow or in an irregular rhythm. If this is the case, doctors can insert an artificial pacemaker, which is a small battery-operated electrical device that sits under the skin. The device has wires that go to the heart. The artificial pacemaker sends electrical impulses along these wires to produce normal contractions in the heart. The inserting of artificial pacemakers is one of the most common heart surgeries in the UK.