The mass transport system in mammals is the circulatory system. This system uses the blood to transport substances between the heart and tissues.
Mass transport systems are used to carry raw materials from specialised exchange organs to the body cells and remove waste.
The bad news is this is quite a big section with a lot to get your head around, but the good news is learning how your heart works is pretty interesting!
The mass transport system is all linked to the heart in mammals. The electrical stimulation of the heart is generated by the sinoatrial node (SAN). The SAN acts as the heart’s pacemaker. It does not need stimulation from a nerve in order to contract. We refer to the heart as being myogenic.
Collagen prevents the electrical activity generated by the SAN passing directly from the atria to the ventricles. This is because collagen is non-conducting and so the electrical impulses have to pass via the atrioventricular node in order to progress any further down the heart.
Little bit confusing I know, but in simple terms the heart doesn’t need the brain to tell it to pump – it can do it automatically thanks to the SAN.
Carrying on with the formation of the heart; coronary arteries can be found on the surface of the heart muscle. They provide the heart muscle with oxygen for respiration.
The ventricles contract from the bottom upwards to ensure all the blood is squeezed from the ventricles. There can’t be any blood left in the ventricles otherwise the heart will not be performing at its maximum and the atria will not be able to empty all of their blood into the ventricles.
Ventricles have thicker walls than atria because they must pump blood further. The atria only push blood into the ventricles, whereas the ventricles have to pump the blood either to the lungs or all the way around the body. The thicker muscle can contract with greater force, and so pump blood at higher pressure.
The muscle around the left ventricle is thicker than that around the right ventricle because the left ventricle has to pump blood all the way around the body which is further than just the lung.
The left side of the heart pumps blood all the way around the body, whereas the right side of the heart only pumps blood to the lungs.
You would find the semi-lunar valve between the left ventricle and the aorta. They are there to prevent backflow of blood into the ventricles. You will also find one in-between the right ventricle and the pulmonary artery.
The bundle of His is located between both ventricles. The bundle of His carries the electrical impulse from the atrio-ventricular node (AVN) down to the base of the heart so that the impulses can spread up the side of the ventricles via the Purkyne fibres.
When the AVN receives the electrical impulse from the SAN, there is a slight delay before the impulses are sent down the bundle of His.This is to ensure the ventricles contract after the atria have completely emptied.
That was a lot of information so it’s probably not a bad idea at this point to give it a re-read and take a look at a diagram of the heart to see how all the different parts fit together.
To understand how well your heart in functioning, both cardiac output and stroke volume can be calculated.
Cardiac output is the volume of blood pumped out of the heart per minute. The heart rate is the number of beats per minute. Your heart rate can be measured by feeling your pulse. Your pulse is surges of blood forced through arteries by the heart contracting.
Your stroke volume is the volume of blood pumped during each contraction of the ventricles. This is measured in centimetres cubed. It can be calculated by using the following formula: cardiac output / heart rate.
And that’s it – you now know how hard your heart works 24/7, 365 days of the year!