????️ Circulation

The circulatory system


Blood vessels



Control of heart rate

Interpreting heart function data



Coagulation (clotting)







The circulatory system




In my quest to find a suitable diagram for the heart, this is what I found:



Definitely use your textbook as a guide on this. It only takes a google search to realise the ridiculous number of variations of diagrams for the heart and different annotations.


You need to be able to sketch a heart and label the main veins, valves, arteries and aorta, and the ventricles and atria.


There are two types of circulation going on via the heart: pulmonary circulation and systemic circulation. Pulmonary circulation is a short-distance route between the heart and the lungs, where deoxygenated blood is taken to be replenished with oxygen. Although normally veins take blood away, and arteries take blood to, in the case of pulmonary circulation things are the opposite way around. The pulmonary vein brings freshly oxygenated blood into the heart – left atrium -, while the pulmonary artery takes deoxygented blood back from the right ventricle into the lungs.


Here’s a quick nifty video that shows what happens as the bigger picture…



The advantages of double circulation in mammals as opposed to single circulation (such as in bony fish) include the option to have a higher blood pressure and splitting oxygenated and deoxygenated blood. As blood gets oxygenated in the lungs, the diffusion process takes time, which has the blood at lower pressure. On the other hand, the already oxygenated blood can be pumped around the body at higher pressure, allowing for bigger organisms and increased metabolic activity. Splitting deoxygenated blood from oxygenated blood is key to this.


The atrioventricular valves and semilunar valves play an important role in ensuring proper heart function. The former ensure no blood flows back into the atria from the ventricles, while the latter ensure no blood flows from the ventricles into the atria.


Electrical impulses cause heart muscle contraction which creates an increased pressure of blood, resulting in it being pushed in a certain direction, with the valves opening in its way. The sequence of events in heart contraction is this:


Both atria contract – atrial systole

Both ventricles contract – ventricular systole

All chambers relax – diastole


The heart muscle contracts without brain stimulation – the brain only controls the speed. Electrical impulses start in the..

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