Video: Anatomy of the heart
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Okay, I'm so excited to start this quiz. Let's start with the first question. The narrowing of the inner walls of which type of exemplary structure is the most frequent cause of heart attack – hmm,... Read more
Okay, I'm so excited to start this quiz. Let's start with the first question. The narrowing of the inner walls of which type of exemplary structure is the most frequent cause of heart attack – hmm, I don't know, but we'll try another one. As the tricuspid valve opens, which structure is filled with deoxygenated blood? Okay, shoot. I always get valves confused somehow. Next one! Which heart valves are open during ventricular diastole? And my answer is – not a clue. And what on earth is the cor-on-ary sinus? Oh man – I am going to fail so bad.
Hang on a minute! It' not that bad. You just need to get back to the basics, get the right resources to help you out, and for goodness sake, stop watching Netflix for the next 10 minutes if you can. We’ll give these questions another try in just a short while – after we get to grips with heart anatomy 101.
So, learning about the heart need not be a fog of mystery and confusion. In fact, it can actually be pretty straightforward. You just need to break it down into manageable parts like these to help you master this topic. So, we know that the heart is a muscular organ which pumps blood around the body. It is located in the middle mediastinum, which is a fancy name for a space between your two lungs, and covered in a strong fibrous double-layered sac known as the pericardium.
Let's take a look at the general anatomy of the heart. It has five surfaces, and to understand how they are oriented, you need to think of the heart as being positioned like an overturned pyramid. This will help you remember that the base of the heart is actually its posterior surface, the diaphragmatic surface is the inferior surface which as the name suggests faces the respiratory diaphragm underneath the heart, the part facing the sternum and the ribs is known as the anterior surface, and finally, we have left and right pulmonary surfaces facing the lungs.
In addition to knowing your surfaces, you'll need to remember also that there are four margins of the heart. The right margin is the small section between these two big vessels here, which are the superior and inferior vena cavae. The left is along the left ventricle as far as the left auricle, which is this flap-like extension here. The inferior border is formed mainly by the right ventricle and meets the left border at the apex of the heart. And, finally, we have the superior border seen here, along the atria and great vessels at the top of the heart.
The final major point to remember in learning the basic anatomy of the heart is that it contains four chambers through which blood flows into and out of the heart – the right atrium and ventricle which pump deoxygenated blood to the lungs and the left atrium and ventricle which pump oxygenated blood to the rest of the body. These chambers are separated by interatrial, interventricular, and atrioventricular septa.
And that basically covers the general anatomy of the heart except for one particular important topic, which are the heart valves. Let's take a quick look.
Between the chambers of the heart and vessels which carry blood away from the heart are critical structures known as heart valves, which ensure the unidirectional flow of blood through your heart. The cusps, or the leaflets, are pushed open to allow blood flow in one direction and then closed to seal the orifices and prevent the backflow of blood into the chamber from which it came. The opening and closing of these valves is also what creates the well-known lub-dub sound of the heartbeat.
There are two sets of valves – atrioventricular and semilunar. The atrioventricular valves prevent backflow from the ventricles to the atria. The right atrioventricular or tricuspid valve is between the right atrium and right ventricle. It gets the name tricuspid because it has three cusps or leaflets. The left atrioventricular or bicuspid valve, on the other hand, is also called the mitral valve since it only has two cusps and resembles a miter in shape. It lies between the left atrium and the left ventricle.
Semilunar valves prevent backflow from the great vessels to the ventricles of the heart – and here they are. The pulmonary semilunar valve is between the right ventricle and the opening of the pulmonary trunk. It has three cusps or leaflets, while the aortic semilunar valve is between the left ventricle and the opening of the aorta. It, too, has three semilunar cusps or leaflets.
If you're not sure you can remember all of the valve names, let me give a trusty study hack with the mnemonic, Try Pulling My Aorta. That's all I'm going to say about the valves of the heart for now, but let's earmark these resources for later study when we want to look at these structures in more detail.
Now that we have looked at the anatomy of the heart, let's take a practical look at how the blood flows through the heart.
So, the blood flow through the heart is quite logical. It happens in tandem with the heart cycle which consists of the periodical contraction and relaxation of the muscular walls of the atrial and ventricular myocardium. Two important terms which you should know in relation to this are systole which is the period of contraction of the ventricular walls and opening of the semilunar valves, while the period of ventricular relaxation and the opening of the atrioventricular valves is called diastole.
Note that whenever the atria contract, the ventricles are relaxed and vice versa. The right atrium receives deoxygenated blood from the superior and inferior vena cavae as well as the coronary sinus, which we will look at in a moment. When the right atrium contracts, it pushes blood through the right atrioventricular valve into the right ventricle. The right ventricle then contracts passing the blood into the pulmonary trunk via the pulmonary valve to reach the lungs.
In the lungs, the blood gets oxygenated and makes its way back to the heart entering the left atrium through the pulmonary veins. The left atrium contracts and pushes the blood into the left ventricle through the left atrioventricular valve. The left ventricle pushes oxygenated blood through the aortic semilunar valve into the aorta through which blood is distributed throughout the body.
Now I promised I would keep this brief, so let's quickly look at one last topic – the coronary circulation.
When we think about the heart, we think about an organ pumping blood to all the other organs and tissues of the body, right? Well, in addition to that, it also pumps blood to itself because, after all, it never takes a break from its critical task of pumping blood. This results in the heart having a very high nutrient need and similar critical need of having waste products removed from its tissue. To do this, the heart has its own network of arteries and veins which make up what's called the coronary circulation.
The coronary arteries arise from the aortic sinuses of the beginning of the ascending aorta and then circle the heart giving off several branches. In this way, oxygenated blood reaches every part of the heart. Interesting fact - narrowing of the inner walls of the coronary arteries can lead to ischemia or reduced blood supply to cardiac muscle. This is the most common cause of what we refer to as a heart attack.
Venous blood in the heart is collected into the cardiac veins. All of the cardiac veins drain to the posterior aspect of the heart to what's known as the coronary sinus – a large vessel that delivers deoxygenated blood from the heart muscle to the right atrium.
Now you know Kenhub has got you covered with lots of resources about all the specific branches of the major coronary arteries and veins and they're ready and waiting for whenever you need them. We also like to expand your anatomy knowledge with some real-life clinical cases like this one, which describes a rare yet extremely dangerous anatomical variation of the left coronary artery.
And with that, we've covered some of the major topics in relation to the anatomy of the heart. Let's see how we do that dreaded quiz now.
The narrowing of the inner walls of which type of exemplary structure is the most frequent cause of heart attack? We spoke about this earlier, right? Since coronary arteries deliver oxygen and nutrients to cardiac muscle, it must be the blockage of one of them which can cause this to happen.
As the tricuspid valve opens, which structure is filled with deoxygenated blood? Remember, I mentioned before on this video that the tricuspid valve is found between the right atrium and the right ventricle, and since blood flows from the atria to the ventricles, the answer must be – the right ventricle.
To learn more about the valves of the heart, check out our video that goes into all the details that you need to know about the heart valves.
Which heart valves are opening during ventricular diastole? This was a tricky one, but while speaking about blood flow of the heart, we said diastole was when the ventricles relaxed and filled up with blood from the atria. That means the correct answers here should be the right and left atrioventricular valves. Yes!
You can find more information about the blood flow on our article about the heart where we have an easy-to-follow list of all the places the blood will go as it enters and exits the heart.
Coronary sinus? That's that big vein at the back of your heart, right? Yes, it is! Full marks!
See how easy it was to get to grips with the basic anatomy of the heart?