Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the heart in situ. So what we are going to be doing on this tutorial is looking at this image that you see now on the screen which is an image of the open thorax – anterior view of the open thorax – where you see different organs – very important organs. Here are the 2 lungs. You see here the heart enclosed by the pericardium, you see the thymus, the trachea, the diaphragm, the stomach – just a few structures here for a bit of location. We’re going to be exploring the structures that are found as the neighboring structures or nearby structures found on the heart.
Now, if I remove here the pericardium, you can see then exposed the heart. Now, there is no doubt that the heart is a vital muscular organ which functions to then pump blood around the body through blood vessels of the circulatory system. Now, in doing so, the blood is then able to provide your body with oxygen and nutrients which you sure need as well as removing metabolic waste. Now, as you probably know, the heart is located in your chest, specifically in an area known as the mediastinum which is a middle compartment found on the thorax. The heart is divided into 4 main chambers which we will be talking about throughout this tutorial as well. The upper 2 are known as the left and right atria while the lower 2 are known as the left and right ventricles.
Now, let’s start highlighting a few structures that we want to talk about. Now, I’m just looking now at a posterior or inferior view of the heart or diaphragmatic view of the heart where I’m showing one of the structures then we’re going to see on that image – that previous image – but I just wanted to show you here the left atrium. Now, this structure will be receiving oxygenated blood from the pulmonary veins which you can also see here on this image. Then once it receives that oxygenated blood from the pulmonary veins, it will pump it into the left ventricle via the mitral valve.
We’re going to continue on through this image of the anterior view now that you can clearly see another structure which is then the left ventricle. Now, during diastole, the left ventricle will be receiving oxygenated blood from the left atrium and then when systole starts, the muscle cells will be contracting in order to pump blood into your aorta and thus into your whole body.
The next structure that we’re going to be highlighting here, this is an atrium, known as the right atrium. And one important point to mention before I move on and talk about the different structures that we find here on the heart, keep in mind that we’re looking at the subject’s perspective. So, right now, when I talk about the right atrium is the structure that you are seeing then on or the right atrium of the subject is what you see from an anterior view on your left side. That’s why you see it here on the left side, but do not confuse this with the left atrium.
The right atrium will be receiving blood from 2 large veins, the superior vena cava – which you can see a little bit here on this image – and another one coming from below or the inferior vena cava. Now, these collect venous blood from all over your body and then from the right atrium, the blood goes to then the right ventricle, which is the structure that we’re going to be highlighting now. This is then the right ventricle. And as I mentioned before, the right ventricle will be receiving deoxygenated blood from the right atrium and then pumps it into the pulmonary artery, which then the blood goes to the lungs where it gets re-saturated with oxygen.
It’s worth noticing a few appendages here. This one, which is the left atrial appendage. The left atrial appendage or auricle appears to function as a decompression chamber during left ventricular systole and during other periods when the left atrial pressure is high. There is also a right one which you see here highlighted on the image, the right atrial appendage – this pouch-like extension of muscular part of the right atrium that pumps blood to the right ventricle during atrial systole or ventricular diastole.
Another structure that you can see here from an anterior view of the heart, this is known as the conus arteriosus. Now, this is a conical pouch formed from the upper and left angle of the right ventricle from which then the pulmonary trunk arises and you can see a bit of the pulmonary trunk right here which then gives origin to the two pulmonary arteries.
You also find here this highlight which is showing the anterior interventricular sulcus. There are other names. It is also known as anterior longitudinal sulcus. You can also call it the anterior interventricular sulcus as we call it here or anterior longitudinal sulcus. Now, this is basically a groove that is clearly separating the ventricles of your heart so, if you remember, you have here the right ventricle and the left ventricle. Now, this is located, the sulcus is located on the sternocostal surface of the heart. So, the part of the heart that is facing the sternum and the ribs. It’s found close to its left margin.
You also find here the tip of the heart which is known as the cardiac apex. Now, the apex of the heart is the lowest surface of the heart. It is positioned downward, forward, and to the left and is overlapped by the left lung and pleura. In terms of location, the cardiac apex lies behind the 5th left intercostal space 8 to 9 cm from the mid-sternal line slightly medial to the mid-clavicular line. So, this is how you can find the cardiac apex on your chest.
Now, the next structure that we’re going to be talking about, one that I’ve mentioned before, this sac that envelopes your heart, the pericardium. Now, this is a double-walled sac containing the heart and also some of the main blood vessels or the roots of the main blood vessels – as you can see here it enveloping them. The pericardial sac has 2 layers, a serous layer and a fibrous layer, and it encloses the pericardial cavity which contains then pericardial fluid. Now, the pericardium has a few important roles that I would like to add here. One of them is that it fixes the heart to the mediastinum. It also protects it against infections and provides lubrication for the heart.
As we go through the heart in situ, I would like to add this structure here that you see, this membrane which is known or part of a membrane, the parietal pleura, but this specifically is the mediastinal part of the parietal pleura – see here highlighted in green – which is basically enveloping the thoracic viscera. And I can add a few more structures here including the pericardium and the thymus and see how the mediastinal part of the parietal pleura is related to these structures.
We’re ready now to move on to another structure that you see here – a bit of green here – just to mention that you find here the left main bronchus. Now, this one is smaller than the right one but is a bit longer than the right bronchus being about 5 cm long. It is entering the root as you can see here, it enters the root of the left lung just opposite to the 6th thoracic vertebra. The left main bronchus divides into 2 secondary or lobar bronchi to then deliver air to the 2 lobes of your left lung, the superior and inferior lobes, if you remember correctly. You can also see a bit of the lobes here, the superior and the inferior lobes of the left lung.
Another structure that we’re going to be highlighting here, one that we talked about before, the thymus. Now, this is a specialized organ of your immune system, and if we weren’t highlighting it, it is of a pinkish-gray color, soft and lobulated on its surfaces. At birth, it is about 5 cm in length, 4 cm in width, and about 6 mm in thickness. Now, this organ will be enlarging during childhood and atrophies at puberty. And, unlike the liver, kidney and heart for instance, the thymus is at its largest in children. Now, the thymus also has very important roles. Now, in the 2 thymic lobes, the hematopoietic precursors from the bone marrow referred to as thymocytes will mature into T-cells. Once mature, the T-cells will then migrate from the thymus and be part of the peripheral T-cell repertoire responsible for directing many facets of the adaptive immune system. Now, loss of the thymus at an early age through genetic mutation results in severe immunodeficiency and high susceptibility to then infection.
We’re moving on to the next structure that you see here highlighted in green, this is the diaphragm. This is a sheet of internal skeletal muscle that extends across the bottom of the ribcage. In terms of roles, it has a very important role. One of them is that it separates the thoracic cavity containing then the heart and the lungs from the abdominal cavity as you can see here below. It also plays a very important role in respiration – as your diaphragm contracts, the volume of your thoracic cavity will increase and air is drawn into your lungs.
Now, we’re going to continue on and talk about a few arteries that we see here on this image. We’re going to list them before we continue on talking about them in greater detail on the next slides. So, we’re going to be seeing the aortic arch, the brachiocephalic trunk, the left and right common carotid arteries, and the left and right subclavian arteries, the internal thoracic, the pericardiacophrenic, the right coronary artery. We’re also going to be seeing then the pulmonary trunk and the interventricular branch of the left coronary artery.
Let’s start covering that list starting off with this highlight here which you see then, the aortic arch. This is a part of the aorta that begins at the level of the upper border of the second sternocostal articulation on the right side. And as you can see on the image, it first runs upwards then backward and to the left in front of this structure here, the trachea. So, it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes then continuous with the other structure which is then known as the descending aorta. And you can clearly see here on this image of the lateral left side of the thorax – we just removed here the left lung and you can see here your chest, your back and notice here the aortic arch highlighted in green and how it then continues to be the descending aorta. This specific case, this is the thoracic aorta.
Now, the structure that we’re going to be highlighting here, this is known then as the brachiocephalic trunk, also known as the brachiocephalic artery or innominate artery. This is an artery of the mediastinum that supplies blood to the right arm and head and neck. It is the first branch of this arch here that we just talked about, the aortic arch, and soon after, it emerges. This brachiocephalic artery or trunk will be dividing into other 2 very important arteries. One is the right common carotid artery which you can also see here on this image, the other one is the right subclavian artery which you also see here on this image.
We’re going to continue on and talking about these two structures highlighted in green which happened to be the common carotid arteries. On the image on the left side, you see then the left common carotid artery while on the image on the right side, you’re looking at the right common carotid artery. Now, these supply the head and neck with oxygenated blood and, as they go further up, they will be dividing into two other branches – very important branches – which are known as the external and internal carotid arteries. We’ll be talking about these branches on other tutorials.
Now, the left and right common carotid arteries, they follow the same course with the exception of the origin points which we will talk about on the next slides and the bifurcation into the external and internal carotid arteries occurs at the upper border of the thyroid cartilage at around the level of the fourth cervical vertebra.
Let’s take a closer look here at the left common carotid artery, and you can see here on this image that it’s originating from this arch here. So, it originates or branches off of the aortic arch in the thoracic region. So, the left common carotid artery can be thought of as having 2 parts – a thoracic part and also a cervical part.
Let’s now take a closer look at the right common carotid artery to see that it’s branching off of the brachiocephalic trunk – remember this trunk that we highlighted on previous slides. So, this is going to be the origin point or where it’s going to be branching off the right common carotid artery as you can see clearly here.
We’re moving on and talking about these arteries that you see now on the screen highlighted in green. On the left side, we’re seeing the left subclavian artery while on the image on the right side, we’re seeing the right subclavian artery. Now, these arteries are found on the upper thorax just below the clavicle and they arise from – as you can see here – on the left subclavian artery, you can see that it arises from the aortic arch while the right subclavian artery, as you can see here, is coming off of this or branching off of the brachiocephalic trunk which you can see a bit here. The left subclavian artery is going to be supplying blood to the left arm while then the right subclavian artery supplies blood to then the right arm with some branches then supplying the head and thorax.
We’re going to move on and talk about these 2 arteries that you find here highlighted in green found behind these veins that we’re going to be talking about later on. Now, these are the internal thoracic arteries. The internal thoracic artery, previously known as the internal mammary artery, is an artery that supplies the anterior chest wall and also the breasts. This is a paired artery with one running along each side of the sternum to then continue after its bifurcation as the superior epigastric and musculophrenic arteries. And you can see a little bit here on this image, keep in mind that these are not originating or coming from these veins here. They are coming out of certain arteries, specifically, they are coming or they’re branches of the subclavian arteries.
If we continue on, I can show you here this image where we just focused on different bones of the chest wall and the main arteries and you can clearly see here highlighted in green, the internal thoracic arteries. Notice here at the bottom, you see the bifurcation of the internal thoracic artery that I just talked about. There will be several branches coming out of the internal thoracic artery. Mediastinal branches, thymic branches, also pericardiacophrenic arteries will be coming out of the internal thoracic artery, sternal branches, also perforating branches, and the 12th anterior intercostal branches.
Now, after passing the 6th intercostal space, the internal thoracic artery will be splitting into two terminal branches as I talked about before. The musculophrenic artery roughly follows the costal margin and also the superior epigastric artery. So, I talked about these branches that you find here which we will be discussing in more detail on a separate tutorial. But just to note here that the superior epigastric artery continues the course of the internal thoracic artery traveling downward into then the abdominal wall.
We’re going to be talking about one of these branches of the internal thoracic artery that you see now highlighted in green. These are then the pericardiacophrenic arteries. These are long slender branches of then the internal thoracic arteries which you can see here – the branches just coming out of the internal thoracic arteries. These arteries will be then following or accompanying this nerve here, the phrenic nerve, as you can see on both sides, and also the respective veins, as we’re going to also talk about later on on this tutorial. So, between the pleura and the pericardium to then all the way to the diaphragm to which it is then distributes to then supply the diaphragm. The pericardiacophrenic arteries will be then anastomosing or connecting with the musculophrenic and inferior phrenic arteries.
Next we’re going to be zooming in here on the heart to then show you this highlighted structure and artery as well, which is then the right coronary artery. Now, this one originates above the right cusp of the aortic valve which you can’t see clearly here on this image but we will cover this artery in greater detail on a separate tutorial. But it travels down to the right atrioventricular groove towards the crus of the heart. Now, it branches into the posterior descending artery in 85% of the cases and then the right marginal artery. In addition to supplying blood to the right ventricle, the right coronary artery will be supplying 25% to 35% of the left ventricle.
The next important branch here, coronary branch that you see here, is known as the interventricular branch of the left coronary artery. Now, this branch is an important coronary artery and it passes at, first, behind the pulmonary artery and then comes forward between that vessel and the left auricle to then reach the anterior interventricular sulcus. Now, the interventricular branch of the left coronary artery will be supplying the anterolateral myocardium, the apex, and the interventricular septum. It usually supplies 45-55% of the left ventricle.
The next structure that we can also see here, if we remove the thymus, and a bit more structures here to then expose this highlighted structure, which is the pulmonary trunk. Sometimes, referred to as the main pulmonary artery. It carries deoxygenated blood from the heart to then the lungs. It is one of the only arteries that will be carrying deoxygenated blood – keep that in mind. As you can see here, there are 2 branches that will be coming out of the pulmonary trunk. The left pulmonary artery and also the right pulmonary artery which is behind these two structures here, the superior vena cava and also the aorta. Now, the left pulmonary artery or the left branch of the pulmonary trunk, which is shorter and somewhat smaller than the right one, will be passing horizontally in front of the descending aorta and also the left bronchus to the root of the left lung as you can see here. Whereas, you can also notice here – if I zoom in a bit – it is dividing into 2 branches, one for each lobe of the left lung.
Now, the right pulmonary artery or the right branch of the pulmonary trunk longer and also larger than the left one will be running horizontally to the right behind these two structures that I just talked about, the ascending aorta and the superior vena cava, and in front of the right bronchus to then attach to – as you can see a little bit here – to the root of the right lung, and here it will be dividing into two branches. The lower and larger one of these will then go to the middle and lower lobes of the lung and then the upper and smaller one is going to be distributed to the upper lobe.
The next structure that we’re going to be highlighting here on this image of the anterior view of the open thorax is the ligamentum arteriosum. Now, it’s also known as the arterial ligament. This is a small ligament which is attached to the superior surface of the left pulmonary artery – as you can see here – and also the aorta. It is a nonfunctional remnant of the ductus arteriosus and is formed within 3 weeks of birth. The ligamentum arteriosum is closely located to the left recurrent laryngeal nerve which is a branch of the left vagus nerve and after splitting from the left vagus nerve, the left recurrent laryngeal loops around the aortic arch posterior to the ligamentum arteriosum after which it then ascends to the larynx. Now, this ligament also plays a role in major trauma. It will be fixing the aorta in place during rapid decelerations recoil then consequence potentially resulting in ruptured aorta.
We’re now ready to move on and talk about a few veins that we find around the heart. The list includes the internal jugular, the subclavian veins, brachiocephalic, superior vena cava, and pericardiacophrenic. Now, of course, there are few others that we could talk about like the inferior vena cava but I wanted to focus on this image of the anterior view that we’ve been exploring and leave it for another time.
First, we’re going to start off with these highlights here which show the internal jugular veins. On the image on the left side, we’re looking at the left internal jugular vein while on the image on the right side, we see the right internal jugular vein. Now, these veins, they bring deoxygenated blood from the head back to the heart via the superior vena cava. And just a reminder that there are two sets of jugular veins, external and internal, but right now, we’re looking at the internal jugular veins.
But I would like to take this time to just give you an overview of how blood flows from the jugular veins back to the heart. So, they will be coming or the blood will be coming from the left and right external jugular veins as well as these that we have here highlighted on these images on the left side, the left and right internal jugular veins. Then these will be draining into the subclavian veins which are these veins that you find here on the images - we’re going to use this one where you can see a bit more clearly – then blood goes from the subclavian veins back to then the brachiocephalic veins – as you can also see here on the image – then into a major vessel known as the superior vena cava – as you can also see here on the image – and then it goes to the right atrium. So, here, it reaches the heart.
We’re moving on and talking about these veins that we just listed before the subclavian veins. Now, on the image on the left side, we see the left subclavian vein and on the image on the right side, we see then the right subclavian vein. These are relatively large veins on either side of your body. Their diameter is approximately that of your smallest finger. These veins will be receiving blood from the axillary and jugular veins and draining it to the brachiocephalic veins, if you remember from the previous slides.
Next veins that we’re going to be talking about which I also mentioned before on the left side we see here the left brachiocephalic vein while on the right side, we seen then the right brachiocephalic vein. Now, these veins are formed by the joining of the internal jugular veins – as you can see here – and also the subclavian veins. So, they meet here to form then the brachiocephalic veins. The main task of these veins is to then transport deoxygenated blood of the upper extremity and head region towards the superior vena cava and then all the way to the heart where it gets pumped into the lungs for oxygenation.
The next vein that we’ve been talking about that you now see here highlighted in green, you guess – one minute – yes, this one is the superior vena cava. This one is large in diameter. It’s a bit short and this vein will be carrying deoxygenated blood from the upper half of your body to then the right atrium of your heart. It receives blood from the brachiocephalic and also another vein that we didn’t talk about, the azygos vein.
We’re going to be highlighting these veins here that you see in green. I mentioned the versions, the arterial versions of these veins, the pericardiacophrenic veins that we see here highlighted now in green. These are also here following the phrenic nerve and the middle mediastinum of the thorax. Now, these veins will be draining into the internal thoracic vein.
A quick word on the different nerves that you can see here on this image. We’re going to talk about briefly about the left and right vagus nerves, also the left recurrent laryngeal nerve and you see also one that I mentioned before, the phrenic nerve.
Let’s start off with the very first one now seen from a left lateral view of the open thorax. Here you see the vagus nerves, specifically the left vagus nerve. Also known as pneumogastric nerve and is also called the 10th cranial nerve. The right and left vagus nerves descend from the cranial vault through the jugular foramina penetrating the carotid sheath between the internal and external carotid arteries.
Now, let’s take a look here from this perspective at the left vagus nerves seen here highlighted in green. And this one is giving off an important nerve which is the left recurrent laryngeal nerve, which you can see here just leaving the left vagus nerve and going up as you can see looping around the aortic arch. In addition, the left vagus nerve will be giving off thoracic cardiac branches and will be contributing to the pulmonary and esophageal plexuses. And if you follow this highlight, you can see that the left vagus nerve will be then entering the abdomen as it forms the anterior vagal trunk in the esophageal hiatus of the diaphragm – you can see here the esophageal hiatus. So, this hole here where the esophagus and also the anterior vagal trunk or this portion of the left vagus nerve will be passing through into the abdomen.
Next, we’re going to be highlighting the vagus found on the right side which we then call it the right vagus nerve, and this one will be giving in turn the right recurrent laryngeal nerve, which you see here on the image – notice here the right recurrent laryngeal nerve traveling upwards. Now, the right recurrent laryngeal nerve, you can’t see clearly here on this image but hooks around the right subclavian artery which you see a bit here then ascends into the neck between the trachea and the esophagus as you can see here a bit.
Now, the right vagus will be contributing to the cardiac, the pulmonary, and esophageal plexuses. Will be forming the posterior vagal trunk at the lower part of the esophagus and enters the diaphragm through the esophageal hiatus.
We’re going to be highlighting now one nerve that we talked about before, this is the left recurrent laryngeal nerve, which I mentioned before is a branch of the left vagus nerve and it emerges from the vagus nerve at the level of the aortic arch and then travels up to the side of the trachea to then the larynx.
Finally, on our list, we’re going to be talking about these 2 nerves. Now, I’m showing a completely different image now of your neck so we can see where these nerves come from, the phrenic nerves. We’re looking at the anterior view of your neck. Notice here the clavicles, you see the manubrium of the sternum, the different cervical vertebrae, the scalene muscles, and you see here highlighted in green then the phrenic nerves. Now, these nerves will be originating in the neck at C3 to C5 and then pass down between the lungs and heart to reach the diaphragm – so a long course as you can see.
Now, the phrenic nerves originate mainly from the fourth cervical nerve that also receives contributions from the 5th and 3rd cervical nerves – C3, C5. For that reason, the phrenic nerve receives nerve fibers from parts of both the cervical plexus and the brachial plexus.
Now, if we move on and bring you to this, back to this image of the open thorax, you can see now highlighted, the phrenic nerves, to show you here that the phrenic nerves will contain or they contain motor, sensory and sympathetic nerve fibers. Now, these nerves provide only motor supply to the diaphragm as well as sensation to the central tendon and, in the thorax, they will be innervating the mediastinal pleura and pericardium.
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Now, good luck everyone, and I will see you next time.