Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial about the main veins at the trunk. Before we begin talking about the different veins that drain the trunk, let me first answer the question, what is a vein? A vein is a tube that carries deoxygenated blood to the heart from other parts of the body and therefore forms a vital part of our circulatory system. In the image on the right, we can see the main veins of the body color coded in blue. Small veins drain into larger veins until the blood within them finally reaches the heart and these smaller veins are known as tributaries. When a number of veins congregate together, it's known as a venous plexus. We can see an example of a venous plexus highlighted in green in this image representing a section of the spinal cord.
As you've seen from the title of our title, we're going to be talking about the veins of the trunk. So the next question you might ask is what is the trunk? When we talk about the trunk of the body, we're referring to the central part or torso which you can see highlighted in green on our image. The trunk can be divided into two parts – the thorax and the abdomen. The thorax is the chest area and is located above the diaphragm which is a structure that sits about here. Below the diaphragm is the abdomen – the area commonly known as the midriff or the stomach.
Before we start looking at the different veins of the trunk, let us first do a quick overview. As you may expect, there are many important veins found in the trunk. Some like the superior vena cava seen here highlighted in green drain directly into the heart whilst others remove blood from organs, for example, the renal veins which drain the kidneys. In this video, we will focus on the most important veins of the trunk beginning with the veins of the thorax and later moving on to the veins of the abdomen.
So let's start with the very important vein – the superior vena cava – seen here in this image of the open thorax. Please note that the heart and lungs have been removed in this illustration to give us a clearer view of other structures. The superior vena cava is a short wide vein connected to the heart and it's formed when the right and left brachiocephalic veins come together. The superior vena cava receives blood from the upper limbs, neck and eyes and it drains into the right side of the heart specifically the right atrium. The superior vena cava's tributaries are the azygos vein which we can now see highlighted in green and the small veins that drain the pericardium which are unfortunately not visible in this image.
Now we'll move on to the brachiocephalic veins. In this image, it's the left brachiocephalic vein specifically that's highlighted in green. The left brachiocephalic vein is located on the left side of the neck and is between six and eight centimeters long. Moving to the next illustration, we can see the right brachiocephalic vein. The right brachiocephalic vein is found on the right side of the neck and is only about 2 centimeters in length. As I mentioned previously, the right and left brachiocephalic veins come together to form the superior vena cava. The tributaries drained by the brachiocephalic veins are the internal thoracic veins, the inferior thyroid veins and the left superior intercostal vein.
Now let's take a look at the coronary sinus which is the main collector of blood from the heart. This vessel drains into the right atrium and we can see it here on the posterior surface of the heart. The coronary sinus drains the majority of the epicardial ventricular veins. These tributaries include the oblique vein, the great cardiac vein, the posterior vein of the left ventricle, the left marginal vein, and the posterior interventricular vein. During heart surgery, balloon catheters are sometimes placed into the coronary sinus to deliver therapeutics or to take venograms.
Moving on, we can see the azygos vein highlighted in green. The azygos vein is part of the azygos venous system which is found on either side of the vertebral column. This veins drains into the superior vena cava before entering the pericardium. The azygos vein has two main tributaries. These are the hemiazygos vein which is usually connected to the left renal vein and the accessory hemiazygos vein which is formed from veins found in the intercostal spaces and sometimes the left bronchial veins. An enlarged azygos vein can result from overhydration, pregnancy, superior vena cava obstruction and other causes of right heart output failure.
Now we'll look at another important coronary vein – the great cardiac vein – which we can see here on the anterior surface of the heart. It drains into the coronary sinus after draining the anterior surface of both ventricles of the heart, the anterior interventricular septum and parts of the left atria. Moving to the posterior aspect of the heart, we can see the middle cardiac vein highlighted in green. The middle cardiac vein is also known as the posterior interventricular vein that originates near the apex of the heart ascending along the posterior interventricular sulcus. This vessel drains into the coronary sinus or sometimes directly into the right atrium. The middle cardiac vein drains the posterior left and right ventricles and the interventricular septum.
Linked to the middle cardiac vein is the small cardiac vein highlighted here in green. The small cardiac vein is highly variable and arises from the right ventricle. It's a tiny vessel and is actually absent in about sixty percent of hearts. The small cardiac vein drains the posterior part of the right atrium and the right ventricle. It subsequently drains into the middle cardiac vein.
Running along the length of the ribs, we can see the posterior intercostal veins in this posterior view of the thorax. The posterior intercostal veins drain into the azygos on the right hand side and the hemiazygos and the accessory hemiazygos on the left hand side. As seen in the next illustration, a superior intercostal vein can form from the second, third and sometimes fourth posterior intercostal veins. Together, these veins drain into the azygos vein on the right and the left brachiocephalic vein on the left. In addition to the posterior intercostal veins, we also have the anterior intercostal veins which we can see running between the intercostal spaces anteriorly. These veins drain into the internal thoracic veins and the musculophrenic veins.
Next let's move on to the hemiazygos vein which you can see here in green on the lower right hand side of the spine. The hemiazygos vein is part of the azygos venous system and drains into the azygos vein. It often connects to the left renal vein and its tributaries are the left ascending lumbar vein, the left subcostal vein and the lower three posterior intercostal veins.
Moving back to the heart, let's take a look at the right marginal vein shown here in green at the bottom of the heart. The right marginal vein is a small vein that drains blood from the right ventricle and then drains into the right atrium and the anterior cardiac veins. Sister to the right marginal vein is the left marginal vein. Again, we can see it here highlighted in green. The left marginal vein is fairly large and drains blood from the left ventricle of the heart. It then drains into the great cardiac vein.
Continuing with the heart, we'll talk about the ventricular veins starting with the anterior vein of the right ventricle. This vein may be small but is important and functions to drain blood away from the ventral part of the right ventricle. It then drains directly into the right atrium. Posteriorly, we can see this vessel here which is called the posterior vein of the left ventricle. As you might have guessed, this veins drains blood from the posterior surface of the left ventricle and then drains into the coronary sinus of the heart.
Now moving on to the veins of the chest, we'll discuss the internal thoracic veins which are sometimes called the internal mammary veins. These veins which we can see running behind the ribs on either side of the sternum drain blood away from the chest wall and breast via the superior epigastric veins. They then drain this blood into their corresponding brachiocephalic veins.
Next we'll have a look at the thoracoepigastric vein shown here on either side of the body's trunk. The thoracoepigastric vein drains blood away from the superficial epigastric vein. It then drains into the axillary or lateral thoracic vein. This vein forms an important pathway between the tributaries of the inferior and superior vena cavae.
The last thoracic vein we'll look at in this tutorial is the deep cervical vein. We can see it running along the length of the cervical vertebrae on both the right and left side. The deep cervical vein is a large vein that drains the posterior external vertebral plexus of the spine. It then drains into the brachiocephalic veins of the upper chest.
We've now covered the main veins draining the structures in the thorax so it's now time for us to move further down the trunk and talk about the veins draining the abdomen. First let's have a look at one of the most important veins of the abdomen – the inferior vena cava. The inferior vena cava which we can see here highlighted in green plays an important role in draining veins located below the diaphragm. It's found on the posterior wall of the abdomen and it's formed by the union of the common iliac veins. The inferior vena cava drains a number of different tributaries. These include the common iliac veins, four pairs of lumbar veins, the renal veins which drain the kidneys, the right ovarian or testicular vein, the right suprarenal vein which drains the right adrenal gland, the inferior phrenic veins which drain the diaphragm and the hepatic veins which drain the liver. The inferior vena cava like the superior vena cava drains into the right atrium of the heart.
Now let's take a look at the hepatic veins. These veins as the name suggests drain blood away from the liver. They then drain into the inferior vena cava. There are normally three hepatic veins which drain blood from the left, middle and right sides of the liver. We'll now move our focus to the lumbar veins which you can see here highlighted in green in this image showing a posterior view of the lumbar spine. The lumbar veins are found on the posterior wall of the abdomen and they drain blood away from the posterior body wall and the lumbar venous plexuses. The first two lumbar veins drain into the ascending lumbar vein whereas the third and fourth drain into the inferior vena cava.
Next we're going to talk about the epigastric veins of which there are three types. First we'll look at the inferior epigastric veins shown here on either side of the pelvis. The inferior epigastric veins drain blood from the superior epigastric veins which we can see here and then drain into the external iliac veins which are located here and here. Another type of epigastric vein is the superficial epigastric vein which is again a paired structure. This vein drains blood from the lower and medial portions of the anterior abdominal wall and drains it into the great saphenous vein.
Finally, let's look at the superior epigastric vein which we can see here in green on either side of the spine. The superior epigastric vein drains blood from the anterior abdominal wall. It then drains this blood into the internal thoracic vein.
Moving away from the epigastric veins, we'll now focus on the iliac veins. Again, there are several types but we'll start by looking at the common iliac veins. We can see the right common iliac vein specifically highlighted in green in this image. The right and left common iliac veins are a pair of veins that drain into the inferior vena cava. They have no valves and drain blood away from the iliolumbar vein and sometimes the lateral sacral vein. In the next illustration, we can see the left common iliac vein which is longer than the right common iliac vein because the inferior vena cava is positioned to the right of the body. The left common iliac vein can also drain blood from the median sacral vein. In the image on the right, we can see how the left and right common iliac veins unite to form the inferior vena cava.
Next let's take a look at the external iliac veins. You will notice that the right external iliac vein is highlighted in green in this image on the right. The external iliac veins are a pair of large veins that drain blood away from the pelvic region of the body. Specifically, they drain blood away from the inferior epigastric veins, the deep circumflex iliac veins and the pubic veins. The right external iliac vein drains into the right common iliac vein that we mentioned previously. We can now see the left external iliac vein highlighted in green. This vein drains into the left common iliac vein.
The final type of iliac veins that we'll look at are the internal iliac veins. We can see the right internal iliac vein here highlighted in green. Like the external iliac veins, the internal iliac veins are a pair of veins that drain deoxygenated blood from the pelvic region. As their name suggest, they are situated more internally than the external iliac veins. The right internal iliac vein drains into the right common iliac vein. As we can see in this image, the right external and internal iliac veins come together to form the right common iliac vein.
In the next illustration, we can see the left internal iliac vein which drains into the left common iliac vein. The tributaries of the internal iliac veins include the middle rectal veins, the obturator veins, the lateral sacral veins, the inferior gluteal veins and the superior gluteal veins. If you'd like to learn a bit more about the branches of the internal iliac veins, watch our tutorial called veins of the abdomen and pelvis which is available on our website.
Now we'll have a look at the veins of the spine starting with the anterior and posterior spinal veins. We can see one of the anterior spinal veins highlighted in green in the image on the right. Both the anterior and posterior spinal veins drain blood from the spinal cord via the sulcal veins. The anterior spinal veins drain blood away from the anterior portion of the spine specifically.
In the next illustration, we can see one of the posterior spinal veins here which drain blood from the posterior region of the spine. The anterior and posterior spinal veins drain into the cerebral dural venous sinuses, the cerebral veins and the external vertebral plexus. There are usually three anterior spinal veins and three posterior spinal veins, however as I've already said, our images only show one. Together, these spinal veins form an internal vertebral venous plexus.
Another type of spinal vein that we find is the radicular veins consisting of the anterior radicular vein which we can see here and the posterior radicular vein which we can see here. The anterior and posterior radicular veins are very small veins that are found in most segments of the spine. They drain the ventral and dorsal roots and parts of the spinal cord before draining into the intervertebral veins.
Moving away from the spine, let's take a look at veins that drain some organs of the abdomen. Firstly, here we have the renal veins, the left of which you can see just here. The renal veins are a pair of veins that drain filtered blood away from the kidneys before draining into the inferior vena cava. The right renal vein is smaller than the left being just two and a half centimeters long as opposed to seven and a half. This difference is a result of the inferior vena cava being on the right side of the body.
We'll now consider the veins of the gonads. Firstly, those of the female gonads are the ovaries. We can see the left ovarian vein in the ovary it drains in the image on the right. As I've just said, the ovarian veins drain blood from the ovaries. The left ovarian vein then drains into the left renal vein whilst the right ovarian vein drains into the inferior vena cava.
Now let's have a look at the male gonadal veins which are otherwise called the testicular veins or the spermatic veins. These veins drain blood away from their corresponding testes via veins that arise from the epididymis. The right testicular vein drains into the inferior vena cava whilst the left testicular vein drains into the left renal vein.
During this video, we've seen that there's a wide array of veins in the trunk linking together to form a complex web of drainage. As the veins of the trunk often drain important structures like the kidneys and gonads or drain into the heart, problems such as blood clots and blockages can have serious consequences to health. We'll go over some examples of diseases related to the veins of the trunk in our clinical notes.
The first disease we'll talk about is superior vena cava syndrome which is an obstruction in the superior vena cava usually caused by tumors. The next condition we'll look at is pelvic venous congestion syndrome which results from overdilation of the ovarian or pelvic veins. This is caused by a loss of function in the valves of these veins which causes severe abdominal pain. Next, we have renal vein thrombosis which is caused by blood clots in the renal veins often leading to acute kidney damage. And, finally, we have cardiovascular disease which affects the heart and can be caused by blockages in veins connected to it such as the coronary sinus and the great cardiac vein.
So that brings us to the end of our tutorial on the main veins of the trunk. I hope you enjoyed it and thank you for listening.
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