ANAT Week 9.docx

Week 9 **Module: Cardiovascular System 1 - The Heart** =============================================== **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Briefly describe the embryological development of the heart **LO2**: Describe the positio...

Week 9 **Module: Cardiovascular System 1 - The Heart** =============================================== **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Briefly describe the embryological development of the heart **LO2**: Describe the position of the heart in the thoracic cavity **LO3**: Describe the structure and function of the pericardium and the layers of the heart wall **LO4**: Describe the external and internal features of the heart **LO5**: Describe the flow of blood through the heart and explain how this relates to the phases of the cardiac cycle **LO6**: Describe the structure and function of the heart valves and the fibrous skeleton of the heart **LO7**: Describe the components and function of the cardiac conduction system **Embryological Development of the Heart** ------------------------------------------ ***LO1: Briefly describe the embryological development of the heart*** Recall from the Embryology module that all tissues in the body are derived from the three primary germ layers of the embryo, which then arrange themselves to form organs. The primary germ layer that the heart is derived from is the mesoderm. The development of the heart begins in the third week of development when the embryo reaches a size where it requires its own blood supply. Two heart tubes form from the mesoderm and then fuse to form a single primitive heart tube. This single heart tube forms several expansions which ultimately give rise to the structures of the fully developed heart. By day 22 of development, the primitive heart begins to beat and begins to bend and fold on itself. The heart tube then becomes partitioned into the four chambers of the heart and the great vessels entering and leaving the heart form. In utero, the heart has two openings which allow blood to bypass the lungs, as the lungs are not functional until after birth. These openings are called foramen ovale, which can be seen in image \'d\' below, and ductus arteriosus. Later in this module, we will discuss the heart structures that these openings are found between and the embryological remnants of them that remain in the adult heart. **Position of the Heart** ------------------------- ***LO2: Describe the position of the heart in the thoracic cavity*** Now that we have looked at the development of the heart, we are going to look at how it is positioned in the thoracic cavity. The heart is located in a space called the mediastinum, which is the central space in the thoracic cavity between the two lungs. It is orientated in such a way that the right side of the heart is more anterior, while the left side of the heart is more posterior. The apex of the heart points towards the left and approximately 2/3 of the heart sits to the left of the midline. The base of the heart sits opposite to the apex and is directed posteriorly, so it is also referred to as the posterior surface of the heart. Contrary to the name, the heart does not actually sit on its "base". Instead, the heart sits on its inferior surface which is also referred to as the diaphragmatic surface. This is because the inferior surface of the heart sits on the diaphragm and the protective sac around the heart called the pericardium is fused with the central tendon of the diaphragm. **Pericardium** ***LO3: Describe the structure and function of the pericardium and the layers of the heart wall*** Now we are going to look at the pericardium in more detail. The pericardium is the protective sac around the heart. It not only protects the heart, but also keeps it in place within the thorax, as it is fused with the central tendon of the diaphragm. The pericardium has two parts -- the outer fibrous pericardium, which is the part that is fused with the central tendon of the diaphragm, and the inner serous pericardium, which is a serous membrane. Recall from the Skin module, where the concept of body membranes was introduced, that a serous membrane has an outer parietal layer and an inner visceral layer, with a potential space in between them containing a thin film of fluid called serous fluid that is produced by the serous membrane. Like any serous membrane, the serous pericardium has these two layers with a potential space in between them, which in this case is called the pericardial cavity. Click on the hotspots on the image below to learn more about the layers of the pericardium. As the visceral layer of the serous pericardium lines the outer surface of the heart directly, it forms the outer layer of the heart wall. For this reason, it is also called the epicardium ('epi' = above or upon). **Heart Wall** -------------- ***LO3: Describe the structure and function of the pericardium and the layers of the heart wall*** Now that we have looked at the pericardium and noted that the visceral layer of the serous pericardium forms the outer layer of the heart wall, we are going to look at the heart wall itself. The heart wall is composed of three layers -- an outer epicardium, which is the visceral layer of the serous pericardium, a middle myocardium and an inner endocardium. Click on the hotspots on the image below to learn more about these three layers. **External Features of the Heart - Anterior View** -------------------------------------------------- ***LO4: Describe the external and internal features of the heart*** Now that we have looked at the heart wall, we are going to look at the heart's overall structure and its external features. The heart has four chambers -- a left and right atrium and a left and right ventricle. The two atria are the "receiving" chambers as they receive blood from either the lungs or the body, while the ventricles are the "pumping" chambers as they pump blood to either the lungs or the body. From the anterior view of the heart, the surface that can be seen is its anterior surface. Click on the hotspots on the image below to learn about some of the features that can be seen from this view. **External Features of the Heart - Posterior and Inferior Views** ----------------------------------------------------------------- ***LO4: Describe the external and internal features of the heart*** Now we are going to look at the heart from the posterior and inferior views. It is important to note that on the images below, we can see both the posterior and inferior surfaces of the heart and that they are not in the same plane, although they may appear to be on the images. On the first image, the posterior surface is highlighted. This surface is more commonly referred to as the base of the heart and it is formed by the left atrium. On the second image, the inferior surface is highlighted. This surface sits on the diaphragm and is therefore also called the diaphragmatic surface. The posterior interventricular sulcus can be seen running in between the two ventricles and the surface on which it is running is the inferior surface. Similar to the anterior interventricular sulcus that runs between the two ventricles on the anterior surface of the heart, the posterior interventricular sulcus also has blood vessels running in it (note that you do not need to know these blood vessels). On both images, the continuation of the coronary sulcus can be seen with a large vein sitting in it called the coronary sinus. This vein drains blood from the heart itself. **Pulmonary and Systemic Circulation** -------------------------------------- Now that we have looked at the external features of the heart, we are going to look at its internal features. As we do so, we are going to follow the path that a single red blood cell would take through the heart. However, before we do this, it is important to understand a few important concepts, as described on the three images below. Make sure you keep these three things in mind while we look at the internal features of the heart and follow the path of a single red blood cell through the heart. **Internal Features of the Heart - Right Atrium** ------------------------------------------------- ***LO4: Describe the external and internal features of the heart*** To begin our journey through the heart, we are going to look at the right atrium first. The right atrium receives deoxygenated blood from the body and there are three main veins that drain this blood into the right atrium -- the superior vena cava, the inferior vena cava and the coronary sinus. Click on the hotspots on the image below to learn more about these three main veins. Now we are going to look at the other internal features of the right atrium -- fossa ovalis, the interatrial septum and the pectinate muscles. Click on the hotspots on the image below to learn more about these features. **Internal Features of the Heart - Right Ventricle** ---------------------------------------------------- ***LO4: Describe the external and internal features of the heart*** From the right atrium, deoxygenated blood flows into the right ventricle through an opening called the right atrioventricular orifice ('atrioventricular' = in between atrium and ventricle; 'orifice' = opening). This opening is guarded by a valve called the right atrioventricular valve, which can be seen in the right ventricle. The other features that can be seen in the right ventricle are the chordae tendineae, papillary muscles, trabeculae carneae and the interventricular septum. Click on the hotspots on the image below to learn more about these features. From the right ventricle, deoxygenated blood is pumped to the lungs to be oxygenated via a large artery called the pulmonary trunk. The entrance to the pulmonary trunk is guarded by a valve called the pulmonary semilunar valve, which can be seen from the right ventricle. Connecting the pulmonary trunk to the arch of the aorta is a structure called ligamentum arteriosum. Click on the hotspots on the image below to learn more about these structures. **Internal Features of the Heart - Left Atrium** ------------------------------------------------ ***LO4: Describe the external and internal features of the heart*** Once the deoxygenated blood from the right ventricle has been oxygenated in the lungs, this oxygenated blood returns to the left atrium of the heart. There are four veins that drain this blood into the left atrium called pulmonary veins, with two coming from each lung. The walls of the left atrium are smooth and it does not have the same features as the right atrium, although there are some pectinate muscles on the internal surface of the left auricle and the interatrial septum can also be seen from the left atrium. **Internal Features of the Heart - Left Ventricle** --------------------------------------------------- ***LO4: Describe the external and internal features of the heart*** From the left atrium, oxygenated blood flows into the left ventricle through the left atrioventricular orifice. This opening is guarded by the left atrioventricular valve, which can be seen in the left ventricle. This valve is similar to the right atrioventricular valve, but it has two cusps instead of three. For this reason, it is also called the bicuspid valve ('bi' = two). Another name for this valve is the mitral valve, as its cusps resemble a bishop's hat. The other features that can be seen in the left ventricle are the same as those in the right ventricle -- chordae tendineae, papillary muscles, trabeculae carneae and the interventricular septum. The only difference is that there are two papillary muscles in the left ventricle rather than three, as the left atrioventricular valve has two cusps. From the left ventricle, oxygenated blood is pumped to the body via the largest artery in the body called the aorta. The entrance to the aorta is guarded by a valve called the aortic semilunar valve, which can be seen from the left ventricle. Its structure is the same as that of the pulmonary semilunar valve. A feature that is important to note about the left ventricle is that it has the thickest wall of the four heart chambers, as it needs to generate enough pressure to be able to pump blood to the entire body. **Blood Flow through the Heart** -------------------------------- ***LO5: Describe the flow of blood through the heart and explain how this relates to the phases of the cardiac cycle*** Now that we have looked at the internal features of the heart and followed the path of a single red blood cell through the heart along the way, we are going to bring everything together to understand how the heart functions as a whole. Although we have followed the path that a single red blood cell would take through the heart, moving from the right side of the heart to the left side, it is very important to understand that the right and left sides of the heart work together. This means that while the right atrium is receiving deoxygenated blood from the body and this blood is then flowing into the right ventricle, the left atrium is simultaneously receiving oxygenated blood from the lungs and this blood is then flowing into the left ventricle. Similarly, while the right ventricle is pumping deoxygenated blood to the lungs, the left ventricle is simultaneously pumping oxygenated blood to the body. These phases of heart filling and heart pumping are part of the cardiac cycle, which is the cycle of all events that occur within the heart over a single heartbeat. The pumping of blood from the ventricles occurs during ventricular systole, which is when the ventricles are contracting, and the filling of the ventricles with blood occurs during ventricular diastole, which is when the ventricles are relaxing. You may like to watch the video below to summarise the steps in the flow of blood through the heart (please note that the details regarding blood and heart conditions are not examinable). **Heart Valves** ---------------- ***LO6: Describe the structure and function of the heart valves and the fibrous skeleton of the heart*** On our journey through the heart, we have come across the four heart valves -- the right and left atrioventricular valves and the pulmonary and aortic semilunar valves. Now we are going to have a closer look at their functions, but before we do this, it is important to understand a couple of important concepts: 1. 2. These two concepts will hopefully become clearer when we look at the functions of the two different types of valves separately, so make sure you keep them in mind as we do this. ### **Atrioventricular Valves** First, we are going to look at the atrioventricular valves. The function of the atrioventricular valves is to prevent the backflow of blood from the ventricles into the atria when the ventricles contract. Click on each of the cards below to learn more about what is happening with the valves when they are closed and when they are open. **Atrioventricular Valves Closed** **When the ventricles contract (ventricular systole) and the pressure inside the ventricles becomes greater than the pressure inside the atria, the atrioventricular valves close due to blood pushing up on the valve cusps. The papillary muscles pull tight on the chordae tendineae, which in turn pull tight on the valve cusps, keeping the atrioventricular valves closed and preventing the valve cusps from prolapsing into the atria. This therefore prevents the backflow of blood from the ventricles into the atria.** **Atrioventricular Valves Open** **When the ventricles relax (ventricular diastole) and the pressure inside the atria becomes greater than the pressure inside the ventricles, the atrioventricular valves open to allow blood to flow passively from the atria into the ventricles.** **Semilunar Valves** **Now we are going to look at the semilunar valves. The function of the semilunar valves is to prevent the backflow of blood from the pulmonary trunk and aorta into the ventricles when the ventricles relax.** **Click on each of the cards below to learn more about what is happening with the valves when they are closed and when they are open** **Semilunar Valves Closed** **When the ventricles relax (ventricular diastole) and the pressure inside the pulmonary trunk and aorta becomes greater than the pressure inside the ventricles, the semilunar valves close due to blood pushing back on the valve cusps and filling them with blood. This prevents the valve cusps from prolapsing into the ventricles, thus preventing the backflow of blood from the pulmonary trunk and aorta into the ventricles** **Semilunar Valves Open** **When the ventricles contract (ventricular systole) and the pressure inside the ventricles becomes greater than the pressure inside the pulmonary trunk and aorta, the semilunar valves open to allow blood to enter the pulmonary trunk and aorta from the ventricles.** **Fibrous Skeleton of the Heart** --------------------------------- ***LO6: Describe the structure and function of the heart valves and the fibrous skeleton of the heart*** **Now that we have looked at the functions of the heart valves, we are going to look at what supports these valves and the overall structure of the heart -- the fibrous skeleton.** **The fibrous skeleton is located in between the atria and the ventricles. It is made of dense connective tissue and consists of four fibrous rings that encircle the four heart valves, as well as fibrous tissue that connects these rings together. The fibrous skeleton anchors the cusps of the heart valves and provides a framework for the attachment of cardiac muscle tissue. It also acts as an electrical insulator between the atria and the ventricles. This is very important as it prevents the ventricles from being stimulated to contract at the same time as the atria, which allows the ventricles to fill with blood before they contract.** **Cardiac Conduction System** ----------------------------- ***LO7: Describe the components and function of the cardiac conduction system*** **Now that we have looked at the fibrous skeleton of the heart and noted its important function to provide electrical insulation between the atria and the ventricles, we are going to look at what stimulates the heart to contract -- the cardiac conduction system.** **The cardiac conduction system is the intrinsic pace-making system of the heart. It allows the heart to beat on its own at a consistent rhythm without any external input and ensures that the heart chambers are stimulated to contract in a coordinated fashion. However, heart rate and the force of heart contraction can be increased and decreased under the influence of the nervous system as well as hormones such as adrenaline.** **The cardiac conduction system consists of several components -- the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular (AV) bundle, right and left bundle branches and Purkinje fibres. Click on the hotspots on the image below to learn more about these components.** **Module: Cardiovascular System 2 - Blood Vessels** =================================================== **Pulmonary and Systemic Circulation** -------------------------------------- ***LO1: Define the pulmonary and systemic circulations*** **In the Cardiovascular System 1 module, the concept of the pulmonary and systemic circulations was introduced. To refresh, the pulmonary circulation is the circulation between the heart and the lungs, while the systemic circulation is the circulation between the heart and the body. In the Cardiovascular System 1 module, we focused on the pulmonary circulation. In this module, we are going to focus on the system circulation.** **The systemic circulation consists of arteries, veins and capillaries, which are the three main types of blood vessels. Recall from the Cardiovascular System 1 module that no matter what type of blood they are carrying (i.e. oxygenated or deoxygenated), arteries will always bring blood away from the heart, while veins will always bring blood towards the heart. Capillaries are the small blood vessels that connect arteries and veins. Before we look at the major blood vessels of the body, we are going to look at the layers that make up the wall of a typical blood vessel and compare the structure of arteries, veins and capillaries.** **Blood Vessel Wall** --------------------- ***LO2: Describe the three main tunics of the wall of a typical blood vessel*** **A typical blood vessel wall consists of three main layers or tunics ('tunica' = coat) -- an inner tunica intima, a middle tunica media and an outer tunica externa. These tunics surround the lumen of the blood vessel, which is the space in the centre of the blood vessel where blood flows.** **Click on the hotspots on the image below to learn more about these three tunics.** **Arteries vs Veins** --------------------- ***LO3: Compare and contrast the structure of arteries, veins and capillaries and explain how this relates to their functions*** **Now that we have looked at the basic structure of a typical blood vessel, we are going to compare the structure of arteries and veins, which is directly related to their functions.** - - - - - - **Capillaries** --------------- ***LO3: Compare and contrast the structure of arteries, veins and capillaries and explain how this relates to their functions*** ================================================================================================================================ **Now we are going to look at the structure of capillaries compared to arteries and veins. Capillaries are the smallest blood vessels and are formed by the union of arterioles and venules. The union of blood vessels is referred to as an anastomosis. Capillaries are the site of gas and nutrient exchange between the blood and the tissues. Unlike arteries and veins, capillaries only contain a tunica intima in their walls and this layer is composed of only endothelium and a basement membrane. This allows for rapid gas and nutrient exchange.** ================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================ **There are three main types of capillaries, which are continuous capillaries, fenestrated capillaries and sinusoids or discontinuous capillaries. These classifications depend on the nature of the endothelium. In continuous capillaries, which are the most common type of capillaries, the endothelial cells form a complete lining with no gaps. In fenestrated capillaries and sinusoids, the endothelial cells contain gaps which allow larger substances to pass through. As the name suggests, these gaps are called fenestrations or pores in fenestrated capillaries. The gaps are larger in sinusoids than in fenestrated capillaries and the basement membrane is also discontinuous or even absent, unlike in fenestrated capillaries where the basement membrane is continuous** ================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================ **Major Arteries and Veins** ---------------------------- Now that we have looked at the structure of blood vessels, we are going to look at the major arteries and veins in the body. Before we do so, it is important to understand a few important concepts: 1. 2. 3. 4. 5. Make sure you keep these things in mind while we look at the major arteries and veins in the body. **Major Arteries - Aorta** -------------------------- ***LO4: Describe the aorta and the superior and inferior vena cavae*** ====================================================================== **We are going to start by looking at the major arteries in the body. This begins with the aorta, which is the largest artery in the body and is where all arteries in the body ultimately arise from. Recall from the Cardiovascular System 1 module that the aorta arises from the left ventricle of the heart and carries oxygenated blood to all parts of the body. It has three main parts, which are the ascending aorta, the aortic arch and the descending aorta.** =========================================================================================================================================================================================================================================================================================================================================================================================================================================================================== **Click on the hotspots on the image below to learn more about these three main parts.** ======================================================================================== **Major Arteries - Head and Neck** ---------------------------------- ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** Now that we have looked at the aorta, we are going to look at the major arteries of each main body region, starting with the head and neck. This begins with the right and left common carotid arteries, which as we have seen, arise from the brachiocephalic trunk and aortic arch, respectively. Each common carotid artery bifurcates into an external carotid artery and an internal carotid artery. Click on the hotspots on the image below to learn more about these major arteries. The internal carotid arteries form a major contribution to the blood supply of the brain, together with branches of the right and left subclavian arteries called the vertebral arteries. The vertebral arteries travel in the transverse foramina of the cervical vertebrae (although they typically skip C7) before entering the skull through foramen magnum and uniting to form an artery called the basilar artery. Branches of the basilar artery and internal carotid arteries form an anastomosis of arteries supplying the brain called the cerebral arterial circle, or the circle of Willis. **Major Arteries - Thorax, Abdomen and Pelvis** ----------------------------------------------- ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** Now we are going to look at the major arteries of the thorax, abdomen and pelvis. ### **Thorax** The blood supply of the thorax is derived from the thoracic aorta, which begins at approximately the level of the sternal angle. Recall from the Skeletal System 2 module that the sternal angle is at the manubriosternal joint, which is the joint between the manubrium and body of the sternum. This is located at approximately the level of the intervertebral disc between the fourth and fifth thoracic vertebrae. The thoracic aorta descends through the thorax in the posterior part of the mediastinum. Recall from the Cardiovascular System 1 module that the mediastinum is the central space in the thoracic cavity between the two lungs. The thoracic aorta initially travels to the left of the vertebral column, but as it descends it becomes more central and by the time it reaches the aortic hiatus in the diaphragm, it lies anterior to the vertebral column. The thoracic aorta gives rise to many branches that supply the thoracic and abdominal walls and internal thoracic structures such as the lungs and oesophagus. The branches that supply the thoracic and abdominal walls are referred to as parietal branches and an example is the posterior intercostal arteries, which travel in between the ribs ('inter' = between, 'costal' = ribs). The branches that supply the internal thoracic structures are referred to as visceral branches (visceral = organ) and examples include the bronchial arteries for the lungs and the oesophageal arteries for the oesophagus. Remember that the heart, which is also a thoracic structure, is supplied by the coronary arteries which arise from the ascending aorta. ### **Abdomen** The blood supply of the abdomen is derived from the abdominal aorta, which begins once the thoracic aorta has passed through the aortic hiatus in the diaphragm. The abdominal aorta descends through the abdominal cavity anterior to the vertebral column, until it reaches approximately the level of the fourth lumbar vertebra where it bifurcates into the right and left common iliac arteries. The abdominal aorta gives rise to many branches that supply the abdominal wall and the internal abdominal structures. These include, but are not limited to, the renal arteries and the gonadal arteries, both of which are paired, and three unpaired branches called the celiac trunk, superior mesenteric artery and inferior mesenteric artery. Click on the hotspots on the image below to learn more about these major branches. ### **Pelvis** The blood supply of the pelvis is derived from arteries that arise after the bifurcation of the abdominal aorta. Recall that the abdominal aorta bifurcates into the right and left common iliac arteries at approximately the level of the fourth lumbar vertebra. Each common iliac artery then bifurcates into an external iliac artery and an internal iliac artery. The external iliac arteries will ultimately continue into the lower limbs to supply them with blood, while the internal iliac arteries will supply the pelvis via many branches. **Major Arteries - Upper and Lower Limbs** ------------------------------------------ ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** Now we are going to look at the major arteries of the upper and lower limbs. ### **Upper Limb** The blood supply of the right and left upper limbs are derived from the right and left subclavian arteries, respectively. Recall that the right and left subclavian arteries arise from the brachiocephalic trunk and aortic arch, respectively. The continuation of the subclavian artery and the subsequent branching that occurs ultimately gives rise to the major arteries of the upper limb. As well as the subclavian artery, these include the axillary artery, brachial artery, radial artery and ulnar artery. Click on the hotspots on the image below to learn more about these major arteries. The radial and ulnar arteries anastomose to form two arterial arches on the palmar surface of the hand called palmar arches. These arches then give rise to branches that supply blood to the hand. ### **Lower Limb** The major arteries of the lower limb follow a very similar pattern to those of the upper limb. The blood supply of the right and left lower limbs are derived from the right and left external iliac arteries, respectively. Recall that the external iliac arteries arise from the common iliac arteries. Once each external iliac artery passes underneath the inguinal ligament, which is a ligament in the groin region, it becomes the femoral artery. The continuation of the femoral artery and the subsequent branching that occurs ultimately gives rise to the major arteries of the lower limb. As well as the femoral artery, these include the popliteal artery, anterior tibial artery, posterior tibial artery and fibular artery. Click on the hotspots on the image below to learn more about these major arteries. The anterior and posterior tibial arteries continue into the foot on the dorsal and plantar surfaces, respectively, where they give rise to branches that supply blood to the foot. Some of these branches anastomose to form an arterial arch called the plantar arch on the plantar surface of the foot, which gives rise to further branches. **Major Veins - Introduction** ------------------------------ ***LO6: Define tributary, superficial vein, deep vein and venae comitantes*** Now that we have looked at the major arteries of the body, we are going to look at the major veins. Before we do this, we are going to discuss some important concepts regarding veins that were introduced earlier in the module. **1. Veins have tributaries** While arteries have branches, like the branches of a tree, veins have something called tributaries. A tributary is a vein that drains into a larger vein. Think of a river flowing into a lake -- the river is a tributary of the lake. **2. Veins can be classified as either superficial veins or deep veins** It is important to understand the difference between superficial veins and deep veins and also how they are related to one another. - - **3. Deep veins that travel with larger arteries are single veins, while deep veins that travel with smaller arteries are typically paired** Deep veins that travel with large arteries such as the axillary artery in the upper limb and the femoral artery in the lower limb are large, single veins. However, deep veins that travel with smaller arteries such as the radial artery in the upper limb and the fibular artery in the lower limb are typically paired and are called venae comitantes, or accompanying veins. These veins can usually be found travelling on either side of the artery they are accompanying. **Major Veins - Vena Cavae** ---------------------------- ***LO4: Describe the aorta and the superior and inferior vena cavae*** Now we are going to start looking at the major veins of the body. This begins with the superior and inferior vena cavae, which are the two largest veins in the body and are where all veins except those that drain the heart ultimately drain into. Recall from the Cardiovascular System 1 module that the superior and inferior vena cavae drain deoxygenated blood into the right atrium of the heart. The superior vena cava drains all structures above the diaphragm except the heart itself. Remember that the heart is drained by the coronary sinus, which also drains into the right atrium of the heart. The inferior vena cava drains all structures below the diaphragm. Click on the hotspots on the image below to learn more about the superior and inferior vena cavae. **Major Veins - Head and Neck** ------------------------------- ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** Now that we have looked at the superior and inferior vena cavae, we are going to look at the major veins of each main body region. Recall that arteries and deep veins travel together and deep veins follow the same path as their correspondingly named arteries, but in the opposite direction. This will become evident as we look at the major veins of each main body region. We are going to start with the head and neck. However, unlike most of the regions of the body, the major arteries and deep veins of the head and neck do not necessarily have corresponding names. Recall that the major arteries of the head and neck that we have looked at are the right and left common, external and internal carotid arteries. In the head and neck, there are no carotid veins. Instead, there are the right and left external and internal jugular veins. Click on the hotspots on the image below to learn more about these major deep veins **Major Veins - Thorax, Abdomen and Pelvis** -------------------------------------------- ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** ### **Thorax** We did not look closely at any specific arteries of the thorax, so we are not going to look closely at any specific veins. However, it is worth re-highlighting the coronary sinus, which is the vein that drains blood from the heart. Recall from the Cardiovascular System 1 module that it is located in the posterior part of the coronary sulcus on the surface of the heart. ### **Abdomen** Recall that the major arteries of the abdomen that we have looked at are the renal arteries, gonadal arteries, celiac trunk, superior mesenteric artery and inferior mesenteric artery. All of these except the celiac trunk have correspondingly named deep veins that travel with them. The renal veins are tributaries of the IVC. The left renal vein must cross the midline in order to reach the IVC, which sits on the right-hand side of the body. The right gonadal vein is also a tributary of the IVC, but the left gonadal vein is typically a tributary of the left renal vein, as this is closer than the IVC. The superior and inferior mesenteric veins form part of a special venous system within the abdomen called the portal venous system. This system drains all the blood from a part of the digestive system called the gastrointestinal or GI tract and transports it to the liver to be processed before it is returned to the systemic circulation. This is very important, as the blood from the GI tract contains all absorbed nutrients which must be processed in the liver. It may also contain toxins that have been ingested and need to be removed from the blood. The main vein in the portal venous system is called the portal vein, or hepatic portal vein ('hepatic' = liver). We will look more closely at this vein and the portal venous system overall in another module. ### **Pelvis** Recall that the major arteries of the pelvis that we have looked at are the internal iliac arteries, which arise from the common iliac arteries. As we have already seen, there are common iliac veins that travel with the common iliac arteries and these merge to form the IVC. Similarly, there are internal iliac veins that travel with the internal iliac arteries. **Major Veins - Upper and Lower Limbs** --------------------------------------- ***LO5: Describe the major arteries and veins of the following regions: head and neck; thorax, abdomen and pelvis; upper and lower limbs*** Now we are going to look at the major veins of the upper and lower limbs. ### **Upper Limb** Recall that the major arteries of the upper limb that we have looked at are the subclavian artery, axillary artery, brachial artery, radial artery and ulnar artery. All of these have correspondingly named deep veins that travel with them. The subclavian and axillary veins are single veins, as the correspondingly named arteries are large arteries. However, the brachial, radial and ulnar arteries are smaller arteries, so they typically have paired veins called venae comitantestravelling with them -- these would be the brachial veins, radial veins and ulnar veins, respectively. The arterial arches in the hand called palmar arches also have similarly named venous arches travelling with them called palmar venous arches. These are tributaries of the paired radial and ulnar veins, which merge to form the paired brachial veins. The brachial veins then merge with another vein called the basilic vein to form the axillary vein, which continues as the subclavian vein. As we have already seen, the subclavian vein then merges with the internal jugular vein to form the brachiocephalic vein and the two brachiocephalic veins merge to form the SVC. The palmar venous arches, radial veins, ulnar veins, brachial veins, axillary vein and subclavian vein are all deep veins that travel with their correspondingly named arteries. However, there are also superficial veins in the upper limb and these are tributaries of the deep veins. The basilic vein, which was mentioned above as the vein that merges with the brachial veins to form the axillary vein, is one of the superficial veins of the upper limb. The others are the cephalic vein, median cubital vein and dorsal venous network or arch. Click on the hotspots on the image below to learn more about these superficial veins. ### **Lower Limb** Like the major arteries, the major veins of the lower limb follow a very similar pattern to those of the upper limb. Recall that the major arteries of the lower limb that we have looked at are the external iliac artery, femoral artery, popliteal artery, anterior tibial artery, posterior tibial artery and fibular artery. All of these have correspondingly named deep veins that travel with them. The external iliac, femoral and popliteal veins are single veins, as the correspondingly named arteries are large arteries. However, the anterior tibial, posterior tibial and fibular arteries are smaller arteries, so they typically have paired veins called venae comitantes travelling with them -- these would be the anterior tibial veins, posterior tibial veins and fibular veins, respectively. The arteries of the foot also have similarly named deep veins travelling with them. These are tributaries of the paired anterior tibial and posterior tibial veins from the dorsal and plantar surfaces of the foot, respectively. The paired fibular veins are tributaries of the posterior tibial veins. The anterior and posterior tibial veins merge to form the popliteal vein, which continues as the femoral vein. The femoral vein then continues as the external iliac vein, which as we have already seen, merges with the internal iliac vein to form the common iliac vein. The two common iliac veins then merge to form the IVC. The anterior tibial veins, posterior tibial veins, fibular veins, popliteal vein, femoral vein and external iliac vein are all deep veins that travel with their correspondingly named arteries. However, similar to the upper limb, there are also superficial veins in the lower limb and these are tributaries of the deep veins. The superficial veins of the lower limb are the great saphenous vein, small saphenous vein and dorsal venous network or arch. Click on the hotspots on the image below to learn more about these superficial veins. **Skeletal Muscle Pump** ------------------------ ***LO7: Briefly describe the skeletal muscle pump*** As well as the concepts regarding veins that were discussed earlier in the module, there is one more important concept to look at which is that of "pumps" to assist with venous return to the heart. This is important, as the blood pressure in veins is much lower than in arteries, so other mechanisms are needed to assist with pushing blood through them towards the heart. The skeletal muscle pump is particularly relevant to the veins of the lower limb, where venous return occurs against gravity. As skeletal muscles contract, deep veins travelling between them are squeezed to assist with the return of venous blood to the heart, essentially forming a pump. There is also another pump called the respiratory pump that assists with venous return to the heart via the IVC, whereby contraction and relaxation of the diaphragm during breathing (i.e.respiration) causes changes in intra-abdominal pressure (i.e. pressure inside the abdominal cavity) that assist with pushing venous blood through the IVC against gravity towards the heart.