Video: Cardiovascular system

"All by myself, don’t wanna be, all by myself anymore…"

Ahhh, looks like your typical case of a broken heart. I'm sure we've all experienced something similar. Maybe you knew they were trouble from the start but the heart wants what it wants, and after all, you need to follow your heart even if you can't mend a broken heart. Phew! That's tough going but thankfully our hearts don't actually literally stop working when we go through heartbreak. Even though it may feel like your heart is being ripped out of your chest, it actually continues to work hard, pumping blood all around our bodies as an integral component of the cardiovascular system. So let's give our heartbroken friend a little alone time as we delve into the cardiovascular system.

All right, if your heart is racing with anticipation, take a deep breath. We're going to keep this tutorial simple by exploring the cardiovascular system through its three main subdivisions – the heart, the blood vessels, and the blood itself. As we move along, we'll dissect this system into its separate circuits that transmit blood – the pulmonary and systemic circuits, which includes the coronary circuit. We'll also examine the anatomical differences between blood vessels, namely, arteries and veins and take a look at the composition of blood that travels through these vessels. Finally, to consolidate our knowledge, we'll take a look at a clinical scenario surrounding the cardiovascular system.

Before we begin, let's take a moment to identify what the cardiovascular system is all about. The cardiovascular system, or circulatory system, is vital for our survival as it functions to transport blood around the body. The main job of this system is to deliver oxygen to the body tissues while simultaneously removing carbon dioxide produced by metabolism. This intricate system also functions to transport nutrients around the body from the gastrointestinal tract providing all tissues with the energy and nourishment they need to function. The cardiovascular system also plays a role in removing waste products of metabolism and transporting them to the excretory organs for disposal. Finally, it plays a crucial role in protecting the body from infections due to the presence of white blood cells within the blood.

So now that you know a little bit about its function, are you ready to pump up your knowledge on the anatomy of the circulatory system? Hooray! Let's get started with the heart.

As the central component of the circulatory system, the heart is a dynamic muscular pump that is electrically stimulated to propel blood through the entire body. If we take a look at a coronal section of the heart, we can see that it is divided into a right and left side by a muscular septum. The heart is then further divided into four chambers which are known as the right and left atrium and the right and left ventricle. We can also identify these chambers from an external view of the heart. Here is the right and left atrium and here is the right and left ventricle.

Taking a look at this schematic illustration of the cardiovascular system, we can see the four chambers of the heart and the direction of blood flowing in and out of the heart. The atria collect blood returning to the heart while the ventricles pump blood out of the heart. Valves located within the heart prevent backflow of blood into the chambers.

As we look at the different circuits of the circulatory system, we will dive deeper into the structure and function of the heart; however, in general, the heart is a two-way pump that transports blood containing oxygen, nutrients, and hormones to the tissues of the body via arteries. It also receives deoxygenated blood from the periphery of the circulatory system via veins and pumps it to the lungs for gas exchange.

Moving on to the pulmonary circuit. The pulmonary circulation carries blood between the heart and lungs. This system transmits deoxygenated blood from the right side of the heart to the lungs where the exchange of oxygen and carbon dioxide that the body produces occurs. Subsequently, the newly oxygenated blood returns from the lungs back to the left side of the heart.

Let's take a closer look at how this all works. This circuit begins with receiving oxygen-deprived blood from the systemic circulation which we'll meet in just a second. This blood drains into the right atrium from the superior and inferior vena cavae. It then flows into the right ventricle where it's pumped through the pulmonary arteries to the lungs. Following this, the oxygenated blood returns to the left atrium of the heart via the pulmonary veins. Continuing along, the systemic circuit conducts blood between the heart and the peripheral tissues. In the system, oxygenated blood is transported from the left side of the heart to the peripheral tissues and deoxygenated blood is carried from the periphery to the right side of the heart.

In a nutshell, the systemic circuit begins with receiving oxygen-rich blood in the left atrium fresh from the pulmonary circulation. This blood flows into the left ventricle which utilizes its abundance of muscle to pump the blood through the aorta into systemic circulation nourishing the peripheral tissues. At the periphery, oxygen and nutrients flow into the tissues and carbon dioxide and waste products pass into the blood. Deoxygenated blood returns to the heart through the superior and inferior vena cava which drain into the right atrium.

A component of systemic circulation is the coronary circulation. This is a system of arteries and veins dedicated to the heart itself. Coronary arteries supply oxygenated blood to the heart while cardiac veins drain the deoxygenated blood away. Maintaining the health of these coronary arteries is critical to keeping the all-important heart alive and well. Perhaps you have heard of coronary artery disease before given how common and serious it is; however, stay tuned until the end of this tutorial as we'll be tackling all things about coronary artery disease.

Now that we're in the flow of things, let's put the vascular in cardiovascular system and look at the blood vessels.

There are three main types of blood vessels – arteries, veins, and capillaries. They are categorized according to their histologic structure. These vessels are organized in the following order. Arteries undergo a process of ramification and narrow into arterioles and then capillaries. Venules then arise from capillary beds which unite and enlarge into veins. As we previously discussed, arteries transport blood away from the heart and between the tissues. Struggling to remember the direction of blood flow within arteries? All you have to do is look at the first letter. A for arteries and A for away. Arteries have thick muscular walls with small internal lumen, or passageways, that can withstand high pressure blood. They typically carry oxygenated blood except for the pulmonary artery which conveys deoxygenated blood.

On the contrary, veins carry blood towards the heart from the peripheral tissues. They have thin walls, a larger internal lumen than arteries as they contain blood under low pressure, and valves which prevents the backflow of blood. Typically, veins carry deoxygenated blood except for the pulmonary veins. Lastly, capillaries are a microscopic web of vessels with walls measuring one endothelial cell in thickness. They are found in the tissues and only tolerate slow-moving, low pressure blood. This is where the exchange of gases, nutrients, water, and waste products occurs through their thin and fenestrated capillary walls.

All right, with the vessels all wrapped up, let's turn our attention to the blood itself.

When you think of blood, you may envision something like this or this; however, our blood actually has four major components – plasma, red blood cells, white blood cells, and platelets – and if you were to look at your blood under a microscope, it would look like this – not quite your typical gory blood smear. Plasma constitutes approximately 55 percent of total blood volume and forms the liquid component of blood. Plasma functions to help transport carbon dioxide, hormones, and metabolic waste. When separated from red blood cells through centrifugation, it has a clear straw-like color. Red blood cells, also known as erythrocytes, are formed in the bone marrow and function as oxygen carriers. Red blood cells constitute approximately 45 percent of the total blood volume. A decrease in the number of healthy red blood cells can lead to a pathology known as anemia. White blood cells, or leukocytes, are also created in the bone marrow and are a vital part of the immune system. These fighter cells produce antibodies which help destroy harmful microorganisms in order to keep us healthy. Finally, platelets are small cells that clump together to form blood clots and protect the body by preventing bleeding. White blood cells and platelets only account for approximately one percent of the blood volume.

And that's it – an introduction to the cardiovascular system done and dusted. Let's take a look at an important clinical note.

As one of the most prevalent cardiovascular diseases, coronary artery disease is a severe condition that impacts many individuals. This disease is caused by a narrowing of the arteries that supply the heart as a result of atherosclerosis. Atherosclerosis is an accumulation of fatty cholesterol plaque within a vessel. Atherosclerotic buildup leads to narrowing of the blood vessels reducing the oxygen delivery to the heart tissue as the flow of oxygenated blood is diminished. Ultimately, coronary artery disease can lead to two significant conditions. Angina is the painful spasming of the coronary arteries as a result of diminished blood flow. Angina is usually not life-threatening, but may act as a warning sign of a heart attack or stroke. More critically, myocardial infarction, or a heart attack, occurs as a result of a complete blockage of the artery due to the development of a blood clot or dislodged plaque. A myocardial infarction resulting from the complete occlusion of the anterior interventricular artery is gravely known as a widowmaker. This type of infarction can be particularly lethal given that this artery supplies a substantial portion of the heart with blood. Coronary artery disease can be treated with minimally invasive measures such as stent placement, a.k.a. percutaneous transluminal coronary angioplasty, or through coronary artery bypass graft surgery for severe disease.

There you have it! Hopefully now you have a better understanding of the structural components and functions of the cardiovascular system. Before you take off, let's summarize what we learned today.

We began this tutorial by looking at the main subdivisions of the cardiovascular system starting with the heart. Here we discuss the anatomy, blood flow, and function of this organ. Next, we explored the pulmonary circulation, the systemic circulation, and the coronary circulation supplying the heart itself. Moving on, we examined the blood vessels of the cardiovascular system which include the arteries, veins, and capillaries. We differentiated these vessels anatomically and discussed their function. We then discussed the final component of the cardiovascular system – the blood. Here we explored its four major components – plasma, red blood cells, white blood cells, and platelets – and the function of each of these elements. Finally, we explored a clinical scenario surrounding the cardiovascular system – coronary artery disease. We identified the main cause, associated conditions, and treatments.

Excellent work everyone! We hope you enjoyed this tutorial. We'll catch you next time and happy studying!