Heart Anatomy & Circulatory System Blood Flow

The heart is built to efficiently fill, oxidize, and pump blood throughout the body. In order to do this, it requires chambers, valves, and electrical signals to properly accomplish its goals. This chapter also discusses the anatomy of the heart, which acts as a strong background for the the rest of the heart and vasculature unit.

 

Learning Outcomes

In this section you will learn…

  • The general anatomical features of the heart that are important for contraction and blood flow.
  • Why the heart is compartmentalized and how it facilitates function.
  • The pathway of blood flow throughout the body.

Heart Anatomy 

The heart is a composed of two pumps and two pipes. The closed-circuit design of the heart means that no variable is independent from the others. Whenever a variable, such as cardiac output (CO), is altered, it will affect the other variables. This is an important concept to understand as you continue through the units of this subchapter.

 

Tips From Past Students

When you are looking at a heart, remember it is in reference to anatomical position (the left and right of the specimen, not your own).

Specialized Conduction Components of the Heart

This diagram showcases the heart through the orientation of the frontal plane. The figure is labeled to showcase the heart’s basic anatomical structures, including; right and left atria and ventricles, and the aorta. The figure also highlights the specialized electrical conducting components such as; the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and the Purkinje fibers. The white arrows illustrate the pathway of electrical conductance between these structures of the heart.

 

 

A labeled diagram of the heart illustrated in the frontal plane. The diagram lists the four chambers of the heart; right and left atria and the right and left ventricles. The key structures involved in the electrical conductance of the heart are also labeled. The ordered pathway of depolarization is emphasized; Sinoatrial node, Atrioventricular node, Bundle of His, and the Purkinje Fibers.
Figure 1. Schematic cross sectional diagram of the heart. Key anatomical structures are labelled and the flow of electrical activity is illustrated by the white arrows.

When looking at this diagram, take note that the left ventricle of the heart is much bigger and more muscular than the right because it has the hard job of pumping the oxygenated blood through the aorta to the rest of the body.

 

Test Your Knowledge

Thinking Beyond: 

Describe the electrical pathway of depolarization in the heart. Why is this ordered pattern of depolarization important for coordinated contraction of the cardiac myocytes? Hint: Think about the significance the depolarization- contraction relationship has on proper blood flow.

 Compartmentalization of the Circulatory System

The heart is composed of two pumps and pipes. The two pumps that comprise the heart are the left heart and the right heart. These pumps present functionally different purposes. The left heart is responsible for pumping blood from the left ventricle and directing the flow to the tissues, otherwise referred to as systemic circulation. The right heart is responsible for pumping blood across the lungs, referred to as pulmonary circulation.

This figure was included because it shows the path of blood through the heart, body, and lungs on a macroscopic scale. This simplified schematic provides a visualization that may promote a better understanding. The diagram also does an excellent job of solidifying the idea that the left atria and left ventricle are functionally separate from the right atria and right ventricle. Though they can directly impact each other, they receive and send blood to different locations.

A diagram depicting blood flow throughout the pulmonary circulation. The oxygenated status of the blood is emphasized in this diagram. Deoxygenated blood is seen to exit the right heart, where it travels to the lungs. As the blood crosses the lungs, it becomes oxygenated due to the gas exchange in the pulmonary capillary beds. This oxygenated blood is shown to flow from the lungs back to the left heart.
Figure 2. The heart functions as a double ventricle. Blood moves from the body into the right atrium and then into the right ventricle, where it is pumped into the lungs. Blood becomes oxygenated in the lungs, moves into the left atrium and into the left ventricle, where it is pumped into the body again.

Functional Compartmentalization of the Heart

The figure below depicts functional compartmentalization of the human circulatory system which is a key topic to understand before learning details of this system. This section will help with understanding pressure differences and blood flow as it shows you where the structures are located.

 

A simplified schematic of the human circulatory system showing the pathway of oxygenated and deoxygenated blood through the systemic and pulmonary capillaries. Oxygenated blood flows from the left heart into the aorta, arteries, and arterioles to the systemic capillaries. Here gas exchange occurs, and deoxygenated blood travels up the venules, veins, and superior and inferior vena cavas to the right heart. From the right heart, the blood is sent to the lungs to become oxygenated by the gas exchange in the pulmonary capillary beds before returning to the left heart.
Figure 3. Diagram showing the human circulatory system including the contrast of oxygenated and deoxygenated blood, as well as the systemic and pulmonary capillary beds.

Read the diagram clockwise to follow the flow of blood.

Blood oxygenated via the pulmonary capillary bed leaves the heart through the aorta, then travels to the arteries, followed by the arterioles which lead to the systemic capillaries. Oxygen diffuses to the tissues, causing deoxygenated blood to travel back to the heart via the venules. These combine into veins, which drain into the superior and inferior vena cava, then to the right heart. The blood undergoes gas exchange at the pulmonary capillary bed and the cycle begins again.

 

Test Your Knowledge

Thinking Beyond: 

Functional compartmentalization is used by many body systems – not just the circulatory system! In fact, we spoke about functional compartmentalization when discussing the gastrointestinal tract in HK*2810. Try to connect these systems by considering their differences and similarities. What relationship do compartments have with each other? How does this relationship influence the regulation of each system? Hint: Consider how these systems communicate at the cellular level to achieve their shared goal.

 

Comparison of Pulmonary and Systemic Capillaries

The capillary beds of the circulatory system serve the purpose of conducting gas exchange. In the systemic circulation, the capillaries allow for oxygen delivery into the body tissues. In the pulmonary circulation, the capillaries of the lungs allow for the O2 (oxygen) we breathe in to enter the bloodstream while CO2 (carbon dioxide) is removed.

The diagram below illustrates the relative locations of pulmonary capillaries, vasculature, compartments of the heart, and sites of gas exchange. The diagram can also be used to compare systemic and pulmonary capillaries. Notice how in the lung’s pulmonary capillaries, the O2 we inhale is added to the blood, and the CO2 is removed. The systemic capillaries showcase the reverse process as O2 is removed from the blood to be used by active tissues that produce CO2 as a byproduct.

 

A more detailed schematic of the blood flow in the heart and circulatory system. Key anatomical structures are labeled, such as; the four chambers of the heart, the tricuspid valve, bicuspid valve, aorta, and vena cava. The oxygenated status of the blood in circulation is shown with emphasis on the gas exchange occurring in the pulmonary and systemic capillary beds. In the pulmonary capillaries, oxygen is brought into the blood while carbon dioxide is removed. In direct contrast, oxygen is taken from the blood, and carbon dioxide is added in the systemic capillaries.
Figure 4. Image depicting the anatomy of the heart and the circulatory system. Emphasis on how the oxygenation status of the blood changes twice: once in pulmonary capillaries and once in systemic capillaries.

Both systems are composed of arterioles and venules. These arise from arteries and feed into veins. However, systemic capillaries are regulated by resistance arterioles to a greater degree than pulmonary capillaries. This is so that fluctuations in resistance do not affect oxygenation at the lung. We will talk more about resistance later in this section. The big thing to take away from here is that pulmonary and systemic capillaries are set up in the same way but are regulated differently.

 

Test Your Knowledge

Clinical Application: 

In order to determine whether someone is having a left or a right heart attack, doctors will check the systemic and pulmonary compartments for fluid build-up:

  • A RIGHT heart attack = fluid build up in the peripheral tissues.
  • A LEFT heart attack = fluid build up in the lungs.

Using what you’ve just learned about heart anatomy and the direction of blood flow in the circulatory system, explain why this is true. Hint: Think about the pathway of blood after going through the right heart vs. the left heart.

If this clinical example interests you, maybe a career as a cardiologist would too?

 Blood Flow

Pathway of Blood Flow

Now that you understand how the heart and the circulatory system are organized, we can examine the pathway of blood in closer detail.

An in-depth schematic of the heart and circulatory system. The bottom left shows an overview of the entire circulatory system, presenting the pathway of blood from the heart into the systemic circulatory system into the capillary beds. The blood then flows from the capillary beds back up to the right heart into the pulmonary circulation. From here, the blood crosses the lungs and returns to the left heart. The upper right photo shows a labeled schematic of the heart. The flow of blood through the chambers is emphasized. Blood enters the right heart from the superior and inferior vena cavas, where it passes through the right atria to the right ventricle. The right ventricle pumps blood to the lungs through the pulmonary arteries, and this blood returns to the left heart through the pulmonary veins. The blood then passes through the left atria to the left ventricle that ejects it to the aorta and into the systemic circulation.
Figure 5. Two labeled diagrams presenting the anatomy of the heart and the circulatory systems. The top right provides an in-depth diagram of the anatomy of the chambers, valves, and vasculature connected to the heart. The bottom left emphasizes the anatomy of the systemic and pulmonary circulations.

Blood flows from the right atrium to the right ventricle, where it is pumped into the pulmonary circuit. The blood in the pulmonary artery branches is low in O2 but relatively high in CO2. Gas exchange occurs in the pulmonary capillaries (O2 into the blood, CO2 out), and blood high in O2 and low in CO2 is returned to the left atrium. From here, blood enters the left ventricle, which pumps it into the systemic circuit. Following the exchange in the systemic capillaries (O2 and nutrients out of the capillaries and CO2 and wastes in), blood returns to the right atrium, and the cycle is repeated.

 

Tips From Past Students 

An easy way to memorize the direction of blood flow…

  • Arteries carry blood Away from the heart, where as veins carry blood back towards the heart.

Valves of the Heart

The heart’s anatomical structure includes the presence of four valves that function to promote proper blood flow through the organ. Two of the four valves are referred to as atrioventricular valves, including the tricuspid valve located between the right atria and ventricle and the mitral valve located between the left atria and ventricle. The other two valves include; the pulmonary valve located between the right ventricle and the pulmonary arteries and the aortic valve located between the left ventricle and the aorta. All the valves are passive as their opening and closing are controlled by pressure gradients. Contraction of the right atria causes the pressure within the atria to become greater than the pressure in the right ventricle. This opens the tricuspid valve, and blood flows from the right atria to the ventricle. As blood fills the right ventricle, pressure builds, followed by the contraction of the right ventricle. This closes the tricuspid valve and opens the pulmonary valve, permitting blood flow across the lungs. Oxygenated blood returns to the heart through the pulmonary veins and into the left atria, which contracts to open the mitral valve. Blood flows from the left atria to the left ventricle through the mitral valve. Finally, as the left ventricle fills, pressure builds, and the ventricle begins to contract. This causes the closure of the mitral valve and the opening of the aortic valve, facilitating blood flow out of the heart and into the systemic circulation. Proper functionality of these valves is critical for the heart’s efficiency as passage through the valves ensures the adequate filling of the chambers while the closure of the valves prevents back-flow. Refer to figure 5 for a visual representation of these chambers within the structure of the heart.

 

Test Your Knowledge

Real-Life Scenario:

The fossa ovalis is a small region in the interatrial septum (the wall of muscle separating the left and right atria). Prior to birth, this region remains an open hole known as the foramen ovalis which allows blood flow between the right and left heart. In utero, this hole remains open because blood flow is not required across lungs since the fetus is receiving oxygen through the placenta. However, once born, the fetus will utilize their lungs to receive oxygen and the foramen ovalis will close forming the fossa ovalis. What would happen to the heart if this hole did not close?[1] Hint: Think about the flow of blood in the right heart in contrast to the left heart. If this hole failed to close, the two circulations would not be separated.

For more information and the answer to this question, read this short article.

 

Key Takeaways

Consider the following concepts to help guide your studies:

  • The anatomy of the heart and circulatory system is essentially composed of two “pumps” ; the right heart and left heart, and various connective “pipes” ; arteries, veins, and capillaries.
  • Blood flows throughout the closed circuit of the circulatory system following the path of; left ventricle → aorta → systemic arteries → systemic capillaries → systemic veins → superior and inferior vena cava → right atrium → right ventricle → pulmonary arteries → pulmonary capillaries → pulmonary veins → left ventricle.
  • The systemic circulation is responsible for delivering oxygenated blood to the body tissues, whereas the pulmonary circulation is responsible for blood flow across the lungs.
  • Capillary beds facilitate the function of gas exchange. The systemic capillary beds conduct gas exchange supplying oxygen to the tissues. The pulmonary capillary beds conduct gas exchange where new oxygen inhaled is exchanged for carbon dioxide we exhale.

 Subchapter Quiz

The questions below can be used to assess your knowledge within this chapter. There are five multiple-choice questions that you should attempt without referring to your notes. The questions will provide you with responses to your answers to guide your studying but should not be used as your only resource.

 

Media Attributions

  1. Giblett, J.P., Abdul-Samad, O., Shapiro, L.M., Rana, B.S., Calvert, P.A.(2019). Patent Foramen Ovale Closure in 2019. Interv Cardiol, 14(1), 34-41. http://doi.org/10.15420/icr.2018.33.2 ↵
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