Tracing Blood Flow Through the Heart

What is covered in this Lesson

    1. Chambers of the of the Heart
    2. Pulmonary Circulation & Systemic Circulation 
    3. Tracing the Path of Blood

By the end of this lesson you should be able to:

    1. Describe the four chambers of the heart and their role in blood transport. 
    2. Identify the valved of the heart and understand their function in blood transport. 
    3. Compare and contrast the pulmonary circulation and system circulation.
    4. Trace the flow of blood from any starting point in the heart, body or lungs.
    5. List the major vascular componets that transport blood to and from the heart

Key Terms

  • Left & Right Atrium
  • Left & Right Ventricle
  • Aorta
  • Pulmonary Arteries & Veins
  • SuperiorInferior Vena Cava
  • Capillaries
    • • Venules
  • Atrioventircular Valves
    • • Mitral Valve (Bicuspid Valve)
    • • Tricuspid Valve
  • Semilunar Valves
  • Chordae Tendinae

Chambers of the Heart


The human heart consists of four chambers: two artia (singular = atrium) and two ventricles. 

  • • Atria receive blood coming into the heart.
  • • Ventricles pump blood away from the heart.

One either side of the heart – left or right – you will notice one atrium and one ventricle. 

  • Right chambers of the heart contain mostly deoxygenated blood
  • Left chambers of the heart contain mostly oxygenated blood.

All four chambers two separate circulatory circuits that (i) allow for gas exchange at the lungs and (ii) delivery of oxygenated blood to the rest of the body. These are called pulomary and systemic circulation, respectively. 

Author: ZooFari | License: CC BY-SA 3.0


A key feature of the heart is the presence of valves. Located between the each atrium and ventricle is a valve, a specialized structure that ensures one-way flow of blood. The valves between the atria and ventricles are known generically as atrioventricular valves. The valves at the openings that lead to the pulmonary trunk and aorta are known generically as semilunar valves. The interventricular septum is visible in the figure above (noted at ‘Septum’ in the diagram. The atrioventricular septum has been removed to better show the bicuspid valve (or mitral valve) and the tricuspid valve


Each flap of the valve is attached to strong strands of connective tissue called chordae tendineae, literally meaning “tendinous cords,” or sometimes commonly referred to as “heart strings.” They connect each of the valve flaps to a papillary muscles that extends from the inferior ventricular surface. 

When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises. To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction.

Pulmonary Circulation versus Systemic Circulation

The primary function of the cardiovascular system is to deliver oxygen to cells throughout the body, so that each of those cells can use that oxygen in cellular respiration. To achieve this, our cardiovascular system has two distinct but linked circuits in the human circulation called the

pulmonary and systemic circuits. Although both transport blood, they do so to different locations and for different purposes. 

Pulmonary circulation will deliver blood to the lungs for gas exchange. Here, blood will release carbon dioxide into the lungs, and absorb oxygen from it. The webbed like structures on the diagram indicate something called capillary fenestrations; which are porous areas of the capillaries that allow the exchangeof molecules. 


Now that blood has been oxygenated, Systemic cirrOur blood is a carrier for gases and in our body, that’s primarily oxygen gas (O2) and carbon dioxide (CO2). The primary function of the cardiovascular system is to deliver oxygen to cells throughout the body, so that each of those cells can use that oxygen in cellular respiration. In order to oxygenate our blood, we need to send it to the 

Pulmonary Circulation

The pulmonary circuit transports blood to and from the lungs, where it picks up oxygen and delivers carbon dioxide for exhalation.

  • Transportation to and from the lungs.
  • Heart (Right Ventricle) → Pulmonary artery → Lungs
    • This blood is deoxygenated and will pick up oxygen in the lungs.
  • Lungs → Pulmonary vein → Heart (Left Atrium)
    • This blood is oxygenated.


Systemic Circulation

The systemic circuit transports oxygenated blood to virtually all of the tissues of the body and returns relatively deoxygenated blood and carbon dioxide to the heart to be sent back to the pulmonary circulation.

  • Transportation to and from the body.
  • Heart (Left Ventricle) → Aorta → Body
    • This blood is oxygenated and will deliver oxygen to all cells in the body.
  • Body → Inferior & Superior Vena Cava → Heart (Right Atrium)
    • This blood is relatively deoxygenated.

Making Connections – The Heart as an Interchange



Tracing the Path of Blood

The right ventricle pumps deoxygenated blood into the pulmonary trunk, which leads toward the lungs and bifurcates into the left and right pulmonary arteries. These vessels in turn branch many times before reaching the pulmonary capillaries, where gas exchange occurs: carbon dioxide exits the blood and oxygen enters. The pulmonary trunk arteries and their branches are the only arteries in the post-natal body that carry relatively deoxygenated blood. Highly oxygenated blood returning from the pulmonary capillaries in the lungs passes through a series of vessels that join together to form the pulmonary veinsthe only post-natal veins in the body that carry highly oxygenated blood. The pulmonary veins conduct blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and on to the many branches of the systemic circuit. Eventually, these vessels will lead to the systemic capillaries, where exchange with the tissue fluid and cells of the body occurs. In this case, oxygen and nutrients exit the systemic capillaries to be used by the cells in their metabolic processes, and carbon dioxide and waste products will enter the blood.


The blood exiting the systemic capillaries is lower in oxygen concentration than when it entered. The capillaries will ultimately unite to form venules.   These venules – or very small veins – join to form larger veins, eventually flowing into the two major systemic veins: the superior vena cava and the inferior vena cava. These major venae cavae (plural for vena cava) return blood to the right atrium,  which then moves into the right ventricle. This process of blood circulation continues as long as the individual remains alive. Understanding the flow of blood through the pulmonary and systemic circuits is critical to all health professions.





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