The Heart

The heart is a ‘muscular bag’ filled with blood that contributes to the circulatory system by pumping blood around the body. It is about the size of an adult’s fist and weighs around 300g. In humans, the heart is in the chest, enclosed by the ribs and sternum (the breastbone, the bone located in the middle of the chest). Since the heart is filled with blood and constantly pumping, it is surrounded by an inelastic pericardial membrane, which helps prevent the heart from over-distending with blood.

The Heart The Heart

Create learning materials about The Heart with our free learning app!

  • Instand access to millions of learning materials
  • Flashcards, notes, mock-exams and more
  • Everything you need to ace your exams
Create a free account
Table of contents

    The heart is made of specialised muscle cells called cardiac muscles cells. These cells can continuously contract and relax without fatigue. The movement of these cells does not require stimulation by the nervous system.

    The dying off of heart muscles usually signals a heart attack, as the heart muscles do not receive enough oxygen to continue contracting and relaxing.

    What does the heart look like from the outside?

    Let’s explore the heart from the outside first.

    The two sides of the heart

    This muscular organ is divided into two parts: the left side and the right side.

    The Heart, a model of a heart, StudySmarterFig. 1 - A model of the heart

    You may wonder what purpose it serves for the heart to be divided into two. The left side receives oxygenated blood from the lungs and pumps it to the body, and the right side receives deoxygenated blood from the body and pumps it to the lungs. Blood has to pass through the lungs first to be oxygenated. There is a large drop in blood pressure after passing through the lungs, and the heart needs to pump this blood to increase its pressure. Hence, the heart is split into two separate pumps lying side by side instead of one pump.

    Regardless, both sides of the heart contract and relax at the same time.

    The Heart, the heart pumping blood both side sof the heart relax at the same time, StudySmarterFig. 2 - The heart pumping blood. Notice that both sides relax at the same time

    Blood vessels of the heart

    The heart is connected to four blood vessels - two veins (vena cava and pulmonary vein) and two arteries (aorta and pulmonary artery).

    The Heart, labelled diagram of a heart, StudySmarterFig. 3 - The heart labelled

    Veins carry blood to the heart. The two veins that connect to the heart include:

    • Vena cava - brings deoxygenated blood from both the lower and upper body

    • Pulmonary vein - brings oxygenated blood from the left and right lungs

    In contrast, arteries carry blood away from the heart. The two veins that connect to the heart include:

    • Aorta - large and arching, also branches into several smaller arteries to transport oxygenated blood up to the head and the rest of the lower body

    • Pulmonary artery - branches into two to transport deoxygenated blood into the left and right lungs

    Blood vessels supply oxygen and nutrients to the heart muscles; they need to contract and relax throughout the organism’s lifetime. Heart muscles have coronary arteries and cardiac veins. Coronary arteries branch off from the aorta and supply the heart muscles with oxygenated blood, whereas cardiac veins bring deoxygenated blood containing metabolic waste into the vena cava. On the other hand, cardiac veins bring deoxygenated blood containing metabolic waste into the vena cava.

    Study tip: Remember that pulmonary arteries carry deoxygenated blood whereas pulmonary veins carry oxygenated blood, unlike all the other arteries and veins in the body. Many students get confused with pulmonary blood vessels in the exams.

    Four chambers of the heart

    The human heart comprises four chambers – two on the right side and another two on the left. The chambers of the heart are divided by a muscular structure called the septum. The septum stops the blood from both sides of the heart from mixing together (Figure 3).

    The upper chambers that are smaller in size are the atria (singular atrium). The atria are connected to the veins, with the right atrium connected to the vena cava and the left atrium connected to the pulmonary vein. The atria have thin walls as they only pump blood into the small ventricles, whose lower pumping pressure prevents the ventricles from bursting.

    The larger lower chambers are the ventricles. The ventricles are connected to the arteries, with the right ventricle connected to the pulmonary artery and the left ventricle connected to the aorta. The ventricles have thicker walls than the atria as they pump blood into organs further away from the heart. Furthermore, the walls of the left ventricle are thicker than the right. This is because the blood is pumped from the left ventricles to the extremities and needs to overcome the elastic recoil of arteries. As for the thinner walls of the right ventricles, the lungs that receive blood from the right ventricles are closer to the heart and smaller than the rest of the body, but the lungs’ capillaries are extremely delicate.

    Study tip: It may be confusing to remember where veins and arteries connect. Just remember the acronym AV – arteries are connected to ventricles, whereas atria are connected to veins.

    Heart valves

    How the heart achieves a regular direction of blood flow across the different chambers?

    This is due to structures called valves, which prevent the backflow of blood. The valves located between the atria and ventricles are called atrioventricular valves. The left and right sides of the heart each have an atrioventricular valve. The atrioventricular valve on the left side is called the bicuspid (or mitral) valve, whereas the atrioventricular valve on the right side is called the tricuspid valve. The atrioventricular valves have string-like, tendinous support? Atrioventricular valves have tendinous cords to prevent pressure from the heart from turning the valves inside out when the ventricles contract.

    The Heart, heart valves, StudySmarterFig. 4 - Heart valves

    Moreover, there are valves located on the arteries connected to the heart. These valves are called semilunar valves, including aortic valves and pulmonary valves. The name ‘semilunar’ is derived from the shape as the valves look like two crescents. Both atrioventricular and semilunar valves have flaps that open and close. The key difference between bicuspid and tricuspid valves is the number of flaps these valves have. Bicuspid valves have two flaps, whereas tricuspid valves have three flaps. Semilunar valves, like the tricuspid valve, have three flaps.

    Study tip: It might be difficult to remember what type of valve belongs to which side of the heart. It might help to remember that the right ventricle is thinner and needs three flaps to compensate.

    How does the heart function?

    The heart functions by a series of contractions and relaxations of the heart muscles. These move the blood across the different chambers and send it to respective organs via blood vessels. The valves also help regulate the unidirectionality of blood flow.

    As such, the components of the heart all work together to form the cardiac cycle.

    In brief, the heart functions to:

    • Pump oxygenated blood around the body.

    • Receive and pump deoxygenated blood to the lungs for oxygenation.

    • Transport hormones and other vital substances to different parts of the body.

    • Maintain a constant blood pressure across the different vessels.

    The Heart - Key takeaways

    • The heart is a ‘muscular bag’ filled with blood that contributes to the circulatory system by pumping blood around the body. It is divided into the left and right sides and connected to four blood vessels - two veins (vena cava and pulmonary vein) and two arteries (aorta and pulmonary artery).
    • The heart is made up of four chambers - the right atrium and ventricle and the left atrium and ventricle. The veins connect to the atria, whereas the arteries connect to the ventricles.
    • Heart muscles have coronary arteries and cardiac veins. Coronary arteries branch off from the aorta and supply the heart muscles with oxygenated blood, whereas cardiac veins bring deoxygenated blood containing metabolic waste into the vena cava.
    • Valves are present in the heart to prevent backflow. Atrioventricular valves, between the atria and ventricles, include the tricuspid valve at the right side of the heart and the bicuspid valve at the left side of the heart.
    The Heart The Heart
    Learn with 9 The Heart flashcards in the free StudySmarter app

    We have 14,000 flashcards about Dynamic Landscapes.

    Sign up with Email

    Already have an account? Log in

    Frequently Asked Questions about The Heart

    How does the heart work?

    The chambers of the heart regularly contract and relax to transport both oxygenated and deoxygenated blood around the body.

    What is the heart and its function?

    The heart is a bag of muscle that pumps blood around the body.

    What are the 4 main functions of the heart?

    These functions include:

    • Pump oxygenated blood around the body.

    • Receive and pump deoxygenated blood to the lungs for oxygenation.

    • Transport hormones and other vital substances to different parts of the body.

    • Maintain a constant blood pressure across the different vessels.

    What happens during a heart attack?

    During a heart attack, the heart muscles die off due to a lack of oxygen supply to cardiac muscle tissues.

    What are the four parts of the heart?

    The four parts of the heart include the heart chambers, vessels, valves and septum.

    1
    About StudySmarter

    StudySmarter is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.

    Learn more
    StudySmarter Editorial Team

    Team The Heart Teachers

    • 8 minutes reading time
    • Checked by StudySmarter Editorial Team
    Save Explanation

    Study anywhere. Anytime.Across all devices.

    Sign-up for free

    Sign up to highlight and take notes. It’s 100% free.

    Join over 22 million students in learning with our StudySmarter App

    The first learning app that truly has everything you need to ace your exams in one place

    • Flashcards & Quizzes
    • AI Study Assistant
    • Study Planner
    • Mock-Exams
    • Smart Note-Taking
    Join over 22 million students in learning with our StudySmarter App