Human Heart Anatomy Quiz
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Questions and Answers

What is the function of the pericardium?

  • Allows for electrical conduction in the heart
  • Regulates heart valve function
  • Encases and protects the heart (correct)
  • Promotes blood circulation within the heart

    • Which chamber of the heart has the thickest wall?

  • Left ventricle (correct)
  • Right ventricle
  • Right atrium
  • Left atrium

    • What is the role of the atrioventricular (AV) valves?

  • Allow blood flow from the ventricles to the aorta
  • Facilitate oxygen diffusion in the heart
  • Prevent backflow of blood into the atria (correct)
  • Control blood pressure in the pulmonary circuit

    • What conditions may arise from inflammation of the pericardium?

    <p>Pericarditis</p> Signup and view all the answers

    What separates the right and left atria in the heart?

    <p>Interatrial septum</p> Signup and view all the answers

    Which structure allows blood flow from the right ventricle to the pulmonary trunk?

    <p>Pulmonary valve</p> Signup and view all the answers

    How many times will the human heart beat on average in a lifetime?

    <p>2.5 billion</p> Signup and view all the answers

    Which chamber of the heart receives deoxygenated blood from the systemic circuit?

    <p>Right atrium</p> Signup and view all the answers

    What are trabeculae carneae?

    <p>Muscular ridges inside the ventricles</p> Signup and view all the answers

    What distinguishes the workload of the left ventricle from the right ventricle?

    <p>Thicker wall with higher pressure</p> Signup and view all the answers

    Which heart sound indicates the closure of the AV valves and marks the start of ventricular contraction?

    <p>S1</p> Signup and view all the answers

    What happens during isovolumetric contraction?

    <p>All valves are closed with no volume change</p> Signup and view all the answers

    Which component of the cardiac cycle occurs right after ventricular systole?

    <p>Isovolumetric relaxation</p> Signup and view all the answers

    What is the primary function of the sinoatrial (SA) node in the heart's conducting system?

    <p>Acts as a pacemaker for the heart</p> Signup and view all the answers

    What does an increased preload lead to in terms of cardiac function?

    <p>Stronger contractions</p> Signup and view all the answers

    Which factor primarily determines afterload?

    <p>Tension required to open semilunar valves</p> Signup and view all the answers

    Which interval in an ECG indicates the time for ventricles to undergo a complete cycle?

    <p>Q-T interval</p> Signup and view all the answers

    What is the role of the cardioinhibitory center in the medulla oblongata?

    <p>Slows heart rate</p> Signup and view all the answers

    What type of arteries are characterized as large vessels that stretch and recoil near the heart?

    <p>Elastic arteries</p> Signup and view all the answers

    Which type of capillaries are best suited for rapid exchange of larger solutes?

    <p>Fenestrated capillaries</p> Signup and view all the answers

    Which of the following factors will NOT increase stroke volume?

    <p>Decreased venous return</p> Signup and view all the answers

    What happens to the heart rate in bradycardia?

    <p>Heart rate slows below 60 bpm</p> Signup and view all the answers

    What is the purpose of blood being pushed into the capillaries?

    <p>For gas exchange between blood and tissues</p> Signup and view all the answers

    What prevents blood from returning to the atria when the ventricles contract?

    <p>Atrioventricular valves</p> Signup and view all the answers

    Which valves are classified as semilunar valves?

    <p>Pulmonary and aortic valves</p> Signup and view all the answers

    Which structure is responsible for anchoring the atrioventricular valves?

    <p>Papillary muscles</p> Signup and view all the answers

    What is the role of chordae tendineae in the heart?

    <p>Prevent valve inversion during contraction</p> Signup and view all the answers

    How is blood flow maintained through the coronary circuit?

    <p>By changing blood pressure and elastic rebound</p> Signup and view all the answers

    What happens to the semilunar valves when the ventricles are relaxed?

    <p>They close to prevent backflow</p> Signup and view all the answers

    Which artery supplies the left ventricle and left atrium?

    <p>Circumflex artery</p> Signup and view all the answers

    What does the cardiac cycle consist of?

    <p>Contraction and relaxation phases</p> Signup and view all the answers

    What is the primary function of the aortic valve?

    <p>To prevent backflow from the aorta into the left ventricle</p> Signup and view all the answers

    What are the phases when the atria contract to fill the ventricles called?

    <p>Atrial systole</p> Signup and view all the answers

    How long does a typical cardiac cycle last at a heart rate of 75 bpm?

    <p>800 msec</p> Signup and view all the answers

    What does the coronary sinus do?

    <p>Drains blood from the myocardium to the right atrium</p> Signup and view all the answers

    What structural feature of the cardiac skeleton helps stabilize heart valves?

    <p>Interconnected bands of connective tissue</p> Signup and view all the answers

    During which phase do the ventricles fill with blood?

    <p>Ventricular diastole</p> Signup and view all the answers

    What is the primary function of lymphatic tissue in the body?

    <p>Production of lymphocytes</p> Signup and view all the answers

    Which type of white blood cell is primarily responsible for phagocytosing bacteria?

    <p>Neutrophils</p> Signup and view all the answers

    What process occurs to heme units after they are stripped of iron?

    <p>Converted into biliverdin and bilirubin</p> Signup and view all the answers

    Which type of white blood cell is involved in allergic reactions and parasitic infections?

    <p>Eosinophils</p> Signup and view all the answers

    What do macrophages do with old red blood cells?

    <p>Engulf and destroy them</p> Signup and view all the answers

    What is one of the main functions of the circulatory system?

    <p>Delivers oxygen to cells</p> Signup and view all the answers

    Which statement correctly describes red blood cells (RBCs)?

    <p>RBCs are biconcave discs that lack organelles</p> Signup and view all the answers

    What is the primary component of hemoglobin that allows it to interact with oxygen?

    <p>Iron ions</p> Signup and view all the answers

    Where is red bone marrow primarily found in the body?

    <p>In the long bones and cranial bones</p> Signup and view all the answers

    What process refers to the formation of red blood cells?

    <p>Erythropoiesis</p> Signup and view all the answers

    What happens to red blood cells at the end of their life span?

    <p>They undergo hemolysis or are engulfed by macrophages</p> Signup and view all the answers

    How does the circulatory system help maintain body temperature?

    <p>By absorbing and distributing heat throughout the body</p> Signup and view all the answers

    What characteristic of red blood cells aids in their ability to transport gases?

    <p>Large surface area-to-volume ratio</p> Signup and view all the answers

    What distinguishes hemoglobin molecules in red blood cells?

    <p>Each hemoglobin consists of four heme units</p> Signup and view all the answers

    What percentage of circulating red blood cells are typically replaced each day?

    <p>1 percent</p> Signup and view all the answers

    What condition is characterized by excess accumulation of pericardial fluid?

    <p>Cardiac Tamponade</p> Signup and view all the answers

    Which structure is a remnant of the fetal foramen ovale that closes at birth?

    <p>Fossa ovalis</p> Signup and view all the answers

    Which chambers of the heart are divided by the interventricular septum?

    <p>Right ventricle and left ventricle</p> Signup and view all the answers

    What is the purpose of the semilunar valves?

    <p>To control blood flow from ventricles into arteries</p> Signup and view all the answers

    Which ventricle sends blood through the pulmonary circuit?

    <p>Right ventricle</p> Signup and view all the answers

    What is the primary function of the pectinate muscles located in the atria?

    <p>To provide strength to the atrial walls</p> Signup and view all the answers

    What separates the right and left atria of the heart?

    <p>Interatrial septum</p> Signup and view all the answers

    What type of valve is found between each atrium and ventricle?

    <p>Atrioventricular valve</p> Signup and view all the answers

    Which layer of the pericardium is directly attached to the heart?

    <p>Epicardium</p> Signup and view all the answers

    Which valve is also called the tricuspid valve?

    <p>Right atrioventricular valve</p> Signup and view all the answers

    What does the T wave in an electrocardiogram represent?

    <p>Ventricular repolarization</p> Signup and view all the answers

    During isovolumetric relaxation, what occurs in the heart?

    <p>No volume change occurs as all valves are closed</p> Signup and view all the answers

    What primarily affects stroke volume according to the Frank-Starling law?

    <p>Preload</p> Signup and view all the answers

    Which component of the cardiac cycle begins after the semilunar valves open?

    <p>Ventricular ejection</p> Signup and view all the answers

    How does sympathetic stimulation affect heart contractility?

    <p>It increases contractility</p> Signup and view all the answers

    Which heart sound occurs when the semilunar valves close?

    <p>S2</p> Signup and view all the answers

    What does an increased heart rate indicate?

    <p>Increased cardiac output</p> Signup and view all the answers

    What is the function of the conducting system in the heart?

    <p>To initiate and distribute electrical impulses throughout the heart</p> Signup and view all the answers

    Which type of blood vessel has the thinnest walls allowing for substance exchange?

    <p>Capillaries</p> Signup and view all the answers

    What does an abnormal length in the P-R interval indicate?

    <p>Potential damage to the AV node or conducting pathways</p> Signup and view all the answers

    What happens to stroke volume as afterload increases?

    <p>Stroke volume decreases</p> Signup and view all the answers

    Which type of arteries are primarily responsible for distributing blood to specific tissues?

    <p>Muscular arteries</p> Signup and view all the answers

    What physiological condition is characterized by a heart rate slower than 60 bpm?

    <p>Bradycardia</p> Signup and view all the answers

    What effect does venous return have on the end-diastolic volume (EDV)?

    <p>It increases EDV</p> Signup and view all the answers

    What is the primary role of the heart valves?

    <p>To ensure blood flows only in a forward direction</p> Signup and view all the answers

    Which structure specifically prevents blood from returning to the left atrium?

    <p>Mitral valve</p> Signup and view all the answers

    During which phase of the cardiac cycle do the AV valves close?

    <p>Ventricular systole</p> Signup and view all the answers

    What happens to the semilunar valves when the ventricles relax?

    <p>They close to prevent backflow</p> Signup and view all the answers

    What is the function of the chordae tendineae?

    <p>To prevent AV valves from inverting</p> Signup and view all the answers

    Which artery supplies blood to the right atrium and parts of the ventricles?

    <p>Right coronary artery</p> Signup and view all the answers

    Which of the following is a characteristic of semilunar valves?

    <p>They are shaped like half moons</p> Signup and view all the answers

    What provides a rapid conduction path during ventricular contraction?

    <p>Moderator band</p> Signup and view all the answers

    What occurs during the relaxation phase known as diastole?

    <p>Blood fills the ventricles</p> Signup and view all the answers

    What role does the cardiac skeleton play in the heart?

    <p>It stabilizes heart valves</p> Signup and view all the answers

    What structure drains the area supplied by the anterior interventricular artery?

    <p>Great cardiac vein</p> Signup and view all the answers

    Which condition leads to an increase in myocardial blood flow during exertion?

    <p>Increased metabolic demand</p> Signup and view all the answers

    Which phase of the cardiac cycle occurs after atrial systole?

    <p>Ventricular systole</p> Signup and view all the answers

    What role does the elastic rebound of aortic walls play in blood flow?

    <p>Maintains blood flow in arteries</p> Signup and view all the answers

    What function does lymphatic tissue serve in the body?

    <p>Supplement blood cell production</p> Signup and view all the answers

    What occurs after heme units are stripped of iron in macrophages?

    <p>They become bilirubin</p> Signup and view all the answers

    Which type of white blood cell is primarily responsible for engulfing bacteria?

    <p>Neutrophils</p> Signup and view all the answers

    What happens to hemoglobin that is not phagocytized after red blood cells expire?

    <p>It is excreted in urine</p> Signup and view all the answers

    Which of the following is true about lymphocytes?

    <p>They produce antibodies and participate in cell-mediated immunity</p> Signup and view all the answers

    What is the primary function of red blood cells?

    <p>Transport respiratory gases</p> Signup and view all the answers

    Which component of hemoglobin interacts with oxygen molecules?

    <p>Heme units</p> Signup and view all the answers

    How do red blood cells facilitate transport in small vessels?

    <p>By forming stacks called rouleaux</p> Signup and view all the answers

    Where is red bone marrow primarily located in the human body?

    <p>In long and flat irregular bones</p> Signup and view all the answers

    What is the lifespan of a typical red blood cell?

    <p>Typically around 120 days</p> Signup and view all the answers

    Which function of the circulatory system involves maintaining fluid balance?

    <p>Regulation of blood pressure</p> Signup and view all the answers

    What happens to the majority of the red blood cells at the end of their life?

    <p>They undergo hemolysis or are engulfed by macrophages</p> Signup and view all the answers

    What regulates body temperature through changes in blood flow?

    <p>Vasodilation and vasoconstriction</p> Signup and view all the answers

    What percentage of circulating red blood cells are replaced daily?

    <p>1 percent</p> Signup and view all the answers

    What is the name of the process that refers to red blood cell formation?

    <p>Erythropoiesis</p> Signup and view all the answers

    What is the role of the interatrial septum?

    <p>Separates the right and left atria</p> Signup and view all the answers

    What is the function of the trabeculae carneae?

    <p>Increase surface area within the ventricles</p> Signup and view all the answers

    What occurs during cardiac tamponade?

    <p>Excess accumulation of pericardial fluid</p> Signup and view all the answers

    Which valve allows blood to flow from the right atrium to the right ventricle?

    <p>Tricuspid valve</p> Signup and view all the answers

    What describes the workload of the left ventricle compared to the right ventricle?

    <p>The left ventricle pumps blood with 4-6 times the pressure of the right ventricle</p> Signup and view all the answers

    Which structure is primarily responsible for anchoring the atrioventricular valves?

    <p>Chordae tendineae</p> Signup and view all the answers

    What structural feature distinguishes the ventricles from the atria?

    <p>Thickness of the walls</p> Signup and view all the answers

    What describes the pericardium?

    <p>Double-walled sac surrounding the heart</p> Signup and view all the answers

    Which chamber of the heart sends oxygenated blood to the systemic circuit?

    <p>Left ventricle</p> Signup and view all the answers

    What condition is caused by a mother's immune system producing anti-Rh antibodies after exposure to Rh antigens during delivery?

    <p>Hemolytic disease of the newborn</p> Signup and view all the answers

    What treatment can prevent maternal sensitization in future pregnancies for Rh-negative mothers?

    <p>Administration of anti-Rh antibodies (RhoGAM)</p> Signup and view all the answers

    What is a leading cause of death from malaria?

    <p>Rupturing of infected RBCs</p> Signup and view all the answers

    Which vitamin deficiency is commonly associated with pernicious anemia?

    <p>Vitamin B12</p> Signup and view all the answers

    What is the primary reason for the fragility of RBCs in sickle cell disease?

    <p>Abnormal hemoglobin structure</p> Signup and view all the answers

    What is a common symptom of severe hemolytic disease of the newborn?

    <p>High bilirubin concentrations causing jaundice</p> Signup and view all the answers

    What type of leukemia is characterized by impaired production of WBCs from the bone marrow?

    <p>Lymphoid leukemia</p> Signup and view all the answers

    What is the main factor that allows venipuncture to be commonly used for blood withdrawal?

    <p>Vein walls are thinner and seal quickly</p> Signup and view all the answers

    What condition is primarily characterized by a lack of adequate production of normal hemoglobin protein subunits?

    <p>Thalassemia</p> Signup and view all the answers

    Which inherited bleeding disorder is primarily observed in males and is associated with missing clotting factors?

    <p>Hemophilia</p> Signup and view all the answers

    What is the function of the heart valves?

    <p>To control blood flow in one direction</p> Signup and view all the answers

    Where is the tricuspid valve located?

    <p>Between the right atrium and right ventricle</p> Signup and view all the answers

    What prevents backflow of blood from the aorta into the left ventricle?

    <p>Aortic valve</p> Signup and view all the answers

    What role do papillary muscles play in valve function?

    <p>They tighten chordae tendineae to prevent valve inversion</p> Signup and view all the answers

    What happens to the semilunar valves when the ventricles contract?

    <p>They close</p> Signup and view all the answers

    During which phase of the cardiac cycle do the ventricles fill with blood?

    <p>Diastole</p> Signup and view all the answers

    What happens during ventricular systole?

    <p>Blood is pushed into the pulmonary artery and aorta</p> Signup and view all the answers

    What is the main purpose of coronary circulation?

    <p>To deliver oxygen and nutrients to cardiac muscle</p> Signup and view all the answers

    What type of blood is returned to the right atrium by the superior and inferior venae cavae?

    <p>Deoxygenated blood</p> Signup and view all the answers

    When do the atria contract during the cardiac cycle?

    <p>Before the ventricles during systole</p> Signup and view all the answers

    What prevents backflow of blood into the right ventricle?

    <p>Pulmonary valve</p> Signup and view all the answers

    What is the sequence of events during atrial and ventricular contraction?

    <p>Atria contract, then ventricles contract</p> Signup and view all the answers

    How does the blood flow in the coronary circuit maintain itself?

    <p>Through changing blood pressure and elastic rebound</p> Signup and view all the answers

    What structural feature of the cardiac skeleton helps to stabilize heart valves?

    <p>Dense connective tissue bands</p> Signup and view all the answers

    Study Notes

    Human Heart

    • The human heart beats more than 2.5 billion times during an average lifetime, showcasing its crucial role in sustaining life and supporting various physiological functions. This prolific beating facilitates the continuous circulation of blood throughout the body, delivering essential oxygen and nutrients to tissues while removing carbon dioxide and metabolic waste products.
    • The heart is located in the middle mediastinum, a central compartment in the thoracic cavity, along with large vessels entering or leaving the mediastinum. These vessels include the aorta, pulmonary arteries, and veins, which play a pivotal role in blood circulation. The heart’s positioning is crucial for optimal functionality, enabling efficient communication with the surrounding blood vessels as they transport blood to and from the heart.

    Structures Surrounding the Heart

    • The pericardium is a double-walled sac surrounding the heart, providing both protection and structural support. It serves as a barrier against infection and injury while allowing the heart to move freely during its contractions.
    • It has two layers: the fibrous pericardium, which is the tough outer layer that anchors the heart to surrounding tissues, and the serous pericardium, which is further divided into the parietal and visceral layers. The parietal layer lines the fibrous layer, while the visceral layer, also known as the epicardium, tightly adheres to the surface of the heart.
    • The pericardium can become inflamed, a condition known as pericarditis, which can cause chest pain and other complications. Additionally, the accumulation of excessive fluid within the pericardial sac can lead to cardiac tamponade, a serious condition that impairs the heart's ability to pump effectively.

    Heart Chambers

    • The heart has four chambers: two atria located at the top and two ventricles situated at the bottom. The atria receive blood returning to the heart, while the ventricles are responsible for pumping blood out of the heart, playing distinct roles in the heart's functionality.
    • The chambers are divided into right and left sides by the interatrial septum, which separates the right atrium from the left atrium, and the interventricular septum, which separates the right ventricle from the left ventricle. This structural arrangement ensures that oxygenated and deoxygenated blood remain separated, allowing for efficient circulation.
    • The right atrium receives blood from the systemic circuit, primarily through the superior and inferior venae cavae, while the right ventricle pumps this deoxygenated blood into the pulmonary circuit for oxygenation in the lungs.
    • The left atrium receives oxygenated blood from the pulmonary circuit via the pulmonary veins, and the left ventricle pumps this oxygen-rich blood into the systemic circuit, distributing it throughout the body.

    Structures in the Atria

    • The right atrium receives deoxygenated blood from the superior and inferior venae cavae, as well as blood returning from the coronary sinus, which drains the heart muscle itself. This arrangement emphasizes the right atrium's role as the entry point for blood returning from both the entire body and the heart.
    • The fossa ovalis is a remnant of the fetal foramen ovale, an opening that allows blood to bypass the non-functioning fetal lungs. This structure typically closes at birth, becoming a sealed membrane, but can occasionally remain patent in certain individuals.
    • The left atrium receives oxygenated blood from the pulmonary veins, which carry blood from the lungs after gas exchange has occurred, exemplifying the heart's unique role in managing two different circuits—pulmonary and systemic.
    • Both atria contain pectinate muscles, which are muscular ridges located on the anterior wall of the atrium and in the auricles. These muscles aid in the contraction of the atria by increasing surface area and providing structural reinforcement during systole.

    Structures in the Ventricles

    • The right ventricle receives blood from the right atrium through the tricuspid valve, also known as the right atrioventricular valve, which features three cusps that ensure unidirectional blood flow. This valve opens during atrial contraction, allowing blood to fill the ventricle.
    • Upon ventricular contraction, blood exits through the pulmonary valve (pulmonary semilunar valve) into the pulmonary trunk, which then branches into the pulmonary arteries to carry deoxygenated blood to the lungs for oxygenation.
    • The left ventricle, in contrast, has a much thicker muscular wall than the right ventricle, a reflection of the greater force needed to pump blood through the systemic circuit. This chamber must generate sufficient pressure to propel blood throughout the entire body, requiring a robust muscular structure.
    • It receives blood from the left atrium through the mitral valve, also known as the bicuspid valve or left atrioventricular valve, which has two cusps acting as a barrier to prevent backflow into the atrium during ventricular contraction.
    • Once the left ventricle contracts, blood is ejected through the aortic valve (aortic semilunar valve) into the ascending aorta, where it begins its journey to nourish the various tissues and organs of the body.
    • Both ventricles contain trabeculae carneae, muscular ridges that enhance the pumping efficiency of the ventricles by promoting more effective contractions and minimizing blood turbulence.

    Chamber Comparisons

    • The atria, while structurally simpler, have similar workloads and wall thickness, reflecting their role in receiving blood, where low pressure is sufficient.
    • The ventricles, however, have significantly different workloads: the right ventricle pumps blood to the lungs, which are nearby and require less pressure to maintain circulation. In contrast, the left ventricle must pump against systemic vascular resistance, thereby requiring a greater effort and producing significantly higher pressure.

    Heart Valves

    • Four key valves, located at the entrances and exits to the ventricles, control the direction of blood flow through the heart:
      • The tricuspid valve is situated between the right atrium and right ventricle.
      • The pulmonary valve lies between the right ventricle and the pulmonary artery, directing blood towards the lungs.
      • The mitral valve is positioned between the left atrium and left ventricle, facilitating oxygenated blood flow while preventing backflow.
      • The aortic valve separates the left ventricle from the aorta, ensuring that blood flows into the systemic circulation without returning to the ventricle.

    AV Valve Structure

    • The tricuspid and mitral valves are equipped with cusps, which are flexible flaps of tissue attached to tendon-like connective tissue bands known as chordae tendineae. These structures are vital for maintaining the closure of the valves during ventricular contraction.
    • The chordae tendineae are anchored to thickened, cone-shaped papillary muscles, which contract in conjunction with the ventricles, preventing the valves from inverting due to pressure changes during the cardiac cycle.
    • The moderator band, a specialized band of muscle tissue located in the right ventricle, plays a critical role by tensing the papillary muscles prior to ventricular contraction, ensuring the function and integrity of the tricuspid valve.

    Pulmonary and Aortic Valves

    • These pulmonary and aortic valves each have three half-moon-shaped cusps that effectively prevent the backflow of blood into the ventricles following ventricular contraction. Their unique structure enables them to operate passively with the flow of blood, minimizing the need for additional muscular support.
    • Their design is inherently self-supporting; therefore, when the pressure in the ventricles decreases, the cusps close to block backward blood flow, maintaining efficient circulation.

    Valve Function During Heart Cycles

    • During ventricular relaxation (diastole), the atrioventricular (AV) valves are open, permitting blood to fill the ventricles smoothly from the atria while the semilunar valves are closed, preventing blood from flowing back into the ventricles.
    • Conversely, during ventricular contraction (systole), the AV valves close tightly to avoid backflow into the atria while the semilunar valves open to facilitate the ejection of blood into the pulmonary trunk and aorta.

    Heart Surface Anatomy

    • The anterior surface of the heart presents several key anatomical features:

      • All four chambers of the heart, enabling observation of their interrelationships.
      • The auricle of each atrium, which provides additional volume for blood entry.
      • The coronary sulcus, a noticeable groove demarcating the boundary between the atria and ventricles, houses important vessels and fat.
      • The anterior interventricular sulcus, marking the division between the left and right ventricles, plays a crucial role in external heart identification.
      • The ligamentum arteriosum is a fibrous remnant of a fetal connection between the aorta and pulmonary trunk, signaling developmental changes after birth.

    • The posterior surface of the heart displays various features, including:

      • All four chambers visible, which are critical for assessing the heart's functionality.
      • Four pulmonary veins returning oxygenated blood to the left atrium, crucial for systemic circulation.
      • Superior and inferior venae cavae returning deoxygenated blood to the right atrium, emphasizing the heart's pump function.
      • Coronary sinus, which drains blood returned from the myocardium back into the right atrium, highlighting the heart's vascular supply.
      • Posterior interventricular sulcus, further delineating the separation between the two ventricles, is an important landmark for cardiovascular assessments.

    Coronary Circulation

    • The coronary arteries play a critical role in supplying the cardiac muscle (myocardium) with the oxygen and nutrients necessary for its function, ensuring that the heart can effectively pump blood throughout the body.
    • The left and right coronary arteries arise from the ascending aorta and fill with blood during ventricular relaxation (diastole), illustrating the heart's unique vascular anatomy. Their branches distribute oxygenated blood to various regions of the myocardium, maintaining cardiac health.
    • Myocardial blood flow increases significantly during physical exertion or increased activity, demonstrating the heart's ability to respond to metabolic demands, ensuring sufficient oxygen and nutrient supply to meet the heightened activity levels.

    Right Coronary Artery

    • The right coronary artery supplies blood to several critical structures, including the right atrium, parts of both ventricles, and essential components of the cardiac conduction system, which regulates heart rhythm and coordination.
    • This artery follows the coronary sulcus, an anatomical landmark that aids in locating major vessels during surgical procedures or diagnostic imaging.

    Left Coronary Artery

    • The left coronary artery supplies vital oxygenated blood to the left ventricle, left atrium, and interventricular septum, which is essential for the proper functioning of the heart's pumping capability.

    Coronary Veins

    • The great cardiac vein is responsible for draining the area supplied by the anterior interventricular artery and empties into the coronary sinus, ensuring that deoxygenated blood returns to the right atrium efficiently.
    • The anterior cardiac veins drain the anterior surface of the right ventricle and empty directly into the right atrium, reflecting the heart's specialized venous drainage system.
    • The coronary sinus is an expanded vein that collects blood from various cardiac veins and delivers it into the right atrium, serving as a major conduit for the returned blood.
    • The posterior vein of the left ventricle drains the area supplied by the circumflex artery, further illustrating the network of veins associated with cardiac circulation.
    • The middle cardiac vein drains areas supplied by the posterior interventricular artery and also empties into the coronary sinus, providing another route for deoxygenated blood to return to the heart.
    • The small cardiac vein drains blood from the posterior aspect of the right atrium and ventricle, contributing to the coronary sinus and maintaining the efficiency of coronary circulation.

    Blood Flow Maintenance in the Coronary Circuit

    • Blood flow within the coronary circuit is carefully maintained through changes in blood pressure and the elastic rebound of the aorta:
      • During left ventricular contraction, blood pressure increases dramatically in the aorta, causing its elastic walls to stretch and accommodate this surge of blood.
      • Following relaxation of the left ventricle, the elastic recoil of the aortic wall pushes blood forward into the systemic circuit and backward into the coronary arteries, ensuring a consistent supply of oxygenated blood to the myocardium during both systole and diastole.

    Cardiac Skeleton (Fibrous Skeleton)

    • The cardiac skeleton, also known as the fibrous skeleton, serves as a flexible connective tissue framework composed of interwoven bands of dense connective tissue. Its integration into the heart structure provides several important functions:
      • It encircles the heart valves, stabilizing them and playing a role in the unidirectional flow of blood through the heart.
      • It surrounds the base of the aorta and pulmonary trunk, providing structural support to these major vessels.
      • Additionally, it electrically isolates the atrial from ventricular myocardium, ensuring proper sequential contraction of the chambers and preventing premature contractions.

    Cardiac Cycle

    • The cardiac cycle is defined as the period between the start of one heartbeat and the next, encapsulating all phases of heart activity within that timeframe. It is essential for maintaining a regular and efficient heartbeat, essential for survival.
    • Heart rate refers to the number of beats per minute, which is directly influenced by various physiological factors including exercise, stress, and overall health.
    • During the cardiac cycle, the atria contract first, filling the ventricles with blood, followed by ventricular contraction that pumps blood into the pulmonary and systemic circuits, demonstrating the coordination between the heart's chambers.
    • The cardiac cycle consists of two primary phases:
      • Systole is the phase of contraction when blood leaves the chamber, pushing it out into the arteries.
      • Diastole is the relaxation phase during which the chamber refills with blood.

    Sequence of Contractions

    • Atrial systole initiates the sequence, whereby the atria contract first, pushing blood into the relaxed ventricles beneath them, setting up the next phase of contraction.
    • Ventricular systole follows, wherein the ventricles contract to propel blood into the pulmonary and systemic circuits, while the atria are relaxing and refilling with blood, ensuring continuous, cyclic blood flow through the heart.

    Phases of the Cardiac Cycle

    • During (ventricular) diastole, all four chambers are relaxed, allowing passive filling of the ventricles with blood returning from both the kind of circulation.
    • Atrial systole completes the ventricular filling, ensuring the chambers are primed for the next contraction.
    • Atrial diastole continues until the initiation of the next cardiac cycle, emphasizing the rhythmic nature of the heart's functionality.
    • Ventricular systole is divided into two key phases:
      • Isovolumetric contraction is the initial phase where the ventricles contract, causing pressure to rise and the AV valves to close, yet not enough pressure exists to open the semilunar valves.
      • Ventricular ejection occurs when pressure increases sufficiently to open the semilunar valves, ejecting blood from the ventricle into the pulmonary artery and aorta.
    • Ventricular diastole likewise consists of two phases:
      • Early ventricular diastole involves relaxation of the ventricles and a drop in pressure, allowing blood backflow from the aorta and pulmonary trunk, causing closure of the semilunar valves to prevent regurgitation.
      • Isovolumetric relaxation occurs when all valves are closed, and the ventricles are at rest, while the atria passively fill with blood, preparing for the next cycle.
    • Late ventricular diastole sees all chambers relaxed, AV valves open, and passive filling of the ventricles reaching approximately 70% capacity, setting the stage for the next atrial contraction.

    Heart Sounds

    • The heart produces characteristic sounds that can be classified as follows:
      • S1 ("lubb"): This sound is produced when the AV valves close, marking the onset of ventricular contraction, and is typically louder and longer than subsequent sounds.
      • S2 ("dupp"): This sound occurs when the semilunar valves close, signaling the end of ventricular contraction, and is shorter and sharper than S1, often described as a "dupp" sound.
      • S3 and S4 sounds are very faint and rarely heard in healthy adults but can indicate certain conditions; S3 is associated with rapid blood flow into ventricles, while S4 is linked to atrial contraction.

    Cardiac Output (CO)

    • Cardiac output refers to the volume of blood pumped from the left ventricle each minute, a critical indicator of heart function and overall health.
    • This output is influenced by heart rate and stroke volume, both of which can change based on physical activity, emotional state, and overall cardiovascular health.

    Heart Rate (HR)

    • Heart rate is the number of contractions per minute, or beats per minute, and serves as a vital sign of cardiovascular function.

    Stroke Volume

    • Stroke volume refers to the volume of blood ejected from the ventricle per contraction, and it is crucial for understanding the efficiency of the heart’s pumping mechanism.

    Conducting System

    • The conducting system of the heart is characterized by its auto rhythmicity, which is the cardiac muscle's intrinsic ability to contract independently of neural or hormonal stimulation, thus ensuring continuous heartbeat without external input.
    • This system consists of specialized cardiac muscle cells, known as pacemaker and conducting cells, that initiate and distribute electrical impulses through the myocardium, coordinating contraction among the heart chambers.

    Electrocardiogram (ECG or EKG)

    • An electrocardiogram (ECG or EKG) is a diagnostic tool that records the heart's electrical activity from the body surface. This non-invasive procedure assesses the performance of nodal, conducting, and contractile components of the heart.
    • Abnormal patterns observed in an ECG can indicate heart damage, arrhythmias, or other cardiovascular conditions, providing important insights into heart health.
    • The appearance of an ECG varies based on the placement and number of electrodes used, which can be tailored to evaluate specific regions of the heart.

    ECG Components

    • The P wave represents atrial depolarization, with atrial contraction beginning approximately 25 milliseconds after the wave starts, indicating the initial phase of the cardiac cycle.
    • The QRS complex depicts ventricular depolarization; this is a larger wave attributed to the greater muscle mass of the ventricles. The onset of ventricular contraction begins shortly after the peak of the R wave, while atrial repolarization occurs concurrently but is masked by the larger QRS complex.
    • The T wave corresponds to ventricular repolarization, marking the recovery phase after contraction.

    ECG Intervals

    • The P–R interval is the period from the start of atrial depolarization to the onset of ventricular depolarization. A prolonged interval, longer than 200 milliseconds, may indicate damage to the conducting pathways or to the AV node, reflecting potential abnormalities in electrical conduction.
    • The Q–T interval indicates the time for the ventricles to undergo a complete cycle. Lengthening of this interval can occur due to electrolyte disturbances, medications, conduction problems, coronary ischemia, or myocardial damage, all of which may have significant clinical implications.

    Resting Heart Rate

    • The resting heart rate varies with age, general health, fitness level, and lifestyle factors, reflecting an individual’s cardiovascular resilience and functional capacity.
    • Normal resting heart rate is typically within the range of 60 to 100 beats per minute for adults, with well-trained athletes often exhibiting lower rates due to increased cardiovascular efficiency.
    • Bradycardia describes a heart rate slower than normal (less than 60 bpm), which can be a physiological adaptation in some but may also indicate underlying heart conditions in others.

    Cardiac Centers of the Medulla Oblongata

    • The medulla oblongata houses vital cardiac centers that regulate heart rate through autonomic pathways.
    • The cardioinhibitory center primarily controls parasympathetic neurons, which release acetylcholine to slow heart rate during restful states.
    • The cardioacceleratory center governs sympathetic neurons, stimulating the heart to increase heart rate during stress or physical activity via the release of norepinephrine.

    Factors Affecting Stroke Volume

    • End-diastolic volume (EDV) indicates the amount of blood in the ventricle at the end of diastole, significantly impacting stroke volume. Higher EDV correlates with greater ventricular filling, leading to an increase in stroke volume.
    • Venous return defines the amount of venous blood returned to the right atrium, influenced by factors such as blood volume, muscular activity, and the rate of blood flow—all essential components that determine filling pressure and thus stroke volume.
    • Filling time, which is the duration of ventricular diastole, is critical; a longer filling time allows for increased EDV and, consequently, greater stroke volume.

    Preload

    • Preload refers to the amount of myocardial stretch prior to contraction, influenced primarily by EDV. It is a key determinant of contractile strength.
    • A greater EDV results in a higher preload, thus leading to stronger contractions and increased blood ejected from the heart, illustrating the interrelation between volume, pressure, and myocardial performance.
    • The Frank-Starling Law of the Heart elaborates on this relationship, indicating that an increase in end-diastolic volume will invariably lead to an increase in stroke volume, up to a certain physiological limit.

    Contractility

    • Contractility is defined as the amount of force produced during ventricular contraction at a specified preload. It is a crucial factor governing stroke volume independent of preload changes.
    • Sympathetic stimulation and various hormones, including epinephrine, norepinephrine, thyroid hormone, and glucagon, can enhance contractility, thus improving cardiac output.
    • Conversely, contractility may be reduced by medications like beta blockers and calcium channel blockers, which can be utilized therapeutically to manage conditions of excessive cardiac activity.

    Afterload

    • Afterload represents the ventricular tension required to open the semilunar valves and achieve ventricular emptying. In essence, it is the pressure the ventricles must generate to push blood into the aorta and pulmonary trunk.
    • As afterload increases due to factors such as systemic vascular resistance, stroke volume decreases, showcasing the direct impact of arterial health on cardiac performance.
    • Increased afterload is often seen with vasoconstriction, which raises systemic resistance against which the heart must work, illustrating the importance of vascular health in overall cardiac function.

    Factors Affecting Cardiac Output

    • Changes in heart rate or stroke volume significantly alter cardiac output, which is vital for meeting the metabolic demands of the body. Cardiac output is influenced by physical activity, emotional stress, and overall cardiovascular health.

    Heart Failure

    • Heart failure is a serious condition characterized by the heart's inability to meet the demands of peripheral tissues effectively. This may result in insufficient cardiac output, leading to symptoms such as fatigue, fluid retention, and shortness of breath.

    Blood Vessels

    • Blood vessels are integral structures that conduct blood between the heart and peripheral tissues, playing essential roles in sustaining life through nutrient and waste exchange.
    • Arteries are responsible for carrying blood away from the heart, typically oxygenated, except for those in the pulmonary circuit.
    • Veins return blood to the heart, commonly deoxygenated, while accommodating larger volumes of blood with thinner walls compared to arteries.
    • Capillaries facilitate the exchange of substances between blood and tissues, showcasing the intricate network of the circulatory system.

    Three Layers of Arteries and Veins

    • The vessel walls of arteries and veins consist of three distinct layers:
      • The tunica intima, the innermost layer, is composed of a smooth endothelium and subendothelial connective tissue, providing a frictionless surface for blood flow.
      • The tunica media, the middle layer, is primarily made up of smooth muscle cells and elastic fibers, allowing vessels to constrict and dilate as required.
      • The tunica adventitia, the outermost layer, comprises connective tissue that provides structural support and flexibility, alongside vasa vasorum—tiny vessels that supply blood to the vessel walls themselves.

    Types of Arteries

    • Arteries are classified into several types based on their structure and function:
      • Elastic arteries, large vessels near the heart, exhibit the ability to stretch and recoil with each heartbeat, accommodating significant fluctuations in pressure.
      • Muscular arteries are medium-sized arteries that distribute blood to skeletal muscles and internal organs, characterized by a well-developed tunica media that regulates blood flow.
      • Arterioles, the smallest arteries, contain a thin tunica media and poorly defined tunica externa, allowing them to act as resistance vessels that regulate blood flow into capillary beds.

    Capillaries

    • Capillaries serve as the sites for exchange between blood and interstitial fluid, facilitating the transfer of nutrients, gases, and waste products through their thin walls.
    • Their structure is designed for easy diffusion, with a vast network that assures adequate proximity to all body cells.

    Types of Capillaries

    • Capillaries can be grouped into three main types based on their structural features:
      • Continuous capillaries have a complete lining, found throughout the body except for epithelia and cartilage, providing selective permeability.
      • Fenestrated capillaries contain “windows” or pores, allowing rapid exchange of water and larger solutes due to increased permeability, typically located in areas of active absorption or filtration.
      • Sinusoids are special capillaries resembling flattened and irregular fenestrated capillaries with larger gaps between endothelial cells and a thin or absent basement membrane, allowing significant amounts of water and solutes to pass freely.

    Capillary Bed

    • Capillary beds are interconnected networks of capillaries that provide extensive exchange surfaces and facilitate communication between arterioles and venules, adapting efficiently to the local tissue demands.

    Veins

    • Veins vary in size but generally retain all three vessel wall layers, characterized by a thinner tunica media compared to arteries and a thick tunica externa that provides structural integrity.
    • Large veins typically have an internal diameter of 2–9 mm, displaying low-pressure systems suitable for accommodating larger volumes of blood returning to the heart.
    • Venules, which measure smaller than 50 μm, lack a defined tunica media and closely resemble expanded capillaries, playing a critical role in the collection of deoxygenated blood from the capillary beds.

    Pressure and Blood Flow in Veins

    • Blood pressure within peripheral venules is relatively low, highlighting the differences in pressure dynamics within the vascular system compared to arteries. This low-pressure system is essential for allowing controlled and steady blood flow back to the heart without undue stress on venous walls.

    Cardiovascular System

    • The cardiovascular system, also known as the circulatory system, is the body's network of blood vessels and the heart that delivers oxygen, nutrients, and other substances to the body's cells and organs.

    Functions of the circulatory system

    • Transport: Delivers oxygen, nutrients, hormones, and waste products.
    • Regulation: Helps maintain body temperature, blood pressure, and fluid balance.
    • Protection: Fights infection and clotting.

    Blood Vessels and Circuits

    • Pulmonary Circuit: Carries blood to and from the lungs for gas exchange.
    • Systemic Circuit: Carries blood to and from the rest of the body.

    What is Blood?

    • Transports dissolved gases, nutrients, hormones, and metabolic wastes.
    • Carries oxygen from the lungs to peripheral tissues.
    • Carries carbon dioxide from tissues to the lungs.
    • Transports nutrients from the digestive tract or storage in adipose or liver.
    • Delivers hormones from glands to target cells.
    • Transports wastes to kidneys for excretion.

    Blood Temperature Regulation

    • Blood absorbs heat generated in one area and distributes it to other tissues.
    • When body temperature is high, blood is directed closer to the skin to release heat.
    • When body temperature is low, blood is directed to the brain and internal organs to conserve heat.

    Red Blood Cells (RBCs)

    • Biconcave discs, thinner in the center and thicker at the edges.
    • Packed with hemoglobin, a protein that carries oxygen.
    • Form stacks called rouleaux to facilitate transport in small vessels.
    • Flexible, allowing them to move through narrow capillaries.
    • Lack nuclei and ribosomes, unable to divide or repair.
    • Have a lifespan of less than 120 days.
    • Primary function is to transport respiratory gases.

    Hemoglobin

    • A complex protein with a quaternary structure.
    • Each molecule has two alpha (α) chains and two beta (β) chains.
    • Each chain contains a heme molecule with an iron ion that binds to oxygen to form oxyhemoglobin (HbO2).
    • An RBC has about 280 million Hb molecules.

    Red Blood Cell Production

    • 1% of circulating RBCs are replaced each day.
    • Approximately 3 million new RBCs enter circulation every second.
    • When RBCs die, they are engulfed by macrophages in the spleen, liver, or bone marrow.

    Erythropoiesis

    • Red blood cell formation occurs in red bone marrow found in the ends of long bones and flat irregular bones.
    • Lymphatic tissue, found in the spleen, lymph nodes, and thymus gland, supplements blood cell production by producing lymphocytes.

    Hemoglobin Breakdown

    • Macrophages engulf old RBCs.
    • Heme units are stripped of iron, which is stored or enters the bloodstream bound to transferrin (plasma protein).
    • Heme is converted to biliverdin, then bilirubin, which enters the bloodstream and goes to the liver.
    • Globulin proteins are disassembled and amino acids are recycled.

    White Blood Cells (WBCs)

    • Leukocytes are the body's defense against infectious pathogens.
    • Have nuclei and other organelles, unlike RBCs.
    • Capable of movement, allowing them to migrate to infection or injury sites.

    Types of White Blood Cells

    • Neutrophils: Phagocytic cells that engulf and destroy bacteria.
    • Eosinophils: Involved in allergic reactions and parasitic infections.
    • Basophils: Release histamine and other inflammatory substances.
    • Monocytes: Mature into macrophages, phagocytic cells.
    • Lymphocytes: Involved in specific immune responses, including antibody production and cell-mediated immunity.

    Location of the Heart

    • Located in the middle mediastinum, along with large vessels entering or leaving the mediastinum.

    Structures of the Heart

    • Pericardium: A double-walled sac that surrounds the heart, consisting of two layers: fibrous pericardium and serous pericardium.
    • Pericarditis: Inflammation of the pericardium.
    • Cardiac Tamponade: Excess accumulation of pericardial fluid.

    Walls of the Heart

    • Epicardium: Outer layer of the heart, serous pericardium.
    • Myocardium: Middle layer, cardiac muscle tissue.
    • Endocardium: Inner layer, lining the chambers and valves.

    Heart Chambers

    • Atria: Two upper chambers: right atrium and left atrium.
    • Ventricles: Two lower chambers: right ventricle and left ventricle.
    • Interatrial septum: Wall that divides the right and left atria.
    • Interventricular septum: Wall that divides the right and left ventricles.

    Structures in the Atria

    • Right atrium: Receives deoxygenated blood from superior and inferior venae cavae and coronary sinus.
    • Fossa ovalis: Remnant of the fetal foramen ovale that allowed fetal blood to pass between atria.
    • Left atrium: Receives oxygenated blood from pulmonary veins.
    • Pectinate muscles: Muscular ridges located inside both atria.

    Structures in the Ventricles

    • Right ventricle: Receives blood from the right atrium through the tricuspid valve (right atrioventricular valve).
    • Trabeculae carneae: Muscular ridges inside both ventricles.
    • Left ventricle: Has a thicker wall than the right ventricle, receives blood from the left atrium through the mitral valve (bicuspid valve, left atrioventricular valve).

    Comparison between Chambers

    • Atria have similar workloads and walls of similar thickness.
    • Ventricles have different workloads:
      • Right ventricle is thinner and pumps blood to the lungs (pulmonary circuit).
      • Left ventricle is thicker and pumps blood through the entire systemic circuit.

    Heart Valves

    • Atrioventricular (AV) Valves: Located between each atrium and ventricle, allowing one-way blood flow from atrium to ventricle.
      • Tricuspid valve: Right AV valve.
      • Mitral valve (bicuspid valve): Left AV valve.
    • Semilunar Valves: Located at the exit of each ventricle, allowing one-way blood flow from ventricle to aorta or pulmonary trunk.
      • Pulmonary valve: Right ventricle to pulmonary trunk.
      • Aortic valve: Left ventricle to aorta.

    AV Valve Structure

    • Each AV valve has three (tricuspid) or two (mitral/bicuspid) cusps.
    • Cusps are attached to chordae tendineae, tendon-like bands connected to papillary muscles.
    • Moderator band: Thickened muscle ridge in the right ventricle that provides a rapid conduction path for electrical signals.

    Pulmonary and Aortic Valves

    • Each has three half-moon-shaped cusps that prevent backflow of blood.

    Cardiac Cycle

    • The period between the start of one heartbeat and the next.
    • Heart Rate: Number of beats per minute.
    • Consists of two phases:
      • Systole (Contraction): Blood is ejected from the chamber.
      • Diastole (Relaxation): Chamber refills with blood.

    Sequence of Contractions

    • Atrial systole: Both atria contract, pushing blood into the ventricles.
    • Ventricular systole: Both ventricles contract, pushing blood into the pulmonary and systemic circuits.

    Phases of the Cardiac Cycle

    • The cardiac cycle begins with all four chambers relaxed.
    • Atrial systole: Atria contract and finish filling ventricles.
    • Atrial diastole: Continues until the start of the next cardiac cycle.
    • Ventricular systole: The first phase of ventricular contraction.

    Visible Structures on the Anterior Surface

    • All four chambers.
    • Auricle of each atrium.
    • Coronary sulcus.
    • Anterior interventricular sulcus.
    • Ligamentum arteriosum.

    Visible Structures on the Posterior Surface

    • All four chambers.
    • Pulmonary veins.
    • Superior and inferior venae cavae.
    • Coronary sinus.
    • Posterior interventricular sulcus.

    Coronary Circulation

    • Supplies the heart muscle (myocardium) with oxygen and nutrients.
    • Left and Right Coronary Arteries: Arise from the ascending aorta, filling during ventricular relaxation (diastole).

    Right Coronary Artery

    • Supplies the right atrium, parts of both ventricles, and parts of the cardiac conducting system.

    Left Coronary Artery

    • Supplies the left ventricle, left atrium, and interventricular septum.

    Coronary Circulation - Veins

    • Great cardiac vein: Drains the area supplied by the anterior interventricular artery.
    • Anterior cardiac veins: Drain the anterior surface of the right ventricle.
    • Coronary sinus: Expanded vein that empties into the right atrium.
    • Posterior vein of left ventricle: Drains the area supplied by the circumflex artery.
    • Middle cardiac vein: Drains the area supplied by the posterior interventricular artery.
    • Small cardiac vein: Drains the posterior of the right atrium and ventricle.

    Blood Flow in Coronary Circulation

    • Maintained by changes in blood pressure and elastic rebound of the aorta.

    Cardiac Skeleton (Fibrous Skeleton)

    • Flexible connective tissue frame that encircles heart valves, stabilizes their positions, and surrounds the base of the aorta and pulmonary trunk.

    Cardiac Cycle Diagram

    • Shows the timing of atrial and ventricular contraction and relaxation phases.### Heart Contraction Phases

    • Ventricular systole - Phase 1:

      • Isovolumetric contraction: Ventricles contract, increasing pressure, but not enough to open the semilunar valves.
      • No volume change occurs.

    • Ventricular systole - Phase 2:

      • Ventricular ejection: Pressure increases further, opening the semilunar valves.
      • Blood leaves the ventricles.

    • Ventricular diastole - Phase 1:

      • Ventricles relax, pressure drops.
      • Blood flows back in the aorta and pulmonary trunk, closing the semilunar valves.
      • Isovolumetric relaxation: All valves are closed, no volume change.
      • Blood passively fills the atria.

    • Ventricular diastole - Phase 2:

      • All chambers are relaxed.
      • AV valves open, ventricles passively fill to 70%.

    Heart Sounds

    • S1 (Lubb): Caused by the closure of the AV valves, marking the start of ventricular contraction.
    • S2 (Dupp): Caused by the closure of the semilunar valves.
    • S3 & S4: Very faint and rarely heard in adults.
      • S3: Caused by blood flowing into the ventricles.
      • S4: Caused by atrial contraction.

    Cardiac Output

    • Cardiac output (CO): Amount of blood pumped from the left ventricle every minute.
    • Heart rate (HR): Number of contractions per minute (beats per minute).
    • Stroke volume: Volume of blood pumped out of the ventricle per contraction.

    Cardiac Conduction System

    • Autorhythmicity: Ability of cardiac muscle to contract independently of neural or hormonal stimulation.
    • Conduction system: Network of specialized cardiac muscle cells (pacemaker and conducting cells) that:
      • Initiate and distribute a stimulus to contract.

    Electrocardiogram (ECG or EKG)

    • Recording of heart's electrical activity: From the body surface.
    • Purpose: Assess the performance of:
      • Nodal, conducting and contractile components.
    • Abnormal EKG pattern: Indicates heart damage.
    • Appearance varies: Depends on the number and placement of electrodes (leads).

    EKG Waves

    • P wave: Atrial depolarization.
      • Atria begin contracting about 25 msec after the P wave starts.
    • QRS complex: Ventricular depolarization.
      • Larger wave due to the larger ventricle muscle mass.
      • Ventricles begin contracting shortly after the R wave peak.
      • Atrial repolarization also occurs now but is masked by the QRS complex.
    • T wave: Ventricular repolarization.

    EKG Intervals

    • P–R interval: Period between atrial depolarization start and ventricular depolarization start.

      • 200 msec may indicate damage to conducting pathways or the AV node.

    • Q–T interval: Time for ventricles to undergo a single cycle.
      • May be lengthened by:
        • Electrolyte disturbances.
        • Medications.
        • Conduction problems.
        • Coronary ischemia.
        • Myocardial damage.

    Resting Heart Rate

    • Varies: Based on age, general health, and physical conditioning.
    • Normal range: 60–100 bpm.
    • Bradycardia: Heart rate slower than normal (100 bpm).

    Cardiac Centers of the Medulla Oblongata

    • Cardioinhibitory center:
      • Controls parasympathetic neurons that slow heart rate.
      • Parasympathetic supply goes via the vagus nerve (X), synapsing in the cardiac plexus.
      • Postganglionic fibers go to:
        • SA/AV nodes.
        • Atrial musculature.
    • Cardioacceleratory center:
      • Controls sympathetic neurons that increase heart rate.
      • Sympathetic innervation goes to the heart via postganglionic fibers in cardiac nerves, innervating:
        • The nodes, conducting system, atrial and ventricular myocardium.

    Factors Affecting Stroke Volume

    • End-diastolic volume (EDV):
      • Amount of venous blood returned to the right atrium.
      • Varies directly with:
        • Blood volume.
        • Muscular activity.
        • Rate of blood flow.
    • Filling time: Length of ventricular diastole.
      • Longer filling time results in more filling and a higher EDV.
    • Preload: Amount of myocardial stretch.
      • Greater EDV causes greater preload.
      • More stretching causes stronger contractions and more blood ejection (Frank-Starling law of the heart).
    • Contractility: Amount of force produced during contraction at a given preload.
      • Increased by:
        • Sympathetic stimulation
        • Some hormones (epinephrine, norepinephrine, thyroid hormone, glucagon).
      • Reduced by:
        • “Beta blockers” and calcium channel blockers.
    • Afterload: Ventricular tension needed to open semilunar valves and empty.
      • As afterload increases, stroke volume decreases.
      • Afterload increases when blood flow is restricted by vasoconstriction.

    Factors Affecting Cardiac Output

    • Cardiac output varies widely: To meet metabolic demands.
    • Changing cardiac output: By affecting either heart rate or stroke volume.

    Heart Failure

    • Heart cannot meet the demands of peripheral tissues.

    Blood Vessels

    • Blood vessel functions: Conduct blood between heart and peripheral tissues.
    • Types of blood vessels:
      • Arteries: Carry blood away from the heart.
      • Veins: Carry blood to the heart.
      • Capillaries: Exchange substances between blood and tissues.

    Three Layers of Arteries and Veins

    • Tunica intima:
      • Innermost layer, composed of endothelium and subendothelial connective tissue.
    • Tunica media:
      • Middle layer, primarily smooth muscle cells and elastic fibers.
    • Tunica adventitia:
      • Outermost layer, composed of connective tissue and vasa vasorum (vessels supplying blood to the vessel wall).

    Types of Arteries

    • Elastic arteries: Large vessels near the heart that stretch and recoil with each heartbeat.
      • Examples: pulmonary trunk, aorta, and major branches.
    • Muscular arteries: Medium-sized arteries.
      • Distribute blood to skeletal muscles and internal organs.
    • Arterioles: Smaller arteries with a poorly defined tunica externa.
      • Their tunica media is only 1–2 smooth muscle cells thick.

    Capillaries

    • Only blood vessels that allow exchange: Between blood and interstitial fluid.
    • Very thin walls: Allow easy diffusion.

    Types of Capillaries

    • Continuous capillary:
      • Endothelium forms a complete lining.
      • Located throughout the body in all tissues except epithelium and cartilage.
      • Allows diffusion of water, small solutes, and lipid-soluble materials.
      • Prevents loss of blood cells and plasma proteins.
    • Fenestrated capillary:
      • Contain “windows” or pores, penetrating the endothelial lining.
      • Permits rapid exchange of water and larger solutes.
    • Sinusoids (sinusoidal capillaries):
      • Resemble fenestrated capillaries but are flattened and irregularly shaped.
      • Common gaps between endothelial cells, thin or absent basement membrane.
      • Permit even greater exchange of water and solutes (including plasma proteins).
      • Found in liver, bone marrow, spleen, and many endocrine organs.

    Capillary Bed

    • Interconnected network of capillaries.
    • Contains connections between arterioles and venules.

    Veins

    • Functions:
      • Collect blood from the capillaries.
      • Return it to the heart.
    • Types of veins:
      • Large veins:
        • Contain all three vessel wall layers.
        • Have a thick tunica externa.
        • Include superior and inferior venae cavae and their tributaries.
      • Veins:
        • Internal diameter from 2 to 9 mm.
        • Thinner tunica media than arteries.
        • Thickest layer is the tunica externa with longitudinal collagen and elastic fibers.
      • Venules:
        • <50 µm lack a tunica media.
        • Resemble expanded capillaries.

    Pressure and Blood Flow in Veins

    • Blood pressure in peripheral venules is low.

    Cardiovascular System

    • The cardiovascular system is the body's network of blood vessels and the heart that delivers oxygen, nutrients, and other substances to the body's cells and organs.

    Functions of Circulatory System

    • Transport: Delivers oxygen, nutrients, hormones, and waste products.
    • Regulation: Helps maintain body temperature, blood pressure, and fluid balance.
    • Protection: Fights infection and clotting.

    Blood Vessels and Circuits

    • Pulmonary circuit: To and from gas exchange surfaces in the lungs.
    • Systemic circuit: To and from the rest of the body.

    What is Blood

    • Blood transports dissolved gases, nutrients, hormones, and metabolic wastes.
    • Oxygen: Lungs to peripheral tissues.
    • Carbon dioxide: Tissues to lungs.
    • Nutrients: From the digestive tract or storage in adipose or liver.
    • Hormones: Gland to target.
    • Wastes: To kidneys (excretion).

    Red Blood Cells (RBCs)

    • RBCs are biconcave discs - thinner centers, thicker edges.
    • Functional aspects: Large surface area-to-volume ratio, packed with hemoglobin (protein that carries oxygen), form stacks (rouleaux) to facilitate transport in small vessels, flexible to move through narrow capillaries, and can move through capillaries with diameters smaller than RBC.

    Red Blood Cell Characteristics

    • Lose most organelles during development.
    • Mature RBCs lack nuclei (anucleate) and ribosomes.
    • Cannot divide/repair.
    • Life span < 120 days.
    • Primary function: Transport respiratory gases.
    • 95% of RBC intracellular proteins are hemoglobin molecules.

    Hemoglobin

    • Complex quaternary structure.
    • Each Hb molecule has two alpha (α) chains and two beta (β) chains.
    • Each chain has a single heme molecule.
    • Each heme contains an iron ion that interacts with oxygen molecules to form oxyhemoglobin (HbO2).
    • An RBC has ~280 million Hb molecules, each with four heme units.

    Oxygenated vs. Deoxygenated Blood

    • Oxygenated blood: Bright red color, carries a high concentration of oxygen bound to hemoglobin in red blood cells.
    • Deoxygenated blood: Dark red color, carries a low concentration of oxygen bound to hemoglobin, and a higher concentration of carbon dioxide.

    Red Blood Cell Production

    • ~1% of circulating RBCs are replaced each day (short lifespan).
    • ~3 million new RBCs enter circulation each second.
    • End of RBC life: Plasma membrane ruptures (hemolysis), or RBC is engulfed by macrophages in the spleen, liver, or bone marrow.

    Erythropoiesis

    • Red blood cell formation.
    • The body has two types of hemopoietic tissue:
    • Red bone marrow: Found in the ends of long bones and flat bones such as the sternum, cranial bones, vertebrae, and pelvis - produces all types of blood cells.
    • Lymphatic tissue: Found in the spleen, lymph nodes, and thymus gland - supplement blood cell by producing lymphocytes, a specific type of WBC.

    Events Occurring in Macrophages

    • Macrophages monitor the condition of circulating RBCs.
    • Engulf old RBCs before rupture (hemolyze).
    • Remove Hb molecules/cell fragments.
    • Heme units stripped of iron (iron is stored in phagocyte or enters blood and binds to transferrin (plasma protein).
    • Heme → biliverdin → bilirubin → bloodstream → liver.
    • Globular proteins disassembled and amino acids recycled.
    • Hemoglobin that is not phagocytized breaks down into its protein chains and is excreted in urine.

    White Blood Cells (WBCs)

    • Leukocytes are the fewest of the formed elements. They are the body's line of defense against invasion by infectious pathogens.
    • Have nuclei and other organelles, unlike RBCs, but no hemoglobin.
    • WBCs are capable of movement, allowing them to migrate to sites of infection or injury.

    Types of White Blood Cells

    • Neutrophils: Phagocytic cells that engulf and destroy bacteria.
    • Eosinophils: Involved in allergic reactions and parasitic infections.
    • Basophils: Release histamine and other inflammatory substances.
    • Monocytes: Mature into macrophages, which are phagocytic cells.
    • Lymphocytes: Involved in specific immune responses, including antibody production and cell-mediated immunity.

    Hemolytic Diseases of the Newborn (HDN)

    • Many forms - some very dangerous, others undetectable.
    • Most common involves Rh- mother who has carried an Rh+ fetus.

    First Pregnancy and HDN

    • Rarely poses a problem because fetal cells are mostly isolated from maternal blood - mom's immune system is not stimulated to produce anti-Rh antibodies.

    Birth and HDN

    • Bleeding at the placenta/uterus mixes fetal and maternal blood.
    • Mother exposed to Rh antigens, stimulating her immune system to produce anti-Rh antibodies (= sensitization).
    • 20% of Rh- mothers who carried Rh+ children are sensitized within 6 months of delivery, but the first child is usually not affected (antibodies develop after delivery).

    Subsequent Pregnancy and HDN

    • Maternal anti-Rh antibodies can cross the placenta and destroy fetal RBCs, causing severe anemia.
    • Fetal demand for RBCs increases - erythroblasts enter the bloodstream before maturity - leads to alternate name, erythroblastosis fetalis.
    • High fatality rate without treatment.
    • Newborn with severe HDN is anemic/jaundiced (from high bilirubin concentrations).

    Prevention of HDN

    • Maternal antibodies remain active 1-2 months after delivery.
    • May require replacement of the infant's entire blood volume.
    • HDN can be prevented by giving the mother anti-Rh antibodies (RhoGAM) at weeks 26-28 of pregnancy and during/after delivery.
    • The antibodies destroy fetal RBCs that crossed the placenta before RBCs stimulate the maternal immune response - no sensitization.

    Obtaining Blood for Diagnosis

    • Venipuncture: Withdrawal of whole blood from a superficial vein, such as the median cubital vein.
    • Commonly used because: Easy to locate superficial veins, vein walls are thinner than walls of comparable arteries, and venous blood pressure is relatively low, so the vein seals quickly.

    Clinical Case: Pernicious Anemia

    • Vitamin B12 deficiency prevents normal stem cell divisions.
    • Fewer RBCs produced - often misshaped, large (macrocytic).
    • Can be from a lack of intrinsic factor - secreted in the stomach, needed for Vitamin B12 absorption.

    Clinical Case: Calcium and Vitamin K Deficiencies

    • Calcium is required for all clotting pathways.
    • Vitamin K is required by the liver to synthesize clotting factors.

    Clinical Case: Sickle Cell Disease (SDC)

    • Sickle cell disease (SDC) - a group of inherited RBC disorders.
    • Genetic mutation affects the amino acid sequence of the beta globin subunit in hemoglobin.
    • RBCs take on a sickle shape when they release oxygen (more fragile, easily damaged).
    • They can get stuck in smaller vessels, blocking flow.

    Clinical Case: Hemophilia

    • Inherited bleeding disorder.
    • Affects 1 person in 10,000 - ~80-90% are males.
    • Caused by a missing or reduced production of a clotting factor.
    • Severity of disorder varies.
    • In severe cases, extensive bleeding occurs with minor contact.
    • Bleeding also occurs at joints and around muscles.

    Clinical Case: Thalassemia

    • A diverse group of inherited disorders.
    • Unable to adequately produce normal Hb protein subunits.
    • Severity depends on which/how many subunits are abnormal.

    Clinical Case: Sepsis

    • Widespread infection of body tissue.
    • Septicemia: Sepsis of the blood (“blood poisoning”).
    • Pathogens present, multiplying in the blood, and spreading.

    Clinical Case: Malaria

    • Malaria - parasitic disease caused by several species of Plasmodium.
    • Kills 1.5-3 million people per year (up to half under age 5).
    • Transmitted by mosquito.
    • Initially infects the liver - later infects RBCs.
    • Every 2-3 days, all infected RBCs rupture, release more parasites.
    • Causes cycles of fever/chills - dead RBCs block vessels to vital organs.

    Clinical Case: Leukemias

    • Leukemias: Cancers of blood-forming tissues.
    • Cancerous cells spread from origin in red bone marrow.
    • First symptoms appear with the presence of immature and abnormal WBCs in circulation.
    • Fatal if untreated.
    • Two types: Myeloid leukemia and Lymphoid leukemia.
    • Both have elevated WBCs.

    Heart

    • The human heart beats about 100,000 times in one day and about 35 million times in a year.
    • During an average lifetime, the human heart will beat more than 2.5 billion times.

    Location of the Heart

    • The middle mediastinum contains the heart and large vessels entering or leaving the mediastinum.

    Structures of the Heart

    • Surrounding the heart is a double-walled sac called the pericardium, anchored by ligaments and tissue to surrounding structures.
    • The pericardium has two layers:
      • Parietal pericardium: Outer layer that is attached to the chest wall.
      • Visceral pericardium (epicardium): Inner layer that is attached to the heart.

    Relationship Between the Heart and Pericardium

    • Push a fist into a partly inflated balloon (fist = heart, wrist = base of the heart with great vessels, inside of balloon = pericardial cavity).

    Pericarditis

    • Inflammation of the pericardium.

    Cardiac Tamponade

    • Excess accumulation of pericardial fluid.

    Walls of the Heart

    • Epicardium (visceral pericardium): The outermost layer of the heart wall, composed of a thin layer of epithelial tissue and connective tissue.
    • Myocardium: The middle and thickest layer of the heart wall, composed of cardiac muscle tissue.
    • Endocardium: The innermost layer of the heart wall, composed of a thin layer of epithelial tissue and connective tissue.

    Heart Chambers

    • The heart is divided into four chambers or cavities:
      • Two atria: Upper chambers that receive blood from the body and lungs.
      • Two ventricles: Lower chambers that pump blood to the body and lungs.

    Right Atrium

    • Receives blood from the systemic circuit.

    Right Ventricle

    • Pumps blood into the pulmonary circuit.

    Left Atrium

    • Receives blood from the pulmonary circuit.

    Left Ventricle

    • Pumps blood into the systemic circuit.

    Structures in the Atria

    • Right atrium: Receives deoxygenated blood from the superior and inferior venae cavae and coronary sinus.
      • Fossa ovalis: Remnant of the fetal foramen ovale that allowed fetal blood to pass between atria, closes at birth.
    • Left atrium: Receives oxygenated blood from pulmonary veins.
      • Pectinate muscles: Muscular ridges located inside both atria along the anterior atrial wall and in the auricles.

    Structures in the Ventricles

    • Right ventricle: Receives blood from the right atrium through the tricuspid valve (has three cusps or flaps), also called the right atrioventricular (AV) valve.
      • With contraction, blood exits through the pulmonary valve (pulmonary semilunar valve) into the pulmonary trunk.
    • Left ventricle: Much thicker wall than the right ventricle.
      • Receives blood from the left atrium through the mitral valve, also called the bicuspid valve (two cusps) or the left atrioventricular valve.
      • With contraction, blood exits through the aortic valve (aortic semilunar valve) into the ascending aorta.
      • Trabeculae carneae - muscular ridges inside both ventricles.

    Comparison Between Chambers

    • Atria have similar workloads, walls about the same thickness.
    • Ventricles have very different loads.
      • Right ventricle: Thinner wall, sends blood to adjacent lungs (pulmonary circuit). Contraction squeezes against the left ventricle, forces blood out the pulmonary trunk efficiently. Minimal effort, low pressure.
      • Left ventricle: Very thick wall, rounded chamber. 4-6 times the pressure of the right ventricle. Sends blood through the entire systemic circuit. Contraction decreases diameter and apex-to-base distance.

    Interatrial and Interventricular Septa

    • Right and left atria are separated by the interatrial septum.
    • Right and left ventricles are separated by the interventricular septum (much thicker).

    Atrioventricular (AV) Valves

    • Between each atrium and ventricle.
    • Allow only one-way blood flow from atrium into the ventricle.

    Semilunar Valves

    • At the exit from each ventricle.
    • Allow only one-way blood flow from ventricle out into the aorta or pulmonary trunk.

    Heart Valves

    • Four valves act as restraining gates to control the direction of blood flow.
    • Situated at the entrances and exits to the ventricles.
    • Properly functioning valves allow blood to flow only in a forward direction by blocking it from returning to the previous chamber.

    Tricuspid Valve

    • An atrioventricular valve (AV).
    • Controls the opening between the right atrium and the right ventricle.

    Pulmonary Valve

    • A semilunar valve.
    • Located between the right ventricle and the pulmonary artery.
    • This valve prevents blood that has been ejected into the pulmonary artery from returning to the right ventricle as it relaxes.

    Mitral Valve

    • Also called the bicuspid valve.
    • Blood flows through this atrioventricular valve to the left ventricle and cannot go back up into the left atrium.

    Aortic Valve

    • A semilunar valve.
    • Located between the left ventricle and the aorta.
    • Blood leaves the left ventricle through this valve and cannot return to the left ventricle.

    AV Valve Structure (Tricuspid and Mitral Valve)

    • Each has three (tricuspid) or two (mitral/bicuspid) cusps.
    • Cusps attach to tendon-like connective tissue bands = chordae tendineae.
    • Chordae tendineae anchored to thickened cone-shaped papillary muscles.
    • Moderator band: Thickened muscle that provides a rapid conduction path, tenses papillary muscles just before ventricular contraction to prevent slamming or inversion of the AV valve.

    Pulmonary and Aortic (Semilunar) Valves

    • Each has three half-moon-shaped cusps.
    • Prevent backflow of blood from the aorta and pulmonary trunk back into the ventricles.
    • No muscular brace needed - cusps support each other when closed.

    Valve Action: Ventricles Relaxed (Diastole)

    • AV valves open.
    • Chordae tendineae are loose.
    • Semilunar valves closed.
    • Blood pressure from pulmonary and systemic circuits keeps them closed.

    Valve Action: Ventricles Contract (Systole)

    • AV valves closed.
    • Pressure from contracting ventricles pushes cusps together.
    • Papillary muscles tighten chordae tendineae so cusps can't invert into atria - prevents backflow (regurgitation).
    • Semilunar valves open.
    • Ventricular pressure overcomes pressure in the pulmonary trunk and aorta, which held them shut.

    Visible Structures on Anterior Surface

    • All four chambers.
    • Auricle of each atrium (expandable pouch).
    • Coronary sulcus: Groove separating atria and ventricles.
    • Anterior interventricular sulcus: Groove marking the boundary between the two ventricles.
    • Ligamentum arteriosum: Fibrous remnant of the fetal connection between the aorta and pulmonary trunk.

    Visible Structures on Posterior Surface

    • All four chambers.
    • Pulmonary veins (4) returning blood to the left atrium.
    • Superior and inferior venae cavae returning blood to the right atrium.
    • Coronary sinus: Returns blood from the myocardium to the right atrium.
    • Posterior interventricular sulcus: Groove marking the boundary between the two ventricles.

    Coronary Circulation

    • Continuously supplies cardiac muscle (myocardium) with oxygen/nutrients.
    • Left and right coronary arteries arise from the ascending aorta - fill when ventricles are relaxed (diastole).
    • Myocardial blood flow may increase to 9 times the resting level during maximal exertion.

    Right Coronary Artery

    • Supplies the right atrium, parts of both ventricles, and parts of the cardiac (electrical) conducting system.
    • Follows the coronary sulcus (groove between atria and ventricles).

    Left Coronary Artery

    • Supplies the left ventricle, left atrium, and interventricular septum.

    Coronary Circulation - Veins (Anterior)

    • Great cardiac vein - in the anterior interventricular sulcus.
      • Drains area supplied by the anterior interventricular artery.
      • Empties into the coronary sinus posteriorly.
    • Anterior cardiac veins.
      • Drain anterior surface of the right ventricle.
      • Empty directly into the right atrium.

    Coronary Circulation - Veins (Posterior)

    • Coronary sinus: Expanded vein that empties into the right atrium.
    • Posterior vein of the left ventricle: Drains area supplied by the circumflex artery.
    • Middle cardiac vein: Drains the area supplied by the posterior interventricular artery - empties into the coronary sinus.
    • Small cardiac vein: Drains the posterior of the right atrium/ventricle - empties into the coronary sinus.

    Blood Flow Through the Coronary Circuit

    • Maintained by changing blood pressure and an elastic rebound.
    • Left ventricular contraction forces blood into the aorta, elevating blood pressure there, stretching aortic walls.
      • Left ventricular relaxation - pressure decreases, aortic walls recoil (elastic rebound), pushing blood in both directions:
        • Forward into the systemic circuit.
        • Backward into the coronary arteries.

    Cardiac Skeleton (Fibrous Skeleton)

    • Flexible connective tissue frame.
    • Interconnected bands of dense connective tissue, encircle heart valves, stabilize their positions, and surround the base of aorta and pulmonary trunk.
    • Electrically isolates the atrial from ventricular myocardium.

    Cardiac Cycle

    • The cardiac cycle = period between the start of one heartbeat and the next - heart rate = number of beats per minute.
    • Two atria contract first to fill ventricles - two ventricles then contract to pump blood into the pulmonary and systemic circuits.

    Two Phases of the Cardiac Cycle

    • Contraction (systole): Blood leaves the chamber.
    • Relaxation (diastole): Chamber refills.

    Sequence of Contractions

    • Atria contract together first (atrial systole) - push blood into the ventricles - ventricles are relaxed (diastole) and filling.
    • Ventricles contract together next (ventricular systole) - push blood into the pulmonary and systemic circuits - atria are relaxed (diastole) and filling.
    • Typical cardiac cycle lasts 800 msec.

    Phases of the Cardiac Cycle (Diagrammed for a Heart Rate of 75 bpm)

    • Cardiac Cycle begins - all 4 chambers are relaxed (diastole - ventricles are passively refilling).
    • Atrial systole (100 msec) - atria contract - finish filling ventricles.
    • Atrial diastole (270 msec) - continues until the start of the next cardiac cycle through ventricular systole.
    • Ventricular systole (first phase).
      • Isovolumetric contraction (0.03 sec) - ventricles contract and increase pressure, but all valves are still closed - no blood flow.
      • Ventricular ejection (0.25 sec) - pressure in the ventricle exceeds that of the pulmonary trunk and aorta, forcing semilunar valves open - blood is ejected.
      • Isovolumetric relaxation (0.08 sec) - ventricles relax and pressure drops - semilunar valves close to prevent backflow.
    • Ventricular diastole (second phase).
      • Passive ventricular filling (0.34 sec) - blood flows passively from atria into ventricles because pressure is higher in the atria.
      • Atrial systole (0.1 sec) - atria contract and pressure increases - the last 20-30% of ventricular filling occurs.

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    Description

    Test your knowledge about the anatomy of the human heart, including its chambers, surrounding structures, and functions. This quiz covers essential aspects of heart physiology and the conditions that can affect its health.

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