21.5 Internal Anatomy and Organization of the Heart

• • The interatrial septum separates the two atria of the heart, and the interventricular septum separates the two ventricles. The two atria receive blood, and the two ventricles pump it away from the heart. Four sets of valves prevent the backflow of blood, ensuring that blood flows from the atria into the ventricles and from the ventricles into the great arteries exiting the heart.
• The interatrial septum separates the atria
• The interventricular septum separates the ventricles
• Blood flows from each atrium into the ventricle of the same side
• The valves are folds of endocardium extending into the openings between the atria and ventricles
• These valves open and close to prevent the backflow of blood, maintaining a one way flow of blood from atria into ventricles
• Atria collect blood returning to heart and deliver it to attached ventricle
• Internal surface of the right ventricle contains a series of irregular muscular ridges called the trabeculae carnae
• The moderator band is a muscular ridge that extends horizontally fromt he inferior portion of the interventricular septum and connects to the anterior papillary muscle
• The superior end of the right ventricle tapers to the conus arteriosus, a smooth walled cone shaped pouch
• The conus arteriosus ends at the pulmonary valve
• As blood is pumped out of the right ventricle, it passes through this valve and enters the pulmonary trunk
• From the pulmonary trunk, blood flows into both the left pulmonary arteries and the right pulmonary arteries
• SUMMARY

  • Atria are separated by interatrial septum, and ventricles dividded by interventricular septum. Openings between atria and ventricles contain folds of connective tissue covered by endocardium; these valves maintain a one way flow of blood
• SUMMARY - The Right Atrium

  • Right atrium receives blood from systemic circuit through two great veins, the superior vena cava and inferior vena cava. The atrial walls contain prominent muscular ridges, the pectinate muscles. The coronary veins return blood to the coronary sinus, which opens into the right atrium. DUring embryonic development an opening called the foramen ovale penetrates the interatrial septum. This opening closes after birth, leaving a depression termed the fossa ovalis.
• SUMMARY - The Right Ventricle

  • Blood flows from right atrium into right ventricle through right atrioventricular (AV) valve, or tricuspid valve. This valve consists of three cusps or fibrous tissue braced by the tendinous chordae tendineae that are connected to papillary muscles.
  • Blood leaving righr ventricle enters pulmonary trunk after passing through pulmonary valve. The pulmonary trunk divides to form the left and right pulmonary arteries.
• SUMMARY - The Left Atrium

  • Left atrium receives oxygenated blood from left and right pulmonary veins; it has thicker walls than those of the right atrium
  • Blood leaving the left atrium flows into the left ventricle through the left atrioventricular (AV) valve
• SUMMARY - The Left Ventricle

  • Left ventricle is largest and thickest of four chambers because it pumps blood to entire body. Blood leaving the left ventricle passes through the aortic valve and into the systemic circuit via the ascending aorta. Blood passes from the ascending aorta through the aortic arch and into the descending aorta.
• SUMMARY - The Structural Differences between the Right and Left Ventricles

  • Right ventricle has thin walls and develops low pressure when pumping into pulmonary circuit to and from adjacent lungs. Functionally, low pressure is necessary because the pulmonary capillaries at the gas exchange surfaces of the lungs are delicate. Left ventricle has thick wall because it pumps blood throughout the systemic circuit.
• SUMMARY - The Structure and Function of Heart Valves

  • AV valves have four compartments: ring of connective tissue attached to the cardiac skeleton of the heart, cusps, chordae tendineae, papillary muscles.
  • Two semilunar valves, the aortic valve and the pulmonary valve, guarding the exits of the left and right ventricles.
  • Valves normally permit blood flow in only one direction, preventing regurgitation (backflow) of blood.