heart

• heart is contained in a sac called the pericardium
• the three tissue layers of the heart are:

  • endocardium
  • myocardium
  • epicardium
• endocardium is a serous membrane that lines the four chambers of the heart and its valves and is continuous with the endothelium of the arteries and veins
• myocardium is the muscular layer of the heart
• epicardium is the outermost layer of the heart
• heart is a four-chambered muscular pump supplied with an electrical conduction system
• the function of the heart is to propel blood throughout the body through a closed vascular system
• heart is divided into four chambers:

  • right atrium
  • left atrium
  • left ventricle
  • right ventricle
• atria are the upper chambers that collect blood, while ventricles are the lower chambers that pump blood from the heart
• pulmonary circulation is when the right side of the heart pumps blood to the lungs for oxygenation
• systemic circulation is when the left side of the heart pumps oxygenated blood to all body systems
• deoxygenated blood from the body returns to the heart by way of two large veins
• the two large veins are the:

  superior vena cava

  inferior vena cava
• superior vena cava collects and carries blood from the upper part of the body
• inferior vena cava collects and carries blood from the lower part of the body
• from the right atrium, blood passes through the tricuspid valve to the right ventricle
• when the heart contracts, blood leaves the right ventricle by way of the left pulmonary artery and right pulmonary artery and travels to the lungs
• during contraction of the ventricle, the tricuspid valve closes to prevent a backflow of blood to the right atrium
• pulmonic valve prevents a backflow of blood into the right ventricle
• pulmonic valve is also called pulmonary semilunar valve
• in the lungs, the pulmonary artery branches into millions of capillaries, each lying close to an alveolus
• in the alveolus, carbon dioxide in the blood is exchanged for oxygen that has been drawn into the lungs during inhalation
• pulmonary capillaries unite to form four pulmonary veins—two right pulmonary veins and two left pulmonary veins
• the pulmonary veins are the vessels that carry oxygenated blood back to the heart
• pulmonary veins deposit blood in the left atrium. from here, blood passes through the mitral (bicuspid) valve to the left ventricle
• upon contraction of the ventricles, the oxygenated blood leaves the left ventricle through the largest artery of the body, the aorta
• aorta contains the aortic semilunar valve that permits blood to flow in only one direction—from the left ventricle to the aorta
• oxygen cannot be used by the myocardium as a source of oxygen and nutrients
• coronary arteries provides oxygen and nutrients to the heart with its own blood supply
• coronary arteries lie over the top of the heart much as a crown fits over a head
• coronary means pertaining to a crown
• the artery vascularizing the right side of the heart is the right coronary artery
• the artery vascularizing the left side of the heart is the left coronary artery
• the left coronary artery divides into two:

  • left anterior descending artery
  • circumflex artery
• if blood flow in the coronary arteries is diminished, myocardial damage may result; when severe damage occurs, part of the heart muscle may die
• conductive tissue is a specialized cardiac tissue that has the function of initiating and spreading contraction impulses
• conductive tissue has four masses of highly specialized cells:

  • sinoatrial (SA) node
  • atrioventricular (AV) node
  • bundle of His (AV bundle)
  • purkinje fibers
• the SA node, located in the upper portion of the right atrium, possesses its own intrinsic rhythm
• SA node has the ability to initiate and propagate each heartbeat; setting the basic pace for the cardiac rate
• SA node is commonly known as the pacemaker of the heart