Ch. 21-Anatomy

• Heart's 4 muscular chambers

  • Right atrium, right ventricle, left atrium, left ventricle
  • Work together to pump blood through a network of blood vessels between the heart and peripheral tissues
• Pulmonary circuit


  1. Carries carbon dioxide-rich blood from the heart to the gas-exchange surfaces of the lungs

  2. Returns oxygen-rich blood to the heart
• Systemic circuit


  1. Transports oxygen-rich blood from the heart to the rest of the body's cells

  2. Returns carbon dioxide-rich blood back to the heart
• Blood must go through the atrium into the ventricle
• Each circuit begins and ends at the heart
• Arteries


  Transport blood away from the heart
• Veins


  Return blood to the heart
• Blood travels through these circuits in sequence
• Capillaries


  • Small thin-walled vessels that interconnect the smallest arteries and veins
  • Called exchange vessels due to their thin walls that permit exchange of nutrients, dissolved gases, and waste products between the blood and surrounding tissues
• Pericardial cavity


  Portion of the ventral body cavity
• Pericardium


  • Serous membrane lining the pericardial cavity
  • Divided into visceral pericardium and parietal pericardium
• Visceral pericardium


  • Loose connective tissue bound to the cardiac muscle of the heart
• Fibrous pericardium


  • Outer layer of dense, irregular connective tissue containing abundant collagen fibers
  • Reinforces the parietal pericardium
• Pericardial sac


  Formed by the parietal pericardium and fibrous pericardium
• Pericardial cavity


  • Slender gap between the opposing parietal and visceral surfaces
  • Contains 10-20mL of pericardial fluid secreted by the pericardial membranes
  • Pericardial fluid acts as a lubricant, reducing friction between the opposing surfaces
• Heart wall


  • 3 layers: epicardium, myocardium, endocardium
• Epicardium


  • Visceral pericardium forming the external surface of the heart
  • A serous membrane consisting of a mesothelium covering a supporting layer of areolar connective tissue
• Myocardium


  • Multiple, interlocking layers of cardiac muscle tissue with associated connective tissues, blood vessels, nerves
  • Atrial myocardium is relatively thin with layers forming figure-eights
  • Ventricular myocardium is much thicker with muscle orientation changing from layer to layer
• Endocardium


  • Simple squamous epithelium lining the inner surfaces of the heart including the valves
  • Continuous with the endothelium of attached blood vessels
• Cardiac muscle tissue


  • Cardiocytes are cardiac muscle cells that are relatively small, have a single centrally placed nucleus, and have striations
  • Differ from skeletal muscle in being dependent on aerobic respiration, having abundant mitochondria and myoglobin, and not forming triads with the sarcoplasmic reticulum
  • Cardiac muscle cells contract without instructions from the nervous system
  • Cardiac muscle cells are interconnected by specialized cell junctions called intercalated discs
• Intercalated discs


  • Specialized cell-to-cell junctions that connect cardiac muscle cells
  • Involve desmosomes that lock cells together, fascia adherens that anchor myofibrils, and gap junctions that allow direct electrical connection between cells
• Cardiac muscle


  • Functions like a single enormous muscle cell due to the mechanical, chemical, and electrical connections between cells
  • Has been called a functional syncytium (fused mass of cells)
• Fibrous skeleton


  • Connective tissues including large numbers of reticular, collagen, and elastic fibers
  • Wraps each muscle cell in a strong but elastic sheath
  • Ties adjacent cells together with fibrous crosslinks
  • Separates muscle layers with fibrous sheets
  • Continuous with dense bands of fibroelastic tissue encircling the bases of the pulmonary trunk and aorta, as well as the heart valves
• Functions of the fibrous skeleton

  • Stabilizing the positions of the muscle cells and valves
  • Providing physical support for the cardiac muscle cells and associated structures
  • Distributing the forces of contraction
  • Reinforcing the valves and helping prevent overexpansion of the heart
  • Providing elasticity that helps return the heart to its original shape after each contraction
  • Physically isolating the atrial muscle cells from the ventricular muscle cells
• Position and orientation of the heart

  • Lies slightly to the left of the midline within the mediastinum between the two lungs
  • Base is broad and superior where the heart is attached to the major arteries and veins
  • Apex is the inferior rounded tip that points laterally at an oblique angle
  • Heart is rotated slightly toward the left, so the anterior surface is primarily the right atrium and right ventricle, while the posterior surface is the left atrium and left ventricle
• External surface features


  • Shallow interatrial groove separates the two atria
  • Deeper coronary sulcus marks the border between the atria and ventricles
  • Anterior and posterior interventricular sulci indicate the division between the left and right ventricles
  • Sulci contain substantial amounts of adipose tissue as well as arteries and veins supplying the cardiac muscle
• Auricle


  Expandable extension of an atrium that reminds early anatomists of an external ear
• Internal anatomy


  • Atria separated by the interatrial septum
  • Ventricles separated by the interventricular septum
  • Valves are folds of endocardium that open and close to prevent backflow of blood
• Right atrium


  • Receives oxygen-poor venous blood from the systemic circuit through the superior and inferior vena cavae
  • Contains pectinate muscles in the right auricle and adjacent anterior atrial wall
• Foramen ovale


  • Oval opening in the interatrial septum that closes 48 hours after birth
  • Fossa ovalis is the small depression that persists at this site in the adult heart
• Right ventricle


  • Cusps of the tricuspid (right atrioventricular) valve are attached to chordae tendineae arising from papillary muscles
  • Contains trabeculae carneae and the moderator band
  • Tapers to the pulmonary valve at the pulmonary trunk
• Left atrium


  • Receives oxygen-rich blood from the four pulmonary veins
  • Lacks pectinate muscles but has an auricle
• Left ventricle


  Blood flows from the left atrium through the mitral (left atrioventricular) valve into the left ventricle
• Ventricle


  Smooth-walled, cone-shaped chamber which ends at the pulmonary valve
• Pulmonary valve


  Semilunar valve at the start of the pulmonary circuit
• Pulmonary valve


  • Arrangement of cusps prevents the backflow of blood into the right ventricle when it relaxes
• Blood flow from pulmonary trunk

  1. Flows into both left and right pulmonary arteries

  2. Branches repeatedly within the lungs

  3. Supplies the pulmonary capillaries where gas exchange occurs
• Left Atrium


  • Oxygen-rich blood flows into small veins that unite to form 4 pulmonary veins (2 from each lung)
  • Lacks pectinate muscles but has an auricle
• Left Atrioventricular (AV) valve


  Permits the flow of oxygen-rich blood from the left atrium into the left ventricle but prevents blood flow in the reverse direction
• Left Ventricle


  • Has the thickest wall of any heart chamber
  • Trabeculae carneae are more prominent than in the right ventricle
  • No moderator band
  • Has 2 large papillary muscles since the valve has 2 cusps