The Circulatory System

• The circulatory system pumps and directs blood cells and substances carried in blood to all tissues of the body
• The circulatory system includes both the blood and lymphatic vascular systems
• the cardiovascular system consists of the following structure:

  1. heart
  2. arteries
  3. capillaries
  4. veins
• propels blood through the system

  heart
• a series of vessels efferent from the heart that become smaller as they branch into the various organs, carry blood to the tissues


  arteries
• the smallest vessels


  capillaries
• the sites of O2, CO2, nutrients, and waste product exchange between blood and tissues 


  capillaries
• Microvasculature are the anastomosing tubules formed together with the smallest arterial and venous branches carrying blood to and from them
• result from the convergence of venules into the system of larger channels which continue enlarging as they approach the heart, toward which they carry the blood to be pumped again 


  veins
• the arteries, microvasculature and veins make up the pulmonary circulation where blood is oxygenated in the lungs
• circulation where blood brings nutrients and removes wastes in tissues throughout the body

  systemic circulation
• the lymphatic vascular system begins with the lymphatic capillaries which are thin-walled, closed-ended tubules carrying lymph which merge to form vessels of steadily increasing size
• the largest lymph vessels connect with the blood vascular system and empty into the large veins near the heart. This returns fluid from tissue spaces all over the body to the blood
• the internal surface of all components of the blood and lymphatic systems is lined by simple squamous epithelium called endothelium
• cardiac muscle in the four chambers of the heart wall contracts rhytmically pumping the blood through the circulatory system
• the right and left ventricles propel blood to the pulmonary and systemic circulations, respectively
• the right and left atria receive blood from the body and the pulmonary veins
• the walls of the four heart chambers consist of three major layers

  1. internal endocardium
  2. middle myocardium
  3. external epicardium
• lining of endocardium

  endothelium
• supporting layer of endocardium

  fibroelastic connective tissue with scattered fibers of smooth muscle and a deeper layer of connective tissue (continuous with myocardium and called the subendocardial layer) surrounding variable numbers of modified cardiac muscle fibers
• consists mainly of typically contractile cardiac muscle fibers arranged spirally around each heart chamber


  myocardium
• myocardium is much thicker in the walls of the ventricles, particularly the left, than the atrial walls
• the epicardium is a simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves
• in both the subendocardial layer and the adjacent myocardium, modified cardiac muscle cells make up the impulse conducting system of the heart, specialized to generate and conduct waves of depolarization which stimulate rhythmic contractions in adjacent myocardial fibers
• the conducting system of the heart consists of two nodes of specialized myocardial tissue in the atrial wall:

  1. sinoatrial (SA) node
  2. atrioventricular (AV) node
• sinoatrial (SA) node is also known as the pacemaker
• Identify the parts

  A) endocardium

  B) Purkinje fibers

  C) myocardium

  D) subendothelial layer

  
• deeper layer of connective tissue surrounding variable amounts of cardiac muscle specialized for impulse conduction, which is often called the subendocardial layer and is continuous with connective tissue of the myocardium
• the heart's impulse conducting network

  Purkinje fibers
• at the apex of the heart, the bundles subdivide furtherinto a subendocardial conducting network of cardiac muscle fibers, called Purkinje fibers
• pale-staining fibers, larger than the adjacent contractile fibers, with sparse, peripheral myofibrils and much glycogen

  Purkinje fibers
• parasympathetic and sympathetic neural components innervate the heart
• stimulation of the parasympathetic division (vagus nerve) slows the heartbeat
• stimulation of the sympathetic nerve accelerates the activity of the pacemaker
• abnormal heart sound

  heart murmur
• Identify the parts

  A) mesothelium

  B) epicardium

  C) fat

  D) autonomic nerves

  E) loose connective tissue

  F) myocardium

  
• walls of all blood vessels except capillaries contain smooth muscle and connective tissue in addition to the endothelial lining
• factors affecting the amount and arrangement of tissues in vessels

  1. mechanical
  2. metabolic
• endothelium - specialized epithelium that acts as a semipermeable barrier between two major internal compartments: blood and interstitial tissue fluid
• endothelium of the vascular wall presents a non-thrombogenic surface on which blood will not clot and secrete agents that control local clot formation (heparin...)