Circulatory system

• Myocardium lumen


  blood passage where gas exchange is fulfilled
• involuntary contraction is done by cardiac muscle
• Sinoatrial node

  • aka pacemaker
  • heart beat starts through the contractions of this structure located in sinus venosus
• In Mammals: atrioventricular nodes with bundles of Purkinje fibers
• heart rate

  • influenced by the nervous, endocrine, and venous filling
• Frank-Starling Reflex


  venous return increases as muscles increase pressure on veins within
• systems contributing to the heart rate:

  1. nervous
  2. endocrine
  3. venous filling
• In Frank-starling reflex, the returning venous blood to heart chamber stretches them, which created stronger contraction
• In Hagfishes: they have a three chambered heart.

  1. sinus venosus
  2. atrium
  3. ventricle
• Conus arteriosus: with cardiac muscles
• Bulbus arteriosus: without cardiac muscles
• in hagfishes: their ”hearts” do not have cardiac muscles. that is why they have accessory hearts
• Accessory hearts of hagfishes

  1. caudal hearts: comprised of central cartilaginous rods, skeletal muscles, and veins
  2. portal heart: with walls of cardiac muscle; located in hepatic portal system
• In lampreys: they have three chambered hearts like hagfishes, but blood empties into bulbus arteriosus
• In lampreys: Leaflets of the bulbus arteriosus is not just the thickening of the ventral aorta, but it also has innervations.
• One-way valves prevents backflow. leaflets of the bulbus arteriosus contains the semilunar valves in lampreys
• Four chambered hearts started to appear in cartilaginous and bony fishes
• Four chambers of the heart

  1. sinus venosus
  2. atrium
  3. ventricle
  4. conus/bulbus arteriosus
• in teleost fishes: conus arteriosus is regressed/replaced by bulbus arteriosus
• One way valves prevent backflow. the conal valves in shark hearts allows blood flow to the conus arteriosus
• One way valves prevent backflow. the bulbar valves in bony fishes allows blood to the bulbus arteriosus.
• in lungfishes: presence of partial atrial and ventricular divisions.
• in lungfishes, the partial interatrial septum divides the right (larger) and left (smaller) atrial chambers
• in lungfishes, the partial interventricular septum divides the ventricles
• Valves of the lungfishes

  1. sinoatrial valves
  2. atrioventricular PLUG
  3. spiral valves
• Valves of teleost heart:

  1. sinoatrial valve
  2. atrioventricular valve
  3. bulbar valve (singular)
• valves of lampreys

  1. sinoatrial valve
  2. atrioventricular valve
  3. semilunar valves (from the leaflets of the bulbus arteriosus)
• Four chambers of lungfishes

  1. sinus venosus
  2. atrium
  3. ventricle
  4. bulbus/conus arteriosus
• Amphibian hearts do not have internal division of the ventricle
• Amphibian hearts have incomplete internal division of the atrium called interatrial septum. ventricle does not have internal division
• Valves of amphibians

  1. sinoatrial valve
  2. atrioventricular valve
  3. spiral valve
• the pulmocutaneous artery of frogs branches off to form the:

  1. pulmonary artery
  2. cutaneous artery
• Despite absence of the internal septum in the ventricle of frogs, systemic and pulmonary blood still separate
• During diving of frogs:

  • Sphincter of pulmonary artery constricts -> less flow in lung artery -> more flow for cutaneous artery
• The sinus venosus of reptiles is reduced, contains the pacemaker region
• the atrium of reptiles is completely divided into left and right atria
• in reptiles: the bulbus cordis is divided into pulmonary trunk + left and right systemic trunks
• In reptiles: the ventricles have interconnected compartments:

  1. cavum venosum
  2. cavum pulmonale
  3. cavum arteriosum
• In reptiles: the cavum arteriosum connects to cavum venosum via the interventricular canal
• In turtles: during diving, they express cardiac/right-to-left shunt

  • blood, instead of flowing to the right side, proceeds to the left side directly and moves to the systemic circuit