Extra Coronary Arteries

• • The coronary arteries lie in the epicardium of the heart, but give off smaller branches that penetrate the myocardial muscle mass travelling inwards towards the endocardium
  • As the arteries penetrate the mass of the heart they subdivide into arterioles and capillaries
  • The numerous coronary capillaries lie in extremely close proximity to the cardiac myocytes
  • Just as in skeletal muscle, a high capillary to fibre ratio means short diffusion distances and ensure efficient oxygen delivery to the myocytes and effective removal of metabolic waste products from the cells (e.g., CO2 and H+)
• • After passing through the rich myocardial capillary networks, the venous blood enters the coronary veins, which follow roughly the same routes as the arteries
  • The coronary veins join to form the coronary sinus, which empties venous blood directly into the right atrium