Chapter 18 Heart

Coronary Arteries and Veins:
- The arteries that supply the heart are called coronary arteries.
- The veins that drain the heart are known as cardiac coronary veins.
- Together, they form the coronary circulation, providing the functional blood supply to the heart muscle.
Variability in Arterial Supply:
- Coronary arterial supply can vary considerably among individuals, especially in smaller branches off the main arteries.
- Anastomoses are common in cone-shaped organs like the heart, allowing arteries to connect and accommodate blood flow.
Collateral Routes of Circulation:
- Additional routes for blood delivery can develop anywhere in the body, including the heart.
- New vessels can grow in response to blockages or increased blood flow demands.

Right Coronary Artery:
- Originates from the ascending aorta, supplying the right side of the heart.
- Main branches include:
  - Right Marginal Artery: Small artery along the margin of the heart.
  - Posterior Interventricular Artery: Runs along the back between the ventricles.
Left Coronary Artery:
- Peeks out from under the pulmonary trunk, supplying the left side of the heart.
- Main branches include:
  - Anterior Interventricular Artery: Runs along the front between the ventricles.
  - Circumflex Artery: Encircles the heart, supplying blood to the left atrium and ventricle.
Important Note:
- The anterior interventricular artery is often implicated in fatal heart attacks due to blockage.

Main Cardiac Veins:
- Four primary veins drain into the coronary sinus:
  - Great Cardiac Vein: Located on the anterior surface.
  - Small Cardiac Vein: Also on the anterior surface.
  - Middle Cardiac Vein: Located on the posterior surface.
  - Coronary Sinus: Collects blood from other veins and drains into the right atrium.

Angina Pectoris:
- The chest pain resulting from reduced blood flow to heart muscles.
- Can be intermittent or chronic and signifies possible heart issues.
Myocardial Infarction:
- Occurs when blood supply is blocked for an extended period, leading to cell death.
- Damaged muscle tissue is replaced by scar tissue, which does not contract.

Atrioventricular Valves:
- Tricuspid Valve: Located on the right between the right atrium and ventricle.
- Bicuspid (Mitral) Valve: Located on the left between the left atrium and ventricle.
Semilunar Valves:
- Located between the ventricles and great vessels (pulmonary and aortic).
- Control the direction of blood flow out of the heart.

Similarities:
- Both utilize actin and myosin for muscle contraction.
Key Differences:
- Cardiac muscle cells are branched and interconnected, promoting synchronized contraction.
- Cardiac muscle relies heavily on extracellular calcium sources for contraction.
- Mitochondria are abundant in cardiac muscle, necessary for continuous energy requirements.

Intrinsic Conduction System:
- 1% of cardiac cells are autorhythmic, generating impulses independently.
- Main components include:
  - Sinoatrial Node (SA Node): The primary pacemaker of the heart, initiating heartbeat around 75 times per minute.
  - Atrioventricular Node (AV Node): Delays impulses to allow atria to complete contraction before ventricles.
  - Atrioventricular Bundle (Bundle of His): Connects atria and ventricles, propagating impulses into the ventricles.
  - Bundle Branches: Right and left branches spreading impulses through the ventricles.
  - Purkinje Fibers: Distribute impulses across the ventricular muscle, allowing for contraction.

Autonomic Nervous System Influence:
- Influences heart rate via sympathetic (acceleratory) and parasympathetic (inhibitory) pathways.
Hormonal Effects:
- Hormones like epinephrine can increase heart rate and contractility.

This includes tracking the heart's electrical activity, influenced by the conduction system, allowing assessment of rhythmic and structural heart health.