Cardiac A & P

Cardiac Structures

  • Muscular Structure

-2 atria

-2 ventricles

  • Pericardial Sac (2 layers)

-Visceral layer (inner)

-Parietal layer (outer)

  • Cardiac Wall (3 layers)

-Epicardium (outer)

-Myocardium (middle)

-Endocardium (inner)

  • Valves

-Tricuspid (from R atria to R ventricle)

-Mitral (from L atria to L ventricle

-Pulmonic (from R ventricle to pulmonic artery)

-Aortic (from L ventricle to aorta)

  • Blood Supply

-2 main arteries

1. Left coronary artery

-branches into 2 arteries

1. Left anterior descending (LAD)

-supplies blood to the anterior wall of the left ventricle, the anterior ventricular septum, and the bundle branches

2. Circumflex

-supplies blood to the lateral and posterior portions of the left ventricle

2. Right coronary artery

-sends blood to the sinus and atrioventricular nodes

-sends blood to the right atrium

-later becomes the acute marginal artery

-acute marginal artery later becomes posterior descending artery

-the posterior descending artery supplies the posterior and inferior wall of the left ventricle, and the posterior right ventricle

-Coronary arteries receive blood primarily during ventricular relaxation (diastole)

-Blood is pumped out to the systemic circulation during contraction of the ventricle (systole)

  • Pathway of blood

-Inferior vena cava → superior vena cava → R. atrium → tricuspid valve → R. ventricle → pulmonic valve → pulmonary artery → lungs (blood is oxygenated) → pulmonary veins → L. atrium → mitral valve → L. ventricle → aortic valve → aorta → systemic circulation

  • Electrical Conduction

-Heart contains specialized muscle fibers that generate and conduct their own electrical impulses, spontaneously

-Consists of sinoatrial (SA) node, internodal tracts, atrioventricular (AV) node, bundle of His, right and left bundle branches, and purkinje fibers

-These fibers conduct electrical impulses and coordinate chamber contraction

-Impulses move from right to left, and top to bottom

  • Electrical Pathway

-The 1st impulse is initiated in the SA node (the heart’s intrinsic pacemaker)

-After the initial impulse (SA node), the conduction occurs almost simultaneously through

Atrial depolarization

Atrial contraction

Impulse transmission to the AV node

Impulse transmission to the bundle of His, bundle branches, and purkinje fibers

Ventricular depolarization

Ventricular contraction

Ventricular repolarization

Cardiac Function

  • Cardiac Output (CO)

-Total amount of blood ejected per minute

- Equals stroke volume X heart rate (HR) (CO = SV X HR)

-Alterations in CO affect every body system

  • Stroke Volume (SV)

-The amount of blood ejected with each beat

  • Ejection fraction

-Percent of left ventricular end-diastolic volume ejected during systole (60% to 70% is normal)

Blood Vessels

  • Arteries

-Three-layered vessels that carry oxygenated blood from the heart to the tissues

  • Arterioles

-Small-resistance vessels that feed into capillaries

  • Capillaries

-Join arterioles to venules

-Location of gas, nutrient, and waste exchange

  • Venules

-Join capillaries to veins

-Larger, lower-pressured vessels than arterioles

  • Veins

-Large, low-capacity, low-pressure vessels

-Return un-oxygenated blood to the heart

1