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Anatomy and Physiology
Chapter 20: The Heart
Introduction
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Heart beat 100,000X / day ( moves 8000L)
Muscle is never at rest
Pulmonary circuit goes to heart from lungs
Systemic circuit goes to heart from body
Arteries (afferent) – away from the heart
Veins (efferent) – toward the heart
Capillaries – exchange vessels
20.1 Anatomy of the Heart
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Tilts to left of sternum
Between intercostal spaces 3 and 5
Associated with lots of fatty tissue
Pericardial sac – protects and lubricates (fluid)
Myocardium = heart muscle
Coronary arteries = supply blood to heart muscle
itself ( these are “bypassed”)
Chambers and vessels
• Superior vena cava – blood from head/neck/limbs
to RA
• Right Atrium – receives blood from body
• Right ventricle – pump * / to lungs
• Left Atrium– from lungs
• Left ventricle – pump * / to body through; thicker
more muscular side… to whole body
• Aorta
• Inferior vena cava – receives blood from the trunk
to RA
• * RV and LV pump at same time, same amount
Chambers, vessels and valves
• RA and RV separated by tricuspid valve
• Cusps anchored to chordae tendineae that tug
flaps down to prevent backflow
• LA receives blood through mitral valve
• LV is associated with semilunar valve
20.2 Generation of Action Potentials
• Muscle cells in conducting system coordinate
beat
• Contractile cells contract to propel blood
• Electrocardiograph (ECG, EKG) shows electrical
events of heart beat
• App called cardiograph
• Sinoatrial (SA) node in RA
▫ Spontaneous depolarization without neural or
hormonal
▫ 80 – 100 action potentials per minute
▫ Pacemaker cells
• Atrioventricular (AV) node between A and V
▫ 50 msec from SA to AV
▫ Delay at AV node so atria finish contracting before
ventricles
• Conducting cells with internodal pathways do not
have stable resting potential; drift toward threshold
• Purkinje fibers
▫ Rapid conduction of action potentials ventricular
myocardium
Energy
• Heart muscles have lots of mitochondria that
break down both fatty acids and glucose (stored
as glycogen)
• Have heme units (part of hemoglobin) stored as
myoglobin so they can have access to lots of O2
– very aerobic
• Calcium ions are very important to the
conduction of action potentials in the cardiac
muscle cells