CARDIOVASCULAR SYSTEMTHE HEART

Chapter 18

Overview of Cardiovascular

System

Location of the Heart

Pericarium

Coronary Circulation

Anastomoses

Cardiac Muscle

• Autorhythmic cells initiate depolarization

• Na+ influx (depolarization) goes down T-tubules

• depolarization opens slow Ca channels

• Ca2+ influx release of Ca2+ from sarcoplasmic reticulum

• Ca2+ binds troponin cross bridging of sliding myofilaments

• Ca2+ surge across membrane prolongs depolarization (plateau) increases duration of contraction

• K+ channels open and repolarize sarcolemma

Excitation Contraction Coupling

Cardiac Muscle: Energy Requirements

• More mitochondria than skeletal muscle;

– Higher dependence on O2

• Cardiac muscle readily adapts to available fuel sources

• O2 deficit is the cause of system failure with decreased blood flow

Heart Physiology: Electrical

• Intrinsic conduction system – Specialized cells that initiate & distribute impulses

– Autorhythmic cells of nodes & conducting pathway have unstable resting potential & have the capability of spontaneous depolarization