During ventricular filling, the cardiac muscle fibers are stretched pulling the
myofilaments closer together—allowing more cross-bridge interactions once Ca
2+
pulls
the troponin-tropomyosin complex away from actin’s cross-bridge binding sites.
Thus, the length-tension relationship in cardiac muscle depends NOT on muscle fiber
length per se but on the resultant variations in the lateral spacing between actin &
myosin filaments.
°
Coronary Blood Flow: Nutrient supply to the heart itself
Cardiac muscle receives most ( 70%)of its blood during cardiac diastole
o
Diastole= relaxation
During systole:
o
Systole= contraction
o
Compression of major branches of coronary arteries
o
Open aortic valve partially blocks the entrance to the coronary vessels
Partially blocks adequate supply of blood to the heart at the moment
Coronary blood flow adjusts to changes in the heart’s oxygen requirements; high
metabolic activity releases more adenosine (from breakdown of ATP) which causes
dilation of coronary blood vessels.
Anaerobic metabolism very limited—cardiac muscle depends on oxygen
Cardiac muscle fuel sources : free fatty acids >> glucose & lactate
°
Figure 9-31:
Extent of myocardial damage as a function of the size of the
occluded vessel.
o
P wave= atrial depolarization
o
PR segment= AV node delay
o
QRS Complex= ventricular depolarization, atria repolarizing
(simultaneously)
o
ST segment= time during which ventricles are contracting and emptying
o
T wave= ventricular repolarization
o
TP interval= time during which ventricles are relaxing and filling
°
°
°
°
Chapter 10
Blood Vessels and Blood Pressure
°
Figure 10.4:
Basic organization of the cardiovascular system
°
°
Two Systems:
pulmonary circulation & systemic circulation
Artery:
blood from heart
organs
o
Heart
Artery
arteriole
capillary
o
*capillaries rejoin to form venules
Veins:
blood leaves organ
heart
o
Capillary
venule
vein
heart
Arteries progressively branch as they carry blood from the heart to the organs.
A separate small arterial branch delivers blood to each of the various organs.
