Download Cardiovascular System 1

Biology 219 – Human Physiology
Clemens
Cardiovascular System 1: The Heart
Text: Ch. 14
A. Overview of the Cardiovascular System
3 components: heart
blood vessels
blood
Heart
→ arteries → arterioles → capillaries → venules → veins ( → return to heart)
Right heart pumps deoxygenated blood to lungs (pulmonary circulation); lower pressure
Left heart pumps oxygenated blood to entire body (systemic circulation); higher pressure
B. Heart Anatomy
atria - receiving chambers
ventricles - pumping chambers
1. Chambers and Great Vessels
RA ←
vena cavae
RV →
pulmonary trunk (artery)
LA ←
pulmonary veins
LV →
aorta
Pulmonary circulation: RV → pulmonary trunk → LUNGS → pulmonary veins → LA
Systemic circulation: LV → aorta → BODY → vena cavae → RA
2. Heart Valves
a. Atrioventricular (AV) valves - prevent backflow from ventricles to atria
tricuspid valve - RA } RV
bicuspid (mitral) valve - LA } LV
chordae tendineae attached to papillary muscles prevent prolapse of AV valves
b. Semilunar valves - prevent backflow from arteries to ventricles
pulmonary valve - RV } pulmonary trunk
aortic valve - LV } aorta
C. Cardiac Muscle Cells
autorhythmic cells spontaneously initiate APs
intercalated discs allow AP to spread between cardiac muscle cells
sinoatrial (SA) node - primary pacemaker
1. Excitation-Contraction Coupling
- similar to skeletal muscle:
AP → T tubules → SR → releases Ca2+
Ca2+ → troponin → tropomyosin → uncovers myosin binding sites → contraction
- Ca2+ also enters from the ECF through Ca channels during contraction
Ca2+ is pumped back to SR by Ca2+ ATPase during relaxation phase
Ca2+ is also transported back out to ECF `by a Na-Ca exchanger
D. Cardiac Action Potentials
1. Pacemaker Potential in Autorhythmic Cells
(1) slow depolarization toward threshold = pacemaker potential
“funny channels” permeable to Na+ and K+
(2) rapid AP depolarization - due to Ca2+ inflow
(3) repolarization
Autonomic NS control:
sympathetic - faster depolarization → ↑ heart rate
parasympathetic - slower depolarization → ↓ heart rate
2. Myocardial Action Potential in Contractile Cells
(0) initial AP depolarization - similar to other APs (voltage-gated Na+ channels)
(1) slight repolarization
(2) plateau phase (100-200 ms) - due to slow, inward Ca2+ flow (L-type Ca channels)
results in long AP duration and long refractory period (200-300 ms)
Biology 219 – Human Physiology
(3) repolarization - due to delayed opening of voltage-gated K channels
E. Conduction System of the Heart
1. autorhythmic cells - “pacemakers”
2. conduction fibers - specialized to spread AP rapidly through ventricles.
sinoatrial (SA) node
↓
atrial depolarization
↓
atrioventricular (AV) node ~ 0.1 second delay
↓
AV bundle (of His)
↓
R & L bundle branches
↓
Purkinje fibers
↓
ventricular depolarization
F. Electrocardiogram (ECG) [Lab Exercise]
P wave - atrial depolarization
QRS complex - ventricular depolarization
T wave - ventricular repolarization
Clemens