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Cardiovascular Physiology
1) Blood Solution of Nutrients/Wastes
2) Heart Pump
3) Peripheral Circulation Tubes
The primary function of the Cardiovascular system is to
1) deliver nutrients/oxygen and
2)remove wastes/CO2
from the cells in your body
Cardiac Physiology
The primary function of the HEART is
to generate a Pressure gradient in the
vascular system
Pressure gradient allows blood to move
by BULK FLOW through the body & the
lungs
Gradients
A GRADIENT is a difference in any parameter over distance
Molecules move “down” gradients
from “Hi” to “Lo”, spontaneously
e.g.
Pressure, concentration, temperature, energy
Bulk Flow
Many molecules moving simultaneously in one
direction, from an area of high P to low P
PATMOS mm Hg
Lo P
Hi P
Expiration
Inspiration
Hi P
Lo P
PLUNGS mm Hg
Poiseulle’s Law of Bulk Flow: Its all about PRESSURE
P1
P2
FB = kB(P1 - P2) L/min
FB = Bulk Flow L/min
kB = bulk flow constant ~ tube diameter
If P1 > P2, flow goes from 1 to 2
If P1 < P2, flow goes from 2 to 1
If P1 = P2, no flow occurs
Bulk Flow:
Movement DOWN a Pressure Gradient
Cardiac Cycle
The cardiac cycle links
1) Electrical
2) Contractile
3) Pressure
4) Flow
through the heart!
The Heart is surround by cardiac muscle
Pericardium
Myocardium
Endocardium
Myocardial Fibers
Myocardium Anatomy
Myocardium is very similar to
skeletal muscle
Except
•
Intercalated discs form Gap
junctions between adjacent
myocardial fibers
•
Myocardial fibers branch
•
SR and T-tubules are weakly
linked….Ca2+ is slowly
released upon excitation
Pacemaker Cells: Heart is Autorhythmic!
How do pacemaker cells spontaneously
produce action potentials?
Pacemaker cells have an UNSTABLE resting membrane potential!
1) Prepotential: Few Na+ channels open,
Na+ influx = funny current
2
3
2) Depolorization: VG Ca2+ channels open
INFLUX of Ca2+
1
3) Repolarization: K+ channels open
EFFLUX of K+
Drugs to treat Arrhythmias sometimes work on Ca2+ channels!
Myogenic signal propagates down
Myocardium
Electrical Properties of the Myocardium
Plateau
Skeletal muscle AP look and
behave like neural cells
Due to the SLOW CLOSING OF Ca2+,
Myocardium REPOLARIZES VERY SLOWLY
Excitation-Contraction Coupling of Cardiac Muscle
1
ECF
1) Action Potential
Ca2+
Sacrolemna
2) VG Ca2+ channels open,
CA 2+ Influx
ICF
RyR
2
3
SR
Ca2+
4
VG Ca2+ Channel
T-tubule
Ca2+ Spark
3) Ca2+ influx triggers RyR channels
on SR to open
Calcium Induced Calcium Release
4) Ca2+ pours out of SR
Ca2+ Spark!
5) Sparks sum to create Ca2+ signal
5
Ca2+ Signal
6) Ca2+ binds Troponin, crossbridge formation, Contraction!
Sarcomere
6
Contraction
Calcium Sparks Video
Myocardium contraction is GRADED!
Amount of Ca2+ entering myocardium is proportional to contraction strength
Ca2+
Force of Myocardium
Ca2+
Ca2+ Spark
Ca2+ Signal
Contraction
# of Cross bridges Formed
Amount of Calcium INFLUX
Amount of Calcium INFLUX
Excitation-Contraction Coupling in Myocardium vs. Skeletal Muscle
Skeletal Muscle
Refractory
Myocardium
Ca2+ Plateau prolongs the refractory period…..summation cannot happen!
Guarantees that Cardiac Muscle Contract-Relaxes Rhythmically!!!!!
Don’t get CONFUSED!
• Pacemaker Potentials
• Cardiac Muscle Excitation
Pacemaker EXCITATION >>>>>>>>>>>>>>>>>>>>.Cardiac Muscle Excitation- Contraction
Heart’s Electrical Conducting System
SA = 100 min-1
AV node = 40 min-1
AV bundle
Bundle branches
Purkinje Fibers
10-30 min-1
Why do the SA pacemaker cells beat a higher frequency
than AV, Bundle Branches & Purkinje?
SA NODE
AV NODE
SA Node has
More Funny Current (Na+) channels
What about Bundle Branches and Purkinje
(10-30 min-1)?
SA Node
Atrial Muscle
AV Node
AV Bundle
Bundle Branches
Purkinje Fibers
Ventricular Muscle
No Plateau Phase
Shorter Refractory Period
Excitation involves Calcium PLATEAU
Huge Refractory Period
Ventricular Systole: Contraction
Ventricular Diastole: Relaxation
Atria have Systole and Diastole TOO!
1 Late diastole
Atria & Ventricles
START
5
Early Ventricular
DIASTOLE.
2 Atrial systole
S1
S2
4 Late Ventricular
Systole
3 Early Ventricular
SYSTOLE
Cardiac Cycle
The cardiac cycle links
1) Electrical
2) Contractile
3) Pressure
4) Flow
through the heart!
High Ventricular Pressure Forces
AV Valves Shut
Low Ventricular Pressure
Forces Aortic/Pulmonary Valves Shut
Valves respond to pressure!
Guarantees One-Way Blood Flow
Chordae Tendinae
Papillary Muscle
Relaxed ventricular muscle (diastole)
Contracting ventricular muscle (systole)
Low pressure in ventricle
High pressure in ventricle
AV valve flops open
Aortic Valve Shuts
AV valve forced shut
Aortic Valve Opens
Blood Flow through heart is driven by Pressure!
Isovolumetric
CONTRACTION
Isovolumetric
RELAXATION
Blood Flow through Heart
R. AV
Valve
L. AV
Valve
Cardiac Cycle
The cardiac cycle links
1) Electrical
2) Contractile
3) Pressure
4) Flow
through the heart!
Wiggers Diagram
1
2
3
4
1)
No electrical activity
Atrial & Ventricular Diastole
Pressure is low
Volume is increasing
2)
P-wave = Atrial Depol.
Atrial Systole
Atrial Pressure Rises
Ventricular volume increases
5
3)
QRS = Atrial Repol, Ventricular Depol.
Ventricular Systole, Atrial Diastole
Ventricular Pressure rises dramatically
Atrial Pressure rises
Ventricular Volume flat, then decreases
as AV closes and Aortic and Pulmonary
Valves Open
4) T-wave = Ventricular Repol.
Ventricular Diastole
Pressure drops dramatically in ventricle
& rises in Atria
Ventricular Volume decreases then is flat
as aortic and pulmonary valves CLOSE
5) No electrical activity
Atrial & Ventricular Diastole
Pressure & Volume slowly rise as blood fills