Transcript Frank-Starling “Law of the Heart”

The cardiovascular system
The heart
Gunnar Tobin
Department of Pharmacology
The Sahlgrenska Academy at the University of Gothenburg,
Sweden
Heart
 Physiological differences between cardiac muscle, skeletal
muscle and smooth muscle cells.
 Cardiac function and capacity.
 The electrophysiology of the cardiac muscle cell and its
connection to the ECG recording.
 The function of the conductive system.
 The afferent and efferent innervation of the heart and effects at
stimulat ion.
 The cardiac cycle: Different phases, diastole, systole.
 Pressure and volume in the cardiac atria and ventricles.
 Normal sounds of the pumping heart and their relation to the
ECG.
 Two principle mechanisms in the regulation of contraction
force.
 Pre- and after load.
 The metabolism of the heart.
 Basic knowledge of the ECG
The student should be able to understand:
- How the heart functions as a pump.
- Pathophysiological mechanisms at ischemic heart diseases and
cardiac failur e.
HEART
(PUMP)
REGULATION
CARDIOVASCULAR
SYSTEM
VESSELS
(DISTRIBUTION SYSTEM)
AUTOREGULATION
NEURAL
HORMONAL
RENAL-BODY FLUID
CONTROL SYSTEM
ARTERIES
HEART
DIASTOLE
VEINS
CAPACITY
VESSELS
80 mmHg
120 mmHg
SYSTOLE
CAPILLARIES
Work output
External
Kinetic
Functions of the Heart
Generating blood pressure
Routing blood
– Heart separates pulmonary and systemic circulations
Ensuring one-way blood flow
– Heart valves ensure one-way flow
Regulating blood supply
– Changes in contraction rate and force match blood delivery
to changing metabolic needs
Heart Wall
Three layers of tissue
– Epicardium: This serous membrane of smooth
outer surface of heart
– Myocardium: Middle layer composed of cardiac
muscle cell and responsibility for heart
contracting
– Endocardium: Smooth inner surface of heart
chambers
Cardiac muscle
•fibers arranged in a latticework
•is striated
•each cell has one nucleus
•has typical myofibrils that contain actin and myosin filaments
•functions as a Syncytium; intercalated discs and gap
junctions
•autorhythmic cells and action potentials of longer duration
and longer refractory period
CARDIAC MUSCLE
- Functional Syncytium
- Automaticity
STRIATED MUSCLE
SKELETAL MUSCLE
- Motor Units
- Stimulated by Motor Nerves
Unlike skeletal muscles,
cardiac muscles have
to contract in more
than one direction.
Cardiac muscle cells
are striated, meaning
they will only contract
along their long axis.
In order to get
contraction in two
axis, the fibres wrap
around.
The function of valves
Cardiac cycle
LATE DIASTOLE
DIASTOLE
ISOMETRIC
VENTRICULAR
RELAXATION
ATRIAL
SYSTOLE
VENTRICULAR
ISOMETRIC VENTRICULAR
EJECTION
CONTRACTION
Fick’s principle
Right heart: 160 ml/l
Left heart: 200 ml/l
Thus, one liter of blood
has to pass for 40 ml O2 to be
absorbed
200 ml of O2 is absorbed every
min (spirometry)
FICK’S PRINCIPLE
CO= VO2/([O2]a - [O2]v) = 5L/min
Cardiac output=Oxygen absorbed per min/arteriovenous O2 difference (ml/l)
CO= HR x SV
CO
SV =
HR
=
5 L/min = 0.0714 L or 71.4 ml
70 beats/min
Regulation of the Heart
Intrinsic regulation: Results from normal
functional characteristics, not on neural or
hormonal regulation
– Frank-Starling’s law of the heart
Extrinsic regulation: Involves neural and
hormonal control
– Parasympathetic stimulation
• Supplied by vagus nerve, decreases heart rate,
acetylcholine secreted
– Sympathetic stimulation
• Supplied by cardiac nerves, increases heart rate and
force of contraction, epinephrine and norepinephrine
released
Autoregulation
(Frank-Starling “Law of the Heart”)
CARDIAC OUTPUT = STROKE VOLUME x HEART RATE
Contractility
Sympathetic
Nervous System
Parasympathetic
Nervous System
Autonomic innervation
Reflexes in heart regulation
Medulla
Blood pressure
Afferents:
Bainbridge reflex
T-tubule
SARCOLEMMA
20%
80%
Mitochondria
10%
Ca++
SR
THICK
MYOFILAMENT
THIN MYOFILAMENT
Effects of the autonomic nervous systems
CARDIAC MUSCLE
TENSION
TOTAL TENSION
ACTIVE TENSION
PASSIVE
TENSION
MUSCLE LENGTH
HEART
SYSTOLIC PRESSURE CURVE
Isotonic (Ejection) Phase
PRESSURE
After-load
Isovolumetric
Phase
Stroke
Volume
Pre-load
End Systolic Volume
DIASTOLIC
PRESSURE CURVE
End Diastolic Volume
HEART
SYSTOLIC PRESSURE CURVE
Isotonic (Ejection) Phase
PRESSURE
After-load
Isovolumetric
Phase
Stroke
Volume
Pre-load
End Systolic Volume
DIASTOLIC
PRESSURE CURVE
End Diastolic Volume
HEART
SYSTOLIC PRESSURE CURVE
Isotonic (Ejection) Phase
PRESSURE
After-load
Isovolumetric
Phase
Stroke
Volume
Pre-load
End Systolic Volume
DIASTOLIC
PRESSURE CURVE
End Diastolic Volume
HEART
SYSTOLIC PRESSURE CURVE
Isotonic (Ejection) Phase
PRESSURE
After-load
Isovolumetric
Phase
Stroke
Volume
Pre-load
End Systolic Volume
DIASTOLIC
PRESSURE CURVE
End Diastolic Volume
CARDIAC FUNCTION CURVE
STROKE VOLUME
Cardiac Output = Stroke Volume x Heart Rate
If: Constant
Then:  CO reflects SV
DIASTOLIC FILLING
Right Atrial Pressure (RAP) reflects Diastolic Filling
CARDIAC FUNCTION CURVE
15-
10-
Pressure
CARDIAC OUTPUT (L/min)
THE FRANK- STARLING “LAW OF THE HEART”
5-
Volume
-4
0
+4
RAP mmHg
+8
CARDIAC FUNCTION CURVE
CARDIAC OUTPUT (L/min)
THE FRANK- STARLING “LAW OF THE HEART”
15-
10-
5-
-4
0
+4
RAP mmHg
+8