Download Size: 3 MB - Physiology Laws

Physiology Laws
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu),
Dip. Diab.DCA, Dip. Software statistics
PhD (physio)
Some are described
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Laplace law
Frank starling law
Bainbridge relex
Bezold jarisch reflex
Baro receptor reflex
Laplace's Law
• Surface tension properties are described
mathematically by Laplace's law,
• This states that the pressure inside a bubble
(or alveolus) necessary to keep it expanded is
directly proportional to the tension on the
wall of the bubble, which tends to collapse it,
divided by the radius of the bubble.
P = 2T/r
P = 2T/r
pressure
Tension
Surfactant
• If alveolar surface tension properties were not
modified by the presence of surfactant the
lungs would eventually become collapsed,
stiff, and fluid filled.
• lipoprotein secreted by type II alveolar cells
(pneumocytes) lining the alveoli.
• It is a complex consisting of about 85% to 90%
lipids and 10% to 15% proteins. The lipid
portion is about 85% phospholipid,
approximately 75% of which is dipalmitoyl
phosphatidylcholine.
Laplace law- 2 T/ R = P
----- PR/2T = stress
• In aortic stenosis, afterload is increased. The
ventricle has to generate far higher pressure
to overcome the increased load opposing
systolic Aortic
ejection
of blood.
stenosis
– obstructionhighersuch
pressuremore tensionthe
• To generate
high performance,
but LVH occurs
decrease(LV
ventricle– increases
its walltothickness
stress Laplace's law,
hypertrophy). By applying
increased LV wall thickness will decrease wall
stress despite the necessary increase in LV
pressure to overcome the aortic stenosis
Failing heart
Vessels and GI tract( P = 2T/R )
• if an aneurysm forms in a blood vessel wall,
the radius of the vessel has increased. This
means that the inward force on the vessel
decreases, and therefore the aneurysm will
continue to expand until it ruptures. A similar
logic applies to the formation of diverticuli in
the gut
Frank starling law
• E. H. Starling, using an isolated heart-lung
preparation as a model, observed in 1914 that
“the mechanical energy set free on passage from
the resting to the contracted state is a function
of the length of the muscle fibre
• ability of the heart to change its force of
contraction and therefore stroke volume in
response to changes in venous return is called the
Frank-Starling mechanism
• LVEDP – 8 mm Hg
• SV of around 70 ml.
• Starling concluded that the increased twitch
force was the result of a greater interaction
of muscle bundles.
• cardiac reduction in force is only 10% even if
cardiac muscle is at 80% sarcomere length
Frank starling law
• A common clinical application of Starling's
law is the relationship of left ventricular enddiastolic volume (LVEDV) and stroke volume.
• increase in actin and myosin cross-bridging .
• The Frank-Starling mechanism may remain
intact even in a failing heart.
• ventricular remodelling after injury or in
heart failure may modify the Frank-Starling
relationship.
Frank starling law
CARDIAC FUNCTION CURVE
THE FRANK- STARLING “LAW OF THE HEART”
CARDIAC OUTPUT (L/min)
15-
10-
5-
-4
0
RAP mmHg
+4
+8
CARDIAC FUNCTION CURVE
THE FRANK- STARLING “LAW OF THE HEART”
CARDIAC OUTPUT (L/min)
15-
10-
5-
-4
0
RAP mmHg
+4
+8
• Laplace law and frank starling
law – OK
Bainbridge Reflex
• Francis Arthur Bainbridge described this reflex
in 1915 when he was experimenting on dogs.
Bainbridge found that infusing blood or saline
into the animal increased heart rate.
• Increase blood volume – increase heart rate
Bainbridge Reflex
• stretch receptors located in the right atrial
wall and the cavoatrial junction.
• An increase in right-sided filling pressure
sends vagal afferent signals to the cardio
vascular center in the medulla.
• These afferent signals inhibit
parasympathetic activity, thereby increasing
the heart rate.
Bainbridge Reflex
• Acceleration of the heart rate also results
from a direct effect on the SA node by
stretching the atrium. The changes in heart
rate are dependent on the underlying heart
rate before stimulation.
Bainbridge Reflex
• the Bainbridge reflex does occur in humans, as
in after delivery of an infant when a large
volume (up to 800 mL) of uteroplacental
blood is put back into the mother's circulation,
resulting in tachycardia.
Bainbridge Reflex
• Bainbridge Reflex is involved in Respiratory
Sinus Arrhythmia.
• During inhalation intrathoracic pressure
decreases.
• It triggers increased venous return --• stretch receptors, ---- Bainbridge Reflex
increases the heart rate momentarily during
inspiration.
Reverse Bainbridge Reflex
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Spinal
Sympathetic block
Vasodilation
Decreased venous return
Decreased atrial stretch receptors
Bradycardia
The Bezold-Jarisch reflex
• Response to noxious ventricular stimuli sensed
by chemo receptors and mechano receptors
within the LV wall induced the triad of
hypotension, bradycardia, and
• coronary artery dilatation.
• The activated receptors communicate along
unmyelinated vagal afferent type C fibers. These
fibers reflexively increase parasympathetic tone.
The Bezold-Jarisch reflex
• Because it invokes bradycardia, the Bezold-Jarisch
reflex is thought of as a cardioprotective reflex.
• implicated in the physiologic response to conditions
such as myocardial ischemia or infarction,
thrombolysis, or revascularization and syncope.
• Natriuretic peptide receptors stimulated by
endogenous ANP or BNP may modulate the BezoldJarisch reflex.
• less pronounced in patients with cardiac hypertrophy
or atrial fibrillation.
The baroreceptor reflex
• The baroreceptor reflex is responsible for
maintenance of blood pressure.
• This reflex is capable of regulating arterial
pressure around a preset value through a
negative-feedback loop
Bain and baro
• The Bainbridge reflex and the baroreceptor reflex act
antagonistically to control heart rate. The baroreceptor
reflex acts to decrease heart rate when blood pressure rises.
• When blood volume is increased, the Bainbridge reflex is
dominant;
When
blood
volume
is
decreased,
the
baroreceptor reflex is dominant.
• The Bainbridge reflex is seen in dogs, but experiment has
shown that it is not as significant in primates.
Summary
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Laplace law
Frank starling law
Bainbridge relex
Bezold jarisch reflex
Baro receptor reflex
Thank you all