Physiology Laws

Dr. S. Parthasarathy MD., DA., DNB, MD (Acu),

Dip. Diab.DCA, Dip. Software statistics PhD (physio)

Some are described

• 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

Tension

pressure

P = 2T/r

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 ejection of blood.

• To generate such high performance, the ventricle increases its wall thickness (LV hypertrophy). By applying Laplace's law, increased LV wall thickness will decrease wall stress despite the necessary increase in LV pressure to overcome the aortic stenosis

Aortic stenosis – obstruction- higher pressure- more tension – but LVH occurs to decrease

stress

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 end-diastolic 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

CARD

IAC

OU

TPU

T (L

/min

)

RAP mmHg

15-

10-

5-

-4 0 +4 +8

THE FRANK- STARLING “LAW OF THE HEART”

DecreasedHeart Rate

CARDIAC FUNCTION CURVE

CARD

IAC

OU

TPU

T (L

/min

)

RAP mmHg

15-

10-

5-

-4 0 +4 +8

THE FRANK- STARLING “LAW OF THE HEART”

IncreasedHeart Rate

• 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

• 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 Bezold-Jarisch 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

• Laplace law • Frank starling law • Bainbridge relex • Bezold jarisch reflex • Baro receptor reflex

Thank you all