Catecholamines + Heart

Catecholamines and effects on heart

Epinephrine(beta>alfa) and Norepinephrine(alfa>beta) both has effect on Heart(beta 1 receptor) and blood vessels(alfa 1 receptors).Both of these catecholamines increase Heart rate(positive chronotropic action) and force of contraction(positive ionotropic action).However Epinephrine decrease total peripheral resistance and Norepinephrine increase total peripheral resistance.Because Norepinephrine causes vasoconstriction .

Due to vasoconstriction,Norepinephrine increase Blood prassure(both systolic & diastolic),which causes stimulation of Baroreceptors.As a result Reflex Bradycardia occurs.
           So Norepinephrine causes

• Decrease Heart rate and Cardiac Output
• Increase TPR
• Increase Blood pressure.

Again Epinephrine causes vasodilation so it decreases TPR and ultimately Diastolic pressure decrease but Systolic pressure increase(because its not directly depends on TPR).Due to low TPR its not stimulate Baroreceptors sufficiently.
So net effect of Epinephrine

• Increase Heart rate and Cardiac Output
• Decrease TPR
• Widening of pulse pressure(Difference between systolic and diastolic blood pressure,indicate cardiac output)

Collected & Concise only for postgraduate student

Bainbridge Reflex

*Another name- Cardioacceleratory reflex.

* Described by Bainbridge in 1915

*Description : When venous pressure increase, the nerve ending of the wall of the right atrium & the wall of the vena cavae are stimulated.The afferent fibres ascend in the vagus to the medulla oblongata & terminate on the nucleus of the tractus solitarius . Connector neurons inhibit the parasympathetic nucleus(dorsal) of the vagus,& reticulospinal fibres stimulate the thoracic sympathetic outflow to thw heart,resulting in cardiac acceleration. 

*This reflex compets with the Baroreceptor-mediated decrease in heart rate produced by volume expansion.

***There has been much debate about its significance,and its physiologic role remains unsetted.

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Magic bullet (Respiration +Heart rate)

We know parasympathetic stimulation (vagas nerve) decrease heart rate  & force of contraction.
During inspiration this parasympathetic tone falls & heart rate quickens.




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ECG

The letters P,Q,R,S & T were selected in the early days of ECG history & chosen arbitrarily:

P = Pressure

Q=Quantity of blood

R=Resistance

S=Supply

T=Tissue


Collected & Concise only for postgraduate student

Md.Shahinur Rahman
I want to make Physiology & Pathology Easy.