Question

When the SNS increases cardiac output, a series of events occurs through innervation via adrenergic receptors to affect both autorhythmic cells and contractile fibers. Describe and explain the changes in the function of the two cell types as cardiac output is increased, including all the membrane proteins.

Answer 1

Adrenaline is secreted by adreanal medulla and it is a major neurotransmitter in sympathetic nervous system.

cardiac output is abyproduct of heart rate and stroke volume.

Cardiac output = Heart rate x stroke volume

Also Blood pressure = Cardiac output x Systemic vascular resistance.

At Heart--->

Beta -1 adrenergic receptors are present on heart.

Beta 2 receptors nare present on blood vessels

Adrenaline increases heart rate by increasing the slope of diastolic depolarization of cells in the SA node. It also activates latent pacemakers in A-V node and Purkinje fibres.

Force of cardiac contraction is increased which inturn increases stoke volume.Development of tension as well as relaxation are accelerated Thus, systole is shorter than diastole, hence cardiac output is increased.

Conduction velocity through A-V node, bundle of His, atrial and ventricular fibres is increased;

Adrenaline increases systolic blood pressure by increasing the force of contraction of the heart and cardiac output. But, it decreases diastolic blood pressure by reducing the total peripheral resistance by action on Beta -2 receptors on blood vessels.

Mean blood pressure generally rises and pulse pressure is increased.