How do the sympathetic and parasympathetic nervous systems regulate heart rate and blood pressure?

Question

The autonomic nervous system, composed of the sympathetic and parasympathetic divisions, regulates heart rate and blood pressure to maintain homeostasis. The sympathetic nervous system (SNS) increases heart rate and blood pressure in response to stress or physical activity through the release of norepinephrine. This stimulates the beta-1 adrenergic receptors on the heart, increasing heart rate (chronotropy) and force of contraction (inotropy). The parasympathetic nervous system (PNS), through the vagus nerve, decreases heart rate by releasing acetylcholine, which acts on muscarinic receptors. Together, these systems provide a dynamic balance, with the SNS increasing activity during stress and the PNS promoting relaxation and recovery.

Answer 1

The ANS regulates HR and BP through the SNS and PNS.The SNS, activates the body and increases HR and BP under conditions of emergency by releasing Epinephrine that stimulates beta-l adrenergic receptors in the SA node,AV node and in the ventricular myocardium, causing positive chronotropy(faster HR),positive dermotropy(increased electrical impulse conduction), positive intropy( Increased strength of cardiac muscle contraction), respectively. Epinephrine also acts on alpha-l andrenergic receptors in the vascular smooth muscle causing generalized vasoconstriction.Net effect is, elevated HR, contractility and BP( both systolic & diastolic).Parasympathetic nervous system conserves body energy and maintains body activities at basal level by releasing acetycholine that acts on M2-muscarinic receptors in the SA and AV node, causing negative Chronotropy and negative dermotropy. There is minimal direct effect on ventricular contraction. Net effect is reduced HR & BP.Cardiovascular Homeostasis between the two is modulated by the reflex arcs( especially the barorecepters).

Answer 2

The ANS regulates HR and BP via the SNS and PNS to maintain homeostasis. The SNS increases HR and BP in response to stress or activity by releasing norepi, which stimulates beta-1 adrenergic receptors on the heart, enhancing chronotropy (HR) and inotropy (contractility). The PNS, via the vagus nerve, decreases HR by releasing ACh, which acts on muscarinic receptors to slow HR. These systems work in opposition, with the SNS promoting activation during stress and the PNS promoting relaxation.

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