Medical Pharmacology Chapter 4:  Autonomic (ANS) Pharmacology: Introduction

 

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Predominant Sympathetic or Parasympathetic Tone

Antatomical Site

Predominant Autonomic Tone

Arterioles

Sympathetic-adrenergic

Veins

Sympathetic-adrenergic

Heart

Parasympathetic-cholinergic

Ciliary Muscle

Parasympathetic-cholinergic

Gastrointestinal Tract

Parasympathetic-cholinergic

Salivary Glands

Parasympathetic-cholinergic

Sweat Glands

Sympathetic-cholinergic

Taylor, P. Agents Acting at the Neuromuscular Junction and Autonomic Ganglia In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp.193-195. Adapted from Table 9-3

 

 

Baroreceptor Reflexes

  • A principal mechanism for arterial blood pressure control is the baroreceptor reflex.

  • The reflex is initiated by activation of stretch receptors located in the wall of most large arteries of the chest and neck.

  • A high density of baroreceptors is found in the wall of each internal carotid artery (just above the carotid bifurcation i.e. carotid sinus) and in the wall of the aortic arch.

  •  As pressure rises and especially for rapid increases in pressure:

    • baroreceptor input to the tractus solitarius of the medulla results in inhibition of the vasoconstrictor center and excitation of the vagal (cholinergic) centers resulting in:

      • a vasodilatation of the veins and arterioles in the peripheral vascular beds.

      • negative chronotropic and inotropic effects on the heart. (slower heart rate with reduced force of contraction)

 

 

Pharmacological Modification of Autonomic Function

 

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