Tài liệu Color Atlas of Pharmacology (Part 9): Systems Pharmacology pptx

Systems Pharmacology

Lüllmann, Color Atlas of Pharmacology © 2000 Thieme

All rights reserved. Usage subject to terms and conditions of license.

Sympathetic Nervous System

In the course of phylogeny an efficient

control system evolved that enabled the

functions of individual organs to be or￾chestrated in increasingly complex life

forms and permitted rapid adaptation

to changing environmental conditions.

This regulatory system consists of the

CNS (brain plus spinal cord) and two

separate pathways for two-way com￾munication with peripheral organs, viz.,

the somatic and the autonomic nervous

systems. The somatic nervous system

comprising extero- and interoceptive

afferents, special sense organs, and mo￾tor efferents, serves to perceive external

states and to target appropriate body

movement (sensory perception: threat

! response: flight or attack). The auto￾nomic (vegetative) nervous system

(ANS), together with the endocrine

system, controls the milieu interieur. It

adjusts internal organ functions to the

changing needs of the organism. Neural

control permits very quick adaptation,

whereas the endocrine system provides

for a long-term regulation of functional

states. The ANS operates largely beyond

voluntary control; it functions autono￾mously. Its central components reside

in the hypothalamus, brain stem, and

spinal cord. The ANS also participates in

the regulation of endocrine functions.

The ANS has sympathetic and

parasympathetic branches. Both are

made up of centrifugal (efferent) and

centripetal (afferent) nerves. In many

organs innervated by both branches, re￾spective activation of the sympathetic

and parasympathetic input evokes op￾posing responses.

In various disease states (organ

malfunctions), drugs are employed with

the intention of normalizing susceptible

organ functions. To understand the bio￾logical effects of substances capable of

inhibiting or exciting sympathetic or

parasympathetic nerves, one must first

envisage the functions subserved by the

sympathetic and parasympathetic divi￾sions (A, Responses to sympathetic ac￾tivation). In simplistic terms, activation

of the sympathetic division can be con￾sidered a means by which the body

achieves a state of maximal work capac￾ity as required in fight or flight situa￾tions.

In both cases, there is a need for

vigorous activity of skeletal muscula￾ture. To ensure adequate supply of oxy￾gen and nutrients, blood flow in skeletal

muscle is increased; cardiac rate and

contractility are enhanced, resulting in a

larger blood volume being pumped into

the circulation. Narrowing of splanchnic

blood vessels diverts blood into vascular

beds in muscle.

Because digestion of food in the in￾testinal tract is dispensable and only

counterproductive, the propulsion of in￾testinal contents is slowed to the extent

that peristalsis diminishes and sphinc￾teric tonus increases. However, in order

to increase nutrient supply to heart and

musculature, glucose from the liver and

free fatty acid from adipose tissue must

be released into the blood. The bronchi

are dilated, enabling tidal volume and

alveolar oxygen uptake to be increased.

Sweat glands are also innervated by

sympathetic fibers (wet palms due to

excitement); however, these are excep￾tional as regards their neurotransmitter

(ACh, p. 106).

Although the life styles of modern

humans are different from those of

hominid ancestors, biological functions

have remained the same.

80 Drugs Acting on the Sympathetic Nervous System

Lüllmann, Color Atlas of Pharmacology © 2000 Thieme

All rights reserved. Usage subject to terms and conditions of license.