Regulation and Integration of the Body
Antagonistic Interactions
Antagonistic effects, described earlier, are most clearly seen on
the activity of the heart, respiratory system, and gastrointestinal
organs. In a fight-or-flight situation, the sympathetic division in-
creases heart rate, dilates airways, and inhibits digestion and elimi-
nation. When the emergency is over, the parasympathetic division
restores heart rate and airway diameter to resting levels and then
attends to processes that refuel your body cells and discard wastes.
Sympathetic and Parasympathetic Tone
We have described the parasympathetic division as the “rest and
digest” division, but the sympathetic division is the major actor
in controlling blood pressure, even at rest. With few exceptions,
Table 14.4
Effects of the Parasympathetic and Sympathetic Divisions on Various Organs
Eye (iris)
Stimulates sphincter pupillae muscles; constricts
Stimulates dilator pupillae muscles; dilates pupils
Eye (ciliary muscle)
Stimulates muscle, which makes lens bulge for
close vision
Weakly inhibits muscle, which flattens lens for far vision
Glands (nasal, lacrimal, gastric,
Stimulates secretory activity
Inhibits secretory activity; constricts blood vessels
supplying the glands
Salivary glands
Stimulates secretion of watery saliva
Stimulates secretion of thick, viscous saliva
Sweat glands
No effect (no innervation)
Stimulates copious sweating (cholinergic fibers)
Adrenal medulla
No effect (no innervation)
Stimulates medulla cells to secrete epinephrine and
Arrector pili muscles attached
to hair follicles
No effect (no innervation)
Stimulates contraction (erects hairs and produces
Heart (muscle)
Decreases rate; slows heart
Increases rate and force of heartbeat
Heart (coronary blood vessels)
No effect (no innervation)
Dilates blood vessels (vasodilation)*
Urinary bladder/urethra
Contracts smooth muscle of bladder wall; relaxes
urethral sphincter; promotes voiding
Relaxes smooth muscle of bladder wall; constricts
urethral sphincter; inhibits voiding
Constricts bronchioles
Dilates bronchioles*
Digestive tract organs
Increases motility (peristalsis) and amount of
secretion by digestive organs; relaxes sphincters
to allow foodstuffs to move through tract
Decreases activity of glands and muscles of digestive
system; constricts sphincters (e.g., anal sphincter)
Increases glucose uptake from blood
Stimulates release of glucose to blood*
Excites (gallbladder contracts to expel bile)
Inhibits (gallbladder is relaxed)
No effect (no innervation)
Promotes renin release; causes vasoconstriction;
decreases urine output
Causes erection (vasodilation)
Causes ejaculation
Causes erection (vasodilation) of clitoris;
increases vaginal lubrication
Causes vagina to contract
Blood vessels
Little or no effect
Constricts most vessels and increases blood pressure;
constricts vessels of abdominal viscera and skin to divert
blood to muscles, brain, and heart when necessary;
epinephrine weakly dilates vessels of skeletal muscles
during exercise*
Blood coagulation
No effect (no innervation)
Increases coagulation*
Cellular metabolism
No effect (no innervation)
Increases metabolic rate*
Adipose tissue
No effect (no innervation)
Stimulates lipolysis (fat breakdown)
*Effects are mediated by epinephrine release into the bloodstream from the adrenal medulla.
the vascular system is entirely innervated by sympathetic fibers
that keep the blood vessels in a continual state of partial con-
striction called
, or
When blood pressure is too low to maintain blood flow,
the sympathetic fibers fire more rapidly, causing blood vessels
to constrict and raising blood pressure. When blood pressure
becomes too high, sympathetic fibers fire less rapidly and the
vessels dilate.
, drugs that block the responses in
vasomotor fibers
, are sometimes used to treat hyperten-
sion (high blood pressure).
During circulatory shock (inadequate blood flow to body tis-
sues), or when more blood is needed to meet the soaring needs
of working skeletal muscles, blood vessels serving the skin and
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