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U N I T XI
Textbook of Medical Physiology, 11th edition
GUYTON & HALL
Chapter 60:The Autonomic Nervous System (ANS);
The Adrenal Medulla
By
Dr. Mudassar Ali Roomi (MBBS, M.Phil)
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Effect of ANS on heart
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Sympathetic Distribution
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Parasympathetic Distribution
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QUESTIONS??
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Function of the Adrenal Medulla
Adrenal medulla is a large sympathetic ganglion when stimulated releases epinephrine (80%) and norepinephrine (20%)
into the blood stream
causes prolonged activity of the substances (2-4 minutes)
helps the body deal with stress
Difference b/w action of epinephrine and nor-epinephrine:
Epinephrine has greater effect on cardiac stimulation
epinephrine raises the arterial pressure to a lesser extent but increases the
cardiac output more
Epinephrine has 5 to 10 times as great a metabolic effect as
norepinephrine
Importance of adrenal medulla:
1. the dual mechanism of sympathetic stimulation provides a safety
factor, one mechanism substituting for the other if it is missing.
2. to stimulate structures of the body that are not innervated by direct
sympathetic fibers
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Sympathetic and
Parasympathetic Tone
the basal rate of activity of each system
Importance: this background activity allows foran increase or decrease in activity of an organ by a
single system sympathetic tone normally causes about a 50 %
vasoconstriction (so, SANS has more effect on vessels)
increasing or decreasing tone can change vessel
diameterparasympathetic tone provides background G.I. activity
(so, PANS has more effect on GIT)
Mechanism of Denervation Supersensitivity: up-regulation of the receptors
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Autonomic Reflexes
Cardiovascular Autonomic Reflexes
Gastrointestinal Autonomic Reflexes Other Autonomic Reflexes
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Sympathetic System Often Responds by
Mass Discharge Parasympathetic System Usually Causes
Specific Localized Responses.
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Stress Response (fight or flightresponse)
mass sympathetic discharge
increase in arterial pressure, heart rate and contractility, blood flow to muscles,
blood glucose, metabolic rate, muscle strength, mental activity, blood coagulation
prepares the body for vigorous activity need to deal with a life-threatening
situation
1. Increased arterial pressure
2. Increased blood flow to active muscles concurrent with decreased blood flow to
organs such as the gastrointestinal tract and the kidneys that are not needed for
rapid motor activity
3. Increased rates of cellular metabolism throughout the body
4. Increased blood glucose concentration
5. Increased glycolysis in the liver and in muscle
6. Increased muscle strength
7. Increased mental activity
8. Increased rate of blood coagulation
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Pharmacology of the Sympathetic
Nervous System
adrenergic or sympathomimetic drugs act like
norepi and epi
these drugs have an effect which is much more
prolonged than that of either norepi or epiphenylephrine stimulates alpha receptors
isoproterenolstimulates both beta1 and beta2 receptors
albuterol stimulates only beta2 receptors
some drugs act indirectly by increasing the release
of norepi from its storage terminals
ephedrine, tyramine, and amphetamine
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Pharmacology of the Sympathetic
Nervous System
drugs that block the effect of norepi and epi
synthesis and storage
reserpine
release from the nerve terminal guanethidine
alpha blockers
phentolamine and phenoxybenzamine
beta blockers
beta1 and 2 -propranolol, beta1 - metoprolol
ganglionic blockers
hexamethonium
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Pharmacology of the
Parasympathetic Nervous System
parasympathomimetic drugs
nicotine
activates nicotinic receptors (nicotinic agonist)
pilocarpine and methacholine (muscarinic agonist)
activates muscarinic receptors, cause profuse sweating
cholinesterase enzyme inhibitors
neostigmine, pyridostigmine,and ambenonium
potentiates the effect of acetylcholine
antimuscarinic drugs atropine andscopolamine (muscarinic antagonist) blocks the effect of acetylcholine on effector cells
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Some Disorders of the Autonomic Nervous
System
Horner syndrome :
Chronic unilateral pupillary constriction (miosis), sagging of the eyelid
(ptosis), withdrawal of the eye into the orbit, flushing of the skin, and
lack of facial perspiration,
resulting from lesions in the cervical ganglia, upper thoracic spinal
cord, or brainstem that interrupt sympathetic innervation of the head.
Raynaud disease :
Intermittent attacks of paleness, cyanosis, and pain in the fingers and
toes, caused when cold or emotional stress triggers excessivevasoconstriction in the digits;
most common in young women.
In extreme cases, causes gangrene and may require amputation.
Sometimes treated by cutting sympathetic nerves to the affected
regions.