physiology of ans lecture 3,4 by dr. mudassar ali roomi -.ppt

7/30/2019 Physiology of ANS lecture 3,4 by Dr. Mudassar Ali Roomi -.ppt

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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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March 12, 2013 2


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Effect of ANS on heart

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March 12, 2013 4


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Sympathetic Distribution

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Parasympathetic Distribution

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QUESTIONS??

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March 12, 2013 8


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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.

physiology of ans lecture 3,4 by dr. mudassar ali roomi -.ppt

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