Physiology Ch 60 Ans And Adrenal Medulla

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ANS

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Helps to control arterial bp, GI motility, GI secretion, urinary bladder emptying, sweating, body temp...

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ANS can increase HR in _______ and arterial pressure can

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3-5 sec to 2X normal; double in 10-15 sec.

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ANS is activated mainly by centers located in

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spinal cord; brain stem and hypothalamus as well as portions of the cerebral cortex, esp. limbic cortex

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ANS operates through

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visceral reflexes and return subconscious reflex response directly back to the visceral organ

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efferent autonomic signals are transmitted to the various organs through what two major subdivisions?

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Sympathetic and parasympathetic

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Anatomy of Sympathetic Nervous System is organized into what 3 peripheral portions?

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1 of 2 paravertebral sympathetic chains of ganglia that are interconnected with the spinal nerves on the side of the vertebral column
2 paravetebral ganglia (celiac and hypogastric)
Nerves extending from the ganglia to the different internal organs

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Sympathetic Neurons to its target tissue consist of

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2 neurons, pre and post sympathetic

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The cell body of each preganglionic neuron lies in the

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intermediolateral horn of the spinal cord

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3 courses of sympathetic nerve fibers after leaving the spinal cord and passing through anterior root and white ramus are

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-Synapse with postganglionic sympathetic neurons in the ganglion that it enters
-it can pass up or down in the chain and synapse in one of the other ganglion of the cahin
-it can pass for a variable distance through the chain and then through one of teh sympathetic nerves radiating outward from the chain, finally synapsing in a peripheral sympathetic ganglion.

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Postganglionic sympathetic nerves

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originate at either in the sympathetic chain ganglion or in one of the peripheral ganglion then travel to their destination in various organs

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Gray Rami

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postganglionic fibers that pass back from the sympathetic and into the spinal nerves thought this. Its at all levels of the spinal cord.

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type C fibers

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Sympathetic fibers that pass through the gray rami, Are very small and extend to all parts of the body by way of skeletal nerves.

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Percentage of fibers in the average skeletal nerve that is sympathetic

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8%, therefore, very important. Control blood vessels, sweat glands and piloerector muscles

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Segmental Distribution of the sympathetic nerve fibers

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T1---generally up and to the head
T2--terminate in the neck
T3-6--the thorax
T7-11--abdomen
T12, L1-2--The legs

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Sympathetics to the adrenal medulla

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Preganglionics dont synapse and go directly from the intermediolateral horn cells ->sympathetic chain->splanchnic nerves->into medulla

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Parasympathetic fibers originate from

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CN3,7,9,10 and S2-3

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Vagus Nerve

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75% of Parasympathetic fibers. Entire thoracic and abdominal regions
heart, lung esophagus, stomach, small intestine, proximal half of colon, liver, gallbladder, pancreas, kidneys, and upper ureters

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Parasympathetic CN3

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Pupillary sphincter and ciliary eye muscles

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Parasympathetic CN 7

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lacrimal, nasal and submandibular glands

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Parasympathetics CN9

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Parotid gland

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Parasympathetics of sacral nerves

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pelvic nerves (S2-S3) to descending colon, rectum, urinary bladder, and lower portion of ureters. Also to external genitalia for erection

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Parasympathetic Preganglionic neurons synapse

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The wall of the target organ wist post that are extremely short leave the neuron and innervate the tissues of the organ.

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Location of parasympathetic cell bodies

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IN the excited organ instead of the sympathetic ganglion for sympathetic cell bodies

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Cholinergic

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fibers that secrete acetlycholine

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adrenergic

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Fibers that secrete norepinephrin

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All preganglionic neurons are

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cholinergic

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Parasympathetic nerurons are

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almost all cholinergic (pre and post)

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Most postganglionic sympathetics are

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adrenergic. Exception is sweat glands, piloerector muscles of hairs, and a few blood vessels are cholenergic

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Varicosities

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bulbous enlargements were sympathetic/para filaments touch or pass over or near the cells to be stimulated.

They contain transmitter vesicles of acetlycholine or norepinephrine are synthisized and stored. Therefore they also have alot of mitochondria to supply ATP

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Role of Calcium in neuron transmitters

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WHen the action potential spreads over the terminal fibers, the depolarization process increases Ca permeability of the membrane allowing them to diffuse into the nerve terminal or varicosities. The Ca ion then causes the terminal/varicosity to empty theri contents.

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Destruction of acetlycholine

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Split into acetate ion and choline by acetlycholinesterase thats bound to collagen and GAGs.

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Synthesis of Acetylcholine

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In the terminal endings and variscosities of cholinergic nerves were it is stored as a concentrated form.
Acetyl-CoA+Choline--Choline Acetlytransferase-->=Acetylcholine

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Synthesis of Norepinephrine

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Begins in axoplasm of terminal nerve endings but is completed inside the secretory vesicles.
1. Tyrosin--(Hydroxylation)-->Dopa
2. Dopa--(Decarboxylation)-->Dopamine
3. Transport of Dopamine into the vesicles
4. Dopamine--(Hydroxylation)-->Nor-epinephrine

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Synthesis of Epinephrine

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IN the adrenal medulla there is a step 5

Norepinephrine--(Methylation)-->Epinephrine

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Removal of Norepinephrine from secretory site

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1. Reuptake into the adrenergic nerve by active transport (50-80%)
2. Diffusion away from the nerve endings (most of the rest)
3. Destruction of small amounts by tissue enzymes; monoamine oxidase in nerve endings and catechol-O-methyl transferase which is present diffusely in all tissue

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Main place were nor/epinephrine in the blood is destroyed at (secreted from the medulla)

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The liver by catechol-O-methyl transferase
(activity lasts for 10-30 sec)

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Actions of receptor molecules when bound to transmitter

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Conformational change that causes a change in cell membrane permeability to one or more ions; or activating/inactivating an enzyme attached to the other end of the receptor protein.

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Second Messenger System of norepinephrine

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increase the activity of adenylyl cyclase on the outside of the cell causing formation of cAMP inside of the cell which in turn initiates many different intracellular actions

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2 types of acetylcholine receptors

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Muscarinic and Nicotinic; both are activated by acetylcholine

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Muscarinic Receptors

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found on effector cells that are stimulated by postganglionic cholinergic neurons of either sympathetic or parasympathetic nervous systems

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Nicotinic Receptors

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Found in autonomic ganglia at synapses between pre and post ganglionic neurons of symp/parapathetic systems
Also in many non-autonomic nerve endings--i.e. in skeletal muscle neuromuscular junctions.

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two major types of adrenergic receptors

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alpha (1&2) and beta (1,2&3)

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Norepinephrine on adrenergic receptors

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excites mainly alpha but beta to a lesser extent.

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Epinephrine on adrenergic receptors

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both alpha and beta equally

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isopropyl norepinephrine

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synthetic hormone that has extremely strong action on beta, but none an alpha receptors

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Action of alpha 1 receptors

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Vasoconstriction, iris dilation, intestinal relaxation, intestinal sphincter contraction, pilomotor contraction and bladder sphincter contraction

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Action of alpha 2 receptor

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Inhibits neurotransmitter release

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Action of beta 1 receptors

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Cardioacceleration, increased myocardial strength, lipolysis

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Action of beta 2 receptor

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vasodilation, intestinal, uterus and bladder wall relaxation, bronchodialtion, calorigenesis, and glycogenesis

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Action of beta 3 receptor

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Thermogenesis

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Sympathetic stimulation of the eye

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contracts the meridional fibers of the iris that dilate the pupil

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Parasympathetic action of the eye

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contracts the circular muscles of the iris to constrict the pupil
focuses the lens by contracting the ciliary muscle which releases the tension of the ligaments and allows the lens to become more convex (near sight)

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Nasal, lacrimal, salivary and GI glands

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strongly stimulated by parasympathetics resulting in copious secretions. Especially in upper tract (mouth and stomach). Intestines are mainly controlled by intestinal enteric nervous system and less by autonomics

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Sympathetic stimulation of most alimentary glands

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formation of a concentrated secretion that has high % of enzymes and mucus.
Causes vasoconstriction of BV that supply the glands (possibly reducing rate of secretion)

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Sweat glands

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Sympathetics cause large quantities to be secreated. No parasympathetic effect, but receptors are cholinergic

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Apocrine Glands

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sympathetic causes secretion of thick, odoriferous secretion . No response to parasympathetics. Adrenergic, not cholinergic fibers

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intramural plexus / intestinal enteric nervous system

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intrinsic set of nerves in GI tract.

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GI parasympathetic activity

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increases overall degree of activity by promoting peristalsis and tone and relaxing the sphincters allowing for rapid propulsion of contents

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Sympathetic GI stimulation

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strong stimulation inhibits peristalsis and increases tones of sphincters. Can cause constipation

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Heart Sympathetics

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Increased stimulation of rate and force of contractions. Dilates coronary arteries

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Heart Parasympathetics

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decreases HR and strength of contraction, allows heart to rest
Dilates coronary arteries

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Blood Vessels

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Sympathetic- constriction, beta function causes dilation if alpha receptors have been paralyzed.
Parasympathetic: Almost no effect except to dilate bv in certain restricted areas (blushing)

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Arterial Pressure

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Determined by propulsion of blood by the heart and resistance of blood flow through peripheral blood vessels

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Sympathetic stimulation of arterial pressure

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increases propulsion and resistance to flow, causing an acute increase but little long term effect

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Parasympathetic stimulation on arterial pressure

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Decreases pumping of the heart and no effect on peripheral vascular resistance. Usually slight decrease in pressure, but very strong vagal stimulation can almost stop or occasionally stop the heart

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Sympathetic metabolic effects

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release of glucose from the liver, increase in blood glucose concentration, increase in glycogenolysis of liver and muscles, increase in skeletal muscle strength, increase in metabolic rate and increased mental activity

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Proportions of epinephrine and norepinephrine from the adrenal medulla

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80/20

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Circulatory effect time of medulla adrenergics

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5-10 times longer than direct sympathetic stimulation becasue takes 2-4 minutes to remove from the blood

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difference of epinephrine and norepinephrine

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Great effect in stimulating beta receptors and has a greater effect on cardiac stimulation than norepinephrine. Also causes weaker constriction of blood vessels.

Norepinephrin greatly increases total peripheral resistance and elevates arterial pressure while epinephrine raises arterial pressure less but increases cardiac output more.

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Metabolism effects on epinephrine and norepinephrine

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Epinephrine has 5-10 times faster rate, therefore increasing metabolic rate of the whole body by 100%

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2 way organs are stimulated by sympathetics

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directly by sympathetic nerves and indirectly by adrenal medulla hormones (not necessarily to organs directly innervated by sympathetics)

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Basal rates of activity are known as

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sympathetic and parasympathetic tone

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Value of tone

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allows a single nervous system both to increase and decrease the activity of a stimulated organ

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Normal resting rate of secretions of the adrenal medulla

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.2ug/kg/min epinephrine
.05ug/kg/min norepinephrine

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intrinsic tone

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intrinsic compensation that soon develops in order to return the function of the organ almost to its normal basal level after damage to innervation.
Can take up to weeks for sympathetics and months for para

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Denervation supersensitivity

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phenomenon in which an organ becomes more sensitive to injected norepinephrine or acetylcholine after denervation. Occurs in both sympathetic and parasympathetic organs. Caused by upregulation of receptors

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autonomic reflexes

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regulate many of the visceral functions of the body

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Cardiovascular Autonomic reflexes

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Include baroreceptor reflex in the internal carotid artery and arch of the aorta

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GI Autonomic Reflex

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in uppermost part of GI tract and the rectum (smell of food causing salvation and need to poop when fecal matter fills the rectum)

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Mass discharge

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when almost all portions of the sympathetic system discharge simultaneously. Occures when the hypothalamus is activated by fright or fear or sever pain. Results in alarm or stress resoponse

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Alarm or stress response of the sympathetic nervous system

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1. Increased arterial pressure
2. Increased blood flow to active muscles concurrent wiht decreased blood flow to organs such as the GI tract and kidneys 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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Sympathetic stress response

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extra activation of the body in states of stress (mental or physical)

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Brain stem

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control arterial pressure, HR and Respiratory rate

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Methoxamine

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sympathomimetric drug along with epinephrine

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Phenylephrine

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drug that stimulates alpha receptors

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isoproterenol

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stimulates beta receptors

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albuterol

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stimulates beta 2 receptors

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indirect sympathomimetric drugs

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ephedrine, tyramine, and amphetamine. Cause release of norepinephrine from its storage vesicles in the sympathetic nerve endings

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Reserpine

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Prevents the synthesis and storage of norepinephrine

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guanethidine

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blocks release of norepinephrine from nerve endings

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phenoxybenzamine and phentolamine

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blocks alpha receptors

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propranolol

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blocks beta 1 and 2 receptors

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metoprolol

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blocks mainly beta 1 receptors

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hexamethonium

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blocks transmission of nerve impulses through autonomic ganglia. blocks both sympathetic and parasympathetic transmission through the ganglia

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pilocarpine and methacholine

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directly act on muscarinic type cholinergic receptors

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acetylcholinesterases drugs

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neostigmine, pyridostigmine, and ambenonium. Potentiate the effects of the naturally secreted acetylcholine at the neuromuscular juncture by preventing rapid destruction of acetylcholine

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Atropine

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block the action of acetylcholine on the muscarinic type of cholinergic effector organs. These do NOT effect nicotinic action. Similar drugs are homatropine and scopolamine

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injected acetylcholine

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stimulates postganglionic neurons of both systems, thereby causing effects at the same time in both systems.

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Nicotine

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stimulates postganglionic neurons that contain the nicotinic type of acetylcholine receptor. Results in strong sympathetic vasoconstriction in the abdominal organs and limbs but at the same time resulting in parasympathetic effects such as increased GI activity and sometimes slowing heart rate.

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methacholine

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has both nicotinic and muscarinic actions on postganglionic neurons

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Ganglionic blocking drugs

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block impulse from pre to post ganglionic neurons. Drugs include tetraethyl, ammonium ion, hexamethonium ion and pentolinium. Block acetylcholine and usued especially for sympathetic blocking.
Reduce arterial pressure in patients with HTN, arent used clinically bc their effects are difficult to control