Final exam Flashcards
Neurotransmitter release is proportional to what?
Nerve stimulation frequency
What is NT release subject to?
Neuromodulation
What do Alpha 2 adrenergic receptors on the nerve varicosity do when stimulated by Norepi release?
Decrease subsequent neurotransmitter release
What receptors for metabolites and other vasoactive substances decrease neurotransmitter release?
- K+
- Adenosine
- PGE1
- Histamine
- S-HT
- ACH
What receptor for metabolites or other vasoactive substance increases NT release?
Angiotensin 2
What do sympathetic vasoconstrictor nerves also release with NT?
ATP and NPY
What does ATP do when released from sympathetic vasoconstrictor nerves?
Contributes to smooth muscle cell depolarization
What does NPY do when released from sympathetic vasoconstrictor nerves?
- Causes slow, prolonged depoarization of SMC
- Sensitizes SMC to norepi
When is NPY released from sympathetic vasoconstrictor nerves?
in response to high frequency stimulation (stress)
What vessels are most innervated with sympathetic vasoconstrictor nerves?
Arteries and large arterioles
What vessels have poor innervation by sympathetic vasoconstrictor nerves?
- Veins
- Smallest arterioles
- Cerebral arteries
What is the exception to poor venular innervation by sympathetic vasoconstrictor nerves?
veins in skin and splanchnic region are innervated (important for venoconstriction in these regions)
Are sympathetic nerves tonically active?
yes
Where do sympathetic nerves contribute to resting tone?
In many vascular beds
How is sympathetic stimulation regulated in vascular beds?
Each has its own independent sympathetic input represented by a specific region of the ventrolateral brainstem
When may all sympathetic neurons be activated?
During extreme responses (e.g. hemorrhage)
What is released from the adrenal medulla with sympathetic stimulation?
epinephrine and norepi
What is adrenal secretion stimulated by?
- Intense exercise
- Fear
- Hypotension
- Hypoglycemia
- Hemorrhage
What does epinephrine stimulate in the liver?
Glycogenesis
What does epinephrine stimulate in adipose tissue?
lipolysis
What does epinephrine do to beta 1 adrenergic receptors?
acts on them to increase heart rate and contractility
What does epinephrine do in skeletal muscle, myocardium and liver?
Causes vasodilation
Why does epi cause vasodilation in skeletal muscle, myocardium and liver?
Abundance of beta 2 adrenergic receptors
Which receptors does epi have a greater affinity for?
Beta adrenergic
Which receptors does norepi have a greater affinity for?
Alpha adrenergic
What would a injection of norepi into a human do?
Increase total peripheral resistance due to wide-spread activation of alpha adrenergic receptors
What would a injection of epi into a human do?
Slight decrease in total peripheral resistance due to activation of beta 2 adrenergic receptors in large mass of skeletal muscle counterbalanced by activation of alpha adrenergics in other tissues
What do both nor epi and epi do when injected into the body?
Increase heart rate and cardiac contractility by stimulation of cardiac beta 1 adrenergic receptors
What are sympathetic vasodilator nerves in skin called?
Sudomotor-vasodilator cholinergic fibers
What do sympathetic vasodilator nerves in the skin release
Acetylcholine and probably VIP
What do sympathetic vasodilator nerves in the skin do?
Vasodilate skin arterioles and cause sweating
What kind of distribution do parasympathetic vasodilator nerves have?
- Restricted distribution
- skin and muscle have no innervation form these
What are the pre-ganglyonic fibers of parasympathetic vasodilator nerves like?
- Long and synapse within organ (release acetylcholine)
- Leave brain at vagus nerve and course down the spinal cord and leave the sacrum ( sacral spinal nerve)
What does the vagus nerve innervate?
- Coronary arteries
- Salivary glands
- Exocrine pancreas
- Gastrointestinal mucosa
What does the sacral spinal nerve innervate?
- Genitalia
- Bladder
- Colon
Describe post-ganglionic fibers of parasympathetic vasodilator nerves.
Are within the end-organ and terminate on resistance arteries
What is the pathway of ACH when released by parasympathetic vasodilator nerves?
Primary neurotransmitter->binds to M2 receptors on EC-> Causes release of nitric oxide, EDHF, PGI2-> vasodilation
In some cells ACh binds to M3 receptor on SMC-> vasoconstriciton
What does vasoactive intestinal peptide (VIP) and/or substance P do when released by parasympathetic vasodilator nerves?
VIP is predominant in pancreas
->both cause endothelium dependent vasodilation
What does nitric oxide do when released by parasympathetic vasodilator nerves?
- > some parasympathetic vasodilator nerves are “nitridergic”
- >found in resistance vessels of cerebrum, temporal lobe, mesentery, coronary, genitals
What nerves are responsible for erection of genitalia?
Nitridergic nerves
What does viagra (sildenafil) do?
Increases cGMP in arteries of genitalia, which causes vasodilation of the arteries and erection
What PDE is sildenafil specific for?
PDE5
What are nociceptive C-fibers?
sensory nerves
What do nociceptive C-fibers control?
Local vasodilation to painful stimuli (not involved in MAP reg)
What carries painful stimuli to the brain?
Nociceptive C-fibers
What do C-fiber collaterals do?
Innervate blood vessels and sometimes mast cells
What does vasodilation of local blood vessels by Nociceptive C-fibers do?
Causes area of redness, swelling around the injured site (flare) mediated by CGRP
When is RAAS elevated?
In essential hypertension and cardiac failure
What are the three effects of chronically elevated angiotensin 2?
1) enhances platelet aggregation
2) stimulates cardiac hypertrophy (with fibrosis
3) Stimulates inward remodeling and increased wall thickness in arteries
Vasopressin (AVP or antidiuretic hormone) are released from the hypothalamus in response to what?
- Increased plasma osmolality
- Decreased MAP or blood volume
What chain effects does Atrial natriuretic peptide do?
Increased atrial pressure-> Myocytes within atria release ANP-> Increased salt and water excretion by kidney, mild vasodilation, and decreased venular permeability which leads to interstitial volume increase-> Decreased MAP
What can increase atrial natriuretic peptide levels two fold?
Water immersion
What can increase atrial natriuretic peptide levels twenty fold?
Heart failure
What does insulin do?
- Increase NO
- Decrease SMC growth (anti-atherogenic)
What does estrogen do?
Increase NO by activating eNOS
-Increases eNOS expression
What does relaxin do?
Causes vasodilation in uterus, mammary gland, and heart during pregnancy and delivery
Where is relaxin secreted from?
Corpus luteum of ovary
What does thyroxin (T4) do?
- Increase cardiac contractility by increasing Beta1-adrenergic receptor expression
- Increase metabolic rate which causes vasodilation
Where are cardiovascular baroreceptors mainly found?
- Arterial
- Cardiopulmonary
Where are cardiovascular chemoreceptors found?
- Aorta
- Carotid
Where are cardiovascular mechanoreceptors found?
Muscle
How is acute regulation of MAP controlled?
Control of heart and blood vessels
How is chronic regulation of MAP controlled?
Control of plasma volume
Where are baroreceptor nerve endings found?
Adventitia of arteries
Where do baroreceptor afferents travel to?
The nucleus tractus solitarius (NTS) in the brainstem
What do baroreceptors detect?
- Distension of the blood vessel wall
- Both static stretch and rate of change
Describe the A-fiber type of baroreceptor afferent.
- Large diameter
- Fast conducting
- Myelinated
- Low threshold
- High sensitivity
- Detect primarily normal pressure ranges
Describe the C-fiber type of baroreceptor afferents.
- More abundant
- Narrow, slow conducting
- Unmyelinated
- High threshold
- Low sensitivity
- Detect high pressures
What two pressures do baroreceptors detect?
Mean and pulse
What does increased MAP do to baroreceptor firing?
Recruits more afferents to fire
What difference is there between afferent firing rate during pulsatile pressure vs steady pressure?
Higher firing rate during pulsatile, even though mean pressure is same
When is baroreceptor afferent firing rate important?
During orthostasis and moderate hemorrhage
What happens if NTS is destroyed?
Hypertension
What are arterial baroreceptors responsible for?
Baroreflex
What does baroreflex do?
-Acute adjustments in heart rate, contractility and vascular tone to regulate MAP
What is baroreceptor firing proportional to?
MAP
What is baroreflex central resetting?
Inputs from higher centers or other receptors can shift baroreflex curve upward
What does “central command” (signals from cerebral cortex) do in baroreflex re-setting?
Stimulates the brainstem to increase sympathetic nerve activity
What do receptors from working muscle do in baroreflex re-setting?
Stimulate sympathetic nerve activity via the NTS
What is peripheral baroreflex resetting?
Sustained increase in MAP (>15min) causes an upward shift in the baroreflex curve, and it is then regulated around a new set-point
Because of peripheral re-setting, baroreflex primarily controls what?
Acute fluctuations in MAP (buffers MAP around a set point)
-Cannot control long term MAP
What happens to MAP if arterial baroreceptors are cut or damaged?
MAP is unstable with wide fluctuation
- Large increase with exercise at abou 5x
- first could of days after it happens MAP significantly elevated
- After a few days only slightly elevated but still wide fluctuations throughout the day
What causes myelinated venoatrial mechanoreceptors to fire?
Fire in response to expansion of the heart so they are sensitive to changes in CVP and cardiac filling
What path do the myelinated venoatrial mechanoreceptor fibers take?
Travel up vagus nerve to the NTS
What do myelinated venoatrial mechanoreceptors do once they are activated?
- Provoke tachycardia by selective activation of SNA with no change in PNA
- Provoke diuresis (Decrease renal SNA, vasodilate renal arteries and arterioles, decrease volume preserving hormones, increase ANP)
How abundant are non-myelinated mechanoreceptors and chemoreceptors?
More abundant than myelinated fibers (~80% of cardiopulmonary receptors)
When do non-myelinated mechanoreceptors fire?
When heart is overdistended, travel up vagus to NTS and cause decrease in HR and slight vasodilation
What do nonmyelinate chemoreceptors do?
Sense pain associated with ischemia (angina) and converge with central sensory tract
What would happen if all cardiopulmonary afferents were cut or destroyed?
Bothe MAP and HP would be chronically elevated
What would happen if cardiopulmonary afferents were selectively stimulated?
HR would decrease, vasodilation, hypotension
What do arterial baroreceptors do?
Buffer changes in MAP
What do cardiopulmonary baroreceptors do?
Sense changes in central blood volume
