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factors regulating arterioles in various regional circulations
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Left ventricular coronary flow is highly dependent upon?
diastolic arterial pressure since little perfusion is possible in the left ventricle during systole
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Cerebral Blood Flow
- relatively independent of MAP & is regulated by local hyperemia and autoregulation
- however, if MAP is raised higher above this range, or dropped lower, the flow will increase or drop dramatically (respectively)
- if there is a very sudden rise in MAP, there is the risk of causing hemorrhagic stroke (burst vessel in the brain); local hyperemia & autoregulation work in the range of milliseconds (a slightly slower response
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Cerebral Circulation
- Cerebral neurons require an adequate supply of oxygen and glucose at all times for the human being to remain conscious.
- Though only 2% of the body mass, the CNS consumes nearly 20% of the O2 at rest and maintains no energy reserve.
- Cerebral Blood Flow is relatively independent of MAP by local hyperemia and autoregulatory mechanisms.
- Changes in flow regulation via vascular resistance occur gradually (over minutes) and do not protect the brain from sudden changes in MAP.
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Pulpal blood flow
- electrically stimulating the surface of the tooth causes a huge increase of blood flow in the pulp
- if you denerve the tooth, there is not this response
- But sympathetic stimulation of the vessels that supply the pulp reduce their flow.
- sympathetic stimulation is generally a vasoconstrictor, and a decrease in flow makes sense; but here, we increase the flow-
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Antidromic Vasodilation
 - Sensory nerves on gingiva send signals down in the normal direction, then up in the antidromic direction to the pulp to vasodilate
- Can get the same effect by stimulating the sensory nerve directly.
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Pulpal and Gingival Blood Flows
- Stimulation via the cervical sympathetic chain induces severe vasoconstriction in the vessels supplying the pulp and gingiva.
- Stimulation of the parasympathetic fibers of the glossopharyngeal nerve (#9) elicit vasodilation of the gingiva, but not the pulp which has not demonstrated a parasympathetic response.
- Vasodilation in the pulp can be elicited by surface stimulation of the tooth or gingiva by antidromic vasodilation mediated by sensory nerve fibers.
- Thus irritation of the gingiva during dental procedures might increase blood flow to the teeth!
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Saliva and Blood Flow
- flow of saliva is tightly coupled to blood flow.
- salivary blood flow is regulated by both sympathetics, but also parasympathetics; if you increase either sympathetic or parasymp stimulation, you will have increased saliva flow (and blood flow), although the composition of the saliva will be different
- salivary blood flow is regulated by both sympathetics, but also parasympathetics; if you increase either sympathetic or parasymp stimulation, you will have increased saliva flow (and blood flow), although the composition of the saliva will be different
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Circulatory Shock
- Shock exists whenever there is a generalized severe reduction in blood supply to the tissues.
- There are 4 general categories of shock:
- Cardiogenic
- Hypovolemic shock.
- Anaphylactic & Septic shock.
- Neurogenic shock.
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Cardiogenic shock
- occurs whenever the cardiac pumping ability is compromised.
- This can be due to myocardial infarction, valvular disease, heart failure or arrhythmias which reduce the cardiac output.
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Hypovolemic shock
- occurs whenever there is a significant fluid loss.
- This can be due to hemorrhage, severe burns, chronic diarrhea or prolonged vomiting which lead to fluid loss.
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Anaphylactic and Septic shock
- occur whenever vasodilators are activated.
- This can be due to severe allergic reactions or from toxins released by infectious agents which lead to decreased venous pressures and vascular resistance.
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Neurogenic shock
- occurs whenever vascular tone is decreased due to a reduction in sympathetic activity.
- This can be due to severe anesthesia, deep pain or, in a milder form, with strong emotions.
- Certain emotional events can lead to a “Vasovagal” response
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Effect of Anesthesia upon Pressure
- when anesthesia given, the arterial pressure drops significantly; NE causes a spike in arterial pressure, but prolonged anesthesia will bring pressure down again
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Stress
- factor in heart disease
- hypothalamus is sensitive to it, releasing corticotropin releasing hormone, which acts on the anterior pituitary, causing it to release adrenocorticotropin hormone, which acts on the adrenal cortex to release cortisol > various effects (see bottom left), with vasoconstriction affecting the heart
- stress causes sympathetic firing to cause adrenal medulla to release more E and NE (right) > various effects (bottom right)
- Try to minimize
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