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MAP =
Cariac output X Total peripheral resistance
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What part of the CNS adjusts CO and TPR to maintain MAP
Regulation of the sympathetic nervous system
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What are the two sites of high pressure baroreceptors
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When there is an increase in the stretch in a the baroreceptors, what do they do.
They send more afferent signals to the brain
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Where are the low pressure baroreceptors
- Right atria
- Vena cava
- Pulmonary artery
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What are the ways that the body will respond to a change in mean arterial blood pressure
- Modify cardiac output thru contractility and heart rate
- Change vascular resistance through constriction or dilation
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When the baroreceptors are triggered by high MAP what is the signal path
- Increase afferent signals
- Increase signals to Nucleus tractus solarius in brain
- Inhibit vaso motor center (SNS decrease in HR and contractility)
- Trigger cardio inhibitor system to increase PNS decreasing the HR
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During normal resting, what signals are sent from the SNS and PNS in respect to the circulatory system
- SNS sends some inhibitory signals to the vasomotor center
- PNS sends some stimulatory signals to the cardio inhibitory center
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Why are baroreceptors not good for long term pressure control
Because they adapt to pressures after about 48 hours
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What are the two mechanisms for local control of blood flow and their mechanisms
- Metabolic (metabolites & paracrine agents)
- Myogenic (endothelial products and myogenic reflexes)
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What does the increase of O2 do to the vessels
It constricts them
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What does the increase of CO2 do to the blood vessels
It vasodilates them
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How do prostaglandins effect the vessels
It constricts them
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How does adenosine, phosphate, lactate, K+, H+, and Histamine, effect the blood vessels
It dilates them
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What is the production of NO in the endothelial cells stimulated by
- Histamine
- Bradykinin
- ACh
- Shear stress
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What is an important mechanism for increasing coronary blood flow when cardiac output is increased
Shear stress activating the release of NO
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What is autoregulation
The ability of an organ to maintain a constant blood flow when the arterial pressure changes
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What is hyperemia
An increase in the blood flow to different tissue in the body
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What is active hyperemia
Increase in the amount of blood flow due to an increase in metabolism (like active muscle in exercise)
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What is reactive hyperemia
A short interruption of blood flow, causing vasodilation and then increase in blood flow when cleared
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Active hyperemia in the coronary vessels is controlled by what metabolite and what gas
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In the left ventricle the blood flow from the coronary artery is affected how
During diastole the blood flow is high due to low tension, but negative in systole due to the contraction of the muscle
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The right ventricle coronary blood flow is affected how by contractions
It increases with systole because the coronary artery pressure rises
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The control of cerebral blood flow is regulated by
Changes in PCO2 levels
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What happens to skeletal muscles during running and lifting weights respectively
- Running active hyperemia is active
- Lifting reactive hyperemia is predominant
- Both are due to the release of Adenosine and K+
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In the lungs what is the primary factor that alters pulmonary resistance and blood flow
Hypoxia, causing local vasoconstriction in the lungs
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An increase in the right atrial pressure would have what effect on the Venous return
It would decrease the venous return, due to its effect on the driving pressure
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What would a decrease in the right atrium pressure have on the venous pressure
It would increase it due to the increase in driving pressure
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What parameters increase venous return
- Increase in blood volume
- Decrease in venous compliance
- Decrease in ateriole resistance
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What portion of the nervous system controls venous compliance
Sympathetic nervous system
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What does it mean when a heart is hyperactive/hypoeffective
This is when the contractility of the heart is enhanced, giving the heart a greater cardiac output
Hypoeffective is the opposite
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What is an inotropic effect
An increase in the contractility of muscles, the heart in this case
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The baroreceoptor reflex effects the cardiac-vascular function how
- Increases contractility moving the cardiac output curve up
- Increases blood volume by venous constriction
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What happens to the veins in the lower extremeties when one stands
- Firstly they collect loads of blood from the effects of gravity
- Secondly sympathetic innervation causes constriction
- Thridly skeletal muscle contracts moving the bulk of blood pooled back up
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Orthostatic hypertension
Inabilty to restore blood pressure to normal with a change in body position like standing
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What happens when one stands motionless for over five minutes
- Blood pools in the lower extremities due to gravity
- Increase in filtration in LE
- There is a decrease in the central venous pressure
- Decrease flow to brain due to lower in VR and CO
- Syncope occurs
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What happens to the blood in the thoracic region when one breaths deep
- Decrease in Intrathoracic pressure
- Decrease in Central VP and Right atrial pressure
- An increase in driving pressure from the lower extremities to the central venous space
- Therefore an increase in venous return
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How does the body meet the needs of oxygen during excersise
- The cardiac output is increased by the SANS
- Local dilation to the muscles used increases the blood flow
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What happens if one excersises at an HR above 200bpm
The stroke volume begins to reduce due to the reduced filling time
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During exercise the increase in stroke volume comes from
- Increase in venous return from increased preload
- Increased contractillity causing a reduced ESV
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If the SNS during exercise causes a systematic vasoconstriction, how is there an overall reduced TPR
The muscles being used have a local metabolic effect causing massive dilation that overrides the SNS effects
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Why doesn't the diastolic/systolic pressure change much during exercise
The massive vasodilation of the skeletal muscles almost compensates for the elevation of CO
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Valsalva maneuver
A large breath is taken exhaling against a glottis resistance for ten seconds to test baroreceptor reflexes
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What happens in the Valsalva response to the pressures of the blood initially
There is an increase in intrathoracic pressure which causes an increase in the Aortic pressure and central venous pressure
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What are the fluctuations in the Aortic pressure during the valsalva maneuver and why
- 1. Large increase in pressure due to the compression of the intrathoracic vessels
- 2. Large decrease in pressure due to a decrease in blood flow from the LE to the thoracic region
- 3. A quick small decrease due to the patient exhaling lowering the intrathoracic pressure
- 4. A large increase in pressure due to the thoracic veins and RA filling rapidly
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What are the HR changes during the valsalva maneuver and why
- 1. A slight increase and then an immediate large decrease afterward due to an increase in baroreceptor firing
- 2. A large increase due to a decrease in baroreceptor firing as a result of decreased aortic pressure
- 3. A quick spike due to another decrease in aortic pressure after the patient relaxes
- 4. A large decrease due to the increase baroreceptor firing as a result of the increase aortic pressure
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What activities can cause the valsalvar maneuver and how is it dangerous
- Weight lifting and passing stool
- People with a weak heart can have adverse affects due to the increase in pressure and heart rate
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Hypovolemic shock
Drop in blood volume due to hemorrhages, dehydration, or burns
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At what percent blood loss is the body affective at responding
10-20%, higher is considered irreversible shock
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What is systolic dysfunction and some causes
Pathologies that cause reduced pumping ability of the heart such as an MI, Aortic stenosis, or chronic hypertension
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What is Diastolic dysfunction and some causes
Pathologies that cause inadequate filling of the heart such as LV hypertropy, Mitril stenosis
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How do you calculate a cardiac index, and what is the normal range
- CO/Body surface area
- 2.6-4.2 L/min
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The baroreceptor in the aortic arch responds only to
An increase BP where as the carotid responds to an increase or decrease in BP
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The baroreceptor in the aortic arch uses what nerve to communicate with the medulla
Vegus
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Chronotropic
Changes in heart rate
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Dromotropic
Changes in conduction velocity, primarily in AV node
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