Cardiovascular Control Flashcards
How is blood flow regulated?
It is regulated so that the minimum amount of blood required to meet metabolic demands is delivered to each tissue
Why doesn’t the heart deliver excess blood to each tissue so there is a reserve?
CO would increase dramatically and thus the work of the heart would be increased
What determines the amount of blood a tissue receives?
It depends on the tissue’s metabolic activity
What regulates tissue blood flow?
Resistance regulates tissue blood flow
What are the two local mechanisms to control blood flow?
Myogenic
Metabolic
What is the mechanism of myogenic local control of blood flow?
The smooth muscle in the vessels sense a stretch that activates Ca channel opening causing a depolarization and contraction of the smooth muscle (can be overridden by metabolic response)
What type of vessel typically exhibits the Myogenic local response?
Arterioles has the largest amount of smooth muscle in comparison to other vessels in the body
What are the two metabolic mechanisms that control local blood flow?
O2 Lack theory
Vasodilator Theory
What is the difference between the two metabolic mechanisms that control local blood flow?
The vasodilatory theory senses excess waste products and increases blood flow accordingly and the O2 lack theory senses a deficit of nutrients and oxygen and increases blood flow accordingly
What vasodilating products arise from metabolism?
Adenosine CO2 H+ K+ Histamine
Intermittent contraction of pre capillary sphincters and metarterioles
Vasomotion
What two organ systems autoregulation overrides a neural response?
Brain
Kidneys
In what three scenarios could angiogenesis occur?
Exercise
Disease
Altitude changes
What cytokine stimulates angiogenesis?
VEGF
What two factors make up Humoral control of blood flow?
Hormones
Ions
What ions are released by the skeletal muscle during high metabolic activity thus increasing O2 to the tissues?
K+
H+
Mg
All of these are vasodilator which increases the blood flow to tissues in need, an appropriate homeostatic response
What three factors can neural control of blood flow affect?
Distribution of blood flow
Heart pumping function
TPR
What is the neural pathway to effect the control of blood flow?
Sensory afferent to NTS, the NTS talks to the vasomotor cortex which sends an efferent signal back to the effector (think autonomic nervous system)
What part of the autonomic nervous system innervates the vasculature?
Sympathetic nervous system
What three reflex mechanisms are used to maintain arterial pressures?
Baroreceptors
Chemoreceptors
CNS ischemic response
What four areas make up the vasomotor center?
Vasoconstrictor area
Vasodilator area
Lateral VMC (cardiac function)
NTS
What carries afferent information to the NTS from the baroreceptors and chemoreceptors?
Vagus nerve
Glossopharyngeal nerve
How can emotional stress trigger an increase in blood pressure and heart rate?
The vasomotor center can be inhibited or excited by areas in the brain such as the hypothalamus, cerebral cortex, motor cortex and hippocampus (limbic system)
What type of fibers carry an inhibitory signal to the heart and what types of fibers carry an acceleratory signal to the heart?
Inhibit: Vagus nerve
Accelerate: sympathetic nerve fibers
Why can’t the PSNS effect inotropy of the heart?
The PSNS only innervates the nodal regions of the heart, there is no muscle innervation, only the SNS innervates both the nodes and the muscle of the heart
What part of the vasculature does the SNS not innervate?
The capillaries, metarterioles and precapillary sphincters
In what way does the PSNS indirectly affect circulation?
PSNS has vagal input on the heart, profound bradycardia can significantly impact circulation
What is the most rapid mechanism for blood pressure control?
The autonomic nervous system responses
If n increase in pressure is sensed by the baroreceptor, what is the response?
Baroreceptor sensed an increase in pressure, sends more afferent messages as pressure increases to NTS via cranial nerves X and IX, the NTS fires to the vasodilator center which then sends an inhibitory signal to the vasoconstrictor center of the vasomotor center. By inhibiting the vasoconstrictor system the SNS backs off and the vessels are able to dilate and accommodate to the high pressures
Why don’t baroreceptors contribute to long term blood pressure control?
The baroreceptors reset after a small time period
What is the neural mechanism for increasing the heart rate after sensing an increase in volume by the atrial receptors?
Increased firing to the NTS by mechanoreceptors in the atria and large veins via cranial nerves, NTS communicates with the cardioaccelerator center which increase SNS
What is the intrinsic mechanism for increasing the heart rate after sensing an increase in volume by the atrial receptors?
A stretched SA node influences pacemaker cells of the heart (ion channel conductance) by increasing the action potential frequency
How is ANP stimulated when there is an increase in circulating volume?
Stretch of the cardiomyocytes release stored granules of ANP which circulate to the kidneys and promote the loss of sodium in the urine
