MAPIISG1 - Nervous Regulation of Circulation Flashcards
How does nervous regulation have more of a global effect on circulation (3)?
- Redistributes blood to different areas of body prn
- Affects heart rate
- Can rapidly change arterial blood pressure
What role doe the SNS play in circulation?
primary nervous system influence in regulating circulation
What role does the PSNS play in circulation?
Assists in regulation of heart function
The SNS innervates all vessels except (3)?
- Capillaries
- Precapillary Sphincters
- Metarterioles
The SNS allows stimulation to vasoconstrict, what is the result on arteriole system?
small artieries and arterioles vasoconstrict which increases TPR and BP.
The SNS allows stimulation to vasoconstric, what is the result on the venous system?
large vessels, especially veins decreases storage and increase venous return which increases stroke volume and blood pressure.
Describe the path of sympathetic motor nerve fibers
leave spinal cord thru T1-L1/2 spinal nerves –> sympathetic chain –> spinal nerves, sympathetic nerves
What is the response of the body with blood loss, trauma, etc?
Reflexes elicited from aortic bodies and carotid sinus that pick up change in pressure, stimulate sympathetic nervous impuses to the veins. Result is almost normal circulation can be maintained w/ 20% blood loss.
Define circulatory shock
condition in which blood vessels are inadequately filled and blood can’t circulate normally
Define hypovolemic shock
low blood volume can be from burns
Define vascular shock
excessive vasodialation due to anaphylactic shock (histamine release), septic shock (infection using vasodialation)
Define cardiogenic shoc
heart stops working, pump failure (cardiac muscle - MI)
Sympathetic nerves carry ___ vasoconstrictor fibers and ___ vasodialater fibers.
Sympathetic nerves carry MANY vasoconstrictor fibers and FEW vasodialater fibers.
Where are vasoconstricter fibers distributed?
all segments of circulation
Where is the largest distribution of vasoconstrictor fibers, why?
kidneys, intestines, spleen, skin as these are resevoirs for blood and can be shunted
Where are the least distrubuted vasoconstrictor fibers, why?
skeletal muscle and brain as always need blood here and want to be able to run from bear
Where is the vasomotor center located
Located bilaterally in reticular substance of medulla, lower pons
How does the vasomotor center transmit parasympathetic impulses?
vagus nerve to heart
How does the vasomotor center transmit sympathetic impulses?
via spinal cord, peripheral nerves to arteries, arterioles, veins
What are the three areas of the vaasomotor center?
- Vasoconstrictor
- Vasodilator
- Sensory Areas
What is the purpose of the vasoconstrictor area?
continuous impulses from vasoconstrictor nerve fibers maintain partial state of contraction of blood vessels = vasomotor tone
What role does vasomotor tone provide?
contributes to maintenance of BP
What do neurons in the vasoconstrictor area secrete
norepinephrine (NE)
What effect does norepinephrine have when released?
acts on adrenergic receptors of vascular smooth muscle causing vasoconstrictor
What is the purpose of the vasodialator area?
fibers project up, to inhibit vasoconstrictor area
What is the purpose of the sensory area?
receives sensory impulses from circulatory system via vagus, glossopharyngeal nerves –> helps regulate vasoconstrictor and vasodilator areas
What is the role of the Adrenal Medulla?
receives SNS stimulation simultaneous with blood vessels and secretres NE and epinephrine into blood stream causing vasoconstriction
T/F: Epinephrine occasionally causes vasodilation in some tissues.
True
What does the cardiac center adjust?
heart rate and force of contraction
How does the cardioacceleratory center of the Cardiac Center work?
SNS–> increase HR and Force of Contration
How does the cardioinhibitory center work?
PSNS–> decrease HR
What is the cardiovasular center?
Cardiac Center and Vasomotor center
Under normal circumstances, stimulation of vasomotor center also stimulates
cardiac centers, therefore control heart function and vascular function simultaneously.
Due to simultaneous control of centers, if you increase HR you get ___
increased vasoconstriction (SNS)
Due to simultaneous control of centers, if you decrease HR you get ___
vasodilation (PSNS)
Describe the speed of the nervous system control of blood pressue
most rapid of responses
-can increase BP within seconds, 2-fold increase within 5-10 seconds, decrease to 1/2 normal can occur in 10-40 seconds
What systems does the nervous system use to rapidly increase BP?
simultaneous stimulation of vasoconstrictor and cardioaccelerator – reciprocal inhibition of PSNS vagal signals to heart
What are the three major changes to increase BP?
- Most arterioles constrict
- Veins and other large vessels constrict
- SNS stimulation of heart
What are the two reflex mechanisms to maintain normal arterial pressure?
- Baroreceptor Reflex
2. Cehmoreceptor Reflex
What are baroreceptors and where are they located?
neural receptors in the carotid sinus, aortic arch, and walls of nearly every large artery in neck and thorax
What are Baroreceptors sensitive to?
pressure sensitive: respond to stretch of lack of stretch in vessel walls.
What happens when Baroreceptors are triggered?
Stretch sends rapid impusles to the vasomotor center and cardiac center
What effect would a decrease in MAP have on Baroreceptors
detect lack of stretch, initiates reflex vasoconstriction and increases CO - BP rises
How do Baroreceptors act as a “pressure buffer system”
protect circulation from acute changes in BP via Carotid Sinus Reflex and Aortic Reflex, decreases variation in BP.
How can Baroreceptors become ineffective with prolonged pressure changes?
they adapt by resetting at a higher point with hypertension which limits their long term response to perceived higher pressure.
What do Chemoreceptors respond to?
changes in O2 (lack), CO2, and H+ excess in arterial blood
Where are Chemoreceptors located?
carotid bodies and aortic bodies
What do Chemoreceptors stimulate?
nerve fibers traveling to the vasomotor centers to increase arterial pressure
When are Chemoreceptors important?
only at low arterial pressures
Describe the action mechanism of Chemoreceptors.
In contact with arterial blood, senses low O2 or high levels of CO2 or H+ that results with a drop in arterial pressure, initations reflexive vaso/venoconstriction
What are Atrial reflexes - low-pressure receptors?
receptors are stretch receptors in walls of atria which minimize arterial pressure changes in response to change in blood volume
What are Atrial reflexes - bainbridge reflex?
stretch receptors that with increase in arterial pressure, will get increase in HR and strength of constriction to prevent blood from “backing up” into system
What is CNS Ischemic Response?
occurs when blood flow to vasomotor center severely decreased - comproises nutritional access = cerebral ischmia
What happens with a CNS Ischemic Response?
get strong reaction of vasoconstrictor and cardioaccelerator centers, large rise in systemic arterial pressure
What effect can CNS Ischemic Response have on MAP?
increase MAP ~250mmHG for up to 10 minutes, most powerful activator of SNS vasoconstrictor system.
