Exam 2 – Cardio Ch 18 Flashcards
What roles does the nervous system have in regulation of the circulation?
Redistribution of blood flow
increasing or decreasing pumping activity of heart
rapid control of arterial pressure
regulates via autonomic nervous system
What is the sympathetic nervous system important in?
Control of circulation
What is the parasympathetic nervous system important in?
Regulating heart function
What do sympathetic nerve fibers innervate?
All vessels except capillaries and precapillary sphincters and some metarterioles
Large veins and the heart
What do innervation of small arteries and arterioles allow sympathetic nerves to do?
Increase vascular resistance
What is the parasympathetic nervous system mainly important in control of?
Heart rate via the vagus nerve
Where are vasocontrictor fibers distributed?
Throughout all segments of circulation
What are the areas of greater distribution of vasoconstrictor fibers?
Kidneys
Gut
Spleen
Skin
What are the areas of less potent vasoconstrictor fibers?
Coronary circulation
Brain
What is arterial pressure?
Cardiac output X total peripheral resistance
What can arterial pressure be increased by?
Constricting almost all arterioles of body = increased total peripheral resistance
Constricting large vessels (veins) of circulation = increasing venous return and cardiac output
Directly increasing cardiac output by increasing heart rate and contractility
What is VMC?
Vasomotor center
Where does VMC transmit impulses?
Downward through cord to almost all blood vessels
Where is VMC located?
Bilaterally in the reticular substance of the medullar and the lower third of pons
What is the VMC composed of?
Vasoconstrictor area
Vasodilator area
Sensory area
What does the VMC have input to?
Both sympathetic and parasympathetic
How do many higher centers of the brain influence VMC?
Many higher centers of brain such as the hypothalamus can exert powerful excitatory or inhibitory effects of VMC
Define sympathetic vasoconstrictor tone
Vasoconstrictor area of VMS transmits signals continuously to sympathetic nerve fibers
Define vasomotor tone
Maintain partial state of contraction in blood vessels
What do large portions of VMC do?
Increase heart rate and contractility
What do medial portion of VMC do?
Transmit via vagus nerve to heart to decrease heart rate
How does VMC increase arterial pressure within seconds by?
Constricting almost all arterioles of the body which increases total peripheral resistance
Constricting large vessels of the circulation thereby increasing venous return and cardiac output
Directly increases cardiac output by increasing heart rate and contractility
When can rapid increases of arterial pressure occur?
During exercise or with fright
Look at arterial pressure chart
Look at arterial pressure chart
What is the neurotransmitter for vasoconstrictor nerves?
Norepinephrine
What does the adrenal medulla secrete?
Epinephrine and norepinephrine which constricts blood vessels via alpha adrenergic receptors (circulates in blood)
What can epinephrine also dilate?
Vessels through a potent Beta2 receptor
LOOK AT VASOVAGAL SYNCOPE
LOOK AT VASOVAGAL SYNCOPE
What are baroreceptors?
Spray type nerves endings located in the walls of the carotid bifurcation called the carotid sinus and in the walls of the aortic arch
What does carotid sinus transmit?
Via hering’s nerve to the glossopharyngeal nerves and then to the nucleus tractus solitarius (NTS) to medulla
What does the arch of the aorta transmit?
Via vagus to nucleus tractus solitarius
LOOK AT ANATOMY OF BARORECEPTORS
LOOK AT ANATOMY OF BARORECEPTORS
What is the arterial baroreceptor reflex?
Short term regulation of arterial pressure
What is the arterial baroreceptor reflex initiated by?
Baroreceptors in walls of large systemic arteries
How does a ride in pressure affect baroreceptors?
Stretches baroreceptors and causes them to transmit signals to VMC and feedback signals are sent via the autonomic nervous system to the circulation to reduce arterial pressure back to normal
What pressures do carotid sinus baroreceptors response to?
Between 60 and 180 mmHg
What pressure does baroreceptors respond to changes in?
Arterial pressure
What pressure is baroreceptor reflex most sensitive at?
100 mmHg
As pressure increases the number of impulses from carotid sinus increases, which results in what?
- Inhibition of vasoconstrictor
2. Activation of vagal center
LOOK AT BARORECEPETOR PICTURE SLIDES
LOOK AT BARORECEPETOR PICTURE SLIDES
How do baroreceptors reduce daily variations in arterial pressure?
By opposing increases or decreases in arterial pressure
Why are baroreceptors unimportant in long term control of arterial pressure?
Because they adapt
What are chemoreceptors?
Chemosensitive cells sensitive to oxygen lack, CO2 excess or H+ ion excess
Where are chemoreceptors located?
In carotid bodies near the carotid bifurcation and on the arch of the aorta
What does activation of chemosensitive receptors result in?
Excitation of vasomotor center
When are secondary chemoreceptors stimulated?
Not stimulated until pressure falls below 80mmHg
LOOK AT CAROTID AND AORTIC CHEMORECEPTORS CHART
LOOK AT CAROTID AND AORTIC CHEMORECEPTORS CHART
What is CNS ischemic response activated by?
Cerebral ischemia
What does reduced cerebral blood flow elevate?
CO2 and pH which activates VMC to increase arterial pressure
What is one of the most powerful activators of the sympathetic vasoconstrictor system?
VMC ischemic response
Look at CNS ischemic response chart
Look at CNS ischemic response chart
When is CNS ischemic response activated?
When pressure falls below 60 mmHg
When is CNS ischemic response maximized?
At pressures of 15-20 mmHg
What effect does prolonged CNS ischemia have?
A depressant effect on the vasomotor center
What do low pressure receptors in atria and pulmonary arteries minimize?
Arterial pressure changes
What do artial and pulmonary artery reflexes try to do to pressure?
Keep pressure within a lower range
What does increases in blood volume activate?
Low pressure receptors which in turn lower arterial pressure
Activation of low pressure receptors enhances Na and water excretion by?
Decreasing rate of ADH
Increasing glomerular filtration rate
Decreasing Na reabsorption
What does the bainbridge reflex prevent?
Damming of blood in veins, artia, and pulmonary circulation
What does an increase in atrial pressure in bainbridge reflex cause?
Increases heart rate
In bainbridge reflex, what does stretching of atria cause?
Sending signals to VMC via vagal afferents to increase heart rate and contractility
Look at bainbridge reflex chart
Look at bainbridge reflex chart
Look at atrial and pulmonary artery reflexes
Look at atrial and pulmonary artery reflexes
