Chapter 18 - Guyton Flashcards
The nervous system controls the circulation almost entirely through the ________ nervous system.
autonomic
The most important part of the autonomic nervous system for regulating the circulation is the __________ nervous system.
sympathetic
The ______________ nervous system contributes specifically to regulation of heart function.
parasympathetic
Sympathetic fibers innervate the vessels of most tissues except for which structures?
capillaries, precapillary sphincters, metarterioles
The innervation of the small arteries and arterioles allows sympathetic stimulation to increase resistance to blood flow and thereby to ________ rate of blood flow through the tissues.
decrease
The innervation of the large vessels, particularly of the veins, makes it possible for sympathetic stimulation to ________ the volume of these vessels.
decrease
What is the vasomotor center and where is it located?
reticular substance of the medulla and of the lower third of the pons; it transmits parasympathetic impulses through the vagus nerves to the heart and transmits sympathetic impulses through the spinal cord and peripheral sympathetic nerves to virtually all arteries, arterioles, and veins of the body
Why do blood vessels maintain a state of partial contraction?
Under normal conditions, the vasoconstrictor area of the vasomotor center transmits signals continuously to the sympathetic vasoconstrictor nerve fibers over the entire body, causing continuous slow firing of these fibers at a rate of about one half to two impulses per second (sympathetic vasoconstrictor tone).
How can the vasomotor center increase or decrease heart activity?
lateral portions of the vasomotor center transmit excitatory impulses through the sympathetic
nerve fibers to the heart to increase heart rate and contractility; medial portion of the vasomotor center sends signals to the adjacent dorsal motor nuclei of the vagus nerve transmitting parasympathetic impulses to the heart to decrease heart rate and heart contractility
The substance secreted at the endings of the
vasoconstrictor nerves is almost entirely ______________.
norepinephrine (acts on alpha adrenergic receptors of smooth muscle to cause vasoconstriction)
Sympathetic impulses are transmitted to the adrenal medullae at the same time that they
are transmitted to the blood vessels, causing release of which hormones?
epinephrine and norepinephrine (mainly vasoconstriction)
Emotional fainting begins with disturbing thoughts in the cerebral cortex. The pathway probably then goes to the vasodilatory center of the anterior hypothalamus next to the vagal centers of the medulla, to the heart through the vagus nerves, and also through the spinal cord to the sympathetic vasodilator nerves of the muscles. What is this known as?
vasovagal syncope
What three major changes occur to increase arterial pressure?
arterioles of systemic circulation are constricted, veins are strongly constricted (more blood to heart and heart beats stronger), heart itself is stimulated to beat stronger (increase heart rate)
Why does arterial pressure almost immediately increase with exercise?
At the same time that the motor areas of the brain become activated to cause exercise, most of the reticular activating system of the brain stem is also activated, which includes greatly increased stimulation of the vasoconstrictor and cardioacceleratory areas of the vasomotor center.
Baroreceptors are what type of nerve endings in the artery walls?
spray-type
In what two locations are baroreceptors particularly abundant (although they are found in nearly every large artery of the thoracic and neck region)?
carotid sinus and aortic arch
What is the pathway of nerve transmission of the baroreceptors in the carotid sinus?
Hering’s nerves–>glossopharyngeal nerves–>tractus solitarius (solitary tract) in the medullary area of the brain stem
What is the pathway of nerve transmission of the baroreceptors in the aortic arch?
arch of the aorta–>vagus nerves–>tractus solitarius (solitary tract) of the medulla
After the baroreceptor signals have entered the tractus solitarius of the medulla, second order neurons do what?
inhibit the vasoconstrictor center of the medulla and excite the vagal parasympathetic center to cause vasodilation, decreased heart rate, and decreased heart contractility
When a person goes from supine to standing, what prevents fainting?
the falling pressure at the baroreceptors after standing elicits an immediate reflex, resulting in strong sympathetic discharge throughout the body
Are baroreceptors considered to be a short-term or long-term regulator of arterial pressure?
short-term, primary purpose of the arterial baroreceptor system is to reduce the minute by minute variation in arterial pressure
The chemoreceptors are located in the same areas as the baroreceptors (same pathways), except they respond to what?
lack of oxygen, excess carbon dioxide or hydrogen (these receptors are more sensitive at the extremes)
What are the low-pressure receptors?
located in the atria and pulmonary arteries, they are similar to the baroreceptor stretch receptors of the large systemic arteries, the minimize arterial pressure changes in response to changes in blood volume
What is the Bainbridge reflex?
The stretch receptors of the atria that elicit the Bainbridge reflex transmit their afferent signals
through the vagus nerves to the medulla of the brain. Then efferent signals are transmitted back through vagal and sympathetic nerves to increase heart rate and strength of heart contraction.
