Chapter 18 - Guyton

Question 1

The nervous system controls the circulation almost entirely through the ________ nervous system.

Answer 1

autonomic

Question 2

The most important part of the autonomic nervous system for regulating the circulation is the __________ nervous system.

Answer 2

sympathetic

Question 3

The ______________ nervous system contributes specifically to regulation of heart function.

Answer 3

parasympathetic

Question 4

Sympathetic fibers innervate the vessels of most tissues except for which structures?

Answer 4

capillaries, precapillary sphincters, metarterioles

Question 5

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.

Answer 5

decrease

Question 6

The innervation of the large vessels, particularly of the veins, makes it possible for sympathetic stimulation to ________ the volume of these vessels.

Answer 6

decrease

Question 7

What is the vasomotor center and where is it located?

Answer 7

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

Question 8

Why do blood vessels maintain a state of partial contraction?

Answer 8

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).

Question 9

How can the vasomotor center increase or decrease heart activity?

Answer 9

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

Question 10

The substance secreted at the endings of the

vasoconstrictor nerves is almost entirely ______________.

Answer 10

norepinephrine (acts on alpha adrenergic receptors of smooth muscle to cause vasoconstriction)

Question 11

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?

Answer 11

epinephrine and norepinephrine (mainly vasoconstriction)

Question 12

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?

Answer 12

vasovagal syncope

Question 13

What three major changes occur to increase arterial pressure?

Answer 13

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)

Question 14

Why does arterial pressure almost immediately increase with exercise?

Answer 14

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.

Question 15

Baroreceptors are what type of nerve endings in the artery walls?

Answer 15

spray-type

Question 16

In what two locations are baroreceptors particularly abundant (although they are found in nearly every large artery of the thoracic and neck region)?

Answer 16

carotid sinus and aortic arch

Question 17

What is the pathway of nerve transmission of the baroreceptors in the carotid sinus?

Answer 17

Hering’s nerves–>glossopharyngeal nerves–>tractus solitarius (solitary tract) in the medullary area of the brain stem

Question 18

What is the pathway of nerve transmission of the baroreceptors in the aortic arch?

Answer 18

arch of the aorta–>vagus nerves–>tractus solitarius (solitary tract) of the medulla

Question 19

After the baroreceptor signals have entered the tractus solitarius of the medulla, second order neurons do what?

Answer 19

inhibit the vasoconstrictor center of the medulla and excite the vagal parasympathetic center to cause vasodilation, decreased heart rate, and decreased heart contractility

Question 20

When a person goes from supine to standing, what prevents fainting?

Answer 20

the falling pressure at the baroreceptors after standing elicits an immediate reflex, resulting in strong sympathetic discharge throughout the body

Question 21

Are baroreceptors considered to be a short-term or long-term regulator of arterial pressure?

Answer 21

short-term, primary purpose of the arterial baroreceptor system is to reduce the minute by minute variation in arterial pressure

Question 22

The chemoreceptors are located in the same areas as the baroreceptors (same pathways), except they respond to what?

Answer 22

lack of oxygen, excess carbon dioxide or hydrogen (these receptors are more sensitive at the extremes)

Question 23

What are the low-pressure receptors?

Answer 23

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

Question 24

What is the Bainbridge reflex?

Answer 24

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.

Question 25

Arterial pressure elevation in response to cerebral ischemia is known as the?

Answer 25

central nervous system ischemic response, this is a very strong reaction (basically this is the “last-ditch” effort to keep you and your brain alive)

Question 26

What is the Cushing reaction?

Answer 26

with increased pressure of CSF in the brain, the CNS ischemic response is to raise arterial pressure to match so that blood flow can resume in the arteries of the brain

Question 27

Why are people whose skeletal muscles have been paralyzed considerably more prone to hypotensive episodes than are people with
normal skeletal muscles?

Answer 27

abdominal compression reflex is not effective, normally it compresses all the venous reservoirs of
the abdomen, helping to translocate blood out of the abdominal vascular reservoirs toward the heart

Question 28

What causes respiratory waves in arterial pressure?

Answer 28

“breathing signals” in the respiratory center of the medulla “spill over” into the vasomotor center; during inspiration, the pressure in the thoracic cavity becomes more negative than usual, causing the blood vessels in the chest to expand; pressure changes caused in the thoracic vessels by respiration can excite vascular and atrial stretch
receptors

Question 29

The net result during normal respiration is usually an _________ in arterial pressure during the early part of expiration and a _________ in pressure during the remainder of the respiratory cycle.

Answer 29

increase; decrease

Question 30

Any reflex pressure control mechanism can oscillate if the intensity of “feedback” is strong enough and if there is a delay between excitation of the pressure receptor and the subsequent pressure response. This is known as?

Answer 30

vasomotor waves (Mayer waves); this occurs with baroreceptors, chemoreceptors, and CNS ischemic response