Chapters 34: Perfusion/Circulation: Review Questions
1. Trace the path of normal electrical impulses in the heart
The heart contains specialized areas of nerve tissue that initiate electrical impulses
without external nervous system stimulation.
The sinoatrial (SA) node acts as the pacemaker. Located in the right
atrium
1. initiates an impulse that triggers each heartbeat. The impulse
travels down the atrial conduction system so that both atria
contract as a unit.
ii. At the atrioventricular (AV) node, there is a slight delay. From the AV
node, impulses pass into the left and right bundles of His and into the
Purkinje fibers to the ventricles.
iii. In this way, myocardial fibers are electrically stimulated almost
simultaneously to create a unified cardiac muscle contraction strong
enough to pump blood out of a heart chamber. This spontaneous
rhythm of the heart is called automaticity.
1. If there are defects in this electrical system, impulses travel more
slowly through the heart, and some areas contract before others.
This can lead to ineffective heart pumping and decreased
cardiac output.
iv. Normally, the SA node is in charge and initiates a rate of 60 to 100
beats/min, depending on the body’s oxygen needs.
v. If the SA node fails, the AV node can take over as the pacemaker, but it
generally triggers a slower heart rate.
If both the SA and AV nodes fail, the conduction fibers in the ventricles can
initiate impulses. Ventricular conduction generates a very slow rate, usually less
than 40 beats/min; however, this can be lifesaving if no other node or fiber is
initiating an impulse.
2. How is the cardiovascular system regulated?
Autonomic nervous system: Sympathetic and parasympathetic fibers
i. Heart: Regulate heart rate and contractility
ii. Vascular system: Maintain vascular tone
§ Brainstem centers: Regulate cardiac function and blood pressure
• Baroreceptors: Sensitive to pressure changes
• Vascular system: Sensitive to blood pH, oxygen levels, and CO2
The structures of the cardiovascular system are the heart, the systemic and
pulmonary blood vessels, and the coronary arteries.
The cardiovascular system circulates oxygenated blood to organs and tissues and
returns deoxygenated blood to the heart.
Cardiovascular function is regulated by the autonomic nervous system (ANS)
and by control centers in the brainstem.
, The ANS regulates cardiovascular function through its influence on
cardiac rate, muscle contractility, and vascular tone.
Heart:
1. Through branches at the thoracic level of the spinal cord:
a. Sympathetic fibers stimulate the heart to beat faster and
contract more strongly.
b. Parasympathetic fibers innervate the heart through the
vagus nerve. Parasympathetic stimulation results in a
slowed heart rate, but it does not influence myocardial
contractility.
Vascular System:
1. All blood vessels are innervated by sympathetic fibers. The
parasympathetic nervous system has no significant control over
blood vessels.
a. Sympathetic control maintains the blood vessels in a
constant baseline state of partial contraction (tone).
Vascular tone maintains BP and blood flow even when a
person is resting or asleep.
b. Sympathetic stimulation above and beyond baseline tone
varies in response to body needs. Increased sympathetic
stimulation causes (1) constriction of some vessels (e.g.,
skin, gastrointestinal [GI] tract, and kidneys) and (2)
dilation of other vessels (skeletal muscle). This shunts
blood flow to the skeletal muscles for a fight-or-flight
response.
Brainstem Centers
The brainstem centers integrate feedback from baroreceptors and
chemoreceptors in the body to regulate cardiac function and BP.
1. The vasomotor center controls sympathetic stimulation of the
heart and vascular system.
2. The cardioinhibitory center controls parasympathetic slowing
of the heart rate.
Baroreceptors
1. Baroreceptors located in the walls of the heart and blood vessels
are sensitive to pressure changes. The aortic arch and carotid
artery baroreceptors are particularly important in the regulation
of heart rate and vascular tone. When baroreceptors sense even
a small drop in pressure, they send messages to the brainstem
centers to stimulate the sympathetic nervous system to increase
heart rate and induce vasoconstriction. This mechanism allows
us to change positions and maintain BP.
Chemoreceptors
1. Chemoreceptors located in the aortic arch and the carotid
arteries are sensitive to changes in blood pH, oxygen levels, and
carbon dioxide levels. Their main function is to regulate
ventilation, but they also send information to the vasomotor
1. Trace the path of normal electrical impulses in the heart
The heart contains specialized areas of nerve tissue that initiate electrical impulses
without external nervous system stimulation.
The sinoatrial (SA) node acts as the pacemaker. Located in the right
atrium
1. initiates an impulse that triggers each heartbeat. The impulse
travels down the atrial conduction system so that both atria
contract as a unit.
ii. At the atrioventricular (AV) node, there is a slight delay. From the AV
node, impulses pass into the left and right bundles of His and into the
Purkinje fibers to the ventricles.
iii. In this way, myocardial fibers are electrically stimulated almost
simultaneously to create a unified cardiac muscle contraction strong
enough to pump blood out of a heart chamber. This spontaneous
rhythm of the heart is called automaticity.
1. If there are defects in this electrical system, impulses travel more
slowly through the heart, and some areas contract before others.
This can lead to ineffective heart pumping and decreased
cardiac output.
iv. Normally, the SA node is in charge and initiates a rate of 60 to 100
beats/min, depending on the body’s oxygen needs.
v. If the SA node fails, the AV node can take over as the pacemaker, but it
generally triggers a slower heart rate.
If both the SA and AV nodes fail, the conduction fibers in the ventricles can
initiate impulses. Ventricular conduction generates a very slow rate, usually less
than 40 beats/min; however, this can be lifesaving if no other node or fiber is
initiating an impulse.
2. How is the cardiovascular system regulated?
Autonomic nervous system: Sympathetic and parasympathetic fibers
i. Heart: Regulate heart rate and contractility
ii. Vascular system: Maintain vascular tone
§ Brainstem centers: Regulate cardiac function and blood pressure
• Baroreceptors: Sensitive to pressure changes
• Vascular system: Sensitive to blood pH, oxygen levels, and CO2
The structures of the cardiovascular system are the heart, the systemic and
pulmonary blood vessels, and the coronary arteries.
The cardiovascular system circulates oxygenated blood to organs and tissues and
returns deoxygenated blood to the heart.
Cardiovascular function is regulated by the autonomic nervous system (ANS)
and by control centers in the brainstem.
, The ANS regulates cardiovascular function through its influence on
cardiac rate, muscle contractility, and vascular tone.
Heart:
1. Through branches at the thoracic level of the spinal cord:
a. Sympathetic fibers stimulate the heart to beat faster and
contract more strongly.
b. Parasympathetic fibers innervate the heart through the
vagus nerve. Parasympathetic stimulation results in a
slowed heart rate, but it does not influence myocardial
contractility.
Vascular System:
1. All blood vessels are innervated by sympathetic fibers. The
parasympathetic nervous system has no significant control over
blood vessels.
a. Sympathetic control maintains the blood vessels in a
constant baseline state of partial contraction (tone).
Vascular tone maintains BP and blood flow even when a
person is resting or asleep.
b. Sympathetic stimulation above and beyond baseline tone
varies in response to body needs. Increased sympathetic
stimulation causes (1) constriction of some vessels (e.g.,
skin, gastrointestinal [GI] tract, and kidneys) and (2)
dilation of other vessels (skeletal muscle). This shunts
blood flow to the skeletal muscles for a fight-or-flight
response.
Brainstem Centers
The brainstem centers integrate feedback from baroreceptors and
chemoreceptors in the body to regulate cardiac function and BP.
1. The vasomotor center controls sympathetic stimulation of the
heart and vascular system.
2. The cardioinhibitory center controls parasympathetic slowing
of the heart rate.
Baroreceptors
1. Baroreceptors located in the walls of the heart and blood vessels
are sensitive to pressure changes. The aortic arch and carotid
artery baroreceptors are particularly important in the regulation
of heart rate and vascular tone. When baroreceptors sense even
a small drop in pressure, they send messages to the brainstem
centers to stimulate the sympathetic nervous system to increase
heart rate and induce vasoconstriction. This mechanism allows
us to change positions and maintain BP.
Chemoreceptors
1. Chemoreceptors located in the aortic arch and the carotid
arteries are sensitive to changes in blood pH, oxygen levels, and
carbon dioxide levels. Their main function is to regulate
ventilation, but they also send information to the vasomotor
