Heart - MCAT Biological and Biochemical Foundations of Living Systems
Card 1 of 200
The firing of which group of cells initiates contraction of the left and right ventricles?
The firing of which group of cells initiates contraction of the left and right ventricles?
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After axons from the sinoatrial node flow through the atria to cause atrial contraction, the depolarization pauses in the atrioventricular node. Once the atrioventricular node depolarizes, the electrical signal travels though the bundle of His to the walls of the ventricles via purkinje fibers. The atrioventricular node initiates ventricular contraction, the bundle of His carries the signal, and the purkinje fibers allow for synchronized contraction of different regions of the ventricular wall.
After axons from the sinoatrial node flow through the atria to cause atrial contraction, the depolarization pauses in the atrioventricular node. Once the atrioventricular node depolarizes, the electrical signal travels though the bundle of His to the walls of the ventricles via purkinje fibers. The atrioventricular node initiates ventricular contraction, the bundle of His carries the signal, and the purkinje fibers allow for synchronized contraction of different regions of the ventricular wall.
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Which nerve, as part of the parasympathetic nervous system, serves to decrease heart rate?
Which nerve, as part of the parasympathetic nervous system, serves to decrease heart rate?
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The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.
The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.
The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.
The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.
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A patient presents with signs of fatigue and elevated heart rate. It is found that the patient's blood supply is not fully saturated with oxygen because not all of the blood is passing through the patient's lungs. It is found that the patient has a birth defect. Which structure in the patient originally diverted blood from the lungs while the patient was a fetus?
A patient presents with signs of fatigue and elevated heart rate. It is found that the patient's blood supply is not fully saturated with oxygen because not all of the blood is passing through the patient's lungs. It is found that the patient has a birth defect. Which structure in the patient originally diverted blood from the lungs while the patient was a fetus?
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In a fetus, there are three fetal shunts: the ductus arteriosus, the ductus venosus, and the foramen ovale. Failure to fully close the foramen ovale during birth will allow blood to shunt directly from the right atrium to the left atrium, diverting the blood from the lungs. The ductus arteriosus also shunts blood away from the fetal non-functional lungs, allowing it to pass directly from the pulmonary artery to the aorta. Additionally, after birth, the ductus arteriosus becomes the ligamentum arteriosum.
Conversely, the ductus venosus is a structure in the fetus that diverts blood away from the fetal liver.
In a fetus, there are three fetal shunts: the ductus arteriosus, the ductus venosus, and the foramen ovale. Failure to fully close the foramen ovale during birth will allow blood to shunt directly from the right atrium to the left atrium, diverting the blood from the lungs. The ductus arteriosus also shunts blood away from the fetal non-functional lungs, allowing it to pass directly from the pulmonary artery to the aorta. Additionally, after birth, the ductus arteriosus becomes the ligamentum arteriosum.
Conversely, the ductus venosus is a structure in the fetus that diverts blood away from the fetal liver.
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You encounter a patient that has an atrial-septal defect (ASD), in which a hole in the cardiac septum persists from cardiac development. Which of the following chambers of the heart will not receive its normal volume of blood due to this condition?
You encounter a patient that has an atrial-septal defect (ASD), in which a hole in the cardiac septum persists from cardiac development. Which of the following chambers of the heart will not receive its normal volume of blood due to this condition?
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The left atrium has a higher pressure than the right atrium. As a result of the hole between the atria, there will be a left-to-right shunt of blood in the heart. Blood would normally go from the left atrium into the left ventricle. The shunt will allow blood from the left atrium to return to the right atrium, instead of proceeding to the left ventricle. Because of the shunt, less blood will go into the left ventricle.
The left atrium has a higher pressure than the right atrium. As a result of the hole between the atria, there will be a left-to-right shunt of blood in the heart. Blood would normally go from the left atrium into the left ventricle. The shunt will allow blood from the left atrium to return to the right atrium, instead of proceeding to the left ventricle. Because of the shunt, less blood will go into the left ventricle.
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Valves in the heart serve the chief function of preventing backflow during systole. Which of the following prevents blood from flowing from the right ventricle to the right atrium?
Valves in the heart serve the chief function of preventing backflow during systole. Which of the following prevents blood from flowing from the right ventricle to the right atrium?
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There are four principle heart valves, each classified as either an atrioventricular (AV) valve or a semilunar valve. The atrioventricular valves separate the atria from the ventricles, while the semilunar valves separate the ventricles from arteries.
The tricuspid valve prevents backflow between the right atrium and right ventricle. The bicuspid, or mitral, valve prevents backflow between the left atrium and left ventricle. The pulmonary semilunar valve separates the right ventricle from the pulmonary artery, and the aortic semilunar valve separates the left ventricle from the aorta.
There are four principle heart valves, each classified as either an atrioventricular (AV) valve or a semilunar valve. The atrioventricular valves separate the atria from the ventricles, while the semilunar valves separate the ventricles from arteries.
The tricuspid valve prevents backflow between the right atrium and right ventricle. The bicuspid, or mitral, valve prevents backflow between the left atrium and left ventricle. The pulmonary semilunar valve separates the right ventricle from the pulmonary artery, and the aortic semilunar valve separates the left ventricle from the aorta.
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What specialized area of tissue delays the proliferation of electrical stimulation in the heart, allowing the heart chambers to fill with blood?
What specialized area of tissue delays the proliferation of electrical stimulation in the heart, allowing the heart chambers to fill with blood?
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The atrioventricular (AV) node is located in the lower intratrial septum and receives impulses from the sinoatrial node. The sinoatrial node is termed the pacemaker of the heart and is located in the wall of the right atrium. It initiates normal heart beats and is innervated by the vagus nerve, which helps control the rate of impulses. Once an impulse causes the atria to contract, it travels to the atrioventricular node. Once the AV node receives the impulse, cellular mechanisms initiate a delay. This prevents simultaneous atrial and ventricular systole, allowing the ventricles to receive the blood exiting the contracted atria. Following the delay, the impulse travels from the AV node to the bundle of His.nThe bundle of His is a pathway for electrical signals to be transmitted to the ventricles. The Purkinje fibers spread through the myocardium and distribute electical stimuli to cause contraction of the ventricular myocardium. The bundle branches supply the two ventricles with electrical stimuli.
The atrioventricular (AV) node is located in the lower intratrial septum and receives impulses from the sinoatrial node. The sinoatrial node is termed the pacemaker of the heart and is located in the wall of the right atrium. It initiates normal heart beats and is innervated by the vagus nerve, which helps control the rate of impulses. Once an impulse causes the atria to contract, it travels to the atrioventricular node. Once the AV node receives the impulse, cellular mechanisms initiate a delay. This prevents simultaneous atrial and ventricular systole, allowing the ventricles to receive the blood exiting the contracted atria. Following the delay, the impulse travels from the AV node to the bundle of His.nThe bundle of His is a pathway for electrical signals to be transmitted to the ventricles. The Purkinje fibers spread through the myocardium and distribute electical stimuli to cause contraction of the ventricular myocardium. The bundle branches supply the two ventricles with electrical stimuli.
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Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control.
There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system.
When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).
In patients with heart failure, the physician might prescribe a beta blocker to help with the condition. How will a beta blocker be useful in patients with heart failure?
Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control.
There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system.
When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).
In patients with heart failure, the physician might prescribe a beta blocker to help with the condition. How will a beta blocker be useful in patients with heart failure?
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The heart has the beta-1 receptor on its surface. When norepinephrine binds to beta-1 receptors on the heart, the effect is an increase in heart rate. In patients with a heart problem, increasing the heart rate might exhaust the heart and provoke heart failure. By blocking this receptor with a beta blocker, agonists to the beta-1 receptor cannot increase the heart rate.
The heart has the beta-1 receptor on its surface. When norepinephrine binds to beta-1 receptors on the heart, the effect is an increase in heart rate. In patients with a heart problem, increasing the heart rate might exhaust the heart and provoke heart failure. By blocking this receptor with a beta blocker, agonists to the beta-1 receptor cannot increase the heart rate.
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Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:
A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.
In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride 
in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases.
When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more 
being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.
Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.
How can taking a carbonic anhydrase inhibitor help a patient with signs of heart failure?
Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:
A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.
In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride
When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more
Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.
How can taking a carbonic anhydrase inhibitor help a patient with signs of heart failure?
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As mentioned in the passage, carbonic anhydrase inhibitors will prevent the reabsorption of sodium and water at the proximal tubule. By preventing water reabsorption, the blood volume decreases. Lowering the blood volume will lower the blood pressure. The heart is constantly pushing blood against a pressure. The higher the blood pressure is, the more work the heart will have to do to push the blood out. Therefore, by lowering the blood pressure, the heart does not have to work as hard.
As mentioned in the passage, carbonic anhydrase inhibitors will prevent the reabsorption of sodium and water at the proximal tubule. By preventing water reabsorption, the blood volume decreases. Lowering the blood volume will lower the blood pressure. The heart is constantly pushing blood against a pressure. The higher the blood pressure is, the more work the heart will have to do to push the blood out. Therefore, by lowering the blood pressure, the heart does not have to work as hard.
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Which of the following structures prevents blood flow to the lungs during development?
I. Ductus arteriosus
II. Ductus venosus
III. Foramen ovale
IV. Ligamentum arteriosum
Which of the following structures prevents blood flow to the lungs during development?
I. Ductus arteriosus
II. Ductus venosus
III. Foramen ovale
IV. Ligamentum arteriosum
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The lungs remain non-functional in the developing fetus. Instead, the fetus receives oxygen via gas exchange between maternal and fetal circulation in the placenta. To prevent inefficient blood flow to the lungs, blood is shunted in two ways. The ductus arteriosus shunts blood directly from the pulmonary artery to the aorta, allowing it to bypass the pulmonary circuit. After birth, this duct quickly collapses to become the adult structure known as the ligamentum arteriosum. The second shunt is the foramen ovale, which allows blood to pass directly from the right atrium to the left atrium. In adults, this structure becomes the fossa ovalis.
The ductus venosus is not found in the heart, and is used to direct blood from the umbilical vein to the inferior vena cava. This allows the oxygenated blood (returning from the placenta through the umbilical vein) to bypass systemic circulation and enter directly into the heart. The heart can then direct the blood through circulation.
The lungs remain non-functional in the developing fetus. Instead, the fetus receives oxygen via gas exchange between maternal and fetal circulation in the placenta. To prevent inefficient blood flow to the lungs, blood is shunted in two ways. The ductus arteriosus shunts blood directly from the pulmonary artery to the aorta, allowing it to bypass the pulmonary circuit. After birth, this duct quickly collapses to become the adult structure known as the ligamentum arteriosum. The second shunt is the foramen ovale, which allows blood to pass directly from the right atrium to the left atrium. In adults, this structure becomes the fossa ovalis.
The ductus venosus is not found in the heart, and is used to direct blood from the umbilical vein to the inferior vena cava. This allows the oxygenated blood (returning from the placenta through the umbilical vein) to bypass systemic circulation and enter directly into the heart. The heart can then direct the blood through circulation.
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Which of the following is true about cardiac muscle?
Which of the following is true about cardiac muscle?
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The correct answer is "it is striated." Similiar to skeletal muscle, cardiac muscle is striated. It has only one nucleus per cell, and its action is involuntary. Futhermore, it is composed of sarcomeres, which give it its striated appearance.
The correct answer is "it is striated." Similiar to skeletal muscle, cardiac muscle is striated. It has only one nucleus per cell, and its action is involuntary. Futhermore, it is composed of sarcomeres, which give it its striated appearance.
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Systolic blood pressure measures .
Systolic blood pressure measures .
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Systolic blood pressure measures the force of blood exiting the heart into the arteries during contraction. This can measure how strong the heart tissue is. Diastolic pressure indicates the pressure when the heart is relaxed. Healthy systolic blood pressue is 120mmHg, and diastolic is 80mmHg.
Systolic blood pressure measures the force of blood exiting the heart into the arteries during contraction. This can measure how strong the heart tissue is. Diastolic pressure indicates the pressure when the heart is relaxed. Healthy systolic blood pressue is 120mmHg, and diastolic is 80mmHg.
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Blood returning from the lungs enters into which chamber of the heart?
Blood returning from the lungs enters into which chamber of the heart?
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Oxygenated blood returning to the heart from the lungs enters the left atrium. It then goes to the left ventricle and out the aorta.
Oxygenated blood returning to the heart from the lungs enters the left atrium. It then goes to the left ventricle and out the aorta.
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Cardiac output is directly affected by .
Cardiac output is directly affected by .
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Cardiac output is defined as the volume of blood pumped per minute. The two factors that will directly affect the cardiac output will be stroke volume (volume pumped per beat) and heart rate (beats per minute).
Cardiac output is defined as the volume of blood pumped per minute. The two factors that will directly affect the cardiac output will be stroke volume (volume pumped per beat) and heart rate (beats per minute).
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What is the definition of systole and diastole?
What is the definition of systole and diastole?
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Systole can apply to either te atria or the ventricles and refers to the period during which the chambers contract. Diastole, in contrast, described the period of relaxation. During diastole, blood fills the relaxed chambers. During systole, blood is forced out of the chambers as they contract. Systole and diastole are coordinated between chambers such that both atria contract together (atrial systole) and both ventricles contract together (ventricular systole) in a rhythm that allows coordinated filling and emptying of the chambers without backflow or disruption.
Note that systolic blood pressure refers to blood pressure during ventricular systole, and diastolic blood pressure to pressure during ventricular diastole.
Systole can apply to either te atria or the ventricles and refers to the period during which the chambers contract. Diastole, in contrast, described the period of relaxation. During diastole, blood fills the relaxed chambers. During systole, blood is forced out of the chambers as they contract. Systole and diastole are coordinated between chambers such that both atria contract together (atrial systole) and both ventricles contract together (ventricular systole) in a rhythm that allows coordinated filling and emptying of the chambers without backflow or disruption.
Note that systolic blood pressure refers to blood pressure during ventricular systole, and diastolic blood pressure to pressure during ventricular diastole.
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Which of the following accurately shows the electrical pathway through the heart?
Which of the following accurately shows the electrical pathway through the heart?
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The correct electrical path through the heart is the SA (sinoatrial) node, AV (atrioventricular) node, bundle of His (AV bundle), then purkinje fibers.
The sinoatrial node initiates the electrical signal and acts as the heart's natural pacemaker. Innervation from the parasympathetic nervous system is crucial in maintaining a normal heart rate from the SA node, but is not required to initiate electrical signals. The signal travels to the atrioventricular node and is briefly delayed, allowing the atria to finish contracting before initiaing ventricular systole. The signal travels down the bundle of His and is quickly distributed to the purkinje fibers, which initiate ventricular systole.
The correct electrical path through the heart is the SA (sinoatrial) node, AV (atrioventricular) node, bundle of His (AV bundle), then purkinje fibers.
The sinoatrial node initiates the electrical signal and acts as the heart's natural pacemaker. Innervation from the parasympathetic nervous system is crucial in maintaining a normal heart rate from the SA node, but is not required to initiate electrical signals. The signal travels to the atrioventricular node and is briefly delayed, allowing the atria to finish contracting before initiaing ventricular systole. The signal travels down the bundle of His and is quickly distributed to the purkinje fibers, which initiate ventricular systole.
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Which valve in the heart separates the right atrium from the right ventricle?
Which valve in the heart separates the right atrium from the right ventricle?
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The tricuspid valve separates the right atrium from the right ventricle. The bicuspid valve (also known as the mitral valve) separates the left atrium from the left ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery and the aortic valve separates the left ventricle from the aorta (these are known as the semilunar valves).
The tricuspid valve separates the right atrium from the right ventricle. The bicuspid valve (also known as the mitral valve) separates the left atrium from the left ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery and the aortic valve separates the left ventricle from the aorta (these are known as the semilunar valves).
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Which of the following statements most accurately describes the cardiac output (CO) of the heart?
Which of the following statements most accurately describes the cardiac output (CO) of the heart?
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Cardiac output is the product of heart rate (HR) and stroke volume (SV). Heart rate is equal to beats per minute, while stroke volume is equal to volume per beat. The "beat" units cancel, and leave the cardiac output equal to volume per minute.
cardiac output = (beats/min) * (volume/beat) = volume/min.
Cardiac output is the product of heart rate (HR) and stroke volume (SV). Heart rate is equal to beats per minute, while stroke volume is equal to volume per beat. The "beat" units cancel, and leave the cardiac output equal to volume per minute.
cardiac output = (beats/min) * (volume/beat) = volume/min.
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Which of the following may occur if the mitral valve were to undergo ischemic damage?
Which of the following may occur if the mitral valve were to undergo ischemic damage?
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The mitral (or bicuspid) valve is the atrioventricular valve that is located between the left atrium and left ventricle. Filling of the left ventricle requires that the valve stay open so that blood can enter into the ventricle from the left atrium. With ischemic damage to the valve, abnormal flow between the left atrium and ventricle will occur.
The aortic valve is located between the left ventricle and the aorta. The tricuspid valve separates the right atrium and right ventricle. The pulmonic valve is located between the right ventricle and pulmonary artery.
The mitral (or bicuspid) valve is the atrioventricular valve that is located between the left atrium and left ventricle. Filling of the left ventricle requires that the valve stay open so that blood can enter into the ventricle from the left atrium. With ischemic damage to the valve, abnormal flow between the left atrium and ventricle will occur.
The aortic valve is located between the left ventricle and the aorta. The tricuspid valve separates the right atrium and right ventricle. The pulmonic valve is located between the right ventricle and pulmonary artery.
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Cardiac muscle cells are electrically linked to each other through which of the following?
Cardiac muscle cells are electrically linked to each other through which of the following?
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Electrical coupling of cells is mediated through gap junctions—ions are able to immediately flow through adjacent cells through these transmembrane protein channels. Cardiac muscle requires such syncytial connections in order to most effectivey synchronize muscle contraction.
Neurotransmitters, synaptic junctions, and cholinergic receptors would necessitate a nervous system communication, but the heart is electrically-coupled without neural mediation. Pressure receptors are not involved in cardiac muscle activity.
Electrical coupling of cells is mediated through gap junctions—ions are able to immediately flow through adjacent cells through these transmembrane protein channels. Cardiac muscle requires such syncytial connections in order to most effectivey synchronize muscle contraction.
Neurotransmitters, synaptic junctions, and cholinergic receptors would necessitate a nervous system communication, but the heart is electrically-coupled without neural mediation. Pressure receptors are not involved in cardiac muscle activity.
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What are the valves between the right atrium and right ventricle, and between the left atrium and left ventricle, respectively?
What are the valves between the right atrium and right ventricle, and between the left atrium and left ventricle, respectively?
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The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.
The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.
The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.
The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.
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