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Questions and Answers
What mechanism primarily allows the cardiac muscle cells to act as a functional syncytium?
What mechanism primarily allows the cardiac muscle cells to act as a functional syncytium?
Which of the following statements accurately describes the heart's pacemaker activity?
Which of the following statements accurately describes the heart's pacemaker activity?
During the cardiac cycle, which phase lasts the longest?
During the cardiac cycle, which phase lasts the longest?
What is the heart rate that the atrioventricular node can typically achieve if the Sino-atrial node fails?
What is the heart rate that the atrioventricular node can typically achieve if the Sino-atrial node fails?
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Which cardiac property refers to the heart's ability to contract after responding to an electrical impulse?
Which cardiac property refers to the heart's ability to contract after responding to an electrical impulse?
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What is the relationship between coronary blood flow and diastolic blood pressure?
What is the relationship between coronary blood flow and diastolic blood pressure?
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Which mechanism can lead to acute coronary occlusion?
Which mechanism can lead to acute coronary occlusion?
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What characterizes the condition of myocardial infarction?
What characterizes the condition of myocardial infarction?
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In most individuals with progressive coronary arterial vasoconstriction, which symptom is most likely to occur?
In most individuals with progressive coronary arterial vasoconstriction, which symptom is most likely to occur?
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What occurs within seconds after a sudden occlusion in a large coronary artery?
What occurs within seconds after a sudden occlusion in a large coronary artery?
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What is the main effect of parasympathetic stimulation on the sinoatrial (SA) node?
What is the main effect of parasympathetic stimulation on the sinoatrial (SA) node?
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Which structure acts as the primary pacemaker of the heart?
Which structure acts as the primary pacemaker of the heart?
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Which of the following correctly describes the role of baroreceptors?
Which of the following correctly describes the role of baroreceptors?
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What ultimately occurs during 'ventricular escape'?
What ultimately occurs during 'ventricular escape'?
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In the context of heart rate regulation, what characterizes bradycardia?
In the context of heart rate regulation, what characterizes bradycardia?
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What happens to cardiac output (COP) when heart rate increases while stroke volume remains constant?
What happens to cardiac output (COP) when heart rate increases while stroke volume remains constant?
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Which factor does NOT directly influence venous return?
Which factor does NOT directly influence venous return?
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What is the most likely effect of elevated thyroid hormone levels on heart activity?
What is the most likely effect of elevated thyroid hormone levels on heart activity?
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Which nerve primarily supplies the A-V node with parasympathetic innervation?
Which nerve primarily supplies the A-V node with parasympathetic innervation?
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How does a marked decrease in heart rate, such as in complete heart block, affect cardiac output?
How does a marked decrease in heart rate, such as in complete heart block, affect cardiac output?
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Which of the following increases coronary blood flow during muscular exercise?
Which of the following increases coronary blood flow during muscular exercise?
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What is a direct consequence of hypoxia on cardiovascular function?
What is a direct consequence of hypoxia on cardiovascular function?
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What is the primary effect of increasing arterial blood pressure on cardiac output?
What is the primary effect of increasing arterial blood pressure on cardiac output?
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Which condition can lead to decreased cardiac output due to poor myocardial function?
Which condition can lead to decreased cardiac output due to poor myocardial function?
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What is the resting value for stroke volume in milliliters per beat?
What is the resting value for stroke volume in milliliters per beat?
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During which phase of the heart cycle does maximal coronary blood flow occur?
During which phase of the heart cycle does maximal coronary blood flow occur?
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What primarily influences the resistance to blood flow in blood vessels?
What primarily influences the resistance to blood flow in blood vessels?
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How does vessel radius affect blood flow and resistance?
How does vessel radius affect blood flow and resistance?
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What is the relationship between pressure difference and blood flow through a vascular bed?
What is the relationship between pressure difference and blood flow through a vascular bed?
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Which of the following factors does NOT affect vascular resistance?
Which of the following factors does NOT affect vascular resistance?
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What is the main site of peripheral resistance in the circulatory system?
What is the main site of peripheral resistance in the circulatory system?
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What significantly contributes to blood viscosity?
What significantly contributes to blood viscosity?
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What effect does increased vascular resistance have on upstream and downstream pressures?
What effect does increased vascular resistance have on upstream and downstream pressures?
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Which statement correctly describes the factors influencing vascular resistance?
Which statement correctly describes the factors influencing vascular resistance?
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What does systolic blood pressure measure?
What does systolic blood pressure measure?
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How is pulse pressure calculated?
How is pulse pressure calculated?
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Which factor primarily affects diastolic blood pressure when increased?
Which factor primarily affects diastolic blood pressure when increased?
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What is the typical normal range for average systolic arterial pressure?
What is the typical normal range for average systolic arterial pressure?
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Which of the following is NOT a determinant of peripheral resistance?
Which of the following is NOT a determinant of peripheral resistance?
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Mean arterial blood pressure is considered a better indicator of perfusion to vital organs than systolic blood pressure because:
Mean arterial blood pressure is considered a better indicator of perfusion to vital organs than systolic blood pressure because:
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The average normal diastolic arterial pressure typically ranges from:
The average normal diastolic arterial pressure typically ranges from:
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What is a characteristic of mean arterial blood pressure?
What is a characteristic of mean arterial blood pressure?
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Study Notes
Cardiovascular System
- The heart is a myogenic organ; it does not need nerve stimulation to initiate its contraction.
- The heartbeat originates in the Sino-atrial node (SA node). Specialized cells spontaneously discharge at a frequency of 60-100 per minute (automaticity or rhythmicity).
- The SA node is the normal cardiac pacemaker. Its discharge rate determines the heart rate (HR).
Cardiac Cycle
- The cardiac cycle is comprised of systole and diastole.
- Normal cardiac cycle duration is 0.8 seconds (for a heart rate of 60/75 bpm).
- Atrial systole is 0.1 seconds.
- Ventricular systole is 0.3 seconds.
- Diastole of the whole heart is 0.5 seconds.
Cardiac Muscle Properties
- Automaticity: The ability to spontaneously generate an electrical impulse.
- Excitability: The ability to respond to an electrical impulse.
- Conductivity: Transmission of electrical impulses between cardiac cells.
- Contractility: Ability to contract after receiving an electrical impulse.
Cardiac Automaticity (Rhythmicity)
- Cardiac muscle beats at regular intervals due to pacemaker cells spontaneously depolarizing and generating an action potential.
- The coordinated activation of the cardiac muscle cells is achieved by the conduction of action potentials through gap junctions.
- The heart's cells form a functional syncytium, acting as a single, synchronous unit.
Sinoatrial Node (SAN)
- The SAN is the heart's primary pacemaker.
- The SAN initiates depolarization, setting the rhythm for the entire heart.
- Normal sinus rhythm (NSR): Sinus node discharge rate of 100 beats per minute (bpm).
- Atrioventricular node (AVN): 60 bpm.
- Atria: 45 bpm.
- Ventricles (idioventricular rhythm): 25-40 bpm.
Conductivity
- Conductivity is the ability of cardiac muscle to transmit cardiac impulses originated in the SAN to all parts of the heart.
- Cardiac cells are electrically coupled via gap junctions.
- The excitation of one cell propagates the action potential throughout the entire heart.
Specialized Excitatory and Conductive System of the Heart
- Sinoatrial (SA) node
- Internodal pathway
- Atrioventricular (AV) node
- Atrioventricular bundle (Bundle of His)
- Purkinje fibers
Conduction Rate
| Tissue | Conduction Rate (m/s) |
|---|---|
| SA node | 0.05 |
| Atrial pathways | 1 |
| AV node | 0.05 |
| Bundle of His | 1 |
| Purkinje system | 4 |
| Ventricular muscle | 1 |
Control of Heart Rhythmicity and Conduction
- The heart receives input from both sympathetic and parasympathetic nerves.
- Parasympathetic nerves (vagus nerves) primarily affect the SA and AV nodes.
- Sympathetic nerves affect all parts of the heart, with a stronger influence on the ventricles.
Sympathetic Stimulation
- Increases the heart rate of the SA node.
- Increases the transmission of impulses to the AV node.
- Increases the force of contraction.
Parasympathetic Stimulation
- Decreases the heart rate of the SA node.
- Decreases the transmission of impulses to the AV node.
- Stops rhythmical excitation by the SA node.
- Blocks transmission of cardiac impulses from atria to ventricles.
- Might cause ventricular escape.
Heart Rate Regulation
- Normal heart rate: 60-90 beats per minute.
- Tachycardia: Increased heart rate.
- Bradycardia: Decreased heart rate.
Nervous Regulation (Baroreceptors)
- Baroreceptors are stretch receptors in the carotid sinus and aortic arch.
- They're stimulated by changes in blood pressure (60-180 mmHg).
- Increased blood pressure leads to vasodilation of veins and arterioles, decreased heart rate, and decreased strength of heart contraction.
- Low blood pressure has the opposite effects, reflexly increasing pressure.
Nervous Regulation (Peripheral Chemoreceptors)
- Peripheral chemoreceptors are located in the aortic and carotid bodies.
- Hypoxia, increased CO2, and increased H+ concentrations stimulate them.
- This stimulation leads to increased heart rate (tachycardia), vasoconstriction (systemic VC), and hyperventilation.
Atrial Stretch Receptors (Bainbridge Reflex)
- Atrial stretch receptors (Bainbridge reflex) prevent blood stasis in the venous system.
- Increased venous return stretches the atria, initiating a reflex that increases heart rate.
Impulses from Higher Centers (Cerebral Cortex and Hypothalamus)
- Visual and auditory stimuli can affect heart rate.
- Hypothalamus plays crucial role in modulating sympathetic and parasympathetic activity.
Chemical Regulation (Blood Gas Changes)
- Changes in blood gases (hypoxia, high CO2, and high H+) directly affect the heart rate.
- Peripheral chemoreceptors also play a role in responding to the aforementioned changes.
Chemical Regulation (Hormones)
- Adrenaline and noradrenaline increase heart rate through beta-adrenergic receptors.
- Thyroid hormone increases heart rate by directly stimulating the SA node and increasing metabolic rate.
Physical Regulation (Temperature)
- Increased body temperature increases heart rate by directly affecting the SA node.
- The hypothalamus and Cardiovascular Centers (CVCs) also exhibit a significant influence.
Cardiac Output (COP)
- Cardiac output is the volume of blood pumped by each ventricle per unit time (rest).
- Normal COP is 5-6 L/min.
- COP = Stroke Volume x Heart Rate
- Stroke Volume is the volume of blood pumped per beat (resting = 70 ml/ beat).
Factors Affecting COP
- Venous Return: The volume of venous blood returning to the right atrium.
- Factors affecting venous return include rate of tissue metabolism, thoracic and muscle pumps, arteriolar diameter, capillary tone, gravity, and venous pressure gradients.
Factors Affecting COP (HR)
- Increased heart rate (within limits, not exceeding 200 beats/minute) leads to increased COP.
- During exercise, an increased venous return will increase stroke volume and cardiac output for better perfusion.
Factors Affecting COP (Severe HR Changes)
- Markedly increased heart rate can lead to decreased cardiac output due to shortened diastolic filling time, resulting in reduced stroke volume.
- Conversely, a marked decrease in heart rate due to complete heart block may lead to low ventricular pumping power and decreased cardiac output due to prolonged diastole.
Arterial Blood Pressure
- Increased arterial blood pressure (ABP) transiently decreases cardiac output.
- The healthy heart can pump up to 30L/min.
Coronary Circulation
- Normal coronary blood flow at rest: 225 ml/min.
- During severe muscular exercise, coronary blood flow increases significantly to 1000 ml/min.
- Maximal coronary blood flow occurs during heart's diastole.
Factors Controlling Coronary Blood Flow
- Oxygen need (Hypoxia): The most powerful coronary vasodilator.
- Metabolic factors (waste products like CO2, hydrogen ions, potassium ions, lactic acid): Dilate coronary vessels.
- Cardiac output (COP) and arterial blood pressure (ABP): Directly proportional to coronary blood flow.
- Nervous control: Sympathetic nerves dilate, while parasympathetic nerves constrict coronary vessels.
Ischemic Heart Disease
- Reduced coronary blood flow.
- Atherosclerosis is a major cause of compromised blood flow. Plaques commonly develop in the first few centimeters of major coronary arteries.
Acute Coronary Occlusion
- Acute occlusion of a coronary artery can result from a thrombus (blood clot) formation or from local vascular spasm.
- Sudden occlusion triggers collateral dilation to improve blood flow. If the resulting infarction is not massive, recovery is possible.
Myocardial Infarction
- Myocardial infarction occurs when insufficient blood flow leads to damaged or dead cardiac muscle cells in the area beyond the occlusion.
Angina Pectoris
- Angina pectoris is chronic chest pain caused by progressive coronary artery vasoconstriction.
- Pain is typically felt beneath the sternum and is sometimes referred to the left arm, left shoulder, neck, and jaw.
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Description
Test your knowledge on the cardiovascular system, focusing on the heart's anatomy, the cardiac cycle, and the properties of cardiac muscle. This quiz covers key concepts such as the SA node, heart rate, and the phases of the cardiac cycle. Perfect for students studying anatomy or physiology.
