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Questions and Answers
What is the formula for calculating stroke volume?
What is the formula for calculating stroke volume?
During rest, what is the approximate end diastolic volume (EDV) in milliliters?
During rest, what is the approximate end diastolic volume (EDV) in milliliters?
Which factor is primarily responsible for increasing venous return during physical activity?
Which factor is primarily responsible for increasing venous return during physical activity?
What is the typical cardiac output during mild exercise?
What is the typical cardiac output during mild exercise?
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What does the P wave specifically represent in an ECG?
What does the P wave specifically represent in an ECG?
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What happens to stroke volume when the heart fills with more blood, according to the preload concept?
What happens to stroke volume when the heart fills with more blood, according to the preload concept?
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What does a prolonged PR interval indicate?
What does a prolonged PR interval indicate?
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Where does ventricular contraction begin in relation to the QRS complex?
Where does ventricular contraction begin in relation to the QRS complex?
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What is the purpose of the PR segment in an ECG?
What is the purpose of the PR segment in an ECG?
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Which part of the ECG represents the depolarization of the ventricular muscle?
Which part of the ECG represents the depolarization of the ventricular muscle?
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What is the main factor that alters the rate of ion movement across the cell membrane?
What is the main factor that alters the rate of ion movement across the cell membrane?
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Which ions primarily contribute to the membrane potential?
Which ions primarily contribute to the membrane potential?
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What happens to the transmembrane potential (TMP) when there is a net movement of positive ions into a cell?
What happens to the transmembrane potential (TMP) when there is a net movement of positive ions into a cell?
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What type of ion channels are specifically permeable to a single type of ion?
What type of ion channels are specifically permeable to a single type of ion?
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What is required for a voltage-sensitive ion channel to be in an open configuration?
What is required for a voltage-sensitive ion channel to be in an open configuration?
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Which of the following processes helps maintain ionic concentration gradients across the cell membrane?
Which of the following processes helps maintain ionic concentration gradients across the cell membrane?
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What is the electrical potential difference across a cell membrane called?
What is the electrical potential difference across a cell membrane called?
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What drives ions across cell membranes according to both chemical and electrical potentials?
What drives ions across cell membranes according to both chemical and electrical potentials?
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What does afterload refer to in the context of heart function?
What does afterload refer to in the context of heart function?
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How does the Frank-Starling mechanism affect heart contractions?
How does the Frank-Starling mechanism affect heart contractions?
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What physiological effect does increased stretch of ventricular muscle have?
What physiological effect does increased stretch of ventricular muscle have?
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What role do inotropic agents like adrenalin play in heart function?
What role do inotropic agents like adrenalin play in heart function?
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According to the length-tension relationship, what is necessary for achieving maximum contraction?
According to the length-tension relationship, what is necessary for achieving maximum contraction?
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What role does the autonomic nervous system play in cardiac function?
What role does the autonomic nervous system play in cardiac function?
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What effect does sympathetic stimulation have on the sinoatrial (SA) node?
What effect does sympathetic stimulation have on the sinoatrial (SA) node?
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Which neurotransmitter is primarily involved in the positive chronotropic effect on the heart?
Which neurotransmitter is primarily involved in the positive chronotropic effect on the heart?
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In cardiovascular disease states, what typically happens to parasympathetic activity?
In cardiovascular disease states, what typically happens to parasympathetic activity?
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What characteristic of heart function allows adaptation to changes in venous return?
What characteristic of heart function allows adaptation to changes in venous return?
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Which receptors are activated by norepinephrine in the SA node to increase heart rate?
Which receptors are activated by norepinephrine in the SA node to increase heart rate?
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Which of the following correctly describes chronotropic effects?
Which of the following correctly describes chronotropic effects?
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How does the autonomic nervous system contribute to the balance of output between the right and left sides of the heart?
How does the autonomic nervous system contribute to the balance of output between the right and left sides of the heart?
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What effect does vasoconstriction have on blood vessels?
What effect does vasoconstriction have on blood vessels?
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Which of the following factors is primarily responsible for vasodilation?
Which of the following factors is primarily responsible for vasodilation?
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According to Poiseuille’s law, how does the radius of the arterioles affect blood flow?
According to Poiseuille’s law, how does the radius of the arterioles affect blood flow?
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What is the primary role of arterioles in the circulatory system?
What is the primary role of arterioles in the circulatory system?
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Which of the following statements about arterial blood pressure is true?
Which of the following statements about arterial blood pressure is true?
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What happens to resistance in blood vessels during vasodilation?
What happens to resistance in blood vessels during vasodilation?
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What primarily causes the increase in arterial pressure with advancing age?
What primarily causes the increase in arterial pressure with advancing age?
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What effect does sympathetic nerve activity have on blood vessels?
What effect does sympathetic nerve activity have on blood vessels?
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Study Notes
Cardiac Physiology
- The heart is a dual pump within one organ, with each side having an atrium and ventricle.
- The heart pumps blood from low-pressure veins to high-pressure arteries
- The right ventricle's output enters the pulmonary artery.
- The left ventricle's output enters the aorta.
- Cardiac output is controlled intrinsically but can be influenced extrinsically by autonomic nerves and circulating hormones.
Cardiovascular System
- Blood pressure in the pulmonary circuit is approximately 28/8 mmHg.
- Blood pressure in the systemic circuit is approximately 120/80 mmHg.
Heart Valves and Circulation of Blood
- Bicuspid valve cusps open and close to regulate blood flow.
- Chordae tendineae, which support the cusps, become taut during valve closure.
- Papillary muscles contract, maintaining tension on the chordae. This prevents valve inversion.
Duration of Atrial and Ventricular Diastole and Systole
- The atria contract for 0.1-0.3 seconds before ventricle contraction.
- The ventricles contract before relaxing.
Cardiac Cycle
- The cardiac cycle describes a coordinated sequence of electrical and mechanical events from one heartbeat to the next.
- A single cycle includes complete relaxation and contraction of both atria and ventricles.
- Relaxation phase is diastole, contraction phase is systole.
- Pressure and volume changes within the heart are driven by conductive electrochemical changes in the myocardium leading to cardiac muscle contraction.
- Heart valves direct blood flow within the heart's chambers.
Heart Failure
- Heart failure is defined as the heart's inability to pump blood at the required rate for metabolizing tissues, possibly needing elevated filling pressure.
- In adults, left ventricular inability to fill (diastolic performance) or eject blood (systolic performance) frequently results in heart failure.
Conduction System of the Heart
- The Sinoatrial (SA) node, located in the right atrium is the heart's natural pacemaker.
- Impulses travel through the atria via internodal pathways, causing atrial contraction.
- The atrioventricular (AV) node coordinates and delays the transmission of impulses to the ventricles.
- The impulse propagates through the ventricles through specialised conduction pathways including the AV bundle (bundle of His), and the right and left bundle branches via purkinje fibers, leading to ventricular contraction.
Sequence of Depolarization in Cardiac Tissue
- Depolarization sequence starts with the SA node, moves through the atria and then the AV bundle, and spreads throughout the ventricles.
Phases of the Cardiac Cycle
- Atrial systole: Atria contract, forcing blood into ventricles. Mitral valve closes
- Ventricular systole (first phase): Ventricles contract, closing the AV valves.
- Ventricular systole (second phase): Semilunar valves open, blood ejected
- Ventricular diastole (early): Semilunar valves close, blood flows into atria
- Ventricular diastole (late): Chambers relax, blood passively fills ventricles.
Cardiac Tissue Physiology
- Cardiac tissue has distinct electrical characteristics.
- Intercalated discs allow action potentials to pass to adjacent cells.
- Myocardial cells are spontaneously depolarized, a property known as automaticity.
- Spontaneous depolarization generates a pacemaker potential.
- Cardiac muscle forms a syncytium, composed of two syncytiums (atrial and ventricular) separated by fibrous tissue. The fibrous tissue electrically isolates the atria from ventricles.
The Action Potential
- Cardiac action potentials are associated with changes in cell membrane permeability, primarily due to Na+, K+, and Ca++ ions.
- Changes in permeability alter membrane voltage, facilitated by ion channel opening/closing.
Pacemaker Potentials
- Pacemaker cells have a unique, slow drift in membrane potential, that leads to spontaneous depolarization.
- The gradual depolarization is driven by 'funny' channels, T- type 'transient' Ca2+ channels, and L-type voltage-gated Ca2+ channels.
- Repolarization is mainly due to K+ efflux.
Calcium-Induced Calcium Release
- A rapid increase in calcium influx initially triggers a massive release of calcium from sarcoplasmic reticulum, causing a contraction.
- The influx of calcium through L-type Ca2+ channels is insufficient to trigger contraction. It’s amplified and leads to greater release of Ca2+ from sarcoplasmic reticulum which is called calcium-induced calcium release (CICR).
Electrocardiogram (ECG or EKG)
- An ECG is an electrical trace that records action potentials in the heart muscle.
- The shape and duration of the different ECG waves (P, QRS, and T waves) indicate events in the cardiac cycle, including depolarization and repolarization of different parts of the heart.
- The PR segment and interval show conduction time through the AV node, indicating any potential AV block.
Electrical Vectors
- Action potentials, creating small depolarizing waves in the myocardium, generate electrical vectors or impulses.
- Depolarization's average direction through the myocardium represents the main electrical vector.
- ECG represents the average electrical vectors during the cardiac cycle.
Cardiac Volumes and Output
- End-diastolic volume (EDV): Blood volume in ventricles at diastole's end (~130ml)
- End-systolic volume (ESV): Blood volume in ventricles at systole's end (~60ml)
- Stroke volume (SV): Volume of blood ejected from ventricles per beat (SV = EDV - ESV)
- Cardiac output (CO): Total blood volume ejected from ventricles per minute. (CO = SV × HR)
Regulation of Stroke Volume
- Preload: Extent of heart muscle stretch during filling (related to EDV).
- Afterload: Resistance against which the heart pumps.
- Contractility: Ability of heart muscle to contract forcefully given its preload.
Frank-Starling Mechanism
- The heart's contractility is directly related to its preload.
- Increased blood returning to the heart (increased end-diastolic volume) stretches the cardiac muscle fibers, leading to increased force of contraction and increased stroke volume.
Physiological Basis of Starling's Law
- Increased stretch of ventricular muscle results in greater overlap of actin and myosin filaments, increasing available cross-bridges.
- Optimal sarcomere length correlates with maximum contraction.
- Increased stretch enhances sensitivity of contractile proteins to calcium, resulting in more forceful contraction.
- Intracellular calcium required to generate 50% maximum tension is lower when muscle fiber is stretched.
Neural Control of the Heart Rate
- Sympathetic and parasympathetic nervous systems oppose each other to regulate cardiac function.
- Sympathetic stimulation increases heart rate, contractility and conduction velocity
Systemic hypertension
- Essential hypertension typically involves sustained elevations in peripheral vascular resistance without significant changes in cardiac output.
- Secondary hypertension is associated with an underlying cause; often kidney diseases or endocrine disorders.
Mechanisms of Hypertension and Related Factors
- Hypertension can result from mechanisms involving elevated cardiac output, elevated peripheral vascular resistance, or changes in blood volume.
- Age, salt intake, lifestyle factors, genetics, and kidney disease are relevant risk factors.
Atherosclerosis and the Response to Injury Hypothesis
- Atherosclerosis involves injury to the vascular endothelium, triggering a response.
- A variety of injurious agents can trigger this inflammation in which leucocytes, primarily monocytes migrate to the injury, initiating a cascade of events leading to atherosclerosis and its associated complications.
- Oxidized lipoproteins lead to fatty streaks in the vascular walls (early atherosclerosis) that progress to more complex atherosclerotic lesions.
Determinants of Vascular Resistance
- Viscosity, length, and radius of the blood vessels impact vascular resistance (r⁴).
Effects Of Hypertension
- Damage to capillaries in the eyes (loss of vision).
- Damage to kidney blood vessels (renal failure).
- Stroke.
- Oedema.
- Left ventricular hypertrophy leads to heart failure
The Arterioles
- Arterioles control blood flow to individual organs and tissues through changes in their diameter.
- Vasoconstriction (narrowing) and vasodilation (widening) of arterioles regulate blood flow distribution in response to various physiological signals.
- Changes in arteriole diameter primarily regulate blood flow to specific tissues and organs.
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Description
Test your knowledge on cardiovascular physiology with this quiz focusing on stroke volume, cardiac output, and ECG interpretation. Covering key concepts such as end diastolic volume and the implications of the P wave, this quiz assesses understanding of how the heart functions during exercise and at rest.
