Physiology Flashcards
Q: What is the approximate weight of the heart?
A: The heart weighs approximately 200-300 grams.
Q: Where is the base of the heart located?
A: The base of the heart is located on the superior surface, pointing towards the right shoulder.
Q: Where is the apex of the heart located?
A: The apex of the heart is located on the inferior surface, pointing to the left hip.
Q: In which part of the thoracic cavity is the heart located?
A: The heart is located in the middle mediastinum, covered by a pericardial covering.
Q: What structures are anterior to the heart?
A: The sternum and costal cartilage are anterior to the heart.
Q: What structures are posterior to the heart? 4
A:
1. The vertebral column from (T5-T8),
2. esophagus, and
3. carina of trachea and
4. primary bronchi are posterior to the heart.
Q: Which tissues make up the endocardium?
A: The endocardium is composed of simple squamous epithelial tissue with areolar connective tissue.
Q: What is the function of the endocardium? 3
A:
1. The endocardium keeps blood in the heart,
2. prevents clotting, releases PGI2 and Nitric oxide to inhibit platelet activation and aggregation, and
3. acts as a barrier between blood and tissue.
Q: Which layer of the heart contains contractile cardiac muscle?
A: The myocardium contains contractile cardiac muscle.
Q: What is the role of non-contractile cardiac muscle in the heart?
A: Non-contractile cardiac muscle generates and conducts action potentials.
Q: What is the visceral layer of serous pericardium also known as?
A: The visceral layer of serous pericardium is also called epicardium.
Q: What is the function of the pericardial cavity?
A: The pericardial cavity contains serous fluid, which lubricates the tissue layers and prevents friction between the two serous layers.
Q: Where else is the endothelium of the endocardium found?
A: The endothelium of the endocardium continues as the endothelium in blood vessels.
Q: What lines the outer layer of the valves in the heart?
A: The endocardium lines the outer layer of the valves in the heart.
Q: Name the components of the non-contractile cardiac muscle.
A: The non-contractile cardiac muscle includes the
*
- SA node,
- AV node,
- bundle of His,
- bundle branches (right and left), and
- Purkinje fibers.
Q: What substances are secreted by the contractile cardiac muscle when stretched, and what is their effect?
A: When stretched, contractile cardiac muscle secretes
1. atrial natriuretic peptide (ANP) and
2. brain natriuretic peptide (BNP).
- These peptides increase sodium and water excretion,
- dilate blood vessels,
- decrease blood volume, and
- decrease stretch of the myocardium.
Q: What does the visceral layer of serous pericardium secrete, and what is the purpose of this secretion?
A: The visceral layer of serous pericardium secretes pericardial serous fluid into the cavity. This fluid lubricates the tissue layers, reducing friction between them.
Q: Under normal physiologic conditions, is there blood in the pericardial cavity?
A: Under normal physiologic conditions, there is usually no blood in the pericardial cavity.
Q: What condition can occur when there is less fluid in the pericardial cavity, and what are the associated symptoms?
A: When there is less fluid in the pericardial cavity, pericarditis can occur.
Symptoms may include severe stabbing pain due to increased friction between the serous layers.
Q: What is the composition and function of the parietal layer of serous pericardium?
A:
The parietal layer of serous pericardium is continuous with the epicardium and consists of
1. mesothelium (simple squamous epithelium) with loose areolar connective tissue.
2. It secretes pericardial serous fluid into the cavity to lubricate the tissue layers.
Q: Describe the composition and function of the fibrous pericardium.
A:
* The fibrous pericardium is made of dense fibrous irregular connective tissue.
* Its functions include
1. anchoring the heart to surrounding structures,
2. preventing the heart from overfilling with blood due to its non-distensible nature, and
3. protecting the heart due to its tough tissue.
Q: What vessels deliver deoxygenated blood to the right atrium? 3
A:
1. The superior vena cava brings blood from structures above the diaphragm (e.g., head, neck, and arms),
2. the inferior vena cava brings blood from structures below the diaphragm (e.g., abdomen and liver), and
3. the coronary sinus brings blood from the coronary circulation.
Q: What is the role of the fossa ovalis in the right atrium?
A:
* The fossa ovalis is a scar tissue remnant of the foramen ovale, a hole between the RA and LA in the embryo.
- It closes up at birth to prevent blood from moving from the RA to the RV and into the pulmonary circulation.
Q: Where does the left atrium receive oxygenated blood from?
A:
- The left atrium receives oxygenated blood from the four pulmonary veins:
- two from the left lung and two from the right lung.
Q: What purpose do the auricles serve in the atrial chambers?
A: The auricles (atrial appendages) increase the space and volume of the atria.
Q: What purpose do the auricles serve in the atrial chambers?
A: The auricles (atrial appendages) increase the space and volume of the atria.
Q: What is the clinical relevance of thrombi formation in the left and right auricles during atrial fibrillation?
A:
* Thrombi (blood clots) commonly form in the left atrial appendage during atrial fibrillation, while
- thrombi formation is less common in the right atrial appendage.
Q: What is the clinical correlate of a ventricular septal defect?
A: A ventricular septal defect is the most common type of heart defect and causes mixing of blood between the RV and LV.
Q: Describe the structure of the heart valves.
A:
- The valves have four annulus rings of fibrous tissue from which leaflets hang.
- The leaflets consist of an endothelial layer, zona spongiosa, zona fibrosa, and zona ventricularis/atrialis.
- Chordae tendineae anchor the leaflets to papillary muscles, preventing them from ballooning back into the atrium and causing blood backflow.
Q: What is the function of the heart valves? 2
A:
1. The heart valves ensure a one-way flow of blood and prevent backflow.
2. They are also anchored to the cardiac skeleton and act as electrical insulators between the atria and ventricles, ensuring all electrical signals go through the atrioventricular (AV) node.
Q: How many leaflets does the tricuspid valve have?
A: The tricuspid valve contains three leaflets.
Q: How many leaflets does the bicuspid/mitral valve have?
A: The bicuspid/mitral valve contains two leaflets.
Q: What are the two coronary arteries and where do they originate from?
A:
- The two coronary arteries are the left coronary artery (LCA) and the right coronary artery (RCA).
- They arise from the aorta just beyond the semilunar valves.
Q: What is the function of the coronary arteries?
A:
The coronary arteries supply oxygenated blood to the myocardium (musculature of the heart) during diastole when the increased aortic pressure above the semilunar valves forces blood into the coronary arteries.
Q: What is the function of non-contractile myocardial cells in the heart?
A:
- Non-contractile myocardial cells, such as the SA node, AV node, bundle of His, bundle branches, and Purkinje fibers,
- are responsible for generating and conducting action potentials.
- They stimulate contractile myocardial cells, causing them to contract.
: What are the “funny” Na+ channels (If channels) and their role?
A:
- The “funny” Na+ channels (If channels) are open when the cell is at rest.
- They allow a slow movement of Na+ into the cell, making the inside of the cell more positive.
- This gradual increase in positive charge moves the resting membrane potential from -60mV to -55mV, which stimulates further depolarization.
Q: What are T-type calcium channels and their role in depolarization?
A:
- T-type calcium channels open at -55mV.
- They allow calcium to move into the cell, further increasing the positive charge inside the cell.
- This moves the voltage from -55mV to -40mV, which is the threshold voltage to stimulate L-type calcium channels.
Q: What are L-type calcium channels and their role in depolarization?
A:
- L-type calcium channels open at -40mV.
- They allow an explosive influx of calcium ions into the cell, significantly increasing the positive charge.
- This moves the voltage from -40mV to +40mV, leading to depolarization of the nodal cell.
: How does depolarization spread from nodal cells to adjacent contractile myocardial cells?
A:
through intercalated discs.
- These discs contain gap junctions, which are channel proteins (connexin proteins) allowing ions, including calcium, to move from the depolarized nodal cell into the adjacent contractile myocardial cell.
Q: What happens when voltage-gated Na+ channels open in contractile myocardial cells?
A:
- When voltage-gated Na+ channels open in contractile myocardial cells at the threshold voltage of -70mV,
- Na+ rushes into the cells, causing the inside of the cell to become highly positive.
- The voltage inside the cell goes from -70mV to +10mV.
Q: How does calcium contribute to muscle contraction in contractile myocardial cells?
A:
- L-type Ca++ channels on contractile myocardial cells are activated by the voltage-gated Na+ channels, causing calcium to rush into the cell.
- This calcium activates proteins on the sarcoplasmic reticulum, leading to the release of more calcium into the cytoplasm of the muscle cell.
- The rise in intracellular calcium triggers muscle contraction by interacting with troponin C and tropomyosin.
Q: What is the mechanism of repolarization in nodal cells?
A:
- After nodal depolarization and the entry of calcium into nearby myocardial cells via intercalated discs,
- voltage-gated K+ channels in nodal cells open at +40mV.
- This allows K+ to leave the cell, making the inside of the cell increasingly negative and preparing the nodal cell for the next stimulation.
Q: How does repolarization occur in contractile myocardial cells?
A:
- At +10mV, voltage-gated K+ channels in contractile myocardial cells open, allowing K+ to move out of the cell, which makes the inside of the cell negative.
- However, L-type Ca++ channels are still open, and calcium is entering the cell while K+ is leaving.
- This maintains the voltage at 0mV for a short period, knownas the plateau phase.
Q: What happens during the plateau phase of repolarization in contractile myocardial cells?
A:
- During the plateau phase at 0mV, the movement of K+ out of the cell is balanced by the entry of calcium, keeping the voltage plateaued.
- This phase is sustained for a brief period, contributing to the extended duration of muscle contraction.
Q: How is the voltage restored to the resting membrane potential in contractile myocardial cells?
A:
- After contraction, the L-type Ca++ channels close, and K+ continues to leave the cell while no further calcium enters.
- This causes the voltage to drop from 0mV to -90mV, which is the resting membrane potential of the contractile myocardial cell.
Q: How is calcium removed from the cytoplasm of contractile myocardial cells after contraction?
A:
- Calcium in the cell is shunted back into the sarcoplasmic reticulum (SR) or out of the cell to prevent prolonged contraction.
- This is accomplished through ATP-dependent Ca++/H+ exchange mechanisms and
- the Na+/Ca++ exchanger via secondary active transport.
Which nodal cell ensures synchronized contraction of the ventricular myocardium?
Answer: Purkinje fibers
What is the function of Purkinje fibers?
Answer: Purkinje fibers receive impulses from the bundle branches and
ensure synchronized contraction of the ventricular myocardium.
Where are the bundle branches located?
Answer: The bundle branches span along the length of the interventricular septum until the apex of the heart.
Which nodal cell reduces high-frequency impulses from traveling into the ventricles from the atria?
Answer: The Bundle of His reduces high-frequency impulses from traveling into the ventricles from the atria.
What is the function of the AV node?
Answer: The AV node receives impulses from the SA node and conducts them slowly, creating a delay to allow for sequential atrial and ventricular contraction.
What is the location of the SA node?
Answer: The SA node is located near the entrance of the superior vena cava (SVC) into the right atrium.
What is the function of the parasympathetic nervous system (PSNS) on the heart?
Answer: The PSNS decreases heart rate (chronotropy) and conduction (dromotropy), but has no direct effect on contractility.
How does the PSNS exert its effect on heart rate and conduction?
Answer: PSNS fibers
1. release acetylcholine (Ach), which binds to muscarinic type 2 receptors.
2. This activates inhibitory proteins, leading to hyperpolarization of cells,
3. decreased action potentials, and a
4. decrease in heart rate and conduction.
What is the intracellular mechanism of action of the PSNS on nodal cells?
Answer:
1. PSNS activation leads to increased K+ efflux through binding to K+ channels, hyperpolarization of cells, and decreased phosphorylation of L-type Ca++ channels.
2. This results in reduced calcium influx, decreased action potentials, and a decrease in heart rate.
What is the function of the sympathetic nervous system (SNS) on the heart?
Answer: T
he SNS increases
- heart rate (chronotropy),
- conduction (dromotropy), and
- contractility (inotropy).
How does the SNS exert its effect on heart rate and conduction?
Answer:
- The SNS releases norepinephrine (NE), which binds to beta one -adrenergic receptors.
- This increases cAMP levels, leading to enhanced phosphorylation of L-type Ca++ channels and
- increased calcium influx.
- This results in increased action potentials, heart rate, and conduction.
What are the effects of the SNS and PSNS on heart rate?
Answer: The PSNS decreases heart rate, while the SNS increases heart rate.
A heart rate below 60 bpm is called bradycardia, while a heart rate above 100 bpm is called tachycardia.
What is the intracellular mechanism of action of the sympathetic nervous system (SNS) on nodal cells?
Answer:
- SNS fibers release norepinephrine (NE) and epinephrine, which activate beta-1 adrenergic receptors.
- This leads to increased cAMP levels, phosphorylation of L-type Ca++ channels,
- increased calcium influx, depolarization rate, action potentials, heart rate, conduction, and contractility.
What is the intracellular mechanism of action of the sympathetic nervous system (SNS) on contractile cells?
Answer:
1. SNS fibers release NE and epinephrine, which activate beta-1 adrenergic receptors.
2. This increases cAMP levels, phosphorylation of phospholamban, enhanced influx of Ca++ back into the sarcoplasmic reticulum, increased speed of relaxation,
3. phosphorylation of L-type Ca++ channels, increased calcium influx in contractile cells, increased Ryr-2 activity,
4. increased Ca++ in the sarcoplasm,
5. increased interactions with troponin,
6. increased cross-bridge formation,
7. increased contraction rate and speed, increased heart pumping,
8. increased stroke volume (SV), and
9. increased cardiac output (CO).
What is the refractory period in cardiac action potentials?
Answer:
- The refractory period occurs during phases 3 and 4 (repolarization and resting membrane potential) of the cardiac action potential.
- It consists of an absolute refractory period and a relative refractory period, during which the heart is in a resting state and less responsive to stimuli.
What is the duration of the relative refractory period?
Answer: The relative refractory period lasts about 250 ms.
Which type of channels are phosphorylated by stimulation of the sympathetic nervous system (SNS)?
Answer: L-type Ca++ channels are phosphorylated by SNS stimulation.
Can the parasympathetic nervous system (PSNS) affect the contractility of the heart?
Answer: False. T
he PSNS has no direct effect on contractility; it primarily influences heart rate and conduction.
Does the sympathetic nervous system (SNS) have a positive chronotropic action?
Answer: True. The SNS increases heart rate (chronotropy).
Can action potentials be triggered during the relative refractory period?
Answer: True.
- Action potentials can be triggered during the relative refractory period,
- although a stronger stimulus is required compared to the absolute refractory period.
What is the duration of the average cardiac cycle?
Answer: The average cardiac cycle takes approximately 0.8 seconds.
What are the four phases of the cardiac cycle?
Answer: The four phases of the cardiac cycle are
ventricular filling,
isovolumetric contraction,
ventricular ejection, and
isovolumetric relaxation.
During which phase does ventricular filling occur?
Answer: Ventricular filling occurs during the mid to late ventricular diastole (relaxation) phase.
How does blood passively flow from the atria into the ventricles during ventricular filling?
Answer: Without contraction, 70-80% of the blood passively flows down from the atria into the ventricles due to gravity.
What happens during the reduced filling phase of ventricular diastole?
Answer: During the reduced filling phase,
- the SA node fires, depolarizes the atria, and
- the atria contract to actively push the remaining blood down into the ventricles.
What occurs during the isovolumetric contraction phase?
Answer: The isovolumetric contraction phase is
- when the ventricles start to depolarize and contract,
- increasing ventricular pressure.
- No blood enters or leaves the ventricles during this phase.
What is the end diastolic volume?
Answer:
The end diastolic volume refers to the blood accumulated in the left ventricle before it contracts.
What causes the closure of the AV valves during isovolumetric contraction?
Answer:
The rise in ventricular pressure above atrial pressure causes the AV valves to shut close, producing the first heart sound (S1).
What happens during the mid to late ventricular systole phase?
Answer: Blood leaves the ventricles, and ventricular pressure continues to rise as the ventricles depolarize and contract more intensely.
When do the semilunar valves open during the cardiac cycle?
Answer: The semilunar valves open during the mid to late ventricular systole phase when the ventricular pressure becomes greater than the pressure in the arteries.
What occurs during the isovolumetric relaxation phase?
Answer:
- In the isovolumetric relaxation phase, no blood enters or leaves the ventricles as they relax.
- The ventricular pressure decreases, but it is still greater than the atrial pressure, keeping the semilunar valves closed.
What causes the closure of the semilunar valves during isovolumetric relaxation?
Answer:
- The arterial pressures are higher than the ventricular pressures,
- causing the semilunar valves to shut close and producing the second heart sound (S2).
What is the end-systolic volume?
Answer:
The end-systolic volume refers to the amount of blood left in the left ventricle after it contracts.
What happens to the atrial pressure compared to the ventricular pressure during isovolumetric relaxation?
Answer: The atrial pressure is lower than the ventricular pressure during isovolumetric relaxation, causing the AV valves to remain closed.
What is the significance of the T wave on the ECG during phase 4?
Answer:
The T wave on the ECG represents ventricular repolarization, indicating that the ventricles are relaxed and repolarized.
What is the formula for cardiac output?
Answer: Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV)
What factors increase heart rate?
Answer:
Factors that increase heart rate include
1. sympathetic nervous system activation,
2. hormones such as thyroid hormone,
3. exercise, increased body temperature,
4. certain drugs (e.g., epinephrine, atropine), and
5. imbalances in ions such as calcium and potassium.
How does the sympathetic nervous system increase heart rate?
Answer:
The sympathetic nervous system increases heart rate through the release of norepinephrine and epinephrine,
- which stimulate beta-1 adrenergic receptors,
- leading to increased calcium influx and depolarization rate in nodal cells.
What factors decrease heart rate?
Answer:
1. parasympathetic nervous system activation, the release of acetylcholine,
2. certain drugs (e.g., beta blockers, calcium channel blockers),
3. imbalances in ions such as calcium and potassium, and
4. decreased levels of thyroid hormone.
What is the role of the Frank-Starling mechanism in cardiac output?
Answer:
increase in ventricular preload (end-diastolic volume) leads to a more forceful contraction and increased stroke volume, thereby increasing cardiac output.
How does the parasympathetic nervous system decrease heart rate?
Answer:
- The parasympathetic nervous system decreases heart rate by releasing acetylcholine,
- which stimulates M2 receptors on nodal cells,
- leading to increased potassium efflux,
decreased cAMP levels, hyperpolarization, and - a decreased rate of action potentials.
How do imbalances in calcium and potassium affect heart rate?
Answer:
- Hypercalcemia (increased calcium levels) and
hypokalemia (decreased potassium levels) can increase heart rate, - while hypocalcemia (decreased calcium levels) and
- hyperkalemia (increased potassium levels) can decrease heart rate.
How does age and gender influence heart rate?
Answer: In general,
- fetuses/infants have a higher heart rate (120-140 bpm), while
- adults have a normal heart rate range of 60-100 bpm.
- Females tend to have slightly higher heart rates than males.
What is the definition of bradycardia?
Answer: heart rate (HR) below 60 beats per minute (bpm).
What are some causes of bradycardia?
Answer:
1. parasympathetic nervous system activation (PSNS),
2. certain drugs, and
3. endurance activities that increase preload and contractility, leading to an increased stroke volume and compensatory decrease in heart rate.
What is the definition of tachycardia?
Answer: Tachycardia is defined as a heart rate (HR) above 100 beats per minute (bpm).
What are some causes of tachycardia?
Answer:
1. sympathetic nervous system activation (SNS),
2. increased levels of thyroid hormones (T3 and T4),
3. certain drugs, and
4. anxiety.
What is stroke volume (SV)?
Answer: the total volume of blood (in milliliters) pumped out of the ventricle in one heartbeat.
What factors regulate stroke volume?
Answer: Factors that regulate stroke volume include
- end-diastolic volume (EDV),
- end-systolic volume (ESV), and
- ejection fraction (EF).
How does end-diastolic volume (EDV) affect stroke volume?
Answer:
An increase in end-diastolic volume (EDV), which is the pre-pumping volume in the ventricles, leads to an increase in stroke volume assuming normal contractility.
How does end-systolic volume (ESV) affect stroke volume?
Answer:
End-systolic volume (ESV), which is the post-pumping volume in the ventricles, is based on contractility and afterload.
- Good contractility with a constant afterload leads to a decrease in ESV and an increase in stroke volume,
- while bad contractility with increased afterload leads to an increase in ESV and a decrease in stroke volume.
What is ejection fraction (EF)?
Answer:
- Ejection fraction (EF) is the percentage of blood ejected out of the ventricles per beat.
- It is calculated by dividing stroke volume (SV) by end-diastolic volume (EDV) and multiplying by 100.
How does a decreased left ventricular ejection fraction (EF) occur?
Answer:
A decreased left ventricular ejection fraction can occur in conditions such as
- systolic heart failure, where there is a decrease in blood leaving the heart, resulting in more blood remaining after contraction,
- an increase in ESV, a decrease in stroke volume, and a decrease in EF.
What is the definition of preload?
Answer: the degree of stretch of the ventricular myocardium.
How does an increase in preload affect stroke volume?
Answer:
According to Frank Starling’s Law of the Heart,
- an increase in preload leads to an increase in cross-bridge formation and force of contraction, resulting in an increase in stroke volume (SV).
How does an increase in venous return to the heart affect preload?
Answer:
- An increase in venous return to the heart, which can be achieved through factors such as
1. increased blood volume,
2. muscular milking activity,
3. respiratory pump, and
4. venomotor tone or venoconstriction, - leads to an increase in preload.
How does lying supine affect preload?
Answer: Lying supine prevents blood from being pulled down into the lower extremities by gravity, resulting in increased preload.
How does a slower heart rate (bradycardia) affect preload?
Answer: A slower heart rate allows for increased diastolic time, which leads to increased ventricular filling and, subsequently, increased preload.
How does muscle compliance affect preload?
Answer:
- A “stretchy” myocardium with normal compliance allows for normal stretch and preload,
- while a dilated or flabby myocardium with increased stretch leads to increased preload.
How do heart valve abnormalities, such as stenosis or regurgitation, affect preload?
Answer:
- Stenosis, which reduces blood leaving the ventricles, and
- regurgitation, which increases blood backflow into the ventricles,
both lead to increased preload.
What factors decrease preload?
Answer: Factors that decrease preload include
1. decreased venous return to the heart due to decreased blood volume (hemorrhage, dehydration),
2. decreased sympathetic nervous system (SNS) activity,
3. increased vasodilation of veins,
4. expiration (removal of vacuum pressure during respiration),
5. decreased skeletal muscle contractions in the legs (immobility),
6. standing upright for long periods (gravity pulling blood into lower extremities),
7. decreased muscle compliance (damaged or hypertrophied myocardium), and
8. decreased filling time due to a faster heart rate (tachycardia).
How do mitral and tricuspid valve abnormalities, such as stenosis, affect preload?
Answer:
Mitral and tricuspid valve stenosis reduce the flow of blood into the ventricles from the atria, leading to decreased preload.
What is the definition of contractility?
Answer: Contractility refers to the strength or force of ventricular contraction.
How does an increase in contractility affect stroke volume?
Answer: An increase in contractility leads to an increase in stroke volume.
What are some factors that increase contractility?
Answer: Factors that increase contractility include
1. sympathetic nervous system activation (norepinephrine and epinephrine),
2. hormones (thyroid hormone and glucagon),
3. positive inotropic drugs (digitalis, dopamine, atropine, dobutamine, milrinone, norepinephrine, epinephrine), and
4. an increase in intracellular calcium.
What are some factors that decrease contractility?
Answer: Factors that decrease contractility include
1. beta blockers,
2. calcium channel blockers,
3. negative inotropic drugs,
4. decreased calcium levels (hypocalcemia),
5. increased potassium levels (hyperkalemia),
6. increased sodium levels (hypernatremia),
7. acidosis, and
8. . hypoxia.
What is the definition of afterload?
Answer:
the amount of resistance that the ventricles must overcome to eject blood into the aorta or pulmonary trunk.
How does an increase in afterload affect stroke volume?
Answer: An increase in afterload leads to a decrease in stroke volume.
What are some factors that increase afterload?
Answer:
Factors that
1. increase afterload include increased vascular resistance in systemic circulation (diastolic hypertension,
2. atherosclerosis, vasoconstrictive drugs) and
3. increased vascular resistance in pulmonary circulation (pulmonary hypertension, pulmonary valve stenosis).
What are some factors that decrease afterload?
Answer: Factors that decrease afterload include
- decreased vascular resistance and
2. - drugs that vasodilate vessels (
- ACE inhibitors, angiotensin II receptor blockers,
- hydralazine,
- isosorbide dinitrate,
- phosphodiesterase inhibitors).
What is the relationship between stroke volume and cardiac output?
Answer:
- Stroke volume is one of the factors determining cardiac output, which is the product of stroke volume and heart rate.
- An increase in stroke volume leads to an increase in cardiac output.