Cardiac Output and Function

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Questions and Answers

What does the PR interval reflect in cardiac physiology?

Duration of the QRS complex

Ventricular depolarization and repolarization

Total time for ventricular action

Atrial depolarization and conduction through the AV node (correct)

Which statement correctly describes cardiac myocytes?

They can function without a constant blood supply.

They primarily utilize anaerobic metabolism for energy.

They depend on oxidative metabolism and prefer to use fats. (correct)

They have significant glycogen storage.

What is the primary characteristic of heart failure?

Rapid heartbeat exceeding 100 beats per minute

Coronary artery blockage leading to pain

Impaired contractility and reduced ejection fraction (correct)

Sudden cessation of heart pump

What is the main cause of cardiac arrest?

Ventricular arrhythmias such as fibrillation or tachycardia Signup and view all the answers

Which structure brings oxygenated blood to the embryonic heart?

The umbilical vein Signup and view all the answers

Where would you listen to hear the aortic valve using a stethoscope?

2nd right intercostal space at the sternal border Signup and view all the answers

Which phase corresponds to the T wave on an ECG?

Ventricular repolarization Signup and view all the answers

What is the role of papillary muscles in the heart?

To attach to valves and prevent prolapse during contraction Signup and view all the answers

How does an increase in central blood volume affect cardiac output?

It increases cardiac output by enhancing stroke volume. Signup and view all the answers

What is the primary mechanism through which the Bainbridge reflex increases heart rate?

Inhibition of parasympathetic activity. Signup and view all the answers

Why must the cardiac output of the right and left ventricles remain equal?

To avoid pulmonary congestion and systemic hypoperfusion. Signup and view all the answers

What is the role of the SERCA pump in cardiac muscle function?

Promotes calcium reuptake into the sarcoplasmic reticulum after contraction. Signup and view all the answers

What effect does increased preload have on cardiac performance?

It enhances the force of contraction and stroke volume. Signup and view all the answers

How does fever influence cardiac output?

It increases heart rate by approximately 10 beats/min for each degree rise in temperature. Signup and view all the answers

What limits the increase in cardiac output as blood pressure rises?

Increased afterload resulting from elevated blood pressure. Signup and view all the answers

What is the consequence of a decrease in SERCA activity in cardiac myocytes?

Decreased calcium reuptake leading to potential contractile dysfunction. Signup and view all the answers

What is defined as the development of brand-new blood vessels from mesodermal cells?

Vasculogenesis Signup and view all the answers

At what stage in embryonic development does primitive circulation primarily begin to develop?

Week 3 Signup and view all the answers

Which type of vein returns poorly oxygenated blood from the umbilical vesicle?

Vitelline vein Signup and view all the answers

What is the process called when existing blood vessels 'sprout' into adjacent areas and fuse with other vessels?

Angiogenesis Signup and view all the answers

During which week does the heart tube position itself within the chest cavity due to lateral folding?

Week 4 Signup and view all the answers

What primarily develops into the muscular and connective tissue of a blood vessel?

Mesenchyme Signup and view all the answers

Which vein is responsible for carrying well-oxygenated blood from the chorion to the fetus?

Umbilical vein Signup and view all the answers

What occurs first during the process of vasculogenesis?

Cavities appear within blood islands Signup and view all the answers

What is the primary mechanism by which calcium is removed from the cytosol of myocytes?

SERCA pumps Signup and view all the answers

Which response correctly describes the impact of sympathetic nervous system stimulation on calcium handling in myocytes?

Increases cAMP which enhances calcium release Signup and view all the answers

What is the effect of phosphorylation of phospholamban on SERCA activity?

It increases SERCA activity Signup and view all the answers

Calcium sparks in a myocyte are primarily caused by what mechanism?

Calcium release from the sarcoplasmic reticulum due to calcium influx Signup and view all the answers

Which of the following best describes the role of the sodium-calcium exchanger in myocytes?

It regulates membrane potential by moving three sodium for one calcium Signup and view all the answers

What is the function of calcium-induced calcium release (CICR) in muscle contraction?

It amplifies the calcium signal to initiate contraction Signup and view all the answers

Which of the following statements about the absolute refractory period (ARP) of muscle contraction is true?

ARP ensures that no new action potentials can trigger contraction Signup and view all the answers

What role do L-type calcium channels play in the excitation-contraction coupling process?

They facilitate calcium entry into the myocyte during action potential Signup and view all the answers

What develops from the anterior cardinal veins?

Superior vena cava Signup and view all the answers

Which statement accurately describes the function of the ductus venosus?

Bypasses the liver to direct blood to the heart Signup and view all the answers

What remnant is left after the closure of the ductus venosus?

Ligamentum Venosum Signup and view all the answers

Which shunt connects the pulmonary trunk directly to the aorta?

Ductus arteriosus Signup and view all the answers

What happens to the left atrial pressure after birth?

It increases significantly. Signup and view all the answers

What is the primary clinical significance of an atrial septal defect (ASD)?

It shunts blood from left atrium to right atrium. Signup and view all the answers

What remnant is associated with the closure of the umbilical arteries?

Medial Umbilical Ligament Signup and view all the answers

Which congenital heart defect is characterized by a failure of the septum primum to seal over?

Atrial septal defect Signup and view all the answers

What is a potential consequence of severe atrial septal defect (ASD)?

Increased pulmonary blood flow by 2-4 times Signup and view all the answers

Study Notes

Cardiac Output

Cardiac output (CO) is the amount of blood pumped by the heart per minute.
It is calculated by multiplying the stroke volume (SV) by the heart rate (HR): CO = SV x HR
Increased preload (the stretch of the ventricles at the end of diastole) results in increased venous return to the heart and increased CO
Sympathetic nervous system stimulation increases CO by increasing the force of contraction (inotropy) and the heart rate (chronotropy).
CO is also influenced by afterload (the resistance the heart must overcome to eject blood), contractility, and heart rate.

Equal Cardiac Output: Right and Left Ventricles

The right and left ventricles must pump the same amount of blood per minute.
This ensures proper tissue perfusion, oxygen delivery, and prevents pulmonary congestion and systemic hypoperfusion.
Preload of one ventricle depends on the CO of the other, ensuring equal volume pumped by both.

SERCA Pump and Cardiac Function

SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase) plays a crucial role in calcium reuptake into the sarcoplasmic reticulum (SR) after a contraction.
Reduced SERCA activity would lead to decreased calcium reuptake, prolonged contraction, and potentially weakening of cardiac muscle.
This would negatively impact overall cardiac function by reducing contractility and potentially leading to heart failure.

Calcium Handling in Myocytes

Calcium influx through voltage-gated calcium channels (L-type calcium channels) and calcium-induced calcium release (CICR) from the SR triggers muscle contraction.
Calcium sparks are small calcium releases from individual ryanodine receptor channels, summing up to create the overall calcium increase in the myocyte.
Calcium sequestration occurs through SERCA (most prominent), sodium-calcium exchanger, and sarcolemma calcium ATPase.

Sympathetic Nervous System Impact on Calcium Handling

Sympathetic stimulation increases cAMP, leading to phosphorylation of several proteins:
- Phospholamban: This increases SERCA activity, boosting calcium reuptake into the SR.
- Troponin: This decreases calcium affinity, promoting faster relaxation.
- L-type calcium channels: This increases calcium entry, enhancing calcium release from the SR and promoting stronger contractions.

Cardiac Metabolism

Cardiac myocytes highly depend on oxidative metabolism and use fats as their primary energy source.
They have limited glycogen storage and rely on circulating free fatty acids (FFAs).
Minimal anaerobic metabolism capacity makes them vulnerable to oxygen deprivation, leading to "stunning" and cell death within minutes.

Terminology

Heart failure: Contractility is significantly impaired, leading to reduced ejection fraction (the percentage of blood ejected with each contraction).
Cardiac arrest: Sudden and unexpected cessation of heart function, often caused by ventricular fibrillation or ventricular tachycardia.
Angina: Pain caused by ischemia (lack of blood flow) that doesn't result in permanent heart damage.
Tachyarrhythmia: Abnormal heart rhythm with a heart rate exceeding 100 beats per minute (tachycardia).

Cardiovascular Embryology

Vasculogenesis is the development of new blood vessels directly from mesodermal cells (angioblasts).
Angiogenesis is the sprouting of existing blood vessels, formed by vasculogenesis, connecting them to each other.

Embryonic Vessels

Three paired veins drain into the heart tube of a 4-week embryo:
- Vitelline vein: Returns poorly oxygenated blood from the umbilical vesicle.
- Umbilical vein: Carries oxygenated blood from the chorion to the fetus.
- Common cardinal veins: Return poorly oxygenated blood from the body.

Fetal Circulation

The ductus arteriosus connects the pulmonary trunk to the aorta, bypassing the fetal lungs.
The foramen ovale allows blood to bypass the fetal lungs by shunting oxygenated blood from the right atrium to the left atrium.
The ductus venosus bypasses the liver, allowing oxygenated blood from the umbilical vein to directly enter the inferior vena cava.

Circulation After Birth

The closure of the umbilical arteries, veins, and the ductus venosus redirects blood flow, adapting to the newborn's pulmonary system.
The closure of the foramen ovale is driven by increased pressure in the left atrium and decreased pressure in the right atrium, redirecting oxygenated blood to the systemic circulation.

Congenital Heart Disease

Congenital heart disease affects about 1% of live births, requiring various interventions depending on the severity.
Atrial septal defects (ASDs) are common, with most being septum secundum ASDs, shunting blood from the left atrium to the right atrium, potentially increasing pulmonary blood flow.
Patent foramen ovale is a condition where the septum primum doesn't fully seal, allowing potential blood flow between atria under pressure.

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Description

This quiz covers the concepts of cardiac output, its calculation, and the factors influencing it, including heart rate and stroke volume. It also examines the relationship between the right and left ventricles in maintaining equal cardiac output and the role of the SERCA pump in cardiac function. Test your understanding of these essential cardiovascular principles.