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Questions and Answers
Which of the following accurately describes the function of the ductus venosus in fetal circulation?
Which of the following accurately describes the function of the ductus venosus in fetal circulation?
- It allows oxygenated blood to flow directly from the right atrium to the left atrium.
- It permits blood returning from the placenta to bypass the liver and enter the caudal vena cava. (correct)
- It shunts blood from the pulmonary trunk to the aorta, bypassing the fetal lungs.
- It transports deoxygenated blood from the fetus to the placenta for oxygenation.
Why does most of the foetal blood bypass the lungs and flow through the ductus arteriosus?
Why does most of the foetal blood bypass the lungs and flow through the ductus arteriosus?
- Foetal lungs have a high oxygenating capacity, resulting in increased blood flow.
- The pressure in the foetal pulmonary circulation is lower than systemic circulation.
- Foetal lungs lack oxygenating capacity and exhibit high resistance in the pulmonary circulation. (correct)
- The increased pulmonary venous return to the left atrium prevents proper lung function.
In fetal circulation, oxygenated and deoxygenated blood flows from the caudal vena cava to the heart. How is this blood distributed upon arrival to the heart?
In fetal circulation, oxygenated and deoxygenated blood flows from the caudal vena cava to the heart. How is this blood distributed upon arrival to the heart?
- The oxygenated blood flows preferentially into the left atrium via the foramen ovale while the deoxygenated blood flows into the right ventricle. (correct)
- Two distinct streams of oxygenated and deoxygenated blood remain within the vessel, and are kept separate upon reaching the heart.
- The oxygenated blood preferentially flows through the tricuspid valve into the right ventricle, while the deoxygenated blood flows through the foramen ovale.
- The oxygenated and deoxygenated blood mixes completely in the right atrium, then flows to the right ventricle.
What is the primary factor influencing the closure of the ductus arteriosus after birth?
What is the primary factor influencing the closure of the ductus arteriosus after birth?
What is the primary source of oxygen for a fetus's blood?
What is the primary source of oxygen for a fetus's blood?
Why is it essential for the fetal circulation to have mechanisms that bypass the lungs?
Why is it essential for the fetal circulation to have mechanisms that bypass the lungs?
Why is coordinated cardiac contraction essential for proper cardiac function?
Why is coordinated cardiac contraction essential for proper cardiac function?
A calf is diagnosed with Tetralogy of Fallot. This condition is classified as which type of congenital defect?
A calf is diagnosed with Tetralogy of Fallot. This condition is classified as which type of congenital defect?
Which vessel carries oxygenated blood from the placenta to the fetus?
Which vessel carries oxygenated blood from the placenta to the fetus?
Which of the following is responsible for the rapid spread of depolarization throughout the heart?
Which of the following is responsible for the rapid spread of depolarization throughout the heart?
Flashcards
Ductus arteriosus
Ductus arteriosus
A fetal blood vessel connecting the pulmonary artery to the aorta, allowing blood to bypass the non-functioning lungs.
Patent ductus arteriosus
Patent ductus arteriosus
A condition where the ductus arteriosus remains open after birth, affecting normal circulation.
Foramen ovale
Foramen ovale
An opening between the right and left atria in the fetal heart that usually closes at birth.
Cardiac conduction system
Cardiac conduction system
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Atrial septal defect
Atrial septal defect
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Foetal Circulation
Foetal Circulation
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Ductus Venosus
Ductus Venosus
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Actin-Myosin Crossbridge Cycle
Actin-Myosin Crossbridge Cycle
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Study Notes
Foetal Circulation and Postnatal Transition
- Foetal circulation relies on the mother for nutrients and waste removal, via diffusion.
- This occurs via the placenta until birth.
- Lungs are non-functional until birth, leading to specific foetal circulatory features.
- Foramen ovale: permits blood flow between the right and left atria.
- Ductus arteriosus: allows blood flow from the pulmonary trunk to the aorta, bypassing the lungs.
- Ductus venosus: permits blood returning from the placenta to bypass the liver.
- Umbilical arteries: carry blood to the placenta for oxygenation, and the umbilical vein returns oxygenated blood to the foetus.
- Deoxygenated blood from the body (gut, kidneys, limbs) mixes with oxygenated blood returning from the placenta.
- Oxygenated blood goes from the right atrium (RA) to the left atrium via the foramen ovale, then to the left ventricle, and finally to the aorta.
- Deoxygenated blood flows from the RA to the RV and then to the pulmonary trunk towards the pulmonary circulation.
- Foetal lungs have high resistance compared to adult lungs, thus most blood is diverted via the ductus arteriosus to the aorta.
- Coronary and subclavian/carotid vessels receive blood before the major mixing of blood streams.
- At birth, structural changes occur:
- Umbilical vessels rupture.
- Air enters the lungs, decreasing resistance and increasing blood flow to the lungs.
Cardiac Conducting System
- Cardiac function depends on coordinated contraction.
- Sinoatrial (SA) node generates action potentials.
- Gap junctions spread depolarisation from cell to cell.
- Cardiac muscle acts as a functional syncytium.
- Specialized conducting tissue transmits depolarisation rapidly.
- Conducting tissue is located beneath the endocardium.
- Branches extend into muscle layers.
- Atrioventricular (AV) node transmits the signal to the ventricles.
- AV bundle (bundle of His) passes through the fibrous connective tissue.
- Bundle branches extend from the AV bundle, transmitting the signal to the ventricles.
- Purkinje fibres distribute signal through the ventricle walls, causing contraction.
Histology of the Heart
- Myocardium: largely contractile tissue composed of branched cardiomyocytes.
- Intercalated discs: specialized junctions between cardiomyocytes (adherens junctions, desmosomes, gap junctions).
- Endocardium: single layer of flattened endothelial cells.
- Subendothelial tissue: contains blood vessels and conducting system branches.
- Epicardium: visceral pericardium, consisting of connective tissue and blood vessels.
- Pericardium: double-layered serous membrane surrounding the heart (visceral and parietal layers).
Cardiac Muscle Contraction
- Cardiac cells are characterized by their striated appearance.
- Myofibrils are organized into sarcomeres.
- Sarcomeres contain thin filaments (actin) and thick filaments (myosin), which shorten during contraction.
- Cross-bridge cycling: ATP binding releases myosin from actin; hydrolysis of ATP causes myosin head to flex, moving the actin filaments; ADP and Pi release strengthens the bond, and then ATP binding begins the cycle again.
- Depolarization triggers Ca2+ influx and release, which binds to troponin to expose actin-binding sites on the thin filaments.
- Calcium binding to troponin changes the configuration, enabling myosin binding to actin, leading to the power stroke.
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