Disruption of which neurotransmitter is involved in Parkinson's disease?

Choice A rationale

Left-sided heart failure causes blood to back up into the pulmonary circulation because the left ventricle cannot efficiently pump blood into the systemic circuit. This increase in pulmonary capillary pressure leads to pulmonary congestion and fluid extravasation into the alveoli. This results in symptoms such as dyspnea, orthopnea, and a cough that produces frothy, often pink-tinged sputum. These respiratory findings are classic indicators of left-sided failure as the lungs become the primary site of fluid accumulation.

Choice B rationale

Peripheral and sacral edema occur when there is systemic venous congestion, which is a hallmark of right-sided heart failure. In this condition, the right ventricle fails to pump blood effectively into the lungs, causing pressure to rise in the right atrium and the systemic venous system. Fluid is then forced out of the capillaries into the dependent tissues of the body. While left-sided failure can eventually lead to right-sided failure, isolated peripheral edema is not a primary sign of left-sided dysfunction.

Choice C rationale

Hepatomegaly and splenomegaly result from venous engorgement of the liver and spleen due to increased pressure in the portal and systemic venous systems. This occurs when the right side of the heart is unable to accommodate the venous return. The organs become enlarged and tender as they become congested with blood. These findings are diagnostic of right-sided heart failure and systemic congestion rather than the pulmonary issues that characterize the initial stages of left-sided cardiac pump failure.

Choice D rationale

Jugular vein distention and ascites are classic signs of systemic fluid volume overload and increased central venous pressure. Jugular vein distention occurs when the right atrium cannot handle the blood returning from the superior vena cava. Ascites is the accumulation of fluid in the peritoneal cavity due to high pressure in the hepatic veins. Both are manifestations of right-sided heart failure. Left-sided failure specifically manifests with pulmonary symptoms due to the backup of blood into the lungs.

Choice A rationale

This sequence is incorrect because it places the Bundle of His before the AV node. The electrical impulse must pass through the AV node to allow for a physiological delay, which ensures the ventricles fill with blood from the atria before contracting. The Bundle of His receives the signal from the AV node. Moving from the Bundle of His back to the AV node would represent a retrograde or abnormal conduction pathway, which is not the standard physiological order.

Choice B rationale

The normal cardiac conduction starts at the SA node, the primary pacemaker located in the right atrium. The impulse travels to the AV node, where it is briefly delayed. It then moves to the Bundle of His, which splits into the right and left bundle branches. Finally, it reaches the Purkinje fibers, which distribute the electrical charge throughout the ventricular myocardium to trigger a coordinated contraction. This sequence ensures efficient blood flow from atria to ventricles.

Choice C rationale

This sequence incorrectly identifies the AV node as the starting point. While the AV node can act as a secondary pacemaker if the SA node fails, the standard physiological conduction system begins at the SA node. The SA node has the highest inherent firing rate, typically 60 to 100 beats per minute, which suppresses other potential pacemakers. Starting at the AV node would result in a junctional rhythm, which is a slower heart rate than a normal sinus rhythm.

Choice D rationale

This sequence represents the exact reverse of the normal conduction pathway. In a healthy heart, electricity does not move from the ventricles upward to the atria. Starting at the Purkinje fibers would mean the impulse originated in the ventricular tissue, which is characteristic of ventricular escape rhythms or premature ventricular contractions. Such a pathway would be highly inefficient and signifies a significant pathological state or a complete heart block where the primary pacemakers have failed.