Angiotensin-converting enzyme is found only in the kidneys and converts angiotensinogen to angiotensin I. True or False

 

A. papillary muscles: These are specialized muscular projections from the ventricular walls that connect to the chordae tendineae. When the ventricles contract, the papillary muscles also contract to pull the "heart strings" taut. This action prevents the AV valve leaflets from prolapsing or everting back into the atria.

B. pectinate muscles: These are prominent muscular ridges found primarily in the internal walls of the right atrium and both auricles. They help increase the power of atrial contraction without significantly increasing heart mass. They are not found in the ventricles and do not interact with the chordae tendineae.

C. trabeculae carnae: These are internal ridges of myocardium located on the inner surfaces of the ventricles. While they help prevent suction and turbulence during blood flow, they do not serve as the primary anchoring point for the chordae tendineae. Only the specialized papillary muscles perform this specific anchoring function.

D. interventricular septum: This thick muscular wall separates the right and left ventricles to prevent the mixing of deoxygenated and oxygenated blood. While some papillary muscles may originate near its base, the septum itself is a dividing structure. It provides structural integrity rather than acting as a direct anchor for valve cords.

E. interatrial septum: This thin wall divides the right and left atria. It is located superior to the ventricles and is physically separated from the ventricular valves by the fibrous skeleton of the heart. It plays no role in the mechanical anchoring of the chordae tendineae within the ventricular chambers.

A. Sinoatrial (SA) node: This structure is located in the right atrium near the opening of the superior vena cava. It initiates the electrical impulse that starts each heartbeat. Because it has the highest intrinsic firing rate (about 60–100 beats per minute), it determines the heart’s rhythm and is therefore called the pacemaker of the heart.

B. Atrioventricular (AV) node: The AV node is located in the lower part of the right atrium near the interatrial septum. Its main function is to delay the electrical impulse coming from the atria before passing it to the ventricles. This delay allows the ventricles time to fill with blood before they contract. It can act as a backup pacemaker, but its intrinsic rate is slower (40–60 bpm), so it is not the primary pacemaker.

C. Atrioventricular (AV) bundle (Bundle of His): This structure carries the impulse from the AV node into the interventricular septum. It is the only normal electrical connection between the atria and ventricles. It conducts impulses but does not normally initiate them, so it is not the pacemaker.

D. Bundle branches: These pathways run down the right and left sides of the interventricular septum. They rapidly conduct electrical impulses toward the apex of the heart. Their role is conduction, not impulse generation, so they are not pacemakers.

E. Purkinje fibers spread throughout the ventricular myocardium. They distribute the impulse to ventricular muscle cells, causing coordinated ventricular contraction. Although they have an intrinsic firing ability, it is very slow (20–40 bpm) and only takes over if higher pacemakers fail. Therefore, they are not the normal pacemaker.