Which organelle does one expect to be most abundant in cardiac muscle cells?
mitochondria
smooth ER plastids
Golgi complexes
lysosomes
The correct answer and explanation is:
The correct answer is mitochondria.
Cardiac muscle cells, also known as cardiomyocytes, are highly specialized for continuous, rhythmic contractions. These cells need a constant supply of energy to sustain heart function over a lifetime. This energy is primarily produced through aerobic respiration in the mitochondria, which are often referred to as the powerhouse of the cell.
In cardiac muscle cells, mitochondria are more abundant than in many other cell types. The high density of mitochondria allows the heart muscle to generate the large amounts of ATP needed for contraction. This ATP production is particularly important because the heart needs to maintain its activity without interruption, unlike other muscles that may only contract during physical exertion. Mitochondria in these cells are often located near the contractile elements to efficiently supply energy where it is most needed.
Cardiac muscle cells rely on aerobic metabolism, which requires oxygen to produce ATP. The mitochondria in these cells help metabolize fatty acids and glucose to produce ATP through oxidative phosphorylation, a process that occurs in the inner mitochondrial membrane. Given the continuous demands placed on the heart, the mitochondria in cardiac muscle cells are highly adapted, with a large number of cristae (folds in the inner membrane) to maximize surface area for energy production.
The other organelles mentioned—smooth ER, plastids, Golgi complexes, and lysosomes—are also important in cellular functions but are not as critical to the energy demands of cardiac muscle cells. The smooth endoplasmic reticulum, for example, plays a role in calcium storage and lipid metabolism, but the mitochondria are still the most abundant and critical organelle in these cells for energy production.