Heart failure occurs when the heart muscle is too weak to pump enough blood to the body's organs or the heart cannot fill with enough blood to pump efficiently.

Correct answer:

• J: Pulmonary veins
• G: Right ventricle
• D: Pulmonary trunk

J: Pulmonary veins- Pulmonary veins are blood vessels that carry oxygenated blood from the lungs to the left atrium of the heart. Normally, there are four pulmonary veins—two from each lung. They enter the posterior aspect of the left atrium and play a vital role in systemic circulation by delivering oxygenated blood for distribution throughout the body.

G: Right ventricle- The right ventricle is the lower right chamber of the heart responsible for pumping deoxygenated blood to the lungs for oxygenation. It receives blood from the right atrium through the tricuspid valve and ejects it into the pulmonary artery via the pulmonary valve. It generates enough pressure to move blood through the pulmonary arteries to the lungs, where carbon dioxide is exchanged for oxygen.

D: Pulmonary trunk- The pulmonary trunk is a large artery that carries deoxygenated blood from the right ventricle to the lungs. It begins at the pulmonary valve and extends upward before dividing into the right and left pulmonary arteries. It is located anterior to the ascending aorta and it transports blood to the lungs for gas exchange.

A. Myoglobin and lipid inclusions: Both skeletal and cardiac muscle fibers contain myoglobin, which stores oxygen for aerobic metabolism, and lipid inclusions as energy reserves. These features support high metabolic demands in both muscle types and are not unique to skeletal muscle.

B. A single nucleus per cell: Cardiac muscle cells are typically uninucleated, whereas skeletal muscle fibers are multinucleated. However, the presence of a single nucleus is characteristic of cardiac myocytes, not a distinguishing feature of skeletal muscle.

C. Triads formed by long T tubules and cisternae of the sarcoplasmic reticulum: Skeletal muscle fibers have well-organized triads, where a T tubule is flanked by two terminal cisternae of the sarcoplasmic reticulum, allowing rapid calcium release for synchronous contraction. In contrast, cardiac contractile cells have diads (one T tubule with one adjacent cisterna) and smaller T tubules, reflecting slower calcium handling.

D. Sarcomeres along myofibrils: Both skeletal and cardiac muscle fibers contain sarcomeres arranged along myofibrils, giving them striated appearance under microscopy. Sarcomeres are essential for contraction in both types of striated muscle and are not a distinguishing structural feature.