NEET Practice Questions (MCQs) with Answers & Solutions

Blood capillaries are the smallest blood vessels in the body and are composed of a single layer of endothelial cells. This single-cell thickness allows for efficient exchange of gases, nutrients, and waste products between blood and surrounding tissues. Thus, option o1: Blood capillary is correct.

The lifespan of red blood cells (RBCs) in humans is approximately 120 days. This duration allows RBCs to perform their function of transporting oxygen throughout the body before they are broken down and recycled in the spleen.

The 'Dubb' sound, also known as the second heart sound (S2), arises from the closing of the semilunar valves, which include the aortic and pulmonary valves. This sound occurs at the end of systole when the ventricles finish contracting.

The sinoatrial (SA) node, located in the right atrium of the heart, is known as the pacemaker of the heart. It generates electrical impulses that initiate the heartbeat and regulate the heart rate.

Bilirubin is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. It is not involved in blood clotting, whereas fibrin, calcium, and platelets play essential roles in the clotting process.

Tadpoles have a closed circulatory system, meaning their blood circulates within vessels throughout their body. In contrast, insects like cockroaches, mosquitoes, and houseflies have an open circulatory system where blood is not entirely contained within vessels.

The left ventricle has the thickest wall among the chambers of the heart. This is because it needs to pump oxygenated blood with high pressure to the entire body, requiring a strong muscular wall.

A pacemaker is an artificial sino-auricular (SA) node that provides stimulation for the heart to beat. The natural pacemaker of the heart is the sinoatrial (SA) node, which generates electrical impulses causing the heart to contract. In cases where the SA node is not functioning properly, an artificial pacemaker is used to maintain regular heartbeats.

The regulation and initiation of the heartbeat follow a specific pathway: the SA node (sinoatrial node) generates the initial electrical impulse, which then travels to the AV node (atrioventricular node). From the AV node, the impulse moves to the Bundle of His and then to the Purkinje fibers, which distribute the impulse throughout the ventricles, causing them to contract. Therefore, the correct sequence is SA node → AV node → Bundle of His → Purkinje fibers.

The mitral valve, also known as the bicuspid valve, is located between the left atrium and the left ventricle. It allows blood to flow from the left atrium into the left ventricle and prevents backflow when the ventricle contracts.