Biological Systems MCAT Practice Exam

What is the primary function of platelets in hemostasis?

1. To transport oxygen in the blood

2. To prevent bleeding

3. To produce antibodies

4. To regulate blood pressure

The correct answer is: To prevent bleeding

Platelets, also known as thrombocytes, play a crucial role in hemostasis, which is the process that prevents and stops bleeding. Their primary function is to form a platelet plug at the site of a blood vessel injury. When a blood vessel is damaged, platelets are activated and rapidly adhere to the exposed collagen and other components of the damaged tissue. They then undergo a shape change, releasing chemical signals that attract more platelets to the site. This aggregation of platelets forms a temporary plug that seals the breach in the blood vessel wall, thereby preventing further blood loss. In addition to forming a plug, platelets also release growth factors and cytokines that are important for tissue repair and healing. They are involved in the activation of the clotting cascade, which ultimately leads to the formation of a stable fibrin clot, reinforcing the initial platelet plug. The other options are associated with different physiological functions. Transporting oxygen in the blood is primarily the role of red blood cells, producing antibodies is a function of the immune cells, specifically B lymphocytes, and regulating blood pressure is managed by various mechanisms involving the heart, blood vessels, and the nervous and endocrine systems. Thus, the function of platelets in preventing bleeding is vital for maintaining he