Anatomy and Physiology II Practice Test 2025 – Comprehensive All-In-One Guide to Exam Success!

An antigen is a foreign substance that prompts the immune system to produce an antibody. These substances can include pathogens such as bacteria, viruses, and parasites, as well as non-infectious agents like toxins and allergens. When an antigen enters the body, it is recognized by immune cells as a potentially harmful entity, triggering an immune response. This process includes the activation of B cells that produce antibodies specifically designed to bind to the antigen, neutralizing it or marking it for destruction by other immune cells.

Immunoglobulin, while closely related, refers specifically to the antibodies themselves that are produced in response to the presence of an antigen. Albumin is a protein found in blood plasma, primarily responsible for maintaining oncotic pressure and transporting substances, and does not directly stimulate antibody production. Collagen is a structural protein found in connective tissues; although it has important functions in the body, it is not involved in the immune response in the same way as an antigen.