A Level Biology Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

Histamines play a crucial role in the body, especially in the immune response and allergic reactions. When tissue is damaged or when there is an allergic response, histamines are released from mast cells and basophils. This release has multiple effects, one of the primary ones being the dilation of blood vessels, a process known as vasodilation. This dilation increases blood flow to the affected area, which is part of the body’s inflammatory response.

Additionally, histamines increase the permeability of blood vessel walls, leading to what is termed "leaky vessel walls." This permeability allows fluid and immune cells to exit the bloodstream and enter surrounding tissues. Consequently, this action aids in delivering white blood cells to combat pathogens and contributes to the symptoms of inflammation, such as swelling and redness.

This function has critical implications during an immune response, as it facilitates the healing process and the body’s overall ability to respond to injury or infection.