Which cells degranulate during tissue injury releasing histamine and heparin?

• A. Mast cells
• B. Fibroblasts
• C. Neurons
• D. Macrophages

Answer: (A)

Mast cells are the resident sentinels in connective tissue that store histamine and heparin in their granules. When tissue is injured, they degranulate and release these mediators into the local tissue. Histamine rapidly widens nearby blood vessels and increases vascular permeability, causing the familiar redness, warmth, and swelling of acute inflammation. Heparin acts as an anticoagulant locally, helping to keep the area fluid and facilitating immune cells’ access to the site. Fibroblasts, neurons, and macrophages don’t release histamine and heparin from granules in this injury-related degranulation process; fibroblasts are involved in repair by making extracellular matrix, neurons transmit signals, and macrophages focus on phagocytosis and cytokine signaling.