Q.What is the role of histamine released by mast cells ? (A) Lowers blood pressure (B) Causes allergic symptoms (C) Stimulates antibody formation (D) Destroys pathogens

Mast cells release histamine, a chemical mediator crucial for the body's immune responses. When an individual encounters an allergen, these mast cells degranulate, releasing histamine and other substances.

Histamine primarily acts to:

• Increase vascular permeability, allowing immune cells and fluids to reach the site of inflammation.
• Cause vasodilation, leading to redness and warmth.
• Induce contraction of smooth muscles in the bronchi, which can lead to difficulty breathing in conditions like asthma.
• Stimulate nerve endings, causing itching and pain. …

Our immune system is a complex network designed to protect us from harmful invaders. However, sometimes it can overreact to harmless substances, leading to what we call allergies. In these allergic responses, certain cells play a pivotal role, and among them, mast cells are key players, primarily through their release of a chemical called histamine.

Mast cells are a type of white blood cell, specifically granulocytes, that are found in connective tissues throughout the body, particularly in areas exposed to the external environment like the skin, lungs, and digestive tract. They are essentially sentinel cells, poised to respond to perceived threats. When an individual who is sensitive to a particular substance (an allergen) encounters it, their immune system mounts an exaggerated response. This involves the production of specific antibodies, primarily IgE antibodies, which then bind to the surface of mast cells.

Upon subsequent exposure to the same allergen, these allergens bind to the IgE antibodies on the mast cell surface. This binding acts as a trigger, causing the mast cells to degranulate, meaning they release pre-formed chemical mediators stored in their granules into the surrounding tissues. One of the most significant of these mediators is histamine.

The release of histamine by mast cells initiates a cascade of events that manifest as the characteristic symptoms of an allergic reaction. These effects include:

• Vasodilation: Histamine causes the small blood vessels (arterioles) to widen, increasing blood flow to the affected area. This leads to redness and warmth.
• Increased Vascular Permeability: It makes the capillaries more permeable, allowing fluid and immune cells to leak out of the blood vessels and into the surrounding tissues. This leakage of fluid causes swelling (edema).
• Contraction of Smooth Muscles: Histamine can cause the smooth muscles in various organs to contract. For instance, in the bronchi of the lungs, this leads to bronchoconstriction, making breathing difficult (a common symptom in asthma). In the gastrointestinal tract, it can lead to abdominal cramps and diarrhea.
• Stimulation of Nerve Endings: Histamine can stimulate sensory nerve endings, leading to itching and pain.
• Increased Mucus Secretion: In the respiratory tract, it can stimulate glands to produce more mucus, leading to a runny nose and congestion. …