Stinging hair of Urtica dioca

The correct answer is option 'D', which states that the stinging hair of Urtica dioca causes almost unbearable irritation of the skin. Let's understand why this is the correct answer in detail.

Introduction to Urtica dioca:
Urtica dioca, commonly known as the stinging nettle, is a perennial flowering plant found in many parts of the world. It belongs to the family Urticaceae. The plant possesses tiny hairs on its leaves and stems, known as stinging hairs or trichomes.

Structure of stinging hair:
The stinging hair of Urtica dioca consists of a bulbous base and a slender, hollow, and brittle tip. The tip of the hair contains a mixture of chemicals including histamine, acetylcholine, serotonin, and formic acid, which are responsible for the intense irritation caused by the plant.

Mechanism of irritation:
When the stinging hair comes into contact with human skin, the brittle tip easily breaks off, exposing the sharp edges of the hair and releasing the irritating chemicals. The chemicals act as irritants and cause a stinging sensation, followed by redness, itching, and swelling of the affected area.

Role of histamine:
Histamine, one of the chemicals present in the stinging hair, is a well-known mediator of allergic reactions and inflammation. It causes the blood vessels in the affected area to dilate, leading to increased blood flow and the characteristic redness and swelling.

Release of other chemicals:
Apart from histamine, acetylcholine and serotonin released from the stinging hair also contribute to the irritation. Acetylcholine stimulates pain receptors, intensifying the itching and stinging sensation. Serotonin, on the other hand, acts as a neurotransmitter and enhances the inflammatory response.

Duration of the irritation:
The irritation caused by the stinging hair of Urtica dioca can last for several hours to days, depending on the individual's sensitivity and the extent of contact. The severity of the symptoms may vary from mild discomfort to intense pain.

Conclusion:
In conclusion, the stinging hair of Urtica dioca causes almost unbearable irritation of the skin due to the release of chemicals such as histamine, acetylcholine, and serotonin. These chemicals trigger an inflammatory response, leading to redness, itching, and swelling. It is important to avoid contact with this plant to prevent the discomfort caused by its stinging hairs.