Moderate

Mast cells secrete:

Correct answer: D. Histamine

  • A. Haemoglobin
  • B. Hippurin
  • C. Myoglobin
  • D. Histamine

Explanation

Mast cells are granulated wandering cells that are found in connective tissue. Their granules contain histamine which is a vasodilator. It causes a runny nose, sneezing and itching. It also narrows the airways in the lungs. Haemoglobin and myoglobin are the pigments present in the blood and muscles respectively.

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About Respiration

The human respiratory system includes the air passages, lungs, alveoli and breathing muscles, while gaseous exchange explains how oxygen enters blood and carbon dioxide leaves it by diffusion. The effects of smoking include damage to cilia and alveoli, reduced gas exchange, chronic bronchitis, emphysema and increased risk of lung cancer.

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