EVERYDAY SCIENCE

Detailed explanation-1: -The mucous glands, in the form of typical acini, contain a characteristic lumen and secrete hydrophilic mucus that keeps the skin moist, facilitating gas exchanges1, 5, 9, 10.

Detailed explanation-2: -These glands keep the upper airway mucosa moist by direct secretion and transudation of fluid. Respiratory mucus is formed within goblet cells in response to irritation of the tracheal surface. Mucus is secreted in 1-to 2-m droplets that absorb water, swell, and coalesce to form a 10-m film around respiratory cilia.

Detailed explanation-3: -Mucosal glands secrete mucus to maintain the moisture, permeability and elasticity of the skin, all of which are necessary for amphibian homeostasis (2, 9, 44).

Detailed explanation-4: -Note: Skin of animals which respire through the skin is very delicate and moist, so it requires protection from pathogens. This is why their skin has mucus glands. Mammalian skin is not delicate, so it lacks mucus glands.

Detailed explanation-5: -Cells which are specialized to secrete mucus are called mucous cells. Examples in the GI system include secretory cells of the salivary glands, esophageal glands, stomach surface, pyloric glands, and Brunner’s glands of the duodenum. These cells are typically organized into tubular secretory units.