Saliva

Saliva collecting on the lips of a human baby. It mostly comes from salivary glands in the cheek.

Salivais the waterysubstancemade in themouthsofhumansand manyanimals.Saliva beginsdigestingfoodin the mouth, and moistensfoodto make swallowing easier. Saliva consists of 99.5% water.

The mouth is obviously the point of entry to the wholealimentary canal.It follows from this that saliva must both help digestion, and protect againstinfections.

The digestion part is by threeenzymes,one each forcarbohydrates,fatsandproteins.The digestion started here carries on in thestomach.There are some other 'minor' enzymes as well, and we do not know the full story about them yet. Also there is a pain-killing opiorphin, and a wrap-around haptocorrin which keepsvitamin B12safe from stomach acids. Finally, there are a set of anti-bacterial proteins which make life difficult for any bacteria which get in with the food.

Saliva is filtered blood, "These observations are consistent with the fact that saliva is a filtrate of blood, meaning that the contents of blood—water, salts and macromolecules—pass through capillary walls into the salivary glands." Source:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2741028/#:~:text=These%20observations%20are%20consistent%20with,walls%20into%20the%20salivary%20glands.