About how much saliva does a person produce in an entire day?
a. 100 ml
b. 250 ml
c. 500 ml
d. 1500 ml

Hint: Saliva is produced and secreted by salivary glands in the mouth, is extracellular fluid. Saliva is a clear liquid that's made in a person’s mouth 24 hours a day. It is mostly made up of water, with a few other chemicals. In humans, saliva contains water plus electrolytes, mucus, white blood cells, epithelial cells, enzymes (amylase and lipase), antimicrobial agents such as secretory IgA, and lysozymes.

Complete answer:
Saliva is produced by various glands, mainly three pairs of major glands and numerous minor salivary glands located in the oral cavity. The three major salivary glands are parotid, submandibular, and sublingual salivary glands. These contribute to 90% of total saliva secretions, while minor salivary glands contribute to the remaining 10%. Whole saliva is defined as the amount of saliva secreted by the major and minor glands.

In general, acinar cells are responsible for the production of the primary saliva. Saliva is composed of 99% water and 1% protein and salts. The normal daily production of saliva ranges between 0.5 and 1.5 liters. Saliva is always hypotonic to plasma. Salivary glands secretion is mainly controlled by the autonomic nervous system(ANS).

Hence, the correct answer is option (D).

Note: Approximately two-thirds of the total volume of the whole saliva is produced by submandibular glands, in the resting (unstimulated) state. The parotid glands are responsible for at least 50% of the total volume of saliva from the mouth, upon stimulation. Both in the unstimulated or stimulated states, Sublingual glands contribute to a small percentage.