yes true
Saliva is produced in and secreted from salivary glands. The basic secretory units of salivary glands are clusters of cells called an acini. These cells secrete a fluid that contains water, electrolytes,mucusand enzymes, all of which flow out of the acinus into collecting ducts.
Within the ducts, the composition of the secretion is altered. Much of the sodium is actively reabsorbed, potassium is secreted, and large quantities of bicarbonate ion are secreted. Bicarbonate secretion is of tremendous importance to ruminants because it, along with phosphate, provides a critical buffer that neutralizes the massive quantities of acid produced in the forestomachs. Small collecting ducts within salivary glands lead into larger ducts, eventually forming a single large duct that empties into the oral cavity.
Most animals have three major pairs of salivary glands that differ in the type of secretion they produce:
- parotid glandsproduce a serous, watery secretion
- submaxillary (mandibular) glandsproduce a mixed serous and mucous secretion
- sublingual glandssecrete a saliva that is predominantly mucous in character
The basis for different glands secreting saliva of differing composition can be seen by examining salivary glands histologically. Two basic types of acinar epithelial cells exist:
- serous cells, which secrete a watery fluid, essentially devoid of mucus
- mucous cells, which produce a very mucus-rich secretion
Acini in the parotid glands are almost exclusively of the serous type, while those in the sublingual glands are predominantly mucus cells. In the submaxillary glands, it is common to observe acini composed of both serous and mucus epithelial cells
