The Gland Tour: How Saliva Is Made
Scientists have worked hard to figure out how our salivary glands strut their stuff--both because it’s interesting and because knowledge could point the way to therapies.
Structurally, the glands are rather like bunches of grapes. At one end (buried in the flesh of our mouths) are those “grapes”--round clusters of cells that secrete the water and many of the proteins and chemicals of our spit. That saliva oozes into hollow tubes called ducts, ever-widening tributaries that fuse with other tributaries and eventually dump saliva into our mouths.
There are three main pairs of glands--the parotid glands (which are the largest and release saliva through the cheek) and the sublingual and submandibular glands (which release fluid under the tongue). A whole slew of minor glands also oozes fluid. While spit is pretty much the same from gland to gland, there are differences--the parotid gland, for instance, contains more of the enzyme amylase, which is used to digest starch in our food. (It is the parotid that goes into overdrive when we eat--or anticipate eating, for that matter.)
Saliva production is controlled by nerve signals from the brain to the glands. Those nerves release chemicals that stick to the gland cells and tell them to release the proteins, water and other ingredients of spit.
A variety of triggers--the sight or thought of a piece of cheesecake, the taste of lemon or the simple act of chewing--send such signals into overdrive. (Some people with dry mouth syndrome say they try thinking of their favorite foods when they want to get their saliva flowing.) Therapeutically, drugs that mimic the action of the nerves’ chemical signals can help boost saliva flow in many dry mouth patients.
Studies are also revealing why mouths dry up--though there is still much to be learned. Some prescription medications interfere with the nervous system’s stimulation of glands. People who have had radiotherapy for head and neck cancer accumulate damage in the grape-like portion of the salivary glands--the part that oozes water.
And some people’s own bodies attack their glands, in a strange autoimmune disease called Sjogren’s syndrome.
Sjogren’s syndrome affects nine times as many women as men, typically appears in midlife and affects production of other fluids too (causing dry eyes, for instance). Theories about Sjogren’s syndrome are various, and changing: One hypothesis is that the body creates antibodies that bind to the salivary gland cells--blocking the chemical signals from the nerves.
But there is also evidence that people with Sjogren’s syndrome may lose the special protein pores--known as aquaporins--that permit water to flow into the ducts.
Resources
For more information about saliva, Sjogren’s syndrome and other forms of dry mouth, contact:
* National Institute of Dental and Craniofacial Research at NIDCR Public Information and Liaison Branch, 45 Center Drive, MSC 6400, Bethesda, MD 20892-6400; (301) 496-4261; or www.nidr.nih.gov/ health.
* Sjogren’s Syndrome Foundation, a nonprofit organization that offers advice (ranging from coping strategies to cookbooks for those with dry mouth syndrome), information and support groups, at 8120 Woodmont Ave., Suite 530, Bethesda, Md. 20814; (800) 475-6473; or www.sjogrens.com.
