Salivary Glands Definition
A salivary gland is the tissue in our mouths that expels saliva. Anytime our mouth comes near a hot sandwich we feel them activate. Salivary glands are only found in mammals. As exocrine glands, they expel saliva into the epithelial surface of our mouths by way of ducts, rather than through the bloodstream. Each day, our glands produce as much as a quart of saliva. Saliva is a mixture of water, mucus, antibacterial substance, and digestive enzymes. One of the most recognizable digestive enzymes in the human body is alpha-amylase. This enzyme is able to break down the starch in our food to simpler and more easily digestible sugars like glucose and maltose. Whenever we chew, we are activating these glands in preparation for the safe breakdown of our meal.
Salivary Glands Function
Briefly, saliva itself serves many uses. As the only secretion of our salivary glands, it is helpful in creating the food bolus, or the finely packed ball of food that we roll inside our mouths. This shape facilitates its safe passage through our alimentary canal. Saliva has lubricating properties that are protective, as well. Saliva protects the inside of our mouths, our teeth, and our throats as we begin to swallow the bolus. It also cleanses the mouth after a meal, and dissolves food into chemicals that we perceive as taste.
Salivary glands come in three flavors, if you will: the parotid, sublingual, and submandibular glands. Each is aptly named after the area in the oral cavity in which it is located. Let’s begin this discussion with the parotid gland.
Two parotid glands are located within each of our cheeks. Parotid glands are the largest type of salivary gland. They account for up to twenty percent of the saliva in our oral cavity. Their main role lies in facilitating mastication, or “chewing,” and in commencing the first digestive phase of our food. The parotid gland is notably labeled a serous type of gland. Serous glands are those that secrete protein-rich fluid, which in this case is an enzyme-rich suspension of alpha-amylase.
Next, the submandibular gland is located close to our mandible. This is the movable part of our jaw. In essence, this gland lies on the floor of our mouths. Since it is superficially located, we can feel it if we place our fingers about two inches above the Adam’s apple. It is the second-largest salivary gland, and produces the most saliva (up to 65%). It is considered a mixture of serous and mucus glands since the suspension is both rich in enzymes and gooey mucus that is released into the oral cavity through the submandibular ducts.
Lastly, sublingual glands are located under the tongue. They are the smallest and most dispersed salivary gland. Its secretion is mostly mucus, and exits directly through the Rivinus excretory ducts. Only a minimal (~5%) amount of saliva in the oral cavity comes from these.
Salivary Glands Innervation
Salivary glands are innervated by both branches of the autonomic, or “involuntary,” nervous system. This is commonly associated with the fight or flight response. When we see a bear, for instance, we trigger our sympathetic response. This threat triggers the release of norepinephrine, a rise in our heart rate, dilation in our eyes, and notably, slowed digestion and a dry mouth. This means that whereas sympathetic stimulation normally overstimulates its target, it inhibits the salivary gland. So, we produce less saliva. In contrast, parasympathetic stimulation of the salivary gland renders a heavy flow of saliva.
Salivary Glands Infection
There are symptoms that may signal a compromised salivary gland. This includes gland swelling, fever, a foul taste in the mouth, and dry mouth. Measures can be taken to lessen the effects of dry mouth (listed below).
Swollen glands are often caused by “salivary stones,” or buildup of crystalized saliva, that can clog the gland from releasing saliva. This causes pain, and unless the blockage is cleared it can infect the gland. Salivary glands can also be painfully blocked by bacterial infection. Staphylococcus aureus is the most common bacterium that infects it. If left untreated, the bacterium will cause fever, severe pain, and an abscess or pus. Other bacteria that commonly target the salivary gland via exposure or bad hygiene are: Streptococcus viridans, Haemophilus influenza, Streptococcus pyogenes, E. coli. Nevertheless, viruses can also infect the glands. Among them are viral infections in children that were not vaccinated for mumps, but it is also caused by influenza, HIV, and herpes. A tumor can likewise block salivary gland tissue. Most tumors are benign, but salivary gland cancer is a rare type of cancer that develops in 1 of 100,000 people each year.
1. Which enzyme is the primary digestive enzyme in human saliva?
2. Which salivary gland type is the largest contributor to the saliva in our oral cavity?
3. Identify the type of innervation that stimulates saliva flow:
- Anatomy and Physiology (2017). “The Salivary Glands.” Anatomy and Physiology, a learning initiative. Retrieved on 2017-06-19 from http://anatomyandphysiologyi.com/salivary-glands/
- WebMD (2017). “Salivary Gland Problems.” WebMD: Oral Care. Retrieved on 2017-06-20 from http://www.webmd.com/oral-health/guide/salivary-gland-problems-infections-swelling#1
- Krucik, Greg (2015). “What is a salivary gland infection?” Healthline. Retrieved on 2017-06-19 from http://www.healthline.com/health/salivary-gland-infections
- Segal, K et al. (1996). “Parasympathetic innervation of the salivary glands.” Operative Techniques in Otolaryngology-Head and Neck Surgery. 7(4): 333-338