Parotid Gland

Parotid Gland Definition

The parotid gland is one of the three salivary glands contained within the human body. The same applies to many animals. It is the largest of the three glands, as well as the biggest producer of saliva. Saliva, of course, has the lubricating and digestive properties that help protect the alimentary canal linings during meals. Likewise, the antibacterial properties of saliva protect tooth enamel against bacteria.

Our two parotid glands are located bilaterally on the inside of our cheeks. If we were to visualize this, the glands lie in front and behind the ears. The word parotid, in fact, is a literal translation for “beside the ear.” Likewise, the parotid gland can be thought to wrap around the lower jaw bone or mandible. It appears in the shape of a wedge, and can be felt on either side by running our fingers from in front of the ear down the cheek. Each parotid gland channels saliva through the parotid duct. The parotid duct is a long tube that exits in front of the parotid glands and is superficial, or “on top of / closer to the skin’s surface,” to the jaw’s masseter muscles. The saliva secretion itself is very “serous,” or protein-rich, compared to the saliva expelled from the other salivary glands. This will of course aid in the parotid gland’s principal functions.

three types of salivary glands
The figure depicts salivary glands, parotid glands listed as label number one.

Parotid Gland Development

Parotid glands begin to form at around the sixth week of gestation. They are the first salivary gland to form. They start off as little epithelial buds near the lips of the primitive mouth. These buds will move toward the back, closer to the otic placodes of the ears. The ducts that channel through the parotid glands will form at the tenth week. The ends of the ducts will become populated with the secretory acini cells, which only eighteen weeks into gestation will begin to secrete into the parotic duct!

As the parotid gland takes mature form, it will receive innervation from the parotid plexus, or branches of the facial nerve bundle. Parasympathetic innervation by the glossopharyngeal nerve will make us salivate. Meanwhile, the trigeminal nerve will give it sensation. The external carotid artery will be the major supply of blood for the parotid gland, and drainage will be made possible by the retromandibular vein.

Parotid Gland Function

When we are at rest, or not eating, the parotid glands account for about ten percent of the saliva in our mouth. It is essential to keep our mouth lubricated at all times to protect the delicate linings of our alimentary canal as dryness can lead to broken skin through which pathogens can enter. However, once activated they will secrete upwards of twenty-five percent of the saliva in our mouths. This increase is imparted by the body’s need for amylase to start the digestion of starches. The main function of parotid glands, like salivary glands in general, lies in facilitating the digestion of food. How is this done? By secreting saliva!

Mastication, or chewing, is the action that precedes the release of saliva from the salivary glands. Aside from our teeth physically breaking down food, the first step of digestion requires the molecular breakdown of the complex carbohydrates as well. Our gut will need simpler sugars to properly absorb nutrients from our food, so the gentle digestion of starches will begin at the point of entry – the mouth. There are various cell types within the gland that allow saliva secretion. For example, acinar cells are berry-lobed cells that will expel enzymes.

Though salivary glands are always working – especially the parotids as they are the largest and biggest producers of saliva – they are prone to infections and are even affected by our water intake.

Parotid Gland Infection

Parotid glands have the largest surface area, and so there is physically more area for infection. Infection often begins with blockage of the salivary ducts by stones. Salivary stones are calcified masses that form on the inside of a duct. They are more common in submandibular glands, but sometimes the parotid gland will also experience this blockage. This will block the normal flow of saliva through the ducts, which will result in swelling and inflammation.

An affected patient often experiences pain and swelling even at the thought of food. This experience is called the “mealtime syndrome.” This makes sense in the context of the things that stimulate saliva: the sight, smell, thought of food, and of course the chewing of food. While the calcifications can result from long-standing dehydration or infection, most are of idiopathic (“unknown”) origin.

Infection by bacteria or viruses are another type of infection that can block salivary ducts from functioning normally. For example, the mumps virus will cause the parotid glands to swell in an inflammation called parotitis. Those affected will experience tremendous pain. A common way that this illness is detected in the doctor’s office is by testing the blood for high levels of salivary amylase since the parotid glands will work overtime to secrete it.

So how are these blockages removed? Well, salivary stones can be resected by surgically opening the site of blockage. This works particularly well for stones that are located more superficially. However, if the stone is deep in the duct the gland may need to be excised completely. For parotitis, a combination of massage, irrigation, and antibiotics may be in place. In other cases, surgical ligation of the duct may be required to prevent further injury.

Parotid Gland Tumor

Resection of parotid gland tumors is a little more complicated. Of all salivary gland tumors, seven of the ten start in the large parotid glands. About eight of ten parotid tumors will be benign. The salivary mass can be aspirated away with a biopsy. But very rarely, a cancerous tumor emerges. Malignant tumors will be rock hard, and will often include fixed skin or skin ulcers. Many of the cancers are a type of adenocarcinoma, which describes cancers that start at the secreting gland cells.

Treatment for malignant parotid tumors is normally excision and radiation treatment. Radiation will effectively target and destroy cancer cells in the parotid gland. Malignant salivary gland cancers normally come in three grades:

  • Grade 1 cancer: low grade. The salivary gland cells look quite normal, and they grow slowly so they have a better chance of a good prognosis
  • Grade 2 cancer: intermediate grade. Their appearance and prospects are middle of the road between grade 1 and 3 cancers
  • Grade 3 cancer: high grade. The salivary gland cells look very different from normal and will spread rapidly. The outlook is normally lesser than lower grade cancers.

Quiz

1. Which of the following best describes the location of the parotid glands?
A. Behind the jaw
B. Below the nose
C. Inside the cheek
D. Superior to the ear

Answer to Question #1
C is correct. The best answer is inside the cheeks. We have two parotid glands on both sides of our mouth, and although their location can be described relative to the jaw and ear, inside the cheek is the correct choice.

2. Which of the following describes “mealtime syndrome?”
A. When the minerals during a meal calcify and lead to painful blockage
B. A characteristic sensory feeling experienced by patients with parotid tumors
C. When mastication of food overworks the salivary glands to where they are susceptible to painful blockage
D. When the sensory experience of a meal will lead to pain secondary to salivation

Answer to Question #2
D is correct. Mealtime syndrome is a common sensory experience that patients with blockage have at the sight, smell, or thought of food since this will trigger salivation.

References

  • Parotid Surgery MD (2017). “Parotid & Salivary Gland Info.” Center for advanced Parotid and Facial Nerve Surgery.. Retrieved on 2016-06-28 from https://www.parotidsurgerymd.com/education/articles/parotid-salivary-gland-info/
  • Amirlak, Bardia MD (2017). “Malignant Parotid Tumors.” Medscape. Retrieved from http://emedicine.medscape.com/article/1289616-overview
  • Kenhub (2017). “The Parotid Gland.” KenHub. Retrieved on 2017-06-29 from https://www.kenhub.com/en/library/anatomy/the-parotid-gland
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