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Anatomy, innervation and function of the parotid gland.
What’s your favorite type of food? I have a bit of a sweet tooth, so a nice slice of cake is the ideal treat for me. That soft fluffy sponge, the light airy filling, and those sweet juicy strawberries. Is your mouth watering yet? Mine it totally is. But how much do you know about the glands that produce your saliva? Stick around to find out more about one of them in our short tutorial on the parotid gland.
The parotid gland is the largest of the three major salivary glands and you have two of them, one on each side of your face. It’s pyramidal or kind of triangular in shape and can be divided into a deep lobe and a superficial lobe, which are separated by the facial nerve. The parotid gland is enclosed within a product capsule which is derived from the investing layer of the deep cervical fascia. In terms of location, the parotid gland is bordered by various structures. It is bordered superiorly by the zygomatic arch, anteriorly by the masseter muscle, inferiorly by the inferior border of the mandible, and posteriorly by the external ear and the sternocleidomastoid muscle.
The parotid duct, also known as the Stensen duct, transports saliva into the oral cavity. It arises from the anterior surface of the parotid gland and runs across the anterior surface of the masseter muscle before piercing the buccinator muscle. The duct opens into the oral cavity near the upper second molar tooth.
You should have gotten a clue about the function of the parotid gland from the start of our tutorial and when we talked about the parotid duct. Any ideas? Well, the function of the parotid gland is pretty simple. It produces saliva. Specifically, it produces a serous saliva which is watery and rich in enzymes. This saliva is then secreted via the parotid duct into the oral cavity where it lubricates and assists in the breakdown of carbohydrates. It also functions as an antimicrobial agent in the mouth.
Next, we're going to talk about some associated structures of the parotid gland. The structures we’re going to talk about and their relationship with the parotid gland is of great clinical significance particularly during parotid gland surgery. The first structure we're going to talk about is the facial nerve, which as I said earlier, divides the parotid gland into deep and superficial lobes.
The facial nerve gives rise to five terminal branches within the parotid gland which go in to innervate the muscles of facial expression. The external carotid artery enters or passes deep to the parotid gland. As it ascends superiorly, the external carotid artery gives rise to the posterior auricular artery before dividing into its two terminal branches – the maxillary artery and the superficial temporal artery.
The last structure we're going to talk about is the retromandibular vein. This vein is formed within the parotid gland by the union of the superficial temporal and maxillary veins.
It’s time to move on and discuss the blood supply, innervation, and lymphatic drainage of the parotid gland. The parotid gland receives its arterial supply from the branches of the external carotid artery, whereas its venous drainage is carried out by the retromandibular vein. You may have thought that the parotid gland would be innervated by the facial nerve, but that would be too easy.
The parotid receives both sensory and autonomic innervation. It receives its sensory supply from the auriculotemporal nerve and the greater auricular nerve. The parasympathetic supply which stimulates saliva production comes from the glossopharyngeal nerve via the auriculotemporal nerve and it receives the sympathetic supply from the superior cervical ganglion. Lymph from the parotid gland drains to the superior deep cervical nodes.
Now that we're experts on the parotid gland, let's get clinical.
Salivary gland tumors are relatively uncommon, but the most common site is the parotid gland. These tumors are usually benign whereas tumors of the other major salivary glands are more likely to be malignant. Risk factors associated with parotid tumors include radiation exposure, previous Epstein-Barr infection, and smoking.
Patients usually present with a painless lump or swelling in the region of the parotid gland. As the tumor grows, other symptoms may occur such as difficulty swallowing or opening the mouth. Any suspicious lesions undergo ultrasound scan with fine needle aspiration cytology to determine management. Management of benign tumors usually involves observation in older patients and surgical excision in younger patients due to the risk of tumors becoming malignant. Radiotherapy can also be used in the treatment of parotid tumors.
And that brings us to the end of our short tutorial on the parotid gland.