The glands responsible for producing saliva play a significant role beyond simple drool. They secrete a complex fluid that facilitates the initial stages of eating and maintains a healthy oral environment. Their proper function is integral to a dog’s overall well-being, including the ease of swallowing and internal temperature regulation. Understanding the anatomy and function of these organs is important for recognizing potential problems.
Identifying the Major Salivary Glands
Dogs possess four pairs of major salivary glands, delivering secretions into the mouth through dedicated duct systems. The Parotid gland is an elongated, V-shaped structure that lies superficially, wrapping around the base of the ear canal. Its margins are often indistinct because it lacks a well-defined capsule, blending with the surrounding soft tissue. The Parotid duct courses forward over the masseter muscle before opening into the oral cavity on a small papilla, situated opposite the upper fourth premolar tooth.
The Mandibular gland is spherical and situated slightly lower and behind the Parotid gland, nestled caudomedial to the mandibular lymph nodes. This gland shares a common connective tissue sheath with one part of the Sublingual gland. The Mandibular duct travels forward beneath the tongue, ultimately emptying into the mouth at the sublingual caruncle.
The Sublingual gland is composed of two distinct parts: the monostomatic and polystomatic portions. The monostomatic part is closely associated with the Mandibular gland, and its main duct often joins or runs alongside the Mandibular duct to open at the sublingual caruncle. The polystomatic part consists of smaller, scattered lobules, each with tiny ducts that open directly into the oral cavity along the floor of the mouth.
Located deep within the eye socket, or orbit, is the Zygomatic gland, which lies just beneath the eye and medial to the zygomatic arch. This gland is sometimes called the orbital gland due to its position on the orbital floor. Multiple small ducts emerge from the Zygomatic gland and drain into the mouth near the upper first molar tooth.
The Role of Canine Saliva
The fluid produced by these glands serves multiple physiological purposes, focused on mechanical and protective functions. A primary function is to lubricate the food, assisting in forming a cohesive bolus that can be easily swallowed without damaging the throat lining. This moisture also protects the sensitive mucous membranes of the mouth during chewing and swallowing.
Canine saliva differs significantly from human saliva because it contains little to no salivary amylase, the enzyme that initiates starch breakdown. Chemical digestion in dogs does not begin until the food reaches the stomach and small intestine. Instead, dog saliva is rich in proteins related to immune defense, including Immunoglobulin A, which helps guard against oral pathogens.
The fluid also possesses a higher buffering capacity and a more alkaline pH compared to human saliva, which helps neutralize acids produced by bacteria in the mouth. Beyond digestion, saliva is utilized for thermoregulation through panting. As the fluid evaporates from the tongue and oral surfaces, it draws heat away from the body, providing an effective cooling mechanism.
Common Health Issues Affecting the Glands
The most frequently encountered condition affecting canine salivary glands is a Sialocele. This occurs when a duct is damaged or obstructed, causing saliva to leak into the surrounding soft tissues and accumulate. Sialoceles most commonly originate from the mandibular and sublingual glands, resulting in a noticeable, non-painful swelling beneath the jaw or in the upper neck area.
If the leakage occurs under the tongue, the resulting swelling is specifically termed a ranula. Alternatively, if the Zygomatic gland is affected, the saliva accumulation can cause swelling and a noticeable bulging or displacement of the eye. The cause of the duct damage is often a result of minor trauma, though the exact trigger is sometimes unknown.
Another condition is Sialadenitis, which involves inflammation or infection of the gland tissue itself. Dogs with this issue may present with fever, lethargy, and painful swelling in the region of the affected gland. Although less common, Sialadenitis can be triggered by a blockage, such as a salivary stone, or by systemic infections.
Salivary gland tumors are relatively rare, but when they do occur, they tend to be malignant, with adenocarcinomas being the most frequent type. These tumors generally affect older animals and may cause a firm, localized swelling that gradually increases in size. Due to their proximity to surrounding structures, these tumors often show a tendency to locally infiltrate the surrounding tissue.