Anatomy and Physiology of Salivary Glands

Anatomy and Physiology of Salivary Glands

Introduction to Salivary Glands

  • Salivary glands are exocrine glands located in and around the oral cavity within the head.
  • Their primary function is to secrete salivary contents directly into the mouth.
  • They play crucial roles in protecting and lubricating the oral mucosa.
  • They assist in the initial stages of digestion by facilitating mastication and forming a food bolus ready for swallowing.
  • Salivary glands contribute to digestion through the enzymes they excrete with saliva, predominantly amylase, which initiates carbohydrate breakdown.
  • These glands vary significantly in size and are classified based on the nature of the saliva they produce (serous, mucous, or mixed).

Function and Classification

  • Overall Function: Secrete saliva for the initial phases of digestion and for the protection and lubrication of the oral cavity.
  • Types of Saliva Secreted by Glands:
    • Serous: Parotid gland
    • Mucous: Sublingual gland, minor salivary glands
    • Mixed: Submandibular gland
Major vs. Minor Salivary Glands
  • Salivary glands are broadly divided into major and minor glands.
  • Major Glands:
    • Significantly larger in size.
    • Are collections of exocrine tissue that secrete as a whole into a single salivary duct.
    • Produce a much larger amount of saliva per day compared to minor glands.
    • Primarily responsible for digestive and protective saliva.
  • Minor Glands:
    • Main role is to lubricate the walls of the oral cavity.

Saliva

  • Saliva is a seromucinous liquid with several critical functions within the oral cavity:
    • Lubrication: Keeps oral tissues moist.
    • Digestion: Contains enzymes like amylase.
    • Antimicrobial Action: Helps control oral bacteria.
    • Buffering: Maintains pH balance.
    • Hormone Regulation: Plays a minor role.
    • Taste Sensation: Aids in dissolving taste molecules.
Composition of Saliva
  • Comprises 99.5%99.5\% water.
  • The remaining 0.5%0.5\% consists of electrolytes, mucus, glycoproteins, enzymes, and antibacterial compounds.
Types of Saliva and Gland Specificity
  • There are two major types of saliva: serous and mucous.
  • Submandibular Gland: Secretes both serous and mucous saliva in a 3:23:2 ratio (serous to mucous, respectively).
  • Parotid Gland: The only gland that secretes purely serous saliva.
  • Sublingual Gland and Minor Salivary Glands: Secrete mainly mucous saliva.
  • The total daily output of saliva in an adult ranges between 11 to 1.51.5 liters.

Major Salivary Glands

Parotid Gland
  • The largest of the major salivary glands.
  • Sits bilaterally between the ramus of the mandible and the sternocleidomastoid muscle.
  • Produces between 25−30%25-30\% of the total daily salivary output.
  • Saliva is released through Stensen's duct (parotid duct).
  • The orifice of Stensen's duct is visible on the buccal wall at the level of the maxillary second molar.
Submandibular Gland
  • The second largest of the major salivary glands.
  • It is a paired gland.
  • Produces the largest amount of saliva among all glands, accounting for up to 70%70\% of the total daily output.
  • Wharton's duct (submandibular duct) opens at the sublingual papilla under the tongue.
Sublingual Gland
  • The smallest of the major salivary glands.
  • Unique for having several ductal openings that run along the sublingual folds.
  • Secretes the smallest portion of saliva per day among the major glands, contributing just 5%5\%.
  • Located beneath the sublingual fold.

Minor Salivary Glands

  • Account for approximately 1%1\% or less of the total daily salivary output.
  • Can be found in patches throughout the oral cavity, including:
    • The bucca
    • The labia
    • The lingual mucosa
    • The soft palate
    • The lateral parts of the hard palate
    • The floor of the mouth
    • Between the muscle fibers of the tongue
  • They amount to approximately 800−1000800-1000 individual glands in total.

Clinical Aspects

  • Salivary Gland Cysts:
    • Can develop due to injuries, tumors, infections, or salivary stones.
    • Mechanism: Salivary stones or other obstructions can block the flow of saliva, preventing it from escaping into the ducts. Saliva then accumulates within the tissues, causing swelling.
    • Symptoms: Usually painless, but can lead to difficulties with eating or speaking.
    • Treatment: Involves removal of the underlying cause.
    • Recurrence: Uncommon after treatment.
  • Other clinical relations include inflammation and tumors of the salivary glands.

Factors Affecting Salivary Flow

Important Factors
  • Degree of hydration
  • Body position
  • Exposure to light
  • Olfaction (sense of smell)
  • Previous stimulation
  • Circadian rhythms
  • Drugs
Unimportant Factors
  • Gender
  • Age (above 1515 years)
  • Body weight
  • Gland size
  • Psychic effects (e.g., thought/sight of food, appetite, mental stress)
  • Functional stimulation

Innervation

Autonomic Innervation
  • Secretomotor innervation to the salivary glands originates in the facial nerve (cranial nerve VII).
  • This innervation is transmitted to the submandibular ganglion via the chorda tympani.

Vascular Supply

  • The vascular supply to the submandibular region and the floor of the mouth is primarily provided by the lingual and facial arteries.