Salivary Gland Embryology, Physiology, and Stem Cell Complexity

Introduction

Salivary glands play an essential role in maintaining oral homeostasis by secreting saliva under unstimulated (resting) and stimulated (neuronal-regulated) conditions. For example, saliva functions as a barrier for bacterial infestations due to its antibacterial composition. It also plays the essential roles of oral lubricant, protecting tooth enamel, providing enzymes for digestion of food, and is an indicator of overall health. Unfortunately, cancer treatments (radiation and/or chemotherapy), certain drug medications, and/or immune system disorders, such as Sjögren syndrome, can all lead to severe hyposalivation. Radiation in particular propagates a multitude of chronic oral health-related ailments such as xerostomia or dry mouth, which entails difficulty in swallowing, increased risk for dental caries, oral fungal infections, and overall poor quality of life. Combatting these conditions and/or syndromes requires a deep understanding of factors and mechanisms regulating glandular physiology, development, homeostatic maintenance and/or repair by stem/progenitor cells, which are described below.