Biology
Physiology of Saliva Production
Quick fact
An average person produces about 0.5 to 1.5 liters of saliva every day, but this volume drops dramatically during sleep and in old age, a key reason why many older adults suffer from dry mouth.
Why this is interesting
Your mouth waters at the smell of food, but did you know that your saliva is a carefully regulated fluid that changes throughout your life?
Read the full explanation
Understanding Physiology of Saliva Production
Saliva is produced by three major pairs of salivary glands: the parotid (near the ear), submandibular (under the jaw), and sublingual (under the tongue), along with hundreds of minor glands. These glands release saliva through ducts into the mouth. The fluid consists of water (about 99%), electrolytes, mucus, enzymes like amylase and lysozyme, and immunoglobulins. Saliva has several vital functions: it lubricates food for easier swallowing, begins the digestion of starches, protects the oral cavity by neutralizing acids, and contains antibacterial agents that help prevent infection. The production of saliva is not constant; it is controlled by the autonomic nervous system. When you eat or even think about food, signals from the brain stimulate the glands to produce more saliva. At night, this stimulation drops, leading to the reduced saliva flow that causes 'morning breath' and a dry sensation upon waking.
A deeper explanation
The secretory units of salivary glands, called acini, are surrounded by myoepithelial cells that contract to expel saliva. The entire process of saliva formation begins with the acinar cells producing a primary fluid that is isotonic with blood, containing all major electrolytes. This primary saliva is then modified as it travels through the duct system. The ducts reabsorb sodium and chloride, while secreting potassium and bicarbonate, making the final saliva hypotonic at rest. The rate of saliva production is largely governed by neural input. The parasympathetic division (via the facial and glossopharyngeal nerves) is the main driving force, increasing flow dramatically and producing a watery, enzyme-rich saliva. The sympathetic division generally reduces flow, producing a thicker, mucus-rich saliva. This balance is influenced by factors such as taste, chewing, smell, and even stress. Over a lifetime, saliva production is not constant. In infants and young children, the flow rate is relatively high, and drooling is common as they learn to control it. During puberty, hormonal changes can affect saliva composition. In older adults, a natural decline in glandular function, along with the side effects of medications, often leads to xerostomia, or dry mouth, which increases the risk of tooth decay, gum disease, and oral discomfort.