Saliva: Composition and Function
Saliva is commonly found as an evidence in cases involving sexual assaults, homicides, burglaries, etc. In sexual assault cases, saliva can be found on the victim's body, clothing, or bedding. In addition, in some cases, saliva can be found on stamps, envelopes, cigarette butts, plastic and glass bottles, metal cans, and other surfaces that have come in contact with the oral cavity.
INTRODUCTION
Saliva is a clear, watery fluid that is produced by the salivary glands in the human body. It is secreted into the oral cavity to help with the digestion of food, to protect the teeth and gums, and to keep the oral cavity moist.
Humans have 3 pairs of major salivary glands- parotid (located in the cheeks), submandibular (located under the jaw) and sublingual (located under the tongue) glands, along with numerous minor salivary glands located throughout the oral cavity, including the lips, cheeks, tongue, and floor of the mouth. About 70% of saliva is produced from the submandibular salivary glands, 25% from the parotids, and 5% from the sublingual salivary glands.
Figure: Human salivary glands
An average person produces about 1-1.5 liters of saliva per day. However, the amount of saliva produced can vary depending on factors such as diet, medications, hydration levels, and overall health. The pH of saliva is typically between 6.2 and 7.6, which is slightly alkaline. Saliva acts as a buffer and helps neutralize the acid produced by bacteria in the mouth, which helps to protect the teeth and gums.
COMPOSITION OF SALIVA
Saliva is composed of 99% water and 1% other substances such as enzymes (salivary amylase, lingual lipase, and lysozymes), hormones (cortisol, testosterone, estradiol, and melatonin), electrolytes (sodium, potassium, calcium, magnesium, phosphate, and bicarbonate ions), proteins (statherin, mucin, immunoglobulins, growth factors, etc.), and cheek epithelial cells.
Amylase
Amylase is an enzyme that plays a crucial role in the digestion of carbohydrates. There are two main types of amylase:
Alpha-Amylase: In humans, alpha-amylase is predominantly secreted by the salivary glands (salivary alpha-amylase or ptyalin) and pancreas (pancreatic alpha-amylase), and is present in other tissues at minimal levels. It begins the process of starch digestion in the oral cavity by breaking down long chains of starch into maltose and other smaller oligosaccharides.
Beta-Amylase: Beta-amylase is found in certain plants and microorganisms but is not produced by humans. It plays a role in breaking down starches into maltose by removing maltose units from the non-reducing ends of starch molecules.
FUNCTIONS OF SALIVA
Saliva plays several important functions in the oral cavity, including:
Digestion: Saliva contains enzymes such as salivary amylase (also called ptyalin) that help to break down starch into simpler sugars such as maltose and dextrin, starting the process of digestion. About 30% of starch is digested in the oral cavity. Saliva also contains an enzyme called lingual lipase, which breaks down fats.
Lubrication: Saliva contains a lubricant called mucin that helps to lubricate and moisten food and prevent it from sticking to the walls of the oesophagus.
Protection: Saliva contains antibodies (IgA and I) and enzymes that help to protect the oral cavity from infection by neutralizing harmful microorganisms. The lysozymes present in saliva help in the lysis of bacteria and prevent the overgrowth of oral microbes. Additionally, saliva contains a protein called statherin that inhibits the precipitation of calcium and phosphate salts from saliva and helps in protecting the teeth from demineralization.
Buffering: The bicarbonate and phosphate ions present in saliva act as buffers and help to neutralize acids in the oral cavity that can cause tooth decay and other oral health problems.
Taste: Saliva acts as a solvent and helps to dissolve food in the mouth, allowing us to taste it.
Speech: Saliva plays an important role in speech by keeping the oral cavity moist and lubricating the vocal cords, allowing for smooth speech production.