Enzymes in Digestion

Lingual Lipase

• Lingual lipase is a lipid-digesting (lipolytic) enzyme that digests milk fats (pre-emulsified fats).
• It hydrolyzes triglycerides into fatty acids and diacylglycerol.

Salivary Enzymes

• Salivary amylase:
  • Secreted by all salivary glands
  • Activated by acid medium
  • Converts cooked starch into maltose
• Maltase:
  • Secreted by major salivary glands
  • Activated by acid medium
  • Converts maltose into glucose
• Lingual lipase:
  • Secreted by lingual glands
  • Activated by acid medium
  • Converts triglycerides of milk fat into fatty acids and diacylglycerol

Functions of Saliva

• Cleansing and protective functions:
  • Rinses the mouth and teeth to remove food debris, shed epithelial cells, and foreign particles
  • Prevents bacterial growth by removing materials that may serve as culture media
  • Contains lysozyme, which kills certain bacteria
  • Contains proline-rich proteins and lactoferrin, which possess antimicrobial properties and protect teeth by stimulating enamel formation
  • Contains secretory immunoglobulin IgA, which has antibacterial and antiviral actions
  • Contains mucin, which protects the mouth by lubricating the mucous membrane
• Role in speech:
  • Moistens and lubricates soft parts of the mouth and lips to facilitate speech
• Excretory function:
  • Excretes substances like mercury, potassium iodide, lead, and thiocyanate
  • Excretes some viruses, such as those causing rabies and mumps
  • May excrete certain substances in pathological conditions, such as glucose in diabetes mellitus
• Regulation of body temperature:
  • In dogs and cattle, excessive dripping of saliva during panting helps in loss of heat and regulation of body temperature
• Regulation of water balance:
  • Decreased salivary secretion causes dryness of the mouth, inducing thirst
  • When water is taken, it reduces thirst and restores body water content

Regulation of Salivary Secretion

• Salivary secretion is regulated only by nervous mechanism through autonomic nervous system
• Parasympathetic fibers:
  • Stimulate salivary secretion, causing a large quantity of watery saliva with less organic constituents
  • Activate acinar cells and dilate blood vessels of salivary glands
  • Neurotransmitter is acetylcholine
• Sympathetic fibers:
  • Stimulate salivary secretion, causing less secretion of thick, rich-in-mucus saliva
  • Activate acinar cells and cause vasoconstriction by secreting noradrenaline

Reflex Regulation of Salivary Secretion

• Salivary reflexes:
  • Unconditioned reflex: present since birth, induces salivary secretion when any substance is placed in the mouth
  • Conditioned reflex: acquired by experience, needs previous experience, and is elicited by sight, smell, hearing, or thought of food

Effect of Drugs and Chemicals on Salivary Secretion

• Substances that increase salivary secretion:
  • Sympathomimetic drugs like adrenaline and ephedrine
  • Parasympathomimetic drugs like acetylcholine, pilocarpine, muscarine, and physostigmine
  • Histamine
• Substances that decrease salivary secretion:
  • Sympathetic depressants like ergotamine and dibenamine
  • Parasympathetic depressants like atropine and scopolamine

Applied Physiology

• Hyposalivation:
  • Reduction in salivary secretion
  • Temporary hyposalivation occurs in emotional conditions, fever, and dehydration
  • Permanent hyposalivation occurs in obstruction of salivary duct, congenital absence or hypoplasia of salivary glands, and paralysis of facial nerve
• Hypersalivation:
  • Excess secretion of saliva
  • Physiological condition: pregnancy
  • Pathological conditions: decay of tooth or neoplasm in mouth or tongue, diseases of esophagus, stomach, and intestine, neurological disorders, and some psychological and psychiatric conditions
• Other disorders:
  • Xerostomia (dry mouth): due to hyposalivation or absence of salivary secretion
  • Drooling: uncontrolled flow of saliva outside the mouth, often seen in children during teeth eruption, upper respiratory tract infection, or nasal allergies
  • Chorda tympani syndrome: sweating while eating due to trauma or surgical procedure affecting parasympathetic nerve fibers to salivary glands

This quiz covers the functions and characteristics of lingual lipase, salivary amylase, and maltase in breaking down fats and carbohydrates in the digestive system.