Clase 48 Fisiología Gastrointestinal - Secreción Salival (IG:@doctor.paiva)

Secretion of Saliva: An Overview

Introduction to Salivary Secretion

• The 48th class on gastrointestinal physiology introduces the topic of salivary secretion, led by Eduardo Paiva.

• Approximately 800 to 1500 ml of saliva is secreted daily, averaging around 1000 ml.

Types of Salivary Secretion

• Saliva consists of two types of secretions: serous (rich in amylase for starch digestion) and mucous (rich in mucin for lubrication and protection).

• Major salivary glands include the parotid, submandibular (submaxillary), and sublingual glands; smaller minor salivary glands are also present throughout the oral mucosa.

Composition and pH of Saliva

• Parotid glands secrete serous saliva, while submandibular and sublingual glands produce mixed saliva. Minor salivary glands primarily secrete mucous.

• Saliva has a pH range of 6 to 7, containing high levels of bicarbonate and potassium but low sodium and chloride concentrations compared to plasma.

Mechanism of Salivary Secretion

Phases of Secretion

• The secretion occurs in two phases: initial secretion by acini followed by modification through salivary ducts.

• Sodium is actively reabsorbed from saliva into extracellular fluid, exchanged with potassium, leading to lower sodium concentration in saliva.

Ionic Concentrations

• A negative charge develops due to higher sodium reabsorption than potassium secretion, affecting chloride ion behavior during secretion.

• Chloride ions are less concentrated due to their exchange with bicarbonate ions; thus, saliva has high potassium and bicarbonate levels but low sodium and chloride levels.

Saliva's Role in Oral Hygiene

Daily Production Rates

• Basal conditions yield about 0.5 ml/minute during wakefulness; even lower amounts during sleep help wash away germs.

Antimicrobial Properties

• Saliva contains bactericidal agents like lysozyme that target bacteria; it also helps digest food particles which can serve as nutrients for bacteria.

Nervous Regulation of Salivation

Autonomic Nervous System Influence

• Salivation is regulated by the autonomic nervous system; parasympathetic stimulation significantly increases salivation compared to sympathetic stimulation.

Pathways Involved

Salivary Secretion Mechanisms

Neural Pathways and Salivary Glands

• The glossopharyngeal nerve (cranial nerve IX) innervates the optic ganglion, which ultimately influences the parotid gland's secretion.

• The facial nerve (cranial nerve VII) directs signals to the submandibular and sublingual glands, with inputs originating from superior and inferior salivary nuclei located between the medulla oblongata and pons.

Stimuli Affecting Salivation

• Tactile stimuli from smooth objects significantly enhance salivation, while rough objects can inhibit it.

• Bitter tastes, particularly those caused by acids, can increase salivation dramatically—up to 20 times normal levels—while undesirable food triggers minimal stimulation.

Reflexes and Gastrointestinal Influence

• Reflexes from the stomach and upper intestine (duodenum) are activated by irritating foods, leading to increased saliva production aimed at neutralizing irritants.

Vascular Influences on Salivation

• Parasympathetic stimulation enhances blood flow to salivary glands through vasodilation, thereby increasing saliva secretion.

• Saliva itself promotes vasodilation via bradykinin formation, further boosting salivary output.

Sympathetic Stimulation Effects

• Sympathetic stimulation may cause vasoconstriction if a parasympathetic stimulus is already present; otherwise, it can moderately increase secretion in isolation.

Esofágica Secretion Overview

Mucosal Secretion in Esophagus

• Esophageal secretions are primarily mucosal, crucial for lubricating food during swallowing to prevent mucosal abrasions.

Protection Against Gastric Acid