Human Anatomy Digestive System Quiz

Physiology of the Digestive System

• The digestive system comprises the alimentary canal and associated glands.
• The alimentary canal includes the mouth and anus.
• Associated glands include salivary glands, liver, gallbladder, and pancreas.

Introduction

• The digestive system is responsible for the structure and functions of the digestive system.
• The functions of the digestive system include digestion, secretion, absorption, endocrine function, and immune function.

Digestive System Components

• The digestive system is composed of the alimentary canal and associated glands.
• The alimentary canal is a continuous tube running from the mouth to the anus.
• Associated glands include the salivary glands, liver, gallbladder, and pancreas, which produce digestive fluids.

Functions of the GIT

• The GIT (Gastrointestinal Tract) performs multiple essential functions.
• Digestion: breaking down food into smaller molecules.
• Secretion: releasing digestive juices.
• Absorption: taking up nutrients into the bloodstream.
• Endocrine function: producing hormones to regulate digestion.
• Immune function: protecting the body from pathogens.

Digestion

• Primarily occurs in the proximal part of the small intestine.
• Duodenum and first part of the jejunum are key locations.
• Digestion can be mechanical (physical breakdown) or chemical (by enzymes).
• It involves the breakdown of food into smaller particles and absorption by the body.

Absorption

• Transferring intestinal contents into the mucosa.
• Then, transferring contents into blood.
• Primarily occurs in the small intestine, especially the jejunum.
• Involves the transfer of digested food from the lumen into the bloodstream.

Secretion

• Digestive juices are secreted, 7000-7500 ml daily into the gut.
• Daily secretion of digestive juices.
• Different parts of the GIT secrete different substances needed for digestion.

Water Balance in GIT

• Ingested water:2000 mL.
• GIT secretions : ~9000 mL.
• Daily reabsorbed water: ~8800 mL.
• Balance in stool: ~200 mL(undigested).

Endocrine Function

• Hormones are released to regulate digestion.
• Gastrin: from the stomach, regulates gastric juice secretion.
• Secretin: from the intestines, regulates pancreatic juice secretion.
• Cholecystokinin (CCK): from the intestines, regulates gallbladder contraction.

Immune Function

• Lymphocytes secrete immunoglobulins for body protection.
• Immunoglobulins are proteins that fight micro-organisms in the gut.
• Peyer's patches collect lymphocytes in the intestine.

Innervation of the Digestive Tract

• The digestive tract has both extrinsic and intrinsic nervous systems.
• Extrinsic systems include the parasympathetic and sympathetic nervous systems.
• Intrinsic systems include the enteric nervous system with Auerbach and Meissner plexuses.

Myenteric Plexus (Auerbach's Plexus)

• This plexus regulates motility in the digestive tract

Submucosal Plexus (Meissner's Plexus)

• This plexus regulates secretion

Extrinsic Innervation of the Gut

• The parasympathetic system typically stimulates motility and secretion.
• The vagus nerve and pelvic nerve are involved in parasympathetic regulation.
• The parasympathetic nervous system contributes to digestion.
• The sympathetic system typically inhibits motility and secretion and contains excitatory fibers to gut sphincters.

Salivary Glands

• Salivary glands are exocrine glands with ducts that open into the oral cavity.
• Major types are Parotid, Submandibular, and Sublingual glands.
• Parotid: largest, 25% of saliva.
• Submandibular: 70% of saliva (main gland).
• Sublingual: 5% of saliva.

Composition of Saliva

• Saliva volume: 1-1.5 liters/day.
• pH: 6.8-7.2 (nearly neutral).
• Components are water (99.5%), inorganic constituents (0.2%), and organic constituents (e.g., mucin and enzymes: 0.3%).

Functions of Saliva

• Moistening and lubricating food for swallowing and speech.
• Protective function, such as mechanical cleaning, bactericidal action, and preventing putrefaction
• Saliva contains antibodies to destroy oral bacteria.
• Saliva's buffering action protects the mouth from acids and alkalis.
• Saliva role in starch digestion by amylase (ptyalin).
• Saliva dissolves food materials to stimulate taste buds.
• Saliva's role in water balance.

Control of Salivary Secretion

• Regulated by nervous control.
• Unconditioned reflexes: presence of food, chemical stimulation, mechanical stimulation.
• Conditioned reflexes: depend on training and stimuli like smell, taste, etc.
• Parasympathetic response results in profuse watery saliva, and sympathetic response results in small amount of viscid saliva.

Clinical Relevance

• Xerostomia: dryness of the mouth.
• Ptyalism: excessive salivation.

Physiology of the Esophagus and Swallowing

• The esophagus is a muscular tube carrying food from the mouth to the stomach.
• Swallowing (deglutition) is a complex process with voluntary and involuntary phases.
• Voluntary phase includes moving bolus into oropharynx.
• Involuntary includes three phases (oral, pharyngeal, and esophageal).
• During the swallowing reflex, the soft palate elevates to prevent food from entering the nasal passages.
• The larynx elevates, and the epiglottis covers the glottis to prevent food from entering the trachea.
• Protective phases: The muscles of the pharynx contract to move food and there is receptive relaxation of the upper esophageal sphincter.
• The third phase (esophageal phase) is involuntary with peristaltic contractions to move food to the stomach.
• The upper third muscles are striated and directly controlled by the vagus nerve.
• The lower third muscles are smooth and are indirectly controlled via the Auerbach plexus, while the middle third has a mixture of striated and smooth muscles.
• Difficulty swallowing is called Dysphagia, often due to nerve or swallowing center damage.

Upper and Lower Esophageal Sphincters

• Upper esophageal sphincter (UES) prevents air from entering the esophagus.
• Lower esophageal sphincter (LES) prevents reflux of gastric contents into the esophagus.

Anti-Reflux Function of LES

• The LES is a 3-5 cm section of the esophagus at the bottom of the stomach.
• Tonically contracted between meals to prevent gastric reflux.
• RELAXES during swallowing (inhibitory signal from the vagus nerve -> Auerbach plexus initiates -> NO and VIP release).

Clinical Relevance (LES)

• Achalasia: failure of the LES to relax.
• Gastroesophageal reflux disease (GERD): failure of the LES to close.

The stomach

• The stomach stores food and mixes it with gastric secretions.
• It has secretory functions (produces gastric juices).
• The amount of gastric juice ~2.5-3 liters/day.
• Most acidic secretion (pH = 1-2).
• Gastric juice contains mucin, HCl, pepsinogen, and intrinsic factor.
• The stomach also has motor functions like mixing and grinding food.
• Regulates the rate of evacuation of chyme into the duodenum-the pyloric pump.

Secretory Functions of Gastric Juice

• Secretion of mucin (protective against ulcers)
• Secretion of pepsinogen (begins protein digestion to peptides)
• Secretion of HCI (acidifies the gastric juice)
• Release of intrinsic factor (for vitamin B12 absorption).

Mechanism of HCI Formation

• CO2 from blood or cell metabolism reacts with water = carbonic acid.
• Carbonic anhydrase is the enzyme.
• HCO3- travels to the blood and Cl- moves from blood into cell (chloride-bicarbonate exchanger)
• Proton pump actively transports H+ ions into gastric lumen.
• H+ ions combine with Cl- to create HCI.

Stimulation of Parietal Cells to Secrete HCI

• Stimulated by H2 receptors, muscarinic (M3) receptors, gastrin receptors.
• Inhibited by some prostaglandins & somatostatin.

Functions of Gastric HCl (HCI)

• Activates pepsinogen to pepsin.
• Has antibacterial action.
• Facilitates the absorption of calcium and iron.

Motor Functions of the Stomach

• Stores large quantities of food by receptive relaxation in the fundus and body.
• Mixes and grinds food with gastric secretions via peristalsis in the antrum.
• Regulates the rate of chyme evacuation into the duodenum by peristalsis in the antrum-the pyloric pump.

Vomiting

• Outward expulsion of gastric and intestinal contents through the esophagus, pharynx, and mouth.
• Vomiting occurs via relaxation of the stomach body/fundus, opening of esophageal sphincter, contraction of diaphragm and abdominal wall muscles, and contraction of the pyloric portion of the stomach.
• Protective mechanisms prevent vomit entry into the respiratory passages.
• Various causes include central (increased intracranial pressure, chemoreceptor trigger zone stimulation) and peripheral (upper GIT irritation, and other GIT irritations) stimuli.

Effects of Severe Vomiting

• Dehydration, alkalosis, and malnutrition/weight loss.

Test your knowledge on the anatomy and functions of the esophagus and related swallowing processes. This quiz covers various aspects including muscle types, reflexes, and common conditions affecting swallowing. Perfect for students studying human anatomy or physiology!