Digestive System Overview

Digestive System Overview

• The digestive system breaks down food into simple chemicals, absorbed as nutrients.

Digestive System Organs (Primary)

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine

Digestive System Organs (Accessory)

• Teeth
• Tongue
• Salivary glands
• Pancreas
• Liver
• Gallbladder

Primary Functions of the Digestive System

• Motility: Movement of food through the digestive tract.
• Secretion: Exocrine and endocrine secretions aiding digestion.
• Digestion: Breakdown of food molecules into absorbable subunits.
• Absorption: Passage of digested products into blood or lymph.

Wall of the Gastrointestinal Tract

• Mucosa (innermost layer)
• Submucosa
• Muscularis
• Serosa (outermost layer)

Nervous Supply of the GI Tract

• Intrinsic:
  • Submucosal plexus (Meissner's plexus)
  • Myenteric plexus (Auerbach's plexus)
• Extrinsic:
  • Sympathetic system (T5 to L2)
  • Parasympathetic system (cranial nerves 8, 9, 10 and sacral nerves 2, 3, 4)

Functions of the Nervous Supply

• Submucosal plexus: Regulates secretory functions of the GI tract.
• Myenteric plexus: Regulates movements of the GI tract.
• Sympathetic nerve fibers: Inhibits movements and secretions of the GI tract.
• Parasympathetic nerve fibers: Accelerates movements and increases secretions of the GI tract.

Hormones of the GI Tract

• Gastrin: Stimulates gastric secretion and motility (proteins in stomach)
• Secretin: Stimulates secretion of watery and alkaline pancreatic secretion (acids in duodenum)
• Cholecystokinin: Contracts gallbladder, stimulates pancreatic secretion with enzymes (Fat in duodenum)
• Gastric inhibitory peptide (GIP): Stimulates insulin secretion (glucose in duodenum)

Mouth (Specifics)

• Chewing/Mastication is the first step, saliva moistens and dissolves food.
• Saliva contains enzymes (amylase, maltase, lingual lipase) to aid digestion.
• Saliva has antimicrobial properties and cleanses the mouth.
• Saliva helps maintain water balance.
• Important for swallowing, taste, speech, and social functions.

Esophagus

• 25 cm long muscular tube connecting pharynx to the stomach.
• Swallowing initiates peristaltic wave, pushing food toward the stomach.
• Two sphincters (upper and lower esophageal) regulate movement.
• Lower esophageal sphincter prevents reflux.

Stomach (Parts)

• Cardiac region (cardiac sphincter)
• Fundus
• Body/Corpus
• Pyloric region

Stomach (Functions)

• Mechanical:
  • Storage: Stores food for 3-4 hours, empties slowly.
  • Chyme Formation: Mixes food with gastric juice, forming chyme.
• Protective: Gastric juice functions.
• Digestive: Gastric juice is highly acidic (pH 0.9-1.2).
• Hematopoietic: Intrinsic factor for vitamin B12 absorption.
• Excretory: Excretion of substances through gastric juice.

Small Intestine (Overview)

• Majority of digestion and absorption occurs here.
• Divided into duodenum, jejunum, and ileum.
• Chyme entering, digested and absorbed in the duodenum and parts of the jejunum.
• Enzymes break down carbohydrates, proteins, fats, and nucleic acids.
• Absorbs vitamins, minerals, and water.

Pancreas

• Dual function organ: endocrine and exocrine.
• Endocrine: Produces hormones (e.g., insulin).
• Exocrine: Secretes pancreatic juice, which is alkaline.
• Pancreatic juice aids digestion of proteins, lipids, and carbohydrates.

Liver

• Largest gland in the body.
• Receives blood flow from hepatic artery and portal vein.
• Metabolic function: Processes carbs, fats, and proteins; vitamins and hormones.
• Storage: Stores substances like glycogen, amino acids, iron, vitamins.
• Synthetic: Produces key plasma proteins and glucose.
• Bile secretion: Produces bile, aiding fat digestion.
• Excretory: Eliminates toxins, cholesterol, and other waste products.
• Heat production: Important metabolic center.
• Hematopoietic: Makes blood cells during fetal development.

Gallbladder

• Concentrates and stores bile.
• Releases bile into the duodenum during meals.
• Bile salts emulsify fats for digestion.

Large Intestine

• Stores undigested material.
• Absorbs water and ions, concentrates wastes.
• Defecation expels feces.

Explore the components and functions of the digestive system in this quiz. Delve into the roles of various organs, both primary and accessory, as well as the physiological processes involved in digestion. Understand the structure of the gastrointestinal tract and its nervous supply.