CH 15 PPT

Introduction to the Digestive System

  • The Digestive System is responsible for processing food and nutrients vital to health.

  • The alimentary canal (GI tract) is a muscular tube extending from the mouth to the anus.

  • Functions:

    • Ingest food

    • Break down food into small molecules

    • Absorb nutrient molecules

    • Eliminate non-digestible wastes

Anatomy of the Digestive System

Major Components

  • Accessory Organs:

    • Salivary Glands: Parotid, sublingual, and submandibular that secrete saliva and digestive enzymes.

    • Liver: Major metabolic organ; processes nutrients, produces bile.

    • Gallbladder: Stores and concentrates bile.

    • Pancreas: Produces pancreatic juice and insulin.

  • Digestive Tract Organs:

    • Mouth: Teeth chew food; tongue aids in tasting and swallowing.

    • Pharynx: Passageway for food.

    • Esophagus: Transports food to stomach via peristalsis.

    • Stomach: Secretes acid and enzymes; mixes food into chyme.

    • Small Intestine: Further breaks down food; absorbs nutrients.

    • Large Intestine: Absorbs water; forms and stores feces.

    • Rectum: Stores feces before elimination.

    • Anus: Regulates feces elimination.

Structure of the Mouth and Salivary Glands

The Mouth (Oral Cavity)

  • Tongue: Skeletal muscle; assists in food handling, contains taste buds.

  • Palate: Divides oral and nasal cavities (hard palate and soft palate).

Salivary Glands

  • Types:

    • Parotid Glands: Located anterior to the ears.

    • Sublingual: Beneath the tongue.

    • Submandibular: Under the mandible.

  • Saliva Composition:

    • Mucus and water for moisture.

    • Salivary Amylase: Begins carbohydrate digestion.

    • Antibacterial components.

The Esophagus and Pharynx

The Pharynx

  • Parts:

    • Nasopharynx: Air only.

    • Oropharynx: Air and food.

    • Laryngopharynx: Food only.

Swallowing Process

  • Begins voluntarily; reflex action once bolus is formed.

  • Epiglottis: Prevents food from entering the trachea.

The Stomach

Structure and Function

  • Anatomy: Thick-walled J-shaped organ with regions (cardiac, fundic, body, pyloric).

  • Functions:

    • Stores and liquefies food.

    • Begins digestion of proteins.

    • Moves food to small intestine as chyme.

Gastric Secretions

  • Digestive Components:

    • Gastric Juice: Pepsinogen, HCl, intrinsic factor, mucus.

    • Secretory cells:

      • Chief Cells: Secrete pepsinogen.

      • Parietal Cells: Secrete HCl.

      • Gastrin-producing Cells: Regulate stomach functions.

The Small Intestine

Structure and Regions

  • Extending from pyloric valve to ileocecal valve; approximately 18 feet long.

  • Regions:

    • Duodenum: Receives pancreatic secretions and bile.

    • Jejunum: Absorption of nutrients.

    • Ileum: Contains Peyer’s patches.

Functions

  • Digestion and Absorption: Completes digestion of fats, proteins, carbohydrates.

  • Nutrient absorption: Sugars enter blood, fats enter lacteals.

  • Movement: Segmentation mixes chyme; peristalsis moves it forward.

The Large Intestine

Functions and Structure

  • Regions: Cecum, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.

  • Functions:

    • Absorbs water, salts, and some vitamins.

    • Stores indigestible materials for elimination.

Fecal Composition and Formation

  • Feces Components:

    • 75% water, 25% solids (bacteria, fiber).

  • Defecation Reflex: Involves contraction of rectal muscles.

Accessory Organs of Digestion

The Liver

  • Two main lobes; performs multiple functions including detoxification and bile production.

  • Functions:

    • Maintains blood glucose levels.

    • Produces plasma proteins and urea.

The Pancreas

  • Endocrine functions (insulin secretion) and exocrine functions (secretion of enzymes).

  • Pancreatic Juice Components: Sodium bicarbonate, digestive enzymes like amylase, lipase, proteases.

Chemical Digestion

Digestive Enzymes

  • Types: Hydrolytic enzymes that perform reactions involving water.

  • Carbohydrate Digestion: Salivary amylase and pancreatic amylase.

  • Protein Digestion: Pepsin and pancreatic proteases.

  • Fat Digestion: Emulsified by bile, digested by lipase.

  • Nucleic Acid Digestion: Broken down by nucleases.

Hormonal Control of Digestion

  • Hormones Involved:

    • Gastrin: Stimulates gastric juice production.

    • Secretin: Stimulates bicarbonate release from pancreas.

    • CCK: Stimulates enzyme secretion from pancreas and bile release from gallbladder.

Effects of Aging on the Digestive System

  • Increased incidence of disorders such as GERD and constipation.

  • Slowed peristalsis and increased risks of gastrointestinal disorders.

Nutrition

Nutritional Essentials

  • Essential nutrients must be ingested (e.g., amino acids, fatty acids).

  • A balanced diet is crucial for health; nutrients support energy and metabolic functions.

  • Importance of vitamins (fat-soluble and water-soluble) and minerals for body functions.