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.