marieb-ehap13-ch14-lecture-presentation

Chapter 14: The Digestive System and Body Metabolism

Functions of the Digestive System

  • Ingestion: Taking in food.

  • Digestion: Breaking food into nutrient molecules.

  • Absorption: Movement of nutrients into the bloodstream.

  • Defecation: Excretion of indigestible waste from the body.

Anatomy of the Digestive System

  • Alimentary Canal: Continuous, coiled, hollow tube.

    • Pathway: Runs from the mouth (stomach to anus).

    • Functions: Ingest, digest, absorb nutrients, and defecate waste.

  • Accessory Digestive Organs: Include teeth, tongue, liver, gallbladder, pancreas; assist digestion in various ways.

Organs of the Alimentary Canal

  • Mouth: Starts the process of digestion.

  • Pharynx: Passageway for food.

  • Esophagus: Conducts food to the stomach.

  • Stomach: Breaks down food and begins digestion.

  • Small Intestine: Major site for the absorption of nutrients.

  • Large Intestine: Removes water and compacts waste products.

  • Anus: Excretion of feces.

Mouth Anatomy and Functions

Mouth Structure

  • Mouth (oral cavity): Lined cavity with mucous membrane.

  • Lips: Protect anterior opening; also known as labia.

  • Cheeks: Form lateral walls of the mouth.

  • Palates:

    • Hard Palate: Forms the anterior roof.

    • Soft Palate: Forms the posterior roof and has a fleshy projection called the uvula.

  • Vestibule: Space between the lips and teeth.

  • Tongue: Moves food during mastication and helps in swallowing.

Functions of the Mouth

  • Mastication: Chewing food into smaller fragments.

  • Mixing with Saliva: Tongue assists in the mixing.

  • Taste: Taste buds located on the tongue allow us to experience flavors.

Pharynx

Pharynx Structure

  • Serves as a passageway for food and air.

  • Divided into:

    • Oropharynx: Posterior to oral cavity.

    • Laryngopharynx: Below oropharynx; connected to the esophagus.

Pharynx Function

  • Propels food to esophagus using two muscle layers (longitudinal and circular).

Esophagus

Esophagus Anatomy

  • Length: About 10 inches long; connects pharynx to stomach.

Esophagus Physiology

  • Conducts food through peristalsis (rhythmic muscular contractions).

  • Serves only as a passageway for food.

Layers of Tissue in the Alimentary Canal

Four Layers (Tunics)

  1. Mucosa: Innermost layer; moist membrane with epithelium.

  • Surface Epithelium: Mostly simple columnar (except in esophagus—stratified squamous).

  1. Submucosa: Connective tissue with blood vessels, lymphatics, and nerves.

  2. Muscularis Externa: Contains smooth muscle layers (inner circular and outer longitudinal).

  3. Serosa: Outermost layer; secretes serous fluid.

Stomach Anatomy and Functions

Stomach Overview

  • Shape: C-shaped organ on the left abdomen.

  • Sphincters:

    • Cardioesophageal Sphincter: Food enters from esophagus.

    • Pyloric Sphincter: Food exits into the small intestine.

Regions of the Stomach

  • Cardia: Surrounds the cardioesophageal sphincter.

  • Fundus: Expanded portion beside the cardia.

  • Body: Main central area.

  • Pylorus: Terminal funnel-shaped portion.

Functions of the Stomach

  • Stretch capacity: Holds up to 4 liters of food.

  • Produces gastric juices for digestion (mucus, hydrochloric acid, enzymes).

  • Churns food to form chyme before it enters the small intestine.

Small Intestine Overview

Characteristics

  • Longest portion of the alimentary canal (2-4 meters).

  • Main site for nutrient absorption.

Subdivisions

  • Duodenum: First section; receives bile and pancreatic juices.

  • Jejunum: Middle section for absorption.

  • Ileum: Final section, leading to the large intestine (ileocecal valve).

Structural Modifications

  • Villi: Projections for surface area, containing capillaries and lacteals.

  • Microvilli: Tiny projections on villi for further absorption.

  • Circular Folds (Plicae Circulares): Increased surface area; deep folds.

Peyer’s Patches

  • Lymphatic tissue increasing in number toward the end of the small intestine to combat bacteria.

Large Intestine Overview

Characteristics

  • Length: Shorter than small intestine (1.5 meters) but larger in diameter.

  • Subdivisions:

    • Cecum: First part with attached appendix.

    • Colon: Ascending, transverse, descending, sigmoid regions.

    • Rectum and Anal Canal: End portions for feces elimination.

Functions

  • Absorbs water, vitamins, and minerals.

  • Forms and eliminates feces via peristalsis and haustral contractions.

Accessory Digestive Organs

  • Teeth: Chew food.

  • Salivary Glands: Produce saliva for digestion.

  • Pancreas: Produces digestive enzymes and hormones (insulin, glucagon).

  • Liver: Produces bile, processes nutrients, detoxifies substances.

  • Gallbladder: Stores and concentrates bile for fat digestion.

Nutrition and Metabolism

Nutrients

  • Major Nutrients: Carbohydrates, lipids, proteins, water.

  • Minor Nutrients: Vitamins, minerals.

Metabolism

  • Metabolism: All chemical reactions necessary for maintaining life.

    • Catabolism: Breaking down substances for energy.

    • Anabolism: Building larger molecules from smaller ones.

Energy Balance

  • Energy Intake: Equals total energy output (heat + work).

  • Influencing Factors: Metabolic rate, body surface area, gender, age.

Digestive Hormones

  • Gastrin: Stimulates gastric juice production.

  • Secretin: Increases pancreatic juice output and decreases gastric activity.

  • Cholecystokinin (CCK): Stimulates bile and pancreatic enzyme secretion.

Developmental Aspects

  • Fetal Development: Alimentary canal develops early.

  • Newborns: Frequent feeding; peristalsis is inefficient.

  • Age-Related Issues: Problems like GERD, constipation, and liver function changes in elderly.