Chapter 3 Nutrition

Review of Digestion

Definition of Digestion

  • Digestion: The process of breaking down food into smaller nutrient structures.

  • Key point: Digestion occurs before absorption; food must be processed into smaller components before nutrients can be absorbed.

Gravity's Role in Digestion

  • Impact on Digestion: While gravity does not directly control digestion, it can influence the digestive process.

    • Effects of Body Position: Eating close to bedtime can slow down digestion. Remaining upright allows for better digestive flow.

Organs Involved in Digestion

  • Locations of Digestion:

    • Digestion occurs not only in the stomach and small intestine but also starts in the mouth.

  • Process of Digestion: Food begins breaking down immediately in the mouth with mechanical (chewing) and chemical (saliva with enzymes) actions.

Overview of the Digestive System Components

  • Main Organs:

    • Mouth

    • Esophagus

    • Stomach

    • Small intestine

    • Large intestine

  • Accessory Organs:

    • Salivary glands

    • Liver

    • Gallbladder

    • Pancreas

Digestion Types

  • Mechanical Digestion:

    • Mechanical processes such as chewing and peristalsis (muscle contractions) break down food.

  • Chemical Digestion:

    • Involves enzymes from saliva, stomach, and pancreas to further breakdown food into nutrients.

Mouth

  • Mastication: Chewing which is mechanical breaking down of food particles.

  • Saliva: Contains enzymes (like amylase) for chemical digestion, mainly targeting carbohydrates.

Stomach

  • Composition:

    • Three muscle layers: longitudinal, circular, and diagonal muscles for churning.

  • Churning action: Mixing food mechanically with gastric juices.

  • Gastric Secretions: Produce enzymes and acids essential for protein digestion.

  • Bolus to Chyme:

    • Once the food transitions from the stomach to the small intestine, it becomes known as chyme.

Small Intestine

  • Parts:

    • Duodenum: 10 inches long, initial segment where chyme mixes with bile and pancreatic juices.

    • Jejunum: 8 feet long, continues digestion and absorption.

    • Ileum: 12 feet long, final segment leading into the large intestine.

  • Total Length of Small Intestine: Approximately 21 feet.

  • Surface Area: Structure of villi and microvilli greatly increases the absorptive surface area of the intestine.

Large Intestine

  • Structure: About 5 feet long, comprised of cecum, colon (ascending, transverse, descending, and sigmoid), and rectum.

  • Function: Major site for water absorption.

Checkpoints in the Digestive System

  • Sphincters:

    • Muscular structures that control the flow of content between organs. Important sphincters include:

    • Upper Esophageal Sphincter: Controls food entry from the throat into the esophagus.

    • Lower Esophageal Sphincter: Controls food entry from the esophagus into the stomach; prevents backflow of stomach content.

    • Pyloric Sphincter: Controls entry from the stomach into the small intestine.

    • Ileocecal Valve: Controls entry from the ileum of the small intestine into the cecum of the large intestine.

Importance of Accessory Organs

  • Gallbladder: Stores bile but is not essential for life; a person can live without it.

  • Liver and Pancreas: Essential organs for digestion; responsible for producing bile and digestive enzymes, respectively.

Concluding Remarks

  • Continuity of Digestion: Digestion is a continuous process that occurs at various stages in different parts of the digestive tract, transitioning from one phase to another without a complete stop.

  • Next Steps: Focus will shift to detailed studies regarding absorption and elimination processes in the subsequent classes.