NURS 651 Digestive System (1) (1)

Structure and Function of the Digestive System

• Presenter: Lakesha T. Thomas DNP, APRN, FNP-C

Digestive System Overview

• Gastrointestinal Tract:

  • Mouth

  • Esophagus

  • Stomach

  • Small Intestine

  • Large Intestine

  • Rectum

  • Anus

• Accessory Organs:

  • Liver

  • Gallbladder

  • Exocrine pancreas

Gastrointestinal Tract

• Also known as the alimentary canal.

• Key Digestive Processes:

  • Ingestion: Intake of food.

  • Propulsion: Movement of food and waste.

  • Secretion: Mucus, water, and enzymes.

  • Mechanical Digestion: Physical breakdown of food.

  • Chemical Digestion: Enzymatic breakdown of food.

  • Absorption: Uptake of nutrients.

  • Elimination: Removal of waste through defecation.

  • Immune Protection: Against infections.

Mouth

• Function:

  • Reservoir for chewing and mixing food with saliva.

  • Digestion initiates here.

  • Taste Buds: Identify tastes (salty, sour, bitter, savory, sweet).

  • Teeth: 32 permanent teeth assist in mechanical digestion.

Salivary Glands

• Three Pairs:

  • Submandibular

  • Sublingual

  • Parotid

• Saliva Composition:

  • Water, mucus, sodium, bicarbonate, chloride, potassium, and salivary α-amylase (for carbohydrate digestion).

• Controlled by Sympathetic and Parasympathetic nervous systems.

Esophagus

• A hollow muscular tube measuring ~25 cm.

• Conducts food from oropharynx to stomach.

• Sphincters:

  • Upper esophageal sphincter: Prevents air entry during respiration.

  • Lower esophageal sphincter (LES): Prevents stomach contents from refluxing.

Stomach

• Hollow, muscular organ for storing and mixing food.

• Secretes digestive juices to produce chyme.

Stomach Sphincters

• Lower Esophageal Sphincter: Prevents reflux

• Pyloric Sphincter: Controls movement of chyme into the duodenum.

• Limited substances absorbed here: alcohol, aspirin; impermeable to water.

Gastric Motility

• Swallowing: Relaxes the fundus of the stomach.

• Hormonal Influence:

  • Gastrin & Cholecystokinin enhance relaxation, stimulate peristalsis.

  • Sympathetic activity and secretin inhibit peristalsis.

Gastric Mixing and Emptying

• Gastric Emptying: Movement of gastric contents to the duodenum.

  • Influences: Larger food volumes increase, solids and fats delay gastric emptying.

Gastric Secretion

• Types of Secretion:

  • Mucus: Protective barrier

  • Hydrochloric acid: Dissolves food, bactericide, activates pepsinogen.

  • Enzymes: Pepsinogen (converted to pepsin) for protein breakdown.

• Intrinsic Factor: Necessary for vitamin B12 absorption.

• Gastric Pits: Ducts where gastric glands discharge secretions.

Function of Gastric Acid

• Dissolves food fibers

• Converts pepsinogen to pepsin

Small Intestine

• Length: 5 to 6 m.

• Segments:

  • Duodenum

  • Jejunum

  • Ileum

Intestinal Digestion and Absorption

• Nutrient Breakdown:

  • Carbohydrates to monosaccharides/disaccharides

  • Proteins to amino acids/peptides

  • Fats emulsified to fatty acids/monoglycerides

• Water and electrolytes absorption (~85%-90% in small intestine).

Large Intestine

• Functions: Massages fecal matter, absorbs water and electrolytes.

• Structure:

  • Cecum

  • Vermiform Appendix

  • Colon (Ascending, Transverse, Descending, Sigmoid)

  • Rectum and Anus

Liver

• Largest solid organ; attaches to the abdominal wall with the falciform ligament.

• Lobes:

  • Right Lobe (Caudate and Quadrate lobes)

  • Left Lobe (Glisson capsule covers the liver).

Liver Functions

• Bile Secretion:

  • Contains bile salts, cholesterol, bilirubin, and water.

  • Bile salts necessary for fat digestion.

• Metabolism:

  • Bilirubin breakdown, fat storage, production of plasminogen, and protein synthesis.

Gallbladder

• Function: Store and concentrate bile between meals.

• Hormonal Regulation: Contraction regulated by cholecystokinin.

Exocrine Pancreas

• Location: Head in the curve of duodenum, tail near spleen.

• Composed of acini and ducts secreting enzymes/alkaline fluids for digestion.

Disorders of Motility

• Gastroesophageal Reflux Disease (GERD):

  • Acid reflux causing esophagitis.

• Clinical Manifestations: Heartburn, chronic cough, upper abdominal pain.

Peptic Ulcer Disease

• Duodenal Ulcers: Most common peptic ulcer type.

• Manifestations: Chronic epigastric pain, relief with food/antacids.

Gastric Ulcer

• Location: Antral area adjacent to acid-secreting mucosa.

• Causes: Usually due to H. pylori infection; mucosal barrier damage.

Disorders of the Gallbladder

• Cholelithiasis: Gallstone formation.

  • Clinical Manifestations: Pain in the right hypochondrium, intolerance to fatty foods.

Disorders of the Pancreas

• Pancreatitis: Inflammation of the pancreas from enzyme leakage.

• Clinical Manifestations: Epigastric pain, nausea, elevated serum lipase levels indicating acute cases.