Digestive System Flashcards

Digestive System

Main and Accessory Organs

• Main Organs:
  • Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
• Accessory Organs:
  • Teeth, tongue, gallbladder, salivary glands, liver, and pancreas.

Main Functions of the Digestive System

1. Ingestion:
   • Occurs in the mouth.
2. Propulsion (Peristalsis):
   • Movement of food through the digestive tract.
3. Digestion:
   • Breakdown of food into absorbable components.
     • Mechanical Digestion: Prepares food for chemical digestion (chewing, churning).
     • Chemical Digestion: Complex molecules broken down by enzymes.
4. Absorption:
   • Transport of digested nutrients into the blood and lymph.
5. Defecation:
   • Elimination of indigestible substances as feces.

Peritoneum and its Subdivisions

• Peritoneum: Serous membrane.
  • Visceral Peritoneum: Surrounds digestive organs.
  • Parietal Peritoneum: Lines the body wall.
• Peritoneal Cavity: Potential space between the visceral and parietal peritoneum.
• Mesentery: Double layer of peritoneum.
  • Holds organs in place (e.g., loops of small intestine).
  • Sites of fat storage.
  • Provides a route for circulatory vessels and nerves.
• Mesocolon: Specific to the large intestine.

Peristalsis and Segmentation

• Peristalsis: Waves of muscle contraction and relaxation that propel food.
• Segmentation: Rhythmic local constrictions of the intestine that mix food with digestive juices and enhance absorption.

Layers of the Alimentary Canal

• Same four layers from esophagus to anus (lumen outward):
  1. Mucosa: Innermost layer.
     • Epithelium: Absorbing and secreting.
     • Lamina Propria:.
     • Muscularis Mucosae: Produces local movements of the mucosa (twitching).
  2. Submucosa: External to the mucosa.
     • Contains blood vessels, lymphatic vessels, and nerve fibers.
  3. Muscularis Externa: External to the submucosa; responsible for peristalsis.
     • Circular Layer: Inner layer; squeezes the gut tube.
     • Longitudinal Layer: Outer layer; shortens the gut tube.
  4. Serosa: Outermost layer.
     • Same as the visceral peritoneum.
     • Made up of simple squamous epithelium.

Oral Cavity Borders

• Lips: Anteriorly.
• Cheeks: Laterally.
• Palate: Superiorly.
  • Hard palate, soft palate, and uvula (end of soft palate).
• Tongue: Inferiorly.
• Fauces of Oropharynx: Posteriorly.

Functions of the Tongue

• Sense of taste.
• Manipulation of food during chewing.
• Mixing food with saliva to form a bolus.
• Moving the bolus into the pharynx during swallowing.
• Lingual Frenulum: Secures tongue to floor of mouth.

Deciduous and Permanent Teeth

• Deciduous (Baby) Teeth: 20.
  • First appear at 6 months.
• Permanent Teeth: 32.
  • Erupt by the end of adolescence.
• Dental Formula: 2I, 1C, 2P, 3M (divided in quarters; 8 \, x \, 4 = 32).
  • 2 Incisors
  • 1 Canine
  • 2 Premolars
  • 3 Molars

Parts and Layers of a Tooth

• Parts:
  1. Crown: Exposed surface.
  2. Neck: Where regions meet at the gum line.
  3. Root: In tooth socket.
• Layers:
  1. Enamel: Outer layer.
     • Hardest tissue in the body.
  2. Dentin: Underlies enamel.
  3. Pulp Cavity: Center of tooth.

Major Salivary Glands

• Saliva Composition: Water, ions, mucus, and enzymes.
• Saliva Functions: Moistens mouth, dissolves food chemicals, wets food, and binds food into a bolus.
  • Parotid Glands:
    • Parotid duct runs parallel to the zygomatic arch (angle of the jaw).
  • Submandibular Glands:
    • Lie along the medial surface of the mandible (under the mandible).
  • Sublingual Glands:
    • Under the tongue, in the floor of the oral cavity.
    • Contain primarily mucus cells.

Cardiac Sphincter

• Importance: Prevents regurgitation of acidic stomach juices into the esophagus.
• Location: Between the stomach and esophagus.

Main Parts of the Stomach

• Function: Storage tank where food is churned into chyme.
• Chyme: Paste-like substance formed in the stomach.
• Food remains in the stomach for approximately 4 hours.
  • Cardiac Region (Cardia)
  • Cardiac Sphincter
  • Fundus
  • Body
  • Pyloric Part
    • Pyloric antrum
    • Pyloric canal
    • Pyloric sphincter (valve for stomach and duodenum)
  • Rugae of Mucosa: Mucosal folds.
  • Greater Curvature
  • Lesser Curvature
• Muscularis Externa: Contains three layers (longitudinal, circular, and oblique).
  1. Longitudinal layer
  2. Circular layer
  3. Oblique layer

Main Parts of the Small Intestine

Three subdivisions:

1. Duodenum:
   • Small C-shaped loop.
   • Most chemical digestion occurs here.
   • Receives enzymes and bile.
   • Main pancreatic duct and common bile duct enter the duodenum.
     • Sphincters control the entry of bile and pancreatic juices.
2. Jejunum:
   • Most nutrient absorption takes place.
3. Ileum:
   • Absorbs most vitamins and minerals.

Main Functions of the Small Intestine

• Longest portion of the alimentary canal.
• Completion of Digestion:
  • Bile from the liver/gallbladder.
  • Enzymes from the pancreas.
• Site of Most Enzymatic Digestion and Absorption

Modifications for Absorption in the Small Intestine

• Circular Folds: Transverse ridges of mucosa and submucosa.
• Villi: Fingerlike projections of the mucosa covered with simple columnar epithelium.
• Microvilli: Further increase surface area for absorption.

Main Parts of the Large Intestine

1. Cecum
   • Opening of the appendix.
2. Ascending Colon
3. Transverse Colon
4. Descending Colon
5. Sigmoid Colon
6. Rectum
7. Anus

Special Features of the Large Intestine

• Teniae Coli: Thickening of longitudinal muscularis externa.
• Haustra: Bumps or puckering created by teniae coli.
• Epiploic Appendages: Fat-filled pouches of visceral peritoneum.
• Right Colic (Hepatic) Flexure: Between the ascending and transverse colon.
• Left Colic (Splenic) Flexure: Under the spleen.
• Ileocecal Valve: Prevents backflow.
• Rectum
• Anal Canal
  • External anal sphincter

Main Functions of the Large Intestine

• Main Function: Absorb water and electrolytes.
• Digested residue contains few nutrients.
• Small amount of digestion by bacteria.
• Mass peristaltic movements force feces toward the rectum.

Main Parts of the Liver

• Located in the RUQ under the diaphragm, extends to the LUQ.
• Liver Capsule: Connective tissue sheet covering the liver.
  • Falciform Ligament: Anterior thickened part of the capsule that separates the larger right lobe from the left lobe.
    • Left and right lobe
  • Round Ligament: Posterior thickened part of the capsule that separates the left lobe from the quadrate lobe.
  • Ligamentum Venosum: Separates the caudate lobe from the left lobe.

Elements Passing Through Porta Hepatis

Allows passage of:

1. Hepatic Portal Vein: Brings blood toward the liver.
2. Hepatic Artery Proper
3. Common Hepatic Duct (Bile Duct): Brings bile out of the liver.
   • Cystic duct takes bile to the gallbladder; the bile duct takes bile to the duodenum.

Main Functions of the Liver Regarding the Digestive System

• Bile Production
  • Emulsification of fats (lipids).

Bile Storage and Delivery

• Location of bile storage: Gallbladder.
• Delivery: Contracts and secretes bile to the duodenum via ducts.

Main Functions of the Pancreas

• Amylase
• Lipase – lipids
• Endocrine Function:
  • Produces insulin and glucagon.
• Exocrine Function:
  • Acinar cells make, store, and secrete enzymes that digest food in the small intestine.
• Main Pancreatic Duct:
  • Extends the length of the pancreas.
  • Joins the bile duct to form the hepatopancreatic ampulla.
    • Empties into the duodenum.

Main Cause of Peptic Ulcer

• Caused by Helicobacter pylori.