BIO 108 Digestive System Lab Study Guide

Digestive System: Lab Structures and Functions

Overview of the Digestive System

The digestive system is responsible for the mechanical and chemical breakdown of food, absorption of nutrients, and elimination of waste. It consists of the alimentary canal (gastrointestinal tract) and accessory organs that aid in digestion.

Major Anatomical Divisions

Peritoneum and Associated Structures

• Peritoneum: A serous membrane lining the abdominal cavity and covering abdominal organs.

• Parietal peritoneum: Lines the internal surface of the abdominal wall.

• Visceral peritoneum: Covers the external surfaces of most abdominal organs.

• Peritoneal cavity: The potential space between the parietal and visceral peritoneum, containing lubricating serous fluid.

Layers of the Alimentary Canal

• Mucosa: The innermost layer, consisting of epithelium, lamina propria, and muscularis mucosae; involved in secretion and absorption.

• Submucosa: Connective tissue layer containing blood vessels, nerves, and glands.

• Muscularis externa: Two layers of smooth muscle (inner circular, outer longitudinal) responsible for peristalsis and segmentation.

• Serosa (or adventitia): Outermost layer; serosa is a serous membrane, while adventitia is connective tissue (in regions outside the peritoneal cavity).

Oral Cavity and Associated Structures

Teeth

• Incisors: Chisel-shaped teeth for cutting food.

• Canines: Pointed teeth for tearing food.

• Molars: Broad, flat teeth for grinding food.

• Enamel: Hard, outermost layer of the tooth; the hardest substance in the body.

• Dentin: Calcified tissue beneath the enamel, forming the bulk of the tooth.

• Cementum: Bone-like material covering the tooth root.

• Crown: Exposed part of the tooth above the gum line.

• Root: Portion of the tooth embedded in the jawbone.

• Alveolar socket: Bony cavity in the jaw where the tooth root sits.

• Periodontal ligaments: Connective tissue fibers anchoring the tooth to the alveolar socket.

Tongue and Salivary Glands

• Lingual papillae: Projections on the tongue surface; types include filiform, fungiform, circumvallate, and foliate papillae (involved in taste and texture detection).

• Parotid glands: Largest salivary glands, located near the ear; secrete serous, enzyme-rich saliva.

• Submandibular glands: Located beneath the jaw; produce both serous and mucous saliva.

• Sublingual glands: Located under the tongue; primarily secrete mucous saliva.

Pharynx and Esophagus

• Pharynx: Muscular tube connecting the oral cavity to the esophagus; involved in swallowing.

• Esophagus: Muscular tube transporting food from the pharynx to the stomach.

• Gastroesophageal sphincter (lower esophageal sphincter): Ring of muscle at the junction of the esophagus and stomach; prevents reflux of stomach contents.

Stomach

• Cardia: Region where the esophagus enters the stomach.

• Fundus: Dome-shaped region above the cardia.

• Body: Main central region of the stomach.

• Pyloric antrum: Lower portion leading to the pylorus.

• Pylorus: Terminal region of the stomach, leading to the small intestine.

• Pyloric sphincter: Muscular valve controlling passage of chyme into the duodenum.

Small Intestine

• Duodenum: First segment; receives chyme from the stomach and digestive secretions from the pancreas and liver.

• Jejunum: Middle segment; primary site for nutrient absorption.

• Ileum: Final segment; absorbs remaining nutrients and connects to the large intestine.

• Circular folds (plicae circulares): Folds of the mucosa and submucosa that increase surface area for absorption.

• Villi: Finger-like projections of the mucosa that further increase surface area.

• Microvilli: Microscopic extensions of epithelial cell membranes, forming the "brush border" for maximum absorption.

Large Intestine

• Cecum: Pouch-like first part of the large intestine; receives material from the ileum.

• Colon: Divided into ascending, transverse, descending, and sigmoid regions; absorbs water and forms feces.

• Rectum: Terminal section storing feces before elimination.

• Anal canal: Final passageway for feces to exit the body.

• Taenia coli: Three longitudinal bands of smooth muscle on the colon surface.

• Haustra: Pouch-like segments of the colon formed by contraction of the taenia coli.

• Epiploic appendages: Small, fat-filled pouches attached to the colon.

• Variform appendix (vermiform appendix): Narrow, worm-like extension of the cecum; contains lymphoid tissue.

Accessory Organs

Pancreas

• Regions: Head (nestled in the duodenum), body, and tail (extends toward the spleen).

• Major ducts: Main pancreatic duct (duct of Wirsung) and accessory pancreatic duct; transport digestive enzymes to the duodenum.

Liver

• Lobes: Right, left, caudate, and quadrate lobes.

• Ligaments: Falciform ligament (separates right and left lobes), round ligament (remnant of fetal umbilical vein), and others anchoring the liver to the diaphragm and abdominal wall.

• Lobule organization: Hexagonal structural units composed of hepatocytes arranged around a central vein; portal triads at each corner contain branches of the hepatic artery, portal vein, and bile duct.

Gallbladder

• Major ducts: Cystic duct (from gallbladder), common hepatic duct (from liver), and common bile duct (formed by the union of cystic and common hepatic ducts); these ducts transport bile to the duodenum.

Summary Table: Digestive System Structures and Functions

Structure	Main Function
Peritoneum	Protects and supports abdominal organs; reduces friction
Mucosa	Secretion, absorption, and protection
Incisors	Cutting food
Canines	Tearing food
Molars	Grinding food
Parotid gland	Secretes serous saliva (amylase)
Stomach	Mixes and digests food; secretes acid and enzymes
Small intestine	Digestion and absorption of nutrients
Large intestine	Absorbs water; forms feces
Pancreas	Secretes digestive enzymes and bicarbonate
Liver	Produces bile; processes nutrients
Gallbladder	Stores and concentrates bile

Example: Pathway of Food Through the Digestive Tract

1. Mouth (teeth, tongue, salivary glands)

2. Pharynx

3. Esophagus

4. Stomach (cardia, fundus, body, pylorus)

5. Small intestine (duodenum, jejunum, ileum)

6. Large intestine (cecum, colon, rectum, anal canal)

Additional info: The digestive system's structure is closely related to its function, with specialized regions for mechanical breakdown, enzymatic digestion, absorption, and waste elimination. Accessory organs (pancreas, liver, gallbladder) play crucial roles in producing and delivering digestive secretions.