Digestive System Anatomy

Oral Cavity

The oral cavity is the entry point for food into the digestive tract and is responsible for the initial mechanical and chemical breakdown of food.

• Hard palate: The bony anterior portion of the roof of the mouth, separating the oral and nasal cavities.

• Soft palate: The muscular posterior portion of the palate, which rises during swallowing to close off the nasopharynx.

• Uvula: A small, fleshy extension at the back of the soft palate, aiding in speech and swallowing.

• Lingual frenulum: A fold of mucous membrane that anchors the tongue to the floor of the mouth.

• Palatine tonsil: Lymphatic tissue located on either side of the oropharynx, involved in immune defense.

Pharynx

The pharynx is a muscular tube that serves as a passageway for both air and food, connecting the oral cavity to the esophagus and the nasal cavity to the larynx.

• Nasopharynx: The upper part of the pharynx, connecting to the nasal cavity.

• Oropharynx: The middle part, located behind the oral cavity.

• Laryngopharynx: The lower part, leading to the larynx and esophagus.

• Epiglottis: A flap of cartilage that covers the trachea during swallowing, preventing food from entering the airway.

Esophagus

The esophagus is a muscular tube that transports food from the pharynx to the stomach via peristaltic movements.

• Gastroesophageal sphincter: A ring of muscle at the junction of the esophagus and stomach that prevents reflux of stomach contents.

Stomach

The stomach is a muscular organ that continues the mechanical and chemical digestion of food, mixing it with gastric juices.

• Pyloric sphincter: Controls the passage of chyme from the stomach to the duodenum.

• Greater curvature: The long, convex lateral border of the stomach.

• Lesser curvature: The short, concave medial border of the stomach.

• Rugae: Folds in the stomach lining that allow expansion as the stomach fills.

Small Intestine

The small intestine is the primary site for digestion and absorption of nutrients. It is divided into three regions.

• Duodenum: The first section, where most chemical digestion occurs.

• Jejunum: The middle section, specialized for absorption.

• Ileum: The final section, leading to the large intestine.

• Ileocecal valve: Controls flow from the ileum to the cecum.

• Circular folds: Folds of the mucosa that increase surface area for absorption.

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

• Lacteals: Lymphatic vessels within villi that absorb dietary fats.

• Microvilli/brush border: Microscopic extensions of epithelial cells that maximize absorption.

Large Intestine

The large intestine absorbs water and electrolytes, forming and storing feces.

• Cecum: The pouch-like beginning of the large intestine.

• Vermiform appendix: A narrow, worm-like extension of the cecum.

• Ascending colon: Travels upward on the right side of the abdomen.

• Transverse colon: Crosses the abdomen from right to left.

• Descending colon: Travels downward on the left side.

• Sigmoid colon: S-shaped segment leading to the rectum.

• Rectum: Stores feces before elimination.

• Haustra (sing. haustrum): Pouches formed by the contraction of the colon's muscular bands.

• Anus: The terminal opening of the digestive tract.

Accessory Organs

Teeth

Teeth are essential for mechanical digestion, breaking food into smaller pieces.

• Numbers, types & locations: Humans typically have 20 deciduous (milk) teeth and 32 permanent teeth.

• Deciduous (milk) teeth: The first set of teeth, which are eventually replaced by permanent teeth.

• Permanent teeth: The adult set of teeth.

• Incisors: Chisel-shaped teeth for cutting food.

• Canines: Pointed teeth for tearing food.

• Pre-molars (bicuspids): Teeth with two cusps for grinding.

• Molars: Large, flat teeth for crushing and grinding food.

Tongue

The tongue is a muscular organ involved in taste, speech, and manipulation of food.

• Salivary glands: Produce saliva to moisten food and begin digestion.

• 1. Parotid gland: Largest salivary gland, located near the ear.

• 2. Submandibular gland: Located beneath the jaw.

• 3. Sublingual gland: Located under the tongue.

Pancreas

The pancreas produces digestive enzymes and hormones.

• Digestive juice: Contains enzymes for breaking down carbohydrates, proteins, and fats.

• Pancreatic duct: Delivers pancreatic juice to the duodenum.

Liver

The liver is the largest internal organ, involved in metabolism, detoxification, and bile production.

• Bile: A digestive fluid that emulsifies fats.

• Common hepatic duct: Transports bile from the liver.

Gallbladder

The gallbladder stores and concentrates bile, releasing it into the small intestine as needed.

• Bile: Stored and released by the gallbladder.

• Cystic duct: Connects the gallbladder to the common bile duct.

• Common bile duct: Delivers bile to the duodenum.

Other Structures

Mesenteries

Mesenteries are folds of the peritoneum that support and stabilize the digestive organs.

• Mesentery proper: Attaches the small intestine to the posterior abdominal wall.

• Greater omentum ("fatty apron"): A large fold of peritoneum that hangs from the stomach, containing fat deposits and immune cells.

• Lesser omentum: Connects the stomach and liver.

• Mesocolon: Attaches the colon to the posterior abdominal wall.

Summary Table: Digestive System Structures

The following table summarizes the main regions and accessory organs of the digestive system.

Additional info:

• Digestive system anatomy is foundational for understanding physiology, pathology, and clinical medicine.

• Each structure plays a specific role in the breakdown, absorption, and transport of nutrients.