Gastrointestinal Anatomy I

Gastrointestinal (GI) system

A continuous muscular tube extending from mouth to anus (≈5–7 m) through which food is digested and absorbed.

Mechanical digestion

Physical breakdown and mixing of food to aid digestion.

Chemical digestion

Enzymatic and acidic breakdown of food into absorbable molecules.

Oral cavity

The mouth region containing teeth, gums, tongue, palate, and tonsils where food is prepared for digestion.

Oral vestibule

Slit-like space between the teeth and the lips/cheeks.

Oral cavity proper

Space within the upper and lower dental arches; fully occupied by the tongue at rest.

Lips

Mobile muscular folds surrounding the mouth, covered externally by skin and internally by mucous membrane; used for grasping food, speech, and kissing.

Labial frenulum

Midline mucosal fold that attaches each lip to the gingiva.

Cheeks

Lateral walls of the oral cavity formed over zygomatic bones; similar structure to lips.

Buccal fat pad

Fatty pad in infants that reinforces cheeks and prevents collapse while sucking.

Gingivae (gums)

Fibrous tissue covered by mucous membrane firmly attached to alveolar processes and teeth.

Gingivitis

Inflammation of the gums that can spread to teeth and connective tissues.

Teeth

Hard conical structures in jaw alveoli used for mastication and speech.

Primary teeth

First (deciduous) set of teeth appearing in childhood.

Secondary teeth

Permanent adult dentition; normally 32 teeth.

Incisor

Chisel-shaped front tooth; one medial and one lateral per quadrant.

Canine

Pointed tooth lateral to incisors; one per quadrant.

Premolar

Transitional tooth between canines and molars; two per quadrant in adults.

Molar

Large grinding tooth; three per quadrant in adults.

Crown (tooth)

Exposed portion of a tooth above the gum line.

Neck (tooth)

Constricted region of a tooth between crown and root.

Root (tooth)

Portion of tooth within the alveolus anchoring it to the jaw.

Dentin

Bone-like primary substance forming the bulk of a tooth.

Enamel

Hard, protective outer covering over the crown of a tooth.

Cement (cementum)

Bonelike covering over the root of a tooth.

Pulp cavity

Central space in a tooth containing connective tissue, blood vessels, and nerves (from CN V).

Root canal

Canal within the root through which nerves and vessels enter the pulp cavity.

Tongue

Mobile muscular organ involved in mastication, taste, swallowing, speech, and oral cleansing; motor innervation by CN XII.

Root of tongue

Posterior one-third of the tongue; relatively fixed.

Body of tongue

Anterior two-thirds; visible and highly mobile part of the tongue.

Lingual papillae

Projections on the anterior tongue mucosa containing taste buds.

Foliate papillae

Leaf-like papillae on posterolateral tongue edges; house taste buds.

Vallate (circumvallate) papillae

Large papillae arranged in a V-shape anterior to tongue root; contain many taste buds.

Fungiform papillae

Mushroom-shaped papillae scattered on tongue surface with taste buds.

Filiform papillae

Thread-like papillae providing friction; lack taste buds.

Parotid gland

Largest salivary gland located near the ear; secretes watery saliva rich in amylase.

Submandibular gland

Salivary gland beneath the mandible producing mixed (serous and mucous) saliva.

Sublingual gland

Smallest major salivary gland under the tongue secreting mainly mucous saliva.

Saliva – key functions

Moistens mucosa, lubricates food, begins starch digestion, acts as intrinsic mouthwash, and prevents tooth decay.

Esophagus

Muscular tube carrying food from laryngopharynx to stomach; upper third voluntary muscle, lower third smooth muscle.

Esophageal hiatus

Opening in the diaphragm at T10 through which the esophagus passes.

Cardial orifice

Opening where the esophagus enters the stomach.

Stomach

Expandable digestive organ (holds 2–3 L) acting as blender and reservoir; converts food to chyme.

Rugae (gastric folds)

Longitudinal folds of gastric mucosa that increase surface area when stomach contracts.

Greater curvature

Convex inferior border of the stomach.

Lesser curvature

Concave superior border of the stomach.

Cardia (stomach)

Region surrounding the cardial orifice.

Fundus

Stomach’s domed superior part adjacent to the left diaphragm dome.

Body (stomach)

Central portion between fundus and pyloric part.

Pyloric part

Distal funnel-shaped region of the stomach leading to the duodenum.

Pyloric sphincter

Thickened circular muscle controlling gastric emptying into the duodenum.

Small intestine

Long convoluted tube (duodenum, jejunum, ileum) where most digestion and absorption occur.

Duodenum

First, shortest, widest, and most fixed small-intestine part; major site of digestion and nutrient absorption.

Jejunum

Middle section of the small intestine following the duodenum.

Ileum

Terminal portion of the small intestine ending at the ileocecal valve.

Bile

Digestive fluid produced by liver and stored in gallbladder; emulsifies fats.

Gallbladder

Small sac under the liver that stores and concentrates bile for release into the duodenum.

Pancreas

Retroperitoneal gland posterior to the stomach with head, body, and tail; both digestive and endocrine functions.

Pancreatic duct

Duct running the length of the pancreas, emptying exocrine secretions into the duodenum.

Pancreatic juice

Alkaline fluid containing digestive enzymes that neutralizes chyme and aids digestion.

Insulin

Pancreatic hormone that facilitates glucose uptake into muscle and other cells.

Glucagon

Pancreatic hormone that stimulates conversion of glycogen to glucose, raising blood sugar.