Mouth, Pharynx , oesophagus

1. Introduction to the Gastrointestinal Tract

  • Overview of structures involved in ingestion and digestion:

    • Mouth/oral cavity

    • Pharynx

    • Oesophagus

    • Stomach

    • Small intestine (Duodenum, Jejunum, Ileum)

    • Large intestine (Colon, Rectum, Anus)

    • Accessory organs (Liver, Gallbladder, Pancreas)

2. Functions of the Gastrointestinal Tract

  • Main Functions:

    1. Nutrient absorption

    2. Water absorption

    3. Electrolyte balance

    4. Vitamin extraction

  • Other Functions:

    • Food intake

    • Metabolism and detoxification

    • Defecation

3. Structures of the Oral Cavity

3.1 Bones

  • Maxilla:

    • Fuses during development.

    • Forms the upper part of the oral cavity, nasal cavity sides, and floor of the orbit.

  • Mandible:

    • Fuses during development.

    • Bears lower teeth and forms temporomandibular joint (TMJ) for chewing.

3.2 Anatomy of the Oral Cavity

  • Divisions:

    • Vestibule: Between lips, cheeks, and gums.

    • Oral Cavity Proper: Enclosed by teeth and gums.

  • Boundaries:

    • Roof: Hard & soft palates.

    • Floor: Tongue and floor of the mouth.

    • Lateral: Cheeks.

    • Posterior: Leads to oropharynx.

3.3 Palate

  • Hard Palate: Formed by maxilla and palatine bones.

  • Soft Palate: Composed of muscles and an aponeurosis; the uvula hangs from it.

4. Tongue Anatomy and Function

4.1 Structure

  • Composed of intrinsic and extrinsic muscles.

  • Sensory receptors:

    • Taste buds for different modalities (e.g., vallate, foliate, fungiform, filiform).

4.2 Frenulum

  • Midline mucosal fold.

  • Tongue Tie: Condition where a short frenulum restricts tongue movement.

5. Teeth

  • Types of Teeth:

    • Deciduous teeth: 20 total.

    • Permanent teeth: 32 total.

      • 8 incisors (cut food)

      • 4 canines (tear food)

      • 8 premolars (crush food)

      • 12 molars (crush food)

  • Structure of a Tooth:

    • Enamel, Dentine, Cementum, and Pulp (connective tissue).

6. Salivary Glands

  • Major Glands:

    • Parotid, Submandibular, Sublingual.

  • Functions: Producing saliva to aid in digestion.

  • Minor salivary glands also present throughout the oral cavity.

7. Pharynx Structure

  • Division by Function:

    • Nasopharynx: Air only.

    • Oropharynx: Air & food.

    • Laryngopharynx: Air & food.

8. Tonsils

  • Parts:

    • Pharyngeal, Tubal, Palatine, Lingual tonsils as part of Waldeyer’s Ring.

  • Common site for infections (e.g., tonsillitis).

9. Swallowing Phases

9.1 Phases of Swallowing

  • Oral Stage: Voluntary; food formed into bolus.

  • Pharyngeal Stage: Involuntary; reflex action.

  • Oesophageal Stage: Peristalsis moves food through the oesophagus.

10. Oesophagus Anatomy

  • Muscular tube ~25 cm long, located behind trachea and heart.

  • Passes through diaphragm into the stomach.

  • Sphincters:

    • Upper oesophageal sphincter relaxes during swallowing.

    • Lower oesophageal sphincter prevents acid regurgitation.

  • Layers:

    1. Mucosa

    2. Submucosa

    3. Muscle layer (circular and longitudinal muscles)

    4. Serosa (visceral peritoneum).

11. Nerve Control in the GI Tract

  • Myenteric Plexus: Regulates GI motility.

  • Submucosal Plexus: Controls glandular secretions and mucosal smooth muscle.

  • Autonomic Nervous System Influence:

    • Sympathetic: Inhibits secretion and motility.

    • Parasympathetic: Stimulates functions.