A&P2 - Stomach

Oral Cavity Structures

  • The oral cavity consists of various structures relative to digestion, focusing primarily on teeth and accompanying features.
  • Function of Teeth:
    • Teeth are essential for mastication (chewing).
    • They break down food into smaller pieces for easier digestion.

Anatomy of Teeth

  • Three Main Portions of a Tooth:
    • Crown: Portion visible when mouth is open, covered by enamel which protects against abrasion during chewing.
    • Neck: Joins crown to root; covered by gums (gingiva).
    • Root: Anchors tooth to mandible/maxilla, fits into the alveolar process, connected by ligaments.
  • Tooth Structure:
    • Dentin: Main structure covered by enamel (crown) or cementum (neck/root).
    • Pulp Cavity: Found within the dentin; contains connective tissue, blood vessels, lymphatic vessels, and nerves.

Types of Teeth

  • Deciduous Teeth (baby teeth): Typically 20, appear early in childhood.
  • Permanent Teeth: Adult teeth replace deciduous teeth as they are lost.

Boundaries of the Oral Cavity

  • Anterior Boundary: Lips.
  • Lateral Boundary: Cheeks and the buccinator muscle.
  • Superior Boundary: Hard and soft palate, with uvula suspended.
  • Inferior Boundary: Floor of the mouth, largely made up of the tongue.

Taste Buds

  • Taste buds are located between the papillae on the sides of the tongue, known as lingual moats.

Salivary Glands

  • The oral cavity contains three main salivary glands:
    • Parotid Glands: Largest, located anterior and inferior to the ear.
    • Submandibular Glands.
    • Sublingual Glands.
  • They produce mucus, watery fluid, and enzymes, forming saliva that aids in food preparation for digestion.

Pharynx

  • Function: Tube that transports the swallowed bolus (chewed food) from oral cavity to esophagus.
  • Part of both the digestive and respiratory systems, where air and food travel.
  • The epiglottis: Prevents food from entering the trachea during swallowing.

Esophagus

  • A tube extending from the pharynx to the stomach; first segment exclusively for digestion.
  • Two Sphincters:
    • Upper Esophageal Sphincter: Allows passage of food from pharynx.
    • Lower Esophageal Sphincter (Cardiac Sphincter): Prevents acid reflux by ensuring stomach acid does not enter the esophagus.
  • Hiatal Hernia: Condition where part of the stomach protrudes through the diaphragm, potentially causing reflux issues.

Stomach Anatomy

  • Capacity: Approximately 1.5 liters when fully distended.
  • Positioned beneath the liver and diaphragm in the upper abdominal cavity.
  • Four Portions of the Stomach:
    • Cardia: Connects to esophagus.
    • Fundus: Upper left portion above the cardia.
    • Body: Main central portion.
    • Pylorus: Connects to the small intestine (duodenum).
  • Rugae: Folds that allow stomach expansion and prevent damage during distension.

Layers of Stomach Wall

  • Muscularis Layer: Composed of three muscle layers (longitudinal, circular, and oblique) aiding in food mixing and breakdown.
  • Two Sphincters:
    • Cardiac Sphincter: Same as lower esophageal sphincter, controls food entry from esophagus.
    • Pyloric Sphincter: Controls food entry from stomach into the small intestine.

Stomach Functions

  • Physically mixes food and breaks it down into the liquid form known as chyme.
  • Chyme is expelled slowly into the small intestine (1-2 teaspoons at a time) and requires 2-6 hours for the stomach to empty following a meal.

Enzymatic Actions in the Stomach

  • Chief Cells:
    • Secrete pepsinogen, an inactive enzyme that becomes active pepsin when combined with hydrochloric acid (HCl).
    • Pepsin aids in protein digestion.
  • Parietal Cells:
    • Produce hydrochloric acid (HCl), creating an acidic environment crucial for enzymatic activity and bacterial control.
    • Produce intrinsic factor, essential for Vitamin B12 absorption leading to prevention of pernicious anemia.
  • Gastric Juices: Mixture of these secretions helps in digestion and preparation for nutrient absorption in the intestines.