Gastrointestinal System

Swallowing and Gastric Filling

Anisha ValliLeave a comment

MOUTH

Physical breakdown

  • Food into smaller particles → mastication (chewing)

Chemical breakdown

  • Carbohydrates → salivary secretions

Secretions

  • Secreted by salivary glands (parotid gland, sublingual, sbmandibular)
  • Secreted in anticipation of and during food consumption.
  • Salivary secretions:
    – Salivary amylase: breaks down polysaccharides → maltose
    – Mucus: moistens food, forms bolus
    – Lysozyme: lyses bacteria
    0.5% of saliva is enzymes and electrolytes; the rest is water.

PHARYNX AND ESOPHAGUS

Motility (movement)

  • Food from oral cavity to stomach

SWALLOWING ORAL, PHARYNGEAL AND ESOPHAGEAL PHASES.

Tongue

  • Pushes to the back of the pharynx to initiate swallowing.

Pharynx

  • Common passageway for both food and air, continuous with trachea

Epiglottis

  • Laryngeal flap that prevents the bolus from entering the trachea.

Esophagus

  • Esophageal sphincter is open (relaxed) to let passage of food
    – Sphincters: modified, one-way valves that comprise smooth muscle; they regulate food movement through the alimentary canal.
    – Peristalsis: unidirectional wave-like smooth muscle contractions to push food down the esophagus and into stomach

GASTRIC DIGESTION

  • Peristalsis deposits food in the stomach
  • Bolus passes through the gastroesophageal sphincter

Clinical Correlation: heartburn occurs when acidic contents of the stomach backflow into the esophagus.

STOMACH KEY FUNCTIONS

  • Temporary storage
  • Slows food transit to the small intestine.
  • Maximizes nutrient absorption.
  • Physical breakdown (like in the mouth)
  • Chemical breakdown of proteins → amino acids
    – Salivary amylase (from mouth) continues carbohydrate breakdown in the stomach.

GASTRIC PHASES

  1. Filling: food enters the stomach (through the gastroesophageal sphincter).
  2. Mixing: peristaltic contractions churn the food.
    – Gastric juices secretion to produce chyme (solution of partially digested macromolecules)
  3. Emptying, in which peristaltic contractions propel chyme into the small intestine.

GASTRIC FILLING PHASE IN DEPTH

  • Gastroesophageal sphincter is a passage-way for food between esophagus and stomach
  • Anatomical divisions of stomach: fundus, body, antrum
  • Smooth muscle lining
    – Receptive relaxation: Stomach muscles “relax” to “receive” food
  • Smooth muscle walls reduce tone to expand stomach volume (in response to food reception)
    – Stomach volume = 0.5L empty → expands to 0.8L to 4.0L during receptive relaxation
    – Increase in volume allows stomach to accommodate food with little rise in pressure
    (Note: Intertextual variation exists regarding the stomach’s full capacity during receptive relaxation.)
    – Facilitates temporary storage – stomach secretes chyme slowly, gives the small intestine more time to absorb nutrients.

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