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Swallowing & Gastric Filling
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Swallowing & Gastric Filling

SWALLOWING & GASTRIC FILLING
Mouth
Physical breakdown
Chemical breakdown
  • Carbohydrates - salivary secretions
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
Stomach
  • Temporary storage
  • Slows food transit to the small intestine.
  • Maximizes nutrient absorption.
  • Physical breakdown (like in the mouth)
  • Chemical breakdown of proteins to 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
  • 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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