Gastrointestinal Lecture 1 Part 4 The Mouth and Stomach Flashcards
Anatomy of the digestive system
Functions of the mouth
Mechanical breakdown of food
- Mastication (chewing)
- teeth and facial muscles help to move jaw for chewing
Preparation for swallowing
- Moistening of food bolus
- saliva produced by salivary glands
Onset of digestion
- Enzymatic breakdown of carbohydrates
- minor contribution
- salivary amylase
What is swallowing?
Reflex response under control of the autonomic nervous system which includes includes closure of the glottis and inhibition of respiration
Phases of respiration
- oral phase
- pharyngeal phase
- esophageal phase
oral phase of swallowing
- Initiated by voluntary collection of food bolus into the pharynx by the tongue (oral phase)
- Tongue pushes food to bolus to back of mouth
- conscious act of swallowing triggers reflex
Pharyngeal phase of swallowing
Triggers involuntary contraction of pharyngeal muscles, pushing bolus into esophagus
- Soft palate elevates to prevent food entering the nasal passage
- Epiglottis covers the glottis, preventing bolus entry into the trachea, upper esophageal sphincter relaxes
Esophageal phase of swallowing
Bolus driven down esophagus by peristaltic contraction (speed = ~4 cm/s)
- Foods descends the esophagus
What is extreme mastication called?
fletchication
What is fletchication?
Coined by Horace Fletcher
- Food faddist
- Targeting economic hardship (not weight loss!)
- Advocated for “Fletcherizing”: chewing food until it is liquified to enhance nutrient absorption (100s chews/bite)
- Claimed to decrease food consumption by 1/3 and decreased feces production by 1/10! Unsubstantiated.
- Ignored millions of years of evolution that optimized the gut for nutrient absorption, including the stomach’s role in breaking down and liquifying ingested food
Anatomy of the stomach
FUnctions of the stomach
- Stores ingested material
- Continues digestion (dissolves and breakdowns food bolus and macromolecules)
- Regulates emptying into small intestine and makes sure it is not overwhelmed by the food
How does digestion occur within the stomach?
mechanical and chemical
Mechanical digestion in the stomach
facilitated by folded surface (rugae) which facilitate mixing and grinding
Chemical digestion of food
HCl
- acidity denatures proteins (more soluble) cleaves pepsinogen → pepsin
Pepsin
- Enzyme that breaks down protein
Purpose of different parts of the stomach