Gastrointestinal Lecture 1 Part 4 The Mouth and Stomach

Question 1

Anatomy of the digestive system

Answer 1

Question 2

Functions of the mouth

Answer 2

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

Question 3

What is swallowing?

Answer 3

Reflex response under control of the autonomic nervous system which includes includes closure of the glottis and inhibition of respiration

Question 4

Phases of respiration

Answer 4

• oral phase
• pharyngeal phase
• esophageal phase

Question 5

oral phase of swallowing

Answer 5

• 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

Question 6

Pharyngeal phase of swallowing

Answer 6

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

Question 7

Esophageal phase of swallowing

Answer 7

Bolus driven down esophagus by peristaltic contraction (speed = ~4 cm/s)

• Foods descends the esophagus

Question 8

What is extreme mastication called?

Answer 8

fletchication

Question 9

What is fletchication?

Answer 9

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

Question 10

Anatomy of the stomach

Answer 10

Question 11

FUnctions of the stomach

Answer 11

• 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

Question 12

How does digestion occur within the stomach?

Answer 12

mechanical and chemical

Question 13

Mechanical digestion in the stomach

Answer 13

facilitated by folded surface (rugae) which facilitate mixing and grinding

Question 14

Chemical digestion of food

Answer 14

HCl

• acidity denatures proteins (more soluble) cleaves pepsinogen → pepsin

Pepsin

• Enzyme that breaks down protein

Question 15

Purpose of different parts of the stomach

Answer 15

Question 16

What does ingested food leave the stomach as?

Answer 16

`chyme