9.4 Digestion in the mouth and stomach

Question 1

Digestion in the mouth

Answer 1

Food is broken down by teeth using the incisors and molars
Food in the mouth triggers the formation of saliva
Saliva contains enzymes that help to chemically break down the food
One enzyme produced is a amylase which breaks down starches into disaccharides
Saliva also secretes mucus, used to lubricate food to make swallowing easier, turning the food into a bolus.

Question 2

What happens to food once it enters the esophagus?

Answer 2

The esophagus is a long muscular tube that carries food from the pharynx to the stomach.
The food stretches the walls of the esophagus, activating smooth muscles to contract the food to travel.
This is called peristalsis
Peristalsis takes about 8 seconds long

Question 3

What happens when food enters the stomach?

Answer 3

The stomach has a J-shape and can store up to 2L of food.
Proteins are partially digested in the stomach, but lipids and carbs are not.
The movement of food in and out of the stomach is controlled by the circular motion of sphincter muscles
The gastroesophageal sphincter is where the esophagus and stomach join, allowing food to enter the stomach and preventing it from leaving.

Question 4

4 layers of the stomach

Answer 4

Mucosa, submucosa, muscularis, and serosa

Question 5

Mucosa

Answer 5

Innermost layer, secretes gastric juice. Epithelial cells in stomach regenerate every 3 days

Question 6

Submucosa

Answer 6

Layer of connective tissue containing network of nerves and blood vessels

Question 7

Muscularis

Answer 7

Muscle layer, that consists of smooth muscles, frequently churns and mixes food to make a semi-liquid called chyme.

Question 8

Serosa

Answer 8

Smooth, outermost layer, holds the stomach in place and secretes fluids to reduce friction with organs.

Question 9

Digestion in stomach

Answer 9

Nerves in the submucosa detect food and release a hormone called gastrin.
Gastrin is released into the bloodstream and transported to gastric cells in the stomach, stimulating release of gastric juice (PH 2-3)
The low PH is required to activate a digestive enzyme called pepsinogen which can be converted into pepsin
This protein breaks down proteins in the stomach into their individual amino acids.

Question 10

Acid reflux

Answer 10

If the gastroesophageal sphincter does not close completely, acid from the stomach enters the esophagus

Question 11

Stomach ulcer

Answer 11

A bacteria called Heliobacterialor is able to survive in stomach acid
The bacteria burrows through the mucosa, exposing the stomach lining to strong stomach acid, which can open a sore called an ulcer.
They can bleed and be painful.