Lectures 1.1 + 1.2 - Introduction to GI

Question 1

Define digestion

Answer 1

The conversion of what we eat, by both chemical and physical disruption, into a relatively sterile, neutral and isotonic solution from which we can absorb our nutrients

Question 2

What are the 4 histological layers of the wall of the GI tract?

Answer 2

Mucosa - epithelia, lamina propria and muscularis mucosae
Submucosa
Muscularis externa - circular and longitudinal
Serosa

Question 3

What sort of epithelium lines the GI tract?

Which areas are the exceptions, and what sort lines these?

Answer 3

Simple columnar epithelium

Upper oesophagus and distal anus = stratified squamous

Question 4

What is significant about the muscularis externa of the stomach?

Answer 4

3 layers - oblique, circular and longitudinal

Question 5

What is the function of the duodenum?

Answer 5

Dilution and neutralisation of acidic chyme from stomach - addition of water from ECF and alkaline secretions from pancreas

Question 6

What is the function of the jejunum and ileum?

Which area is this especially performed in?

Answer 6

Absorption of nutrients, especially in the terminal ileum

Question 7

What is the major function of the large intestine?

Answer 7

Absorption of water, as well as vitamins and small molecules

BUT although major role is absorption of water, still absorbs less than the small intestine

Question 8

Name two microscopic features present in the colon

Answer 8

Crypts of Lieberkuhn

Peyer’s patches

Question 9

How many litres of fluid are required to digest 1kg of food?

Include a breakdown of the figure into its components

Answer 9

13 Litres -

• 1.5L of saliva
• 2.5L of gastric secretions
• 9L of water/alkali from small intestine

Question 10

If 13L of fluid is required to digest a kilo of food, where is this absorbed? How much is excreted?

Answer 10

12.5L in small intestine
1.35L in large intestine
Just 0.15kg in faeces

Question 11

How is fluid balance in the gut controlled?

Answer 11

Neurocrine, endocrine and paracrine control

Question 12

What aspects of the GI tract are under somatic/voluntary control?

Answer 12

Mouth and upper oesophagus - i.e. ingestion

External anal sphincter - i.e. excretion

Question 13

Which substances are involved in paracrine control of the GI tract?

Answer 13

Histamine

Vasoactive substances

Question 14

What sort of hormones are involved in GI tract control?

Answer 14

Peptide hormones only

Question 15

What are the 2 overall functions of the GI tract?

Answer 15

Breaking down large food molecules into small ones

Absorbing small molecules, minerals and water into the body