Session 1 - Introduction to the GI system

Question 1

What is the overall function of the gastrointestinal system?

Answer 1

• Secretion
• Digestion
• Motility
• Absorption

Question 2

What are the qualities of the products of digestion?

Answer 2

• Sterile
• Neutral
• Isotonic

Question 3

What solutions does the process of digestion create?

Answer 3

• Small sugars
• Amino acid and small peptides
• Lipids in very small particles

Question 4

Define absorption

Answer 4

• Specific active or passive uptake of nutrient molecules, water and electrolytes

Question 5

Give three waste products of the GI tract

Answer 5

• Residue from food
• Gut debris
• Materials secreted from liver

Question 6

What needs to happen to food for digestion to occur?

Answer 6

• Disrupted physically to release large molecules

* Broken down chemically to release small molecules

Question 7

Why do ingested foods need to be stored?

Answer 7

• We can eat much faster than we can digest

Question 8

Outline the overall process of digestion

Answer 8

• Initial physical disruption
• Ingestion & transport to storage
• Initial chemical disruption & creation of suspension – forming chyme
• Disinfection
• Controlled release of chyme
• Dilution and neutralisation of chyme
• Completion of chemical breakdown
• Absorption of nutrients and electrolytes
• Final absorption of water and electrolytes,
• Producing faeces for controlled excretion

Question 9

List the two mechanisms involved in physical disruption of food

Answer 9

Mastication

Saliva

Question 10

Outline the functions of saliva

Answer 10

• Protects mouth
• Lubricates food
• Starts digestion

Question 11

Give four ways in which saliva protects the mouth

Answer 11

• Wet - maintains mucosae
• Bacteriostatic
• Alkaline - protects teeth
• High calcium - protects teeth

Question 12

What does saliva initially digest?

Answer 12

• Sugars

Question 13

What is food called after it has been physically disrupted?

Answer 13

• Bolus

Question 14

Where does storage, initial disruption and disinfection take place?

Answer 14

Stomach

Question 15

How is chyme produced in the stomach?

Answer 15

• Action of acid, enzymes and agitation

Question 16

Where does dilution and neutralisation of chyme take place?

Answer 16

• Duodenum and jejunum

Question 17

Why does dilution take place?

Answer 17

• To ensure that the chyme is of the same osmotic potential as the small intestine

Question 18

What do enzymes from pancreas and intestine do?

Answer 18

• Cleave peptides to amino acids
• Cleave polysaccharides to monosaccharaides
• Breakdown and re-form lipids
• Break down nucleic acids

Question 19

How does absorption of nutrients and electrolytes take place?

Answer 19

• Intestine has large SA due to brush border
• Epithelial cells absorb small molecules - some actively, some passively
• Often coupled to sodium absorption

Question 20

What are absorbed nutrients taken into?

Answer 20

• Hepatic portal circulation

Question 21

Where does final absorption of water and electrolytes occur?

Answer 21

• Large intestine

Question 22

Where does faeces accumulate?

Answer 22

• Descending and sigmoid colon

Question 23

How does defecation occur?

Answer 23

• Faeces propelled into rectum

* Controlled relaxation of sphincters and expulsion of faeces occurs

Question 24

What is the function of the stomach?

Answer 24

• Relaxes to accommodate food
• Rhythmical contraction
• Secretes acid and proteolytic enzymes to break down tissues
• Disinfects bolus

Question 25

Outline the process of receptive relaxation

Answer 25

* Stomach strongly contracted between meals * Relaxes as bolus enters * Prevents a rise in pressure of the stomach

Question 26

What takes place in the duodenum and jejunum?

Answer 26

* Water drawn in from ECF * Bile added to chyme * Pancreas, liver and intestinal secretions (enzymes and bile acids) * Liver and pancreas secrete alkali and neutralise acid

Question 27

How is duodenum adapted to the highly concentrated chyme it receives from the stomach?

Answer 27

* Wall permeable to water | * Draws water in to dilute contents

Question 28

Outline the four layers of alimentary canal

Answer 28

* Mucous membrane * Submucosa * Muscularis externae * Serosa

Question 29

What makes up the mucous membrane?

Answer 29

* Lining epithelium * Connective tissue * Thin layer of smooth muscle

Question 30

What makes up the submucosa?

Answer 30

* Fibroelastic tissue with * Vessels * Nerves of the submucosal plexus * Leucocytes * Fat cells

Question 31

What makes up the muscularis externa?

Answer 31

An inner circular layer | Outer longitudinal layer

Question 32

What lies between the two layers of the muscularis externae?

Answer 32

• Myenteric plexus

Question 33

What is the serosa?

Answer 33

• A thin outer covering of connective tissue

Question 34

What is endoscopy?

Answer 34

• A long, thing tube which allows direct visual examination, biopsy sampling and therapeutic treatment of the gastro-intestinal tract

Question 35

What is nasendoscopy?

Answer 35

• Allows visualisation of the nose, mouth and pharynx

Question 36

What structure marks the beginning of the oesophagus?

Answer 36

• Cricopharyngeal sphincter

Question 37

Where does the diaphragm cuff the oesophagus, and why is this clinically relevant?

Answer 37

* At the oesophagogastric mucosal junction | * This relationship may be disrupted by a hiatus hernia, which allows the stomach to herniate into the thorax

Question 38

Outline the venous drainage of the oesophagus

Answer 38

• Drains into the left portal system via the left gastric vein

Question 39

How is the oesophagus adapted to rapid transport?

Answer 39

• Streamlined structure which minimises friction

Question 40

What are the longitudinal ridges of the stomach called?

Answer 40

• Rugae, increase SA

Question 41

Where is gastric ulceration most common?

Answer 41

• Lesser curve at the angulus

Question 42

What is the normal maximal fluid contents of the gut?

Answer 42

* 14L | * 1kg food, 1.5L saliva, 2.5L gastric secretions, 9l of water and alkali

Question 43

How are the contents of the gut removed?

Answer 43

* Small intestine absorbs 12.5l * Large intestine absorbs 1.35 * 150g faeces expelled

Question 44

What happens if the balance between secretion and absorption altered?

Answer 44

* Considerable loss of water and electrolytes, mostly from body fluids * Rapid dehydration and electrolyte disturbance

Question 45

Name three control systems of the gut

Answer 45

* Neural * Paracrine * Endocrine

Question 46

Why are three overlapping control systems needed in the gut?

Answer 46

• Motility and secretion need precise control

Question 47

What is the somatic motor used for in the gut?

Answer 47

• Ingestion (chewing) and excretion (defecation)

Question 48

What is the most significant neural control system of the gut?

Answer 48

• Autonomic (specifically parasympathetic) control

Question 49

What do post ganglionic neurones form in the gut?

Answer 49

• Plexuses

Question 50

What does the "gut nervous system" control?

Answer 50

• Coordinates secretion and motility

Question 51

What enteric nervous system of the gut made up of?

Answer 51

• Two nerve plexuses which may act independently of CNS and be modified by both branches of the ANS

Question 52

What is paracrine secretion?

Answer 52

• Chemical messengers diffuse locally

Question 53

Name a chemical messenger secreted via the paracrine method

Answer 53

Histamine

Question 54

Give three factors the endocrine system controls in the digestive system

Answer 54

* Stomach acid * Alkali secretion from liver and pancreas * Enzyme secretion

Question 55

What type of structure do gut hormones share?

Answer 55

• All peptide derived

Question 56

What are the two groups of gut hormones?

Answer 56

* Gastrin group | * Secretin group