INTEGRATED FUNCTION OF THE GUT

Question 1

What are the two plexi found within the wall of the GI tract?

Answer 1

Myenteric plexus

Submucosal plexus

Question 2

Where is the myenteric plexus found in the wall of the GI tract?

Answer 2

Between the longitudinal and the circular layers of the muscle.

Question 3

What is another name for the myenteric plexus?

Answer 3

Auerbach’s plexus

Question 4

What is another name for the submucosal plexus?

Answer 4

Meissner’s plexus

Question 5

What is the main function of the myenteric plexus?

Answer 5

Coordinates gut movement

Question 6

What is the main function of the submucosal plexus?

Answer 6

Control glands

Question 7

What is another name for the mixing process that occurs in the large intestine?

Answer 7

Haustral contractions

Segmental contractions

Question 8

What causes haustral contractions?

Answer 8

Contraction of the taeniae coli

Question 9

What is the gastrocolic reflex?

Answer 9

Food leaving the stomach to reach the duodenum sets of a reflex which sends a massive intense contraction through the transverse colon and pushes contents into rectum.

Question 10

What is the role of the pacemaker cells in the stomach?

Answer 10

Set the basic electrical rhythm for contractions - about 3 per minute

Question 11

How does the mixing of food happen within the stomach?

Answer 11

Contractions push the food down the stomach, however, because the pyloric sphincter is closed, the smaller bits get pushed back up into the body of the stomach, while the bigger bits get squashed and broken up.

Question 12

What do the force and frequency of contractions in the stomach depend on?

Answer 12

Intrinsic neural activity
Myogenic properties of smooth muscle
Hormones being secreted

Question 13

Which type of food will empty from the stomach first? Carbohydrate, Fat, Protein

Answer 13

Carbohydrate

Question 14

Which type of food will take the longest to empty from the stomach? Carbohydrate, Fat, Protein

Answer 14

Fat

Question 15

What affect do fatty acids have on the pyloric sphincter?

Answer 15

Increases contractility

Question 16

How does osmotic pressure of the contents of the duodenum affect rate of gastric emptying?

Answer 16

Hyperosmotic (very concentrated) chyme activates osmoreceptors in the duodenum that decrease gastric emptying.

Question 17

What nerves is responsible for allowing the stomach to distend?

Answer 17

Vagus

Question 18

Where in the GI tract is the Auerbach plexus not between the circular and longitudinal muscle? Where is it found?

Answer 18

In stomach

Between the oblique and the circular layers.

Question 19

Which hormones are released by the duodenum in response to the presence of chyme coming through the pyloric sphincter? What is their function?

Answer 19

Somatostatin
Secretin
Cholecystokinin
Gastric intestinal peptide

All inhibit gastric empyting

Question 20

Is the small intestine doing anything in the fasting state?

Answer 20

Yes. There are migrating motor complexes that occur every 90-120 mins.

Question 21

What is the role of the migrating motor complexes that occur in the small intestine during the fasting state?

Answer 21

Move indigestible food such as tomato skins, nuts and sweetcorn

Remove dead epithelial cells

Prevent bacterial overgrowth

Stop colonic bacteria entering the small intestine.

Question 22

What is the medical term for vomiting?

Answer 22

Emesis

Question 23

What are the associated symptoms to vomiting?

Answer 23

Tachycardia
Sweating
Nausea
Pallor
Salivation

Question 24

How does the body make sure that vomit does not make its way into the nasopharynx?

Answer 24

The soft palate rises to block entry into it

Question 25

What are the different classes of drug that increase GI tract motility?

Answer 25

``` Fecal softeners Bulk laxatives Osmotic laxatives Stimulant laxatives Motility stimulants ```

Question 26

Name 2 types of osmotic laxatives and describe how they work.

Answer 26

Lactulose - disaccharide of fructose and galactose which is degraded by bacteria. Monosaccarides ferment to produce lactate and acetate which draw water into intestine. Saline purgatives - such as magnesium sulphate and magnesium hydroxide. Increases tonicity hence drawing more water into the lumen.

Question 27

What are the different classes of drug that decrease GI tract motility?

Answer 27

Anti-diarrhoeal drugs Antipasmodics

Question 28

How do the anti-pasmodic drugs work? (They decrease gut motility)

Answer 28

2 types: Anti-muscarinics - decrease muscle tone by inhibiting parasympathetic activity Mebeverine - acts directly on smooth muscle

Question 29

What is the role of somatostatin?

Answer 29

Inhibits most secreting cells of the GI tract and pancreas.

Question 30

What is the role of cholecystokinin?

Answer 30

Inhibits gastrin production from the stomach and hence slows emptying Stimulates gallbladder contraction

Question 31

What is the role of leptin?

Answer 31

Signals satiety to the central nervous system

Question 32

What is the role of ghrelin?

Answer 32

Signals hunger to the central nervous system?

Question 33

What stimulates the release of secretin?

Answer 33

Acid in the duodenum

Question 34

What is the role of secretin?

Answer 34

Reduces stomach motility Inhibits acid production Stimulates pancreas to release enzyme

Question 35

What is the role of vasoactive intestinal peptide?

Answer 35

Increases secretion of fluid and chloride into the lumen by the wall of the GI tract

Question 36

What is the role of glucagon?

Answer 36

Counteracts insulin by increasing sugar levels in the blood by stimulating glycogenolysis and gluconeogenesis.

Question 37

Where is glucagon released from?

Answer 37

Alpha cells of the pancreas

Question 38

What stimulates the release of enteroglucagon?

Answer 38

Food in the lumen

Question 39

What is the role of enteroglucagon?

Answer 39

Proliferation of cells in the small intestine

Question 40

Where is gastrin release from?

Answer 40

G cells in the stomach.

Question 41

What is the role of gastrin?

Answer 41

Increased HCl production

Question 42

What stimulates cholecystokinin release?

Answer 42

Free fatty acids in the small intestine

Question 43

What is the role of peptide YY?

Answer 43

Slows peristalsis in the large intestine.

Question 44

What is the role of motilin?

Answer 44

Stimulates migrating motor complex during fasting

Question 45

Which is more precise sensation? Visceral or somatic?

Answer 45

Somatic

Question 46

Where is pain from appendicitis initially felt?

Answer 46

Peri-umbilical pain

Question 47

Why does the pain from appendicitis spread or progress?

Answer 47

inflammation initially only affects the inner layers of the appendix, which have only visceral nerve supply. However, as the inflammation spreads the parietal and visceral peritoneum become involved and the somatic nerves to the peritoneum are stimulated. Pain is now localized to the right iliac fossa.

Question 48

Which part of the small intestine is very specialized for the absorption of folic acid?

Answer 48

Jejunum

Question 49

Where do the capillaries from the small intestine eventually drain into?

Answer 49

Hepatic portal vein

Question 50

What are lacteals (found in the small intestine)?

Answer 50

They are lymphatic capillaries that absorb dietary fats and pass them through the lymphatic system.

Question 51

How are the fat soluble products of digestion carried in the lacteals?

Answer 51

In protein bound bundles called chylomicrons. (Lipoproteins)

Question 52

What is the main component of mucus in the small intestine which prevents self-digestion?

Answer 52

Mucin

Question 53

Why do some cancer drugs affects the small bowel so much?

Answer 53

Because there is relatively rapid turnover of the cells. Average life of mucosal epithelial cell is 48 hours.

Question 54

What are the monomers that make up sucrose?

Answer 54

Glucose and fructose

Question 55

Where are the enzymes that breakdown polysaccharides and disaccharides of carbohydrates secreted from?

Answer 55

The villi of the wall of the small intestine

Question 56

How is glucose taken up from the lumen of the small intestine?

Answer 56

Taken up by sodium/glucose cotransporter.

Question 57

How is galactose taken up from the lumen of the small intestine?

Answer 57

Competes with glucose for the same sodium/glucose cotransporter.

Question 58

In what form are most of the dietary fats the we ingest?

Answer 58

Triglycerides

Question 59

What percentage of our energy intake do triglycerides make up?

Answer 59

30-40%

Question 60

What is the difference between a saturated and a non-saturated fatty acid?

Answer 60

Presence or lack of double bonds

Question 61

Other than, triglycerides what other forms of dietary fat are there?

Answer 61

Phospholipids | Cholesterol and steroids

Question 62

Which bond do lipases cleave in a triglyceride?

Answer 62

Two of the bonds between the glycerol molecule and the fatty acid. This leaves a monoacylglycerol molecule.

Question 63

What enzyme(s) cleave(s) the final bond between the glycerol molecule and the fatty acid in the monoacylglycerol molecule?

Answer 63

Pancreatic esterases | Intracellular lipases

Question 64

Which hormone is responsible for the contraction of the gall bladder and hence the secretion of bile?

Answer 64

Cholecystokinin

Question 65

What is the role of bile?

Answer 65

Emulsifies fats and package them into small micelles

Question 66

How are primary bile salts broken down?

Answer 66

By bacteria in the large bowel

Question 67

What do amino-peptidases do?

Answer 67

Breakdown of proteins from the amino end.

Question 68

What do endopeptidases do?

Answer 68

Breakdown of proteins from the middle.

Question 69

What do carboxypeptidases do?

Answer 69

Breakdown of proteins from the carboxy end.

Question 70

Where are dipeptidases and tripeptidases found?

Answer 70

In the brush border.

Question 71

Is there are single type of amino acid transporter?

Answer 71

No. There are different sodium dependent transporters which are all side chain specific.

Question 72

What is phytic acid (phytate) and why can it be a problem in the diet of some people?

Answer 72

It is found in unleavened wheat diets. It can bind to certain minerals such as iron and zinc and prevent them from being absorbed.

Question 73

What is the role of vitamin C in the absorption of iron?

Answer 73

Reduces iron from Fe3+ to Fe2+

Question 74

What is the vitamin required to absorb calcium from the gut?

Answer 74

Vitamin D

Question 75

How is vitamin B12 taken up in the small intestine?

Answer 75

Bound to intrinsic factory by receptor-mediated endocytosis

Question 76

What is the action of trehalase and where is it found?

Answer 76

Converts trehalose into glucose at the brush border in the small intestine.

Question 77

What are the four components of chylomicrons?

Answer 77

Triglycerides (85-92%) Phospholipids Cholesterol Protein

Question 78

What are the two pathways by which information from the GI tract can regulate hunger and satiety?

Answer 78

Gut hormones | Vagal afferent nerves

Question 79

What are the two hormones involved in long term signals of how much body stores of energy we have?

Answer 79

Leptin | Insulin

Question 80

Where does leptin come from?

Answer 80

Adipose tissue

Question 81

Where are the leptin receptors found in the brain?

Answer 81

Hypothalamus

Question 82

How does the digestion of food lead to the feeling of satiety via that the vagus nerve?

Answer 82

Amino acids and monosaccharides are detected by receptors in the gut lining. These cells release paracrine hormones that are detected by nerve ending of the vagus nerve, which in turn transmits information to the hypothalamus.

Question 83

What stimulates the release of cholecystokinin?

Answer 83

Fat and protein in the duodenum.

Question 84

What are the roles of cholecystokinin?

Answer 84

Stimulants gall bladder to secrete bile. Stimulate vagal nerve endings to transmit presence of meal to hypothalamus.

Question 85

Where is polypeptide Y secreted from?

Answer 85

Ileum

Question 86

What is the role of polypeptide Y?

Answer 86

Signal satiety. Decreases ileal motility to allow full absorption of nutrients.

Question 87

What is the role of Glucagon-like peptide-1?

Answer 87

Decreases GI motility Causes insulin release (its an incretin)

Question 88

Where is ghrelin released from?

Answer 88

Fundus of the stomach

Question 89

What is the role of ghrelin?

Answer 89

Triggers appetite in the absence of food

Question 90

Which patients might you give glucagon-like peptide-1 (GLP-1) agonists to?

Answer 90

Diabetics

Question 91

What is the role of dipeptidyl peptidase 4 (DPP-4)?

Answer 91

The enzyme that breaks down glucagon-like peptide-1 (GLP-1). It is a therapeutic target for diabetics.

Question 92

Give an example of a dipeptidyl peptidase 4 (DPP-4) inhibitor which might be used to treat a diabetic?

Answer 92

Sitagliptin Gemigliptin (All end in liptin)