Transport along gut

Question 1

The vagal efferent fibres can evoke at least 2 responses in the alimentary tract. Name these and their functions.

Answer 1

Inhibitory fibres –> relaxation of fundic area

Excitatory fibres –> contraction of antral wall

Question 2

Name 2 mechanisms that move the chyme from the fundic to the antral areas of the stomach

Answer 2

Tonic contraction (BER/slow waves from ICC)
Peristalsis

Question 3

List 2 reasons why gastric emptying into the duodenum is regulated

Answer 3

Coordinates mechanical/chemical breakdown with absorption
Reduces swamping of duodenum with acidic chyme (may cause damage to the duodenum)
Particles that are large (>2mm) cannot pass the pylorus (cleared by MMC - occurs much later on)

Question 4

Name three substances that are important in the reciprocal control of gastrointestinal motility

Answer 4

Acetylcholine, NO, VIP, CCK, somatostatin

Question 5

State whether the following statement is true or false – you also need to justify your answer: Mr Joystone is a 56-year old Mechanical Engineer (55kg in weight) who has suffered with excessive acid production for some 30 years for which he recently underwent vagotomy in conjunction with partial removal of his stomach. Dr Knowhow, his consultant told him that a side effect of the operation is that his appetite will now improve and that this will help him gain some weight which Mr Joystone was pleased to hear about. Is this true or false and justify your answer?

Answer 5

False;
Vagotomy/stomach: size of the stomach is reduced, so not much food can be accommodated; also the reduction in vagal innervation as a results of the vagotomy will remove the capacity of the now reduced stomach to relax and accommodate more food – mechanical stimulation of the pharynx will have no effects; increased tension in the gut will have little effect in stimulating fundic relaxation; the effects of NO/VIP may be minimal

Question 6

What is the difference between segmentation and peristalsis?

Answer 6

(key points)
Peristalsis –global movement of food/chyme towards the large intestine, propulsive in nature

Segmenting - localised movement of food in the small intestine towards the anus; it chops and churns (mixing movements)

Question 7

There are 3 interdigestive cycles. Name these and state which cycle is the most important and also list 2 of its functions

Answer 7

Phase I, phase II and Phase III
Phase III is most important and its functions are to cleanse alimentary tract; prevents bacterial overgrowth in the gut (housekeeper)

Question 8

Name the peptide hormone that is secreted in response to feeding and known to be important in the control of phase III of the interdigestive cycle

Answer 8

Motilin

Question 9

The action of which neurotransmitter(s) mediate the receptive relaxation of the fundus of the stomach?

Answer 9

NO and VIP

Question 10

Three phases (phase I, II and III) which dominate the motor activity of the alimentary tract. Which of the following adequately describes the passage of food substances along the alimentary tract?

Answer 10

Liquids pass in spurts without any lag time, solids are ground into smaller pieces (~2mm) whilst indigestible materials are cleared by the migrating motor complex

Question 11

Which of the following best describes phase III of the motor activity of the alimentary tract?

Answer 11

The contractions are generally loud and gurgling which may be embarrassing if heard in public

Question 12

Summarise the emptying of food contents

Answer 12

large food particles are retained in the proximal part of the stomach -antrum repulses them (mixing and grinding with digestive juices)

1. contraction around antrum area
2. over time, sphincter will contract and food will be pushed - grinding action of the antrum will cause the food to get smaller (retropulsion and grinding of particles)
3. continues until most of the things will digest
4. propulsive force

Question 13

What does gastric emptying depend on?

Answer 13

propulsive force generated by tonic contractions of proximal stomach

stomach’s ability to differentiate types of meals ingested and their components

effects of fatty, hypertonic, acidic chyme in the duodenum decrease force and rate of gastric emptying

Question 14

Summarise emptying of different food components

Answer 14

liquids - rapidly disperse, empty without lag time
- rate of emptying influenced by nutrient content

solids - 2 phases (lag time and linear phase), duration of lag time related to size of particle

• liquid part emptied and solid part retained in proximal stomach
• trituration (form of reducing particle size or creating homogenous solution through mixing) of larger particles into smaller ones

Question 15

What regulates the passage of material in emptying?

Answer 15

Pylorus

Question 16

How does the type of food eaten affect rate of gastric motility?

Answer 16

carbohydrates > protein > fatty foods > indigestible solids

Question 17

How does the osmotic pressure of duodenal content affect rate of gastric motility?

Answer 17

hyperosmolar chyme decrease gastric emptying

Question 18

How does vagal innervation upon overdistention affect gut motility?

Answer 18

decreases gastric motility

Question 19

How do hormones and injury to intestinal wall and bacterial infects affect gastric motility?

Answer 19

Hormones: inhibit emptying

Injury to intestinal wall and bacterial infections: decrease motility

Question 20

Where does segmentation originate?

Answer 20

Pacemaker cells (ICC)

Question 21

What is MMC?

Answer 21

Migrating motor complex 
highly organised motor activity 
cyclically recurring sequence of events 
occurs between meals when stomach/intestine are empty 
starts in lower portion of stomach

Question 22

What is motor activity like in the small intestine in the fed state?

Answer 22

Mixing contractions: segmentation, mixes and stirs contents with enzymes - prevents unstirred layer formation

Peristaltic contractions (slow waves) - move contents in oral to anal direction (law of gut)

Question 23

Features of motility of large intestine

Answer 23

intensive missing
fermentation
slow propagating - slow aboral flow

Question 24

Explain motility of the large intestine

Answer 24

LI is composed of 2 areas; taenia coli and haustra (sacks/pouches)

1. Segemental of haustral contractions - mix contents/key role for taenia coli longitudinal muscle
2. Peristalsis - slow in large intestine in comparison to SI, moves content towards anus, distension increases contraction
3. Mass movement: powerful contraction of mid-transverse colon that sweeps colon contents into rectum (responsible for colonic evacuation)