Transport along the alimentary tract

Question 1

What is transport of digesta from gastric reservoir into antral pump caused by?

Answer 1

Tonic contractions

peristaltic waves

Question 2

What is gastroparesis (gastric stasis)?

Answer 2

Chronic condition where the stomach can’t empty itself of food in the normal way, causing food to pass through it slowly.

Question 3

What are the 3 processes of food mixing in antrum?

Answer 3

1) Propulsion- initial movement of food in antrum towards pylorus through a peristaltic wave created by ICC
2) Grinding- as material approaches pylorus it begins to get churned by the continuing peristaltic waves
3) Retropulsion- pyloric end acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material back into the stomach.

Question 4

Describe the sieving function of the pyloric sphincter.

Answer 4

Only chyme of 1-2 mm is allowed to pass into duodenum.

Large food particles are retained in the proximal stomach and the antrum repulses them, leading to mixing and grinding with digestive juices.

Question 5

What does gastric emptying dependent on?

Answer 5

• Force generated by tonic contraction of the proximal stomach
• Type of food ingested

Question 6

What decreases the force and rate of gastric emptying?

Answer 6

Fatty, hypertonic acidic chyme.

Question 7

Describe the emptying of liquids.

Answer 7

Passes in spurts

Rapidly disperse

Rate of emptying influenced by nutrient content (nutrient containing liquids retained longer).

Question 8

Describe the emptying of Solids.

Answer 8

Broken down to 1-2 mm sizes (trituration)

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

Liquid part emptied and solid component retained in proximal stomach

Pylorus regulated passage of material.

Question 9

Describe the emptying of fatty foods.

Answer 9

Liquiefy at body temperature and float on top of liquid layer and empty slowly

Potent inhibitors of gastric motor events and gastric emptying.

Question 10

Describe the emptying of indigestible solids.

Answer 10

Not emptied in immediated post-prandial period.

Cleared by Migrating Motor Complex (MMC) or vomiting.

Question 11

Give factors that determine rate of gastric motility.

Answer 11

Type of food eaten (carbs>protein>fatty food>indigestable solids)

Osmotic pressure of duodenal contents (hyperosmolar chyme decreases gastric emptying)

Vagal innervation upon over-distension of duodenum decreases gastric motility

Hormones (somatostatin, secretin, CCK and GIP) inhibit gastric emptying.

Injury to intestinal wall and bacterial infections decrease motility

Question 12

What is Myogenic Control of Gastric Motility?

Answer 12

Interstitial Cells of Cajal (ICC) are pacemaker cells of the gut which undergo rhythmic depolarisation and repolarisation, creating a slow wave of regular recurring migrating ripples (3 waves/min) towards the antrum known as intrinsic basic electric rhythm (BER).

Question 13

What is the role of the Basic Electrical Rhythm (BER)?

Answer 13

Transmitted to smooth muscle cells, allowing them to depolarise and contract rhythmically when exposed to hormonal signals.

Question 14

What decreases BER?

Answer 14

The release of noradrenaline by the sympathetic nervous system.

Question 15

What are the Hormones that increase fundic motor activity (and hence gastric motility)?

Answer 15

Motilin

Question 16

What are the Hormones that decrease fundic motor activity (and hence gastric motility)?

Answer 16

• CCK
• Secretin
• VIP
• Somatostatin
• Glucagon
• Duodenal distension, duodenal acid
• GRP

Question 17

Give Hormones that increase intestinal motility.

Answer 17

CCK
Gastrin
Motilin
Serotonin
Insulin

Note: CCK decreases fundic motor activity but increase intestinal motility.

Question 18

Give Hormones that decrease intestinal motility.

Answer 18

Secretin

Glucagon

Question 19

What is the function of the Gastro-gastric reflex.

Answer 19

Provide balance between gastric reservoir and antral pump

Distension of gastric reservoir stimulates antral contractions (excitatory reflex)

Distension of the antrum stimulates relaxation of gastric reservoir (inhibitor reflex).

Question 20

What is gastric emptying regulated by?

Answer 20

Gastric emptying is regulated by negative feedback systems

1) Antral-Over Distension
- vagovagal reflex where it elicits an inhibitory reflex and enhances and prolongs relaxation of gastric reservoir via NO/VIP

2) Duodenal-Over Distension
- vagovagal reflex and hormones where it elicits an inhibitory reflex and enhances and prolongs relaxation of gastric reservoir via NO/VIP.

Question 21

What is pyloric activity modulated by?

Answer 21

Pyloric activity is modulated by antral inhibitory and duodenal excitatory reflexes:

• Contraction of middle antrum elicits a descednign inhibitor reflex causing pyloric relaxation via NO/VIP
• Presence of duodenal stimuli (acid) induces an excitatory reflex, causing pyloric contractions increasing tone, preventing duodenal gastric reflux.

Question 22

Name the stages of motility in the intestine.

Answer 22

Segmentation
Peristalsis
Migrating Motor Complex
Mass Movements.

Question 23

What is segmentation?

Answer 23

Originates in the ICC

Contraction of circular muscles in small intestine

divides chyme and brings it closer to intestinal mucosal cells for absorption

bidirectional movement.

Question 24

What is peristalsis?

Answer 24

Propulsive contraction of successive sections of circular smooth muscle preceded by relaxation/dilation and rhythmic contractions of longitudinal muscle in the GI tract.

Regulation requires neural reflexes.

Question 25

What is the Migrating Motor Complex (MMC)?

Answer 25

Waves of electrical activity that sweep residual undigested material through digestive tube during fasting (after digesting and absorbing a meal) by opening pyloric sphincter during phase III.

(serves a housekeeping role)

Question 26

Give other functions of MMC.

Answer 26

Removes dead epithelial cells by abrasion

Prevents bacterial overgrowth

Prevents colonic bacteria from entering small intestine.

Question 27

Explain the regulation of motor activity in the small intestine.

Answer 27

Local reflex mediated via ENS can be enhanced or suppressed by extrinsic innervation from autonomic nervous system. Increased sympathetic and parasympathetic innervation inhibits the local reflex and stimulates intestinal motility.

Pain and fear (fight or flight response) decrease intestinal motility.

Question 28

Describe the mass movement in the Large Intestine.

Answer 28

Powerful contraction of mid-transverse colon that sweeps colon contents into rectum

(large amplitude, long duration).

Question 29

Describe the Motor Activity in the Large Intestine.

Answer 29

Like the small intestine, there is segmentation and peristalsis.

Peristalsis however is slower in large intestine and moves contents towards the anus. These contractions are initiated due to distention of the large intestine.

There is also mass movement.

Question 30

What is appendigitis?

Answer 30

Fat structure called Appendices Epiplocae on large intestine can be inflamed, causing appendigitis (commonly mistaken for appendicitis).

Question 31

What is Diarrhoea?

Answer 31

Discharge of liquid faeces.

Question 32

What is Constipation?

Answer 32

Difficulty/some constraint in the opening/emptying of the bowels, causing hard faeces.