Gastric Motility

Question 1

Gastic pacemaker cells

Answer 1

Interesitial cells
Initiate basal electrical rhythm
Sensitive to stretch-> stretch increases excitability-> BER over threshold->muscle contractions
Myenteric plexus-> Ach upstream-> contraction
VIP downstream-> relaxation

Question 2

Modification by extrinsic nerves, oesophagus

Answer 2

Sympathetic-> NA-> inhibitory -> directly by beta adrenoceptors, indirectly by Ach release
Parasympathetic->Ach-> stimulatory

Question 3

Oesophageal peristalsis

Answer 3

Mechanorecptors in pharynx detect food bolus
Initiate peristaltic wave
Controlled by vagus
5cm/sec every 7-10 seconds
Gravity assisted
Second wave initiated if food not projected in to stomach by vago-vagal

Question 4

Empty oesophagus

Answer 4

Salivary swallowing
Awake 70/h
Asleep 7/h
Small peristaltic waves

Question 5

Gastric motility

Answer 5

Primed by pacemaker cells-> BER-> 3-5 mins-> only associated with peristaltic wave when smooth muscle is excitable enough 
Acts as a storage organ 
Controlled by:
Myogenic 
Intrinsic nerves 
Extrinsic nerves 
Hormones

Question 6

Empty stomach

Answer 6

Feeble contractions as underlying smooth muscle not excited

Question 7

Full stomach

Answer 7

1st hour peristaltic waves are weak
Pyloric sphincter remains closed 
Later waves more powerfull
Higher pressure in stomach than duodenum 
Food pushed in to duodenum 
Also help mix food

Question 8

Control of gastric motility

Answer 8

Neural:
Vagus-> VIP-> relaxatory in fundus-> stimulated by oesophageal and gastric distension 
Vagus-> Ach-> stimulate motility 
Sympathetic-> NA-> inhibits motility 
Hormones
Stimulatory:
Gastrin (Antrum) 
Motility
Inhibitory:
Gastrin (proximal stomach)
Secretin
CCK

Question 9

Rate at which food appears in duodenum depends on:

Answer 9

Meal composition:
Protein-> slow-> gastrin and CCK release
Carbs-> fast
Fat-> really slow
Increase meal volume, increase speed of emptying
Fragments have to be smaller than 1mm
Osmolality above or bellow 200mosm, decrease emptying speed
Excess acid decreases emptying speed

Question 10

Small intestinal motility

Answer 10

Segmenting contraction 
smooth circular muscle 
moves chyme to and fro 
Increase exposure to mucosal surface 
BER 12/min duodenum 
BER 9/min ileum 

Peristaltic contractions 
Longitudinal muscle 
Short distance 
After meal 
Occasional migrating motility complex-> shift remaining food in to colon

Question 11

Control of small intestinal motility:

Answer 11

Myogenic 
Myenteric plexus
       Stimulatory-> Ach, gastrin, CCK 
       Inhibitory-> VIP, opioids, NO 
Extrinsic nerves, mainly sympathetic 
Local chemicals

Question 12

Large intestinal motility

Answer 12

12 hours
Ileal-caecal sphincter, ZEP, prevents retrograde movement of bacteria
Water reabsorption and storage of faeces
Movement mostly slow and non propulsive
Haulstral contraction every 2h
3-4 times per day powerful contractions moving food to distal colon

Question 13

Defeacation

Answer 13

Rectum usually empty
Arrival of faeces induces desire to poo via sensory nerves, peristaltic wave in colon
Internal anal sphincter relaxes
Voluntary relaxation of external sphincter
Parasympathetic reflex and voluntary effort

Question 14

Layers of gastrointestinal tract

Answer 14

Longitudinal muscle
Myenteric plexus
Circular muscle
Submucosal plexus
Submucosal
Mucosa