Gastric Motility Flashcards Preview

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Flashcards in Gastric Motility Deck (14):
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Layers of gastrointestinal tract

Longitudinal muscle
Myenteric plexus
Circular muscle
Submucosal plexus
Submucosal
Mucosa

1

Gastic pacemaker cells

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

2

Modification by extrinsic nerves, oesophagus

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

3

Oesophageal peristalsis

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

4

Empty oesophagus

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

5

Gastric motility

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


6

Empty stomach

Feeble contractions as underlying smooth muscle not excited

7

Full stomach

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

8

Control of gastric motility

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

9

Rate at which food appears in duodenum depends on:

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

10

Small intestinal motility

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

11

Control of small intestinal motility:

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

12

Large intestinal motility

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

13

Defeacation

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