GI motility lecture

Question 1

In GI tract

what are slow waves?

what are spikes? what are they stimulated by?

what stimulates hyperpolarization

Answer 1

slow waves are oscillating rest potential.

spikes: slow waves excite spike action potentials, calcium influx and muscle contraction. stimulated by stretch, ACh, parasympathetics

norepinephrine
sympathetics

Question 2

intrinsic enteric nervous system (ENS) is made up of which two interconnected plexuses in GI tract wall

Answer 2

myenteric plexus: between longitudinal and circular muscles > controls GI motility

submucosal plexus > controls secretion and local blood flow

Question 3

Hirschsprung’s disease

Answer 3

congenital abscence of myenteric plexus usually involving part of distal colon. The pathologica section of colon lacks peristalsis and undergoes cont spasm leading to obstruction/ severe constipation

Question 4

describe oral phase swallowing

Answer 4

1) oral: voluntary initiation of swallowing in oral cavity. Tongue pushes against hard palate and contracts to force lubricated bolus into oropharynx.

Question 5

Achalasia

GORD

Answer 5

Achalasia: LES fails to relax causing food to remain in oesophagus, caused by vagal of myenteric defect

GORD: LES tone lost leading to flow of gastric acid into oesophagus. may be linked to hiatus hernia
results in inflammation, ulceration

Question 6

3 stages as food enters stomach

Answer 6

storage: vagovagal reflex reduces muscle tone
mixing: spontaneous slow waves initiate weak peristaltic mixing producing retropulsion
emptying: pyloric pump contracts forcing chyme into duodenum

Question 7

Which hormones trigger decreased gastric emptying. Which cells are the hormones secreted from.
What factors trigger the hormone release

Answer 7

mucosal cells in duodenum:
secretin released by S cells
GIP (K cells) and CCK (I cells)
other endocrine cells release unidentified enterogastrone

triggered by pH less than 3.5, hyper/hypotonic solutions and fat digestion products

Question 8

Dumping syndrome

Answer 8

Dumping syndrome: rapid emptying of gastric contents into s.intestine occurs following a large meal after gastrectomy.

symptoms: nausea, pallor, sweating, vertigo and sometimes fainting
cause: hypertonic duodenal contents

Question 9

Gastroparesis

Answer 9

stomach fails to empty, preventing proper digestion

symptoms: bloating/ nausea

Question 10

what is migrating motor complex (MMC)

Answer 10

cyclic motor pattern occurs during fasting state. peristaltic sweep of intestinal contents every 90 mins

intrinsic control but modified by vagal and hormonal (Eg motilin) stimulation

absence can lead to bacterial overgrowth

Question 11

Order of layers of gi tract from outside in

Answer 11

Serosa > muscularis externa > submucosa > mucosa

Question 12

With regards to slow waves/ spike potential.. what does excitatory transmitters do and what does inhibitory transmitters do ? Give examples of each

Answer 12

Excitatory: ca2+/na + channels open, resting membrane potential depolarised, slow waves cross threshold to generate a spike potential
Eg stretch, acetylcholine, parasympathetics

Inhibitory: k+ channels open, efflux occurs, hyperpolarising membrane potential so slow waves can’t reach threshold
Eg noradrenaline, sympathetics

Question 13

2 types smooth muscle contraction in gi tract

Answer 13

1) segmentation for mixing: bursts of circular muscle contraction and relaxation. Back and forth pendular movements also occur. Both results in small food particles developing
2) peristalsis for propulsion: requires innervation from myenteric plexus. Distension from compression of bolus stimulates intrinsic primary afferent neurons (IPAN) which synapse with cholinergic interneurons. Excitatory efferent motor neurons release ACh and SP = contraction behind bolus. Inhibitory efferent motor neurons release NO, VIP and ATP= relaxation in front of bolus .

Question 14

Extrinsic ANS control, sympathetic and parasympathetic vertebral origin and effects on gi tract

Answer 14

Symp(T8-12): inhibits secretomotor activity and causes vasoconstriction. Noradrenaline directly inhibits smooth muscle or inhibits enteric neurons

Para(Vagal and Sacral nerves): excitatory effect on gi tract

Question 15

Gastrin
A) site of secretion
B) stimulus for secretion
C) actions

Answer 15

A) g cells of antrum, duodenum and jejunum
B) protein, distension, nerve( inhibits release)
C) stimulates gastric acid secretion and mucosal growth. Stimulates gastric emptying

Question 16

CCK
A) site of secretion
B) stimulus for secretion
C) actions

Answer 16

A) I Cells of small intestine
B) protein, fat,acid
C) stimulates pancreatic secretions, gallbladder contraction. Inhibits gastric emptying.

Question 17

Secretin
A) site of secretion
B) stimulus for secretion
C) actions

Answer 17

A) s cells small intestine
B) acid,fat
C) stimulates pepsin secretion and bicarbonate secretion. Inhibits gastric acid secretion. Inhibits gastric emptying

Question 18

Gastric inhibitory peptide (GIP)
A) site of secretion
B) stimulus for secretion
C) actions

Answer 18

A) k cells duodenum and jejunum
B) protein, fat, carbohydrate
C) stimulates insulin release, inhibits gastric acid secretion, inhibits gastric emptying.

Question 19

Motilin
A) site of secretion
B) stimulus for secretion
C) actions

Answer 19

A) m cells of duodenum and jejunum
B) fat, acid, nerve
C) stimulates gastric and intestinal motility

Question 20

Describe pharyngeal phase swallowing

Answer 20

Involuntary. Bolus causes glossopharyngeal stimulation of swallowing centre in medulla oblongata. Motor efferents cause muscle contraction in trigeminal, glossopharyngeal and vagal nerves

Soft palette elevates over posterior nares
Epiglottis closes off larynx
Respiration inhibited
Upper oesophageal sphincter relaxes
Pharyngeal muscle contraction propels bolus into oesophagus

Question 21

Describe oesophageal phase swallowing

Answer 21

1) primary peristaltic wave. Striated and smooth muscle contraction
2) secondary wave (stretch)
Intrinsic myenteric nerves, vagal excitation, vagal inhibition for relaxation if lower oesophageal sphincter

Question 22

Regulation of emptying of stomach

Answer 22

Excitatory: neuronal stimulation of myenteric reflexes
Gastrin (some motility)

Inhibitory: duodenal enterogastric reflexes
Hormones

Question 23

What controls segmentation and peristalsis in small intestine (neuronal and hormonal)

Answer 23

Stretch/ gastroenteric reflex

Endocrine hormones :
Excite: Gastrin, CCK, insulin, motilin, serotinin
Inhibit: glucagon and secretin

Question 24

Stimulation of what opens ileocaecal valve, and two things that can go wrong

Answer 24

Gastroileal reflex

1) peristaltic rush: mucosal irritation, ANS
2) paralytic Ileus: loss of peristalsis following mechanical trauma

Question 25

A) Describe the large intestine anatomically briefly
B) function (3 things)
C) motility

Answer 25

A) 3 bands longitudinal muscle form taeniae coli with haustral bulges
B) absorption of water and electrolytes by enterocytes. Formation of faeces (distal), commensal microbiome
C) motility: mixing contractions from haustrations
Propulsion: slow peristaltic and mass movement

Question 26

Process of elimination of faeces

Answer 26

Filling following mass movement stimulates stretch receptors and defecation reflex
Involuntary internal anal sphincter relaxation occurs via ENS and P/S ANS
external sphincter relaxation via somatic pudendal nerve