The stomach: acid production, swallowing and vomiting

Question 1

Oesophagus histology

Answer 1

• Circular and longitudinal muscle layers
• Epithelium: stratified squamous - good protection from trauma, smooth for food to glide over , poor protection from acid

Question 2

Muscular externa

Answer 2

• Layers of longitudinal and circular smooth muscle - reduce length and constrict lumen of GI respectively

Question 3

How is muscular external controlled?

Answer 3

Controlled by myenteric plexus which increases smooth muscle tone, intensity of rhythmic conduction, frequency of contraction and velocity of contraction

Question 4

Motility of oesophagus

Answer 4

• Primary wave innervated by vagus nerve 10

Question 5

Innervation of oesophagus

Answer 5

Vagus nerve 10

Question 6

Swallowing sequence

Answer 6

Swallowing sequence:

• Food bolus pushed back by tongue
• Nasopharynx closes: prevents nasal reflux
• Glottis closes: larynx pulled upwards
• Food channelled via pyriform fossae
• Peristaltic wave down oesophagus
• Glottis innervated by recurrent and superior laryngeal nerves which is critical to protect airways
• Epiglottis diverts food laterally through pyriform fossae, acts as a snowplough over larynx rather than lid

Question 7

Lower oesophageal sphincter

Answer 7

Lower oesophageal sphincter opens transiently as longitudinal muscle contracts and circumferential muscle relaxes

Question 8

Stomach functions

Answer 8

• In: intermittent delivery sizeable quantities, particulate food, microbes
• Out: steady flow, partially digested, liquid chyme, largely sterile
• Vagus nerve important
• Achieved by storage/outflow regulation, enzyme secretion, mechanical food breakdown, sterilisation

Question 9

Parietal cells

Answer 9

Secrete intrinsic factor and HCl

Question 10

Chief cells

Answer 10

Secrete pepsinogen

Question 11

Mucous cells

Answer 11

Secrete mucous

Question 12

G cells

Answer 12

Release gastrin

Question 13

D cells

Answer 13

Release somatosensin

Question 14

Gastric acid function

Answer 14

• Kills ingested bacteria
• Denatures proteins - particle breakdown
• Facilitates action of gastric lipase
• Lipid digestion
• Converts pepsinogen to pepsin

Question 15

Cephalic gastric acid regulation

Answer 15

Initiated by smell and taste

Mediated by vagus

Question 16

Gastric acid regulation

Answer 16

Initiated in stomach - distension, protein
Gastrin mediated: released by local and neural control (vagus)
Action direct and indirect (histamine)

Question 17

How is the gastric lining protected against auto digestion?

Answer 17

mucus secreted by surface epithelial and mucous neck cells, bicarbonate secreted by epithelial cells under mucus layer

Question 18

Stomach motility

Answer 18

Weak peristaltic constrictor waves mix food
Begins in upper portion of stomach wall moving towards antrum
Waves continue towards pylorus

Question 19

Neuronal regulation of stomach emptying

Answer 19

mucus secreted by surface epithelial and mucous neck cells, bicarbonate secreted by epithelial cells under mucus layer

Question 20

Stomach emptying regulation

Answer 20

• Neuronal regulation: myenteric reflexL stretching of stomach promotes and increases effect of pyloric pump and inhibits pylorus tone
• Enterogastric nervous reflex increases pyloric tone
• Distension, irritation of duodenum mucosa, protein by products, acidity, osmolarity
• Hormonal regulation: CCK, GIP, secretin released in response to acidic and fatty chyme entering duodenum

Question 21

Function of vomiting

Answer 21

• Protection against toxins
• Multiple triggering pathways
• Physical mechanism is a sequential reflex

Question 22

How is gastric contents ejected?

Answer 22

Inspiration increases abdomen pressure
Glottis closes to prevent aspiration 
Duodenum contracts
Gastro-oesophageal sphincter relaxes
Abdominal wall contracts abruptly