L4: Stomach – regulation of acid production and motility

Question 1

What are the triggers for gastric acid secretion?

How are Signals relayed?

Answer 1

Cephalic: (35%) Triggered by smell/ taste/ anticipation of food

Gastric: (60%) Triggered by gastric distension and digested proteins

Intestinal: (10%) Trigger: ACID IN DUODENUM

Question 2

How are signals for Gastric Acid Secretion Transmitted?

• _______________ in the stomach trigger G- Cells to produce GASTRIN:
• _______________ act on Parietal Cells=> increases HCl secretion
• ________________ on ECL Cell => ECL cells release _____________ =>Parietal Cells increase HCl

Answer 2

• Distention + peptides in stomach triggers G- Cells to produce GASTRIN:
• Gastrin + ACh (autonomic) act on Parietal Cells=> increases HCl secretion
• Gastrin acts on ECL Cell => ECL cells release Histamine =>parietal cells increase HCl

Question 3

Drivers of Gastric Acid Secretion?

Answer 3

GASTRIN

HISTAMINE

ACh

Question 4

Inhibitors of Gastric Acid Secretion?

Answer 4

SOMATOSTATIN

SECRETIN

PROSTAGLANDINS

Question 5

_______ of stomach is non-rhythmic, instead generating tone of proximal stomach

Answer 5

FUNDUS of stomach is non-rhythmic, instead generating tone of proximal stomach

Question 6

Rhythmic pacemaker activity is not the same along length of the GIT. Why?

Answer 6

Helps create gradient pressure towards ileocecal sphincter

Question 7

What are Slow waves and what is their function?

Answer 7

Waves of transient depolarization that increase the probability of opening for Voltage-dependent Ca2+ channels=> contraction of GIT (cannot elicit action potential on their own)

Question 8

How are slow waves generated in the GIT and what is their function?

Answer 8

Slow waves are generated by Interstitial Cells of Cajal. These waves of transient depolarization that increase the probability of opening for Voltage-dependent Ca2+ channels=> contraction of GIT (cannot elicit action potential on their own)

Interstitial Cells of Cajal:

• Nerve-like cells at the end of motor neurons in organs innervated by PNS
• Have Gap Junctions w/ smooth muscle cells allowing easy relay of electrical activity

Question 9

Evidence that ICCs regulate slow wave contractions?

Answer 9

Kit mutants are deficient in ICCs and have impaired contractile waves in the small intestine!

Blocking Kit with antibodies impairs GI motility

Question 10

Control of Force of Gastric Emptying (Rhythm/Magnitude)

Answer 10

Pacemaker cells / slow waves set the rhythm

Distension / hormones/ vagal stimulation determine the magnitude

Question 11

Rate of Gastric Emptying?

Answer 11

Liquids >Solids

Carbohydrates > Proteins > Fatty meals

Question 12

________________ is a key Physiological Factor that accelerates gastric emptying rate

Answer 12

Gastric Distention is a key Physiological Factor that accelerates gastric emptying rate

Question 13

Particles larger than _______empty slowly or not at all (> pyloric sphincter)

Answer 13

Particles larger than 7mm empty slowly or not at all (> pyloric sphincter)

Question 14

Role of Duodenal Feedback?

Answer 14

negative enterogastric reflex triggered by vagal sensory fibres in the duodenum which detect:

• pH
• Osmolality
• Fatty Acids
• Amino Acids

Secretin (S Cells) and CCK (I-cells) DECREASE gastric emptying rate

Question 15

____________ and __________ DECREASE gastric emptying rate

Answer 15

Secretin (S Cells) and CCK (I-cells) DECREASE gastric emptying rate

Question 16

Vomiting Phases?

Answer 16