Stomach

Question 0

Retropulsion

Answer 0

Occurs when peristaltic contractions originating from the pacemaker region in the midstomach reach the pyloric sphincter in cloe it

=>Chyme propelled back into stomach to be further digested

Question 1

Receptive Relaxation

Answer 1

Mediated by a vagovagal reflex, this is the relaxation of the stomach to accommodate to a recently ingested meal

Question 2

Migrating Myoelectric Complex

Answer 2

Contractions occurring in 90 minute intervals during fasting to clear the stomach of any residual food

*Mediated by motilin; hunger pangs will disappear after 3-4 day

Question 3

Order of gastric emptying

Answer 3

Liquids>Carbs>Proteins>Fats

Question 4

Gastric Emptying

Answer 4

Controlled by signals from the duodenum in response to:

Decreased pH
Distention of proximal stomach
Increased fat/protein digestion products

Question 5

Gastroparesis

Answer 5

Impaired emptying of the stomach producing symptoms of fullness, nausea, vomiting

*Most commonly caused by diabetes or anticholinergics

Question 6

Dumping Syndrome

Answer 6

Lower end of S.I. fills to quick w/ undigested food; nausea, vomiting, eventually sweating and dizziness

• Common after stomach surgery
• Symptoms due to hypoglycemia

Question 7

Oxyntic Gland mucosa

Answer 7

Found in the proximal stomach; secrete primarily acid, pepsinogen, intrinsic factor, and mucus

*Mucus neck cells in isthmus serve as stem cell; chief cells and parietal cells also present

Question 8

Pyloric gland mucosa

Answer 8

Found in the distal stomach; secretes primarily gastrin

Question 9

HCl

Answer 9

1. Begins digestion of protein
2. Activates pepsinogen
3. Kills bacteria

Question 10

Pepsin

Answer 10

Released by vagal stimulation and splits interior peptide bonds of proteins

Question 11

Mucus

Answer 11

Soluble: Secreted in active stomach; lubricates chyme

Insoluble: Secreted in inactive stomach to trap HCO3- in layer on mucosa to protect from acidic damage

Question 12

Intrinsic Factor

Answer 12

Binds Vitamin B12 and allows for absorption in the ileum

*Lack of IF=>pernicious anemia

Question 13

Tubulovesicles

Answer 13

Inserted into the luminal membrane of parietal cells when gastric acid is secreted

*Become H+ pumps/K+ antiporter

Question 14

Mechanism of Acid Secretion

Answer 14

Carbonic anhydrase converts CO2 from cell metabolism to H+ and HCO3-

H+ => secreted out of H+/K+ ATPase

HCO3- => Antiported out w/ Cl-; Cl- travels thru membrane channels to the lumen

*K= enters via a Na/K+ ATPase and leaves via a K+ channel to power the H+/K+ ATPase on the luminal side

Question 15

Ionic Composition of Gastric Juices

Answer 15

Low flow => NaCl

High Flow => HCl

*Vomiting may lead to hypokalemia due to high presence of K+ in the lumen

Question 16

Stimulants of Acid Secretion

Answer 16

1. Ach-binds to muscarinic receptors and activates PLC
2. Gastrin- binds to gastrin receptors and activates PLC
3. Histamine- binds to H2 receptors and activates AC
   * All eventually raise intercellular Ca2+ and insert H+-pumps in the apical membrane

Question 17

H2 receptor blockers

Answer 17

Blocks the potentiating effects of histamine on gastrin and Ach; effectively lowers the secretion of gastric acid

Question 18

Inhibitors of acid secretion

Answer 18

1. Decreased pH
   - pH will drop after initial rise from ingested meal
2. Somatostatin
   • released in response to acid in the antrum

3 Chyme in the duodenum
-Neural and hormonal mechanisms inhibit gastrin release

Question 19

Basal secretion phase

Answer 19

Occurs in absence of gastric stimulation; pH is low causing the mucosa to be acidified

Question 20

Cephalic phase of acid secretion

Answer 20

Initiated by the though, taste, smell of food; afferent pathways to vagus nerve stimulate efferent impulses to the stomach

=>Stimulates parietal cell and GRP release

Question 21

Gastric phase of acid secretion

Answer 21

Rise in pH once food enters stomach causes gastrin to be released; stretched mechanoreceptors stimulate local and vagovagal reflexes to secrete acid

• AAs and peptides can also cause release of gastrin from G-cells
• Strongest phase of acid secretion

Question 22

Intestinal phase of secretion

Answer 22

Initiated by presence of protein digestion products in the duodenum

=>Increased gastrin secretion

Question 23

Gastric ulcers

Answer 23

Breakdown of the protective barrier of the stomach

Question 24

Duodenal ulcers

Answer 24

Increased levels of acid/gastrin/pepsin damage the lining of the duodenum

• Pts also have lower HCO3- secretion and defective defensive mechanisms against acid
• Much more common than gastric ulcers and often have H. Pylori infxn

Question 25

H.pylori

Answer 25

Produces urease to neutralize acid in the stomach and corkscrews in thru the mucosa; might even poison nearby cells w/ ammonia

*Inhibits secretion of somatostatins to further cause ulcerations

Question 26

Retching

Answer 26

Involuntary motions of vomiting w/o production

*Includes esophageal dilation, flaccid fundus, abominal contration, closure of soft palate over nasopharynx

Question 27

Vomiting Center

Answer 27

Found in the medulla and activated by:
Tickling throat
Distention of stomach
Vestibular stimulation
Pain
Sights/smell

*Direct activation will cause vomiting w/o nauseas or retching

Question 28

Chemoreceptor Trigger Zone

Answer 28

In area postrema and is activated by radiation, motion sickness, drugs

=>Sends signals to vomiting center and NTS

Question 29

Hyperemesis of Pregnancy

Answer 29

Severe vomiting and nausea causing weight loss during pregnancy

-Baby will come out normal though

Question 30

Effects of protracted vomiting

Answer 30

1. Metabolic alkalosis
2. Dehydration
3. Hypokalemia
4. Hyponatremia

Question 31

Possible inhibitors of gastric emptying

Answer 31

Decreased pH
Increased fat/protein digestion products
Increased distention of the stomach
Increased duodenal pressure

*Inhibits the flow of excess chyme into the SI

Question 32

Treating ulcers

Answer 32

Antibiotics and H+ pump inhibitors