GI Physiology

Question 1

Swallowing Mechanism

Answer 1

1. Nasopharynx closes and breathing is inhibited
2. Laryngeal muscles contract to close the glottis and elevate the larynx
3. Peristalsis begins in the pharynx to propel the food bolus toward the esophagus
4. UES relaxes to allow the bolus of food in

Question 2

Swallowing reflex

Answer 2

Coordinated in the medulla via vagus and glossopharyngeal nerves

Question 3

Primary peristaltic contraction mechanism

Answer 3

The contraction creates an area of high pressure behind the food bolus. Food propelled down esophagus. Gravity accelerates the movement

Question 4

MMC

Answer 4

• Occurs at 90 minute intervals during fasting and clears the stomach of residual food
• Motilin is the mediator of these contractions

Question 5

What stimulates gastric emptying?

Answer 5

-Isotonic contents

Question 6

What inhibits gastric emptying?

Answer 6

• Fat by stimulating release of CCK

- H+ in the duodenum via direct neural reflexes

Question 7

Peristaltic contractions in the small intestine (Mechanism w/ Histamine)

Answer 7

Coordinated by enteric nervous system

1. Food in intestinal lumen sensed by ECL cells, which releases 5-HT
2. 5-HT binds to receptors on intrinsic primary afferent neurons, which initiate peristaltic reflex
3. Behind food bolus, excitatory transmitters cause contraction of circular muscle and inhibitory transmitters cause relaxation of the longitudinal muscle
4. In front of the food bolus, circular muscle relaxes while longitudinal muscle contracts.

Question 8

Gastroileal Reflex

Answer 8

• Mediated by extrinsic ANS and possibly by gastrin
• Presence of food in stomach triggers increased peristalsis in the ileum and relaxation of the ileocecal sphincter–>intestinal contents delivered to the large intestine

Question 9

What part of the colon has the most water absorption?

Answer 9

Proximal colon

Question 10

When does retching occur?

Answer 10

When the reverse peristalsis begins and upper esophageal sphincter remains closed.

Question 11

Where is the Chemoreceptor Trigger Zone located?

Answer 11

4th ventricle and activated by emetics, radiation and vestibular stimulation

Question 12

What weakens the mucosa?

Answer 12

Bile salts, Histamine, NSAIDs, H. pylori, catecholamines

Question 13

Composition of secretions in glands

Answer 13

Parotid = entirely serous, watery (70%)
Submandibular = Mixed (70%)
Sublingual = mainly mucous (5%)-->mucin secreting

Question 14

Parasympathetic and sympathetic nerves on saliva secretion

Answer 14

Parasympathetic = VII and IX
Sympathetic = cervical sympathetic chain

Question 15

Types of saliva parasympathetics and sympathetics stimulate

Answer 15

Watery (para) and viscous (symp)

Question 16

Two main enzymes in saliva?

Answer 16

Salivary amylase: activated by Cl- in saliva and hydrolyzes alpha 1,4 glycosidic linkages in starch; active until acid gets to bolus
Lingual lipase: Breaks down triglycerides