(5) GI & Endo: GI (1.1-1.3)

Question 1

What is the neuroanatomical name for the vomiting center?

Answer 1

nucleus tractus solitarius

Question 2

Which cranial nerves signal to the nucleus tractus solitarius?

Answer 2

(1) CN X
(2) CN VIII

Question 3

which serotonin receptor mediates the vagal afferents from the GI tract?

Answer 3

5-HT₃

Question 4

what is the neuroanatomical name for the chemoreceptor trigger zone?

Answer 4

Area postrema

(Located in the fourth ventricle, but outside the BBB)

Question 5

MOA: Ondansetron

Answer 5

5-HT₃ receptor antagonist

(“On -DANCE-atron”)

Question 6

Adverse Effects (4) : Ondansetron

Answer 6

(1) Constipation
(2) Headache/Dizziness
(3) Torsades
(4) Serotonin syndrome

Question 7

what type of nausea can first-generation antihistamines (H1 receptor blockers) treat?

Answer 7

vestibular

(motion sickness)

Question 8

name 2 receptors found in high concentration throughout the vestibular system

Answer 8

(1) H₁
(2) M₁

Question 9

name 2 receptors found in high concentration in the area postrema

Answer 9

(1) D₂
(2) NK₁
* (NK₁ = neurokinin 1 receptors, which are activated by substance P)*

Question 10

MOA: Metoclopramide

Answer 10

D2 receptor antagonist

(In area postrema ∴ Good at treating drug-induced nausea)

Question 11

what drug can be used to treat delayed gastric emptying (unrelated to cholinergics)?

Answer 11

Metoclopramide

(Notice completely different MOA but many similarities to Bethanochol)

Question 12

Contraindication: Metoclopramide

Answer 12

Bowel obstruction

(Parkinson’s)

Question 13

Adverse Effects (7): Metoclopramide

Answer 13

(1) Diarrhea
(2) Drowsiness
(3) Depression
(4) Extrapyramidal effects
(5) Neuroleptic malignant syndrome
(6) Elevated prolactin
(7) Torsades de Pointes

Question 14

what adverse effect is associated with chronic Metoclopramide use?

Answer 14

Tardive dyskinesia

• (causes repetitive, involuntary movements, such as grimacing and eye blinking;*
• due to long-term use of neuroleptic drugs used to treat psychiatric conditions)*

Question 15

what is the endogenous ligand for the NK1 receptor?

Answer 15

Substance P

Question 16

MOA: Aprepitant

Answer 16

NK₁ receptor antagonist

(Often preferred over other anti-emetics ∵ it doesn’t affect dopamine or 5-HT ∴ fewer side effects)

Question 17

what neurotransmitter is released at the mucosa in response to GI irritation?

Answer 17

5-HT

Question 18

Which gastric cell secretes HCl?

Answer 18

Parietal cell

(Remember it also secretes intrinsic factor for Vit. B12 absorption)

Question 19

What transporter pumps H+ into the lumen of the stomach?

Answer 19

H+/K+ ATPase

Question 20

What directly stimulates parietal cells to secrete HCl?

Answer 20

(1) Histamine
(2) Gastrin
(3) Acetylcholine

Question 21

Which histamine receptor is responsible for increasing HCl secretion?

Answer 21

H2

Question 22

What paracrine-acting molecule stimulates HCl secretion from parietal cells?

Answer 22

Histamine

(Contrast with gastrin)

Question 23

What stimulates the release of histamine from ECL cells?

Answer 23

Gastrin

(Endocrine molecule, contrast with histamine)

Question 24

What secretes GRP?

Answer 24

Vagus n.

(Thus indirectly stimulating HCl release via GRP and directly stimulating HCl via ACh)

Question 25

**Suffix**: H2 receptor antagonist

Answer 25

"-tidine"

Question 26

**Indications** (2) : PPIs/H2 receptor antagonists

Answer 26

(1) GERD (2) GI Ulcers * (PPIs are first line)*

Question 27

**Adverse Effects** (4) : Cimetidine

Answer 27

(1) Inhibits CYP450 (2) Gynecomastia (3) Impotence (4) Elevated prolactin

Question 28

**MOA**: PPIs

Answer 28

Irreversibly inhibit H+/K+ ATPase

Question 29

**Suffix**: PPI

Answer 29

"-prazole"

Question 30

What is the preferred pharmacologic treatment for Zollinger-Ellison syndrome?

Answer 30

PPI *(Otherwise, octreotide can be used)*

Question 31

**Adverse Effects** (5) : PPIs

Answer 31

(1) C. difficile infection (2) Respiratory infections (3) ↓ Absorption of divalent cations (4) ⇒ ↑ Risk of osteoporosis (5) ⇒ Hypomagnesemia

Question 32

How does somatostatin reduced acid production?

Answer 32

By inhibiting the release of: (1) Histamine from ECL cells (2) Gastrin by G cells

Question 33

What type of gastrinomas can be treated with somatostatin?

Answer 33

SST receptor (+) *(... obviously need the receptor to mediate the ligand's effect)*

Question 34

Which gastric cell secretes histamine?

Answer 34

ECL cells

Question 35

Name 3 osmotic laxatives

Answer 35

(1) Magnesium salts (2) Polyethylene glycol (3) Lactulose * (Magnesium salt = Milk of Magnesia)*

Question 36

**MOA:** Senna

Answer 36

Stimulant laxative

Question 37

What is the etiology of melanosis coli?

Answer 37

Chronic senna use

Question 38

Describe how lactulose helps with hepatic encephalopathy

Answer 38

Metabolism of lactulose by GI bacteria ⇒ ↓ pH ⇒ NH₃ → NH₄⁺ ⇒ Prevents absorption of intestinal ammonia

Question 39

How does liver cirrhosis lead to encephalopathy?

Answer 39

⇒ ↑ NH₄⁺

Question 40

Describe why Rifaximin is useful in the treatment of hepatic encephalopathy

Answer 40

Kills ammonia producing bacteria *(Poorly absorbed lumenal antibiotic, similar to Neomycin)*

Question 41

**MOA**: Psyllium

Answer 41

Indigestible material ⇒ Distention ⇒ Promotes peristalsis

Question 42

**MOA**: Docusate

Answer 42

Stool surfactant agent *(Facilitates penetration of stool by water and lipid ⇒ Softer)*

Question 43

Which opioid receptor is found in high density in the GI tract?

Answer 43

μ *(mu)*

Question 44

Which μ-opioid agonist does not cross the BBB?

Answer 44

Loperamide

Question 45

How do μ-opioid agonist reduce GI motility?

Answer 45

Increase colonic phasic segmenting activity *(↑ Activity of GI circular smooth muscle while ↓ activity of GI longitudinal smooth muscle)*

Question 46

Which antidiarrheal agent is combined with atropine to prevent abuse?

Answer 46

Diphenoxylate

Question 47

Name a contraindication to antidiarrheals

Answer 47

Bloody diarrhea / Fever

Question 48

Name 2 tumors which can cause secretory diarrhea

Answer 48

(1) VIPoma (2) Carcinoid tumor