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FHB Exam 3 > GI: Intestinal Phase > Flashcards

GI: Intestinal Phase Flashcards

1
Q

List some functions of the intestinal phase.

A
  1. secretion of biliary and pancreatic juices
  2. digestion and absorption
  3. large surface area
  4. control of the pylorus to regulate gastric emptying
  5. inhibits gastric secretion
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2
Q

What motility things need to occur to allow for gastric emptying?

A
  1. increased pressure in the proximal stomach
  2. increased contractions of the antrum
  3. relaxed pyloric sphincter
  4. relaxed duodenum
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3
Q

Describe feedback inhibition of gastric emptying.

A
  1. vagal afferents detect the presence of chyme and nutrients in the duodenum
  2. vagal efferents slow down gastric contractions and close up the pyloric sphincter
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4
Q

Describe the effect of fat in the duodenum on gastric emptying.

A
  1. fatty acids stimulate the secretion of CCK
  2. CCK inhibits gastric emptying and closes the pylorus to allow for proper digestion and absorption
  3. CCK allows pancreatic and biliary secretion release to help in fat digestion and absorption
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5
Q

Describe the effect of duodenal acidity on gastric emptying.

A
  1. proton receptors on the duodenal mucosa sense low pH of duodenal contents
  2. signal is sent through the myenteric plexus to the gastric smooth muscle
  3. slows down gastric contractions to allow time for pancreatic HCO3 secretions to neutralize acid in the duodenum
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6
Q

What factors contribute to the inhibition of gastric emptying?

A
  • fat in the duodenum
  • acid in the duodenum
  • chyme in the duodenum
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7
Q

What is the largest contribution to enzymatic digestion?

A

exocrine pancreatic secretions (1L/day)

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8
Q

List the components of exocrine pancreatic secretions.

A

HCO3, aqueous solution

enzymes for macromolecular digestion

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9
Q

What is the purpose of HCO3 in the pancreatic secretions?

A
  • neutralizes incoming acidic chyme
  • allows for correct pH for pancreatic enzymes
  • reduces risk for mucosal damage from the pepsins entering via chyme
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10
Q

What glands make up the endocrine pancreas? What do these glands secrete?

A
  • islet of Langerhans’

- insulin, glucagon, somatostatin, pancreatic polypeptides

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11
Q

Describe the structure of endocrine pancreatic glands.

A
  1. acinus - blind end that secretes enzymes; made of acinar cells
  2. ductules - modify the secretions, adding HCO3 aqueous
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12
Q

What stimulates pancreatic gland secretion (specifically, each part of the gland)?

A
  1. acinus is stimulated by CCK

2. ductules are stimulated by secretin

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13
Q

Describe the cells that line the pancreatic glands.

A
  1. acinus = acinar cells

2. ductules = centroacinar cells, ductal cells

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14
Q

Describe the effect of decreased pH on the pancreatic secretions.

A
  • activate S cells=> secretin
  • stimulates ductule cells to release HCO3
  • negative feedback once lumen pH reaches normal levels to stop secretin secretion
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15
Q

How does secretin work?

A
  1. increases cAMP in ductal cells
  2. opens CFTR Cl- channels
  3. ductal cells release Cl- into the ductal lumen
  4. stimulates Cl-/HCO3- antiporter => secretion of HCO3-, reuptake of Cl-
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16
Q

Where does HCO3 in pancreatic secretions come from?

A
  1. Na-HCO3 co-transporter Type 1 (NBC-1) brings Na and HCO3 into the ductal cells (basolateral membrane)
  2. Carbonic Anhydrase
17
Q

Why does pancreatic venous blood get acidified?

A

Because H+ are produced from carbonic anhydrase and are transported to the blood via Na/H exchangers on the basolateral membrane

18
Q

How does Cystic Fibrosis affect pancreatic secretions?

A
  • mutated CFTR Cl- channel prevents secretion of Cl-
  • secondary prevention of HCO3- secretion
  • highly acidic contents in the glands leads to destruction of exocrine glands
  • impaired pancreatic function
19
Q

List the triggers of CCK release.

A
  1. fatty acids and amino acids bind to I cells
  2. fatty acids and amino acids bind to sensor paracrine cells that release CCK-Releasing Peptide
  3. Monitor Peptide released by acinar cells binds to I cells
20
Q

Where is CCK released from?

A

intestinal I cells

21
Q

What are the effects of CCK?

A
  1. binds to acinar cell CCK-1 receptor => increase intracellular Ca2+ => stimulates secretion of enzymes
  2. neural: stimulates vagovagal reflex => stimulates secretion of ACh, GRP, and VIP from ENS
22
Q

Describe the mechanism of acinar enzymatic secretion.

A
  1. CCK, ACh, and GRP => increase intracellular calcium
  2. VIP and secretin => increase cAMP
  3. phosphorylation cascade
  4. zymogen granules fuse with acinar membrane
  5. exocytosis
  6. ductal secretions wash away enzymes out of the gland
23
Q

How do pancreatic proteases get activated?

A

enterokinase activates trypsinogen to trypsin

trypsin then activates all the other proteases

24
Q

What causes pancreatitis?

A

premature activation of proteases or trypsin is resistant to degradation

25
Q

How does distension and hypertonicity effect pancreatic function?

A

via enteropancreatic reflexes

increases secretion

26
Q

In general, what is the pathway of bile?

A

hepatocytes => bile canaliculi => bile duct => R/L hepatic duct => common bile duct => gallbladder => sphincter of Oddi

27
Q

List the components of bile.

A
  • bile acids
  • phospholipids
  • electrolytes
  • proteins
  • cholesterol
  • bile pigments (bilirubin)
28
Q

Describe enterohepatic circulation of bile acids.

A

liver => duodenum

  1. if unconjugated, can get passively reabsorbed
  2. if conjugated, gets actively reabsorbed in the terminal ileum via ASBT (Na-dependent Bile acid Transporter) => portal vein
29
Q

What is the purpose of motility in the small intestines?

A
  • more digestion
  • increased biochemical digestion by exposing to more enzymes
  • propels the bolus to the epithelium for absorption
30
Q

Describe the migrating motor complex.

A
  • motilin hormone causes periodic contractions every 90 minutes
  • clears the small intestine of its contents by opening pylorus and ileocecal sphincters
  • motilin decreases after a meal (to allow for proper gastric emptying), increased during fasting
31
Q

Define Brunner’s glands.

A
  • located in duodenum

- secrete mucus and HCO3

32
Q

Define Lieberkuhn glands.

A
  • secrete peptidases and amylases
33
Q

Define Paneth cells.

A
  • located at the bottom of villi
  • secrete antimicrobial peptides and enzymes
  • ribonucleases, esterases

FHB Exam 3 (23 decks)

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