Unit 3 Gi Physiology

Front 1

GI Hormones

Back 1

Unit 3, Week 2

Front 2

Gastrin

Back 2

Source: G-cells in Antrum
Released in response to small peptides and amino acids, distention of stomach, and vagus stimulation.
Target: Parietal cells in stomach
Action: increase acid secretion

Front 3

Cholecystokinin (CCK)

Back 3

Source: I-cells in Duodenum (mostly) & Jejunum
Released in response to small peptides and amino acids, and fatty acids
Target: Pancreas, Gall Bladder, & Sphincter of Oddi
Actions: (1) Stimulates enzyme secretion from acinar cells - pancreatic lipases and amylase (2) contract gall bladder (3) relax sphincter of oddi (4) Inhibits gastric emptying (5) Growth of exocrine pancreas and gallbladder - aka trophic effects

Front 4

Secretin

Back 4

Source: S-cells in duodenum & jejunum
Released in response to acid and fatty acids in duodenum
Target: ducts of pancreas and gall bladder
Action: increases pancreatic and bile bicarbonate ion secretion

Front 5

Gastric inhibitory peptide (GIP)

Back 5

Source: K-cells in duodenum and jejunum
Released in response to fatty acids, amino acids, and oral glucose
Target: pancreas
Action: acts on endocrine pancreas

Front 6

Motilin

Back 6

Source: upper duodenum
Target: stomach and small intestine
Action: stimulates migrating motor complex

Front 7

Small intestine secretion and motility (Diarrhea week)

Back 7

Unit 3, week 3

Front 8

Duodenum
description
begins and ends?
function?

Back 8

thickest mucosa
avg 12-14 in long
begins at pyloric junction of stomach
ends at ligament of Treitz
site of pancreatic and biliary secretion entrance
mixing bowl of chyme and digestive enzymes

Front 9

Jejunum
description?
function?

Back 9

slightly ghinner mucosa
avg 7-8 feet long
major site of digestion and absorption

Front 10

Ileum
description?
function?

Back 10

thinnest mucosa
avg 12-14 feet long
site of intrinsic factor and bile absorption

Front 11

Sphincter of Oddi
where?
what stimulates it's relaxation?

Back 11

located at the end of the common bile duct just before entrance into the small intestine.
CCK stimulates it's relaxation

Front 12

What happens when you have significant fluid entering colon due to malabsorption in small intestine?

Back 12

Diarrhea
Colon only absorbs about 1.4 L of fluid
Small intestine absorbs about 7.5 L of fluid

Front 13

Parasympathetic innervation of small intestinal motility?

Back 13

Parasympathetic innervation via vagus nerve - increases contraction of intestinal smooth muscle contraction
Mostly cholinergic nerves, some release other neurocrines (ie peptidergic neurons incl VIP, enkephalins, and motilin)

Front 14

Sympathtic innervation of small intestinal motility?

Back 14

Sympathetic innervation via fibers that originate in celiac and superior mesenteric ganglia - decreases contraction

Front 15

When food and acid enter duodenum, what happens in small intestine?

Back 15

Digestion and food
Neutralization of acid

Front 16

What hormone is released from duodenum thru blood to pancreas to stimulate acinar cells in response to food and acid in duodenum and start digestion?

Back 16

Cholecystokinin (CCK)

also slows gastric emptying and causes gall bladder smooth muscle to contract and sphincter of oddi to relax to allow release of bile

Front 17

What hormone stimulates release of bicarb (HCO3-) from pancreatic and billary ducts in response to acid in duodenum to neutralize this acid in in order to allow optimal enzyme function for digestion?

Back 17

Secretin

Front 18

Digestion and Absorption of the Diet (Diarrhea week)

Back 18

Unit 3, week 3 continued

Front 19

Secretion of acinar cells to stimulate Cl exchange for bicarb via __, unlike in saliva which is based on rate of flow

Back 19

secretin

Front 20

How does pancreatic ductal bicarbonate ion exchange occur?

What is the net result?

Back 20

in presence of carbonic anhydrase, CO2 and H2O combine in cells to form H2CO3 which dissociates into H+ and HCO3-
HCO3- is secreted into pancreatic juice by Cl- HCO3- exchanger
H+ is transported into blood by Na+ H+ exchanger

Net result -> secretion of HCO3- into pancreatic ductal juice and absorption of H+ (which causes acidification of pancreatic venous blood)

Front 21

How is pancreatic acinar zymogens released

Back 21

cck binds pancreatic acinar cells
IP3 mediates release of Ca2+ from endoplasmic reticulum
Ca2+ binds Calmodulin
Zymogen granules released

Front 22

What are bile salts derived from?
What critical property do bile salts have?
Function of bile salts?

Back 22

Cholesterol
They're ampipathic which allow them to emulsify dietary lipids (surround lipids, creating small lipid droplets that repel each other and disperse, increasing surface area for digestive enzymes). Bile salts also form micelles with the products of lipid digestion

Front 23

What happens to bile acids after it's use in duodenum?

Back 23

absorbed in ileum along with intrinsic factor
enters portal circulation
mostly returns to liver for production of more bile salts

Front 24

What does the stomach absorb?

Back 24

ethanol, NSAIDs, aspirin

Front 25

What does the Duodenum and Jejunum absorb?

Back 25

nutrients, vitamins, various ions, water, and electrolytes

Front 26

what does the Ileum absorb?

Back 26

bile salts and vitamin B 12

Front 27

What does the Colon absorb?

Back 27

water and electrolytes

Front 28

What does the Rectum absorb?

Back 28

drugs wuch as steroids and salicylates

Front 29

Four mechanisms are important in transport of substances across intestinal cell membrane

Back 29

1) Active Transport - primary & secondary (co-transport, counter-transport,)
2) Passive Diffusion
3) Facilitated Diffusion - carrier mediated
4) Endocytosis

Front 30

What activates Trypsinogen (secreted by pancreas)?

Back 30

Enterokinase

Front 31

Trypsin

Back 31

Trypsin is autocatalytic and activates other proenzymes secreted by pancreas (chymotrypsinogen -> chymotrypsin,
procarboxypeptidase -> carboxypeptidase,
procolipase -> colipase,
prophospholipase -> phospholipase)

Front 32

What digests proteolytic enzymes?

Back 32

proteolytic enzymes digest themselves

Front 33

Lactose is digested by __ into __ and ___

Back 33

Lactose is digested by lactase into galactose and glucose

Front 34

Sucrose is digested by __ into __ and __

Back 34

Sucrose is digested by sucrose into fructose and glucose

Front 35

starches are digested by __ and __ into __, which is further broken down by __ to form __

Back 35

Starches are digested by alpha amylase and pancreatic amylase into maltose + 3-9 glucose polymers, which is further broken down by maltase + alpha dextinase to form glucose.

Front 36

Glucose and Galactose are absorbed via__

Back 36

Glucose and galactose are absorbed via 2' active transport and facilitated diffusion

compete for membrane symport carrier SGLUT-1 with Na+
energy from Na+ K+ ATPase which pumps Na out and K in

Water follows glucose and glactose b/w cells

Front 37

Fructose is absorbed via __

Back 37

Fructose is absorbed via facilitated diffusion.
GLUT-5 carrier down it's concentration gradient and without energy requirement

Front 38

3 locations where digestion of proteins to amino acids occur

Back 38

1) Intestinal lumen: stomach pepsin (digests collagen) and small intestine endopeptidases and exopeptidases
2) brush border: oligopeptidases and dipeptidases
3) cytoplasm of mucosal cells: dipeptidases

Front 39

Absorption of Amino acids is via __

Back 39

2' active transport (Na+ dependent) and facilitated diffusion

1) AA symport with Na from lumen into cell
energy from Na+ K+ ATPase
2) aa facilitated diffusion down concentration gradient from cell to interstitial fluid

water follows b/w cells from lumen to interstitial fluid

Front 40

In stomach, lipid droplets are emulsified (kept apart) by __

Back 40

dietary proteins
(bile acids, the primary emulsifying agents in small intestine, aren't present in stomach)

Front 41

In small intestine, __ and __ surround and emulsify dietary lipids

Back 41

bile salts and lysolecithin

Front 42

Digestion of Triglycerides/lipids

Back 42

2) Pancreatic lipase (with colipase) breaks down triglyceride into 2-monoglyceride and 2 free fatty acids.
2) cholesterol ester hydrolase breaks 2-monoglyceride into a fatty acid and a glycerol

Front 43

Absorption of Triglyceride/lipid digestion products

Back 43

1) except for glycerol (a cholesterol), all products of lipid digestion are solubilized in micelles and transported to apical membrane of midjejunum intestinal cells for absorption
2) lipids released from micelle and diffuse down their concentration gradient into cell (micelles don't enter cell, bile salts absorbed downstream in ileum)
3) lipid products are reesterified and
4) packaged w/ apoproteins in lipid carrying particles (chylomicrons), which are
5) packaged in secretory vesicles in golgi apparatus, exocytosed, enter lymphatic capillaries (lacteals), and transported to thoracic duct which empties into bloodstream