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Gastrointestinal Physiology
for PHGY 313
55
Physiology
Undergraduate 3
08/21/2012

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Term
Absorptive Columnar Cells
Definition

Have Microvilli

immature golgi, mitochondria

For absorbing

Term

Paneth Cells

Definition

Produce enzymes to breakdown food

Well developed ER and Golgi

Zymogen granules containing enzymes released to lumen via exocytosis

Term
APUD
Definition

Amine Precursor Uptake Decarboxylase

Produce and release peptide hormones into blood stream

 Endocrine cells including G, I, S, D Cells

 A - Lots of amines

 PU - Uptakes many hormonal precursors

D - lots of decarboxylase enzyme to convert precursors into amines

Term
Goblet Cells
Definition
Contain and release mucus granules for intestinal surface
Mucus is carb rich
Term
Crypt Columnar Cell
Definition
Stem cell for other intestinal epithelial cell
Term
Parasympathetic activation of GI
Definition
Increased Activity
Increased blood flow etc.
Term
Sympathetic activation of GI
Definition
decreased activity
decreased blood flow etc.
Term
Gastrin
Definition
Secreted by G cells
Stimulates acid secretions
Stimulates gastric mucosal growth
Works on CCK-B Receptors (enterochromaffin & oxyntic cells) - less on CCK-A receptors (D Cells)
Inhibited by Somatostatin
Stimulated by GRP, Vagal innervation
Term
CCK
Definition
Cholecystokinin
Secreted by I cells
release is inhibited by bile acids
Duodenum and Jejunum
Contracts the gallblader (bile acid release) (most potent stimulus for contraction)
Inhibits stomach contraction - relaxation of sphincter of oddi
Acts on CCK-A (smooth muscle and gallbladder)
competes with gastrin for CCK-B - inhibits acid secretion
Term
Secretin
Definition

Secreted by S cells in response to increase in acidity Duodenum Pancreatic bicarbonate secretion Massive increase in response by presence of phenylalanine

Binding to VIP R ->activation, cAMP production, increased enzymatic release

Term
Motilin
Definition
Upper duodenum during fasting
Increases motility
Stimulates Interdigestive myoelectric complexes
Term
How does gastrin work
Definition

G cell secretes gastrin to blood Gastrin activates CCK-B receptors on Oxyntin Cells to secrete H+ into lumen and indirectly through enterochromaffin cells via histamine.

Activates pepsinogen secretion by chief cells

Term
Nucleus of the Solitary Tract
Definition
Point of convergence of taste chemoreceptor afferents
Origin of salivary glad stimulating efferents
Parotid via S
Term
Parotid gland stimulation
Definition
Nucleus of the Solitary Tract -> (Inferior) Salivary nucleus->Glossopharyngeal nerve (integration of taste) -> Otic ganglion
Term
Submandibular and sublingual gland stimulation
Definition
Nucleus of the Solitary Tract -> Superior Salivary Ganglion -> chorda tympani (integration of taste) -> submandibular ganglion -> Lingual nerve
Term
Intrinsic Factor
Definition
Released by stomach parietal cells
Promotes absorption of B12 in the ileum
Term
Parietal Cell Function
Definition
4 Transfers. 1 out apical, 2 in apical. 2 out lumenal 1 in lumenal
Circulating CO2 is brought in and turned into H2CO3 in presence of carbonic anhydrase with H20. Dissociation turns it into H+ and HCO3-. HCO3- is sent into the circulation in exchange for Cl-. H+ is exchanged into the lumen for K+ (K+/H+ ATPase) coupled to a lumenal Cl- exuding channel.
Apical: CO2 and Cl- in, HCO3- out
Lumenal: H+ Cl- out, K+ in

Also: IF secretion

High mitochondrial function
Term
Chief Cell
Definition
=Peptic Cell
Gastric secretion of Pepsinogen
Zymogenic
Term
D cells
Definition
Release somatostatin in response to low lumenal pH
Slows release of gastrin
Term
Somatostatin
Definition
Inhibits gastrin release on G cells
Activates G protein coupled ST R (somatostatin receptor)
Term
Fat soluble vitamins
Definition
BAKED
Lipid soluble vitamins
B12
A
K
E
D
Term
Cephalic Phase of Digestion
Definition
External Stimuli
Vagal innervation
Ach on muscarinic receptors
G Cells -> Gastrin -> Oxyntic Cells -> H+ Secretion
G Cells -> Gastrin -> Chief Cells -> Pepsinogen
ECL -> Histamine -> H2 Receptor on Oxyntic -> H+
Oxyntic -> H+
low pH and Pepsinogen
Term
Gastric Phase of Digestion
Definition
Mechanical contact with peptides of G cells and distention
Release of Gastrin ->->->Oxyntic cells->H+
Lower pH-> D Cells -> somatostatin -> G Cells -> reduced gastrin
Term
Intestinal Phase of Digestion
Definition
H+ will activate S cells to make and release secretin which will cause pancreas to release HCO3- and enzymes acting on VIP R via cAMP dep. pathway
Metabolites will act on I cells to cause release of HCO3- from gallbladder and pancreas and enzymes via CCK-A and a Ca dep. pathway
CCK will bind competitively with gastrin to CCK-B in the stomach to stop H+ secretion
Term
Pancreas
Definition

Exocrine Function

  • Bicarbonate to buffer acids to maintain pH for optimal enzymatic function, prevent denaturation.
  • Maintaining pH to promote micelle formation
  • digestive enzymes (amylases)
  • Protect intestinal mucosa against acid
  • Glandular portion

Endocrine Function

  • Insulin
  • Glucagon
  • islets of langerhans
Term
Pancreatic Gland
Definition

Exocrine

Acinar - enzymes

middle portion - thinner epithelium, bicarbonate production

duct cells - HCO3-/Cl- exchange

Term
Fe uptake
Definition

Gastroferrin released by oxyntic cells

Iron binding protein which binds iron and absorbs in ileum

Term
Pancreatic Juice
Definition

Na K HCO3 Mg Ca

similar to blood

very high HCO3-

Neutralizes chyme to reach optimal pH for micelle and enzymes

Term
Pancreatic Duct Cells
Definition
At rest CFTR (Cystic fibrosis transporter regulators) are aggregated on the lumenal side.
Activation by secretin causes disaggregation
H+ transporters in vesicles are deposited on the apical membrane
H+ will be pumped into the blood, HCO3- out to lumen and Cl- (lumen) and CO2 (Blood) are taken into cell
Term
Pancreatic Enzymes
(Classes, Activation, Location, Release)
Definition
Lipase
Amylase
Protease
(deoxy/)Ribonuclease
Elastase

Activated by:
Trypsin
Enterokinase
pH

Made by ER, Golgi Released as a zymogen granule into the acinar portion of the lumen
Term
Central Regulation of Energy Balance
Definition
Hedonic System - Pleasure of eating. Controlled by VTA
Homeostatic System - Energy stores are low. Hypothalamus and brainstem
Term
Hypothalamus in food intake
Definition
Lesions caused obesity (PVN, VMN, DMN) or weight loss (LHA)
Term
Ventricular system in food intake
Definition
CSF compartment where signal proteins are released from circulation
Term
Arcuate Nucleus (ARC)
Definition
POMC and NPY/AgRP try to find balance of activation of MC3/4R (Melanocortin) neuron
Term
Lateral Hypothalamic Area (LHA)
Definition
Negative control centre
Lesion caused reduced food intake and weight loss
Term
Leptin
Definition
Hormone
from Adipocytes
Leptin causes decrease in appetite when bound to LepR
As people get larger, leptin increases. Eventually become leptin resistant
Activates POMC
Inhibits NPY/AgRP
Acts on GABAergic neurons to reduce food intake
Term
POMC Neurons
Definition
Anorexic neurons
Stimulation leads to reduced food intake
On Hypothalamic ARC
Activated by Leptin
Term
NPY/AgRP Neurons
Definition
Orexigenic neurons
Stimulation leads to increased food intake
On Hypothalamic ARC
Inhibited by leptin
Activated by Ghrellin
Colocalized neurons
Term
Ghrellin
Definition
Released from GI
Orexigenic
Activates NPY/AgRP
Term
Common hepatic duct
Definition
forms common bile duct after joining with cystic duct and joins pancreatic duct to empty into duodenum at sphincter of oddi
fed by left and right hepatic ducts
Term
Bile Acids
Definition
Secreted in bile from gallbladder reabsorbed in ileum and recycled by the liber
Term
Bilirubin
Definition
Breakdown of Heme from RBCs
Hepatocytes remove the iron by hemeoxygenase
made from biliverdin by biliverdin reductase
Conjugated to glucoronic acid in the liber
secreted to the intestines by bile ducts and gallbladder
Bilirubin is resorbed in the intestin
Conjugated bilirubin is not very lipid soluble - it is negatively charged
Term
Prehepatic or Hemolytic unconjugated bilirubin
Definition
anaemia causing jaundice, increased production of unconjugated bilirubin
dark urine and feces
Term
Intrahepatic or Hepatocellular uncojugated bilirubin
Definition
Damage to liver
Feces are pale, liver is not producing enough bilirubin
Term
Posthepatic or Obstructive conjugated bilirubin
Definition
Blockage in duct urine is dark and feces is pale from under excretion of bile
Term
BIlirubin processing
Definition
Bilirubin is taken up unconjugated in the intestines returned through the portal blood to the liver where it is conjugated to make bilirubin glucuronide.
It is secreted into the intestine at the sphincter of oddi by the common bile duct, via the gall bladder.
After it is unconjugated and reduced it forms urobilinogen which either gets taken back up into the liver where it can be turned back into bilirubin or excreted in the urine or it is oxidized into stercobilinogen in the intestine which then gets excreted in the feces.
Term
BIle canaliculus
Definition
transport vessels formed by adjacent hepatocyte membranes
Term
cMOAT
Definition
Canalicular Multi-organic anion transporter
transports anions
uses electric gradient
transports bilirubin
Term
Gallbladder
Definition
Stores and concentrates bile
Contains lipid peroxidases and induces micelle formation
Can pump using the pressure of the sphincter of oddi
Has muscle to contract and rugae to stretch
Gallbladder bile is more concentrated and has less bicarbonate than hepatic bile
Lecithin, cholesterol and bile salts are concentrated
Term
Hepatocytes
Definition
Absorb bile salts oxygen and nutrients
Conjugate bile salts and secrete to canaliculi
Gluconeogenesis
Glycogen deposition
Oxydation
Neutralizing of toxins
Term
Bile
Definition
Primary Bile acids
Phosphatidyl choline - lipid metabolism
Cholesterol
Term
Migrating myoelectric Complex (MMC)
Definition
Cycles of contractions
Spontaneous and triggered by foood
Triggered by motilin
Term
SGLT1
Definition
Sodium Dependant Glucose transporter
Type 1 is in intestinal wall
2 Na for 1 Glucose
Term
GLUT
Definition
Pure glucose transporters
Differing affinities for glucose and fructose
Term
Innervation of the colon
Definition
Proximal colon - vagus nerve
descending colon and down - Pudendal Nerve (Parasympathetic)
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