Week 1 Flashcards
What is the first line of defense in GI tract against pathogens?
Mucosa which contains antibodies against pathogens
Ratio of GI immune cells vs Body
GI & Body immune cells have equal numbers showing how significant immunity for GI is
Histamine effect on GI
Stimulates Motility & Secretion
Further GI defense lines
1) GALT (waldeyer’s ring)
2) Inflammatory mediators (cytokines/histamine)
3) Host microbe interactions (flora)
2 Types of GI afferent neurons
- Intrinsic afferent (to inter n.)
- Visceral afferent (from organs)
GI sympathetic DIRECT innervation
- Vasoconstriction (a1-R)
- SM of GI (B2-R)
- Sphincter constriction (a1-R)
GI sympathetic INDIRECT innervation
Decreased motility and secretion
(a2-R)
G-cell
Gastrin
(Acid secretion)
I-cell
Cholecyctokinin (CCK)
(pancreas secretion & gallbladder emptying)
S-cell
Secretin
(pancreas & bile secretion)
Low pH in duo. stims this
L-cell
- Proglucagon
- GLP-1/2
GIP-cell
Gastric inhibitory peptide (GIP)
Oral glucose stims this
(inh. gastric emptying)
(K-cells)
P/D1-cell
ghrelin
(hunger / food intake)
D-cell
Somatostatin
(generally inhibitory)
F-cell
Pancreatic Polypeptide (PP)
M-cell
Motilin
EC-cell
Serotonin (enterochromaffin/EC cells)
ECL-cell
Histamine (enterochromaffin-like cell)
(motility & secretion stim.)
Hormones made in the GI but act somewhere else
- CCK
- Ghrelin
- Gastrin
- Secretin
Hormones made somewhere else & act on GI
- Aldosterone
- PTH
What % of the body’s immune cells are in the GI-tract
80%
Sympathetic regulation of GI
- a1 causes contraction of SM sphincters
- a2/B2 cause SM wall relaxation
- a1 Vasoconstriction of splanchnic circulation
3 GI control mechanisms
- Neural
- Paracrine
- Endocrine
What cells in GI secrete hormones
Enteroendocrine cells
What are the wave-like movements in GI
- Not APs
- Originate from interstitial cells of Cajal
Where are Cajal cells found & their function
Myenteric / Submucosal Plexus
Origin of the slow-wave movement of GI
(GI-tract pacemaker)
Phases of Swallowing
1) Oral phase (voluntary)
2) Pharyngeal phase (in-v)
3) Esophageal phase (in-v)
Upper Esophageal Sphincter (UES)
- Striated muscle
- Voluntary
- Relaxed by Bolus detection
Lower Esophageal Sphincter (LES)
- Smooth Muscle
- Involuntary
- Vagovagal reflex
- Relaxed by NO
Retropulsion
Pushback of Chyme from pylorus due to small opening and slow-waves of stomach
Movements in Small Intestine
- Segmentation (mixing)
- Peristalsis (propulsion)
How long does it take for food to go from Pylorus to Ileocecal valve?
3 to 5 hours
What promotes / inhibits Peristalsis of small intestine?
+ : Gastrin, CCK, Insulin, Serotonin
- : Secretin, Glucagon
How does Peristalsis in Small intestine start?
Enterochromaffin (EC) cells detect bolus in mucosa and release Serotonin
= Activation of Peristalsis
What happens in Proximal colon
Anti-peristalsis
What induces opening of Ileocecal valve?
- Gastrin
- Gastroileal reflex
Daily Salivary secretion
800 - 1500 mL / day (pH 7)
(90% during meals)
Saliva composition
- H2O
- Electrolytes
- Salivary Amylase
- Lingual Lipase
- IgA
- Lysozyme
- Mucin
Salivary secretion Pathway
1) Intralobular Intercalated
2) Intralobular Striated
3) Interlobular ducts
4) Interlobular excretory d.
5) Main excretory d.
Parotid Gland is mostly…
Serous
Sublingual Gland is mostly…
Mucous
Submandibular Gland is mostly…
Its MIXED
Intrinsic Salivary Glands
- Buccal
- Labial
- Palatine
(constant mucous secretion)
Parasympathetic Effect on Saliva Secretion
- VIP (vessels): Gs, Vasodilation
- ACh (acini): M3-ACh-R (Gq), Ca2+ signal, Constriction & Exocytosis
Sympathetic Effect on Saliva Secretion
NE mediated
- B2-AR, Mucin secretion, Viscous
- a1-AR, Vasoconstriction, less secretion
Daily Gastric Secretion
1 - 1.5 L /day
What is essential for Vitamin B12 absorption
Intrinsic factor secreted in gastric juice (parietal cells)
Gastric Parietal Cells secrete
- HCl
- Intrinsic factor
Gastric Chief Cells
Pepsinogen
Omeprazol
Inhibits the H+/K+ ATPase in Parietal cell acid secretion
What does prolonged vomiting cause?
Metabolic Alkalosis
Stomach acidity needs to be replenished, so HCO3/Cl exchanger works more, pumping more HCO3 bicarbonate into the blood
Regulators of Parietal cells
- Gastrin from G-cells (main)
- Histamine (paracrine)
- ACh (neural)
What can activate G-cells?
- ACh
- GRP (gastrin releasing peptide)
- Wall tension
- Alcohol
- H.Pylori = ulcers
- NE on B2-AR
What Inhibits G-cells?
- Somatostatin
- Prostaglandins
ECL-cells effect on gastric acid
- Activated by PARA or Gastrin
- Release Histamine which stimulates parietal cell secretion
Gastric acid secretion Cephalic phase
- Smell & Taste of food
- Vagal N stim. GA secretion
Gastric acid secretion phases
- Cephalic phase
- Gastric phase
Vagovagal Reflex
- Activated by presence of food in stomach
- By wall-distension taken by vagal N efferents
Feedback reg. of GA secretion
When low pH is sensed in antrum & pylorus, somatostatin is released from D-cells
Basal G.acid output (BAO)
1.5 - 2.5 mmol H+/hour
Peak G.acid output (PAO)
- F: 25 mmol H+/hour
- M: 35 mmol H+/hour
What stimulates Pepsinogen secretion?
- Gastrin (Gq)
- ACh (M3) via ENS
- Histamine (Gs)
- Secretin
Daily secretion of Small intestine
1.5 - 2 L / day
What does Diarrhea cause?
Metabolic Acidosis
Continuous fluid produced in small intestines which is high in HCO3, so it is lost from blood causing lower pH
PARA effects on Large intestine
VIP (Gs) stimulates cAMP signal, causes translocation of CFTR channels.
= Effects of Cholera toxin making more watery diarrhea
Paracrine mediators of Large intestine
Local immune system activated by Serotonin production so Diarrhea happens to wash-out any harmful material
Pancreatic secretion percentages
- 98% exocrine to intestine
- 2% endocrine to blood
Daily Pancreas secretion
700 - 900 ml / Day
Fat-Soluble vitamins
ADEK
Daily Bile production
200 - 1200 ml / Day
What makes Bile acids more water soluble
Conjugation with:
- Glycine
- Taurine
2 Pathways for entry of solutes into Bile
- Active Secretion (trans.c)
- Passive permeation (para.c)
Bile acid-dependent flow
- Hepatocytes pump bile acids into canaliculi
- Pulls water with it creating a flow
- Gradient maintained by Na+
Bile acid-independent flow
- Carbonic anhydrase in Hepatocytes forms bicarbonate
- HCO3 to canaliculi using Cl exchanger
- Pulls water creating flow
How is Bilirubin removed
Conjugated with Glucuronic acid in Hepatocytes to make it water-soluble
- Goes to canaliculi
- Converted to Urobilinogen & Stercobilin (color)
- Excreted via feces & urine
Fate of bile produced by Hepatocytes
- 450ml as Hepatic Bile to intestines
- 450ml stored in Gallbladder
Daily production of Bile acids in Liver
0.6 g / Day
Entire pool of Bile acids in the body
2 - 5 g
Total Bile acid usage per day
20g Bile acid / Day
Enterohepatic Circulation of Bile
Where one bile acid molecule is used several times
Loss of Bile acids + Salts
0.6 g / Day
Equal to what is produced
Neurohormonal control of Gallbladder Contraction
- NO + VIP relax sphincter of Oddi
- ACh SM contraction of gallbladder
- CCK Enhances effects
