GI Flashcards
MCC cause of ulcers, other than H. pylori?
NSAIDs
Inhibit Prostaglandin. Inhibit secretion of Mucin and Bicarb
What is the effect of insulin on glucose reabsorbtion in Small Intestine?
None! Insulin has no effect on secondary active transport. Only effects transport in adipose and resting muscles.
Glucose absorbed w/ Na into cell, and then transported out of cell into blood. However, Na reabsorbtion is energy dependent, so Glucose is cosnidered secondary ACTIVE transport.
What is the only substance in Small intestine absorbed independently from Na?
Fructose
Lipids
The two main causes of Metabolic Acidosis with normal anion gap are?
Diarrhea
Renal tubular acidosis
Both have high chloride
What is Invasive diarrhea?
Blood and WBCs in stool, and can give fever
Where is Gastrin produced?
Describe its regulation
- G cells in antrum of stomach.
- ↑by stomach distention, alkalinization, amino acids, peptides, vagal stimulation.
- ↓by stomach pH
Which amino acids are potent stimulators for Gastrin release?
Phenylalanine and Tryptophan
What disease increase Gastrin release?
Chronic use of what drug also increase Gastrin?
Disease: Zollinger-Ellison
Rx: chronic use of PPI
What is the Fx of Gastrin?
↑gastric H+ secretion
↑growth of gastric mucosa
↑gastric motility
What effect does Ach have on GI?
Increases contractility and secretion
What is unique to hormone Gastrin?
- only hormone to increase Gastric motility
- only w/ negative feedback by stomach acid
- only one w/ neural innervation (vagus via Ach and GRP)
Function of Cholecystokinin and location of source cells?
↑pancreatic stimulation by acting on neural muscarinic pathway
↑GB contraction
↓gastric emptying
↑sphincter of Oddi relaxation (allows pancreas secretion to move in duodenum
source: I-cells in duodenum, jejunum
What regulates CCK release?
↑by FA mainly, and amino acids
Where is Secretin made and what is its Fx?
S cells in duodenum
↑pancreatic and Liver HCO3- secretion
↑bile secretion
↓gastric acid secretion
HCO3- neutralizes gastric acid in duodenum, allowing pancreatic enzymes to function
What triggers Secretin release?
↑by acid, FAs in lumen of duodenum.
What is Somatostatin? What is it’s Fx?
Inhibitory hormone made by D cells of pancreas islets and GI mucosa. It has anti-growth hormone effects (inhibit digestion and absorption of material needed for growth)
Decreases ↓ the following:
- secretion of gastric acid, pepsinogen, pancreatic and small intestine fluid
- insulin and glucagon release
- GB contraction
What regulates Somatostatin release?
↑by acid
↓vagal stimulation
What is funtion of Motilin and where is it released?
Regulates Migrating Motor Complexes, waves of electrical activity that sweep through the GI in a regular cycle during fasting. MMC trigger peristaltic waves, which facilitate transportation of indigestible substances such as bone, fiber, and foreign bodies from the stomach, through the small intestine, past the ileocecal sphincter, and into the colon. The MMC occurs every 90-120 minutes during the interdigestive phase (between meals), and is responsible for the rumbling experienced when hungry.
What is a Motilin agonist drug?
Erythromycin
Administration of a low dose of erythromycin will induce peristalsis
Does oral or IV glucose trigger higher insulin secretion? Explain
Oral glucose has >insulin release, due to GIP secretion from oral glucose (carbohydrates biggest stimulant of GIP)
What is Glucose-dependent insulinotropic peptide?
Where is it made?
Made from K cells (duodenum, jejunum)
GI hormone that ↓gastric H+ secretion (exocrine) and ↑insulin release (endocrine).
Also called Gastric Inhibitory Peptide (GIP)
What triggers GIP?
Oral glucose, carbohydrates.
Increase FAs, AAs
What is a VIPoma and what disease results?
- non-alpha, non-beta islet cell panreatic tumor.
- Secretes excess VIP
- causes WDHA syndrome: Water Diarrhea, Hypokalemia, Achlorhydria (no HCl acid made for stomach)
What is Fx and source of VIP?
- From parasympathetic ganglia in sphincters, GB, SI.
- ↑Intestinal H2O and electrolyte secretion
- ↑relaxation of intestinal SM and sphincters
- homologous to Secretin: ↑HCO3 pancreas release, decrease gastric H+ release
What stimulates VIP release?
↑by distention and vagal stimulation
↓by adrenergic input
What hormone is possibly implicated in ↑LES tone in Achalasia?
Nitric Oxide
What is Fx of Nitric Oxide?
Increases SM relaxation, including LES sphincter
What do Parietal cells release?
What are the stimuli for Parietal cells?
Parietal cells release HCl and Intrinsic factor.
They have 3 stimuli:
1) Neural: Ach (vagal)
2) Hormonal: Gastrin
3) Paracrine: Histamine
What secretes stomach acid?
What regulates this? What disease causes excess release?
Parietal cells (stomach). Gastrinoma is a tumor that causes continuous levels of acid release and ulcers.
↑by histamine, ACh, Gastrin
↓by Prostaglandin, Secretin, somatostatn, GIP.
“Don’t PaSS Gas”
What is the only part of stomach necessary for life?
What disease affects source cell?
Intrinsic Factor for Vit B12 absorption.
Autoimmune destruction of parietal cells, cause chronic gastritis andPernicious anemia
Where are Chief cells? What do they make, and what stimulates?
Chief cells in stomach. Make Pensinogen (active form Pepsin by H+) which digests Protein.
↑by vagal stiulation and stomach acid
Where is HCO3- made in GI?
Fx?
Mucosal cells in salivary glands, stomach, duodenum (Brunner’s glands), Liver, and Pancreas
Neutralizes acid. Trapped in mucosa and covers stomach epithelium.
What regulates HCO3- release in GI?
↑by panreatic and biliary secretion w/ Secretin (S-cells in duodenum, act on pancreas and Liver)
Effects of stomach distension?
- ↑ACh and GRP (Vagal stimulation both)
- Opens Pylorus
- ↑Mucus lining stomach
What are Brunner’s glands?
What happens in hyertrophy?
Glands in duodenal submucosa. Secrete alkaline mucus.
Hypertrophy seen in Peptic ulcer disease.
What medication can inhibit Parietal cells? Be specific to PC stimuli
Atropine: blocks vagal stimulation by ACh on M3 receptor of PC. Does not effect G-cells. which use GRP.
H2 blockers: Stop Histamine (from ECL cells) action on PCs.
Misoprostal: Inhibit cAMP (Histamine, H2 receptor pathway)
PPIs stop all 3 stimuli (Ach, Gastrin, Histamine) by inhibiting ATPase (releases H+, stimulates by all 3).
What are pathways for Parietal cell production of stomach acid?
ACh acts on M3 receptor, Gastrin acts on CCKB receptor. Both activate Gq →IP3/Ca→activate ATPase (release H+).
Histamine ats on H2 receptor→cAMP→activate ATPase
(Gastrin acts on ECL cells→Histamine release)
What is Gastrin’s primary effect on Parietal cells?
Gastrin increases stomach acid primarily by acting on ECL cells, leading to histamine release Vs. acting directly on parietal cells
MOA of following on Parietal cell:
PG?
Misoprstol?
Somatostatin?
All 3 are Parietal cell inhibitors for Stomach acid release.
Activate Gi→inhibit cAMP→inhibit ATPase
What is pathway for Gastrin on Parietal cell?
Vagus stimulation→GRP acts on G-cells, release Gastrin →act on CCKB receptor→Gq stimulation→IP3/Ca2+→ATPase activation (H+ release)
Describe H+ source for Parietal cells and effect on outgoing venous blood
CO2 from arteria blood becomes H+ via Carbonic anhydrase pathway. HCO3- made as result leaving through venous blood (highest pH of any blood in body!)
CO2 + H2O–(CA)-↔ H2CO3↔ HCO3- + H+
Most basic blood in body location?
“alkaline tide”
highest pH blood is venous blood leaving stomach
What disease decreases?
How to Tx?
Diabetic Gastroparesis, due to neuropathy
Tx: Erythromyin increases GI motility
normal patient, drug would cause vomiting
Saliva source and consistency by source
Parotid gland: serous (THIN no mucin)
SM and SL gland: mixed, mucus and serous), THICK
What controls saliva secretion?
Parasympathetic AND Sympathetic
Para: ↑vol, thinner
Symp: ↓vol, thicker
No hormonal control. All neural control.
What are contents of saliva and purpose?
Tonicity and cause?
- Salivary Amylase and Lipase (partial digestion, enough to taste)
- HCO3-: neutralizes bacterial acids
- Mucins lubricate foods
- IgA
Chloride pump- NaCl reabsorbed into duct, but H2O is not→hypotonic saliva. Necessary for taste (food hypertonic in comparison, molecules flow to saliva).
This type of pump unique to saliva
Why can’t you taste Tofu?
Saliva lacks Proteases, protein digestion.
Tofu 100% pure protein
Rank fastest to slowest substances for stomach digestion
Normal saline > other liquids > CHO > Protein > Fats
Fats have most calories, need more time to absorb.
Stomach distension and duodenum distension effect on pyloric sphincter?
Stomach distension: Opens PS
Duodenum distension: Closes PS
What triggers Ileocecal valve opening and closure?
Opens: distension/stretch of ileum
Closes: cecum distension
What is RLS in bile salt formation?
Deficiency has what effect?
Cholesterol 7alpha- hydroxylase
Defiency: gallstones
What is Bile? Composition and Fx?
Dark green/yellowish fluid made by liver for lipid digestion in small intestine.
Composed of Bile acids, phospholipid, Cholesterol, Bilirubin, H2O, and ions.
Fx:
- Digestion and absorption of lipids and fat-soluble vitamins.
- Chol excretion (only means for body)
- Antimicrobial activiy (via membrane disruption)
Bile salts vs Bile acids. Give pathway.
Bile salts make fat Micelle (fat surrounded by hyrdrophillic surface).
Bile acids are useless; hydrophobic
Chol→Bile acids–(conjugates w/ sugar Taurine or Glycine)–> Primary Bile salts –> Micelles
“MandMs, sugar coated fat candy”
Lack of Bile like what disease?
Pancreatitis
Celiac disease
What are Peyer’s Patches?
Unemcapsulated lymph tissue found in lamina propria and submucosa of ileum. Contain M-cells, which take up Ag. Produce secretory IgA
What is source of secretory IgA in Peyer’s patches?
Stimulated B-cells in germinal center of Peyer’s patches. They differentiate into plasma cells that reside in lamina propria. IgA part of secretary component of gut and line epithelium, targeting intraluminal Ags.
What bug invades Peyer’s patches? Describe disease Sx and bug MOA
Shigellosis-
- Intestinal lumen infection by Shigella (mostly S. Sonnei)
- Invades M cells (via endocytosis)→lyses endosome, multiplies, and spreads LATERALLY into other epithelial cells.
- Sx: Ulcers, bloody stool w/ mucus
Direct vs Indirect Bilirubin
Direct: conjugated w/ gucuronic acid/ Water soluble.
Indirect: unconjugated. Water Insoluble
What is bilirubin pathway?
FA, pg 323
Describe Tonicity of Pancreas secretions and purpose.
Describe flow rate and content.
Isotonic fluid
Low flow: High Cl-
High flow: High HCO3-
Pancreas releases Bicarb rich fluid and digestive enzymes. Essential for life!
Describe Pancreas enzymes released on active form
Alpha-Amylase: Starch digestion
Lipase, Colipase,and Phospholipase A: Fat digestion
Proteases: Protein digestion
List types of Proteases released by Pancreas.
What type of molecule is it released as?
Trypsin, Chymotrypsin, Elastase, Carboxypeptidase.
Secreted as zymogen, a proenzyme
What Pancreatic secretion released in inactive form?
How is it activated?
Premature activation when?
Trypsinogen
Converted to active form, Trypsin, by Enterokinase/Enteropeptidase enzymes only made in duodenal mucosa
Premature activation in Pancreatitis. Seen in Alcoholics,
Function of Trypsinogen
Once activated:
1) Protein digestion
2) Activate other proenzymes, and creation of more trypsinogen (positive feedback loop)
Describe Carbohydrate digestion in mouth
Salivary amylase: hydrolyzes alpha-1,4-linkages to yield disaccharides (maltose and alpha-limit dextrins)
Describe Intestinal Carb digestion.
Pancreatic amylase- Highest concentration in duodenal lumen, hydrolyzes starch to oligosacharide and disaccharides.
Oligosaccharide hydrolases: Brush border of intestine. Produce monosacharides from oligo- and di-
What is RLS for carbohydrate digestion?
Oligosaccharide hydrolases at brush border of intestine