Electrolytes and Motility Flashcards
What are the two membrane pumps of the GI system?
Na/K ATPase
H/K ATPase
What are the important pores of the GI system?
CFTR
K channel
What are the important exchangers (antiporters) of the GI system?
Na/H
Cl/HCO3
What are the important cotransporters (symporters) of the GI system?
2Na/Glucose, bile salts, amino acids
Pept1 H/peptide
What proteins are important for preventing tight junction permeability?
Claudin
Where is a lot of the chloride movement on the intestine lumen?
Crypts
What is an example of electroneutral absorption?
NaCl absorption
What mediates fluid uptake? Electroneutral or Electrogenic absorption?
Electroneutral
What is electrogenic uptake?
No active transport of counterion
What is taken up in electrogenic transport? What happens to anions?
Na and Glucose
Anions follow in tight jinxes
What process is vital for promoting fluid entry into intestinal lumen?
Chloride secretion in crypts of lieberkuhn
What basolateral pump is vital for the chloride secretion?
NKCC1
How does calcium enter the cell?
Transcellular or paracellular
Where is calcium actively absorbed?
Duodenum
What are important luminal transporters for iron?
HT (heme) and DMT1
What effect does gastric secretion have on iron absorption?
Deficiency in acid?
Deficiency in iron.
What hormones stimulate chloride secretion reflex?
ACh/VIP (long reflex)
5HT (short reflex)
Agonists that elevate this promote opening of CFTR.
cAMP (Prostaglandins, VIP, cholera toxin)
What effect does Guanylin have on Cl secretion?
Increases cGMP, increases CFTR activity
What pathogen has the same effect as guanylin?
E. coli heat stable toxin
What facilitates water absorption from stool?
Na+ uptake
What effect does aldosterone have on the stool?
Increases ENaC expression, reclaims sodium, increases stool water absorption
What is the root cause of secretory diarrhea?
Excessive secretion of chloride and NaCl transport inhibition
Hyper motility leads to…
Hypo motility leads to…
Diarrhea
Constipation
What does loperamide do?
Slows transit and increases sphincter tone to increase fluid absorption
What are the four motile processes of the intestine?
Peristalsis to move forward
Segmental contractions to mix
Alterations in surface configuration
Tonic contraction of sphincters
Is the ileum or jejunum more active in mixing?
jejunum
What drives the mixing contractions?
Basal electrical rhythm
What factors increase small intestine motility?
ACh from vagus and enteric plexus Motilin Serotonin Substance P Prostoglandin Gastrin CCK Insulin
What factors decrease intestinal motility?
Epinephrine
Secretin
Glucagon
Opioid receptors
What molecule stimulates the migrating motor complex?
Motilin
What happens to the sphincter of Oddi during MMC?
Relaxes, leading to bile storage in intestine
Where is the MMC active?
Not the large intestine!
Why is the ileocecal sphincter tonically contracted?
Limits reflux into ileum (lots of bacteria in cecum)
What causes opening of ileocecal valve?
Distension of ileum due to peristalsis
What causes closure of ileocecal valve
Dissension of cecum (sympathetic input)
What mediates the gastroileal reflex?
Gastrin and CCK
What mediates ileal-gastric reflex?
Vagus nerve
What mediates intestinointestinal reflex?
Extrinsic neural connections
What mediates peristaltic reflex?
Increased or decreased by autonomics
What role do taeniae coli serve?
Propulsion (but not super good)
What happens between haustra?
Segmental contractions
What mediates colonocolonic reflex?
Enteric nervous system
Modulated by sympathetic input
What mediates gastro-colic reflex?
Serotonin
ACh
What is the role of transverse folds in the rectum?
Retard anal leakage
What is the pathophysiology behind Inflammatory bowel disease?
Release of inflammatory mediators, damaging epithelial barrier, causing NO release and diarrhea
