GI Sectretions Flashcards
What is a secretagogue? Name the three types used in the GI system?
Substance that stimulates cell to secrete.
neurocrine, endocrine, paracrine
neurocrine, endocrine, paracrine secretagogues. Explain
Neurocrine - NT from neuron innervating cell (vagal NT: ACh)
Endocrine - hormone (blood; gastrin)
Paracrine - (local; no blood; histamine)
Secretion - Blood Flow Coupling
More blood flow = more raw materials available to make and secrete whatever
Main Salivary Gland
Parotid
Structure of Salivary Glands
Acinus (contain serous/mucus glands)
Ducts - drainage and modification
Composition of Saliva?
Electrolytes, Water, Protein
Two stage model of salivary secretion?
Remember as Flow Rate increases –> do does secretion (always hypotonic) Na+ absorbing is flow dependent
1) Isotonic Primary Secretion at Acinus
2) Secondary Modification (Ducts):
Reuptake of Na+/Cl- for Secretion of K+/HCO3-
3) Secondary Secretion ⁃ Always hypotonic and alkaline
What type of proteins are found in saliva?
Mucin -aka MUCUS glycoprotein (viscosity -ubiquitous)
Enzymes (lipase, amylase)
IgA
Protective Function of Saliva?
- HCO3-: Acid neutralization ⁃ Antimicrobials ⁃ IgA ⁃ Epidermal Growth Factor (heal) ⁃ Water intake (dry mouth) ⁃ Mouth Hygiene
Digestive Function of Saliva?
⁃ å-amylase/lingual lipase
⁃ R Proteins (Vit B12 binding protect against degradation)
⁃ Mucin glycoproteins - lube
⁃ Dissolving substances for taste mechanism
Regulation of Salivary Secretion?
Mostly Parasympathetic - vasodilation. Short lasting sympathetic - vasoconstricion; for both thing blood flow coupling.
Name the secretory cells found in the stomach?
What are of the stomach has no secretory cells?
Mucous Cells (2) [neck/grandular]
Parietal Cells - HCl, Intrinsic Factor (b12-binging)
Chief Cells - Pepsinogen, Gastric Lipase
Neuroendocrine Cells (3)
What are the neuroendocrine cells in the stomach? What is their function?
Function = regulation
G Cells - Gastrin
D Cells - Somatostatin
Enterochroaffin like Cells - histamine
Pepsinogen in stomach
at low pH cleaved to pepsin (protease). Pepsin cleaves pepsinogen.
Explain Cellular Mechanism of HCL production and Alkaline Tide
C. Anhydrase –> HCO3 (then dissociates)
⁃ H+/K+ ATPase drives H+ to lumen in exchange for K+ to inside cell.
⁃ Cl- electrogenic anion channel follows H+
⁃ HCO3-/Cl- exchange maintains Cl- supply
⁃ Alkaline tide: net HCO3- release into the blood circulation increasing pH of blood
during gastric acid secretion
What controls gastric secretion?
Neural: PS: via vagal nerve
Hormonal: Histamine, Gastrin - HCL, Secretin - Pepsinogen
Distension of duodenum
Secretin has (-) effect on acid secretion
Explain Stimulation of acid in response to food (3)
Cephalic - smell, chewing taste
Gastric - Distension
Intestinal - Protein Digestion, disension, nutrients entering blood
Gastric Mucosal Barriers (3)
1) bicarbonate rich layer
2) tight junctions
3) Luminal Membrabe
What are three mechanisms that lead to peptic ulcers (doudenal/gastric)?
1) hyper-secretion of acid
2) effectiveness of gastric mucosal barrier
(stress = increased sympathetic tone)
3) infection by Helicobacter pylori
(inflammatory effects on mucosa)
Pancreatic Secretory Contrebutions
Exocrine & Endocrine
name of pancreatic sphincter
Endocrine (PIGS) = insulin, glucagon, somatostatin
Exocrine = aqueous component, enzyme component
sphincter of oddi
Aqueous secretions of the pancreas: Explain acid tide. and bicarbonate secretion
Aqueous Component: Isotonic HCO3- rich sol’n
• Incr [HCO3-] & Decr [Cl-] w/ incr’ing secr. rate
• HCO3- production: Carbonic Anhydrase
• HCO3- secr. > Lumen: HCO3-/Cl- exchngr
• Recycling of Cl-: Electrogenic Cl- Channel
• H+ Elimination from Lumen: Na+/H+ exchngr
⁃ Acid Tide: net H+ into Blood decr. pH
Pancreatic Enzyme components breakdown ______. _______ is released by the duodenum and activates _______ from _______. a ______ in pancreatic secretions prevents premature activation of trypsin. ________ is a protein in pancreatic secretions that prevents inactivation of pancreatic lipase by bile salts
lipases, proteolytic, nucleolytic, amyloytic. Enterokinase/Enteropeptidase
Trypsin from Trypsinogen
Trypsin inhibitor
Colipase
Describe the neural and hormonal control of pancreatic secretion:
Neural: Parasympathetic (Vagal, Ach): Stimulatory; Sympathetic: by vasoconstriction mediated decr. in secretion
Hormonal:
⁃ Secretin: HCO3-**
⁃ CCK: Enzyme Secretion**
other secretagogs
Bile is made from _____ by ______; composition includes: ______, bile acids are conjugates of _____ and _____. Bile salts are more soluble than bile _____. They aid in absorption of ______. 95% are reabsorbed in the ______.
Cholesterol, Hepatocytes
Bile Salts, Pigment (bilirubin), Cholesterol, Phospholipids, Proteins (IgA), Electrolytes (isot.)
Taurine or Glycine; Acids; cholesterol (only); ileum
Bile Transport (Reabsorption)
Conjugated - Actively Transported (Na - Co-transport); un-conjugated - Diffusion
Bacteria in ilium and colon un-conjugate bile salt.
Bilirubin is the product of _______. Explain. Bilirubin is used to make ______. It is taken up from the systemic circulation by ______ and can be excreted by kidneys of SI. Jaundice occurs when ______
Heme Degradation (heme(bilirubin+Iron)/ globin Bile; Hepatocytes; Bilirubin in plasma is high!
Bile Regulation (release by gallbladder)
Feedback of bile salt synthesis/secretion by [bile salt] in hepatic portal blood
• CCK**, Gastrin
• Neural Control: Both
Intestinal Secretion (mucin (bicarbonate), electrolytes, water; Describe protective fxn of intestinal secretion.
- volume of secretions are smaller in small intestine.
- Maintain fluidity of chyme (water)
- Dilution of toxic products (water)
- HCO3-
- Lubrication and protection (mucus)
What stimulates gastric secretions?
Stimulated by intraluminal pressure, VIP, and toxins.
