Intestine, Pancreas, Liver, Gallbladder Secretions Flashcards
Duodenum
receives stomach contents, pancreatic juice and bile, neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH increase, pancreatic enzymes
Brunner’s glands - empty into intestinal glands and secrete alkaline fluid (coats duodenum)
jejunum
most nutrient absorption occurs here
Ileum
peyer’s patches – aggregated lymphoid nodules
Monitors intestinal bacterial populations and prevent growth of pathogenic bacteria in intestine
Villi
fingerlike projections 1 mm tall
contain blood vessels and
lymphatics (lacteal)
nutrient absorption
Microvilli
1 micron tall; cover surface brush border on cells brush border enzymes for final stages of digestion
Crypt-villus
functional unit of the small intestine. Stem cell division produces immature cells in crypts of Lieberkühn (intestinal gland) which secrete fluid; mature cells at the villus tip absorb nutrients, electrolytes, and fluid.
Crypt villus unit
Villus tip - fully differentiated and undertake nutrient reabsorption
Maturation zone - intermediate where cells begin to express enzymes and absorptive membrane transport
Crypt - rapidly dividing stem cells that fore migration up villus
Villi secretion
Goblet cells (mucus- lubricates and protects intestinal surface) Enterocytes with brush border - enzymes
Crypt of Lieberkuhn secretion
Intestinal glands and crypts
Paneth cells (lysozyme)
Enterocyte
Enteroendocrine cells
Enteroendocrine cells
I (CCK-Cholecystokinin- stimulates gallblader to release bile)
D (somatostatin)
S (secretin –stimulates pancreas to release acid neutralizer bicarbonate )
Celiac sprue
malabsorption syndrome - hypersensitivity to wheat gluten and gliadin
Pancreas function
Secrete alkaline fluid that neutralises the acidic chyme
Secrete enzymes that breakdown macromolecules
Highest digestive power
Pancreas - exocrine glands
Made up of acinus (digestive enzyme secretion) and duct (bicarbonate secretion)
Secretion delivered to duodenum via large pancreatic duct
Isotonic bicarbonate to intestinal lumen
Pancreas - endocrine glands
4 types of islet cells that release hormones
Pancreatic juice composition
Proteolytic enzymes: trypsinogen 1, 2 & 3, proelastase 1 & 2, chemotrysinogen
Lipolytic enzymes: Lipase Phospholipase A2, Pancreatic lipase
Nuclease: DNase and RNase
Amylolytic enzyme
Regulation of pancreas enzyme secretion
Ach: Bind muscarinic receptor on acing cells -> Increase BF and gastrin
CCK: Released from duodenal I cells when food enters
Regulation of pancreas alkaline secretion
Secretin - Released by S cells in duodenum and stimulated by low pH as food enters -> secretin enters blood - ductal cells
pH rarely low enough to stimulate high levels of secretin
Ducts become hypersensitive to low levels of CCK
Mechanism of enzyme
secretions by acinar cells
Inactive proenzyme on ribosomes and transferred to rER - Golgi complex and acidic condensing vacuoles and zymogen granules
Stimulation of agonist (CCK or Ach or Secretin) = release content into lumen via intracellular 2nd messenger
Fusion and exocytosis of zymogen granules -> move to apical membrane and fuse with plasma membrane and discharge content
Prevent autodigestion
Most enzymes = inactive precursor = zymogen
Enzyme sequestered in membrane-limited vesicles
Activate zymogen occurs in small intestine and process depends on conversion of proenzyme trypsinogen.
Enterokinase - bound to apical membrane of enterocyte lining
Pancreatitis
Pancreatic enzyme activated within pancreas = auto digestion of tissues
Duct cell secretions purpose
Neutralise acidic chyme entering duodenum
HCO3 secretion by ductal cell
Secreted into cell cytoplasm by Cl-/HCO3- exchange in luminal cell membrane
Cl- recycled = supply enough intracellular cl- to sustain rate of cl-/HCO3- exchange
Na+ secreted into duct following HCO3- secretion - water follows
