GI secretory products Flashcards
Where is intrinsic factor released?
Parietal cells of stomach
What is the action of intrinsic factor?
Vitamin B12-binding protein (required for B12 uptake in terminal ileum).
What does autoimmune destruction of parietal cells cause?
Chronic gastritis and pernicious anemia due to B12 deficiency
Where is gastric acid secreted from?
Parietal cells of the stomach
What is the action of of gastric acid?
Decrease stomach pH
What stimulates gastric acid release?
Histamine, ACh, gastrin
What decreases gastric acid release?
Somatostatin, GIP, prostaglandin, secretin
What should be suspected in a pt w/ high levels of acid and ulcers refractory to medical therapy?
Gastrinoma: gastrin-secreting tumor
Where is pepsin secreted from?
Chief cells of the stomach
What is the actin of pepsin?
Protein digestion
What stimulates pepsin release?
vagal stimulation, local acid
In what form is pepsin released?
Pepsinogen, which is converted to pepsin (Active) int he presence of H+
Where is bicarb secreted from?
Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum)
What is the function of bicarb?
Neutralizes acid
What stimulates the release of bicarb?
Secretin increases pancreatic and biliary bicarb secretion
What covers gastric epithelium?
HCO3- is trapped in the mucus covering the epithelium
Which secretory cells are located in the body of the stomach?
parietal cells and Chief cells
What do parietal cells secrete?
Instrinsic factor and Hcl
What do chief cells secrete?
Pepsinogen
What secretory cells are located in the antrum of the stomach?
G cells, Mucuous cells, D cells
What secretory cells are located in the duodenum?
I cells, S cells, K cells
How are G cells stimulated by the vagal nerve?
With gastrin-releasing-peptide (neurotransmitter)
How do G cells secreting gastrin in the antrum lead to increase H+ secretion in the body?
Gastrin goes to circulation, interacts with ECL cells, which secrete histamine. Histamine stimulates acid release from parietal cells.
Where are ECL cells located?
subepithelial cells found in the vicinity of parietal cells
How does Ach transmit an acid releasing signal to parietal cells?
Ach arrivs at M3 receptor
Gq –> Ca2+
Activation of ATPase H+/K+
Where does the secreted H+ from the parietal cell come from?
H+ + HCO3- –> H2CO3 –> H2O + CO2
How does Gastrin directly transmit an acid releasing signal to parietal cells?
GRP arrives at G cells–> gastrin,
Gastrin arrivs at CCK8 receptor of parietal cell
Gq –> Ca2+
Activation of ATPase H+/K+
How does gastrin indirectly cause an increase in acid secretion from parietal cells?
Gastrin –> ECLs–>secrete histamine
Histamine arrvs at H2 receptor
H2 receptor associated with Gs –> cAMP
How do prostaglandins and misoprostol decrease acid secretion from parietal cells?
Arrive at receptor, interact with Gi, decr cAMP, decrease activity of H+/K+ ATPase.
How does somatostatin decrease acid secretion from parietal cells?
Arrives at receptor, interact with Gi, decr cAMP, decrease activity of H+/K+ ATPase.
What is the Cl- vs. HCO3- content in pancreatic secretions?
Low flow, high Cl-
High flow, high HCO3-
What is the purpose of pancreatic alpha amylase?
Starch digestion
In what form is pancreatic alpha amylase secreted?
active form
What is the purpose of pancreatic lipase?
Lipid digestion
What is the purpose of pancreatic protease secretion? What are the proteases?
Protein digestion. Trypsin, chymotrypsin, elastase, carboxypeptidases
How are the pancreatic proteases secreted?
As proenzymes known as zymogens
What is the function of trypsinogen/trypsin?
Active trypsin activates other proenzymes and cleaves additional trypsinogens into active trypsin (postive feedback loop)
What initially converts trypsinogen to trypsin?
Enterokinase/enteropeptidase, a brush border enzyme on duodenal and jejunal mucosa
Which carbohydrates are absorbed by enterocytes?
Monosacchs; glucose, galactose, fructose
What transporters take up glucose, galactose and fructose into the enterocyte?
SGLT1 (Na+ dependent) takes up glucose and galactose
GLUT-5 takes up fructose
What is the D-xylose absorption test?
Distinguishes GI mucosal damage from other causes of malabsorption
