24.8 the stomach: secretions of the stomach Flashcards
what is chyme?
ingested food + stomach secretions
what types of cells in the stomach secrete mucus?
surface mucous and neck mucous cells
describe the mucus secreted by the stomach lining
viscous and alkaline
what protects the stomach from acidic chyme and the enzyme pepsin
mucus
what causes greater mucus production?
irritation of stomach mucosa
what is the fn of mucus secreted by the stomach lining?
protects the stomach from acidic chyme and the enzyme pepsin
irritation of stomach mucosa causes
greater mucus production
what is intrinsic factor?
binds with vit B12 and helps it to be absorbed
from where is the intrinsic factor secreted?
parietal cells
what are the secretions of the stomach?
mucus
intrinsic factor
HCl
pepsinogen
what 2 things do the parietal cells secrete?
intrinsic factor
HCl
what is the fn of HCl in the stomach?
kills bacteria
stops carbohydrate digestion by inactivating salivary amylase
denatures proteins
converts pepsinogen to pepsin
what is pepsinogen?
an inactive form of a digestive enzyme
how is pepsinogen released?
by exocytosis: packaged in zymogen granules
what type of cell is responsible for release of pepsinogen?
cheif cells
how does pepsinogen fn in the stomach?
it is converted to pepsin by a low pH caused by HCl
it catalyzes the breaking of covalent bonds in proteins
how does pepsin work to denature proteins?
breaking the covalent bonds that hold the protein in its shape
what has to diffuse from the blood into the stomach cells to begin production of HCl?
CO_2
what happens to the CO_2 after it diffuses into the stomach cells?
it combines w/ H_2O
carbonic anhydrase catalyzes the rxn to form H_2CO_3 (carbonic acid)
how does the carbonic acid (H_2CO_3) create HCl?
H_2CO_3 dissociates into HCO_3^- and H^+ ions
how does Cl^- enter the lumen of the stomach to form HCl?
HCO_3^- is exchanged for Cl^- in the bl
Cl^- moves to the lumen of the stomach
how do H^+ ions enter the lumen of the stomach?
must be actively transported out of the parietal calls against a [ ] gradient
what decreases the E needed for active transport of H^+?
K+ from the lumen of the stomach moves into the blood
H^+ and Cl^- combine to form
HCl
