Functions of the stomach:

-storage of food

-mechanical breakdown into chyme

-disruption of chemical bonds in food through actions of acids and enzymes

-production of intrinstic factor (for vitamin B 12)

5 cell types found in gastric glands:

Gastric glands produce about 1.5 liters of gastric jucie a day.

1. Parietal cells

2. Cheif cells

3. Mucus Cells

4. Enteroendocrine cells

5. Undifferentiated (stem) cells:

-secrete intrinsic factor and hydrochloric acid

-production of acids occur outside cytoplasm

-produces H ions as enzymes, carbonic anhydrase, and coverts CO2 and H20 to carbonic acid, which is quickly converted to H ion and bicarbonate ions

-then chloride ions are exchanged for bicarbonate ions

-hydrogen and chloride combine to make hydrochloric acid

-pH of stomach is 1.5 to 2

-kills most microbes, denatures proteins, and inactivates enzymes

-breakdown connective tissue and plant cell walls

-activate pepsin for protein digestion

-Intrinsic factor enables vitamin B12 which is needed for RBC formation

-Intrinsic factor is the only substance and function of the stomach that makes it essential for life

-sight, smell, taste, and thought of food

-produces gastric juce in preparation for the arrival of food

-relatively short (minutes)

-neural only (parasympathetic)

-Actions: increase the volume of gastric juices by release of mucus, acid and enzymes, also the release of gastrin is stimulated.

-begins with arrival of food and a continuation of cephalic phase

-proteins activates this phase

-enhance secretion and homogenize and acidify chyme

-hours long

-pH is slighlty high reaches 1.5 to 2 and the amount of undigested protein decreases

-enteric nervous system

-Hormanal response: proteins and amino acids stimulate gastrin secretion

-release of histamine and acid

-increase acids and pepsinogen production, motlitiy and initation of mixing

-controls the rate of chyme enterting the duodenum

-take forever; long (hours)

-when it reaches the duodenum the acid in the chyme triggers entero-gastric reflex, which stimulates contraction of the pyloric sphincter.

-hormal response:

1. CCK (cholecystokinin): inhibits gastric secretion of acids

2. GIP (gastric inhibtory peptide): targets pancreas inhibits gastric secretion and reduce rate and force  of gastric contractions

-drop in pH 4.5 which causes the pancreas to release buffers to protect the duodenum

-reduction in gastric motility, reduction in acid, mucus and enzyme production