Download Stomach

Stomach
Stomach Structure
• J-shaped, pouch-like organ that hangs
inferior to diaphragm in upper left portion
of abdominal cavity
• capacity = 1L or more
• empty = thick folds of mucousal and
submucousal layers mark the stomach’s
inner lining
• full = no folds
• pyloric sphincter controls gastric emptying
into small intestine
Gastric Glands
3 types of cells
1. mucous – thin, mucus secretion
a. alkaline (basic) secretion keeps stomach from
digesting itself
2. chief – digestive enzymes
3. parietal – HCl (hydrochloric acid) and intrinsic
factor
a. helps sm. intestine absorb vitamin B12 (helps keep
nerves and RBC healthy)
*pepsin – most important digestive enzyme;
breaks proteins into polypeptides; secreted as
pepsinogen (converted by HCl)
Review Questions
1. What are the secretions of the chief cells
and parietal cells?
2. What is the most important digestive
enzyme? What does it do?
3. Why doesn’t the stomach digest itself?
Regulation of Gastric Secretions
• gastric juice (HCl and pepsinogen)
secreted continuously
– rate controlled neurally and hormonally
• neural regulation
– ACh stimulates release of gastric juice
• hormonal regulation
– gastrin increases release of gastric juice
Just for Kicks
• ulcers are open sores in skin and mucous
membranes resulting from localized tissue
damage
• originally thought that stress triggered
ulcers to occur, but 2 Australian scientists
proved it was actually a bacterial infection
(Heliobacter pylori) of the stomach lining
by ingesting the bacteria
Gastric Absorption
• some water, certain salts, alcohol, and
some lipid-soluble drugs
Review Questions
1. What is gastric juice?
2. What controls gastric juice secretion?
3. What substances can the stomach
absorb?
Mixing and Emptying Actions
• mixing movements of stomach wall produce a
semi-fluid paste of food and gastric juice called
chyme
• peristaltic waves push chyme toward pyloric
sphincter  muscle relaxes  stomach
contractions push small amounts of chyme into
sm. intestine
• rate of emptying depends on fluidity of chyme
and the type of food present
• liquids < carbohydrates < proteins < fats
• as chyme enters duodenum (1st part of sm
intestine) accessory organs (pancreas, liver,
gallbladder) add their secretions
Just for Kicks
•
•
vomiting is a complex reflex in which the
stomach empties through the
esophagus, pharynx, and mouth rather
than through the sm intestine
irritation or distention send impulses to
the vomiting center of the medulla which
then triggers the vomiting reflex
Review Questions
1. How is chyme produced?
2. What factors influence how quickly
chyme leaves the stomach?