2A: Anatomy & Physiology of the Stomach Flashcards
Where is the stomach located?
The stomach is a muscular organ located on the left side of the upper abdomen.
What are the main 4 regions of the stomach?
1) Cardia
2) Fundus
3) Body
4) Pylorus (pyloric antrum + pyloric canal)
What are the 2 sphincters of the stomach ?
1) LES
2) Pyloric
Describe the gross anatomy of the stomach
- a lesser curvature located on inner portion
- a greater curvature on outer portion
- cardiac notch at the top
- duodenum at the bottom of pyloric canal
What are the 3 layers to the muscularis externa?
1) Outermost longitudinal layer
2) Middle circular layer
3) innermost oblique layer
What property allows the stomach to contain acids and enzymes without having its wall digested ?
The stomach “lining” or mucosa usually is impermeable to the gastric juice it secretes
What is the most important factor that contributes to the protection of the gastric mucosa?
Layer of alkaline MUCUS—> GASTRIC MUCOSAL BARRIER
What role do prostaglandins play?
Role in protecting the stomach mucosa from injury by enhancing mucus production
What is the pH of gastric juice and cells at the surface?
pH of gastric juice = 2
pH of cells at surface=7
Describe the histology of the mucosal surface?
Simple columnar epithelium that is dotted w. millions of deep channels called GASTRIC PITS
what are GASTRIC GLANDS?
Gastric pits which are lined w/ columns of specialized cells called GASTRIC GLANDS (fundic)
What are Gastric folds also known as?
Rugae
What do Mucous neck cells do?
Secrete alkaline mucus
What do Parietal cells do?
secrete HCL & Intrinsic factor (IF)
What do Chief cells do?
secrete pepsinogen & gastric lipase
What do Endocrine cells do?
Some secrete GASTRIN (G cells); others secrete HISTAMINE (ECL cells)
Within a gastric gland describe the cells top to bottom
1) Surface lining cells
2) Regenerative cells
3) Mucus neck cells
4) Oxyntic (parietal) cells
5) Zymogenic (chief) cells
6) Enteroendocrine cells
What are the possible damaging forces of Normal gastric glands?
- Gastric acidity
- Peptic enzymes
What are defensive forces against normal damaging forces?
- Surface mucus secretion
- Bicarb secretion into mucus
- Mucosal blood flow
- Apical surface memb. transport
- Epithelial regenerative capacity
- Elaboration of prostaglandins
What can cause injury?
- H. pylori infections
- NSAIDs
- Aspirin
- Alcohol
- Cigarettes
- Gastric hyperacidity
- Duodenal-gastric reflux
The cells of the ________ ___________ secrete about 2500ml of gastric juice daily
Gastric Glands
What secretes HCL that kills many ingested bacteria, aids protein digestion, provides the necessary pH for pepsin to start protein digestion, and stimulates the flow of bile & pancreatic juice.
Parietal cells
***It is concentrated enough to cause tissue damage, but in normal individuals, the gastric mucosa does not become irritated or digested b.c it also contains mucus.
What does the mucus form?
A flexible gel that coats the gastric mucosa
What does the tight junctions between the cells which are also part of the mucosal barrier do?
Protects the gastric epithelium from damage
What are some substances that tend to disrupt the barrier and cause gastric irruption/injury (gastritis) ?
1 )ethanol
2) bile salts
3) NSAIDS
4) H. pylori
What specific gastric cell acts as an autoimmune effect released by the stomach?
The G cells releasing Gastrin
What does the secretion of Gastrin do?
Stimulates parietal cells to secrete intrinsic factor (IF) and HCL
What are the functions of the stomach?
1) Temporarily stores ingested liquids and solids until they are released into the small intestine
2) Mechanical digestion of the stomach
3) Secretes gastric juice that is involved w/ chemical digestion
4) Secretes the hormones gastrin and histamine
What is chyme ?
The stomach vigorously churns food into a “creamy, soupy paste”
What is an alkaline tide?
As bicab enters blood it will be more alkaline
What is the cephalic phase?
Just the beginning of eating
Vagus nerve weakly stimulates what?
Stimulates gastric juice serration when food is being chewed in the mouth or with the sight, smell, or thought of food
What does the vagus nerve stimulate that is from the enteroendocrine cells of the gastric glands?
Gastrin secretion
What does Gastrin further stimulate?
Stimulates secretion of gastric juice
What phase beings when food reaches the stomach ?
Gastric phase
Distention of the stomach and protein digestion products (amino acids) stimulate what?
What kind of loop is this?
Gastrin secretion and hence more gastric juice secretion this represents a positive feed back loop
What does the Vagus nerve continue to stimulate?
Stimulates gastrin** release and gastric motility***
Elevated levels of gastrin stimulate the release of what?
release of histamine, which in turn INCREASES HCL secretion from PARIETAL cells
Does carbohydrate digestion occur in the stomach?
No, protein digestion occurs in the stomach
Small amounts of acidic chyme enter the duodenum which stimulates the secretion of what 3 hormones ?
What is the effect of these hormones on gastric juice secretion?
What phase is this?
1) CCK
2) Secretin
3) Gastric Inhibitory peptide (GIP)
- **These Inhibit gastric juice secretions
- INTESTINAL PHASE
GIP (Gastric inhibitory peptide) inhibits gastric juice secretion but also can inhibit what?
GIP also inhibits gastric MOBILITY
What are 3 stimulators fro gastric secretion?
1) Histamine
2) Gastrin
3) Vagal stimulation (Acetylcholine)
Why is the control of chyme leaving the stomach and entering the duodenum critical ?
1) So the duodenum DOESNT become TOO FULL (especially w/ acid)
2) So the small intestine can adequately process the incoming chyme
Gastrin and vagus nerve activity can increase what?
Gastric motility– this pushes food towards the duodenum and causes the pyloric sphincter to relax (occurs during the gastric phase)
What is Enterogastric reflex?
How does this affect vagus nerve activity?
What phase does this occur?
Products of protein digestion and H+ in the duodenum
***inhibits vagus nerve activity
**Occurs in the intestinal phase
Fatty, acidic chyme can also stimulate and release what?
How does this affect gastric motility and emptying?
During what phase does this occur?
CCK, secretin, and GIP
***This inhibits gastric motility and emptying
**Occurs during the intestinal phase
What kind of digestion does the stomach do most of?
Mechanical digestion of carbohydrates, proteins, and lipids
Does the stomach do chemical digestion? explain
Yes, but it varies.
- Proteins ( lots)
- Lipids (a little bit)
- Carbohydrates (not much at all)
Is there absorption of nutrients in the stomach?
No
