2A A&P of the stomach Flashcards
What are the four main regions of the stomach?
Cardia, fundus, body, and pylorus (CFBP - can’t find blood pressure)
What are the two sphincters of the stomach?
LES and pyloric
What hangs off the greater curvature of the stomach?
Greater omentum (visceral peritoneum)
What are the three layers of the muscularis mucosa?
Longitudinal (outer), circular(middle), oblique(innermost)
How does the muscularis layer in the stomach differ from most of the GI tract?
Has a third layer (innermost) of muscle fibers running oblique. Most of the GI tract only has two layers - longitudinal and circular
What is the most important protection of the gastric mucosa from gastric acids and enzymes?
A layer of alkaline mucus - gastric mucosal barrier
What role do prostaglandins play in the stomach?
Protect the stomach mucosa from injury by enhancing alkaline mucus production
What does the alkaline mucus contain a lot of?
Bicarbonate
What is the pH at the cell surface of stomach mucosa cells? Stomach pH?
Close to neutral.
pH of 2
How long to cells at the surface of the stomach live?
3-4 days
What kind of epithelium makes up the mucosal surface of the stomach?
Simple columnar epithelium
What is the stomach epithelium dotted with?
Millions of deep channels called gastric pits
what are gastric pits lined with?
Columns of specialized cells called gastric glands
Where do gastric glands reside?
Within the gastric pits
What cells line the gastric pits?
Surface lining cells, regenerative cells, mucous neck cells, Parietal cells, Chief cells, and Enteroendocrine cells
Which cells in the gastric pit produce the most alkaline mucus?
Mucous neck cells
What do parietal cells produce?
HCL and intrinsic factor
What cells secrete pepsinogen and gastric lipase?
Chief cells
What do enteroendocrine cells secrete?
Gastrin (G cells) and histamine (ECL cells)
What part of the stomach are parietal cells found in greatest number? Chief cells? G cells?
Upper, middle, lower - PCG
What are the functions of the stomach?
Temporary storage, mechanical digestion, chemical digestion, and secretion of gastrin and histamine
What is chyme?
A creamy, soupy paste created in the stomach from mechanical digestion of food
What do gastric parietal cells produce from CO2 and water?
H2CO3, which dissociates into H+ and bicarbonate
How does Cl- get into the parietal cell?
Via chloride shift when bicarbonate leaves the cell into the blood, there is the famous chloride shift that occurs!
What is the cephalic phase?
Vagus nerve weakly stimulates gastric juice secretion when food is being chewed in the mouth, or with the sight, smell or thought of food.
Vagus nerves stimulates gastrin secretion, which stimulates secretion of gastric juice
When does the gastric phase begin?
When food reaches the stomach
What stimulates more gastrin secretion?
Distension of stomach and protein digestion products (amino acids) via positive feedback loop. Vagus nerve also continues to stimulate gastrin release and gastric motility
What do elevated levels of gastrin stimulate?
The release of histamine, which in turn increases HCl secretion from parietal cells
Are there enzymes in the stomach to digest carbs?
No, no chemical digestion of carbs happens in the stomach
What activates pepsinogen into pepsin?
HCl
What does pepsin do?
Breaks down peptide bonds of amino acid chains
Can pepsin breakdown all peptide bonds?
No, only certain peptide bond
What is the end result of what pepsin can do?
Partially digest proteins
In what phase is pepsin very active?
Gastric phase
Small amounts of chyme enter the duodenum and stimulate the secretion of what three hormones?
CCK, secretin, and GIP
What do the CCK, secretin, and GIP enzymes do?
Inhibit gastric juice secretion
What does GIP inhibit in addition to gastric juice secretion?
Gastric motility
In what phase are the three ezymes - CCK, secretin, and GIP - produced in the duodenum?
Intestinal phase
Why is the control of chyme leaving the stomach and entering the duodenum critical?
1) so duodenum does not become too full (w/ acid)
2) so small intestine can adequately process the incoming chyme
What increases gastric motility?
Gastrin and vagus nerve activity
During what phase does the pyloric sphincter relax?
Gastric phase
What is the enterogastric reflex?
products of protein digestion and H+ in the duodenum inhibit vagus nerve activity (occurs during the intestinal phase)
What can the stomach mechanically digest? Chemically digest?
All nutrients - carbs, proteins, and lipids.
Varies - quite a bit of protein, a little bit of lipids, and not much at all of carbs
