Download stomach and pH NOTES

General info:
•Holds 1.5 L of food normally or up to 4 L when stretched
(distended)
•Continuous process of mechanical digestion by churning food
•Continues chemical digestion by adding gastric juice.
Gross anatomy:
•Cardiac sphincter: regulates
food entering stomach
•Fundus: enlarged, top of
stomach, close to esophagus
•Pyloris: area closer to small
intestine
•Pyloric sphincter: regulates food
entering duodenum (upper small
intestine)
Internal anatomy:
•Rugae: folds in mucosa and submucosa (stretch as stomach
fills)
•Lining of stomach: surface is columnar epithelial cells
(goblet cells) which: produce mucous to protect stomach lining
from acid
Internal anatomy:
•
Below the surface are gastric glands also lined with
columnar epithelial cells, but are 2 specialized types:
1. Chief cells: make pepsinogen- an inactive enzyme that
is activated by HCl (hydrochloric acid) and then called
pepsin.
2. Parietal cells: found on upper end of the gastric
glands; make HCl and intrinsic factor- allows vitamin
B12 absorption in intestines
Stomach Chemistry:
•The release of gastric juices is caused by:
•The Brain: brought on by the thought or smell of food
•Distention of the stomach
•Low acidity: causes the hormone gastrin to be released which
stimulates the parietal cells to produce HCl
What is low acidity?
The more H+ ions, the lower the pH (which means the higher the acidity)
1.
2.
What is the strongest base listed?
What is the strongest acid listed?
The pH scale: ranges from 0-14 (no units).
It tells the amount of H+ ions present in the solution:
Acids have many H+ ions = low pH
Bases have few H+ ions = high pH
Water (distilled) is neutral (neither acidic or basic)
= pH 7
Acids:
•Tend to come apart in water.
Example:
HCl H+ + Cl•Always produce hydrogen ions when they come apart
•pH is always lower than water or a base ranging from 0.1-6.9
Bases:
•Tend to come apart in water, too, producing hydroxyl ions.
Example:
NaOH Na+ + OH-
•If there are more OH- ions in a solution than H+, then the pH will
be high
•If H+ and OH - molecules are together in a solution, they will react
to create water
•Bases range from 7.1-14 on the pH scale.
Acids: release hydrogen ions, which is just a proton (H+), into a
solution. Have a sour taste and react with metals
Bases: usually release hydroxyl ions (OH-) into a solution; has a
bitter taste, slippery touch.
Outside of the stomach in the rest of the body, especially the blood
stream, must stay at a relatively constant pH. Balance is regulated
by the kidneys and lungs.
Substances called buffers are released into the bloodstream to help
maintain our internal pH at 7.35-7.45. This is slightly basic, just
above neutral.
Medications like Tums and Rolaids act as buffers
in the stomach. How might this work?
If the acidity level in the stomach gets too high,
that can causes symptoms such as heartburn (as
the acid moves up the esophagus) and stomach
pain. Tums/Rolaids are bases that increase the
pH of the stomach so it isn’t so acidic anymore.
Back to the stomach….
Juices released contain:
•Pepsin: gastric glands release pepsinogen which is activated
by HCl and becomes the enzyme pepsin. It hydrolyses (breaks
down) proteins into polypeptides. It is released as pepsinogen
so it won’t digest the gastric gland cells that produce it.
Pepsinogen + HCl pepsin
Juices released contain (continued):
•HCl (hydrochloric acid): is pH of 0.8 when secreted but is
quickly diluted to pH of 2.0 by the stomach contents. Pepsin
works best at pH of 2 and HCl activates pepsinogen to become
pepsin. It also kills bacteria and breaks apart a few of the food
fibers.
The enzyme salivary amylase, secreted by the mouth, is still
working when food hits the stomach. However, the HCl “kills” the
amylase. Starches are about 30% digested by now- the rest is
digested in the duodenum of the small intestine.
When chemicals have worked on food in the stomach, it is now
called chyme- a semifluid, partly-digested mixture of food and
gastric juices.
Stomach Emptying:
It empties a few mL at a time into the
duodenum (top part of the small intestine).
Duodenum signals the stomach to slow down and the pyloric valve
to close if:
1. There is too much chyme in the duodenum
2. The chyme is too acidic
3. There is too much fat present
The duodenum also secretes hormones to slow stomach action.
One is gastric inhibitory peptide.
Problems with the stomach:
Peptic Ulcer and Gastritis:
The stomach is protected by alkaline mucous about 1 mm thick.
However, sometimes a break in the mucosal barrier occurs.
Underlying tissue becomes inflamed causing gastritis. If this
continues the wall becomes eroded causing a peptic ulcer. This is
an actual lesion in the stomach lining.
Ulcer can eat into an artery causing hemorrhage (massive
bleeding) into the abdomen or it can leak bacteria into the
abdomen causing peritonitis.
Ulcers may be due to bacterial invasion. Other contributing
factors are: smoking, alcohol, coffee, stress and genetics.
Pyloric Stenosis:
Pyloric valve is too tightly contracted and won’t let food through
to the duodenum. Causes projectile vomiting in infants. Needs
surgery to correct.
Last note about the stomach…
Epithelial cells in the stomach lining go
through mitosis constantly. Although
many lining cells die due to acid and
friction, cells are replaced very rapidly.
A half a million new cells are replaced
per minute!
This is why chemotherapy patients vomit
so often. Chemotherapy targets cells that
rapidly divide, thereby targeting stomach
lining cells.
The Stomach
General Info
•Holds ___________of food normally or up to __________when stretched
•Continuous process of ___________________________by churning food
•Continues ______________________________by adding gastric juice.
Gross Anatomy
•Cardiac sphincter:
•Fundus:
•Pyloris:
•Pyloric sphincter:
Internal Anatomy
•_________________________: folds in mucosa and submucosa (stretch as stomach fills)
•_________________________: surface is columnar epithelial cells (goblet cells) which: produce mucous to
protect stomach lining from acid.
Below the surface are gastric glands also lined with columnar epithelial cells, but are 2 specialized types:
1.______________________: make pepsinogen- an inactive enzyme that is activated by HCl
(hydrochloric acid) and then called pepsin.
2.______________________: found on upper end of the gastric glands; make HCl and intrinsic factorallows vitamin B12 absorption in intestines
Stomach Chemistry
•The release of gastric juices is caused by:
pH
Draw a diagram of the pH scale including which side is acidic and which side is alkaline.
Acids have __________________= low pH Range on pH scale:
Bases have __________________= high pH Range on pH scale:
Water (distilled) is neutral (neither acidic or basic) = pH 7
Balance of pH is regulated by the ___________________________________.
Substances called _____________________________are released into the bloodstream to help
maintain our internal pH at _______________________. This is slightly basic, just above neutral.
Stomach Chemistry (continued)
Juices released contain:
•
•
______________________: gastric glands release pepsinogen which is activated by HCl and becomes
the enzyme pepsin. It hydrolyses (breaks down) proteins into polypeptides. It is released as
pepsinogen so it won’t digest the gastric gland cells that produce it.
Formula:
___________________________ (hydrochloric acid): is pH of 0.8 when secreted but is quickly diluted to
pH of 2.0 by the stomach contents. Pepsin works best at pH of 2 and HCl activates pepsinogen to
become pepsin. It also kills bacteria and breaks apart a few of the food fibers.
Outline starch digestion up to this point:
What is food now called after it has been digested in the stomach?
Stomach Emptying
Duodenum signals the stomach to slow down and the pyloric valve to close if:
1.
2.
3.
The duodenum also secretes hormones to slow stomach action. One is
___________________________________________
Stomach Problems/Diseases
Peptic Ulcer and Gastritis
• Sometimes a break in the mucosal barrier occurs. Underlying tissue becomes inflamed causing
_________________. If this continues the wall becomes eroded causing a
_____________________________. This is an actual lesion in the stomach lining.
•
Ulcer can eat into an artery causing _____________________________(massive bleeding) into the
abdomen or it can leak bacteria into the abdomen causing _____________________________.
•
Ulcers may be due to ___________________________________. Other contributing factors are:
______________________________________________________________________.
Pyloric Stenosis
Why do cancer patients undergoing chemotherapy treatments usually experience nausea and vomiting?