Physiology 3120 Lecture Notes - Lecture 59: Curvatures Of The Stomach, Gastric Glands, Enteroendocrine Cell
2 May 2018
School
Department
Course
Professor
Human Physiology Lecture 59
Gastrointestinal Physiology
Stomach
- Bolus liquefied to enhance enzymatic digestion and mixed through coordinated muscular
contractions to mechanically break down contents
- 2-3L of gastric juices secreted into stomach daily
- Lower esophageal sphincter: gate keeper
o Must open to permit food to enter the stomach
- Stomach is quite small
o When the lower esophageal sphincter opens, the food enters in
o As the mechanical stretching occurs, the stomach starts to open by receptive relaxation
▪ Receiving the bolus, causing the whole stomach to relax, open up, to permit the rest
of the meal to enter more easily
- Esophageal sphincter opens food enters stomach opens and relaxes
- Upper portion of the stomach, that first receives the food which stimulates receptive relaxation =
Fundus
o OR cardiac region
- Body of stomach = main central portion of the stomach
- Antrum = last part of the stomach
- Pyloric sphincter: keeping the stomach contents inside
o Thickened muscle
o Most open to let the food out
o For most part it is closed, because it needs to be triggered to be opened
- Stomach is curved shape
o Part of the stomach that is larger = greater curvature
▪ Left hand side
o Part of the stomach that is less of a curve = lesser curvature
▪ Right hand side
- If you were to eat a large meal before bed time you feel unwell
o Which side should you lay on to feel better?
▪ LEFT w/ large meal, it will release some pressure
o If you want to increase gastric emptying?
▪ RIGHT
- Rugae: folds inside the stomach
o Closer together when stomach is small
o When stomach stretches out, they spread out
more
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Enterocytes of the Stomach
- Looking at the mucosal layer (enterocytes)
o Both endocrine and exocrine
- EXOCRINE (in fundus and body region)
o Mucus neck cells
▪ Secretes mucus
o Chief cells
▪ Secretes pepsinogen and gastric lipase
• Pepsinogen must be activated in the presence of acid
o Has to be physically cut into something smaller (pepsin = active
enzyme)
• Cleavage event where the actual protein must be cut (like angiotensinogen)
• Gastric lipase works right away – folds and works best in acidic
environment
o Parietal cells
▪ Secretes intrinsic factor, H+ and Cl- (HCl)
- ENDOCRINE (in antral region)
o G cells = enteroendocrine cell
▪ Secrete gastrin (HORMONE)
• Gastrin involved in gastric motility and function
Layers of the stomach
- Mucosa
o Enterocytes secrete acid, gastric lipase, pepsinogen and intrinsic factor
▪ Intrinsic factor binds with vitamin B12 to help with its absorption (can’t absorb B12
without it)
o Folds called rugae, invaginations called pits
▪ Within the pits, there are stem cells that are committed to producing exocrine and
endocrine cells of the stomach so the mucosa layer is being replaced (needs to be
replaced frequently because cells do not live forever, but these cells live in rough
environment – acid containing sac)
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- Submucosa
o Similar characteristics to the rest of the tract
- Muscularis Externa
o Additional oblique muscle layer, provides more strength to mix and churn contents of
irregularly shaped tube
▪ Making contractions and changes to the structure easier to control with an
additional layer of muscle
o Usually have longitudinal and circular muscle only in the digestive tract
- Serosa
o Continuous with the lesser and greater omentum
▪ Continuous with the inside membranes that in our abdominal cavity
Stomach Motility
- There are specific movements that happen in the stomach that can be increased in frequency and
changed with how strong your contraction is and how much it relaxes
- We have to propel the contents of our stomach. not just the bolus we ingest but all the secretions that
are put into the stomach in addition to the bolus
o Propel the contents toward the antral region of the stomach, where the pyloric sphincter is
- Purpose to convert bolus into chyme
o Milk shake type composition
o Can not have solid mass moving through our small intestine. We need it to be liquefied
- By secreting a lot of solution into the stomach and vigorously propelling the food toward the pyloric
sphincter
o We start to grind the food particles into mush smaller pieces
o Mechanical type of digestion
- Emptying of gastric contents regulated by the opening of the pyloric sphincter
- MECHANICAL DIGESTION
o Muscular contractions to grind stomach contents and mix with the secretions of the stomach
o Waves every 15-25 seconds to mix food with the secretions of gastric glands
- Grinding happens because as the food contracts, as the stomach body is contracting and pushing
toward a closed terminal end, it is like a blender
o Compresses, crushes the food
- We have to eventually let some of the content empty out of the stomach
o At some point need to open the pyloric sphincter
- Opening of the pyloric sphincter is VERY BRIEF and SMALL
o What comes out of the stomach into the small intestine MUST be 1-3mm in size (small
particles)
- If the pyloric sphincter opens more frequently, we increase gastric emptying
- If the pyloric sphincter opens less frequently, we slow gastric emptying
- Because only a small amount of the chyme can get through the pyloric sphincter, majority of the
chyme pushing back into the body of the stomach = retropulsion
o Back and forth
o 30 minutes – 1 hour, we mechanically digest our food and empty our stomach
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Document Summary
Bolus liquefied to enhance enzymatic digestion and mixed through coordinated muscular contractions to mechanically break down contents. 2-3l of gastric juices secreted into stomach daily. Lower esophageal sphincter: gate keeper: must open to permit food to enter the stomach. Esophageal sphincter opens food enters stomach opens and relaxes. Upper portion of the stomach, that first receives the food which stimulates receptive relaxation = Body of stomach = main central portion of the stomach. Antrum = last part of the stomach. Pyloric sphincter: keeping the stomach contents inside: thickened muscle, most open to let the food out, for most part it is closed, because it needs to be triggered to be opened. Stomach is curved shape: part of the stomach that is larger = greater curvature, left hand side, part of the stomach that is less of a curve = lesser curvature, right hand side.
