Physiology 3120 Lecture Notes - Lecture 59: Esophagus, Greater Omentum, Curvatures Of The Stomach
15 May 2018
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Lecture 59 – Stomach
- Lower esophageal sphincter: opens to permit bolus enter the stomach
- Stomach is small and when sphincter opens, the food enters and as the mechanical
stretching occurs, stomach starts to open by a process called receptive relaxation
- Receptive relaxation: receiving bolus causes the stomach to relax, open up, and allow the
rest of the meal to enter more easily
- Sphincter opens → food starts to enter → stomach opens and relaxes
- FUNDUS REGION: first portion of the stomach that receives the food and stimulates
receptive relaxation
- BODY: main central portion
- Pyloric sphincter/pylorus: keeping stomach content inside we have a thickened muscle
o Opens to allow food to exit the stomach
o Usually closed and must be trigged to open
- Stomach is J shape
- Greater curvature: part of the stomach has a larger size (left)
- Lesser curvature: part of the stomach that has less of a curve (right)
- Eat a large meal before bed → feel unwell
o Lay on left side with a large meal → releases pressure
o To increase gastric emptying, lay on right side
- Rugae: folds in the interior of the stomach
o Closer together when stomach is small but when the stomach is stretched out they
spread out more
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Enterocytes of the stomach
- Cells of the mucous layer are enterocytes
- EXOCRINE (in fundus and body region)
o Mucus neck cells: secretes mucus
o Chief cells: secretes pepsinogen (protein) and gastric lipase (enzyme)
▪ Pepsinogen is activated by a cleavage event in the presence of acid to pepsin,
the active enzyme
▪ Gastric lipase folds and functions best in an acidic environment
o Parietal cells: secretes intrinsic factor, H+ and Cl- (HCl)
- ENDOCRINE (in antral region)
o G cells: secrete gastrin
Layers of the stomach
- Mucosa
o Enterocytes secrete acid, gastric lipase, pepsinogen and intrinsic factor (helps with
vitamin B12 absorption)
▪ Intrinsic factor binds B12 and without it we cannot absorb it
o Folds called rugae
o Deep invaginations called pits containing stem cells
▪ Stem cells are committed to producing exocrine and endocrine cells of the
stomach so the mucosa layer is replaced
▪ Cells live in an acid environment = need to be replaced!
- Submucosa
o Similar characteristics to the rest of the tract
- Muscularis Externa
o Additional oblique muscle layer (+ circular + longitudinal), provides more strength
to mix and churn contents of an irregular shaped tube
o Makes contractions and changes to the structure more easy to control with an
additional layer of muscle
- Serosa
o Continuous with the lesser and greater omentum (other membranes of our
abdominal cavity)
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Stomach motility
- Movements within the stomach can be increased in frequency and can be changed with how
strong the contraction is and the rate at which it relaxes
- Must propel the contents of the stomach (bolus + contents secreted) towards the antral
region where the pyloric sphincter is
- Purpose of motility to convert bolus into chime
o No solid mass in small intestine
o Contents must be liquefied
o By secreting solution into the stomach and vigorously propelling the food towards
the pyloric sphincter, we can grind the food particles into smaller pieces
- Emptying of gastric contents regulated by the opening of the pyloric sphincter
o Opening is very brief and small
o What comes out of the stomach and into the intestine must be 1-3 mm in size or
liquefied
o If it opens more frequently we increase gastric emptying and vice versa
o Small amount of chyme can get through the pyrloric sphincter which opens very
briefly, majority of chyme pushes back into the body of the stomach called
retropulsion to just be pushed back again
o Chyme moves back and forth for 30 minutes – 1 hour to mechanically digest food
and empty stomach
- MECHANICAL DIGESTION
o Muscular contractions to grind stomach contents and mix with the secretions of the
stomach
o Grinding occurs because the food contracts in the stomach body and pushes the food
towards a closed terminal end (compresses, mixes and crushes the food)
Case study: pyloric stenosis
- Hypertrophy of the pyloric muscles of the sphincter, failure of pylorus to relax - preventing
gastric emptying
- Babies who get this have a normal pylorus at birth and nothing is wrong
- Pylorus muscle becomes thicker and it is unable to relax as frequently
- This prevents gastric emptying
- Infantile Hypertrophic Pyloric Stenosis (IHPS) most common (rare in adults)
- 1 in 500 infants, more frequent in first born males, hereditary linkage (genetic)
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Document Summary
Lower esophageal sphincter: opens to permit bolus enter the stomach. Stomach is small and when sphincter opens, the food enters and as the mechanical stretching occurs, stomach starts to open by a process called receptive relaxation. Receptive relaxation: receiving bolus causes the stomach to relax, open up, and allow the rest of the meal to enter more easily. Sphincter opens food starts to enter stomach opens and relaxes. Fundus region: first portion of the stomach that receives the food and stimulates receptive relaxation. Pyloric sphincter/pylorus: keeping stomach content inside we have a thickened muscle: opens to allow food to exit the stomach, usually closed and must be trigged to open. Greater curvature: part of the stomach has a larger size (left) Lesser curvature: part of the stomach that has less of a curve (right) Eat a large meal before bed feel unwell: lay on left side with a large meal releases pressure, to increase gastric emptying, lay on right side.
