A model of the gastric gland ejection cycle: low ejection fractions require reduction of the glandular dead space

This paper was inspired by the reported results of authors from Uppsala and Lund that gastric glands in rats rhythmically contract 3-7 cycles per minute and develop luminal pressures more than 10 mmHg. To ensure that pepsinogen is not retained in the acid-rich section of the gland, ejection fractions would need to be more than 50% of the gland volume. We have tried to calculate the ejection fraction of such contractions. Dimensions of human gastric glands were measured on the fresh frozen samples of macroscopically and histologically normal gastric mucosa. In total, 18 specimens (from nine persons) were measured under the microscope. The density of glands was 135 +/- 11 (mean +/- S.D.) glands per mm( 2) of gastric mucosa. A typical gastric gland is a tubular structure 1.2 +/- 0.22 mm long and 0.03-0.05 mm wide. We have used 1 mm for length and 0.03 mm for the gland diameter to calculate that each gland approximates a volume of 707 pl, suggesting that the total glandular volume for 15 million glands reaches 10.6 ml. Further calculations based on one to five contractions per minute on an average and on the total volume of gastric glands of 10 ml showed that only ejection fractions less than 10% deliver daily volumes less than 3 l. The presented model of the gastric gland activity is based on the idea that the low ejection fractions require a reduction of the glandular dead space. The reduced luminal pressure during the gland relaxation might cause backflux of hydrophobic viscoelastic mucus through the gland aperture. Repeated glandular contractions and relaxations would move the mucus all the way to the gland bottom, filling the gland cavity below the neck with an axial semisolid mucous cylinder. This filling would reduce the gland dead space. During contractions, the gland would eject mainly the peripheral, the more liquid part of its content. The decreasing luminal pressure in the relaxing gland would pull the outlet mucus inside, protecting gland apertures from the gastric juice.