THE MORPHOLOGY, DEVELOPMENT AND HISTOMETRY OF SWINE GASTRIC WALL IN THE FOETAL PERIOD

Aleksander Chrószcz
Department of Anatomy and Histology, Wrocław Univesity of Environmental and Life Sciences, Poland

ABSTRACT

The aim of the study was the histological investigation of gastric wall in pig's stomch during the foetal period. This work was carried out on 138 domestic pig foetuses, including 68 males and 70 females. Whole investigated material came from Department of Anatomy and Histology collection Agricultural University of Wrocław and it was genetic equal, known origin (including the horn of uterus), sex and age.The histological slides from the cardiac, fundic and pyloric region were stained with H – E and Masson – Goldner stain. The histometric measurements were carried out and statistically analysied. All aquired results were presented as tables, diagrams and figures. During the histological interpretation NH were used. The development of stomach wall layers was described. The developmental investigations proved, the simple columnar epithelium of gastric mucosa in the whole investigated period of pregnancy. The muscular layer of mucosa, the first parietal cells and the muscular layers division occurred in the 60^th day of gestation. The histometric measurements and its statistcal analysis was carried out. It proved the positive allometric growth of gastric mucosa thickness after the 60^th day of gestation according to the rapid gastric glands development. The significant decrease of the mean values of separate muscular layers and mucous membrane thickness in the third group can be explained by the gastric glands development, the submucosa separation and the muscular layer partition.

Key words: pig, stomach, mucosa, submucosa, muscular layer, glands, prenatal development.

INTRODUCTION

The prenatal development of stomach was often described in various mammals [1,4,6,9,10,11,18,20,21,23,27,28,32,33,35,36,38,39,42]. The lack of literature dealing with the exact swine stomach's layer development between the 35^th and 114^th day of pregnancy was the main cause of these investigations. The foetal period (35^th – 114^th day of gestation) proves the occurrence of the great number of dynamic quantitative and qualitative processes according to the stomach's wall development [9,10,11,13,14,15,16,17,21,26,38]. The significant influence on the stomach's wall structures development, especially the gastric glands proved the interaction between the epithelial cells and the mesenchymal tissue [9,34]. The great number of lymphoid nodules were observed in adult domestic mammals, being the cause of fequent embryological investigations [7,8,19,25,29,30,40].

MATERIAL AND METHODS

The investigations were carried out on 138 pig foetuses (68 male and 70 female) from the 35^th – 114^th day of gestation. The whole material came from 13 sows. All animals were breeding in standard husbandry and they are genetic homogenous [37].

The foetus age was estimated on the base of CRL measutements [22,26] and they were divided into six age groups [3] (Table 1):

• 1^st group – the 35^th day of gestation

• 2^nd group – the 56^th – 61^st day of gestation

• 3^rd group – the 70^th – 76^th day of gestation

• 4^th group – the 82^nd – 86^th day of gestation

• 5^th group – the 92^nd – 97^th day of gestation

• 6^th group – the 107^th – 114^th day of gestation.

During the histological investigation, the histological slides were stained with H – E and Masson – Goldner method. The slides of stomach wall was observed in optic microscope Axioskop 2 plus Zeiss with 20x and 40x magnification.

The histometric measurement were carried out with histometric tool OMO ΓOCT 7865 – 56. All measurements were repeated three times and the mean value was calculated.
During the statistical investigations the standard deviation, maximal relative standard deviation and correlation coefficient was estimated. All results are presented in figures, tables and diagrams.
The description of histological analysis results were carried out with use of NH [31].

RESULTS AND DISCUSSION

The stomach wall in the 35^th – 40^th day of gestation consists of three layers. The stomach mucous membrane (tunica mucosa) is covered with the simple columnar epithelium (epithelium simplex cylindricum), which occurred until the end of pregnancy. This finding does not support the thesis of Georgieva and Gerov [5]. These authors observed the double columnar epithelium before the 55^th day of gestation. These differences can be interpreted as the results of different swine breed or the methods of age estimation. The proper layer of mucosa (lamina propria mucosae) was built with mesenchymal tissue and few blood vessels. The gastric glands (glandulae gastricae) do not occur (Fig. 1). The other authors support these findings [5].

The stomach wall in the 56^th day of gestation was covered by the simple columnar epithelium, which forms the gastric pits (foveolae gastricae). The primary lymphoid nodules (noduli lymphatici primarii) were observed in the forming gastric submucosa (Fig. 2). The other authors proved the same developmental changes [5] and the gastric pits are the primordium of the gastric glands [12]. The thesis of early gastric pits occurrence in stomach mucosa was proved in various mammal species [1,21,32]. Simultaneously, the proper layer of gastric mucosa was built with connective tissue, fibroblasts, collagen fibers and capillary blood vessel. Some myocytus bands occurred in gastric wall in order to form the muscular layer of mucosa.

The first more remarkable qualitative changes in the wall of stomach occurrs in the 60^th day of gestation (Fig. 3). The epithelial cells were high and cylindrical, with large well stained nucleus. The myocytes (myocyti) were present as a primodium of the muscular layer of mucosa (lamina muscularis mucosae). The submucosa (tunica submucosa) was divided from the proper layer of mucosa, forming the independent layer of stomach's wall. The gastric pits were clearly visible. Their walls contain some well stained cells with oval, central located nucleus. These cells were classified as the parietal cells (exocrinocyti parietales). They occur no typical pyramidal shape and they were located in groups between the epithelial cells. The first parietal cells were seen in the base of deeper gastric pits. The acquired results are similar to other authors findings [4,5,21,27,34]. The common occurrence of parietal cells in paired groups proves, they derivation from one precursor cell [6]. The presence of parietal cells in superficial parts of gastric pits in the 60^th day of pregnancy is the indirectly proof of gastric pits cells [surface mucous cells (epitheliocyti superficiales)], neck cells (mucocyti cervicales) and parietal (oxyntic) cells (exocrinocyti parietales) directly derivation from the stem cells and the chief (zymogenic) cells (exocrinocyti principales) from neck cells [13,14,15,16,17,18,33].

The investigations of gastric glands in the 107^th day of gestation result the cardiac glands (glandulae cardiacae) occurrence in cardiac region. Simultaneously, the fundic glands were clearly visible in the mucosa of fundic region. Both gland types were formed by the simple cylindrical epithelium. The mucous-like cells and chief-like cells were observed (Fig. 4). Both cell types probably are developing in mucous neck cells and chief cells, which will have been seen in histological slides since the third month of prenatal life within the fundic glands (glandulae fundicae) at the base of gastric pits [34]. The occurrence of mucous neck cells proved also Georgieva and Gerov [5] and they can be also described as mucous cells [24]. The chief cells were observed in bovine foetuses in the second part of pregnancy [1].

The mucosa of glandular region was covered with the simple cylindrical epithelium in the 107^th day of gestation. Similar to observed postnatal life [2]. The proper layer of cardiac region mucosa consists of narrow layer of connective tissue. The muscular layer of mucosa was clearly visible, as the compact layer of myocytes. In fundic region, the proper layer of mucosa contains a lot of fibroblastes and well developed muscular layer of mucosa occurs. The significantly high amount of fibroblastes, blood vessels and connective tissue fibres occurs in the pyloric region. The pyloric glands (glandulae pyloricae) form the deep structures in proper layer of mucosa, the nucleus of pyloric glandular cells (exocrinocyti pylorici) was located basally. The same results were obtained postnatally [2,5]. The cardiac submucosa contains the lymphatic tissue, primary lymphoid nodules (noduli lymphatici primarii) within the wall of ventricular diverticulum (diverticulum ventriculi) (Fig. 5). The investigations on the development and function of the lymphatic tissue are the common aim of the scientific activity [25,19,29,40]. The submucosa of gastric body and pyloric part was thick and well developed (Fig. 5 and 6).

The investigations cared out in foetuses from the 114^th day of pregnancy proved the occurrence of well developed cardiac mucosa and its muscular layer (Fig. 7). The connective tissue of fundic mucosa was relatively poor (Fig. 8), but the muscular layer of mucosa was richer than in the cardiac region. Similar microanatomical architecture occurred in the pyloric region (Fig. 9), where the muscular tissue was the highest developmental level. The significant decrease of connective tissue within the proper layer of mucosa of stomach's glandular region was the result of intensive gastric glands development, which deeply penetrate this layer of stomach wall. The lack of gastric glands in nonglandular mucosa allows the richer connective tissue layer occurrence.

The last period of prenatal life histological investigations proved the cardiac, fundic and pyloric well developed glands occurrence. The chief cells, parietal cells and mucous neck cells were observed within the wall of fundic glands. The majority of parietal cells was located in the base of gland. The glandular cells of cardiac and pyloric glands occur the basal nucleus location. The similar observation were carried out in postnatal life [2,5,34].
Other changes were observed in non glandular gastric mucous membrane, typical for the complex stomach.

In the 56^th day of pregnancy, the nonglandular mucosa was covered with the multistratified plane epithelium (epithelium multistratificatum planum). This epithelium consists of few layers of epithelial cells and the basal membrane (membrana basalis). The proper layer of mucosa occurs the existence of myocytes bands, the primordium of muscular layer of mucosa. The lymphatic tissue, as the primary lymphoid nodules were observed in the proper layer of glandular and non glandular mucosa (Fig. 10). More significant differentation of the stomach's wall were proved in the 80^th day of gestation [5]. The stomach's non glandular mucous membrane in the 82^nd day of pregnancy consists of the multistratified plane epithelium, the proper later of mucosa, well developed muscular layer of mucosa. The submucosa was built with rich layer of the connective tissue (Fig. 11). Simmilar mucous membrane architecture was observed in the 107^th day of gestation. The proper layer of mucosa was relatively thin and the muscular layer of mucosa was thick and clearly visible (Fig. 12). On the contrary, the rat's non glandular mucous membrane development occurs the ceratinization processes within the epithelial cells [12]. The mucous membrane of swine non glandular mucosa proved no ceratinization. In the 107^th day of prenatal life, the submucosa of nonglandular region consists of connective tissue, blood vessels, fibroblastes and fibres.

The mucous membrane was covered by the thick layer of the multistratified plane epithelium in the 114^th day of gestation. The proper mucosa, in this period, occurs the existence of the primary lymphoid nodules and the muscular layer of mucosa forms the bands of myocytes (Fig. 13). The primary lymphoid nodules were observed in stomach's mucous membrane (Fig. 14).

The histometrical measurements of gastric mucosa proved the non linear correlation between the mucosa thickness and the age group. The high square correlation coefficient and standard deviation (R² = 0.99 i SD_max. = 37%) of regression curve stated the mean value of mucosa thickness decrease to 77.053 µm in the 60^th day of gestation and its subsequent increase to 516.44 µm in the 114^th day of prenatal life. The statistical analysis proved the positive allometric growth of gastric mucosa thickness after the 60^th day of gestation according to the rapid gastric glands development (diagram 1).

The investigations devoted to the nonglandular gastric region development rebut the hypothesis on the esophageal primordial of this region [39].
The gastric submucosa thickness mean value equals 265.8 µm in the 60^th day of gestation and this value is rather constant during the whole subsequent foetal period (diagram 2).

The gastric submucosa thickness mean value equals 186.18 µm (the 107^th day of gestation) and 351.43 µm (maximum at birth).
The muscular layer of stomach wall consists of myoblastes and do not divide into two layers in the 35^th – 40^th day of gestation (Fig. 1). The first division signs were seen in the 56^th day of pregnancy and two layers of the muscular layer were clearly visible in the 60^th day of prenatal life (Fig. 15). In humans, the early occurrence of mesenchymal muscular layer primordium does not allow for the two typical layers recognition [32].

The division process is finished in the 70^th day of prenatal life, simultaneously with the muscular layer of mucosa and submucosa occurrence [5]. This study proved the clearly visible occurrence of divided gastric muscular layer after the 60^th day of pregnancy.

The gastric muscular layer was full organized in the 107^th day of prenatal life. It consists of inner circular and outer longitudinal sublayers. The gastric musculare layer within the pyloric torus built the complex architectonical structure of myocytes groups between strong layers of the connective tissue fibres, fibroblastes and blood vessels (Fig. 16). Similar results were obtained by other authors in postnatal investigations [2].

The late changes of gastric muscular layers (the 114^th day of pregnancy), dealt with pyloric region (Figs. 17 and 18). The thick bands of myocytes with varied orientation were divided with thin bands of the connective tissue and its fibres. The investigations carried out in adult animals proved, the pyloric torus muscular layer development from the circular layer of gastric muscular layer [2].
The postnatal occurrence of adipose tissue between two layers of gastric muscular layer were not observed in prenatal life.

The muscular layer in toto, proved non linear correlation between the mean value of muscular layer thickness and the age group. The highest correlation coefficient (R² = 0.84) proved the positive allometric growth of the value during the foetal period (diagram 3). The statistical analysis of the separate muscular layers proved the significant decrease of the mean thichness value in the third group (diagram 4 and 5). Smilar decrease was observed in the mucous membrane thickness (diagram 1). These can be explained with the rapid qualitative and quantitarive changes, according to the gastric glands development, the submucosa separation and the muscular layer partition between the 56^th and 60^th day of prenatal life.

The full development of gastric wall was not finished at birth. Especially in gastric glands, the accessible literature proved the significant quantitative and qualitative changes in perinatal period [5,20,23,41,43,44].

CONCLUSIONS

1. The gastric mucosa was covered with the simple columnar epithelium in whole investigated prenatal life period.
2. The first myocytes form the muscular layer of mucosa in the 60^th day of gestation.
3. The first parietal cells were visible in the 60^th day of pregnancy in the base of deeper gastric pits.
4. The muscular layers divides into internal and external layer between the 56^th and 60th day of gestation.
5. The statistical analysis proved the positive allometric growth of gastric mucosa thickness after the 60^th day of gestation according to the rapid gastric glands development.
6. The statistical analysis of separate muscular layers and mucous membrane thickness proved the significant decrease of the mean values in the third group. These can be explained, according to the gastric glands development, the submucosa separation and the muscular layer partition between the 56^th and 60^th day of prenatal life.

ACKNOWLEDGEMENT

I am very grateful to Prof. dr dr h. c. Hans-Georg Liebich from Institut für Tieranatomie, Tierärztliche Facultät, LMU München for valuable help, cooperation and technical assistance during these investigations.

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Accepted for print: 19.09.2008

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