Ultrastructural and stereological studies of hepatocytes in prenatal development of swine.

Ultrastructure of hepatocytes was investigated during pig fetal development from 18 to 113 day post coitum (dpc). Stereological measurements were taken on the electronograms determining the area and perimeter of the cross-sections of cells, the nucleo-cytoplasmic ratio, and the volume density of hyaloplasm, mitochondria, endoplasmic reticulum, lisosomes, dictyosomes, lipids and glycogen. Hepatocytes are not subjected to any greater changes, apart from their shape, until the last three weeks prior to parturition when they accumulate glycogen. The volume density of particular organelles in hepatocytes is variable. Therefore three periods can be distinguished in their development: period of differentiation (18-40 dpc), period of metabolic activity (40-80 dpc) and period of glycogen accumulation (80-113 dpc). These three phases correspond to three periods of hematopoiesis in the embryonic liver which has already been described [1].

Ultrastructure of mucous areolae in the pig placenta.

The mucous areolae in the pig placenta are characterized by the presence of acid mucopolysaccharides. They have different forms: areas of vascularized trophoblast in early pregnancy, small irregular areolae, vesicles and cysts. The ultrastructure of the mucous areolae in placentae from 18th to 113th day post coitum was investigated. The trophoblast lining the areolae consisted of polarized columnar cells of varied height and width. Only in large cysts that epithelium was extended and flat, only a few micrometers thick. On the free surface of the cells long microvilli formed groups resembling stereocilia. The hyaloplasm of these cells was extremely electron-dense. The apical parts of the cells were filled with mucous granules and exocytosis of their content into the areolar cavity was observed. High synthetic activity of numerous dictyosomes was noted near the nucleus. The basal parts of the cells were divided into lobular processes containing a significant number of elongated mitochondria. In many trophoblastic cells large heterogeneous vacuoles were present. Their content was extruded into areola cavity. The substance filling the mucous areola cavity was heterogenous with some cell debris and whole desquamated cells. The uterine epithelium covering the mucous areolae consisted of high columnar absorptive cells, with the brush border present on their free surface. Apical terminal web contained numerous small coated endocytotic vesicles with a light flocculent content. The filopodia and lamellipodia separated by the intercellular space formed a labyrinth in the basal parts of the cells. The mucous areolae differ from the regular areolae in the ultrastructural and functional features. Possible role of the mucous areolae is discussed.

A new approach to the areolar structures in the pig placenta: histochemistry and development of mucous areolae.

The pig placenta contains specific structures such as regular and irregular areolae, vesicles and cysts. On the basis of histochemical reactions it can be stated, that irregular areolae, vesicles and cysts differ from the regular areolae. Trophoblast of all the former structures and the substance filling their cavities contain glycosoaminoglycans with sulphuric acid residues (acid mucopolysaccharides). The regular areolae contain PAS-positive glycoproteins and active acid phosphatase. The acid mucopolysaccharides were also observed in the small trophoblast areas with vacuolized cells (TAVC) in the early placenta (18-20 days post coitum). The histochemical features of the investigated structures allow to observe the differentiation and development of TAVC in irregular areolar structures, vesicles and cysts in placentas from the time of implantation until the last day of gestation. Some of these structures fuse with regular areolae forming large irregular areolae described in the literature. The uterine epithelium covering all these structures forms festoon-like folds covered with the brush border. All the structures containing acid mucopolysaccharides can be termed the mucous areolae.

Morphometric investigations of the pig developing liver during the prenatal period.

Quantitative changes in the developing liver of the pig embryo have been studied in the light microscope by stereological methods. Between days 18 and 112 of gestation the volumetric fraction of hepatocytes in the liver significantly increased and the volumetric fraction of blood vessels decreased. The haemopoietic cells reached the greater volumetric fraction about day 50 of gestation and thereafter their density declined. On the basis of the measurements of hepatic elements three different periods have been discerned. The first between days 18 and 39 when the differentiation of the liver takes place and the haematopoietic cells colonize it. The second is the period of intensive liver haematopoiesis between days 40 and 80. The third is from about day 80 to the birth when haematopoiesis declines and disappears and the volumetric fraction of hepatocytes significantly increases as a result of glycogen deposition.

Prenatal development of the adrenal gland in the pig (Sus scrofa domestica). Part I. The differentiation and development of the adrenal cortex primordium in the first half of pregnancy.

The differentiation and development of the adrenal gland in pig embryos from 18 to 48 days of pregnancy were investigated with histological and histochemical methods and in electron microscope. Primordia of the adrenal cortex appear at 21st day as two symmetrical streaks of the condensed mesenchymal cells between the mesonephros, aorta dorsalis and mesenterium. The capillaries and chromaffinoblasts penetrate the primordium. The mesenchymal cells differentiate into adrenal cortical cells. In the differentiating cells both, rough and smooth endoplasmic reticulum as well as the number of mitochondria increase. The shape of the cells changes and their projections transform into microvilli. The fetal cortical cells have features of the steroidogenic cells with abundant SER in whorls and numerous mitochondria with tubular cristae. The giant mitochondria and dense lamellar bodies were observed in these cells. The microvilli on cell surfaces form a microlabirynth in intercellular and perivascular spaces.

Prenatal development of the adrenal in pig Sus scrofa dom. Part II. Adrenal cortex development in the second part of pregnancy.

The development of the adrenal cortex in pig fetuses between the 50 and 112 day of pregnancy were investigated with histological and histochemical methods and in electron microscope. Three consecutive generations of the cortical cells were observed. They had features of steroidogenic cells and differed with mature of mitochondria and in amount of SER and in enzyme activity. The earliest differentiated fetal cortical cells demonstrated alkaline phosphatase activity and giant mitochondria. They were translocated from the periphery to the center of the adrenal, where they degenerated and disappeared in the late pregnancy. The second generation--transitional cortical cells appeared about 70 day of development. They have pleomorphic mitochondria and abundant SER and low alkaline phosphatase activity. The last generation--the definitive cortical cells differentiated from 100 day of development and their number increased till the parturition. They had active 3-beta-hydroxysteroid dehydrogenase, spherical mitochondria and characteristic concentric whorls of SER. A probable role of the three generations of cortical cells is was discussed. In the subcapsular region of fetal adrenal undifferentiated and differentiating cells were observed, forming glomerularlike groups. Their role in the formation of cortical blastema and future zona glomerulosa was discussed. In the first part of the studies the formation of the mesenchymal primordium of the adrenal cortex was examined in early fetuses of domestic pig, and then differentiation of mesenchymal cells into steroidogenic cortical cells. The changes encountered then at the ultrastructural level consisted of an increased area of SER and greater number of mitochondria. At the same time, the shape of mitochondria altered and the cristae from lamellar became tubular. In the period around 50 day of development fetal adrenal was already a separate organ, with a capsule, composed of cords of fetal cortical cells divided by the blood vessels and strands of chromaffinoblasts penetrating the adrenal. Fetal cortical cells were characterized by alkaline phosphatase activity. The following study presents farther development of the adrenal cortex till the time of birth.

Ultrastructural and histochemical investigations of the development of the medullary part of the adrenal gland in domestic pig (Sus scrofa dom.) during the prenatal period.

The development of the adrenal medulla was investigated during the prenatal period in the pig. The observations were carried out on 221 embryos from 21 to 112 day post coitum. The histological, histochemical, ultrastructural and stereological methods were performed. First chromaffinoblasts infiltrated the adrenal cortex primordium around the 27-th day pc. They were mixed with cortical cells and just in the last days of pregnancy they were localized only in central part of adrenal. The chromaffinoblasts differentiated gradually from neuron-like cells to typical chromaffinocytes. A centripetal gradient of this differentiation was observed. All chromaffinoblasts contained the chromaffine granules. The size and numerical density of the chromaffin granules increased with development.

Distribution of iron in pig placenta (Sus scrofa dom. L.).

Iron distribution was studied in pig placentae between 21 day till the end of pregnancy (113) with the use of histochemical and cytochemical methods and X-ray microanalysis. Iron content was measured in fetal and maternal part of the placenta with chemical methods. Iron presence was confirmed in maternal and fetal erythrocytes, cells and secretion of uterine glands and trace amount in trophoblast lining regular areolae. No significant differences were found in iron content in fetal and maternal part of the placenta throughout the entire studied period. With the applied histochemical method of iron determination according to Perls, potassium ferrocyanide also adsorbs in sites where mucopolysaccharides are present, in which iron presence has not been detected with the use of X-ray microanalysis.