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R Leiser

Publications and source records attributed to R Leiser.

At least 73 records · Page 4Linked to original sources
PubMed1988

The dynamic structure of rabbit blastocyst coverings. II. Ultrastructural evidence for a role of the trophoblast in neozona formation.

The neozona is the innermost layer of the complex blastocyst coverings of the rabbit and is located between the mucoprotein layer and the trophoblast. As shown previously the neozona begins to replace the zona pellucida from the 4th day post coitum (d p.c.) on (Denker and Gerdes 1979). In the present study, rabbit blastocyst coverings were checked for regional differences in their composition, comparing the embryonic and the abembryonic pole of the blastocyst, at 5 and 6 d p.c. These two stages were chosen because at 5 d p.c. a complete trophoblast layer is still present at both the embryonic disc (Rauber's layer) and the extraembryonic regions (mural and abembryonic pole trophoblast), whereas at 6 d p.c. Rauber's layer has largely degenerated. Correlation of regional differences in blastocyst coverings structure with presence or absence of an intact trophoblast is taken as suggestive evidence for a role of the trophoblast in the formation or the structural modification of blastocyst coverings components. Blastocysts of both stages were fixed in glutaraldehyde with and without ruthenium red and processed for TEM. The neozona was found to be almost equally well developed in all regions at 5 d p.c. On contrast, at 6 d p.c. (Rauber's layer defective) the neozona is consistently found to be much thinner at the embryonic disc than in the extraembryonic regions where the trophoblast is still intact. This is the first report on regional differences of the structural composition of blastocyst covering within the same blastocyst.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Structural and functional aspects of porcine placental microvasculature.

The microvascular architecture of the pig placenta was studied by serial semithin histological sections for light microscopy, which were compared with scanning electron microscopy of artificially exposed materno-fetal contact surfaces as well as of vessel casts prepared from the maternal, fetal, and combined maternal and fetal sides. The superficial reliefs from the exposed surfaces as well as from the casts are almost identical with the complementary maternal and fetal sides. In order to meet the physiological needs of materno-fetal exchange for the rapidly growing fetuses, these reliefs develop from a simple to a more complex system during pregnancy and can be described as follows: (1) The degree of interlocking increases between the fetal ridges or bulbous protrusions and maternal ridges of different orders separated by maternal troughs of variable depth, most clearly seen on vessel casts. It creates a three-dimensional notch-arrangement, giving strength to the materno-fetal contact area. (2) The structure of precapillary vessels as well as of the meshwork, and the diameter of capillaries of the maternal and fetal sides, adapt during gestation giving a good distribution of oxygenated blood into the maternal capillaries; these, with the development of large prevenous connecting capillaries on the fetal side, favour a high arterio-venous difference of fetal blood O2 pressure. (3) The vascular architecture of endometrial and fetal ridges and troughs develop into a crosscurrent to countercurrent materno-fetal blood interrelationship. Our demonstration of the materno-fetal capillary inter-relationship in the porcine placenta thus shows that the latter is a much more efficient organ for exchange than hitherto assumed.

Animals↗
PubMed1988

[Normal cyclical morphology of the endometrium and ovary of swine].

43 sows selected from registered herds without reproductive problems were slaughtered on fixed days of the sexual cycle. The macroscopic appearance of the endometrium and of the ovaries was judged. Endometrial samples from the corpus uteri as well as from the middle part and apex of uterine horns were then examined histologically (optical microscopy, transmission and scanning electron microscopy) especially concerning the epithelia of surface and glands. The variation of endometrial and ovarian morphology during the sexual cycle is described, presented in a summarizing table, documented by illustration and discussed.

Animals↗
PubMed1987

Spatial topography of the excurrent duct system in the bovine testis.

The rete testis of the bull is situated within an axial mediastinum and consists of approximately 30 longitudinally arranged, anastomosing rete channels. At the cranial testicular pole all rete channels empty into a common space, the area confluens retis, which is subdivided by small septa and narrow chordae retis. The area confluens always contains numerous spermatozoa and is connected with the bulbous initial portions of the efferent ductules by short, often tortuous rete tubules. Since the connection between rete and efferent ductules is situated within the tunica albuginea, the bovine excurrent duct system is not provided with an extratesticular rete as in many other mammals. Straight testicular tubules merge from all directions to connect with superficial rete channels, but the inlets are not evenly distributed. In the periphery each straight tubule begins with a cup-like structure followed by a narrow stalk region and a heavily folded portion opening either immediately into a rete channel or into a tube-like lateral rete extension. In close contiguity to the rete testis lie extremely coiled arterial portions connecting the centripetal and the centrifugal branches of the testicular artery. Since intrinsic musculature is scarcely developed in the mediastinum, and transport of rete content relies primarily on massage due to external pressure changes, the pulsatile blood flow through these coiled arteries may influence conveyance processes within the rete testis. An intimate spatial association between area confluens retis and adjacent large, thin-walled lymph vessels may facilitate a transfer of androgens into the fluid of the rete testis.

Animals↗
PubMed1985

The fetal vascularisation of term human placental villi. II. Intermediate and terminal villi.

Vessel arrangement and vessel structure of the intermediate and terminal villi of 50 human normal term placentas have been studied by means of semithin histology, three-dimensional reconstruction of serial sections as well as scanning electron microscopy of vessel casts. The reliability of the methods applied has been checked by a morphometrical comparison of the luminal diameters obtained. The mature intermediate villi are characterized by the presence of 1 to 2 terminal arterioles as well as 1 to 2 postcapillary venules, and a few moderately coiled, mostly narrow capillaries, some of which belong to the so-called paravascular network. The remaining capillaries are continuous with the capillary loops of the terminal villi. The fetal vessels of the terminal villi are represented by capillary loops only, parts of which are sinusoidally dilated, reaching diameters up to 50 micrometers. Depending on the method, the mean vessel diameter of the terminal villi is 12.3 (vessel casts) or 14.5 micrometers (semithin sections). The capillaries of the terminal villi are arranged in such a way that 3 to 5 terminal villi are supplied by the same, multiply coiled capillary loop. The average capillary length of the paravascular net is 1,000 to 2,000 micrometers, that of the terminal villus capillary loops 3,000 to 5,000 micrometers. The extent of sinusoidal dilation rises with increasing capillary length, indicating that the main functional importance of the sinusoids is the reduction of blood flow resistance.

Blood Vessels↗
PubMed1985

The fetal vascularisation of term human placental villi. I. Peripheral stem villi.

The fetal vascularisation of the most peripheral three generations of stem villi has been studied by means of semithin serial sectioning and scanning electron microscopy of vessel casts in 50 human term placentas. The vessel types have been classified according to the structure of the vessel walls. Stem villi with a diameter of 200-400 microns are characterized by one smaller artery and one small vein, some arterioles and venules and capillaries of the paravascular net. Stem villi of about 150 microns diameter contain arterioles and muscular venules besides the paravascular capillary network. The last generation of stem villi measuring 80 to 100 microns in diameter exhibit a terminal arteriole and a collecting venule as well as up to ten paravascular capillaries. The luminal width of the arterial and venous stem vessels is considerably smaller than described for other vascular beds. This may partly be due to postpartal vascoconstriction. The capillaries of the paravascular net normally to not show sinusoidal dilation. They are arranged as long, hairpin-like, poorly branched loops connecting the arterial and venous stem vessels to each other.

Arteries↗
PubMed1984

Vascular morphology of the bovine spermatic cord and testis. I. Light- and scanning electron-microscopic studies on the testicular artery and pampiniform plexus.

This highly coiled testicular artery within the bovine spermatic cord has a constant luminal diameter but a continuously decreasing mural thickness. The pampiniform plexus is composed of three interconnected venous networks differing in mesh sizes and calibres. The large veins of the first network display pouches and permanent constrictions, which may serve as throttle devices. The constitutents of the third network are venules or venous capillaries with diameters between 10 and 20 micron; they favor a periarterial position or even occupy the media-adventitia border of the testicular artery. All plexus veins are devoid of valves. The existence of true arteriovenous anastomoses between smaller branches of the testicular artery and plexus veins was established by serial sections. The vascular morphology of the spermatic cord is discussed with special attention to a postulated venous-arterial steroid transfer in this region.

Animals↗
PubMed1984

The blood vessels of the cat girdle placenta. Observations on corrosion casts, scanning electron microscopical and histological studies. II. Fetal vasculature.

The fetal microvascular architecture of the feline near-term placenta was investigated using scanning electron micrographs of partially fractured corrosion casts from plastic-filled vessels. The findings were compared with those on corresponding semithin histological sections. The branches of both umbilical arteries and veins roughly follow a course parallel to the zonary girdle on the allantochorionic side of the feline placenta in an acute-angled pattern of ramifications. They join the double-layered capillary networks in the chorionic lamellae of the labyrinth, which generally exhibit a chorio-uterine orientation and are partially twirled. On the allantochorionic side of the labyrinth, these fetal capillary networks are "suspended" on the maternal stem-artery-system of the placenta; on the uterine side, they have peduncular or tuft-like endings of capillary loops and are flattened by the uterine septa, which at this level converge into the maternal veins. The chorionic capillary lamellae have a variable breadth and length and therefore need shorter or longer arterioles and venules from the allantochorionic side to become irrigated at any level of the labyrinth. As a result, the feline placenta is characterized by a generally one-way crosscurrent type of materno-fetal blood flow.

Animals↗
PubMed1983

Blood vessels of the bovine chorioidea. A scanning electron microscopic study.

On corrosion casts of the bovine choroidal vessels, the vascular architecture was investigated by means of scanning and corresponding transmission electron microscopy. Complete filling of the vessels produced close-fitting replicas. Thus, based on different luminal structure, the arteries and veins in the lamina vasculosa could be easily distinguished. The branches of these vessels were followed to the choriocapillaris. The complete pattern of afferent and efferent vessels provided the opportunity to establish a scheme of choroidal microcirculation. The choriocapillaris in the bovine as a freely communicating network is subdivided into star-shaped areas of roughly hexagonal form. On the boundaries of these areas the afferent vessels (arterioles) - arranged at regular distances - join the choriocapillaris, whereas drainage of the choriocapillaris is effected by a single efferent vessel (venule) in the center of each area.

Animals↗
PubMed1980

Light- and electron-microscopic study of the near-term paraplacenta of the domestic cat. I. Polar zone and paraplacental junctional areas.

The entire chorioallantoic paraplacenta of the near-term domestic cat shows cytological evidence of maternal-fetal substance transfer, but there are probably qualitative and quantitative differences and increased transfer progressing from the poles to the placental border. In the interfetal polar zone, the cytotrophoblast remains proliferative, is squamous to columnar and shows only a small amount of pinocytotic activity. However, in the adjacent ring of the free polar zone, where the trophoblast is cuboidal or columnar and loosely apposed to the endometrium, material of uterine origin (histotroph) appears to be transferred from the columnar uterine surface epithelium to the trophoblast. The remaining paraplacenta extends from the polar zone to the girdle, forming an extravasate zone that is composed of hematomal areas containing extravasates of maternal blood, and interposed relatively unmodified paraplacental junctional areas. The trophoblast in this hematomal area is columnar and constitutes chorionic villi which face a surface formed by maternal symplasma, degenerative uterine tissue, and disintegrating blood, thus providing 'histolytic' and 'hemolytic' embryotroph to this hemophagous cytotrophoblast. When the junctional area is just forming, a cuboidal cytotrophoblast consisting of resting cells, opposite to the endometrial folds, appears to have both the capacity for digestion and transformation. However, during the recessive junctional stage, this cytotrophoblast is proliferative and absorptive only. Both sources of cuboidal trophoblast may give rise to syncytial trophoblast, which is presumably the invasive form that erodes the uterine tissue, including the interstitial layer and maternal endothelium. As long as there is firm junction of the fetal and maternal tissues, there appears to be a transfer of secretion products to form embryotroph. However, with the regression of the junctional area more products of cell breakdown (histolytic products) are absorbed by the cuboidal cytotrophoblast in the chorionic fossae.

Animals↗
PubMed1980

Light- and electron-microscopic study of the near-term paraplacenta of the domestic cat. II. Paraplacental hematoma.

In the near-term paraplacental extravasate zone of the domestic cat, which includes paraplacental junctional areas and marginal hematomas, the uterine epithelium becomes highly proliferative, especially on the folds or protrusions, This hyperplastic surface and the adjacent connective tissue become symplasmic, degenerate and eroded, eventually resulting in maternal vascular breakdown. The uterine lumen thus contains maternal blood in addition to sloughed uterine cells. The adjacent cytotrophoblast apparently phagocytoses and ingests this material. Various stages of phagolysosomes containing erythrocytes of variable density are seen in these cells, as are myelin-like structures, ferritin, glucogen and lipid droplets. Crystalloid iron deposits are seen in the basal lamina and connective tissue subjacent to the hemophagous cytotrophoblast.

Animals↗