Morphology of the Ovary, Endometrium and Placenta of the Dromedary

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Awatif Fath El Rahman Salman, Salman
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The present investigation is an account on the morphology of camel cortical stroma, corpus luteum, endometrium, placenta and foetal membranes. The study was performed on 58 pregnant female camels. The different cellular populations of the cortical stroma of the camel ovary are described. The changes in the structure of the ovarian surface epithelium during different stages of pregnancy suggest an interaction between these cells and the adjacent extracellular matrix. In addition to the main stromal cells, there are other cell types: cells similar to plasma cells, plasma cells and polymorphonuclear leukocytes. The functions of these cells are discussed in relation to pregnancy. Cells resemble interstitial gland cells of other animal species are encountered during this study of camel ovary. Functional correlates of these morphological findings are discussed. The corpus luteum, one of the biological clocks of the pregnancy, is most notable for its production of progesterone that blocks the pituitary release of gonadotropins and prepares the uterus for pregnancy. In camel corpus luteum, the cellular sources of this progesterone are the steroidogenic small and large lutein cells. The most prominent lutein cell is the large steroidogenic cells are characterised by an abundance of smooth endoplasmic reticulum and densely packed spherical mitochondria that are indicative of its contribution to the most of the circulating progesterone believed to be constantly secreted and not under the control of the luteinizing hormone. Other distinguishing features of the large lutein cells are the presence of rough endoplasmic reticulum, prominent Golgi, and secretory granules that are indicative of endocrine cells. The morphology of camel corpora lutea is compared with steroidogenic tissues of other species and is correlated with the capacity of camel corpora lutea to synthesize oestrogens in addition to progesterone The large lutein cell undergoes dynamic changes during pregnancy, which are believed to reflect a change in progesterone and protein secretion that will eventually influence a successful pregnancy. Based upon morphological evidence, it is suggested that in addition to elaborating steroid hormones, corpora lutea of camel may also secrete a proteinaceous products. Some candidates are relaxin and oxytocin. Other lutein cells that are not steroidogenic but are believed to have an important role in the function of this gland are the fibroblasts, macrophages and endothelial cells. The morphological characteristics of the camel lutein cells during different gestational periods are the focus of this study. In conclusion, the corpus luteum consists of steroidogenic and nonsteroidogenic cells that function together to sustain pregnancy that leads to a successful birth of foetus. The large luteal cell appears to undergo the most pronounced morphological transition reflects important physiological events. Depending on the objective of future experimentation, consideration should to be taken to dated (specific days of pregnancy) versus undated (commercial abattoir) corpus luteum. Light and electron microscopical examination of the maternal placenta (endometrium) revealed that it is composed of uterine (endometrial) surface epithelium, uterine (endometrial) glands and endometrial stroma. The uterine surface epithelium of the camel endometrium remains intact throughout all stages of gestation. The uterine surface epithelium shows an ultrastructure which is correlated with secretion of proteins during early gestation. These cells secrete histotroph (uterine milk) which is a complex embryo culture medium. Other proteins possible to be secreted by these cells are discussed. The numerous lipid droplets in the surface epithelium of the camel uterus are either used for nutrition of the early embryo or as precursors of steroid hormones. Reduction of the height of these cells during the second half of pregnancy is probably in response to the most acute demand of the foetus for gaseous exchange. The fine structure of these cells during mid-pregnant stage indicates their involvement in placental steroid interconversions. It also indicates their involvement in processing and transferance of certain materials to the foetal side during the third trimester of pregnancy. The endometrial glands show proliferation and increased branching resulting in an increase in glandular profiles during the early stage of gestation. Copious flow of PAS-positive; diastase resistant secretion is maintained by the endometrial glands of camel. The glandular epithelium during early gestation possesses features indicative of a high rate of protein synthesis and may be due to either the production of the materials required for cell proliferation or to a role of the cells in the secretion of histotroph (uterine milk). The early development of epithelial stratification and its subsequent extension into the basal coils of the glands indicate that in this species, the glandular epithelium continues to proliferate throughout pregnancy. The similarity of the rough endoplasmic reticulum to that of many glandular cells suggests that it contributes to the production of materials for secretion. The well- developed Golgi apparatus also suggests secretory activity, and the close proximity of the cytoplasmic vacuoles to the apparatus and to the surface membrane suggests involvement in the transmission of materials produced in the apparatus to the lumen. It is suggested that the development of synthetic activity in the glands of the pregnant camel is controlled by oestrogens. In this respect, the endometrial glands of camel are comparable to those of certain species. In addition to the material which is produced by the break down of cells of the glandular epithelium, the histotroph contains numerous leukocytes. It is generally accepted that these are largely maternal in origin and the frequent occurrence of lymphocyte-clear cells between the epithelial cells supports the histotroph by migration throughout the glandular epithelium. Although some of these contain dense granules, they are never seen to be multinucleated and the differences in their morphology are not sufficiently pronounced to enable them to be classified into more than one population. The possibility of secretion of certain proteins and factors by the glandular and/or surface epithelium of the endometrium of camel during early gestation is discussed. Accumulation of glycogen in the glandular epithelium was observed during this study in the early stage of gestation. This finding and the role of glycogen during this stage is discussed. During mid gestation, the glands appear active specially those in the deeper portion of the endometrium, showing lumina filled with PAS-positive diastase-resistant material. At the ultrastructural level, cells with features similar to those present at the earlier stages of development are concentrated in the basal layers of the stratified areas. In the most of the cells, there is no evidence of the onset of changes in the structure of the nuclei which are probably related to a progressive decline in the synthetic activity of the epithelium. In the stratified areas, the development of these changes can be correlated with the transformation of the cells into syncytial masses of degenerated material present in the lumen. The formation of dome-shaped elevations from the surface and the recession of the junctional complexes towards the base of the cells may also be a representative of an early stage in the development of processes of the detachment of cells from the epithelium. Such detachment is clearly evident in the stratified areas in the early stage. Processes of this kind also occur in later stages. Endometrial gland cells of camel endometrium in late pregnancy resemble typical protein secreting cells. The possibility that these cells secrete relaxin during this stage is discussed. Endometrial stroma shows changes in components and arrangement during different periods of gestation. In response to implantation of the embryo, there is an acute inflammation which includes marked changes in the tissues and immune cell components of the camel endometrium. The local immune system is involved in the uterine response to pregnancy in camel and the related events are discussed. The characteristically large oval granulated PAS-positive- diastase resistant cells which populate the deeper portion of the endometrium between the bases of the glands are suspected as decidual cells by previous workers. Examination of these cells by electron microscopy revealed that they are mast cells. The contribution of mast cells to vascularization and angiogenesis by inducing vasodilation and increased vascular permeability during earlier stages of gestation is discussed. Their interactions with endothelial cells, growth factors, and angiogenin are also discussed. The role of mast cells in earlier stages of gestation in camel was compared to that of decidual cells of other mammalian species. Immunohistochemical investigation of the collagen component of the extracellular matrix of the camel endometrial stroma during earlier and later stages of the first trimester of pregnancy was performed during this study. Both collagen type I and collagen type III have been immunolocalized in the components of the collagen fibrillar skeleton of the pregnant camel endometrium. It seems that collagen type I concentration is not affected by pregnancy but a change in its arrangement and distribution is seen. The role of type I in the formation of placental blood vessels is discussed. Collagen type III has shown variations in its amount during the periods examined, indicating that uterine collagenous structures change during different periods of pregnancy. The role of this type of collagen in relation to the other extracellular matrix components of the pregnant camel endometrium is discussed. The foetal placenta (trophoblast, chorion) of the camel was found to be composed of uninucleate cuboidal cells, multinucleate giant cells and the areolar epithelium. Foetal and maternal requirements change during pregnancy. It is not surprising, therefore, that submicroscopic variations in trophoblast morphology were found in this study. The three types of trophoblastic cells showed changes in their ultrastructure as well as variations in the type and number of cell organelles and inclusions all one stage examined. Uninucleate cuboidal epithelial cells during early gestation show features which may be correlated with secretion of a proteinaceous product, and the performance of normal non- endocrine placental activities. During mid-pregnancy, stage their ultrastructure is correlated with production of placental steroid hormones. In late gestation, their fine structure indicates protein secretion. It is speculated that their product may be a placental lactogen. The multinucleate giant cells develop at frequent but irregular intervals along the trophoblast layer and they are often situated over the mouth of an endometrial gland and/or closely associated with a chorioallantoic vessel. Their number varies during different gestational periods. They reach a maximum during earlier and later stages of gestation and a minimum during mid-pregnancy stage. Their ultrastructure indicates presence of two types of cells, one concerned with lipid and glycogen storage and seems to play an important role in the nutrition of the foetus. This type also contains numerous pinocytotic vesicles and transfer tubules which are said to be involved in, or as a bypass for the endocytic lysosomal pathway protein uptake in placenta of some species. Giant cells may also function in the assembly or activation of informational macromolecules stored in the cytoplasm since they contain annulate lamellae. The other type of giant cells shows an ultrastructure indicative of the production of placental steroid hormones. This study provides a morphological evidence for previous hormonal studies which indicated that oestrogen secreted by foetal tissues is the singal for maternal recognition of pregnancy in camel. The site of this oestrogen is the second type of giant cell, since both types are found in large numbers earlier in gestation. The camel multinucleated giant cells are quite unlike the foetal binucleate (giant) cells (BNCs) which characterize the ruminant placenta. They are also very different from the large binueleate foetal endometrial cup cells which are reported in the horse placenta. They are also unlike the various giant cells which are found in the placentae of many rodents. Their differences from all these types of cells are discussed. The camel giant cells remain localized to the trophoblast and they neither fuse with, nor migrate into maternal tissue. The possible functions of these cells during different periods of gestation are discussed. Both regular and irregular areolae are observed in the placenta of the camel during this study. However, mucous areolae are not encountered. In the metabolic economy of the developing camel foetus the areola gland subunits are of fundamental importance since they serve as specialized areas for maternofoetal substance transfer. The fine structure of the areolar epithelium is indicative of highly absorptive epithelium. The areolar specific vessel systems are important for sustaining the characteristic substance transfer in the areola, as well as secretion, metabolism and absorption. The present morphological data give an indirect evidence for a uteroferrin mediated iron transport via the areolae of the camel placenta. In early pregnancy, the camel placenta consists of a simple apposition of foetal and maternal epithelia, but it becomes more complex with the formation of the foetal villi during mid and late stages of gestation. Although the placental barrier maintains an epitheliochorial arrangement throughout the course of pregnancy, a thinning of the maternal epithelium and a progressive indentation of the chorionic epithelium by foetal capillaries shortens the length of diffusion pathway and reduces the amount of placental tissue between foetal and maternal blood streams. These structural modifications may reflect the changing requirements of the foetus for oxygen and other metabolites as gestation proceeds. During the first half of pregnancy, there is an evidence of intense pinocytotic activity by the cells of the trophoblast. During mid pregnancy, there is a pronounced development of smooth endoplasmic reticulum, while rough endoplasmic reticulum and irregular, dense, membrane-bound bodies are a prominent feature of the paranuclear cytoplasm during the third trimester of gestation. These changes suggest that the cell of the trophoblast become more highly involved in synthetic processes with increasing gestational age. The allantois of the camel showed a structure similar to that of other mammalian species. The possible function of allantois is discussed. Examination of the fine structure of the additional foetal membrane of camel revealed similarity to the human amnion. The presence of keratin granules in the inner membrane epithelium indicates its origin from the foetal epidermis. The different layers of the membrane have been described in details. Depending on the morphological characteristics, the possible functions are discussed. It seems that this membrane plays an important role, other than just a mechanical one, during gestation and parturition. The present morphological data indicate that there are regional specializations in camel placenta and that the latter is more complex than was thought before.
Morphology of the Ovary, Endometrium and Placenta of the Dromedary