Eclampsia pathophysiology: Difference between revisions
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These consist of the fetal portion of the placenta. They are offshoots or very small finger-like processes, hence called the [[villi]], from the surface of the trophoblast cells. Within the substance of these villi are fetal blood capillaries and fetal blood cells which arise from the [[extra-embryonic mesoderm]]. Since the trophoblast and the extra-embryonic mesoderm constitutes the [[chorion]], these villi are also known as [[chorionic villi]]. | These consist of the fetal portion of the placenta. They are offshoots or very small finger-like processes, hence called the [[villi]], from the surface of the trophoblast cells. Within the substance of these villi are fetal blood capillaries and fetal blood cells which arise from the [[extra-embryonic mesoderm]]. Since the trophoblast and the extra-embryonic mesoderm constitutes the [[chorion]], these villi are also known as [[chorionic villi]]. | ||
=====[[Chorionic fundosum]]===== | =====[[Chorionic fundosum]]===== | ||
Originally the villi are formed all over the trophoblast and commence invading the surrounding decidua. Nevertheless gradually the villi related to the ''[[decidua capsularis]]'' degenerate and in contrast, those associated with the decidua basalis undergo further differentiation and substantial growth and helps form the placenta. This part is known as ''[[chorion fundosum]]''. | Originally the villi are formed all over the trophoblast and commence invading the surrounding decidua. Nevertheless gradually the villi related to the ''[[decidua capsularis]]'' degenerate and in contrast, those associated with the decidua basalis undergo further differentiation and substantial growth and helps form the placenta. This part is known as ''[[chorion fundosum]]''. During the [[differentiation]] process, the trophoblast which is originally a single layer of cells multiplies into two distinct layers. The cells in the superficial layer, that is the layer which is in proximity with the decidua, lose their cell boundaries and mould into one consecutive layer of cytoplasm and several nuclei, known as the ''[[syncytiotrophoblast]]''. The second layer cells, which rest on extra-embryonic mesoderm, however retain their cell walls and are known as the ''[[cytotrophoblast]]''. | ||
====[[Placenta]]==== | ====[[Placenta]]==== | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
While multiple theories have been proposed to explain preeclampsia and eclampsia, it occurs only in the presence of a placenta and is resolved by its removal.[1] E. W. Page suggested that placental hypoperfusion is a key feature of the process. It is accompanied by increased sensitivity of the maternal vasculature to pressure agents leading to vasospasm and hypoperfusion of multiple organs. Further, an activation of the coagulation cascade leads to microthombi formation and aggravates the perfusion problem. Loss of plasma from the vascular tree with the resulting edema additionally compromises the situation. These events lead to signs and symptoms of toxemia including hypertension, renal, pulmonary, and hepatic dysfunction, and - in eclampsia specifically - cerebral dysfunction.[1] Preclinical markers of the disease process are signs of increased platelet and endothelial activation.[1]
Pathophysiology
Anatomy and Physiology of placenta
The formation of the placenta commences with the development of trophoblast. After the fertilization of the ovum in the fallopian tubes, it travels towards the uterus and by the time it reaches the uterus it has already become a morula. The morula is still surrounded by the zona pellucida which prevents it from sticking to the walls of the tube. The zona pellucida disappears soon after the blastocyst reaches the uterine cavity. Now the cells lining the blastocyst constitute the trophoblast whose function is to invade the surrounding uterine tissues to provide nutrition to the developing blastocyst. When the trophoblast attaches to the endometrium, it is known as implantation, which begins on the sixth day after fertilization in humans. This process is additionally enhanced by the proteolytic enzymes produced by the trophoblast and the interaction between the receptors present uterine epithelium and L-selectin and integrins produced by the trophoblast cells. Hence, implantation is a result of mutual exchange between the endometrium of the uterine cavity and the trophoblastic cells surrounding the blastocyst.
Decidua
After the implantation, the uterine endometrium is termed the Decidua. Once the implantation has occurred the stromal cells undergo a decidual reaction which consists of enlargement of the cells, vacuolisation and storage of glycogen and lipids.
Decidua basalis
- The area of the endometrium or decidua that is deep to the blastocyst, where the placenta is to be formed is inferred as decidua basalis. It consists of the terminally differentiated large stromal cells which encompass largely lipids and glycogen that acts as a source of nutrition for the embryo. It also comprises of maternal vascular cells and maternal blood cells inside and outside those vessels.
- This area is also known as the decidual plate and it is firmly united to the chorion.
- The stromal cells also produce a variety of humoral proteins such as insulin-like growth factor binding proteins and prolactin and its family proteins.
Chorionic villi
These consist of the fetal portion of the placenta. They are offshoots or very small finger-like processes, hence called the villi, from the surface of the trophoblast cells. Within the substance of these villi are fetal blood capillaries and fetal blood cells which arise from the extra-embryonic mesoderm. Since the trophoblast and the extra-embryonic mesoderm constitutes the chorion, these villi are also known as chorionic villi.
Chorionic fundosum
Originally the villi are formed all over the trophoblast and commence invading the surrounding decidua. Nevertheless gradually the villi related to the decidua capsularis degenerate and in contrast, those associated with the decidua basalis undergo further differentiation and substantial growth and helps form the placenta. This part is known as chorion fundosum. During the differentiation process, the trophoblast which is originally a single layer of cells multiplies into two distinct layers. The cells in the superficial layer, that is the layer which is in proximity with the decidua, lose their cell boundaries and mould into one consecutive layer of cytoplasm and several nuclei, known as the syncytiotrophoblast. The second layer cells, which rest on extra-embryonic mesoderm, however retain their cell walls and are known as the cytotrophoblast.
Placenta
The tissues of desidua basalis and chorion fundosum jointly form a disc-shaped structure called the placenta.
Pathophysiology
Placental hypoperfusion is linked to abnormal modeling of the fetal-maternal interface that may be immunologically mediated[1] The invasion of the trophoblast appears to be incomplete.[2] Adrenomedullin, a potent vasodilator, is produced in diminished quantities by the placenta in preeclampsia (and thus eclampsia).[3] Other vasoactive agents are at play including prostacyclin, thromboxane A2, nitric oxide, and endothelins leading to vasoconstriction.[4] Many studies have suggested the importance of a woman's immunological tolerance to her baby's father, whose genes are present in the young fetus and its placenta and which may pose a challenge to her immune system.[5]
Eclampsia is seen as form of a hypertensive encephalopathy in the context of those pathological events that lead to preeclampsia. It is thought that cerebral vascular resistance is reduced, leading to increased blood flow to the brain. In addition to abnormal function of the endothelium, this leads to cerebral edema.[6] Typically an eclamptic seizure will not lead to lasting brain damage; however, intracranial hemorrhage may occur.[7]
Histopathology
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References
- ↑ 1.0 1.1 1.2 1.3 JM Roberts, DW Cooper. "Series, Pre-eclampsia trio. Pathogenesis and genetics of pre-eclampsia". The Lancet 2001; 357:53-56.
- ↑ Zhou Y, Fisher SJ, Janatpour M, Gembacev O, Dejana E, Wheelock M; et al. "Human cytotrophoblasts adopt a vascular phenotype as they differentiate: a strategy for successful endovascular invasion?". J Clin Invest 1997;99:2139-51.
- ↑ Hongshi L., Dakour J, Kauman S, Guilbert LJ, Winkler-Lowen B, Morrish DW. "Adrenomedullin is decreased in preeclampsia because of failed response to epidermal growth factor and impaired syncytialization". Hypertension 2003, vol. 42, no5, pp. 895-900.
- ↑ ACOG. "Diagnosis and Management of Preeclampsia and Eclampsia". ACOG Practice Bulletin # 33, 2002,.
- ↑ "Sex Primes Women for Sperm". BBC News. 2002-02-06. Text " http://news.bbc.co.uk/2/hi/health/1803978.stm" ignored (help); Check date values in:
|date=(help);|access-date=requires|url=(help) - ↑ Cipolla MJ (2007). "Cerebrovascular function in pregnancy and eclampsia". Hypertension. 50 (1): 14–24. doi:10.1161/HYPERTENSIONAHA.106.079442. PMID 17548723. Unknown parameter
|month=ignored (help) - ↑ Richards A, Graham D, Bullock R. "Clinicopathological study of neurological complications due to hypertensive disorders of pregnancy". J Neurol Neurosurg Psychiatry 1988;51:416-21.