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Fetal Membranes
The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals.. They are the amnion, chorion, allantois, and yolk sac. The amnion and the chorion are the chorioamniotic membranes that make up the amniotic sac which surrounds and protects the embryo. The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord. Structure The fetal membranes surround the developing embryo and form the fetal-maternal interface. The fetal membranes are derived from the trophoblast layer (outer layer of cells) of the implanting blastocyst. The trophoblast layer differentiates into amnion and the chorion, which then comprise the fetal membranes. The amnion is the innermost layer and, therefore, contacts the amniotic fluid, the fetus and the umbilical cord. The internal pressure of the amniotic fluid causes the amn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extraembryonic Membrane
The extraembryonic membranes are four membranes which assist in the development of an animal's embryo. Such membranes occur in a range of animals from humans to insects. They originate from the embryo, but are not considered part of it. They typically perform roles in nutrition, gas exchange, and waste removal. There are four standard extraembryonic membranes in birds, reptiles, and mammals: the yolk sac which surrounds the yolk, the amnion which surrounds and cushions the embryo, the allantois which among avians stores embryonic waste and assists with the exchange of carbon dioxide with oxygen as well as the resorption of calcium from the shell, and the chorion which surrounds all of these and in avians successively merges with the allantois in the later stages of egg development to form a combined respiratory and excretory organ called the chorioallantois. The extraembryonic membranes in insects include a serous membrane originating from blastoderm cells, an amnion or amniot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amniotic Fluid
The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus. For humans, the amniotic fluid is commonly called water or waters (Latin liquor amnii). Development Amniotic fluid is present from the formation of the gestational sac. Amniotic fluid is in the amniotic sac. It is generated from maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces. When fetal kidneys begin to function around week 16, fetal urine also contributes to the fluid. In earlier times, it was believed that the amniotic fluid was composed entirely of fetal urine. The fluid is absorbed through the fetal tissue and skin. After 22 to 25 week of pregnancy, keratinization of an embryo's skin occurs. When this process completes around the 25th week, the fluid is primarily absor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, and language. Humans are highly social and tend to live in complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established a wide variety of values, social norms, and rituals, which bolster human society. Its intelligence and its desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, philosophy, mythology, religion, and other fields of study. Although some scientists equate the term ''humans'' with all members of the genus ''Homo'', in common usage, it generally refers to ''Homo sapiens'', the only extant member. Anatomically moder ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bilaminar Embryonic Disc
The bilaminar embryonic disc, bilaminar blastoderm or embryonic disc is the two-layered structure of epiblast and hypoblast, differentiated from the inner cell mass also known as the embryoblast. These two layers of cells lie between two cavities: the primitive yolk sac and the amniotic cavity. The inner cell mass, begins to transform into two distinct epithelial layers just before implantation is completed. The epiblast, also known as the primitive ectoderm, is the outer layer that consists of columnar cells. The inner layer is called the hypoblast, also known as the primitive endoderm, which is composed of cuboidal cells. As the two layers become evident, a basement membrane presents itself between the layers. The final two layers of the embryoblast are known collectively as the bilaminar embryonic disc. This bilaminar disc also defines the primitive dorsal ventral axis. Blastocyst implantation will occur during the second week of embryonic development in the endometrium of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypoblast
In amniote embryology, the hypoblast, is one of two distinct layers arising from the inner cell mass in the mammalian blastocyst, or from the blastodisc in reptiles and birds. The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion. The hypoblast is a layer of cells in fish and amniote embryos. The hypoblast helps determine the embryo's body axes, and its migration determines the cell movements that accompany the formation of the primitive streak, and helps to orient the embryo, and create bilateral symmetry. The other layer of the inner cell mass, the epiblast, differentiates into the three primary germ layers, ectoderm, mesoderm, and endoderm. Structure The hypoblast lies beneath the epiblast and consists of small cuboidal cells. The hypoblast in fish (but not in birds and mammals) contains the precursors of both the endoderm and mesoderm. In birds and mammals, it contains precursors to the extraembryonic endoderm of the yolk sac. In chick embr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chorionic Villi
Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood. They are an essential element in pregnancy from a histomorphologic perspective, and are, by definition, a product of conception. Branches of the umbilical arteries carry embryonic blood to the villi. After circulating through the capillaries of the villi, blood returns to the embryo through the umbilical vein. Thus, villi are part of the border between maternal and fetal blood during pregnancy. Structure Villi can also be classified by their relations: * Floating villi float freely in the intervillous space. They exhibit a bi-layered epithelium consisting of cytotrophoblasts with overlaying syncytium ( syncytiotrophoblast). * Anchoring (stem) villi stabilize mechanical integrity of the placental-maternal interface. Development The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Connective Tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. The three meninges, membranes that envelop the brain and spinal cord are composed of connective tissue. Most types of connective tissue consists of three main components: elastic and collagen fibers, ground substance, and cells. Blood, and lymph are classed as specialized fluid connective tissues that do not contain fiber. All are immersed in the body water. The cells of connective tissue include fibroblasts, adipocytes, macrophages, mast cells and leucocytes. The term "connective tissue" (in German, ''Bindegewebe'') was introduced in 1830 by Johannes Peter Müller. The tissue was already recognized as a distinct class in the 18th century. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basement Membrane
The basement membrane is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between Epithelium, epithelial tissues including mesothelium and endothelium, and the underlying connective tissue. Structure As seen with the electron microscope, the basement membrane is composed of two layers, the basal lamina and the reticular lamina. The underlying connective tissue attaches to the basal lamina with collagen VII anchoring fibrils and fibrillin microfibrils. The basal lamina layer can further be subdivided into two layers based on their visual appearance in electron microscopy. The lighter-colored layer closer to the epithelium is called the lamina lucida, while the denser-colored layer closer to the connective tissue is called the lamina densa. The Electron microscope, electron-dense lamina densa layer is about 30–70 nanometers thick and consists of an underlying ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycocalyx
The glycocalyx, also known as the pericellular matrix, is a glycoprotein and glycolipid covering that surrounds the cell membranes of bacteria, epithelial cells, and other cells. In 1970, Martinez-Palomo discovered the cell coating in animal cells, which is known as the glycocalyx. Animal epithelial cells have a fuzz-like coating on the external surface of their plasma membranes. This viscous coating consists of several carbohydrate moieties of membrane glycolipids and glycoproteins, which serve as backbone molecules for support. Generally, the carbohydrate portion of the glycolipids found on the surface of plasma membranes helps these molecules contribute to cell–cell recognition, communication, and intercellular adhesion. The glycocalyx is a type of identifier that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, or invading organisms. Included in the glycocalyx are cell-adhesion molecules that enable cells to adhere to eac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microvillus
Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction. Structure Microvilli are covered in plasma membrane, which encloses cytoplasm and microfilaments. Though these are cellular extensions, there are little or no cellular organelles present in the microvilli. Each microvillus has a dense bundle of cross-linked actin filaments, which serves as its structural core. 20 to 30 tightly bundled actin filaments are cross-linked by bundling proteins fimbrin (or plastin-1), villin and espin to form the core of the microvilli. In the enterocyte microvillus, the structural core is attached to the plasma membrane along its length by lateral arms made of myosin 1a and Ca2+ binding protein calmodulin. Myosin 1a functions through a binding site for filamentous ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fetal Surface Vessels
Chorionic (plate) vessels, also fetal surface vessels are blood vessels, including both arteries and veins, that carry blood through the chorion in the fetoplacental circulation. Chorionic arteries branch off the umbilical artery, and supply the capillaries of the chorionic villi. Increased vasocontractility of chorionic arteries may contribute to preeclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease .... References Embryology of cardiovascular system {{circulatory-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Avascular
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality. There are five types of blood vessels: the arteries, which carry the blood away from the heart; the arterioles; the capillaries, where the exchange of water and chemicals between the blood and the tissues occurs; the venules; and the veins, which carry blood from the capillaries back towards the heart. The word ''vascular'', meaning relating to the blood vessels, is derived from the Latin ''vas'', meaning vessel. Some structures – such as cartilage, the epithelium, and the lens and cornea of the eye – do not contain blood vessels and are labeled ''avascular''. Etymology * artery: late Middle English; from Latin ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
