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The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle . In humans, the yolk sac is important in early embryonic blood supply.
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. [1] It develops mostly from the mesenchyme , derived from the mesoderm , the middle embryonic germ layer . [ 2 ]
1.3.1 Central nervous system. ... This is a list of cells in humans derived from the three embryonic germ layers – ectoderm, ...
Haematopoietic stem cells that give rise to all the blood cells develop from the mesoderm. The development of blood formation takes place in clusters of blood cells, known as blood islands, in the yolk sac. Blood islands develop outside the embryo, on the umbilical vesicle, allantois, connecting stalk, and chorion, from mesodermal hemangioblasts.
The bulk of the villi consist of connective tissues that contain blood vessels. Most of the cells in the connective tissue core of the villi are fibroblasts. Macrophages known as Hofbauer cells are also present.
The blood within the umbilical cord, known as cord blood, is a rich and readily available source of primitive, undifferentiated stem cells (of type CD34-positive and CD38-negative). These cord blood cells can be used for bone marrow transplant.
The amniotic sac, also called the bag of waters [1] [2] or the membranes, [3] is the sac in which the embryo and later fetus develops in amniotes.It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shortly before birth.
Mesenchyme (/ ˈ m ɛ s ə n k aɪ m ˈ m iː z ən-/ [1]) is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. [2] [3] The interactions between mesenchyme and epithelium help to form nearly every organ in the developing embryo. [4]