Many principles of embryology apply to both invertebrate animals as well as to vertebrates. 1 Vertebrate and invertebrate embryology.Human embryo at six weeks gestational age These similarities among species are called analogous structures, which are structures that have the same or similar function and mechanism, but evolved separately. The reason for this similarity is because species have adapted into the environment of pregnancy. Embryos in many species often appear similar to one another in early developmental stages. Beyond the eighth week, the developing human is then called a fetus.
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In humans, the term embryo refers to the ball of dividing cells from the moment the zygote implants itself in the uterus wall until the end of the eighth week after conception. The outer layer of cells, or ectoderm, gives rise to the nervous system and skin.The middle layer, or mesoderm, gives rise to the muscles, skeleton and blood system.The innermost layer, or endoderm, gives rise to the digestive organs, lungs and bladder.The gastrula with its blastopore soon develops three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop: In due course, the blastula changes into a more differentiated structure called the gastrula.ġ - blastula, 2 - gastrula with blastopore orange - ectoderm, red - endoderm. The protostomes include most invertebrate animals, such as insects, worms and molluscs, while the deuterostomes includes more advanced animals including the vertebrates.
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If in the blastula the first pore ( blastopore) becomes the mouth of the animal, it is a protostome if the first pore becomes the anus then it is a deuterostome. In animals, the blastula develops in one of two ways that divides the whole animal kingdom into two halves. After cleavage, the dividing cells, or morula, becomes a hollow ball, or blastula, which develops a hole or pore at one end. An embryo is defined as any organism in a stage before birth or hatching.Įmbryology refers to the development of the fertilized egg cell ( zygote) and its differentiation into tissues and organs.
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It is the process by which genetic instructions are reproduced in anatomical form.An embryo is defined as any organism in a stage before birth or hatching.Įmbryology is of significance to psychologists for a number of reasons:. Please help to improve this page yourself if you can.Įmbryology is the study of the development of an embryo. This article needs rewriting to enhance its relevance to psychologists.