Elementary unit of all life on Earth is a cell.It is the formation of new cells allow the body to grow and develop.Life and the structure of these units is very difficult and depends on the specific destination.
emergence of the term "zygote»
emergence of the term "zygote" is a tribute to the German scholar Edward Strasburger, who dedicated his life to the study of cytology and the chromosomal theory of heredity.It was he who in the late XIX century, first came to the conclusion that cell division in the plant, animal and human body is approximately the same scheme.
Zygote: the definition
sex cells (gametes) perform reproductive function, that is, because of their presence in the body through sexual reproduction possible.Female gametes - the egg is, men - sperm.Each gamete is haploid (single) set of chromosomes.
term "ontogeny" includes all stages of development of an organism from conception to death.Its beginning - is fertilized, that is a fusion of sperm and egg, resulting in the formation of the zygote.It is the genetic information received from both parents.What is a zygote?Biology gives a precise definition of this concept.We will consider it in detail.
So zygote - a diploid cells, which are formed by the fusion of gametes.Due to the full diploid (double) set of chromosomes, equivalent received from the paternal and maternal gametes.The development of the zygote begins immediately after the fertilization process, which is called fertilization.
Upon completion of the process of fertilization to obtain cells moves into the uterus.Along the way, it is already beginning to happen, and the development of crushing the zygote.This is a complex process consisting of several stages.
between fertilization and the first mitotic division takes about 30 hours.This is the time in a woman's body are all the preparatory processes, which are indispensable for the development of a new organism.Prevent further formation of the embryo may be a variety of factors that affect the status of the woman's body.Such factors include chromosomal mutations, wrong lifestyle mother (alcohol, drugs, smoking), use of certain medications, severe viral diseases, etc.
developing embryo from the zygote.The first stage of this process - crushing.This is not a random name.After all, no divisions between the stage of cell growth that is due to each of them exactly in half cells decrease in size, becoming smaller.Daughter cells formed by crushing the zygote, are called "blastomeres."The crushing process lasts until such time as it is not formed from the embryo.Thus, we can say that the human body is a result of multi-billion dollar division of the zygote.
Phase blastula and gastrulation
blastomeres are composed of two layers.External adjacent to the transparent envelope.It is called the trophoblast (nutrient leaf), and the outer - embryoblast (embryonic leaf).Gradually, during the repeated division between these two layers is a cavity inside which there is a fluid buildup.This moment is a phase of blastula.
cell reproduction embryoblast accompanied by its growth of the wall cavity.As a consequence of the emergence of the second layer occurs embryoblast that forms the yolk vesicle.Simultaneously with the process of the bulk embryoblast formed the germ of the fruit are grouped on one of the poles.It is at this stage of the embryo reaches the uterus.In the future, there is its liberation from the transparent cover and implantation.
trophoblast in this process plays an important role, because its cells, having a proteolytic properties melted epithelium in the place of attachment of the embryo to the uterine lining.As a result, the epithelium becomes lactescent mass.
stages of zygote rather quickly succeed each other.Blastula turns to gastrula, which is a dual-layer balloon.The outer layer - the ectoderm is, lower - the endoderm.
zygote - the first cell of new organisms.The entire set of required for life of originally formed from them.The process of formation of organs is called organogenesis.It marked the beginning of the formation of the neural plate, which occurs in the ectoderm on the dorsal side of the embryo.Then there are the rudiments of other organs and systems: the skin and the nervous system (from the ectoderm);digestive and respiratory systems (from the endoderm);musculoskeletal system, circulatory, excretory, and reproductive systems (from the mesoderm).Further, up to the moment of birth, these systems are developed and improved.
This period starts from birth to the onset of puberty.Depending on the level of organization of organisms, there are two types of embryonic development.
- direct development.In this case, the child of the external and internal features similar to their parents.The differences in size and underdevelopment of some organs.Characteristic for birds and mammals, including humans.
- Indirect development.In this type of development, the child (larva) has many differences with their parents.It is characteristic for frogs and insects.
zygote - a cell duplicates genotype parents.But in the process of development of the embryo cells start to vary in structure and perform various functions.This is due to the fact that some types of gene function in some cells, while others elsewhere.Thus, the body is a complex structural system which is based on the zygote.