The embryonic period of development begins. Embryonic period of development

The embryonic period of human development includes the time from the moment and continues until the 8th week of pregnancy. Conventionally, it is customary to subdivide it into 4 stages, each of which has its own characteristics. Let's talk about them in more detail.

What are the stages of embryogenesis?

The embryonic period of development in humans takes 2 months - that is how long the processes of transformation of the embryo into a fetus last. As a result of this process, a body is formed that has practically the same morphological features as the body of an adult.

The first step is the formation of a zygote. It is formed as a result of the fusion of male and female germ cells. This period is rather short. After that comes the crushing stage.

During this period, there is an intensive reproduction of cells. In this case, the cells formed by crushing are called the blastomere. First, a small cluster of these cells is formed, which in its external shape resembles a raspberry, and is called morula. With further crushing, the number of cells increases and the morula takes on a more rounded shape, the blastula.

After crushing, the next, third stage of the embryonic period of development of the organism begins - gastrulation. It involves the transformation of a single-layered embryo into a two-layered one, i.e. Simply put, the shells are doubling. In this case, the gastrula itself consists of 2 germ layers, ecto- and endoderm. In the course of the evolution of all living things, the process of gastrulation became more complicated with the formation of an axial complex (neural tube, axial skeleton, muscles), which is laid on the dorsal side of the embryo from the 3rd germ layer.

The fourth period involves the isolation of the main rudiments of organs and tissues, as well as their further development. Along with this, there is an enhanced integration of parts into a single whole. So, from the outer layer of the endoderm, the epithelial tissue lining the alimentary canal, as well as its glands, is formed. From the mesoderm - the muscles, as well as the epithelium of the genitourinary system, the serous membranes of the brain. From the mesenchyme, connective, cartilaginous, bone tissue, and the vascular system are formed.

How is the laying of the main organs and systems?

Having listed all the stages of the embryonic period of development, we will also tell you what systems and organs are formed in each of its weeks. So, the process of crushing during the formation of a human embryo lasts about 3-4 days. During this time, it moves through the fallopian tubes to the cavity. As a result of the crushing process, from the blastomeres located on the surface, the shell is formed, which is involved in the process of nourishing the embryo - the trophoblast. Those blastomeres that are located directly in the center form the embryoblast, from which the future body of the embryo is formed.

From about the second week of the onset of the development process, the embryo sinks into the wall of the uterus. At the same time, the formation of structures such as the yolk and amniotic vesicles is observed. After they are overgrown with mesenchyme, an amnion is formed. This is essentially a water shell that forms a bag, which is subsequently filled with the well-known amniotic fluid.

Approximately at the 3rd week of embryonic development, a dense strand of growing cells is released from the back of the embryo. Its so-called head section, thickening, forms a primary nodule. It is this structure that gives rise to such an anatomical formation as the neural tube.

At week 4, separating separately from the extraembryonic membranes, as a result of increased growth, the embryo undergoes primary segmentation, i.e. separate segments of the body of the future fetus are formed. Parallel to this, there is First stage process of organogenesis and histogenesis.

Already by the 5th week of pregnancy, the rudiments of the arms and legs can be clearly identified, and by the 6th week the limbs are divided into main segments. Around the end of the 7th week, during an ultrasound scan, you can see the beginnings of the fingers. So, at week 8 (this is how long the embryonic period lasts), the laying of the rudiments of the organs of the embryo ends.

In order to visually present the main stages of the embryonic period of development, we present a table below in which they are displayed.

1. Where does the mammalian embryo develop?

The fertilized egg enters the uterus, where the process of its fixation and development takes place.

2. What is a zygote?

A zygote is a single-celled stage in the development of an organism that occurs as a result of the fusion of a spermatozoon and an egg.

Questions

1. How does the embryonic period of development begin and end?

The embryonic period (embryogenesis) begins at the moment of zygote formation and ends with birth (for example, in mammals) or exit from the egg membranes (for example, in birds).

2. How does the postembryonic period of development begin and end?

The postembryonic period begins from the moment of birth or the release of the organism from the egg membranes and lasts until the end of the life of the individual.

3. What development is called direct? Give examples of animals with direct development.

Postembryonic development is called direct, when a creature similar to an adult (reptiles, birds, mammals) appears from the mother's egg or organism.

4. What development is called indirect? Give examples of animals with indirect development.

Postembryonic development is called indirect, when the larva formed in the embryonic period is simpler than the adult organism, and differs from it in the ways of feeding, movement, etc. (intestinal, flat and annelids, crustaceans, insects, amphibians).

5. What is the Müller-Haeckel biogenetic law?

Individual development individual (ontogenesis) to a certain extent repeats the historical development of the species (phylogenesis) to which the given individual belongs.

6. What is the meaning of the biogenetic law?

The biogenetic law is very important, since it testifies to the common ancestors of animals belonging to different systematic groups. It allows the use of embryological data to reconstruct the course of phylogenesis.

Tasks

1. Using the knowledge gained in the study of the "Animals" section, give examples of postembryonic development associated with a change in lifestyle and habitat.

In a frog, for example, a larva (tadpole) develops from an egg, which differs from adult animals in structure, lifestyle and habitat. The tadpole, like fish, has gills, a lateral line organ, a tail, a two-chambered heart, and one circle of blood circulation. The larva feeds, grows and eventually turns into a frog.

The presence of the larval stage in the development of amphibians and many other animals provides them with the opportunity to live in different environments and use different food sources. Thus, the tadpole lives in water and feeds on plant food, while the frog leads mainly a terrestrial lifestyle and feeds on animal food.

A change in habitat and, as a result, a change in the way of life of an animal during its transition from the larval stage to an adult organism reduces intraspecific competition. In addition, in some sedentary or attached animals ( coral polyps, oysters, mussels, etc.) free-swimming larva contributes to the resettlement of the species, expanding its range. This avoids overpopulation, which would lead to increased competition for food and other resources that would threaten the survival of the species.

2. In early period development, the heart of the human embryo consists of one atrium and one ventricle. Based on the provisions of the biogenetic law, comment on this fact.

The human embryo in the process of individual development repeats the past stage of evolution (a two-chambered heart is a sign of fish).

1. Where does the mammalian embryo develop?

The fertilized egg enters the uterus, where the process of its fixation and development takes place.

2. What is a zygote?

A zygote is a single-celled stage in the development of an organism that occurs as a result of the fusion of a spermatozoon and an egg.

Questions

1. How does the embryonic period of development begin and end?

The embryonic period (embryogenesis) begins at the moment of zygote formation and ends with birth (for example, in mammals) or exit from the egg membranes (for example, in birds).

2. How does the postembryonic period of development begin and end?

The postembryonic period begins from the moment of birth or the release of the organism from the egg membranes and lasts until the end of the life of the individual.

3. What development is called direct? Give examples of animals with direct development.

Postembryonic development is called direct, when a creature similar to an adult (reptiles, birds, mammals) appears from the mother's egg or organism.

4. What development is called indirect? Give examples of animals with indirect development.

Postembryonic development is called indirect, when the larva formed during the embryonic period is simpler than the adult organism, and differs from it in the ways of feeding, movement, etc. (intestinal, flat and annelids, crustaceans, insects, amphibians).

5. What is the Müller-Haeckel biogenetic law?

The individual development of an individual (ontogeny) to a certain extent repeats the historical development of the species (phylogenesis) to which the given individual belongs.

6. What is the meaning of the biogenetic law?

The biogenetic law is very important, since it testifies to the common ancestors of animals belonging to different systematic groups. It allows the use of embryological data to reconstruct the course of phylogenesis.

Tasks

1. Using the knowledge gained in the study of the "Animals" section, give examples of postembryonic development associated with a change in lifestyle and habitat.

In a frog, for example, a larva (tadpole) develops from an egg, which differs from adult animals in structure, lifestyle and habitat. The tadpole, like fish, has gills, a lateral line organ, a tail, a two-chambered heart, and one circle of blood circulation. The larva feeds, grows and eventually turns into a frog.

The presence of the larval stage in the development of amphibians and many other animals provides them with the opportunity to live in different environments and use different food sources. Thus, the tadpole lives in water and feeds on plant food, while the frog leads mainly a terrestrial lifestyle and feeds on animal food.

A change in habitat and, as a result, a change in the way of life of an animal during its transition from the larval stage to an adult organism reduces intraspecific competition. In addition, in some sedentary or attached animals (coral polyps, oysters, mussels, etc.), the free-swimming larva contributes to the dispersal of the species and the expansion of its range. This avoids overpopulation, which would lead to increased competition for food and other resources that would threaten the survival of the species.

2. In the early period of development, the heart of the human embryo consists of one atrium and one ventricle. Based on the provisions of the biogenetic law, comment on this fact.

The human embryo in the process of individual development repeats the past stage of evolution (a two-chambered heart is a sign of fish).

"Introduction to General Biology and Ecology. Grade 9". A.A. Kamensky (gdz)

Embryonic and postembryonic periods of development of the organism. biogenetic law

Question 1. How does the embryonic period of development begin and end?
Embryonic period(Greek embryon - embryo) begins with fertilization and the formation of a zygote. The end of this period in different types of ontogeny is associated with different moments of development.
The embryonic period is divided into the following stages:
1) fertilization - the formation of a zygote;
2) crushing - the formation of blastula;
3) gastrulation - the formation of germ layers;
4) histo- and organogenesis - the formation of organs and tissues of the embryo.
In the larval form of ontogenesis, the embryonic period begins with the formation of a zygote and ends with the exit from the egg membranes.
In the non-larval form of ontogenesis, the embryonic period begins with the formation of a zygote and ends with the exit from the embryonic membranes.
With the intrauterine form of ontogenesis, the embryonic period begins with the formation of a zygote and lasts until birth.

Question 2. How does the postembryonic period of development begin and end?Postembryonic period begins with the birth (for example, in mammals) or the release of the body from the egg membranes (for example, in reptiles, birds) and lasts until the end of his life. From the moment of the birth of the organism or the release of the organism from the egg membranes, a period of postembryonic development begins. Postembryonic development can be direct, when a creature similar to an adult (reptiles, birds, mammals) appears from an egg or mother's body, and indirect, when a larva formed in the embryonic period is simpler than an adult organism, and differs from it in ways of feeding, movement and others (coelenterates, flat and annelids, crustaceans, insects, amphibians).
Postembryonic development of animals is divided into three periods:
The period of growth and shaping (pre-reproductive). This period is characterized by the continuation of organogenesis that began in embryonic life and an increase in body size. By the beginning of this period, all organs have reached the degree of differentiation at which the young animal can exist and develop outside the mother's body or outside the egg membranes. From this moment, the digestive tract, respiratory organs and sensory organs begin to function. The nervous, circulatory and excretory systems begin their function even in the embryo. During the period of growth and shaping, the species and individual characteristics of the organism are finally formed, and the individual reaches the dimensions characteristic of the species. Later, other organs differentiate the reproductive system. When its formation ends, the second stage of postembryonic development begins.
Maturity (reproductive). During this period of maturity, reproduction occurs. The duration of this period is different for different species of animals. In some species (mayflies, silkworm) it lasts only a few days, in others it lasts for many years.
The period of old age (post-reproductive). It is characterized by a decrease in the intensity of metabolism and involution of organs. Aging leads to natural death.

Question 3. What organ systems are formed from the ectoderm; endoderm; mesoderm?
At the end of the crushing period, the embryos of all multicellular animals enter the period of formation of germ layers (leaves). This stage is called gastrulation.
There are two stages in the process of gastrulation. First, an early gastrula is formed, which has two germ layers: the outer one is the ectoderm and the inner one is the endoderm. Then comes the late gastrula, when the middle germ layer is formed - the mesoderm. At this stage, the third layer of cells appears - the mesoderm, which is laid between the ecto- and endoderm. Initially, it looks like two pockets, the cavities of which are called the secondary cavity of the body. In the embryo of chordates, this is followed by the stage of neurula - an axial complex is formed, consisting of a notochord and neural plate, located parallel to each other. The notochord arises from the endoderm (more precisely, from the chordomesoderm), and the neural plate from the ectoderm. In the future, cell differentiation occurs: the integumentary epithelium, tooth enamel, the nervous system, and sensory organs are formed from the ectoderm. From the endoderm - intestinal epithelium, digestive glands, lungs. From the mesoderm - the skeleton, muscles, circulatory system, excretory organs, reproductive system. In all animals and in humans, the same germ layers form the same organs and tissues. This just indicates that the germ layers are homologous and have a single origin in evolution.

Question 4. Give examples of animals with direct and indirect development.
Postembryonic development can be direct, when a creature similar to an adult (reptiles, birds, mammals) appears from an egg or mother's body, and indirect, when a larva formed in the embryonic period is simpler than an adult organism, and differs from it in ways of feeding, movement and others (coelenterates, flat and annelids, crustaceans, insects, amphibians).

Question 5. What is the meaning of the biogenetic law?
biogenetic law, formulated by F. Müller and E. Haeckel, makes it possible to use embryological data to reconstruct the course of the historical development of a species.

During the classes

1. Organizational moment.

2. Checking d / z:

a) define the words: mitosis, meiosis, gametes, zygote, gametogenesis, oogenesis, spermatogenesis;

b) students' story about asexual reproduction;

c) the story of students about sexual reproduction.

3. The message of the topic and purpose of the lesson: "Individual development of the body."

Teacher's word:

So, during sexual reproduction, the beginning of the whole organism is given by one cell - the zygote, during asexual reproduction - one or more cells of the parent individual.

But in any case, in order for a small number of cells to turn into a full-fledged organism, a whole series of complex, successive transformations is necessary.

4. Work on new material.

Ontogeny (individual development of the organism) is the period of development of the organism from the inception and formation of the zygote until the end of the life of the individual.

Ontogeny is divided into 2 periods: embryonic and postembryonic development.

5. Embryonic development (embryogenesis, on the example of the lancelet).

Embryogenesis is the development of an organism from the moment a zygote is formed to birth or exit from the egg membranes.

Stages of embryogenesis:

a) Blastula (crushing) - during which the zygote is divided by mitosis, and the cells formed during crushing are smaller than the zygote.

Cleavage ends with the formation of a blastula - a hollow ball or vesicle; blastula cells - blastomeres (located on the surface).

The cavity of the blastula is called the blastocoel, and the process of formation of a single-layer embryo is called blastulation.

b) Gastrula (gastrulation) - the formation of a two-layer embryo, and a two-layer ball is a gastrula.

The outer layer of cells (or germ layer) is called the endoderm.

The cavity inside the gastrula is the primary intestine, and the opening leading to the primary intestine is the primary mouth (they are formed by invagination or movement of cells).

c) Neirula - the formation of the third germ layer - the mesoderm. The peculiarity of the stage is that the formation of tissues and organs of the future organism (organogenesis) begins.

Derivatives of the germ layers.

6. Postembryonic development.

This is the development of the organism from the moment of birth and lasts until the end of the life of the individual (exit from the egg membranes).

Postembryonic development is divided into 3 periods:

1. Pre-reproductive - body growth, development and puberty.

2. Reproductive - active functioning of an adult organism, reproduction.

3. Post-reproductive - aging, the gradual extinction of vital processes.

Development types:

a) straight

b) indirect (with metamorphosis):

1) complete transformation (in addition to the larval stage, there is a pupal stage - butterflies, beetles),

2) incomplete transformation (there is a larva, but no pupa - grasshoppers, tadpoles).

7. Biogenetic law (comparison of embryos).

K. Baer formulated the law of germline similarity: "Within the limits of the type, embryos, starting from the earliest stages, show a certain general similarity."

Müller and Haeckel formed the biogenetic law: "Ontogeny is a brief repetition of phylogenesis."

The value of the biogenetic law - it testifies to the common ancestors of animals belonging to various systematic groups.

8. "The story of an unborn child. Abortion."

Film snippet: "Development of the human embryo by weeks" (discussion of the act of a failed mother and the harm of abortion).

9. Let's compete (fixing).

10. Summing up.

1) How does the embryonic period of development begin and end?

2) How does the postembryonic period of development begin and end?

3) What organ systems are formed from the ectoderm? endoderm? mesoderm?

4) Give examples of animals with direct and indirect development.

5) What is the meaning of the biogenetic law?