• Rice. 92. Chicken embryo at the stage of 14 somites (35-36 hours of incubation). Neural tube and brain vesicles
  • Rice. 93. Chicken embryo at the stage of 18 somites (43 hours of incubation). The head end of the embryo is elevated above the surface of the germinal disc
  • Rice. 94. Longitudinal (lateral) section of a human embryo 10 mm long. Age - 5 weeks. 1 - anterior cerebral bladder, 2 - middle cerebral bladder, 3 - posterior cerebral bladder, 4 - tongue, 5 - heart, 6 - liver, 7 - lungs, 8 - primary kidney, 9 - spinal nodes, 10 - anlage of vertebral arches
  • Rice. 95. Cross section of a human embryo 12 mm long. Age 5 weeks 1 - spinal cord, 2 - rudiments of the upper limbs, 3 - lungs, 4 - heart

  • Rice. 96. Brain on various stages fetal development (side view): A - 4 months, B - sixth month, C - seventh month, D - eighth month, D - ninth month. 1 - central sulcus, 2 - lateral (Sylvian) sulcus, 3 - superior temporal sulcus, 4 - pole of the temporal lobe, 5 - cerebellum, 6 - parietal-occipital sulcus, 7 - medulla oblongata, 8 - Reil's island at the bottom of the Sylvian sulcus

  • Rice. 97. Topography of the brain immediately after the formation of 5 cerebral vesicles. A - sagittal section, B - side view of the surface of the brain: 1 - spinal cord, 2 - cavity of the medulla oblongata, 3 - thin roof of the medulla oblongata, 4 - cavity of the hindbrain, 5 - meso-metencephalic fold, 6 - cavity of the midbrain, 7 - position of the posterior commissure, 8 - posterior tubercle, 9 - cavity of the diencephalon, 10 - transverse velum, 11 - median region of the cavity of the telencephalon, 12 - terminal plate, 13 - optic recess, 14 - optic chiasm, 15 - funnel, 16 - lateral bladder of the telencephalon, 17 - diencephalon, 18 - ophthalmic cup, 19 - vascular fissure of the eye, 20 - ophthalmic stalk, 21 - accessory nerve, 22 - hypoglossal nerve root, 23 - vagus nerve ganglion, 24 - glossopharyngeal nerve ganglion, 25 - auditory vesicle, 26 - ganglion of the auditory and facial nerves, 27 - ganglion of the trigeminal nerve, 28 - hindbrain, 29 - midbrain, 30 - lateral parts of the cavity of the telencephalon, 31 - Monroy's foramen, 32 - position of the auditory vesicle

    • Rice. 98. Development of the eye cup and lens in a human embryo: A - stage 14 somites, B - embryo 7 mm long, C - embryo 4.5 mm long, D - embryo 5 mm long, E - embryo 10 mm long. 1 - head ectoderm, 2 - wall of the forebrain, 3 - ophthalmic groove, 4 - primary optic vesicle, 5 - optic vesicle, 6 - lens placode, 7 - lens vesicle, 8 - lens, 9 - ophthalmic stalk, 10 - pigment epithelium , 11 - retina


  • Rice. 99. Transverse sections of early human embryos showing the formation of the auditory vesicle: A - 9 somites, B - 16 somites, C - 30 somites. 1 - auditory placode, 2 - dorsal aorta, 3 - pharynx, 4 - auditory fossa, 5 - medulla oblongata, 6 - ventral aorta, 7 - auditory vesicle
  • Rice. 100. Stages of development of the outer ear. The numbers indicate the location of the rudimentary tubercles and their movement during development.

  • Rice. 101. Development of the facial region and external ear, side view: A - 5.5-week-old embryo, B - 6-week-old embryo, C - 7-week-old embryo, D - 8-week-old embryo. 1 - medial nasal process, 2 - lateral nasal process, 3 - nasopharyngeal groove, 4 - maxillary process, 5 - mandibular arch, 6 - auditory tubercles around the hyomandibular fissure merged to form the outer ear

    • Rice. Fig. 102. Sequential stages of face formation, front view: A - 4-week embryo, B - 5-week embryo, C - 5.5-week embryo, D - 6-week embryo, E - 7-week embryo, E - 8 - week-old embryo 1 - frontal protrusion, 2 - olfactory placode, 3 - nasal fossa, 4 - oral plate, 5 - oral opening, 6 - maxillary process, 7 - mandibular arch, 8 - hyoid arch, 9 - medial nasal process, 10 - lateral nasal process, 11 - nasolacrimal groove, 12 - hyomandibular fissure, 13 - filtrum area, 14 - external ear, 15 - auditory tubercles, 16 - hyoid bone, 17 - cartilage of the larynx

  • Rice. 103. Formation of the kidney of the limb in amphibians: 1 - myotome, 2 - spinal cord, 3 - notochord, 4 - pronephros, 5 - endoderm, 6 - presumptive mesoderm of the kidney of the limb, 7 - kidney of the limb, 8 - parietal sheet of the lateral plate of the mesoderm, 9 - visceral layer of the lateral plate of mesoderm
  • Rice. 104. Areas of cell death (shaded) in the kidneys of the lower limbs of chicken (A) and duck (B) embryos, as well as in the kidney of the hand of a human embryo (C)

    • Rice. 105. early stages formation of the intestine and related structures. Sagittal section through an early human embryo at the beginning of 5 (A) and 6 (B) weeks of development: 1 - pharynx, 2 - trachea, 3 - stomach, 4 - liver, 5 - dorsal anlage of the pancreas, 6 - notochord, 7 - posterior intestine, 8 - cloaca, 9 - allantois, 10 - yolk stalk, 11 - ventral anlage of the pancreas, 12 - Rathke's pocket, 13 - body of the tongue, 14 - root of the tongue, 15 - esophagus, 16 - peritoneal cavity, 17 - rectum , 18 - postcloacal intestine, 19 - urogenital sinus, 20 - cloacal membrane, 21 - gallbladder, 22 - hepatic duct, 23 - pituitary gland

  • Rice. 106. Successive stages of the formation of intestinal villi in rat embryogenesis. A - 15-16 days of development, B - 17th day of development, C - 18th day of development, D - villi

  • Rice. 107. Development of the main bronchi of the human lungs. A - embryo 4 mm long, B - embryo 5 mm long, C - embryo 7 mm long, D - embryo 8.5 mm long, D - embryo 10 mm long, E - embryo 20 mm long: 1 - trachea, 2 - kidney of the bronchus, 3 - bronchi of the first order, 4 - right bronchial trunk, 5 - left bronchial trunk, 6 - bifurcation of the trachea, 7 - upper lobe of the lung, 8 - left bronchus, 9 - mesenchymal anlage of the stroma of the lung, 10 - lower lobe of the lung, 11 - pulmonary vein, 12 - cardiac bronchus, 13 - laying of the visceral pleura, 14 - middle lobe of the lung, 15 - right bronchus, 16 - apical bronchus

  • Rice. 108. Gill region of a 5-week-old human embryo: A - appearance, gill arches are visible, B - head section along the midline, pharyngeal pockets are visible. 1 - maxillary process, 2 - gill arches, 3 - nasal fossa, 4 - pharyngeal pockets, 5 - lung kidney, 6 - rudiment of the thyroid gland, 7 - Rathke's pouch

  • Rice. 109. Scheme illustrating the process of separation of the pleural and pericardial regions of the coelom: 1 - pharynx, 2 - epimyocardium, 3 - endocardium, 4 - ventral mesocardium, 5 - coelom, 6 - dorsal mesocardium, 7 - lung kidney, 8 - pleural coelom, 9 - pleuropericardial fold, 10 - arterial trunk, 11 - pericardial coelom, 12 - atrium, 13 - common cardinal vein, 14 - esophagus, 15 - pleural cavity, 16 - lung, 17 - heart, 18 - pericardial cavity, 19 - phrenic nerve

  • Rice. 110. Vessels of pig embryos at different stages of development: A - 10 somites, B - 19 somites, C - 26 somites, D - 28 somites, E - 30 somites, F - 36 somites. 1 - optic sulcus, 2 - left aortic arch, 3 - left dorsal aorta, 4 - 1st somite, 5 - eye vesicle, 6 - auditory fossa, 7 - segmental arteries, 8 - yolk vein, 9 - auditory vesicle, 10 - left 2nd aortic arch, 11 - left 3rd aortic arch, 12 - left dorsal aorta, 13 - dorsal remnant of the left 1st aortic arch, 14 - primary cephalic vein, 15 - left 4th aortic arch, 16 - left pulmonary arch, 17 - left anterior cardinal vein, 18 - arterial trunk, 19 - aorta

  • Rice. 111. Arteries of the body wall of a 7-week-old human embryo: 1 - basilar artery, 2 - vertebral artery, 3 - external carotid artery, 4 - superior intercostal artery, 5 - aorta, 6 - 6th thoracic intercostal artery, 7 - spinal branch , 8 - 1st lumbar segmental artery, 9 - inferior epigastric artery, 10 - middle sacral artery, 11 - sciatic artery, 12 - external iliac artery, 13 - umbilical artery, 14 - internal thoracic artery, 15 - subclavian artery, 16 - middle cerebral artery, 17 - internal carotid artery

  • Rice. 112. Formation of a cardiac loop and division of the heart into sections in a human embryo, ventral view. The embryos are long: A - 2.08 mm, B - 3 mm, C - 5.2 mm, D - 6 mm, D - 8.8 mm. 1 - cone, 2 - arterial trunk, 3 - ventricle, 4 - atrium, 5 - cone-ventricular groove, 6 - right atrium, 7 - left atrium, 8 - right ventricle, 9 - left ventricle. Roman numerals indicate the corresponding aortic arches

  • Rice. 113. Renal tubules. A - transverse section through the embryo at the level of the 12th somite, B - functional tubule of the pronephros, C - transverse section through the embryo at the level of the 17th somite, D - functional tubule of the mesonephros of the primary type: 1 - somite, 2 - posterior cardinal vein, 3 - tubule of the pronephros, 4 - nephrostomy, 5 - whole, 6 - dorsal aorta, 7 - intestine, 8 - intermediate mesoderm, 9 - duct of the pronephros, 10 - glomus, 11 - chord, 12 - duct of the mesonephros, 13 - tubule of the mesonephros, 14 - glomerulus, 15 - Bowman's capsule

  • Rice. 114. Transverse sections through the fetal pig, 9.4 mm long, passing through the meso- and metanephric ducts (A) and the mass of metanephrogenic tissue (B). 1 - dorsal aorta, 2 - mesonephros, 3 - glomerulus, 4 - whole, 5 - kidney of the hind limb, 6 - mesonephros duct, 7 - tail artery, 8 - metanephros duct, 9 - umbilical artery, 10 - subcardinal vein, 11 - veins connecting the posterior cardinal and subcardinal veins, 12 - posterior cardinal vein, 13 - 9th thoracic ganglion, 14 - ventral root of the 10th thoracic nerve, 15 - nephrogenic tissue

  • Rice. 115. Reconstruction of the genitourinary system of an 8-week-old human embryo: 1 - gonad, 2 - mesonephros, 3 - vena cava, 4 - colon, 5 - Müllerian ducts, 6 - metanephros duct, 7 - mesonephros duct, 8 - middle sacral artery, 9 - chord, 10 - neural tube, 11 - rectum, 12 - urorectal septum, 13 - urogenital sinus, 14 - genital tubercle, 15 - symphysis, 16 - bladder, 17 - intestinal loop in the ventral stalk. An asterisk indicates the urethral groove

  • Rice. 116. Differentiation of male and female reproductive organs. A - indifferent stage, B - differentiation of male internal genital organs, C - differentiation of female internal genital organs. 1 - gonads, 2 - müllerian duct, 3 - mesonephros duct, 4 - mesonephros tubules, 5 - urogenital sinus, 6 - vas deferens, 7 - prostatic uterus, 8 - urethra, 9 - duct of epididymis, 10 - testis, 11 - efferent tubules of the testis, 12 - uterus, 13 - oviduct, 14 - ovary, 15 - Gartner's canal, 16 - cervix

The initial organogenesis is neurulation.

In the process of neurulation, the mesoderm is formed.

Method 1: Enterocoelous - protrusions - pockets are formed on both sides of the primary intestine. They completely detach from the primary gut, grow between the ectoderm and endoderm and turn into mesoderm (in chordates)

Method 2: Teloblastic - in the vicinity of the blastopore on both sides of the primary intestine, one large cell is formed - a teloblast. As a result of the reproduction of teloblasts, the mesoderm is formed. (In invertebrates)

Formation of axial organs in chordate embryos

    The ectoderm on the dorsal side of the embryo bends, forming a longitudinal groove, the edges of which close. The resulting neural tube is immersed in the ectoderm

    The dorsal part of the endoderm, located under the nerve germ, gradually separates and a notochord is formed.

    The intestinal tube is formed from the ectoderm and endoderm.

Ectoderm - epidermis, skin glands, hair, enamel, conjunctiva, lens, retina, ears, epithelial lining of the nasal and oral cavity, anus and vagina, anterior and posterior pituitary, CNS, adrenal medulla, jaws.

Mesoderm - skeletal muscles, diaphragm, vertebrae, dentin, renal tubules, ureters, oviducts, uterus, part of the ovaries and testicle, adrenal cortex, heart, blood, lymphatic system, lungs, sclera, choroid and cornea of ​​​​the eye.

Endoderm - chord, most of the digestive tract, lining of the intestines, bladder, lungs, pancreas, thymus, thyroid gland, parathyroid gland.

39. The concept of provisional organs of chordates. Features of the development of these organs in the Anamnia and Amniota groups. Types of placenta. Violation of the processes of development and reduction of the germinal membranes in humans.

Provisional organs are temporary organs necessary for the vital activity of the embryo. The time of their formation depends on the egg and environmental conditions.

The presence or absence of provisional organs underlies the division of vertebrates into groups: Amniota and Anamnia.

The anamnia group includes evolutionarily more ancient animals that develop in an aquatic environment and do not need additional water and other shells of the embryo. (Cyclostomes, fish, amphibians)

The group of amniotes includes primary terrestrial vertebrates, the embryonic development of which takes place in terrestrial conditions. (Reptiles, birds, mammals)

There is much in common in the structure and functions of the provisional organs of amniotes. The provisional organs of higher vertebrates are called germinal membranes. They develop from the cellular material of already formed germ layers.

supervisory bodies.

    The amnion is a sac filled with amniotic fluid, which creates an aquatic environment and protects the embryos from drying out and damage.

    Chorion - the outer germinal membrane adjacent to the shell or maternal tissues. Used to exchange with environment, participates in respiration, nutrition and excretion.

    Yolk sac - it is involved in the nutrition of the embryo and is a hematopoietic organ.

    Alantois - outgrowth of the hindgut is involved in gas exchange, is a receptacle for urea and uric acid. In mammals, together with the chorion, it forms the placenta. Vessels grow from the allantois to the chorion, with the help of which the placenta performs excretory, respiratory and nutritional functions.

Types of placenta.

1. Epitheliochorional - (semi-placenta) has the simplest structure. When it is formed, villi in the form of small tubercles appear on the surface of the chorion. They sink into the corresponding recesses of the uterine mucosa without disturbing it. (the chorion is in contact with the epithelium of the uterine glands) Horse pigs

2. Desmochorionic - characterized by the establishment of the closest connection between the chorion of the embryo and the wall of the uterus. At the point of contact with the villi of the chorion, the epithelium is destroyed. The branched plates are immersed in the connective tissue. (The chorion is in contact with the connective tissue.)

3. Endotelochorional - not only the epithelium is destroyed, but also the connective tissue. The villi are in contact with the vessels and are separated from the maternal blood only by their thin endothelial wall. (predators)

4. Hemochorial - profound changes occur in the uterus. The villi are bathed in blood and absorb nutrients from it.

By appearance:

1 Diffuse - The villi are distributed evenly over the entire surface of the chorion.

2 Cotyledon - villi are collected in groups in the form of bushes

3 Girdle - villi form a girdle around the water bladder.

4 Discoid - Villi are located within the discoid region on the surface of the chorion.

41. Post-embryonic period of ontogenesis, its periodization in humans. Main processes: growth, formation of definitive structures, puberty, reproduction. The role of endocrine regulation in the postnatal period.

The postembryonic period begins from the moment the organism leaves the egg membranes, until the moment of death.

The postnatal period may or may not be direct.

With direct development, a newborn organism is similar to an adult and differs only in size and incomplete development of organs. Direct development is characteristic of humans and other mammals, birds, reptiles and some insects.

Not direct development proceeds with metamorphosis.

With incomplete metamorphosis, the organism goes through three stages of development. Egg, larva and imango.

With complete, it goes through 4 stages (pupa).

Periods of postembryonic human development.

1. Newborn - from the moment of birth to 4 weeks. A non-proportional structure is characteristic, the bones of the skull and pelvis are not fused. Spine without bends.

2. Thoracic - from 4 weeks to 12 months. - the child is seduced by movements, milk teeth appear.

3. Nursery up to 3 years. The proportions of the body change, the brain develops.

4. Preschool up to 7 years. Change of teeth.

5. School age up to 17 years old body proportion as in adults.

6. Youth - 16-20 girls, 17-21 boys. The processes of growth and formation of the body are completed.

7. Mature from 21 years old.

8. Elderly 55-60 years old.

9. Starchisky - 75 years old

Growth - it is manifested in a progressive increase in the mass and size of the body.

In invertebrates, growth is determined by an increase in cell size.

Proliferative growth is more common - it is based on cell division. cells increases exponentially. N n \u003d 2 n Where N is the number of cells, n is the order of division.

In the process of individual development, growth indicators change. In many animals, growth is confined to certain stages of ontogeny. Such growth is called limited.

There are organisms that grow throughout life (fish) but upon reaching puberty, the growth rate slows down. This type of growth is called unlimited.

On the one hand, growth rates are limited genetically, and on the other hand, they depend on the environment.

The role of the endocrine glands in postembryonic development is great.

E. produce hormones that affect the growth of the body, on puberty. Particularly important are the hormones produced by the pituitary, thyroid and sex glands. Questions of influence e. and. on the growth and development of the organism was considered by Zavodskoy.


The development (differentiation) of germ layers during embryogenesis is accompanied by the fact that various tissues and organs are formed from them.

In particular, the epidermis of the skin, nails and hair, sebaceous and sweat glands develop from the ectoderm, nervous system(brain, spinal cord, ganglia, nerves), receptor cells of the sense organs, lens of the eye, epithelium of the mouth, nasal cavity and anus, tooth enamel. From the endoderm, the epithelium of the esophagus, stomach, intestines, gallbladder, trachea, bronchi, lungs, urethra, as well as the liver, pancreas, thyroid, parathyroid and goiter glands develop. From the mesoderm develop smooth muscles, skeletal and cardiac muscles, dermis, connective tissue, bones and cartilage, dental dentin, blood and blood vessels, mesentery, kidneys, testes and ovaries. In humans, the brain and spinal cord are the first to separate. 26 days after ovulation, the length of the human fetus is about 3.5 mm. At the same time, the rudiments of the arms are already visible, but the rudiments of the legs are just beginning to develop. 30 days after ovulation, the length of the embryo is already 7.5 mm. At this time, it is already possible to distinguish segmentation of the limb buds, eye cups, cerebral hemispheres, liver, gallbladder and even division of the heart into chambers.

In an eight-week-old human embryo, with a length of about 40 mm and a weight of about 5 g, almost all body structures appear. Organogenesis ends by the end of the embryonic period. At this time, the embryo in appearance acquires features of resemblance to a person.

The length of a 12-week-old human fetus is already about 87 mm, and the weight is about 45 g. Further growth and development of the fetus continues. For example, in the 4th month of development, hair appears, and in the 20th week, blood cells begin to form.

If the definitive oral opening is formed at the site of the primary mouth (blastopore), then these animals are called protostomes (worms, molluscs, arthropods). If the definitive mouth is formed in the opposite place, then these animals are called deuterostomes (echinoderms, chordates).

To ensure the connection of the embryo with the environment, it develops the so-called provisional organs, which exist temporarily. Depending on the type of oocytes, provisional organs are different structures. In fish, reptiles and birds, the yolk sac is the provisional organ. In mammals, the yolk sac is formed at the beginning of embryogenesis, but does not develop. Later it is reduced. In the course of evolution, reptiles, birds, and mammals have developed embryonic membranes that provide protection and nutrition for embryos (Fig. 91). In mammals, including humans, these germinal membranes are sheets of tissue that develop from the body of the embryo. There are three such membranes - amnion, chorion and allantois. The outer shell of the embryo is called the chorion. She grows into the uterus. The place of greatest growth in the uterus is called the placenta. The fetus is connected to the placenta through the umbilical cord or umbilical cord, in which there are blood vessels that provide placental circulation. The amnion develops from the inner leaf, and the allantois develops between the amnion and the chorion. The space between the embryo and the amnion, called the amniotic cavity, contains fluid (amniotic). This fluid contains the embryo, and then the fetus until birth. The metabolism of the fetus is provided through the placenta.

At the heart of the formative interaction of the parts of the embryo are coordinated metabolic processes in a certain way. The pattern of development is heterochrony, which is understood as the formation of organ anlages different in time and the different intensity of their development. Those organs and systems that should start functioning earlier develop faster. For example, in humans, the rudiments of the upper limbs develop faster than the rudiments of the lower ones.

The development of the embryo and fetus is greatly influenced by the living conditions of the mother. The embryo is extremely sensitive to various influences. Therefore, the so-called critical periods are distinguished, i.e., the periods in which the embryos, and then the fruits, are most sensitive to damaging factors. In the case of humans, the critical periods of embryonic ontogenesis are the first days after fertilization, the time of placenta formation and childbirth, and the damaging factors are alcohol, toxic substances, lack of oxygen, viruses, bacteria, pathogenic protozoa, helminths and other factors. These factors have a teratogenic effect and lead to deformities and disruption of normal development.

Ever since the time of Hippocrates (5th century AD), the question of the causes that initiate the birth of the fetus has been discussed. In particular, Hippocrates himself assumed that the development of the fetus initiates its own birth. The latest experimental work of British researchers, carried out on sheep, showed that in sheep the initiation of lambing is controlled by the hypothalamus + pituitary gland + adrenal glands of the fetus. Damage to the nuclei of the hypothalamus, removal of the anterior pituitary gland or adrenal glands prolongs the pregnancy of sheep. On the contrary, administration of adenocorticotropic hormone (anterior pituitary secretion) or cortisol (adrenal gland secretion) to sheep shortens their pregnancies.

So, in the process of development of higher eukaryotes, a single fertilized zygote cell in the course of further development as a result of mitosis gives rise to cells different types- epithelial, nervous, bone, blood cells and others, which are characterized by a variety of morphology and macromolecular composition. However, cells of different types are also characterized by the fact that they contain the same sets of genes, but are highly specialized, performing only one or several specific functions, i.e. some genes "work" in cells, others are inactive. For example, only erythrocytes are specific in the synthesis and storage of hemoglobin.

Similarly, only epidermal cells synthesize keratin. Therefore, questions have long arisen about the genetic identity of somatic cell nuclei and about the control mechanisms of the development of fertilized oocytes as a prerequisite for understanding the mechanisms underlying cell differentiation.

Since the 1950s, experiments have been carried out in many laboratories on the successful transplantation of somatic cell nuclei into eggs artificially devoid of their own nuclei. The study of DNA from the nuclei of different differentiated cells showed that in almost all cases the genomes contain the same sets of nucleotide pair sequences. Only exceptions are known when mammalian erythrocytes lose their nuclei during the last stage of differentiation. But by this time, pools of persistent hemoglobin mRNAs have already been synthesized, so the nuclei are no longer needed by red blood cells. Other examples are immunoglobulin and T cell genes that are modified during development.

One of the major stages in the direction of understanding the control mechanisms of embryonic ontogenesis was the results of experiments carried out in 1960-70. English researcher D. Gurdon in order to find out whether the nuclei of somatic cells have the ability to ensure the further development of eggs, if these nuclei are introduced into eggs from which their own nuclei have been previously removed. a scheme of one of these experiments is given, in which the nuclei of tadpole somatic cells were transplanted into frog eggs with previously removed nuclei. These experiments showed that the nuclei of somatic cells are indeed capable of ensuring the further development of eggs, since they were able to fertilize eggs and “forced” them to develop further. This showed the possibility of animal cloning.

Later, other researchers performed experiments in which it was shown that the transfer of individual blastomeres from 8- and 16-day-old sheep embryos of one breed into the non-nuclear half of the egg (after dissection of the latter in half) of another breed was accompanied by the formation of viable embryos, followed by the birth of lambs.

In early 1997, British authors showed that the introduction of somatic cell nuclei (cells of embryos, fetuses and udders of adult sheep) into artificially deprived nuclei of sheep eggs, and then the implantation of eggs fertilized in this way into the uterus of sheep, is accompanied by the onset of pregnancy followed by the birth of lambs.

Evaluation of these results shows that mammals can be propagated asexually, obtaining offspring of animals whose cells contain nuclear material of paternal or maternal origin, depending on the sex of the donor sheep, in such cells only the cytoplasm and mitochondria are of maternal origin. This conclusion is of extremely important general biological significance, expanding our views on the potential for animal reproduction. But it is also important to add that we are talking about genetic manipulations that do not exist in nature. On the other hand, in practical terms, these genetic manipulations represent a direct way of cloning highly organized animals with desired properties, which is important. economic importance. IN medically this path may be used in the future to overcome male infertility.

So, the genetic information necessary for the normal development of the embryo is not lost during cell differentiation. In other words, somatic cells have a property called totipotency, i.e., their genome contains all the information they received from a fertilized egg that gave them a start as a result of differentiation. The presence of these data certainly means that cell differentiation is subject to genetic control.

It has been established that intensive protein synthesis following fertilization in most eukaryotes is not accompanied by mRNA synthesis. The study of oogenesis in vertebrates, in particular. In amphibians, it has been shown that intense transcription occurs even during prophase I (especially diplotene) of meiosis. Therefore, gene transcripts in the form of mRNA or pro-mRNA molecules are stored in the egg in an inactive state. It has been established that the so-called asymmetric division takes place in embryonic cells, which consists in the fact that the division of the embryonic cell gives rise to two cells, of which only one inherits the proteins involved in transcription. Thus, the unequal distribution of transcription factors between daughter cells leads to the expression of different sets of genes in them after division, i.e., to cell differentiation.

In amphibians, and perhaps most vertebrates, the genetic programs that control early development (up to the blastula stage) are established during oogenesis. Later stages of development, when cellular differentiation begins (approximately from the gastrula stage), require new programs for gene expression. Thus, cell differentiation is associated with the reprogramming of genetic information in one direction or another.

A characteristic feature of cell differentiation is that it irreversibly leads to one or another cell type. This process is called determination and is also under genetic control, and as it is now assumed, cell differentiation and determination is regulated by cell interaction based on signals carried out by peptide growth factors through tyrosine kinase receptors. There are probably many such systems. One of them is that the differentiation of muscle and nerve cells regulated by neuroregulins, which are membrane proteins that act through one or more tyrosine kinase receptors.

The genetic control of determination is also demonstrated by the existence of so-called homeiotropic or homeotic mutations, which have been shown in insects to cause changes in determination in specific imaginal discs. As a result, some parts of the body develop out of place. For example, in Drosophila, mutations transform the determination of the antennal disc into a disc that develops into an appendix of a limb extended from the head. In insects of the genus Ophthalmoptera, wing structures may develop from the disc for the eyes. In mice, the existence of the Hox gene cluster (complex) has been shown, which consists of 38 genes and controls the development of limbs.

Of independent importance is the question of the regulation of gene activity during embryonic development. It is believed that during differentiation, genes act in different time, which is expressed in transcription in different differentiated cells of different mRNA, i.e., there is repression and derepression of genes. For example, the number of genes transcribed into RNA in blastocytes sea ​​urchin, equal to 10%, in rat liver cells - also 10%, and in cattle thymus cells - 15%. It is assumed that nonhistone proteins are involved in the control of the transcriptional status of genes. The following data support this assumption. When cell chromatin in phase is transcribed in the in vitro system, only histone mRNA is synthesized, followed by histones. In contrast, when G 1 cell chromatin is used, no histone mRNA is synthesized. When non-histone proteins are removed from the G1-phase chromatin and replaced by non-histone chromosomal proteins synthesized in the S phase, histone mRNA is synthesized after transcription of such chromatin in vitro. Moreover, when non-histone proteins originate from the G 1 phase of cells, and DNA and histones from the S phase of cells, no histone mRNA is synthesized. These results indicate that non-histone proteins contained in chromatin determine the possibility of transcription of genes encoding histones. Therefore, it is believed that non-histone chromosomal proteins can play important role in the regulation and expression of genes in eukaryotes.

The available data suggest that protein and steroid hormones are involved in the regulation of transcription in animals. Protein (insulin) and steroid (estrone and testosterone) hormones are two signaling systems used in cell-to-cell communication. In higher animals, hormones are synthesized in specialized secretory cells. Being released into the bloodstream, they enter the tissues, since the molecules of protein hormones are relatively large, they do not penetrate into the cells. Therefore, their effects are mediated by receptor proteins localized in target cell membranes and by intracellular levels of cyclic AMP (cAMP). On the contrary, steroid hormones are small molecules, as a result of which they easily penetrate into cells through membranes. Once inside the cells, they bind to specific receptor proteins that are present in the cytoplasm of only target cells. It is believed that hormone + protein receptor complexes, concentrating in the nuclei of target cells, activate the transcription of specific genes through interaction with certain non-histone proteins that bind to the promoter regions of specific genes. Therefore, the binding of the hormone + protein complex (protein receptor) to non-histone proteins releases the promoter regions for the movement of RNA polymerase. Summarizing the data on the genetic control of the embryonic period in the ontogeny of organisms, it can be concluded that its course is controlled by the differential switching on and off of the action of genes in different cells (tissues) through their derepression and repression.



The neurula stage follows the gastrula stage. At this point, mesoderm is laid between the ectoderm and endoderm. It is a rather "new" group of cells, which is not laid down in all embryos of multicellular animals. The laying of the mesoderm is the brightest event of the neurula stage.

The neural plate is formed from the ectoderm. Further, its edges are folded, a neural tube is formed, from which the brain and spinal cord develop in vertebrates. It is very easy to remember that the nervous system is formed from the ectoderm. After all, the ectoderm is the outer leaf, and the nerve endings penetrate the periphery of our body, they are concentrated in the skin and provide the body with the perception of environmental stimuli.

Under the chord is located intestinal tube formed from the endoderm. The intestine is located in the bowels of the body, so it is easy to remember that the intestinal tube develops from the innermost sheet - the endoderm.

Not all embryos have a single body axis, chord, and there is a reason for that. The notochord develops from the most "modern", "late" layer of cells - the mesoderm. It is very important to understand that the chord is formed precisely under the neural tube. This fact is easy to remember - the nerves, as mentioned above, are located "outside", closer to the surface of the body, and the chord, the axis of the body, is located deeper, inside, being the basis, the core of the body.

The secondary body cavity is also formed from the mesoderm - in general. As you remember, it consists of two layers of epithelium inside the body, between which there is a coelomic fluid.

So, what are the main results of neurula? An axial complex of organs is formed: neural tube, notochord, intestinal tube.

The interaction of parts of the embryo

The embryo is a single organism. In the embryo, any cellular and tissue structures, as well as organs, are in deep interaction. Scientists have proven that mesoderm and chord cells interact very strongly with the neural tube and determine its development. Such cells are called germinal inductorsororganizers. In fact, the neural tube is stimulated by these cells. This phenomenon is called embryonic induction. How is this stimulation done? By isolating special substances. At the early gastrula stage, the ectoderm cells do not yet seem to know which way to develop: if they are transplanted from the upper part to the belly of the embryo, they will lose the influence of the notochord and mesoderm and turn into ordinary cells of the abdominal epithelium.

What influences the growth and development of the embryo? Undoubtedly, the range of factors of internal and external environment. During certain periods of development, the embryo is especially sensitive to external factors(oxygen content, temperature, etc.) Sensitivity increases in the middle of crushing, at the stage of neurula, at the beginning of gastrulation.

In women, oocytes of the 1st order are very sensitive to environmental factors. They are influenced for many years, as they are formed in the embryo. As a result, their anomalies can lead to impaired development of children. The child's central nervous system suffers from a lack of oxygen, which causes the mother's consumption of alcohol - alcohol can lead to mental retardation child. Each cigarette smoked reduces the oxygen supply to the fetus by 10 percent. Viruses, antibiotics, hormones, ionizing radiation (X-ray), drugs can have the strongest effect on the embryo.

In 1901, the German embryologist Hans Spemann transplanted a section taken from the dorsal lip of the blastopore of one amphibian into the body of another at the gastrula stage. As a result, the transplanted cells took root in the body of the amphibian, which was transplanted, and an additional embryo developed. If the patch had remained in the host's body, it would have grown into a body part (such as the skin). But since it was taken very early and had not yet been differentiated, it grew into a different germ.

Organ education

At the neurula stage, the laying of organs is just beginning. This process unfolds during the formation of organs. I would call it proper organogenesis. This topic is very important for the exam in biology, as well as for the exam at Moscow State University.

What is the significance of the three germ layers? What structures can be formed from different leaves?

From the ectoderm, epithelial and nervous tissues and some glands are formed. By epithelial tissue, we mean primarily the epidermis of the skin. This traditionally includes nails, sebaceous and sweat glands, hair and tooth enamel. In addition to nerve structures, sensory organs are formed from the ectoderm. For glands formed from the ectoderm, internal secretion is characteristic. The leaders of the list of glands: the pituitary gland and the pineal gland (they started from the neural tube). This includes another gland located close to the surface of the body - the thyroid.

Endoderm provides the formation of epithelial tissue. But not the one that lines the skin, but the one that is on the inner surface of the organs digestive system and respiratory organs, as well as inside the urinary, circulatory and reproductive systems. In addition, the digestive glands are formed from it: the pancreas and the liver. The lungs also originated from the endoderm.

The mesoderm forms muscle tissue. The main types of connective tissue are formed from it, including blood, lymph and the third part. internal environment body - tissue fluid. The notochord as a structure of mesodermal origin subsequently gives a cartilaginous or (in certain organisms) a bone skeleton. The lateral portions of the mesoderm are the sources of muscles and the heart. They form blood vessels, as well as kidneys. Mesoderm cells are the source for the organs of the reproductive system (testes, ovaries), as well as the adrenal glands.

Types of postembryonic development

direct development in which a young organism is predominantly similar in structure to an adult. The only difference from it is in size and lack of puberty. Classical examples of this development are the cycles of representatives of the classes of reptiles, birds, and mammals. But among invertebrates, these types of development are also often found, for example, among mollusks, some worms.

Indirect development (with metaformosis) is characteristic of fish, amphibians, and is very common in invertebrates. An example - a larva is radically different from an adult, but in the process of development it undergoes a number of changes. In this matter, there is one important point for the exam in biology. You need to know that only in insects indirect development is divided into complete transformationAndincomplete. At complete transformation the larva turns into a pupa, from which a new insect emerges. This process has four stages: egg - larva - pupa - adult. With incomplete transformation, there are three stages, since there is no pupa. In the exam, it is necessary to give examples of insect orders for which each of these transformations is characteristic.

Importance of indirect development

1. Absence competition larvae with adults for food resources and territory. It is known that the frog larva (tadpole) feeds on plants, and the frog itself feeds on insects. Larvae and adult insects often live in different environments, for example, a dragonfly (or butterfly) larva - on leaves land plants, unlike the flying adult.

2. Larvae can contribute resettlement kind. For example, the larva of coelenterates planula has cilia and moves. Unlike adult attached forms, such as coral polyps.

3. In the larva stage easier to bear adverse conditions. The larva of the May beetle burrows into the soil and exists for several years, feeding on the underground parts of plants.

4. In general, we can conclude that indirect development allows the body to make the most full use of the resources of the environment, increases the survival of the species.

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breeding season

Once in the ovary, the gonocytes become oogonia. Oogonia carry out the breeding season. During this period, oogonia divide by mitosis. This process occurs only during the embryonic development of the female.

growth period

Sex cells in this period are called oocytes of the first order. They lose the ability to mitotic division and enter prophase I of meiosis. During this period, the growth of germ cells occurs.

Ripening period

Oocyte maturation is a process of successive passage of two divisions of meiosis. As mentioned above, in preparation for the first division of maturation, the oocyte is at the prophase I stage of meiosis for a long time, when it grows. Exit from prophase I of meiosis is timed to the achievement of sexual maturity by the female and is determined by sex hormones.

2 As a result of oogenesis, only 1 egg is formed, and during spermatogenesis, 4 ready-made spermatozoa are formed.

TICKET-44

The most obvious distinguishing feature of the egg is its big sizes. A typical egg is spherical or oval in shape. The size of the nucleus can be just as impressive, in anticipation of the rapid divisions immediately following fertilization, reserves of proteins are deposited in the nucleus.

The cell's need for nutrients is satisfied mainly by the yolk, a protoplasmic material rich in lipids and proteins. It is usually found in discrete formations called yolk granules.

Another important specific structure of the egg is the outer egg shell - a cover of a special non-cellular substance, consisting mainly of glycoprotein molecules, some of which are secreted by the egg itself, and the other part by the surrounding cells. In many species, the shell has an inner layer directly adjacent to the plasma membrane of the egg. . This layer protects the egg from mechanical damage, and in some eggs it also acts as a species-specific barrier to spermatozoa, allowing only spermatozoa of the same species or very closely related species to enter.

Many eggs contain specialized secretory vesicles located under the plasma membrane in the outer, or cortical, layer of the cytoplasm. When the egg is activated by sperm, these cortical granules release the contents by exocytosis, as a result, the properties of the egg membrane change in such a way that other sperm can no longer penetrate the egg through it.

Spermatozoa- The head of the spermatozoon has an oval shape, and at its top is the so-called acrosome - a vesicle with enzymes that ensure the penetration of the spermatozoon through the protective outer layer of the egg during fertilization. Behind the acrosome is the nucleus, which contains half of the male genetic material (DNA) encoded on 23 chromosomes. Through the process of meiosis, each sperm carries a unique genetic information. The cervix is ​​the fibrous region where the middle part of the sperm connects to its head. This flexible structure allows the head to oscillate from side to side to help propel the sperm.

tail structure- The sperm tail contains 2 central and 9 pairs of peripheral microtubules. The initial part of the tail is covered by a dense ring of connective tissue and a protective sheath. The tail has three sections: intermediate, thickest, producing energy for the movements of the spermatozoon; the main one, consisting of 20 microtubules covered with an outer layer of dense fibers and a vagina; terminal, where dense fibers and the vagina become thinner; this part of the tail is covered only by a thin cell membrane.

TYPES OF OVA IN ANIMALS.

1. Alecithal (non-yolk). 2. Oligolecital (small yolk), in them the yolk is evenly distributed throughout the cytoplasm, therefore they are called isolecithal. Among them, primary isolecithal (in the lancelet) and secondary isolecithal (in mammals and humans) are distinguished, 3. Polylecital (multi-yolk) The yolk in these eggs can be concentrated in the center - these are centrolecital cells. Among telolecithal eggs, in turn, moderately telolecital or mesolecital with an average content of yolk (in amphibians) and sharply telolecithal, overloaded with yolk from which only a small part of the animal pole is free (in birds)

TICKET-45. SPERMATOGENESIS AND OVOGENESIS, SIMILARITIES AND DIFFERENCES?

spermatogenesis- the development of male germ cells (spermatozoa), which occurs under the regulatory influence of hormones. One of the forms of gametogenesis.

Ovogenesis- in animals, the development of the female germ cell - the ovum (eggs). During the embryonic development of the body, gonocytes infiltrate the rudiment of the female genital gonad (ovary), and all further development of the female germ cells occurs in it.

1 In contrast to the formation of spermatozoa in men, which begins only during puberty, the formation of eggs in women begins even before they are born and is completed for each given egg only after its fertilization.

2 As a result of oogenesis, only 1 egg is formed, and during spermatogenesis, 4 ready-made spermatozoa are formed.

Similarities:

1 The process of oogenesis has a fundamental similarity with spermatogenesis and also goes through a series of stages: reproduction, growth and maturation. Oocytes are formed in the ovary, developing from immature germ cells - ovogonia containing a diploid number of chromosomes. Owogonia, like spermatogonia, undergo successive mitotic divisions, which are completed by the time the fetus is born.

TICKET-46. MEIOSIS, ITS BIOLOGICAL SIGNIFICANCE, PHASES? DOES CROSSINGOVER AFFECT MEIOSIS RESULTS?

Meiosis- this is a special way of dividing eukaryotic cells, as a result of which the transition of cells from a diploid state to a haploid one occurs. Meiosis consists of two consecutive divisions preceded by a single DNA replication.

First meiotic division (meiosis 1) called reduction, because it is during this division that the number of chromosomes is halved: from one diploid cell, two haploid ones are formed.

Interphase- synthesis and accumulation of substances and energy necessary for the implementation of both divisions, an increase in cell size and the number of organelles, doubling of centrioles, DNA replication, which ends in prophase 1. Prophase 1-, the divergence of centrioles to different poles of the cell, the formation of spindle fibers, the "disappearance" of the nucleoli, the condensation of two-chromatid chromosomes, the conjugation of homologous chromosomes and crossing over. Prophase 1 is subdivided into stages: leptotene (completion of DNA replication), zygoten (conjugation of homologous chromosomes, formation of bivalents), pachytene (Crossing-over, gene recombination), diplotene (detection of chiasma), Metayaza1 - alignment of bivalents in the equatorial plane of the cell, attachment of the fission spindle filaments at one end to centrioles, others - to the centromeres of chromosomes. Anaphase 1- random independent divergence of two-chromatid chromosomes to opposite poles of the cell, recombination of chromosomes. Telophase 1- formation of nuclear membranes, division of the cytoplasm.

Second meiotic division (meiosis 2)

Interphase 2, is a short break between the first and second meiotic divisions during which no DNA replication occurs. Prophase 2- divergence of centrioles to different poles of the cell, the formation of spindle fibers. Metaphase 2- alignment of two-chromatid chromosomes in the equatorial plane of the cell, attachment of the fission spindle threads with one end to the centrioles, the other - to the centromeres of the chromosomes; 2 block of oogenesis in humans. Anaphase 2- division of two-chromatid chromosomes into chromatids and the divergence of these sister chromatids to opposite poles of the cell, recombination of chromosomes. Telophase 2- the formation of nuclear membranes around each group of chromosomes, the disintegration of the fission spindle threads, the appearance of the nucleolus, the division of the cytoplasm (cytotomy) with the formation of four haploid cells as a result.

The biological significance of meiosis. Meiosis is the central event of gametogenesis in animals and sporogenesis in plants. Being the basis of combinative variability, meiosis ensures the genetic diversity of gametes.

Crossing over.

During pachytene, homologous chromosomes are in a state of conjugation for a long period: in Drosophila - four days, in humans - more than two weeks. All this time, individual parts of the chromosomes are in very close contact. If in such a region DNA chains break simultaneously in two chromatids belonging to different homologues, then when the break is repaired, it may turn out that the DNA of one homologue will be connected to the DNA of another, homologous chromosome. This process is called crossover.

Since crossing over is a mutual exchange of homologous regions of chromosomes between homologous (paired) chromosomes of the original haploid sets, individuals have new, differing genotypes. In this case, a recombination of the hereditary properties of the parents is achieved, which increases variability and provides richer material for natural selection.

TICKET-47. PARTHENOGENESIS, ITS SIGNIFICANCE?

Parthenogenesis- one of the forms of sexual reproduction of organisms, in which female germ cells (eggs) develop into an adult organism without fertilization. Although parthenogenetic reproduction does not involve the fusion of male and female gametes, parthenogenesis is still considered sexual reproduction, since the organism develops from a germ cell. It is believed that parthenogenesis arose in the process of evolution of organisms in dioecious forms.

In cases where parthenogenetic species are represented (always or periodically) only by females, one of the main biological advantages parthenogenesis is to accelerate the rate of reproduction of the species, since all individuals of such species are able to leave offspring. This method of reproduction is used by some animals (although relatively primitive organisms resort to it more often). In cases where females develop from fertilized eggs, and males develop from unfertilized ones, parthenogenesis contributes to the regulation of the numerical ratio of sexes (for example, in bees). Often parthenogenetic species are also polyploid and arise as a result of distant hybridization, revealing in connection with this heterosis and high viability. Parthenogenesis should be attributed to sexual reproduction and should be distinguished from asexual reproduction, which is always carried out with the help of somatic organs and cells (reproduction by division, budding, etc.).

TICKET-48. STAGES OF EMBRYOGENESIS, CRUSHING AND ITS CHARACTERISTICS IN DIFFERENT ANIMALS, BLASTUL TYPES?

Embryogenesis is a part of individual development, ontogenesis.

Human embryology studies the process of development

human being from conception to birth. human embryogenesis,

lasting an average of 280 days (10 lunar months), is divided into

three periods: initial (first week of development), embryonic (second-

eighth week), and fetal (from the ninth week to the birth of the child). I know

of human embryology at the department of histology, the early

stages of development.

In the process of embryogenesis, the following main stages can be distinguished:

1. Fertilization ~ the fusion of female and male germ cells. As a result

a new single-celled zygote is formed.

2. Crushing. A series of rapidly successive zygote divisions. This

vertebrates.

3. Gastrulation. As a result of division, differentiation, interaction and

moving cells, the embryo becomes multilayered. Embryonic

sheets of ectoderm, endoderm and mesoderm, bearing linings of various

tissues and organs.

4. Histogenesis, organogenesis, systemogenesis. During differentiation

germ layers form the rudiments of tissues that form organs and systems

human body.

Cleavage is the second stage of embryogenesis, which consists in a series of rapidly successive divisions of the zygote. This

stage ends with the formation of a multicellular embryo with

human form of a vesicle-blastocyst, corresponding to the blastula of other

vertebrates.

Fragmentation can be: deterministic and regulatory; complete or incomplete; uniform (blastomeres are more or less the same in size) and uneven (blastomeres are not the same in size, two to three size groups are distinguished, usually called macro- and micromeres); finally, according to the nature of symmetry, radial, spiral, etc. are distinguished

Holoblastic cleavage - The cleavage planes separate the egg completely. There are complete uniform crushing, in which blastomeres do not differ in size (this type of crushing is typical for homolecital and alecital eggs), and complete uneven crushing, in which blastomeres can vary significantly in size. This type of crushing is typical for moderately telolecithal eggs.

meroblastic fragmentation

    discoidal

    limited to a relatively small area at the animal pole,

    cleavage planes do not pass through the entire egg and do not capture the yolk.

This type of crushing is typical For telolecithal eggsrich in yolk(birds, reptiles). This crushing is also called discoidal, because as a result of crushing, a small disk of cells (blastodisk) is formed at the animal pole.

    superficial

    the nucleus of the zygote divides in the central island of the cytoplasm,

    the resulting nuclei move to the surface of the egg, forming a superficial layer of nuclei (syncytial blastoderm) around the yolk lying in the center. Then the nuclei are separated by membranes, and the blastoderm becomes cellular.

This type of fragmentation is observed at arthropods.