Type of ontogeny characteristic of humans. Features of ontogenesis characteristic of humans
Remember!
What type of development is typical for a person?
Direct development - this type of development is typical for organisms whose cubs are born already similar to adults. Direct intrauterine development.
What is a placenta?
The placenta ("baby place") is the most important and absolutely unique organ that exists only during pregnancy. It connects two organisms - the mother and the fetus, providing it with the necessary nutrients.
How does a mother's lifestyle during pregnancy affect the health of the unborn child?
Throughout the entire period of intrauterine development, the fetus, which is directly connected with the mother's body through a unique organ - the placenta, is in constant dependence on the state of the mother's health. AT recent times There is a lot of debate about whether smoking affects the unborn child. It is known that nicotine entering the mother's blood easily penetrates through the placenta into the circulatory system of the fetus and causes vasoconstriction. If the blood supply to the fetus is limited, then its supply of oxygen and nutrients is reduced, which can cause developmental delay. In women who smoke, a child at birth weighs an average of 300-350 g less than normal. There are other problems associated with smoking during pregnancy. These women are more likely to have preterm births and miscarriages in late pregnancy. Children whose mothers were unable to give up cigarettes during pregnancy are 30% more likely to die early in childhood and 50% more likely to develop heart defects.
Alcohol passes through the placenta just as easily. Drinking alcohol during pregnancy can cause a condition known as fetal alcohol syndrome in the baby. With this syndrome, mental retardation, microcephaly (underdevelopment of the brain), behavioral disorders (excitability, inability to concentrate), a decrease in growth rate, and muscle weakness are observed. Viral diseases of the mother during pregnancy pose a serious danger to the development of the fetus. The most dangerous are rubella, hepatitis B and HIV infection. In the case of rubella infection in the first month of pregnancy, 50% of children develop congenital malformations: blindness, deafness, disorders of the nervous system and heart defects.
Review questions and assignments
1. Name the features of ontogeny that are characteristic of a person. What are the benefits of these features?
1) Embryonic The process of human embryonic development lasts about 280 days and is divided into three periods: initial (1st week), embryonic (2-8th weeks) and fetal (from 9th week to birth).
2) Post-embryonic: subdivided into three periods: pre-reproductive, the period of maturity (reproductive) and the period of aging (post-reproductive).
Such features give maximum survival and adaptation to the environmental conditions of the offspring.
2. How do nicotine, alcohol and drugs affect the development of the human fetus?
Recently, there has been a lot of controversy about whether smoking affects the unborn child. It is known that nicotine entering the mother's blood easily penetrates through the placenta into the circulatory system of the fetus and causes vasoconstriction. If the blood supply to the fetus is limited, then its supply of oxygen and nutrients is reduced, which can cause developmental delay. In women who smoke, a child at birth weighs an average of 300-350 g less than normal. There are other problems associated with smoking during pregnancy. These women are more likely to have preterm births and miscarriages in late pregnancy. Children whose mothers were unable to give up cigarettes during pregnancy are 30% more likely to die early in childhood and 50% more likely to develop heart defects. Alcohol passes through the placenta just as easily. Drinking alcohol during pregnancy can cause a condition known as fetal alcohol syndrome in the baby. With this syndrome, there is mental retardation, microcephaly (underdevelopment of the brain), behavioral disorders (irritability, inability to concentrate), decreased growth rate, muscle weakness
3. What environmental factors influence the development of the human embryo?
All types environmental factors are mutagens for the development of the embryo:
Chemical - solvent, alcohols, dietary supplements, drugs, etc.
Physical - temperature, radiation (radiation)
Biological - bacteria, viruses (rubella, HIV, hepatitis, etc.)
4. Name the periods of postembryonic development of a person.
The most important feature of a person, acquired by him in the process of evolution, is the lengthening of the pre-reproductive period. Compared to other mammals, including the great primates, human sexual maturity occurs most late. The lengthening of childhood and the slowing of growth and development expand the opportunities for learning and acquiring social skills. The reproductive period is the longest stage in the postembryonic development of a person, the completion of which indicates the onset of a post-productive period, or a period of aging. The aging process affects all levels of the organization of the living. Aging inevitably leads to death - the end of the individual development of organisms common to all living beings. Death is necessary condition for the change of generations, i.e. for the continuation of the existence and evolution of mankind as a whole.
5. What are the developmental consequences of vitamin D deficiency and malnutrition?
Vitamins of group D are formed under the influence of ultraviolet radiation in the tissues of animals and plants from sterols. Group D vitamins include:
- vitamin D2 - ergocalciferol; isolated from yeast, its provitamin is ergosterol;
- vitamin D3 - cholecalciferol; isolated from animal tissues, its provitamin - 7-dehydrocholesterol;
- vitamin D4 - 22, 23-dihydro-ergocalciferol;
- vitamin D5 - 24-ethylcholecalciferol (sitocalciferol); isolated from wheat oils;
- vitamin D6 - 22-dihydroethylcalciferol (stigma-calciferol).
Today, vitamin D is called two vitamins - D2 and D3 - ergocalciferol and cholecalciferol - these are colorless and odorless crystals that are resistant to high temperatures. These vitamins are fat soluble, i.e. fat soluble and organic compounds and insoluble in water. Vitamin D is formed in the skin under the action of sunlight from provitamins. Pro-vitamins, in turn, are partly supplied in the body in finished form from plants (ergosterol, stigmasterol and sitosterol), and partly formed in the tissues of their cholesterol (7-dehydrocholesterol (vitamin D3 provitamin). Provided that the body receives a sufficient amount of ultraviolet radiation , the need for vitamin D is fully compensated.However, the amount of vitamin D synthesized under the action of sunlight depends on factors such as:
- wavelength of light (the most effective is the average spectrum of waves that we receive in the morning and at sunset);
- initial skin pigmentation and (the darker the skin, the less vitamin D is produced under the action of sunlight);
– age (aging skin loses its ability to synthesize vitamin D);
- the level of air pollution (industrial emissions and dust do not pass the spectrum of ultraviolet rays that potentiate the synthesis of vitamin D, this explains, in particular, the high prevalence of rickets in children living in Africa and Asia in industrial cities).
Additional food sources of vitamin D are dairy products, fish oil, egg yolk. However, in practice, milk and dairy products do not always contain vitamin D or contain only trace (minor) amounts (for example, 100 g of cow's milk contains only 0.05 mg of vitamin D), so their consumption, unfortunately, cannot guarantee coverage of our requirements for this vitamin. In addition, milk contains a large amount of phosphorus, which prevents the absorption of vitamin D. The main function of vitamin D is to ensure normal growth and development of bones, preventing rickets and osteoporosis. It regulates mineral metabolism and promotes the deposition of calcium in bone tissue and dentin, thus preventing osteomalacia (softening) of the bones. Entering the body, vitamin D is absorbed in the proximal small intestine, and always in the presence of bile. Part of it is absorbed in the middle sections of the small intestine, a small part - in the ileum. After absorption, calciferol is found in the composition of chylomicrons in a free form and only partially in the form of an ester. Bioavailability is 60-90%. Vitamin D affects general exchange substances in the metabolism of Ca2+ and phosphate (HPO2-4). First of all, it stimulates the absorption of calcium, phosphate and magnesium from the intestines. An important effect of the vitamin in this process is to increase the permeability of the intestinal epithelium for Ca2+ and P. Vitamin D is unique - it is the only vitamin that acts both as a vitamin and as a hormone. As a vitamin, it maintains the level of inorganic P and Ca in the blood plasma above the threshold value and increases the absorption of Ca in the small intestine.
Symptoms of hypovitaminosis
The main symptom of vitamin D deficiency is rickets and softening of the bones (osteomalacia).
- milder forms of vitamin D deficiency are manifested by symptoms such as:
- Loss of appetite, weight loss
- burning sensation in the mouth and throat,
- insomnia,
- blurred vision.
Think! Remember!
1. Discuss in class how the lengthening of the pre-reproductive period has played a role in human evolution.
The most important feature of a person, acquired by him in the process of evolution, is the lengthening of the pre-reproductive period. Compared to other mammals, including the great primates, human sexual maturity occurs most late. The lengthening of childhood and the slowing of growth and development expand the opportunities for learning and acquiring social skills. This is important for the preservation of offspring, which means maintaining the abundance of the species, the maximum adaptation of a person to environmental conditions.
2. For which organisms do the concepts of "cell cycle" and "ontogenesis" coincide?
For unicellular organisms, in which the life cycle is the life of a cell from the moment it appears to division or death.
4. Using additional literature and Internet resources, find out what acceleration is, what hypotheses currently exist about the causes of acceleration. Discuss in class the information you found on this topic.
Acceleration or acceleration (from Latin acceleratio-acceleration) is the accelerated development of a living organism.
To justify acceleration, a wide variety of hypotheses have been proposed, which can be conditionally divided into several groups:
- First of all, nutraceutical, associated with a change (improvement) in the nature of nutrition, especially in the last three decades after the Second World War.
– Hypotheses associated with biological selection (first reports of accelerated development of children - Ghent, 1869; Roberts (Ch. Roberts), 1876), with an increase in the number of heterolocal (mixed) marriages - heterosis, an attraction to urban life, as a result of which people arrive in cities the most developed inhabitants from the countryside - Mauer's hypothesis (G. Mauer), 1887, as well as other hypotheses about constitutional selection - for example, the desire to occupy the upper strata of society or the resettlement of people with a more developed intellect to cities.
- A group of hypotheses related to the influence of environmental factors (hypotheses of the 30s) associated changes in the rate of growth and development with natural and artificial changes in environmental conditions. Koch (E. W. Koch), 1935, who proposed the term acceleration, attached importance to heliogenic influences, an increase in daylight hours due to electric lighting. Treiber (T. Treiber), 1941 associated acceleration with the influence of radio waves - although the acceleration of the growth of children began before the widespread use of radio on Earth, and Mills (C. A. Mills), 1950 - with an increase in the temperature of the Earth's atmosphere. There are other hypotheses, for example, related to radiation or cosmic radiation. But then the phenomenon should have manifested itself in all the children of one locality. However, all authors note differences in the growth rate of children of different population groups.
Each of the hypotheses separately could not explain all the phenomena of the secular trend, and data on acceleration would be convincing evidence. ontogenetic development and increase in body size not only in humans, but also in various animals
Question 1. Name the features of ontogeny that are characteristic of humans.
Humans are characterized by an intrauterine type of development. After fertilization, during crushing, a ball appears, consisting of two types of cells: darker, located inside and slowly dividing, and lighter, located outside. From dark cells, the body of the embryo will be formed in the future, from light cells - special organs that provide communication with the mother's body (embryonic membranes, umbilical cord, etc.).
The first 5-6 days the embryo moves through the oviduct to the uterus. Then it is introduced into its wall and begins to receive oxygen and nutrients from the mother. By this time, the stages of blastula and gastrula have already been passed. After the appearance of the third germ layer, organogenesis begins: the notochord is laid, then the neural tube, then all the other organs. Organogenesis is completed by the 9th week; from this moment, a rapid increase in the mass of the embryo begins and they begin to call it the “fetus”.
A long (38-40 weeks) pregnancy, characteristic of a person, allows a child to be born well-formed, capable of many movements, with a developed taste, hearing, etc. Another feature of human ontogenesis is an increase in the pre-reproductive period, which expands opportunities for learning and acquiring social skills.
Question 2. How do nicotine, alcohol and drugs affect the development of the human embryo?
When ingested by the mother, nicotine easily penetrates through the placenta into the circulatory system of the fetus, causing a narrowing of its vessels. This leads to a deterioration in the supply of oxygen and nutrients to the child, which can cause developmental delay. Women who smoke are more likely to have preterm labor or miscarriage in late pregnancy. Nicotine increases the likelihood of infant mortality by 30% and the likelihood of developing heart defects by 50%.
Alcohol also easily passes through the placenta, causing mental retardation, microcephaly, behavioral disorders, decreased growth rate, and muscle weakness in the fetus. Alcohol significantly increases the likelihood of abnormalities in the development of the child.
Drugs have a very strong effect on the fetus. They not only cause severe developmental disorders, but can also lead to the formation of dependence, when a withdrawal syndrome occurs in a child after birth.
Question 3. What environmental factors have an impact on the development of the human embryo?
The development of the embryo can be influenced by:
- the level of provision of the mother's body with nutrients;
- environmental ecology;
- mother's use of nicotine, alcohol, narcotic and medicinal substances;
- viral diseases of the mother during pregnancy: hepatitis, HIV, rubella, etc.;
- stress endured by the mother (strong negative emotions, excessive physical activity).
Question 4. List the periods of postembryonic development of a person.
Postembryonic human development is divided into three stages:
- pre-reproductive stage - the period of childhood, which is noticeably increased in humans compared to other mammals;
- the reproductive stage is the longest period of post-embryonic development, it begins from the moment of puberty (11-14 years); post-reproductive stage (aging): occurs after the end of the reproductive period.
Aging affects all levels of organization of the human body: there is a violation of DNA replication and protein synthesis, the intensity of metabolism in cells decreases, their division and tissue recovery after injuries slow down, and the work of all organ systems worsens. However, with a reasonable diet, active lifestyle and proper medical care, this period can be extended by several decades. material from the site
Question 5. What consequences in human development can lead to a lack of vitamin D and inadequate nutrition?
Vitamin D is known to regulate calcium absorption in the intestines and its deposition in the bones. Lack of vitamin D leads, first of all, to disorders in the formation of the skeleton (rickets).
Malnutrition, and first of all, a lack of proteins of animal origin, leads to a slowdown in the growth of children and the appearance of mental disorders in them (lag in mental development). This state is called protein starvation. It is due to a deficiency in vegetable proteins of most of the essential amino acids necessary for our body. Proteins of animal origin (dairy, egg, meat, fish) can partly be replaced only by proteins of legumes.
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On this page, material on the topics:
- human ontogeny
- features of ontogeny are characteristic of humans
- human ontogeny, reproductive health abstract
- human reproductive health brief essay
- human ontogeny reproductive health
I. Embryonic period development (from the Greek word embryon - embryo) -
First 8 weeks of development: splitting up - the formation of a single-layer embryo of the blastula; gastrulation - the formation of first two, and then a three-layer embryo - gastrula, the resulting layers are called germ layers; histogenesis - formation of tissues; organogenesis - the formation of organs.
Each of the germ layers gives rise to certain organs. From ectoderm are formed: nervous system, the epidermis of the skin and its derivatives (horny scales, feathers and hair, teeth). From mesoderm musculature, skeleton, excretory, reproductive and circulatory systems are formed. From endoderm the digestive system and its glands (liver, pancreas), respiratory system are formed.
I - zygote;
II, 2 blastomeres;
II - 8 blastomeres;
II - 32 blastomeres (morula);
III - blastula stage;
IV - gastrula;
V - laying of tissues and organs:
1 - neural tube;
2 - chord;
3 - ectoderm;
4 - endoderm;
5 - mesoderm.
Rice. Early stages of lancelet development
Fetal (fetal) period of development. (fetis - fruit). From the 9th week, when the fetus already has all the organ systems. Starting at 9 weeks, the human fetus is called fruit . In humans, antenatal development lasts 38-42 weeks (from the Greek "ante" - before, "natus" - birth)
II. Postembryonic period of development - from the moment of birth to death of the organism.
Juvenile period(before puberty) proceeds depending on the type of ontogenesis: direct type or developed with metamorphosis
Straight type of development - a born organism has all the main characteristics of an adult animal, it differs mainly in size and proportions of the body. For higher mammals and humans, an intrauterine type of development is characteristic, for reptiles and birds - oviparous.
Exception: oviparous mammals - platypus and yachidna.
Indirect type of development - embryonic development leads to the development of a larva, which differs from an adult organism in external and internal signs. Characteristic of many invertebrates, often fish. Example: a caterpillar develops from butterfly eggs, tadpoles develop from frog eggs.
Depending on the characteristics of the transformation of the larva into an adult form, 2 types of indirect ontogenesis are distinguished:
FROM incomplete transformation - larvae develop gradually, consistently losing temporary larval organs and acquiring permanent ones characteristic of an adult. Example: tadpoles - live in aquatic environment, have temporary organs gills, tail, 2-chambered heart; adult frogs - lungs, 3-chambered heart, limbs. It is also typical for: ticks, bedbugs, orthoptera (grasshoppers, lice, dragonflies, cockroaches). in the process of growth and development, the larvae molt several times (cockroaches molt 6 times) and after each molt they become more and more like an adult.
FROM complete transformation (metamorphosis ) is characteristic of several orders of insects, butterflies, beetles, Diptera (mosquitoes, flies), Hymenoptera (bees, wasps, ants), fleas, etc. The larvae have a worm-like structure and are completely different from adults.
Rice. Development of insects with incomplete (I) and complete (II) cessation. 1 - eggs, 2,3,4,5,6 - larvae; 7 - pupa; 8 - adult form (imago).
At the end of the feeding period, the larva turns into an immobile stage - chrysalis covered with a dense chitinous sheath. Inside the pupa, special enzymes lyse all organs except for a few cells called imaginal discs. Adult organs develop from disc cells.
Mature, puberty. It is characterized by the greatest independence, activity of the organism in the environment.
The period of old age.
Growth and development.
The transition of functional systems to the mode of maturation of the body is characterized by the growth of organs and tissues of the body, the establishment of appropriate proportions of the body. In the process of individual development, several types of growth are distinguished: limited and unlimited; isometric and allometric.
Limited(definite). Growth is confined to certain stages of ontogeny. Example: insects grow only during molts; in humans, growth stops at the age of 13-15 years. During puberty, there may be a pubertal growth spurt.
Unlimited growth is seen in fish, lifelong houseplants, or perennials.
Isometric growth Growth in which an organ grows at the same rate as the rest of the body. A change in body size does not accompany a change in its shape. Characteristic of fish and insects with incomplete metamorphosis (locusts, except for wings and genitals)
allometric called growth in which this organ grows at a rate greater than the rest of the body. The growth of an organism leads to a change in its proportions. They are characteristic of mammals and humans. In almost all animals, the reproductive organs develop last.
BASICS OF GENETICS.
Genetics- a science that studies the patterns of inheritance and variability.
The task of genetics: the study of the problems of storage, transmission, implementation of the variability of hereditary information.
Methods:
1. hybridological method(crosses) - developed by G. Mendel, is the main one in genetic research. The method makes it possible to reveal patterns of inheritance of individual traits and properties during sexual reproduction of organisms.
2. Cytogenetic method- allows you to study the karyotype of body cells and identify genomic and chromosomal mutations. With the advent of this method, the causes of multiple human diseases have been established (Downa village, etc.)
3. genealogical method(pedigrees) - studies of inheritance of any trait in a person in a number of generations (a pedigree is compiled, family members with the studied trait are noted)
4. twin method- study twins with the same genotypes, one hundred allows you to identify the influence of the environment on the formation of traits.
5. Biochemical method– studies metabolic disorders resulting from gene mutations.
6. Population-statistical method- allows you to calculate the frequency of occurrence of genes and genotypes in a population.
Basic concepts.
Ontogeny is the process of individual development of various organisms from the beginning of existence to the very end of life. This term was proposed by a German scientist in 1886. In the article, we will briefly consider ontogeny, its types and their specificity in various kinds.
Ontogeny of unicellular and multicellular
In protozoa and bacteria, it almost coincides with In these organisms, ontogeny begins with the appearance unicellular organism by cell division. ending this process death resulting from adverse influences, or another division.
The ontogenesis of multicellular species that reproduce asexually begins with a group of cells separating from the mother's organism (remember, for example, the process of hydra budding). Dividing by mitosis, these cells form a new individual with all organs and systems. In species that reproduce sexually, the process of ontogeny begins with the fertilization of the egg, after which a zygote is formed, which is the first cell of a new individual.
Ontogenesis is the transformation of an organism into an adult?
We hope you answered this question correctly, since at the beginning of the article the concept of interest to us is revealed. And the types of ontogenesis, and this process itself, as you remember, refer to the entire life of the organism. They cannot be reduced to the growth of an individual before its transformation into an adult. Ontogeny is a chain of complex processes that occur at all levels of the body. Their result is the formation of vital functions, structural features inherent in individuals of this species, and the ability to reproduce. Ontogeny ends with processes that lead to aging and then to death.
The following 2 main periods are distinguished in ontogenesis - embryonic and postembryonic. On the first of them, an embryo is formed in animals. It forms the main organ systems. Then comes the post-embryonic period. During it, shaping processes end, then puberty occurs, then reproduction, aging and, finally, death.
Implementation of hereditary information
The new individual receives with the genes of the parents a kind of instructions that indicate what changes will occur in the body for it to successfully pass life path. Therefore, the process of interest to us is the realization of hereditary information. Next, we will consider in more detail ontogeny (types and their features).
Direct and indirect ontogeny
With the direct type, the organism that was born is basically similar to an adult, there is no stage of metamorphosis. With an indirect type, a larva appears, which differs in its internal and external structure from an adult organism. It differs in the way of movement, the nature of nutrition, and also has a number of other features. The larva turns into an adult as a result of metamorphosis. It gives organisms great benefits. This type of development is sometimes called larval. The direct type is found in fetal and non-larval form.
Let's consider each of them in more detail.
Indirect ontogeny: types, periods
The larvae that are born live independently. They actively feed, develop and grow. They have a number of special temporary that are absent in adults. The larval (indirect) type of development occurs with complete or incomplete transformation. This division is carried out on the basis of the characteristics of metamorphosis, which characterizes one or another ontogeny. Its types require more detailed consideration, so we will talk about them in more detail.
If a we are talking o the larva that is born loses its larval organs over time and receives in return permanent ones that are characteristic of adult organisms (remember, for example, grasshoppers). If development is carried out with complete transformation, then the larva first becomes an immobile doll. Then an adult comes out of it, which is very different from the larva (remember butterflies).
Why do we need larvae
The reason for their existence may be that they do not use the same food as adults, thereby expanding the food base of this species. You can compare, for example, the food of caterpillars and butterflies (leaves and nectar, respectively) or tadpoles and frogs (zooplankton and insects). In addition, many species, being in the larval stage, actively develop new territories. Larvae, for example, are capable of swimming, which cannot be said about adults, which are practically motionless.
Development with metamorphosis in amphibians and fish
The types of development (ontogenesis) that occur with metamorphosis are characteristic of such vertebrates as amphibians and fish. For example, a tadpole (larva) is formed from a frog egg, which in its structure, habitat and lifestyle is very different from adults. The tadpole has gills, a tail, a lateral line organ, and a two-chambered heart. Like fish, it has one circulation. When the larva reaches a certain level of development, its metamorphosis takes place, during which the signs characteristic of an adult organism appear. This is how the tadpole eventually turns into a frog.
In amphibians, the existence of a larval stage provides the opportunity to live in different environment and use different foods. The tadpole, for example, lives in water and eats vegetable food. The frog, on the other hand, eats animal food and leads a mostly terrestrial lifestyle. Many insects have a similar phenomenon. A change in the habitat, and hence in the way of life, during the transition from the larval stage to the stage of an adult organism reduces the intensity of the struggle for survival within a given species.
Direct type of development
We continue to describe the main types of ontogeny and move on to the next - direct. It is also called non-larval. It is intrauterine and oviparous. Let us briefly characterize these types, the stages of ontogeny of which differ significantly from each other.
Oviparous type
It is observed in a number of vertebrates, as well as in birds, reptiles, fish and some mammals, in which the eggs are rich in yolk. The embryo develops inside the egg for a long time. The main vital functions are carried out by the embryonic membranes - special provisional organs.
Mammals that lay eggs
There are 3 types of mammals that lay eggs, which is generally not characteristic of this class. However, at the same time, the cubs are fed with milk. This is typical of mammals in general. (pictured above), long-nosed and short-nosed echidna. They live in Australia, Tasmania and New Guinea and belong to the order Monotremes.
These animals resemble reptiles not only in laying eggs, but also in the structure of the excretory, reproductive and digestive systems, as well as many anatomical features (the structure of the spine, ribs and shoulder girdle, the structure of the eye). Monotremes, however, are classified as mammals, since their heart has 4 chambers, they are warm-blooded, covered with fur, and feed their young with milk. In addition, mammals are also characterized by a number of structural features of their skeleton.
intrauterine type
The topic "Types of ontogeny and their characteristics" is practically covered by us. However, we have not yet talked about the last, intrauterine type. It is characteristic of humans and higher mammals, in whose eggs there is practically no protein. In this case, all the vital functions of the formed embryo are realized through the maternal organism. For this purpose, the placenta, a special provisional organ, develops from the tissues of the fetus and mother.
Placenta
This organ exists only during pregnancy. The placenta in humans is located in the body of the uterus more often along its posterior wall, less often along the anterior one. It is completely formed at about 15-16 weeks of pregnancy. At the 20th week, an active exchange begins to occur through the placental vessels.
The human placenta is a round flat disc. Its weight at the time of birth is about 500-600 g, thickness - 2-3 cm, and diameter - 15-18 cm. There are 2 surfaces in the placenta: fetal and maternal.
At the end of pregnancy, a physiological reaction occurs. It is accompanied by the appearance of areas of salt deposition, a reduction in the exchange surface area. The process of childbearing continues ontogeny.
The types we have considered have only been briefly described. We hope you found all the information you need in this article. The definition and types of ontogeny should be well known if you are preparing for an exam in biology.
Ontogenesis(from the Greek όntos - being) or individual development - the development of an individual from the moment of formation of a zygote or other germ to the natural completion of its life cycle (until death or cessation of existence in its former capacity). From a genetic point of view, ontogeny is a process of deployment, implementation of hereditary information embedded in germ cells.
Ontogeny is an integral property of any individual, independent of its systematic affiliation. Without the emergence of ontogeny, the evolution of life would be unthinkable. Individual development organisms are closely related to historical development – phylogenesis(from the Greek phyle - tribe).
The ontogeny of individuals of different species varies in duration, rate, and character of differentiation. In multicellular animals and humans, the beginning of ontogeny is preceded by a period proembryonic (pre-embryonic) development - progenesis . During this period, germ cells are formed, the process of fertilization and the formation of a zygote takes place.
In ontogeny, four periods are distinguished - pre-embryonic, embryonic (prenatal ), postembryonic (postnatal ) and state of the adult body including aging and death. In animals, the embryonic period is usually rich in differentiation, while in plants, the postembryonic period is rich. Each of these periods of ontogeny, in turn, can be subdivided into successive qualitative stages.
pre-embryonic includes gametogenesis and fertilization.
Embryonic period is characterized by the development of the embryo in external environment or in the genital tract of the maternal organism and rapid processes of morphogenesis. As a result of these processes, a multicellular organism appears in a short time.
There are three periods in human embryonic development: elementary , embryonic , fetal (fetal ).
Elementary period covers the first week of embryonic development. It starts from the moment of fertilization and continues until the implantation of the embryo in the uterine mucosa.
Embryonic the period in humans begins from the moment of implantation to the completion of the process of organogenesis (weeks 2–8). This period is characterized by the processes of organogenesis, specific features of the nature of nutrition - histiotrophic nutrition, when the embryo feeds on the secretion of the uterine glands and the decay products of the tissues of the uterine mucosa. In this period of development, placental circulation is absent for a long time, and character traits characteristic of the human fetus.
Fetal, or the fetal period of human embryonic development, begins from the 9th week after fertilization and continues until birth. This period is characterized by increased growth, rapid shaping processes, specific features of the nature of nutrition - hemotrophic nutrition that occurs in connection with the functioning of the placental circulation. Characteristics of the periods of human embryonic development are presented in table 5 .
Table 5
Characteristics of periods of human embryonic development
Postembryonic the period in humans and mammals begins from the moment of birth, exit from the embryonic membranes until the end of life and lasts until puberty. In oviparous animals, this period begins from the moment the young individual leaves the egg membranes; in plants - from the moment the primary root appears.
Transition to adult organism can be done directly or indirectly. In this regard, three types of ontogeny are distinguished: larval , non-larval and intrauterine .
Larval, or indirect the type of development is characteristic of many coelenterates, worms, molluscs, crustaceans, insects, lancelet, lungfish and some bony fish, amphibians. This type of development is distinguished by the presence of larval stages. After leaving the egg, the larvae lead an active lifestyle and forage for food themselves. The larvae are not similar to the parental form - they are much simpler, have provisional organs, which are subsequently resorbed (dissolved) and are not observed in an adult.
Further transformation - metamorphosis - larvae into an adult can be carried out according to the type complete transformation , in which the larva differs sharply from the adult and goes through a number of stages of development, of which the main stage is the pupa (butterfly). Or development occurs without a pupal stage - according to the type incomplete transformation , and the larva itself is similar to an adult animal, but smaller (grasshopper, locust).
non-larval (straight ) the type of development is characterized by the fact that an organism appears, similar to the adult parental form, but differing from it in smaller sizes and not fully developed reproductive apparatus. In such forms of animals (fish, reptiles, birds, oviparous mammals, cephalopods, coelenterates), all organs are formed in the embryonic period of development, and growth, puberty and differentiation of functions occur in the postembryonic period. Direct development is associated with a large supply of yolk in the egg and the presence of protective devices for the developing embryo, or with the development of the embryo in the mother's body.
intrauterine (straight ) is the latest phylogenetic type of development. It is characteristic of higher mammals and humans, in which the eggs are poor in yolk and the development of the embryo occurs in the uterus of the mother's body. In this case, provisional extra-embryonic organs are formed, the most important of which is the placenta.
Life cycles of organisms
Life cycle, or development cycle, consists of successive phases (which are often called stages), marking the most important, nodal states of the body - birth , development and reproduction .
In the life cycles of sexually reproducing organisms, two phases are distinguished - haploid and diploid . The relative duration of these phases varies among representatives of different groups of living organisms. So, in protozoa and fungi, the haploid phase predominates, while in higher plants and animals, the diploid one.
The elongation of the diplophase during evolution is explained by the advantages of the diploid state over the haploid one. Due to heterozygosity and recessiveness in the diploid state, various alleles are preserved and accumulated. This increases the amount of genetic information in the gene pools of populations and species, leading to the formation of a reserve of hereditary variability, which is promising for further evolution. At the same time, in heterozygotes, harmful recessive alleles do not affect the development of the phenotype and do not reduce the viability of organisms.
Life cycles are simple and complex . Complex ones consist of simple cycles, which in this case turn out to be open links of a complex cycle.
The alternation of generations is characteristic of almost all evolutionarily advanced algae and all higher plants. A generalized diagram of the life cycle of a plant in which alternation of generations is observed is shown in Fig. eleven.
Rice. 11. A generalized scheme of the life cycle of a plant in which alternation of generations is observed
An example of a plant with a simple cycle would be the single-celled green alga Chlorella, which reproduces only by spores. The development of chlorella begins with autospores. Even inside the shell of the mother cell, they dress with their own shells, becoming completely similar to an adult plant.
Young chlorella grow, reach maturity and become an organ of sporogenesis - receptacle dispute. In the mother cell, 4-8 autospores appear - daughter chlorella. As a result, the life cycle of chlorella is represented as a sequence of three key phases: autospore → vegetative plant → reproductive cell (receptacle) → autospore etc.
Thus, a simple life cycle during reproduction by spores has a sequence of only three nodal phases: 1 - a unicellular germ as the initial phase of the plant, 2 - an adult unicellular or multicellular organism, 3 - the mother (reproductive) cell of the germ. After the third phase, the course of life leads again to the phase of a unicellular germ.
Such simple life cycles are not characteristic of plants. In the vast majority of plant groups, complex life cycles are observed. They usually include two, sometimes three simple cycles. In addition, in complex cycles (during sexual reproduction) there are necessarily 1–2 separate gamete phases and zygotes .
For example, an isosporous fern in nature is represented by two forms of individuals - the fern itself and the fern growth. Fern growth (small green plates, barely visible on the soil) is the direct offspring of large pinnate fern specimens. It is short-lived, but manages to give rise to the life of a single large-leaved individual. As a result, alternation of generations is observed: fern → sprout → fern.
A fern that reproduces by spores is called sporophyte (asexual generation), and the outgrowth reproduces by gametes and is called gametophyte (sexual generation). Gametophyte and sporophyte are determined only by the method of reproduction of the individual. The separate existence of sporophyte and gametophyte is impossible, and they only apply to plants with a strict alternation of generations.
In angiosperms, the female gametophyte is usually reduced to seven cells, has no archegonia, and is called the embryo sac. The embryo sac, homologous to the outgrowth, is microscopically small and is located deep in the flower.
The male gametophyte of seed plants develops from a microspore and is a pollen grain (pollen) that germinates into a pollen tube with the formation of two spermatozoa. The life cycle of a flowering plant is shown in Fig. 12.
Rice. 12. Life cycle of a flowering plant
Life cycles become much more complicated if sexual reproduction alternates with parthenogenetic and asexual reproduction. There are haplo-diploid organisms in which one sex is always only in the haplophase, and the other in both the diplo- and haplophase. Such organisms include the honey bee (Fig. 13).
Rice. 13. Life cycle of a bee
somatic cells the uterus of the bee family is diploid, and the haplophase is represented in it only by gametes. In the worker bee, the ovaries are reduced, and there is no haplophase in its life cycle. Drones develop parthenogenetically from unfertilized eggs and have a haploid set of chromosomes. Due to the replacement of meiosis by mitosis in the gametogenesis of drones, their spermatozoa also turn out to be haploid. Therefore, drones exist only in the haplophase.
Fungi are distinguished by especially wide variability of life cycles (Fig. 14). In their life cycle, three nuclear phases are clearly expressed - haploid, diploid and dikaryon.
The dikaryon is found in Ascomyces and Basidiomyces; in the latter it makes up the greater part of the cycle.
The haploid state in Basidiomyces is transient, while the diploid state exists only as a zygote.
In fungi and algae, the ratio of the duration of the haplophase and diplophase changes, so different intermediate variants of life cycles are observed.
Rice. 14. Scheme of the main life cycles in fungi
(changes in the nuclear phase are indicated by different shading,
arrows show the direction of development)