GENERAL EMBRYOLOGY - PERIODS IN DEVELOPING FETUS
Embryology studies will develop human from fertilization until birth (gestation-38th weeks, or 40 wks).
Periods of fruit development are: preembrionski (lasting from fertilization until the end of the second week), Embryonic (lasts from the third to the end of 8 weeks) and fetal (runs from 9 to 38 weeks). The fruit in the embryonic period is called an embryo, fetus and fetal. The origins of all organs are formed in the embryonic period. In the fetal period comes to strong growth of the fetus, especially in the region of the head, as well as to morphological and functional differentiation of all organs are formed in the embryonic period. Further differentiation processes continue even after birth (postnatal period of development).
Part of the embryo and fetus on whose head is referred to as cranial (head), the last part of the caudal (tail), the ventral side of the ventral and dorsal side of the dorsal.
MAIN CHARACTERISTICS OF DEVELOPMENT
The main characteristics of development includes processes that occur in the process of creating every tissue and organ in the human body. This includes the following processes:
1. The proliferation - increasing the number of cells that occurs as a result of a number of asymmetric cell division by division (when the mother of one daughter cells are formed identical to the mother cell and daughter cell that directs the differentiation);
2. Growth - weight gain and the size of the formed tissue, organ, or whole organism, which occurs as a result of proliferation, ie. creating a large number of cells and the formation of a large amount of extracellular matrix;
3. Determination - predestination cells to be under the influence of inductive factors differentiate into specific cell types (in the body there are about 200 types of cell phenotype). Determination is a restriction mechanism to reduce, limit the ability of cells to develop into all cell types (Totipotency, pluripotency);
4. Induction - the process of operation of a cell or group of cells that secrete inductors (hormones, growth factors, cytokines, etc..) To neighboring (paracrine action) or distant (endocrine action) cells to differentiate; inducer cells can secrete inductive molecules can produce extracellular matrix containing inductive molecules, or can be transferred to a neighboring cell inductive molecules in direct contact (communicant). An example of the inductor is notohorda.
5. Differentiation - the ability of cells to morphologically and functionally differentiate into a specific cell type; The process starts with operation of the inductive factors on cell receptors, followed by a nucleus initially creates a specific mRNA which is determined by the synthesis of specific proteins characteristic of the differentiated cells (e.g., muscle cells contain specific proteins, actin and myosin);
6. Migration - the ability of cells in embryogenesis change position, will help companies move;
7. Integration - the process of connecting or switching cells deriving from various germinal sheets (ectoderm, endoderm and mesoderm); so the epithelial cells of the colon arise from the endoderm, connective tissue and muscles of the mesoderm, and ectoderm of intestinal ganglia.
Sex cells (gametes)
Sperm
Sperm is a male sex cells (Figure). It occurs in the testes in the process of spermatogenesis. Of undifferentiated spermatogonia, starting from the onset of puberty, mitosis and meiosis I and II, occur four spermatozoa with a haploid set of chromosomes (22, 22, or X, Y). Each sperm has a head (containing lysozyme-Akroza sail) and a tail that is movable because it has a flagellum (tail movement is first acquired graduating sperm from the testicles into the epididymis, where they spend two weeks -maturacija, and mobility is considerably increased by the accidental displacement of sperm into the vagina where spend around 7 hours - capacitation). From the moment the sperm are in the male genital tract expelled into the vagina their fertilizing power lasts for one to three days.
Oocyte
Oocyte is female gamete. Undifferentiated oogonia settled gonads late embryonic period in the fetal period are included in meiosis I and stop the diktiotenom stage (primary oocytes to 5 months IU). The process of follicular maturation, which begins at the age of puberty, the mature tertiary follicles during ovulation frees the secondary oocyte, and only after the entry of sperm into the secondary oocyte meiosis II ends with the ovum to form the haploid number of chromosomes (22, X) and three small non-functional cell-position.
The process of releasing the oocytes from a tertiary ovarian follicle is called ovulation and lasts from the first period - menarche to menopause and last-going in the middle of the menstrual cycle (14 days if the cycle lasts 28 days). Oocyte is a large circular cells. It has a nucleus and numerous organelles including cortical granules and Balbijanijevo vitelinsko little body. The secondary oocyte, after leaving the ovary during ovulation is capable for fertilization following 12 - 24 hours.
Impregnation
Fertilization or fertilization represents the entry of sperm into the secondary oocyte (Figure). From the ovary during ovulation releases secondary oocytes wrapped in a thick glycocalyx, with porcine zona pellucida and follicular cells that build the corona radiata. She gets affected fimbriae of the fallopian tubes (the tiny, finger extensions) and enters the lumen of the initial, expanded part of the fallopian tubes (vial), where he meets with a lot of sperm. Only one sperm succeeds in entering that. impregnates secondary oocytes. On the large lysozyme on the head, akrozoma released hydrolytic enzymes (hijalorunidaza and acrosin) enabling it to break through the layer of follicular cells and pass through the zona pellucida - akrozomska reaction. The penetration of sperm through the membrane of oocytes enabled by the existence of specific receptors on the membrane of sperm cells that bind to specific receptor sites in the zone pellucida and the cell membrane of oocytes. Immediately after the passage of sperm through the membrane of oocytes, oocyte cortical granules are released which are located directly below the membrane (cortical reaction or reaction zone) whose content changes transience membrane (becomes impassable), and prevents the penetration of other sperm in her, that is preventing polispermiju.
When the first sperm penetrates the secondary oocytes, fertilization occurs. Then secondary oocytes finishes second meiotic division and becomes the egg or ovum. In the egg A merging of male and female pronuclei, ie. connecting two sets of haploid number of chromosomes. The result of fertilization is the creation of the first cell of a new organism - a zygote that has a diploid number of chromosomes and has a certain gender (male or female, depending on the sperm that fertilized oocyte, ie. Whether he owned the X or Y sex chromosome), as well as the initiation of grooving .
PREEMBRIONSKI PERIOD OF DEVELOPMENT
Preembrionski period covers the first two weeks of development. In this period comes to segmentation (scratching) zygote, morula creation, blastocyst, its implantation, creating dvolisnog embryonic disk, trophoblast differentiation, creating ekstraembrionskog mesoderm, amnion, chorion and yolk sac.
First week of development
During the first week of development zygote, surrounded with porcine zona pellucida, from ampoules fallopian tube to the uterus moves (figure). On that occasion, the zygote is subject to segmentation (rutting). First the zygote splits into two cells, two blastomeres (dvoćelijski stage), followed by four (four-cell stage). The cells continue to divide by mitosis, and the germ, which makes 16-32 blastomeres, called morula. At the end of the first week, the morula is transformed into a structure known as a blastocyst (blastula). It consists of embryoblast (inner cell mass), the trophoblast (the outer cell mass) and blastocistne cavity (blastocel). At the end of the first week of development the blastocyst reaches the uterine cavity, get the zone pellucida and begins implantation (implantation of the blastocyst in the endometrium of the uterus).
The second week of development
In the second week of coming to the end of the implantation of the blastocyst and its differentiation (Figure). A blastocyst immersed in its embryonic pole of the endometrium (where the embryoblast, part of which creates the fruit). At this point the trophoblast differentiates into the outer part - syncytiotrophoblast (composed of multinucleated cytoplasm) and the inner part - cytotrophoblasts (composed of blocky stem cells). Trophoblast cells proliferate, creating finger-like extensions (future chorionic villi are absent or villus). These cells their hydrolytic enzymes break down the structure of the endometrium and allow penetration of the blastocyst in the endometrium. In syncytiotrophoblast appear cavities - lacunae (as intervilozni spaces of the placenta), which will be the endometrial blood vessels to enter the mother's blood.
At the same time, in the differentiation blastocyst embryoblast. Its cells are grouped into two layers, the epiblast and the hypoblast, building a double-layer (bilaminar) embryonic disc. Epiblast cells are cylindrical, and the cells hypoblast polygonal shape. Peripheral epiblast cells differentiate, proliferate and migrate creating amnion cells, amnioblaste containing the amniotic cavity. At the same time and by the same token, peripheral hypoblast cells lining the inner surface of cytotrophoblasts, creating Hojzerovu membrane, where blastocistna cavity now becomes the primary yolk sac.
New differentiation of peripheral epiblast cells produce cells that make the extra- mesoderm. He separates the interior - visceral and external - parietal list. Visceral sheet coated Hojzerovu membrane and amnion and the parietal aligns with cytotrophoblasts. Visceral sheet will redraw the primary yolk bag, and the greater part of its arise secondary yolk sac. Between two sheets ekstraembrionskog mesoderm, which they keep in touch via mesenchymal stem end (future umbilical cord), is the chorionic cavity. Thus were the amnion and chorion, ie. extra- envelope.
Amnion consists of amniotic epithelium and list ekstraembrionskog visceral mesoderm. On the epiblast closes the amniotic cavity where the fetus develops surrounded by amniotic fluid. Amnion protects the fruit from mechanical injury. Horion make parietal list ekstraembrionskog mesoderm and trophoblast. Horion on embryonic sex shows numerous extensions - shaggy chorion (chorion frondozum), while in other parts of the smooth surface - smooth chorion (chorion left) who do not participate in the formation of the placenta and the membranes than amniohoriona. Implantation of the blastocyst
Horion frondozum will be included in the fetal part of the placenta that helps metabolism and synthesizes many hormones. The reaction of progesterone prepared endometrium to the presence of the blastocyst, in the sense that its cells enlarge and they are filled with nutrients, referred to as the decidual reaction, and so altered endometrium decidua. By its localization according to the fruit decidua may be: basal decidua (endometrium below horion frondozuma, forms part of the placenta), kapsularis decidua (endometrium around the smooth chorion and above the implanted embryos) and parietal decidua (the rest of the endometrium).
Nutrition fruit
The fruit (blastomeres) in the first week of food stocks present in the egg cell. During implantation, until the beginning of the third week of development, the embryo (blastocyst) is fed histotrofnim diet of mother's tissues, transport of nutrients from the tissue altered decidual endometrial cells in the blastocyst. When in embryonic tissues at the beginning of the third week of development, create blood vessels (first in extra- mesoderm), will enable hemotrofna phase nutrition of the fetus, at which the transport of nutrients and harmful substances and gases carry the blood of the fetus (the placental chorionic Cupic) and maternal blood (in interviloznim areas of the placenta), through the placental barrier.
Embryonic PERIOD OF DEVELOPMENT
Embryo developmental period lasts from the beginning of the third by the end of 8 weeks of development. During this period creates a three-layer (trilaminarni) embryonic disc composed of three germ layers, ectoderm, endoderm and mesoderm, forming the beginnings of organs, and the fruit receives human form.
Third week of development
In the third week, in the process of gastrulation, creates a gastrula, ie. formation that has three germ layers: ectoderm, endoderm and mesoderm. At the beginning of the third week, the embryonic disc is twofold. On it differs HEAD part, where the oropharyngeal membrane and beyond prehordalna plate, and tail (caudal) part, which contains the cloacal membrane. At the rear of the epiblast, from the cloacal membrane to primitive nodes (node Hensenov) occurs and extends primitive streak (Fig). The primitive streak has primitive groove, primitive nodule and primitive dimple. Primitive streak cells differentiate, proliferate and plunge through the dimple, migrate toward the hypoblast replacing its cells and building new layer - endoderm (Fig.). The second wave of differentiation, proliferation and cell migration primitive streak continues and the newly created cells settled

Primitive streak
FORMATION OF HUMAN trefoil space between the epiblast mesoderm and endoderm creating (intraembrionski mesoderm) (Fig.). Epiblast (the current primitive ectoderm), or cells that do not gastruliraju become definitive ectoderm.
The level of oropharyngeal and cloacal membrane comes to the separation of the ectoderm and the endoderm. Migrating cells intraembrionskog mesoderm from the primitive streak occurs in the cranial direction, laterally and centrally. Central cell migration takes place from Hensenovog nodules according prehordalnoj panel. Created tape cell is referred to as notohordalni extension or axial mesoderm. It creates a central cavity, and the extension becomes notohordalni channel. Cells of this channel interact with the endoderm, after which the channel is again transformed into a solid tape - notohordu (Fig.). Notohorda located in the axis of the embryo, that embryo divides into two equal parts. All described processes are essentially regulated by a gene. Particularly important role is regulatory Hox genes, which are expressed in the cells of all three germ layers, and that their activity regulates the creation of specific transcription factors responsible for activating the structural gene important for cranio-caudal and left-right orientation.
The differentiation of germinal sheets
Derivatives of the ectoderm
Ectoderm to differentiate the superficial ectoderm and neuroektoderm. Neuroektoderm be differentiated into neural tube and neural crest. The creation of the neural tube is called neurulation. This process is enabled by inductive influence notohorde the ectoderm. Above notohorde, which extends along the axis of the body, the ectoderm thickens, creating the neural plate, and then invaginiše, creating a gradual nerve groove and nervous gutter. He is separated from the rest of the ectoderm (superficial ectoderm) and form the neural tube. It is at the front and rear of the first open, but soon these openings (cranial and caudal Neuropa) close (25-27, day).
In the cranial region of the neural tube will expand and form the cerebral vesicles (since the brain), while from its rear, weakening labor incurred spinal cord. On the lateral ends of the nerve plate, later on tops nervous gutters, in the form of linear thickening, create the neural crest. Neural crest cells are capable of migration, so they can settle parts of the body to give the corresponding derivatives (in the head migrate into the mesoderm of the head and form ektomezenhim; in the adrenal glands give her medulla, and intestines enteric plexus).
Since there will be superficial ectoderm: epidermis of the skin and its derivatives (nails, hair and glands of the skin), the front part of the mouth - stomodeum (epithelium of the oral cavity, tooth enamel and adenohypophysis), plakode nose, ears and lenses, corneal epithelium and the outer ear canal and epithelium of the inner ear; of neural tube will occur: central nervous system (brain and spinal cord), the retina of the eye and the neurohypophysis; from the neural crest will occur: the peripheral nervous system (spinal and vegetative ganglia), endocrine cells (medulla of the adrenal gland and calcitonin cells of the thyroid gland), melanocytes of the epidermis and connective tissue, cartilage, bones and muscles of the head and neck.
Derivatives of the endoderm
Due to the latero-lateral bending embryonic disc when an embryo receives a body cavity, endoderm turns into a primitive intestine. That, based on topographic and spatial division can be the front, middle (communicates with the secondary yolk bag) and rear hose (Fig.).
From the endoderm occur: primordium pharynx (the middle ear epithelium cells of the thyroid gland, parathyroid gland cells, epithelial cells of the thymus and tonsils), and gland epithelium of the respiratory system (trachea, bronchi, bronchioles, alveoli), epithelia and glands of the esophagus, stomach, small and colon, including the parenchyma of the liver (hepatocytes) and pancreatic and epithelium and glands of the urogenital sinus (will give the epithelium of the bladder, urethra and paired vestibular glands, and vaginal epithelium). Derivatives of the mesoderm
Mesoderm may be extra- and intraembrionski. Extra- mesoderm becomes part of the amnion and chorion. It first formed blood vessels.
Intraembrionski mesoderm differentiate, watching from the axis of the body, the following sections: axial (notohorda), paraksijalni, intermediate and lateral (Fig.). The lateral mesoderm separates the part that abuts the ectoderm (somatopleuralni mesoderm), part of which abuts the endoderm (splanhnopleuralni mesoderm).
From notohorde will arise pulpozus nucleus (part of the intervertebral disc) which is located between the vertebrae.
Paraksijalni mesoderm will be in all parts of the body except the head (this will form the mesoderm, endoderm head DERIVATIVES
DERIVATIVES mesoderm segmentisati in somite. Each somit will be further differentiated into three parts: dermatome (will give the dermis of the skin), sclerotic (will give connective tissue, cartilage and bone walls of the body and extremities) and Miot (skeletal muscle will give body and limbs).
Intermediate mesoderm will give the urogenital system (kidneys, ureters, gonads and genital ducts).
Somatopleuralni lateral mesoderm will give parjetalne leaves the pericardium, pleura and peritoneum and dermis lateral and ventral body wall.
Splanhnopleuralni lateral mesoderm will give heart, connective tissue and smooth muscle organs whose epithelium arises from the endoderm (eg, trachea, intestine, liver), as well as parts of the pericardium visceral pleura and peritoneum.
From intraembrionskog mesoderm, in addition to such derivatives are formed and: muscle, cartilage, bone, blood and lymph vessels, blood cells, the cortex of the adrenal gland, lymph nodes and spleen.
Extra- STRUCTURES
The extra- structures include: the amnion, chorion, yolk sac, allantois, the umbilical cord and placenta (Figure). Amnion and chorion Figure is described above.
Placenta
The placenta (placenta) consists of two parts: fetal and maternal. Fetal part, viewed from the side of the fruit, it chorionic plate (amnion and chorion, since it is due to growth of the fruit of a merger between the amnion and chorion) of which, to her mother's work are due or adherent stem Vilusi
(Chorionic villi are absent). They branch out on intermediate villus which, in the last trimester of pregnancy branches out into a multitude of tiny terminal villus. In chorionic Vilusi are the blood vessels of the fetus. In the process of maturation Vilusi placenta passes through three stages. First, the primary (make them trophoblastic extensions furry villus sampling), followed by secondary (when they invade the parietal list ekstraembrionskog mesoderm) and finally tertiary (when in their appearance mesoderm blood vessels of the fruit). Vilusi covered sincicijumtrofoblastom and about villus placenta are intervilozni spaces that meet the mother's blood reached the maternal blood vessels.
Mother makes part of the placenta decidua basalis where decidualne cells (arising from endometrial stromal cells) surrounded by fibrinoid. Fibrinoid is very red substance made up of fibrin, the immunoglobulin secretion of placental cells and dead trofoblasnih. It can accumulate under the chorionic plate (subhorionski Langerhans), through chorionic villus (Rorovi) and the place of separation of the placenta from the uterine endometrium (Nitabuhov). Placental septa extend towards horionskoj board and incomplete parts of the fetal part of the placenta at 15-20 režnjeva- cotyledons.
Nutrition fetus, ie. delivering nutrients and oxygen to the fetus, as well as the removal of carbon dioxide and harmful products from the fetus takes place as there is exchange of the said substances between blood fetus and the mother's blood through the placenta barrier. This exchange mostly takes place through the placental barrier terminal villi. Placental barrier consists of the following structures (viewed from the intervillous space): sincicijum and cytotrophoblasts, basal membrane of the trophoblast, chorionic thinned binder, basement membrane and capillary endothelium of the capillaries. Through this barrier from the mother to the fetus include: oxygen, water, various ions, carbohydrates, amino acids, hormones, antibodies, vitamins, drugs and alcohol. On the other hand, the fetus in the mother's blood carry carbon dioxide, urea, bilirubin and others. metabolites.
The functions of the placenta are numerous: respiratory (transport of gases involved in breathing), nutrition (through her fetus receives nutrients), excretion (decomposition products of the metabolism of the fetus through the placenta leaving), endocrine (placental cells secrete a number of hormones, for example, human chorionic gonadotropin and lactogen, progesterone).
Umbilical cord
The umbilical cord (umbilical funiculus) arises from mesenchymal stem end and connects the fetus and the mother and the blood vessels of the fetus and placenta. It is about 50cm. Cross section of the umbilical cord vary following structure: amniotic epithelium (envelops the umbilical cord), three-vessel, two umbilical artery (carry venous blood), single umbilical vein (artery carrying blood from the placenta) and mucosal connective tissue (surrounding blood vessels ).
STEM CELLS
Stem (stem) cells can be extracted from embryoblast blastocyst (embryonic) tissue of the fetus (fetal), or from the body of an adult (adult). These cells have an unlimited capacity for self-renewal may be in artificial conditions, under the influence of specific inductive factors, differentiate into different cells (pluripotency), have the ability and the migration of immune tolerance. These cells represent the future of medicine, because it will not be able to be used in transplantation therapy for a variety of disease (leukemia, neurological diseases, etc.).

Congenital anomalies - Causes
Congenital anomalies are disorders (structure and function) that occur during development and are present at birth. The cause of these, developmental disorders, in most cases is vague. However, the appearance of anomalies of development (backlog growth, mental retardation, microcephaly, anencephaly, cardiac septum defects and many others) are blamed: genetic factors (eg, chromosomal aberrations), maternal infection (rubella virus, varicella, HIV), physical factors ( ionizing radiation, elevated temperature), chemical agents and drugs (methotrexate, amphetamines, ACE-inhibitors, streptomycin, tetracycline, mercury, lead, alcohol, cigarettes, drugs and others.