La semana 4: Derivados de las capas germinales y plegamientos

Neurulacin: Sistema nervioso y cresta neural Derivados mesodrmicos Derivados endodermicos

El embrin trilaminar: el destino de las capas embrionarias

Derivados de las capas germinalesEctodermo axial: cerebro, mdula espinal Ectodermo para-axial (cresta neural) Ganglios raqudeos, melanocitos, mdula adrenal, Ectodermo para-axial (placodas) Odo, cristalino, epitelio nasal, ganglios craneales Ectodermo lateral: Epidermis Mesodermo axial: Notocorda Mesodermo para-axial: Esqueleto axial, msculo, dermis Mesodermo intermedio: Aparato uro-genital Mesodermo lateral (somatico): Tejido conectivo del tronco y extremidades Mesodermo lateral (visceral): Corazn, vasos, musculatura visceralmesenterio Endodermo: Epitelios respiratorios, digestivos y bucofarngeos A 21.70

Los derivados del ectodermo: La neurulacin

Ectodermo axial: cerebro, mdula espinal Ectodermo para-axial (cresta neural) Ganglios raqudeos, melanocitos, mdula adrenal, Ectodermo para-axial (placodas) Odo, cristalino, epitelio nasal, ganglios craneales Ectodermo lateral: Epidermis

Los derivados del mesodermo

Mesodermo axial: Notocorda Mesodermo para-axial (somites): Esqueleto axial, msculo, dermis Mesodermo intermedio: Aparato urogenital Mesodermo lateral (somatico): Tejido conectivo del tronco y extremidades Mesodermo lateral (visceral): Corazn, vasos, musculatura visceral, mesotelios

El mesodermo para-axial se organiza en bloques: los somites El nmero de somites es caracterstico de cada especie. La generacin de los somites es cclica: El reloj somtico. El gen hairy se expresa de forma cclica en el mesodermo presomtico y la parte posterior de los somites. Los somites forman bloques epiteliales. La especificacin AP de los somites depende del cdigo HOX. La especificacin DV genera dos grandes dominios: eclerotomo y dermomiotomo.

Los somites son bloque epitelizados de mesodermo

Los derivados del endodermo

Endodermo: Epitelios respiratorios, digestivos y buco-farngeos

4 Semana: Plegamiento lateral

4 Semana: Plegamiento lateral

4 Semana: Plegamiento antero-posterior

4 Semana: Plegamientos (resumen)

El plan corporal al inicio del perodo fetal: estadio 23 de CarnegirTelencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon Spinal cord

Del tercer mes al nacimiento: El perodo fetal y la placentaLas primeras 8 semanas tras la fecundacin se denominan el perodo embrionario. Durante esta fase tiene lugar la formacin del plan corporal y la organognesis. Por ello, durante esta fase el embrin es particularmente vulnerable a los agentes teratgenos. El perodo fetal comienza a partir de la 8 semana y acaba con el parto. El perodo fetal se caracteriza por el crecimiento y maduracin de los rganos, aunque una buena parte de la maduracin sucede durante los primeros meses de vida post-natal. Los cambios son continuos y no se establecen sub-perodos durante la fase fetal como se hace con los estadios de Carnegie durante el desarrollo embrionario.

El tamao del fetoEl tamao del feto se expresa como la longitud vrtex-nalga (VN) o vrtex-taln (VT) expresadas en cm, y que se pueden estimar por mtodos no invasivos.

The comparison of the fetal crown-rump length shows the enormous increase in size during the fetal period. The fetal crown-rump length at 8 weeks amounts to just 3 cm while that of the fetus at birth comes to over 30 cm (highly schematic drawing).

El peso del feto

The weight of the fetus experiences its largest increase in the third trimester. The variations, though, are quite large. This is emphasized with the scatter (light pink in the diagram). Various hormones influence intrauterine growth. Initially they are mainly maternal hormones passing through the placenta, but later, in the fetal period, hormones produced by the fetus itself are also responsible for the weight increase. The weight of the embryo/fetus can only be estimated with the help of length sectional ultrasound measurements of various structures

La placenta

La placenta humana es un rgano transitorio que media los intercambios fisiolgicos entre la madre y el feto. Su origen determina que tenga una parte fetal y otra materna, con cargas genticas diferentes. Aunque las circulaciones materna y fetal estn muy cerca, stas permanecen separadas por lo que se llama la barrera placentaria. Durante la vida fetal, la placenta cumple las funciones respiratorias, digestivas y renales. Adems, la placenta es un rgano endocrino, que mantiene la actividad de las hormonas hipotalmicas, hipofisarias y ovricas de la madre y el feto. La placenta es por lo tanto un rgano autnomo que toma funciones reguladoras muy importantes y su disfuncin es fuente de importantes patologas.

El origen de la placenta: el trofoblastoLas cluas exteriores de la blstula, el trofoblasto, originan la placenta. La actividad secretora diferencial de las culas de la mrula tras el proceso de compactacin genera la ICM y las culas del trofoblasto. 7d La actividad enzimtica en contacto con el endometrio permite la eclosin de la blstula y la implantacin. 9d El epitelio uterino recubre completamente el embrin. Las clulas uterinas en la proximidad, bajo la influebcia de la progesterona del cuerpo lteo, reaccionan a la presencia del blastocisto y se activan, convirtiendose en las clulas de la decidua.

La formacin de las membranas fetales y placentaEl embrin se nutre durante las primeras semanas por difusin simple a travs de las vellosidades corinicas. Posterioremente, la demanda de gases requiere el desarrollo de un sistema circulatorio utero-placentario, en donde las circulaciones materna y fetal estn en estrecho contacto y se maximiza el intercambio. 4s A partir de este momento, los gases y nutrientes deben pasar la barrera placentaria: Endotelio capilar de la vellosidad, tejido conectivo, citotrofoblasto, Sincitiotrofoblasto. 3s

La formacin de las vellosidadesAl inicio de la gastrulacin, el trofoblasto forma vellosidades corinicas que se vascularizan y se adentran en el endometrio. Las vellosidades estn recubiertas por citotrofoblasto. Durante esta fase, toda la cavidad celmica est rodeada por velolosidades La membrana corinica en la 3s El sincitiotrofoblasto forma la capa ms externa sin lmites celulares (sincitio), formando cordones que infiltran el endometrio. La actividad apopttica del estroma uterino forma cavidades llamadas lagunas. El sistema lacunar dura hasta el 9d, cuando se inician las vellosidades. Vellosidades en la 4s

La circulacin y barrera placentariasvasos espirales decidua espacio intervilloso: capilares maternos

corion vasos umbilicales cordn umbilical vellosidades corinicas y capilares fetales

Circulacin fetal

Circulacin materna

Algunas preguntasWhy is the embryo more sensitive than the fetus regarding infections and teratogenic substances? Into how many stages can pregnancy be subdivided? Which diagnostic possibilities are available today in order to judge the healthy development of the fetus?

ReferenciasLANGMANS, Lippincot Wiliams & Wilkins 9-10th editions, 2004, 2006 LARSENS HUMAN Elsevier, 2008 EMBRYOLOGY, Churchill Livinstone,

EMBRYOLOGY.CH http://www.embryology.ch/genericpages/moduleembryoen.html PATHOPHYSIOLOGY OF THE REPRODUCTIVE SYSTEM: http://www.vivo.colostate.edu/hbooks/pathphys/reprod/index.html

Ms informacin: edad fetalIn obstetrics the pregnancy weeks (PW) are normally reckoned from the date of the Last Menstrual Period (LMP). This is a point in time that many women can easily remember. Computed this way, the pregnancy lasts 40 weeks and the embryonic period accordingly - 10 weeks. Caution is advisable, though, when wishing to calculate the moment of ovulation - and thus fertilization, closely connected with it because the moment of ovulation can vary and depends on many factors (conditioned by the environment and psychological aspects). In embryology the temporal indices (i.e., the PW), therefore, always refer to the moment of fertilization even though in practical midwifery the time following the LMP is still used for computations. After the 8th week, the fetus takes on typical human features, even though at the end of the first trimenon, the head is still relatively large in appearance. The eyes shift to the front and the ears and nasal saddle are formed. The eyelids are also clearly recognizable now. On the body, fine lanugo hairs are formed, which at the time of birth are replaced by terminal hairs. The physiologic umbilical hernia that arises in the embryonic period has mostly disappeared. In the second trimenon the mother feels the first movements of the child. In the last trimenon the subcutaneous fatty tissue is formed and stretches the still wrinkled skin of the fetus. The skin becomes covered more and more with vernix caseosa. This is a whitish, greasy substance und consists of flaked off epithelial cells and sebaceous gland secretions. In neonatology this vernix caseosa is an important criterion for judging the maturity of the child. If the birth occurs post-term, it disappears again

Ms informacin: crecimiento fetalThe following hormones are responsible for the intrauterine growth of the child: Growth hormone (somatotropin), produced in the adenohypophysis, and insulin-like factors from the liver stimulate the growth and metabolism of cartilage, bones and muscles. Glucocorticoid (e.g. ACTH), produced in the adrenal cortex, accelerates fetal maturation. Thyroid hormones (T3 and T4) released by the thyroid gland have an influence on fetal growth. Insulin is an endocrine regulator of prenatal growth. Local growth factors influence tissue growth and development. Placental hormones have a large influence on the child's growth. The placenta produces factors that are partly protective and partly stimulating. Prenatal growth thus depends on various elements. Sufficient and balanced maternal nourishment is the prerequisite for the normal thriving of a child. Further maternal factors are her size, her parity (i.e., how many children the woman she has already given birth to), diseases such as hypertonia, diabetes mellitus, etc., as well as her living conditions (smoking, drinking and/or other unhealthy habits).

Mas info: estimacin del peso fetal por medio de ultrasonidosFig. 13 - Normal weight distribution curve The intrauterine weight measurements are based on extrapolated values of various diameters obtained with ultrasound (green). They do not correlate exactly with the postnatal weight measurements. One distinguishes three phases in the weight distribution curve: the intrauterine period, the transition period (or the perinatal period the first 6 - 12 days) and the extra-uterine period (from 6 - 12 days following delivery

Ms informacin: perodo de sensibilidad fetal (teratognesis)Segment A represents the embryonic period in which the embryo is especially sensitive with respect to deformities. Within the first eight weeks, the incidence of deformities (blue curve), that lead to miscarriages, decreases from more than 10% to 1% during the fetal period (B). The frequency of neural tube defects decreases from 2.5% to 0.1% (green curve) by the end of the embryonic period

Ms informacin: la placenta humanaThe development of the placenta begins when the blastocyst evokes the decidual reaction in the maternal endometrium and transforms this into an exceedingly well perfused source of nutrition - the basal plate. The neighboring glands of the endometrium develop and the uterine wall gets to be turgid locally. If an implantation has taken place the trophoblast cells release a multiplicity of hormones (HCG = human chorionic gonadotrophine, HCS = human chorionic somatomammotrophine, and also HPL = human placental lactogen) that are necessary to coordinate the nourishment of the endometrium and to maintain the corpus luteum which, over roughly 12 weeks of the embryonic development, continues to secrete sexual steroids. Later, the placenta itself starts to secrete large amounts of progesterone and thereby takes over the glandular function of the corpus luteum. Through the lytic activity of the syncytiotrophoblast the maternal capillaries are eroded and anastomose with the trophoblast lacunae, forming the sinusoids. At the end of the pregnancy the lacunae communicate with each other and form a single, connected system that is delimited by the syncytiotrophoblast and is termed the intervillous space After the 16th day the extra-embryonic mesoblast also grows into this primary trophoblast villus, which is now called a secondary villus 5c and expands into the lacunae that are filled with maternal blood. As was already mentioned, the ST forms the outermost layer of every villus. + At the end of the 3rd week the villus mesoblast differentiates into connective tissue and blood vessels. They connect up with the embryonic blood vessels. Villi that contain differentiated blood vessels are called tertiary villi

Ms informacin: la estructura de la barrera placentariaThe structure of the placental barrier changes throughout development. In the first trimester it consists of the syncytiotrophoblast, the cytotrophoblast (Langhans' cells), the villus mesenchyma (in which numerous ovoid Hofbauer cells that exhibit macrophage properties are found) and the fetal capillary walls. During the 4th month the cytotrophoblast disappears from the villus wall (interactive diagram) and the thickness of the barrier decreases while the surface area increases (roughly 12 m2 towards the end of the pregnancy). In the 5th month the fetal vessels have multiplied their branches and gotten closer to the villus surface. During the 6th month the nuclei of the syncytiotrophoblast group together in the socalled proliferation knots. The other zones of the syncythiothrophoblast lack nuclei and are adjacent to the capillaries (exchange zones). The fetus is not rejected even though its set of chromosomes differs from that of its mother and halfway represents an allogenic transplantation to the maternal organism (two individuals of the same kind, but genetically only half identical). This phenomenon remains an enigma. After birth the maternal organism rejects any tissue of the newborn, even though the same tissue (''natural allogeneic transplantation'') was accepted, protected and nourished for nine months. During pregnancy, the mother developed a tolerance to her child. This phenomenon is based on the specific antigen property of the embryo and the placenta as well as on the transitory changes of the maternal immune system during pregnancy. Sexually transmitted diseases:In addition, the placenta also presents an incomplete barrier against certain injurious effects of drugs: Antibiotics and corticoids can pass through the placental barrier. Depending on their size, certain steroid hormones get through as well.

Ms informacin: barrera placentaria

1. Espacio intervelloso con sangre materna 2. Barrera placentaria Placental barrier of a terminal villus 3. Capilares fetales 4. Membranas basales de los capilares fetales y del sincitio trofoblasto fundidas 5. Endotelio del capilar fetal 6. Clula citotrofoblstica (infrecuente) 7. Membrana basal del capilar fetal 8. Membrana basal del trofoblasto 9. Sincitiotrofoblasto (zona rica en ncleos (proliferation knots)

Ms informacin: La deciduaEn el lugar de la implantacin, el endometrio sufre la reaccin decidual: transformacin epitelial de los fibroblstos del estroma uterino y la acumulacin de lpidos y glucgeno: la decidua. Decidua basalis, donde sucede la implantacin y tiene lugar la formacin de la placa basal (3). Esta a su vez se divide en zona compacta y zona esponjosa (la que se desprende en el parto) La decidua capsular es la que rodea el corion (2), y la decidua parietal (1) recubre el resto de la cavidad uterina (4). Alrededor del 4 mes, el fecimiento fetal colapsa el espacio uterino y ambas entran en contacto. membrana amnio-corinica

Carnegie Stages of Human Development

The embryonic time comprises 56 days, i.e., 8 weeks from the moment of fertilization. This time span is divided into 23 Carnegie stages and the stage classification is based solely on morphologic features. Carnegie stages are thus neither directly dependent on the chronological age nor on the size of the embryo. This can be illustrated by two examples: The closure of the rostral neuropore occurs by definition in stage 11 and that of the caudal neuropore in stage 12. Further, between the 25th and 32nd days of the pregnancy, the stages are determined according to the number of the somites that have been engendered. The individual stages thus differ in how long they last .

Carnegie Stages of Human DevelopmentEmbryonic period 0-8 weeks

week 4

week 8

Fetal periodBirth

Estadios de Carnegie 7-10 (1-4s)http://www.embryology.ch/francais/iperiodembry/carnegie02.html1 Vescula vitelina 2 Lnea primitiva 3 Nodo 4 Ectodermo/disco embrionario

C7/19d

C9/21d

C10/23d

1 Lnea primitiva 2 Pliegues neurales 3 Borde de seccin del amnios 4 Canal neural 5 Somites (1-3ss)

1 Borde de seccin del amnios 2a Surco neural 3 Pliegues neurales 4 Somites (4-12ss)

Estadios de Carnegie 11-12 (4-5s)C11/24d1 Tubo neural 2 Neuroporo caudal 3 Neuroporo anterior 4 Somites (13-20ss) 5, 6 arcos branquiales

C12/26d

1a Mameln maxilar 1b Mameln mandibular 2,3 Arcos branquiales (2 y 3) 4 Somites (21-29ss) 5 Tubo neural 6 Corazn P prosencfalo M Mesencfalo R romboencfalo

Fotografa de un embrin humano de 23dCavidad corinica amnios Pedculo

cabeza

Saco vitelino 2

Larsen

Ms informacin: Diagnstico prenatalNon-invasive methods of prenatal diagnoses Among today's non-invasive methods for prenatal diagnostics ultrasound stands at first place. Further possibilities, especially in advanced stages of the pregnancy and at the time of delivery, consist in the symphysisfundus uteri distance (SFD) as well as the cardiotocography (simultaneous recording of infantile heart beats and maternal labor activity). Moreover, the first infantile movements, with those giving birth for the first time (primipara) after the 18th week (20th week after the LMP), with those giving birth again (pluripara) after the 16th week (18th week after the LMP), can yield a surprisingly precise due-date. Like no other method an ultrasound examination makes it possible to obtain information - non-invasively - about the gestation age and thus about the upcoming date of birth, as well as about the intactness of the gravidity. In a normal pregnancy, an ultrasound examination has the following goals: Determining the location of the implantation Determining the vitality of the fetus/embryo Diagnosis of a multiple pregnancy Establishing the gestation age Establishing fetal growth with the aid of growth curves Determining the fetal position Determining the fetal morphology and sex Determining the position and morphology of the placenta Determining the volume of amniotic fluid Examining regions outside the cavum uteri

Ms informacin: diagnstico por ultrasonidos

Very early picture of an incipient pregnancy. An echoyielding zone of a few millimeters indicates an incipient pregnancy. This picture shows the young embryo shortly after the implantation

Ultrasound image of a multiple pregnancy. Ultrasound image from a triplet pregnancy in the 11th week.