ETAPA PRENATAL Su desarrollo es: Desarrollo Físico -Etapa Germinal -Etapa Embrionaria -Etapa Fetal Desarrollo Cognoscitivo. Incluso antes de que inicie la etapa fetal, un embrión humano de 6 semanas puede arquear su espalda y cuello. Para la. Durante esta etapa, llamada período fetal, el cuerpo crece en tamaño y los on the time elapsed since the first day of the last menstrual period prior to fertilization . . Las células del embrión en crecimiento comienzan a producir una hormona.
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All embryonic and fetal ages in this program refer to the time since fertilization. Age and stage conventions adopted during the embryonic embrionari are listed in Appendix B. Researchers now know that many of the routine functions performed by the adult body become established during pregnancy — often long before birth. The developmental period before birth is increasingly understood as a time of preparation during which the developing human acquires the many structures, and practices the many skills, needed for survival after birth.
LA BIOLOGIA DEL DESARROLLO PRENATAL
Los investigadores ahora saben que muchas de las funciones rutinarias que realiza el cuerpo humano adulto se establecen durante el embarazo – a menudo mucho antes del nacimiento. Pregnancy in humans normally lasts approximately 38 weeks  as measured from the time of fertilization or conception until birth. During the first 8 weeks following fertilization, the developing human is called an embryo which means “growing within.
From the completion of 8 weeks until the end of pregnancy, “the developing human is called a fetus ,” which means “unborn offspring. A partir de semana 8 y hasta el fin del embarazo, “el ser humano en desarrollo se llama feto”, lo cual significa “hijo no nacido”. Click any footnote number to view source text. Click on any author name to view the full reference in the Bibliography.
Each of the 23 Carnegie Stages has specific structural features. As we describe various milestones of development, the Carnegie Stage at which they occur will be noted by a designation such as: See Appendix B for eftal information relating embryonic staging and age assignments. Therefore, postmenstrual age equals approximately 2 weeks at the time of fertilization. Biologically speaking, “human development begins at fertilization,”  when a woman and a man each combine 23 of their own chromosomes through the union of their reproductive cells.
The resulting single-celled embryo is called a zygote,  meaning “yoked or joined together. The zygote’s 46 chromosomes  represent the unique first edition of a new individual’s complete genetic blueprint. This master plan resides in tightly coiled molecules called G. They contain the instructions for the development of the entire body. DNA molecules resemble a twisted ladder known as a double helix. Guanine pairs only with cytosine, and adenine with thymine.
The DNA of a single cell contains so much information that if it were represented in printed words, simply listing preemrionaria first letter of each base would require over 1.
If we could uncoil all of the Embgionaria within an adult’s trillion 10 14 cells, it would extend over 63 billion 6.
Período Preembrionario y Embrionario by Doris León on Prezi
This distance reaches from the earth to the sun and back times. Approximately 24 to 30 hours after fertilization, the zygote completes its first cell division. As early as 24 to 48 hours after fertilization begins, pregnancy can be confirmed by detecting a hormone called ” early pregnancy factor ” in the mother’s blood.
Contienen las instrucciones para el desarrollo de todo el cuerpo. Esto es veces la distancia desde la tierra hasta el sol ida y vuelta. By 4 to 5 days, a cavity forms within this ball of cells and the embryo is then called a blastocyst.
The cells inside the blastocyst are called the inner fetak mass and give rise to the head, body, and other structures vital to the developing human.
Cells within the inner cell mass are called embryonic stem cells because they have the ability to form each of the more than cell types contained in the human body. After traveling down the uterine tube, the early embryo embeds itself into the inner wall of the mother’s uterus.
This process, called implantationetaps 6 days and ends 10 to 12 days after fertilization. HCG directs maternal hormones to interrupt the normal menstrual cycle, allowing pregnancy to continue. The placenta delivers maternal oxygen, nutrients, hormones, and medications to the developing human; removes all waste products; and prevents maternal blood from mixing with the blood of the embryo and fetus.
The placenta also produces hormones and maintains embryonic and fetal body temperature slightly above that of the mother’s. The life support capabilities of the placenta rival those of intensive care units found in modern hospitals. La capacidad de soporte vital de la placenta iguala la de las unidades de terapia intensiva de los hospitales modernos.
For a detailed description of the placenta vasculature see Harris and Ramsey See Cunningham et al. By 1 week, cells of the inner cell mass form two layers called the hypoblast and epiblast. The hypoblast gives rise to the yolk sac which is one of the structures through which the mother supplies nutrients to the early embryo. Ectoderm gives rise to numerous structures including the brain, spinal cord, nerves, skin, nails, and hair.
Endoderm produces the lining of the respiratory system and digestive tract and generates portions of major organs such as the liver and pancreas. Mesoderm forms the heart, kidneys, bones, cartilage, muscles, blood cells, and other structures. By 3 weeks the brain is dividing into 3 primary sections called the forebrain, midbrainand hindbrain.
Development of the respiratory and digestive systems is also underway. As the first blood cells appear in the yolk sac,  blood vessels form throughout the embryo, and the tubular heart emerges. Almost immediately, the rapidly growing heart folds in upon itself as separate chambers begin to develop. The heart begins beating 3 weeks and 1 day following fertilization. The circulatory system is the first body system, or vetal of related organs, to achieve a functional state.
Between 3 and 4 weeks, the body plan emerges as the brain, spinal cord, and heart of the embryo are easily identified alongside the yolk sac.
Rapid growth causes folding of embrionaia relatively flat embryo. Este proceso incorpora parte del saco vitelino en el revestimiento del aparato digestivo y forma las cavidades del pecho y el abdomen del ser humano en desarrollo. The technically preferred term is umbilical vesicle. By 4 weeks the clear amnion surrounds the embryo in a fluid-filled sac.
The heart typically beats about times per minute. The heart will beat approximately 54 million 5. Rapid brain preembrionria is evidenced by the changing appearance of the forebrain, midbrain, and hindbrain. Upper and lower limb development begins with the appearance of the limb buds by 4 weeks. As the skin thickens, it preembrionaira lose this transparency, which means that we will only be able to watch internal organs develop for about another month.
Between 4 and 5 weeks, the brain continues its rapid growth and divides into five distinct sections. The head comprises about one-third of the ekbrionaria total size.
Functions eventually controlled by the cerebral hemispheres include thought, learning, memory, speech, vision, hearing, voluntary movement, and problem-solving.
For information about the first-trimester, direct-imaging technique used in this program called embryoscopysee Cullen et al. The permanent kidneys appear by 5 weeks. The yolk sac contains early reproductive cells called germ cells.
By 5 weeks these germ cells migrate to the reproductive organs adjacent to the kidneys. By 6 weeks the cerebral hemispheres are growing disproportionately faster than other sections of the brain. The embryo begins to make spontaneous and reflexive movements.
A touch to the mouth area causes the embryo to reflexively withdraw its head. Este movimiento es necesario para promover un desarrollo neuromuscular normal. The external ear is beginning to take shape. By 6 weeks, blood cell formation is underway in the liver where lymphocytes are now present.
A portion of the intestine now protrudes temporarily into the umbilical cord. At 6 weeks the hand plates develop a subtle flattening. Primitive brainwaves have been recorded as early as 6 weeks and 2 days. A las 6 semanas las paletas de las manos se aplanan levemente. Nipples appear along the sides of the trunk shortly before reaching their final location on the front of the chest. Leg movements can now be seen, along with a startle response.
Se observan movimientos en las piernas y el reflejo del sobresalto. The four-chambered heart is largely complete.
LA BIOLOGIA DEL DESARROLLO PRENATAL
In females, the ovaries are identifiable by 7 weeks. En las mujeres, a las 7 semanas ya se identifican los ovarios. The hands can now come together, as can the feet. At 8 weeks the brain is highly complex  and constitutes almost half of the embryo’s total body weight. By 8 weeks, 75 percent of fetap exhibit right-hand dominance. The remainder is equally divided between left-handed dominance and no preference.
This is the earliest evidence of right- or left-handed behavior.
Del resto, la mitad demuestra ser zurdos y la otra mitad no demuestra ninguna preferencia. Pediatric textbooks describe the ability to “roll over” as appearing 10 to 20 weeks after birth. Head rotation, neck extension, and hand-to-face contact occur more often. Touching the embryo elicits squinting, jaw movement, grasping motions, and toe embrionaaria.
Between 7 and 8 weeks, the upper and lower eyelids rapidly grow over the eyes and partially fuse together. Although there is no air in the uterus, the embryo displays intermittent breathing motions by 8 weeks. By this time, kidneys produce urine which is released into the amniotic fluid. The bones, joints, muscles, nerves, and blood vessels of the limbs closely resemble those in adults. By 8 weeks the epidermis, or outer skin, becomes a multi-layered membrane,  losing much of its transparency.