The embryonic time comprises 56 days, i.e., 8 mainly from the minute of fertilization. This time span is divided into 23 Carnegie stages and the stage classification is based specifically on morphologic features. Carnegie stages are hence neither directly dependent ~ above the chronological age nor on the dimension of the embryo. This can be depicted by two examples: The closure that the rostral neuropore occurs by an interpretation in phase 11 and that the the caudal neuropore in stage 12. Further, in between the 25th and 32nd work of the pregnancy, the step are identified according to the number of the somites 9-13 that have actually been engendered. The individual stages for this reason differ in exactly how long they critical .

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During the embryonic period most that the body organ systems are established and also this through an enormous rapidity. Cell divisions, movement and also differentiation are the basic processes acquisition place during this phase. It is for this reason hardly surprising that this pregnancy phase is an extremely vulnerable and that deformities are developed most often during this time. The kind of deformity relies on the embryonic developmental stage.

Fig. 1 - Incidence of deformities throughout pregnancyLegend
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AB
Embryonic periodFetal period

Fig. 1Segment A represents the embryonic duration in i beg your pardon the embryo is especially sensitive v respect come deformities. In ~ the very first eight weeks, the incidence of deformities (blue curve), that bring about miscarriages, to reduce from more than 10% come 1% during the fetal duration (B). The frequency that neural tube defects decreases indigenous 2.5% to 0.1% (green curve) by the finish of the embryonic period. (2)

Fetal period

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Quiz 05

According come estimates, over 90% the the 4500 designated structures of the adult human body are already established - and can be identified - throughout the embryonic duration (1). During the fetal period the organs that formed throughout the embryonic duration grow and differentiate (organogenesis). Figure 2 shows the various temporal phases during a pregnancy. A rough classification is made by assigning trimesters (trimenon). The LMP (Last Menstruation Period) is no the real beginning of the pregnancy yet serves together a point of referral for identify the date of ovulation and thus the moment of fertilization. Usually this wake up 14 days after the beginning of menstruation, but can vary a many temporally. From the moment of the last period, one approximates 40 weeks after the last menstruation in order to determine the approximate day of bear (the second and 3rd grid marks stand for the lunar month or 4 weeks). ~ above average, though, the expression of an really pregnancy amounts to 266 days or 38 weeks (fourth grid). The embryonic duration (A) large 8 weeks and also the fetal period (B) indigenous the ninth week come the birth.

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Quiz 06

Fig. 2 - Time calculations during a pregnancyLegend
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AB
Embryonic periodFetal period

Fig. 2The schematic diagram shows the various time periods during the entire pregnancy. LMP = critical Menstruation Period. The embryonic period (A) large 8 weeks and the fetal period (B) from the 9th week to the birth, i.e., 30 weeks.

In obstetrics the pregnant weeks (PW) are usually reckoned from the day of the Last Menstrual duration (LMP). This is a suggest in time that numerous women can quickly remember. Computed this way, the pregnant lasts 40 weeks and also the embryonic period - appropriately - 10 weeks. Fist is advisable, though, as soon as wishing to calculate the minute of ovulation - and thus fertilization, closely connected with it - since the moment that ovulation have the right to vary and depends on many factors (conditioned by the environment and also psychological aspects). In inter-base.net the temporal indices (i.e., the PW), therefore, always refer come the minute of fertilization even though in handy midwifery the time complying with the LMP is still provided for computations. After the 8th week, the fetus take away on usual human features, even though in ~ the end of the first trimenon, the head is tho relatively big in appearance. The eyes change to the front and the ears and nasal saddle are formed. The eyelids are also plainly recognizable now. Top top the body, well lanugo hairs room formed, i beg your pardon at the moment of birth are replaced by terminal hairs. The physiologic umbilical hernia that arises in the embryonic duration 15-20 has mostly disappeared. In the second trimenon the mother feels the very first movements that the child. In the critical trimenon the subcutaneous fatty tissue is formed and stretches the tho wrinkled skin the the fetus. The skin becomes covered an ext and more with vernix caseosa. This is a whitish, greasy problem und is composed of flaked off epithelial cells and also sebaceous gland secretions. In neonatology this vernix caseosa is crucial criterion because that judging the maturity that the child. If the bear occurs post-term, the disappears again.

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Umbilcal cord through herniaNoseEyeEyelidEar (a: tragus, b: antitragus )MouthElbowFingerToesAtrophied embryonic tail bud
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Telencephalon
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Diencephalon
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Mesencephalon
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Metencephalon
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Myelencephalon
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Spinal cord
Fig. 3The fetus still has a big head in relationship to the rest of the body.
© Professor Kohei Shiota, Kyoto University

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