formation of basic organs and systems
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55 terms
Terms | Definitions |
|---|---|
 4 | neural tube is formed opposite the somites but it is widely open at the rostral and caudal neuropores |
| 4 | pharyngeal arches are visible |
| 4 | first arch and second arche are distinct, mandible and maxilla are formed |
| 4 | embryo is slightly curved because of the head and tail folds |
| 4 | heart produces a large ventral prominence and pumps blood |
| 4 | 3 pairs of pharyngeal arches are visible |
| 4 | rostral neuropore is closed |
| 4 | forebrain produces a prominent elevation of the head and folding of the embryo has given the embryo a characteristic c shaped curvature |
| 4 | long curved tail is present |
| 4 | upper limb buds become recognizable as small swellings on the ventrolateral body walls |
| 4 | otic pits are visible |
| 4 | ectodermal thickening indicating the future lenses of the eyes called lens placodes are visible on the sides of the head |
| 4 | fourth pair of pharyngeal arches and lower limb buds are visible |
| 4 | attenuated tail is characteristic feature |
| 4 | rudiments of many of the organ systems especially the cardiovascular system are established |
| 4 | caudal neuropore is usually closed |
| 5 | changes in body form are minor |
| 5 | growth of head exceeds that of other regions |
| 5 | enlargement of head is caused by the rapid development of the brain and facial prominences |
| 5 | face soon contacts the heart prominence |
| 5 | rapidly growing second pharyngeal arch overgrows the third and fourth arches forming a lateral ectodermal depression on each side = cervical sinus |
| 5 | upper limb buds are paddle shaped and lower limb buds are flipperlike |
| 5 | mesonephric ridges indicate the site of the mesonephric kidneys which are interim kidneys in humans |
| 6 | upper limbs begin to show regional differentiation as the elbows and large hand plates develop |
| 6 | primordia of the digits called digital rays begin to develop in the hand plates, indicates the formation of digits |
| 6 | it has been reported that embryos show spontaneous movements such as twitching of the trunk and limbs |
| 6 | development of the lower limbs occurs somewhat later than that of the upper limbs |
| 6 | several small swellings called auricular hillocks develop around the pharyngeal (brachial) groove (or cleft) between the first 2 pharyngeal arches, groove becomes the external acoustic meatus |
| 6 | auricular hillocks around external acoustic meatus fuse to form the auricle |
| 6 | eye is now obvious because of retinal pigment |
| 6 | head is now much larger relative to the trunk and is bent over the large heart prominence, due to bending in the cervical region |
| 6 | the trunk and neck have begun to straighten |
| 6 | embryos show reflex responses to touch |
| 6 | intestine enters the extraembryonic coelom in the proximal part of the umbilical cord |
| 6 | umbilical herniation occurs because the abdominal cavity is too small at this age to accommodate the rapidly growing intestine |
| 7 | the limbs undergo considerable change |
| 7 | notches appear between the digital rays in the hand plates, clearly indicating the future digits |
| 7 | communication between the primitive gut and yolk sac is now reduced to a relatively slender duct, the yolk stalk |
| 7 | ossification of the bones of the upper limbs has begun |
| 8 | digits of the hand are separated but webbed |
| 8 | notches are now clearly visible between digital rays of the fan shaped feet |
| 8 | tail is still present but stubby |
| 8 | the scalp vascular plexus has appeared and forms a band around the head |
| 8 | all regions of the limbs are apparent, the digits have lengthened and are completely separated |
| 8 | purposeful limb movements first occur |
| 8 | ossification begins in the lower limbs and is first recognizable in the femur |
| 8 | all evidence of tail has disappeared |
| 8 | scalp vascular plexus now forms a band near the vertex (crown) of the head |
| 8 | hands and feet approach each other ventrally |
| 8 | embryo has distinct human characteristics, head is still disproportionately large, almost half the embryo |
| 8 | neck region is established and the eyelids are more obvious |
| 8 | eyelids are closing and they begin to unite by epithelial fusion |
| 8 | intestines are still in the proximal portion of the umbilical cord |
| 8 | auricles of the external ears begin to assume their final shape but they are still low set on the head |
| 8 | sex differences exist in the appearance of the genitalia though not distinctive enough to permit accurate sexual identification |
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