Talk:Rat Development Stages

Rat Development

rat

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Standard Stages (Witschi)

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Age (days)

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Size (mm)

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Identification of Stages

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Cleavage and Blastula

Day 1

| 1 | 1 | 0.07 | 1 cell (in oviduct)

Day 2

| 2 | 2 | 0.08 x 0.06 | 2 cells (in oviduct)

Day 3

| 3 | 3 | 0.08 x 0.05 | 4 cells (in oviduct)

| 4 | 3.5 | | 8-12 cells (in oviduct)

|- | 5 | 3.25 | 0.08 x 0.04 | Morula (in uterus)

Day 4

| 6 | 4 | (0.08 x 0.03) | Early blastocyst (in uterus)

Day 5

| 7 | 5 | (0.12 x 0.05) | Free blastocyst (in uterus)

Day 6

| 8 | 6 | (0.28 x 0.07) | Implanting blastocyst, with trophoblastic cone and inner cell mass; outgrowth of endoderm (hypoblast)

|- | 9 | 6.75 | | Diplotrophoblast; inner cell mass (pendant), covered with endoderm

Day 7

| 10 | 7.25 | (0.3 x 0.1) | Near complete implantation; pendant begins differentiation into embryonic and extra-embryonic parts

|- | 11 | 7.75 | (0.5 x 0.1) | Completion of implantation; primary amniotic cyst; ectoplacental cone

Day 8

| 12 | 8.5 | (1.04 x 0.26) | Connecting ectochorionic and amniotic cavities; rudiments of amniotic folds; primitive streak; start of 3rd layer formation; blastemas of heart and pericardium

Day 9

| 13 | 9 | 1.0 | Presomite neurula; fusion of chorio-amniotic folds, chorio-amniotic stalk; neural plate; embryo bent dorsally; bud of allantoic stalk

| 14 | 9.5 | 1.5 | Somites 1-4 (occipital); pendant with 3 cavities: ectochorionic cyst, exocoelom, and amniotic cavity; ectochorionic cyst collapsing; allantoic stalk projects into exocoelom; embryo bent dorsally

Day 10

| 15 | 10 | 2 | Somites 5-12 (cervical); 1st visceral arch; ectochorionic cyst fused with ectoplacenta and with allantoic stalk; regression of peripheral (distal) yolk sac and trophectoderm (diplotrophoblast); Reichert's membrane; gonia in endoderm; embryo bent dorsally

| 16 | 10.5 | 2.4 | Somites 13-20 (upper thoracic); 2 visceral arches; disc and yolk sac placentas; appendicular folds; embryo reverses, curves ventrally

Day 11

| 17 | 11 | 3.3 | Somites 21-25 (lower thoracic); yolk stalk closes at level of 15th somite; primary gonia in mesentery; primitive streak disappears; tail bud becomes organized; arm and leg buds recognizable

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Tail Bud Embryo

| 18 | 11.5 | 3.8 | Somites 26-28 (upper lumbar); 3 visceral arches; arm buds recognizable

|- | 19 | 11.75 | 4.2 | Somites 29-31 (lower lumbar); visceral arches I-IV; cervical folds; appendicular folds and buds

| 20 | 11.875 | 5 | Somites 32-33 (upper sacral)

Day 12

| 21 | 12 | 5.1 | Somites 34-35 (lower sacral); deep cervical sinuses

| 22 | 12.125 | 5.2 | Somite 36 (1st caudal); olfactory pits

|- | 23 | 12.25 | 5.6 | Somites 37-38 (caudal); start of umbilical herniation

| 24 | 12.375 | 6 | Somites 39-40 (caudal)

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Complete Embryo

|- | 25 | 12.5 | 6.2 | Somites 41-42 (caudal); occipital somites dispersing; 4 visceral arches; deep cervical sinuses; arm buds at somite levels 8-14, about as high as long; leg buds at somite levels 28-31, smaller; body forms a spiral of about 11/2 turns, the left face and trunk applied to yolk sac, the right side turned toward placenta; tail and allantoic stalk rise to the placenta

| 26 | 12.75 | 7 | Somites 43-45 (caudal); mandibular, maxillary, and frontonasal processes; cervical sinuses closing; mammary welts; differentiaion of handplates; arm buds vascularized, brachial nerves entering; beginning of umbilical hernia

Day 13

| 27 | 13 | 8 | Somites 46-48 (caudal); prominent facial processes and clefts; nose-snout projecting; cervical sinuses closed; primordia of mammary glands; round handplates and footplates; larger umbilical hernia

| 28 | 13.5 | 8.5 | Somites 49-51 (caudal); 1st visceral cleft transforms into external ear duct; precartilaginous condensations in handplates

Day 14

| 29 | 14 | 9.5 | Somites 52-55 (caudal); auricular hillocks on visceral arches I and II

| 30 | 14.5 | 10.5 | Somites 56-60 (caudal); body uncoils; mandibular precartilage; nearly round opening of external ear duct; pleuroperitoneal canal has become very narrow

Day 15

| 31 | 15 | 12 | Somites 61-63 (caudal); facial clefts closed; pleuroperitoneal canal closed; complete diaphragm

| 32 | 15.5 | 14.2 | Somite 64 (caudal); pinna turns forward; maximal size of umbilical hernia

Day 16

| 33 | 16 | 15.5 | Somite 65 (usually this is last caudal); snout lifts off chest; last stage of metamorphosis

Day 17-18

| 34 | 17-18 | 16-20

  | 1st fetal stage: rapid growth of eyelids (eyes entirely covered at end of 18th day); palate complete; pinna covers ear duct; umbilical hernia withdraws

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Day 19-22

ante-natal | 19-22 | 20-40

  | 2nd fetal stage: sealed eyelids; fetal membranes and placentas reach peak of development; tail grows to 10mm;

Neural System Development Pathways to the supraoptic nucleus from the brainstem and the main olfactory bulb - on the expected day of parturition, but before birth, projections from the organum vasculosum of the lamina terminalis to the supraoptic nucleus became significantly activated. PMID: 11113350

Birth occurs (22nd day in rat, 19th day in mouse)

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Postnatal

| 1-16 post-partum | 40-1001 | After birth, fetus becomes a breathing and suckling nestling2; during 1st 16 days (22 to 38 days total age), eyelids remain sealed and external ear ducts plugged with periderm

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post-natal | 17+ post-partum | 100+1 | Periderm seals of ears and eyelids vanish; active feeding begins within next 3 days and weaning after 1 week (total weaning age, 45-48 days for rats and mice)

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* Age (days)- days after fertilization

* Size (mm)- largest and smallest dimensions