Template talk:Week 4 Embryo Stages and Events table
Template:Week 1 Embryo Stages and Events table
Week 2 - Human Embryo Stages and Events (GA week 4) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Stage 5 | Implantation | |
X inactivation | ||
Stage 6 | Chorionic Cavity | |
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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Week 3 - Human Embryo Stages and Events (GA week 5) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Stage 7 | Gastrulation primitive node (Hensen's node, primitive knot) The small circular region located at the cranial end of the primitive streak, where gastrulation occurs, and is a controller of this process. The process establishes the 3 germ cell layers: Endoderm, Mesoderm and Ectoderm. The second role is to act as an initial generator of the left-right (L-R) body axis. | |
Stage 8 | Neural - neurogenesis, neural groove and folds are first seen | |
Stage 9 | Musculoskeletal - somitogenesis, first somites form and continue to be added in sequence caudally (1 - 3 somite pairs).
Neural - the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open Neural Crest - mesencephalic neural crest is visible[1] | |
Heart - cardiogenesis, week 3 begins as paired heart tubes. | ||
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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Week 4 - Human Embryo Stages and Events (GA week 6) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Stage 10 |
neural crest - differentiation at spinal cord level from day 22 until day 26 neural - neural folds begin to fuse near the junction between brain and spinal cord, when neural crest - cells are arising mainly from the neural ectoderm neural crest - trigeminal, facial, and postotic ganglia components visible[1] neural crest - migration of vagal level neural crest cells begins (7-10 somite stage) neural - Brain rostral neural tube forms 3 primary brain vesicles (week 4) respiratory - Week 4 laryngotracheal groove forms on floor foregut. | |
heart - begins to beat in Humans by day 22-23, first functioning embryonic organ formed. | ||
Stage 11 |
thyroid - thyroid median endodermal thickening in the floor of pharynx neural - rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in two areas simultaneously. The two lips, however, behave differently. Optic ventricle appears | |
Stage 12 |
pituitary - Week 4 hypophysial pouch, Rathke's pouch, diverticulum from roof liver septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae[2] neural - caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2) neural - secondary neurulation begins neural crest - cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus arteriosus[1] neural crest - vagal neural crest enter the foregut (20-25 somite stage) | |
Stage 13 | Neural - the neural tube is normally completely closed, ventricular system now separated from amniotic fluid. Neural crest at spinal level is segregating, and spinal ganglia are in series with the somites. Spinal cord ventral roots beginning to develop.[3]
telencephalon cavity appears liver epithelial cord proliferation enmeshing stromal capillaries[2] smell Crest comes from the nasal placodes[4] integumentary - 4 weeks simple ectoderm epithelium over mesenchyme integumentary - 1 to 3 months ectoderm - germinative (basal) cell repeated division of generates stratified epithelium; mesoderm - differentiates into connective tissue and blood vessels | |
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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Week 5 - Human Embryo Stages and Events (GA week 7) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
pituitary - Week 5 elongation, contacts infundibulum, diverticulum of diencephalon
heart - Week 5 septation starts, atrial and ventricular respiratory - Week 5 left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity) respiratory - Week 5 to 17 lung histology - pseudoglandular hearing - Week 5 cochlear part of otic vesicle elongates (humans 2.5 turns) | ||
Stage 14 | ectoderm - sensory placodes, lens pit, otocyst, nasal placode, primary/secondary vesicles, fourth ventricle of brain
mesoderm - continued segmentation of paraxial mesoderm (somite pairs), heart prominence Head - 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum Body - heart, liver, umbilical cord, mesonephric ridge visible externally as bulges. Limb - upper and lower limb buds growing neural - first appearance of the future cerebral hemispheres. Cerebellar plate differentiated to an intermediate layer, and future rhombic lip identifiable[1] liver hepatic gland and its vascular channels enlarge, hematopoietic function appears[2] | |
Stage 15 |
neural - cranial nerves (except olfactory and optic) are identifiable in more advanced embryos[3] | |
vision - 35 to 37 days retinal pigment present | ||
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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Week 6 - Human Embryo Stages and Events (GA week 8) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Pituitary - Week 6 connecting stalk between pouch and oral cavity degenerates
Parathyroid - Week 6 diverticulum elongate, hollow then solid, dorsal cell proliferation Thymus - Week 6 diverticulum elongate, hollow then solid, ventral cell proliferation Adrenal - Week 6 fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla neural crest cells from adjacent sympathetic ganglia Respire - Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes Tongue Week 6 - gustatory papilla, caudal midline near the foramen caecum (week 6 to 7 - nerve fibers approach the lingual epithelium) | ||
Stage 16 | Neural - first parasympathetic ganglia, submandibular and ciliary, are identifiable[1]
Limbs upper limb bud nerves median nerve, radial nerve and ulnar nerve entered into hand plate, myoblasts spindle shaped and oriented parallel to limb bud axis. Heart - outflow tract elliptical configuration with four cushions, the two larger fusing at this stage. Semilunar valve leaflets form at the downstream end of the cushions Head lip and palate components of the upper lip, medial nasal prominence and maxillary process present, median palatine process appears. | |
Stage 17 |
Neural - telencephalon areas of the future archicortex, paleocortex, and neocortex, visible. Beginning of future choroid plexus[2] Sense - Smell olfactory nerve fibres enter the brain[3] Neural - primordium of the epidural space appears first on the ventral part of the vertebral canal and develops rostro-caudally[4] Pancreas - rotation of the developing stomach moves ventral bud dorsally and fuses with the dorsal bud. | |
Heart - separation of common cardiac outflow (aortic arch and pulmonary aorta) | ||
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References |
Week 7 - Human Embryo Stages and Events (GA week 9) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
{{Pancreas{{ Week 7 to 20 pancreatic hormones secretion increases, small amount maternal insulin
respiratory Week 7 - enlargement of liver stops descent of heart and lungs | ||
Stage 18 |
limb bone form by endochondrial ossification and throughout embryo replacement of cartilage with bone (week 5-12). smell vomeronasal fibres and nervus terminalis[1] liver obturation due to epithelial proliferation, bile ducts became reorganized, continuity between liver cells and gut[2] | |
liver (stage 18 to 23) biliary ductules developed in periportal connective tissue produces ductal plates that receive biliary capillaries[2] | ||
Stage 19 | Neural System Development accessory olivary nucleus appears[4] | |
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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Week 8 - Human Embryo Stages and Events (GA week 10) | ||
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Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | ||
Event | ||
Stage 20 |
Head scalp vascular plexus visible limb upper limbs begin to rotate ventrally neural - amygdaloid body has at least four individual nuclei[1] oculomotor nerve shows a dorsolateral and a ventromedial portion rhombic lip (rhombencephalon) formation of the cerebellum (intermediate layer) and of the cochlear nuclei cerebellum cell layer (future Purkinje cells) develops choroid plexuses of the fourth and lateral ventricles | |
Gastrointestinal Tract anal (cloacal) membrane perforates | ||
Stage 21 |
neural - cortical plate appears in the area of future insula[2] limb upper and lower limbs rotate Intraembryonic Coelom pericardioperitoneal canals close | |
Stage 22 |
neural - neocortical fibres project to epithalamus, to dorsal thalamus, and to mesencephalon[2] limb fingers and toes lengthen Sense - Smell Stage 22 to early fetal period - migratory streams of neurons from the subventricular zone of the olfactory bulb towards the future claustrum[3] | |
Genital 8 Weeks Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione
Genital 8 to 12 Weeks - hCG stimulates testosterone production Tongue Week 8 - nerves penetrate epitheilai basal lamina and synapse with undifferentiated, elongated, epithelial cells (taste bud progenitor cell) | ||
Stage 23 | Stage 23 defines the end of the embryonic (organogenesis) period
mesoderm heart prominence, ossification continues Head nose, eye, external acoustic meatus, eyelids, external ears, rounded head Body - straightening of trunk, heart, liver, umbilical cord, intestines herniated at umbilicus limb upper limbs longer and bent at elbow, hands and feet turned inward, foot with separated digits, wrist, hand with separated digits Extraembryonic Coelom chorionic cavity is now lost by fusion with the expanding amniotic cavity neural - rhombencephalon, pyramidal decussation present, nuclei and tracts similar to those present in the newborn cerebellum present as only a plate connected to midbrain and hindbrain through fibre bundles[4] axial skeleton vertebral column 33 or 34 cartilaginous vertebrae (20-33 mm in total length), vertebral pedicles, articular and transverse processes identifiable (no spinous processes)[5] | |
Week 8 | stomach - Week 8 - Gastrin containing cells in stomach antrum. Somatostatin cells in both the antrum and the fundus. | |
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below. | ||
References
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