Template:First Trimester Timeline
|Links: human timeline | first trimester timeline | second trimester timeline | third trimester timeline|
|Proliferative Phase||menstrual cycle changes: uterus endometrium (proliferation), ovary (Follicle Development)|
|menstrual cycle - Mid proliferative|
|menstrual cycle - Late Proliferative|
|Secretory Phase||fertilization, zygote, Secretory Phase|
|Stage 2||morula, Blastula|
|Stage 3||blastocyst Hatching (zona pellucida lost)|
|Late Secretory, blastocyst (free floating)|
|Stage 6||Chorionic Cavity|
|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
|heart cardiogenesis, week 3 begins as paired heart tubes.|
Neural Crest differentiation at spinal cord level from day 22 until day 26
Neural Crest migration of vagal level neural crest cells begins (7-10 somite stage)
neural 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.|
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.
pituitary Week 4 hypophysial pouch, Rathke's pouch, diverticulum from roof
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 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.
telencephalon cavity appears
Neural - Vascular Development - hindbrain is supplied by two parallel neural arteries (or channels) that obtain their blood supply from carotid-vertebrobasilar anastomoses given by the pharyngeal arch arteries; trigeminal artery, the otic artery, hypoglossal artery, and the proatlantal artery.
integumentary 4 weeks - simple ectoderm epithelium over mesenchyme
integumentary 1-3 months ectoderm- germinative (basal) cell repeated division of generates stratified epithelium; mesoderm- differentiates into connective tissue and blood vessels
|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|| Placodes sensory placodes, lens pit, otocyst, nasal placode, primary/secondary vesicles, fourth ventricle of brain
somite 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
limb upper and lower limb buds growing.
Neural - Vascular Development - vertebral arteries form from transverse anastomoses between cervical intersegmental arteries, beginning with the proatlantal artery and proceeding downward to the 6th intersegmental artery,
|vision 35 to 37 days retinal pigment present|
|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
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
Neural - Vascular Development - development of the middle cerebral artery is first identified as small buds originating proximal to the anterior cerebral artery on the anterior division of the primitive internal carotid artery.
limb 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.
|heart separation of common cardiac outflow (aortic arch and pulmonary aorta)|
|pancreas Week 7 to 20 pancreatic hormones secretion increases, small amount maternal insulin|
Abdominal Wall separation of the myoblasts into distinct inner and outer layers, with unidirectional orientation. Abdominal wall thicker in the region where secondary structures were forming compared with the primary body wall region, dorsally outermost layer of connective tissue approximately half of this thickness.
liver (stage 18 to 23) biliary ductules developed in periportal connective tissue
produces ductal plates that receive biliary capillaries
Head scalp vascular plexus visible
limb upper limbs begin to rotate ventrally
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 membrane perforates|
limb upper and lower limbs rotate
Intraembryonic Coelom pericardioperitoneal canals close
Abdominal Wall Myoblasts have reached the ventral midline and myotubes were present and oriented uniformly within all muscle groups. The rectus abdominis formed distinct bundles of muscle. Connective tissue layers comprised the majority of the thickness of the abdominal wall, outermost layer of connective tissue accounted for the majority of this thickness.
|Stage 22|| neural neocortical fibres project to epithalamus, to dorsal thalamus, and to mesencephalon
limb fingers and toes lengthen
|Genital 8 Weeks Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione
Genital 8 to 12 Weeks - hCG stimulates testosterone production
|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, 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
Abdominal Wall Rectus muscle forms 2 or 3 distinct layers with myotube orientation uniform in all muscles. The external oblique and internal oblique started to expand in thickness, transversus a thin layer of muscle.
|Week 8|| Stomach Week 8 - Gastrin containing cells in stomach antrum. Somatostatin cells in both the antrum and the fundus.
Genital - Female Development paired paramesonephric (Müllerian) ducts contact each other and are fused into a single tube that separates again and returns to the mesonephric (Wolffian) ducts. The paramesonephric ducts have not yet reached the urogenital sinus.
|Week 9||Beginning of Fetal Development
CRL 43 mm, femur length 6 mm
uterus - paramesonephric ducts come into apposition with the urorectal septum and begin to fuse
Gastrointestinal Tract Week 10 intestines in abdomen
Pituitary growth hormone and ACTH detectable
Pancreas Week 10 glucagon (alpha) differentiate first, somatostatin (delta), insulin (beta) cells differentiate, insulin secretion begins
Tongue Week 10 shallow grooves above the taste bud primordium
Stomach Week 10 - Glucagon containing cells in stomach fundus.
Nail Development fingernails appear
outer ear Week 10 - Meatal plug extends in a disc-like fashion, the meatus is boot-shaped with a narrow neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. Proximal portion of the neck starts to be resorbed.
inner ear Week 10 - neural-crest-derived melanocytes migrate into the cochlea. They penetrate the basement membrane of the lateral wall epithelium and develop into the intermediate cells of the stria vascularis.
|Week 10 - CRL 55 mm, femur length 9 mm, biparietal diameter 17 mm|
Thyroid colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis
Stomach Week 11 - Serotonin containing cells in both the antrum and the fundus.
|Week 11 - CRL 68 mm, femur length 12 mm, biparietal diameter 20 mm|
- O'Rahilly R & Müller F. (2007). The development of the neural crest in the human. J. Anat. , 211, 335-51. PMID: 17848161 DOI.
- O'Rahilly R & Müller F. (1990). Ventricular system and choroid plexuses of the human brain during the embryonic period proper. Am. J. Anat. , 189, 285-302. PMID: 2285038 DOI.
- Godlewski G, Gaubert-Cristol R, Rouy S & Prudhomme M. (1997). Liver development in the rat and in man during the embryonic period (Carnegie stages 11-23). Microsc. Res. Tech. , 39, 314-27. PMID: 9407542 <314::AID-JEMT2>3.0.CO;2-H DOI.
- Müller F & O'Rahilly R. (1988). The development of the human brain from a closed neural tube at stage 13. Anat. Embryol. , 177, 203-24. PMID: 3354839
- Menshawi K, Mohr JP & Gutierrez J. (2015). A Functional Perspective on the Embryology and Anatomy of the Cerebral Blood Supply. J Stroke , 17, 144-58. PMID: 26060802 DOI.
- Müller F & O'Rahilly R. (2004). Olfactory structures in staged human embryos. Cells Tissues Organs (Print) , 178, 93-116. PMID: 15604533 DOI.
- Pearson AA. (1980). The development of the eyelids. Part I. External features. J. Anat. , 130, 33-42. PMID: 7364662
- Clugston RD, Zhang W & Greer JJ. (2010). Early development of the primordial mammalian diaphragm and cellular mechanisms of nitrofen-induced congenital diaphragmatic hernia. Birth Defects Res. Part A Clin. Mol. Teratol. , 88, 15-24. PMID: 19711422 DOI.
- Nichol PF, Corliss RF, Yamada S, Shiota K & Saijoh Y. (2012). Muscle patterning in mouse and human abdominal wall development and omphalocele specimens of humans. Anat Rec (Hoboken) , 295, 2129-40. PMID: 22976993 DOI.
- Müller F & O'Rahilly R. (1988). The first appearance of the future cerebral hemispheres in the human embryo at stage 14. Anat. Embryol. , 177, 495-511. PMID: 3377191
- Patelska-Banaszewska M & Woźniak W. (2005). The subarachnoid space develops early in the human embryonic period. Folia Morphol. (Warsz) , 64, 212-6. PMID: 16228957
- Müller F & O'Rahilly R. (1988). The development of the human brain, including the longitudinal zoning in the diencephalon at stage 15. Anat. Embryol. , 179, 55-71. PMID: 3213956
- Müller F & O'Rahilly R. (1989). The human brain at stage 16, including the initial evagination of the neurohypophysis. Anat. Embryol. , 179, 551-69. PMID: 2751117
- Müller F & O'Rahilly R. (1989). The human brain at stage 17, including the appearance of the future olfactory bulb and the first amygdaloid nuclei. Anat. Embryol. , 180, 353-69. PMID: 2802187
- Patelska-Banaszewska M & Woźniak W. (2004). The development of the epidural space in human embryos. Folia Morphol. (Warsz) , 63, 273-9. PMID: 15478101
- Hashimoto R. (2003). Development of the human Müllerian duct in the sexually undifferentiated stage. Anat Rec A Discov Mol Cell Evol Biol , 272, 514-9. PMID: 12740945 DOI.
- Keibel F. and Mall FP. Manual of Human Embryology II. (1912) J. B. Lippincott Company, Philadelphia.
- Congdon ED. Transformation of the aortic-arch system during the development of the human embryo. (1922) Contrib. Embryol., Carnegie Inst. Wash. Publ 277, 14:47-110.
- Teal SI., Moore GW. and Hutchins GM. Development of aortic and mitral valve continuity in the human embryonic heart. (1986) Amer. J. Anat., 176:447-460.
- Wells LJ. Development of the human diaphragm and pleural sacs. (1954) Contrib. Embryol., Carnegie Inst. Wash. Publ. 603, 35: 107-134.
- Jirásek JE. Development of the Genital System and Male Pseudohermaphroditism. (1971) Johns Hopkins Press, Baltimore.
- Wilson KM. Origin and development of the rete ovarii and the rete testis in the human embryo. (1926) Carnegie Instn. Wash. Publ. 362, Contrib. Embryol., Carnegie Inst. Wash., 17:69-88.
- Gasser RL. Atlas of Human Embryos. (1975) Harper & Row, Hagerstown, Maryland.
- Müller F & O'Rahilly R. (1990). The human brain at stages 18-20, including the choroid plexuses and the amygdaloid and septal nuclei. Anat. Embryol. , 182, 285-306. PMID: 2268071
- Müller F & O'Rahilly R. (1990). The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum. Anat. Embryol. , 182, 375-400. PMID: 2252222
- Witt M & Reutter K. (1996). Embryonic and early fetal development of human taste buds: a transmission electron microscopical study. Anat. Rec. , 246, 507-23. PMID: 8955790 <507::AID-AR10>3.0.CO;2-S DOI.
- Müller F & O'Rahilly R. (1990). The human rhombencephalon at the end of the embryonic period proper. Am. J. Anat. , 189, 127-45. PMID: 2244584 DOI.
- O'Rahilly R, Muller F & Meyer DB. (1980). The human vertebral column at the end of the embryonic period proper. 1. The column as a whole. J. Anat. , 131, 565-75. PMID: 7216919
- Streeter GL. Developmental horizons in human embryos (fourth issue). A review of the histogenesis of cartilage and bone. (1949) Carnegie Instn. Wash. Publ. 583, Contrib. Embryol., 33: 149-169. PMID: 18144445
- Wünsch L & Schober JM. (2007). Imaging and examination strategies of normal male and female sex development and anatomy. Best Pract. Res. Clin. Endocrinol. Metab. , 21, 367-79. PMID: 17875485 DOI.
- Locher H, de Groot JC, van Iperen L, Huisman MA, Frijns JH & Chuva de Sousa Lopes SM. (2015). Development of the stria vascularis and potassium regulation in the human fetal cochlea: Insights into hereditary sensorineural hearing loss. Dev Neurobiol , 75, 1219-40. PMID: 25663387 DOI.
- Afif A, Bouvier R, Buenerd A, Trouillas J & Mertens P. (2007). Development of the human fetal insular cortex: study of the gyration from 13 to 28 gestational weeks. Brain Struct Funct , 212, 335-46. PMID: 17962979 DOI.