EMBRYOLOGY • Implantation. • Changes in blastocyst during implantation. • Differentiation of embryoblast. • Development of the extraembryonic structures extraembryonic mesoderm, extraembryonic coelom, yolk sac, fetal membranes: amnion and chorion. Development of the placenta. • Germ disc. Development of embryonic mesoderm and notochord. Somites. The other axial organs of embryo. • Flexion of embryo. Development of the umbilical cord. PRIMORDIAL FOLLICLES PRIMARY UNILAMINAR FOLLICLE PRIMARY MULTILAMINAR FOLLICLES SECONDARY FOLLICLE GRAAFIAN FOLLICLE GROWTH AND MATURATION OF OVARIAN FOLLICLES PRIMARY OOCYTE in these follicles SECONDARY OOCYTE Corona radiata Zona pellucida Follicular fluid Meiotic spindle in metaphase 2 OOCYTE Theca lutein cells Fibrin clot CORPUS LUTEUM Granulosa lutein cells OVULATION Ruptured follicle Theca folliculi externa and interna Membrana granulosa Zona pellucida CORTEX OVARII oocyte II sperm penetration ovum beginning of cleavage pronuclei diploid set of chromosomes polar body meiotic spindle cleavage secondary oocyte in metaphase 2 implanted blastocyst FERTILIZATION AND IMPLANTATION cumulus oophorus zona pellucida FERTILIZATION Zygote – 18 h after fertilization 24 h 45 h 72 h Morula – 96 h Blastocyst CLEAVAGE AND IMPLANTATION Mitotic spindle within zygote Polar bodies MORULA BLASTOCYST Syncytiotrophoblast Primitive chorionic cavity Embryonic pole ENDOMETRIUM UTERINE GLANDS Trophoblast Embryoblast Extraembr. mesoderm Primitive yolk sac Chorion Operculum Amniotic cavity Trophoblastic lacunae Cytotrophoblast Hypoblast Epiblast Connecting stalk Amnion Germ disc Definitive yolk sac Extraembryonic coelom IMPLANTATION – DAY 7 Trophoblast Primitive chorionic cavity Hypoblast Uterine epithelium Syncytiotrophoblast Epiblast Blood capillary Uterine gland IMPLANTATION – DAY 8 1/2 Trophoblast Primitive chorionic cavity Hypoblast Cytotrophoblast Amniotic sac Syncytiotrophoblast Uterine gland Trophoblastic lacune IMPLANTATION – DAY 10 Primitive (primary) yolk sac Extraembryonic mesoderm Hypoblast Epiblast Cytotrophoblast Syncytiotrophoblast Trophoblastic Amnionic Cytototrophoblastic lacune cavity bud (primary chorionic villus) IMPLANTATION – DAY 13 Extraembryonic Definitive (secondary) coelom yolk sac Secondary chorionic villus Hypoblast Epiblast Cytotrophoblast Syncytiotrophoblast Connecting stalk Trophoblastic lacune (extraembryonic mesoderm) (with capillary outlet) DORSAL SIDE OF GERM DISC – DAY 14 Wall of amniotic cavity Prochordal plate Connecting stalk Wall of yolk sac Hypoblast Epiblast Primitive streak GERM DISC - DAY 16 Yolk sacCut edge of amnion Primitive streak Primitive node Ectoderm Amnion Wall of yolk sac Mesoderm Endoderm A – view on dorsal side: B – transverse section through germ disc: GERM DISC - DAY 16 Amniotic wall Amniotic cavity Prochordal plate Notochordal process Cloacal membrane Primitive node Primitive streak Allantois Ectoderm Primitive pit Notochordal Primitive process streak Prochordal plate A – view on dorsal side B – longitudinal section GERM DISC - DAY 17 A – longitudinal section, B, C – transversal sections Canal of Lieberkühn Wall of yolk sac Prochordal plate Notochordal process Connecting stalk Primitive pit Cloacal membrane Notochordal Embryonic /head/ process mesoderm Embryonic Endoderm mesoderm Notochordal plate Ectoderm Amnion Allantois DIFFERENTIATION OF MESODERM Somite Sclerotome Nephrotome Paired aorta dorsalis Aorta dorsalis Primitive gut Aorta dorsalis Dermatome Myotome Basis of arcus vertebrae Basis of corpus vertebrae paraxial MESODERM intermediate lateral Splanchnopleura Somatopleura Amnionic cavity Neural plate Septum transversum Connecting stalk Allantois Nephrotom Intreembryonic coelom Pericardiac cavity Yolk sac Paraxial mesoderm Embryonic somatopleura Embryonic splanchnopleurasection plane section plane Umbilical vein incorporation of yolk sac into primitive gut Anterior and posterior neuroporus Pharyngeal membrane Neural tube Ectoderm Cloacal membrane Neural tube Somite Dorsal aortae Communication between extra and intraembryonic coelom Primitive umbilical cord Primary brain vesicles Forgut Midgut Hindgut Cranial (head) fold Caudal (tail) fold Yolk sac Midgut Lateral folds Ductus omphalomesentericus Yolk sac EMBRYO FLEXION EMBRYOLOGY Set of embryological images I, II