Ziyini izigaba ze-embryogenesis?
Isikhathi sokutholwa kwabantu esibhedlela sithatha izinyanga ezingu-2 - lokhu kungakanani izinqubo zokuguqulwa kwe-embryo zibe fetus ekugcineni. Ngenxa yalesi nqubo, umzimba wakhiwa ophethe izici ezifanayo zokuziphatha njengomuntu omdala.
Esigabeni sokuqala, i-zygote yenziwa. Yakhiwe ngenxa yokuhlanganiswa kwamaseli wesilisa nowesifazane wesini. Lesi sikhathi siphelile isikhathi esifushane. Ngemuva kokufika kwesigaba sokuhlukaniswa.
Phakathi nalesi sikhathi, ukwanda kwesitembu esinamandla kwenzeka. Kulesi simo, amangqamuzana akhiwa ngokuchoboza ayebizwa ngokuthi i-blastomer. Okokuqala ukuqoqwa okuncane kwala maseli kwakha, okufana ne-berry okusajingijolo ngendlela yayo yangaphandle, futhi yayibizwa ngokuthi i-morula. Ngokuhlukaniswa okuqhubekayo, inani lamaseli liyakhula futhi i-morula ithatha isimo esingaphezulu, i-blastula.
Ngemuva kokuchoboza, okulandelayo, isigaba sesithathu se-embryonic sokuthuthukiswa kwenyama, ukugcoba. Iqala ukuguqulwa kombungu owodwa-ungqimba ube yilezi ezimbili ezicwebezelekile, isb. ukukhuluma nje - kukhona kabili ama-shells. Kulesi simo, i-gastrula ngokwayo iqukethe amaqabunga amabili e-embryonic, i-ecto- ne-endoderms. Phakathi nokuziphendukela kwazo zonke izinto eziphilayo, inqubo yokugcoba kwaba yinkimbinkimbi ngokubunjwa kwe-axial complex (i-neural tube, axial skeleton, musculature), ebeka eceleni kwesigxathu se-embryo kusuka eqabeni lesi-3 lama-embryonic.
Isikhathi sesine sihilela ukuhlukaniswa kwezingxenye eziyinhloko zezitho nezicubu, kanye nokuthuthukiswa kwazo okuqhubekayo. Kanye nalokhu, kukhona ukuhlanganiswa okuqinile kwezingxenye zibe yinye elilodwa. Ngakho-ke, kusukela engxenyeni yangaphandle ye-endoderm, ukwakheka kwezicubu ze-epithelial ezifaka umsele wokugaya, kanye nama-glands ayo. Kusukela ku-mesoderm - imisipha, kanye ne-epithelium yesistimu ye-genitourinary, izinambuzane ze-serous zobuchopho. I-mesenchyme yenza i-connectif, i-cartilaginous, i-bone tishu, isimiso sezinsiza.
Ukubeka izitho ezisemqoka kanye nezinhlelo zenzeka kanjani?
Ngemuva kokubhalisa zonke izigaba zenkathi yokuthuthukiswa kwe-embryonic, sizobuye sitshele ukuthi yiziphi izinhlelo nezinhlaka ezakhiwe kumasonto onke. Ngakho-ke, inqubo yokuchoboza ngesikhathi sokubunjwa kombungu womuntu ihlala cishe kwezinsuku ezingu-3-4. Phakathi nalesi sikhathi, lihamba ngezinyawo zamathambo eziya emgodini. Ngenxa yendlela yokuchotshozwa kusuka eblastomeres esezulwini, i-shell, eyabamba iqhaza ekwakheni imbungu, i-trophoblast. Lawo ma-blastomeres, atholakala ngqo phakathi nendawo, yakha i-embryoblast, okuvela kuyo umzimba we-embryo ozayo.
Cishe ngesonto lesibili ekuqaleni kwenqubo yokuthuthukiswa, umbungu ususelwe emdongeni wesibeletho. Ngesikhathi esifanayo, ukubunjwa kwezakhiwo ezifana ne-yolk nama-amniotic vesicles kuyabonakala. Ngemuva kokuthi bakha i-mesenchyme, i-amnion yenziwa. Lokhu kubaluleke kakhulu ukuba kube nekhanda elimnandi elenza isikhwama, esilandelayo ngaso sonke isikhathi sigcwele wonke amniotic fluid eyaziwayo.
Cishe ngesonto lesithathu lokuthuthukiswa kwe-embryonic, ihlumela elincane lamaseli akhula likhishwa ngemuva kombungu. Isigaba saso okuthiwa ikhanda, ukuqina, sakha i-nodule eyinhloko. Yilesi sakhiwo esibangela ukubunjwa okunjalo njenge-tube neural.
Emasontweni ama-4 ngaphandle kwezingqimba ze-extraembryonic, i-embryo ihamba ngokuhlanganyela okuyinhloko ngenxa yokukhula okuthuthukisiwe, njll. kuhlanganiswe izingxenye ezihlukene zomzimba we-fetal body. Ngokufanayo nalokhu, isigaba sokuqala senqubo ye-organogenesis ne-histogenesis yenzeka.
Ngeviki le-5 lokukhulelwa, ukukhishwa kwamandla nemilenze kungachazwa ngokucacile, futhi ngesonto le-6 izitho zihlukaniswe zibe izingxenye eziyinhloko. Cishe ekupheleni kwamasonto angu-7 ekusebenzeni kwe-US kungenzeka ukuthi ubone iminwe yeminwe. Ngakho-ke, ngeviki 8 (yilapho isikhathi eside esiyi-embrionic sihlala), ama-embrasi emithombeni e-embryo agcwaliswe.
Ukuze ubone ngeso lengqondo izigaba eziyinhloko zesikhathi sokuthuthukiswa kwe-embryonic, ake sibeke ngezansi kwetafula lapho ziboniswa khona.
