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The Biology of Prenatal Development




IBHAYOLOJI YANGAPHAMBILI KOKUBELETHWA KOMNTWANA

.Ndebele [Sindebele (Ndebele)]


 
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The Embryonic Period (The First 8 Weeks)

Embryonic Development: The First 4 Weeks

Chapter 3   Fertilization

Ngokwebhayiloji, "ukukhula komuntu kuthoma ngesikhathi sokumumatha''(fertilization) ngesikhathi umama nobaba bahlanganisa ama-chromosomes wabo angu 23 ngamunye ngokuhlanganisa amaseli wabo wokubeletha.

Iseli lokubeletha likamama livamise ukubizwa ngokuthi ``liqanda''(egg) kodwa igama ekungilo yi-oocyte.

Iseli lendoda lokubeletha laziwa ngama "sperm" kodwa igama elikhethekileko yi-spermatozoon.

Ukulandela ukuphuma kwe-oocyte kuqanda lomuntu wesifazane kukambiso ebizwa nge-ovulation, i-oocyte ne-spermatozoon ziyahlangana ngaphakathi kwethumbu lesizalo, avamise ukubizwa ngama Fallopian tubes.

Amathumbu wesizalo ahlanganisa amaqanda womuntu wesifazane nesibeletho.

Isiphumelo salokho liseli elibizwa nge-zygote, okutjho "okuhlangeneko."

Chapter 4   DNA, Cell Division, and Early Pregnancy Factor (EPF)

Ama-chromosomes angu 46 we-zygote's ajamele umphumela wokuthoma ohlukileko wokwakheka okupheleleko komuntu oyedwa. Ukuhleleka lokho kuhlala ngeencenyana ezincane ezihlangeneko zamamolekyula ezibizwa nge-DNA. Zinemilayezo yokukhula komzimba woke.

Amamolekyuli we-DNA afana Nesikhwelo esihlangeneko esibizwa nge-double helix. Amafindo wesikhwelo enziwe mamolekyuli amabili, noma ukwakheka okubizwa nge-guanine, cytosine, adenine, ne thymine.

I-Guanine ihlangana kwaphela ne-cytosine, begodu i-adenine yona ihlangane ne-thymine. Iseli elinye nelinye Lomuntu pheze libe neengidigidi ezi-3 zemakhiwo engamibili le.

I-DNA yeseli ngalinye inemininingwane eminengi kangangokuthi nakube beyijanyiselwe ngamagama abhaliweko, ngokubhala igama ngalinye lesakhiwo ngasinye kungadinga amaphepha abhaliweko angaphezulu kwesigidigidi esi 1.5!

Nakube ama-DNA ahlanganisiwe, aba liseli linye lomuntu elingange 3 1/3 yeenyawo noma imitha eli-1.

Nakube besingathathulula i-DNA ngaphakathi kwamaseli womuntu omdala amabhiliyoni amantathu ali-100, ingathabuluka ibe ngaphezulu kwamamayela amabhiliyoni ama-63. Ubude lobu bungangokusuka emhlabeni ukuya elangeni ukubuya kuze kube ziinkhathi ezi-340.

Isikhathi esinganga ma-24 ukuya kuma-30 wamahora ngaphambili kokumumatha (fertilization), i-zygote yakha beyiqede ukuhlukana kweseli lokuthoma. Ngenkambiso ye-mitosis, iseli ngalinye lihlukana kabili, nalikabili lihlukane kane, njalo njalo.

Kusese mahora ama 24 ukuya kwama 48 ngemva kokuthoma ukumumatha (fertilization), ukukhulelwa kungafakazelwa ngokuzwa i-homoni elibizwa "ngebanga lokukhulelwa lokuthoma" ngaphakathi kweengazi zikamama.

Chapter 5   Early Stages (Morula and Blastocyst) and Stem Cells

Emva kwamalanga ama 3 ukuya kwama 4 ngemva kokumumatha, amaseli ahlukanako we-embryo aba yindilinga begodu i-embryo ibizwa ngokuthi yi-morula.

Ukusukela emalangeni ama 4 ukuya kwa 5, Kuba nesikhala hlangana nebholo yamaseli begodu i-embryo leyo ibizwa nge-blastocyst.

Amaseli angaphakathi kwe-blastocyst abizwa ngobunengi bamaseli wangaphakathi begodu akha ihloko, umzimba, nokunye ukwakheka okubalulekile kumuntu okhulako.

Amaseli angaphakathi kobunengi bamaseli wangaphakathi, abizwa ngama embryonic stem cells ngob akwazi ukwenza elinye nelinye lehlobo yamaseli angaphezulu kwa 200, asemzimbeni womuntu.

Chapter 6   1 to 1½ Weeks: Implantation and Human Chorionic Gonadotropin (hCG)

Ngemva kokuya phasi nethumbu lesizalo(uterine tube), i-embryo yokuthoma ihlala ngaphakathi komthangala wesizalo sikamama. Ikambiso le,ebizwa ngokutshaleka yenzeka ngemva kwamalanga asi 6 iphele emva kwamalanga ali 10 ukuya ku 12 ngemva kokumumatha(fertilization).

Amaseli we-embryo ekhulako athoma ukuba namahomoni ebizwa nge human chorionic gonadotropin, noma hCG, okuyinto eveza kuhlolelwa ukukhulelwa.

HCG ithumela amahomoni wesifazane ukuthi athikameze ukuya enyangeni okujayelekile (normal menstrual cycle), avumele ukukhulelwa kuye phambili.

Chapter 7   The Placenta and Umbilical Cord

Ngemva kokutshaleka (implantation), amaseli elipheleleni kwe blastocyst akha incenye yomakhiwo ebizwa nge placenta, ohlukanisa okukamama nekwe-embryo.

Iplasenta ilihlangothi likamama eliletha umoya, okondlako, amahomoni, nemithi kumuntu okhulako; asusa koke okungafunekiko; befuthi avikele igazi likamama lingahlangani nele-embryo ne-fetus.

Iplasenta nayo yenza amahomoni befuthi ibambha ukushisa komzimbha we-embryonic ne-fetus ube ngaphezudlwana kokushisa komzimbha kamama.

Iplasenta ikhulumisana nomuntu osakhulako ngemithambo yenkaba umbilical cord).

Ubukghoni beplasenta bokusekela ubuphilo budlula beendawo zeembhedlela zokunakekela abagula khulu ezitholakala eembhedlela zanamhlanjesi.

Chapter 8   Nutrition and Protection

Evekeni yoku 1, amaseli wamaseli wobudisi wangaphakathi enza amalayini amabili abizwa nge-hypoblast ne-epiblast.

I-hypoblast yenza 147 umgodlana womthubi, okungomunye wemakhiwo umama athumela ngawo izakhiwo zomzimbha ku-embryo nayisathomako.

Amaseli aphuma ku-epiblast akha ithambo elibizwa nge-amnion, ngaphakathi kwalo la i-embryo ngemva kwesikhathi i-fetus ikhula bekufike isikhathi sokubeletha.

Chapter 9   2 to 4 Weeks: Germ Layers and Organ Formation

Ngeemveke ezi 2 no 1/2, i-epiblast yenzekile iinyamana ezi-3 ezikhethekileko, noma imikhakha, ebizwa nge-ectoderm, endoderm, ne mesoderm.

I-Ectoderm yona ibumbha imakhiwo embalwa okufaka hlangana ingqondo, ithambo lomgogodla, imizwa, isikhumba, amazipho, neenhluthu.

I-Endoderm iveza isikhumba sokuphefumula neziko lokugaya ukudla, begodu yakha iincenye zamalunga njengesibindi namanyaka (pancreas).

I-Mesoderm yakha ihliziyo, iziso, amathambo, namathambo amade (cartilage), imisipha, amaseli weengazi, neminye imakhiwo.

Emvekeni ezi 3 ingqondo iyahlukana ngeencenye ezi 3 ezisisekelo ezibizwa ngengqondo yangaphambili (forebrain), ephakathi (midbrain), neyangemuva (hindbrain).

Ukukhula kwehlelo lokuphefumula nelokugaya ukudla nakho kusendleleni.

Njengoba amaseli weengazi athoma ukuvela ngaphakathi komgodlana womthubi, imithambo yeengazi yakheka ku-embryo yoke, begodu nehliziyo elitjhubhu ithoma ukuvela.

Kungasi kudala, ihliziyo ekhula njalo iyabhincana ngokwayo njengendlwana eyodwa ithome ukuvela.

Ihliziyo ithoma ukuphefumula Emva kweemveke ezi-3 nelanga elilodwa ngemva kokumumatha (fertilization).

Ihlelo lokukhambisa iingazi lihlelo lokuthoma lomzimbha, noma isichema samalunga ahlobeneko, ukufikela isikhathi sokusebenza.

Chapter 10   3 to 4 Weeks: The Folding of the Embryo

Phakathi kweemveke ezi 3 ne 4, ihlelo lomzimbha liyathoma njengoba ingqondo, ithambo lomgogodla, nehliziyo ye-embryo zibonakala lula eceleni komgodla womthubi(yolk sac).

Ukukhula okuya phambili kubangela ukugoqana kwe-embryo ethabaleleko. Ihlelweli lifaka hlangana incenye yomgodla womthubi endleleni yehlelo lokuphefumula, yakhe isifuba nesikhala samathumbu womuntu okhulako.


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