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PERUBAHAN MORFOLOGI DAN FISIOLOGI JANINAdenan AbadiFakultas Kedokteran Universitas Sriwijaya1Selama 8 minggu pertama, terminologi embrio digunakan terhadap perkembangan organisme oleh karena pada masa ini semua organ besar sedang dibentukSetelah 8 minggu, terminologi janin digunakan oleh karena sebagian besar organ sudah dibentuk dan telah masuk kedalam tahap pertumbuhan dan perkembangan lanjut.Janin dengan berat 500 1000 gram (22-23 minggu) disebut imature. Dari minggu 28 36 disebut preterm dan janin aterm adalah bila usia kehamilan lebih dari 37 minggu.

PERTUMBUHAN dan PERKEMBANGAN

Panjang 2.1 2.5 cmBerat 1 gramBagian kepala lebih dari setengah tubuh janinDapat dikenali lobus heparGinjal mulai terbentukSel darah merah terdapat pada yolc sac dan hepar

Kehamilan 8 minggu

Panjang 7 9 cmBerat 12 15 gramJari-jari memiliki kukuGenitalia eksterna sudah dapat dibedakan antara laki dan perempuanVolume cairan amnion 30 mlPeristaltik usus sudah terjadi dan memilki kemampuan menyerap glukosa

Kehamilan 12 minggu

Panjang 14 17 cmBerat 100 gramTerdapat HbFPembentukan HbA mulai terjadi

Kehamilan 16 minggu Berat 300 gramDetik jantung dapat terdengar dengan menggunakan stetoskop DeLeeTerasa gerakan janinTinggi fundus uteri sekitar umbilikus

Kehamilan 20 minggu

Berat 600 gramTimbunan lemak mulai terjadiViabilitas mungkin dapat tercapai meski amat jarang terjadi

Kehamilan 24 minggu

Berat 1050 gram ; panjang 37 cmGerakan pernafasan mulai terlihat ; surfactan paru masih sangat rendah

Kehamilan 28 minggu

Berat 1700 gram dan panjang 42 cmPersalinan pada periode ini 5 dan 6 neonatus dapat bertahan hidup Kehamilan 32 minggu

Berat 2500 gram dan panjang 47 cmGambaran kulit keriput lenyapKemungkinan hidup besar

Kehamilan 36 minggu Berat 3200 3500 gram ; panjang 50cmDiameter biparietal 9.5 cm Kehamilan 40 minggu

Initial development of placenta and fetal membranes occurs far more rapidly than development of fetus 2-3 weeks after implantation of blastocyst, the fetus remains almost microscopic in sizeBut thereafter the length of fetus increases in proportion to age:-At 12 weeks: 10 cm- At 20 weeks: 25 cm-At 40 weeks (at term): 53 cmGrowth and Functional Development of FetusGross characteristics of different organs: -Within 1 month after fertilization begun to develop-During the next 2-3 months, most of details are established-Beyond the 4th month: mainly the same as those of the neonateCellular development in each organ is usually far from complete: -Requires the full remaining 5 months for complete development-Even at birth certain structures (nervous system, kidneys, and liver) lack full developmentDevelopment of Organ SystemsHeart: Begins beating during the 4th week after fertilization 65 bpm and increases to 140 bpm before birthBlood cells:-During the midportion of fetal life: Extra marrow areas are the major sources of blood cells-During the latter 3 months of fetal life: Bone marrow gradually take over, while other areas lose their ability, except for lymphocytes and plasma cells produce in lymphoid tissueCirculatory SystemRespiration cannot occur during fetal lifeAt the end of 1st trimester of pregnancy: respiratory movements caused by tactile stimuli or fetal asphyxiaDuring the latter 3-4 months of pregnancy for unclearly reasons:-Respiratory movements are inhibited -Lungs remain almost completely deflated-It prevents filling of lungs with debris from meconium-Fluid is secreted into the lungs by alveolar epithelium up until birth keeping only clean fluid in the lungs

Respiratory SystemMost of skin reflexes are present by 3rd 4th month of pregnancyHowever, functions of central nervous system that involve cerebral cortex are still mainly undeveloped, even at birthMyelinization of some major tracts of central nervous system becomes complete only after 1 year of postnatal lifeNervous SystemBy midpregnancy: fetus ingests and absorbs large quantities of amniotic fluidDuring the last 2-3 months: gastrointestinal function approaches that of normal neonateSmall quantities of meconium are continually formed in gastrointestinal tract and excreted from bowel into amniotic fluidMeconium is composed of: -Residue from amniotic fluid-Excretory products from gastrointestinal mucosa and glandsGastrointestinal TractFetal kidneys are capable of excreting urine during at least the latter half of pregnancy and urination occurs normally in uteroHowever, renal control systems for regulating:-Extracellular fluid electrolytes balances -Acid-base balanceare almost nonexistent until after midfetal life and do not reach full development until a few months after birth

The KidneysFetal uses mainly glucose for energyFetal has a high rate of storage of fat and proteinMost of fat being synthesized from glucose, rather than being absorbed from mothers bloodSome special problems of fetal metabolism in relation to:-Calcium and phosphate-Iron-Some vitaminsFetal Metabolism 22.5 gr of calcium and 13.5 gr of phosphorus are accumulated during gestation: of it accumulates during the last 4 weeks of gestation which is coincident with the period of rapid ossification of fetal bones as well as rapid weight gainDuring the earlier part of fetal life, fetal bones are relatively unossified and have mainly cartilagous matrix until 4th month of pregnancyTotal amount of calcium and phosphate needed during gestation represent only 1/50 quantities of these substances in mothers bone minimal drain from motherA much greater drain occurs after birth during lactationMetabolism of Calcium and PhosphateIron accumulates in fetus more rapidly than calcium and phosphatesMost of iron is in the form of Hb, which begin to be formed at 3rd week after fertilizationSmall amounts of iron are concentrated in mothers uterine progestational endometrium even before implantation, which then ingested into embryo by trophoblastic cells for early formation of RBC 1/3 of iron in a fully developed fetus is stored in liver that can be used for several months after birthMetabolism of IronFetus needs vitamins equally as much as adult and in some instances to a far greater extentVitamins function the same in fetus as in adult:-Vit B: especially B12 and folic acid for formation of RBC and nervous tissue as well as for overall growth-Vit C: for appropriate formation of intercellular substances, especially bone matrix and fibers of connective tissue-Vit D: probably for normal bone growth in fetusBut more important for adequate absorption of calcium from mothers gastrointestinal tract large quantities will be stored by fetal liver to be used for several months after birthMetabolism of Vitamins-Vit E: necessary for normal development of early embryo although the mechanisms are not clearIn its absence in laboratory animals: spontaneous abortion usually occurs at an early age-Vit K: for formation of Factor VII, pro-thrombin, and several other blood coagulation factorsWhen vit K is insufficient in mother: Factor VII and pro-thrombin become deficient in fetus as well as in motherBecause most vit K is formed by bacterial action in colon, neonate has no adequate source of vit K prenatal storage in fetal liver derived from mother is helpful in preventing hemorrhage, particularly when head is traumatized by squeezing through birth canal ..Metabolism of Vitamins