PERUBAHAN MORFOLOGI DAN FISIOLOGI JANIN

Adenan AbadiFakultas Kedokteran Universitas Sriwijaya

PERTUMBUHAN dan PERKEMBANGAN

• Selama 8 minggu pertama, terminologi embrio digunakan terhadap perkembangan organisme oleh karena pada masa ini semua organ besar sedang dibentuk

• Setelah 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.

Kehamilan 8 minggu

• Panjang 2.1 – 2.5 cm• Berat 1 gram• Bagian kepala lebih dari setengah tubuh janin• Dapat dikenali lobus hepar• Ginjal mulai terbentuk• Sel darah merah terdapat pada yolc sac dan

hepar

Kehamilan 12 minggu

• Panjang 7 – 9 cm• Berat 12 – 15 gram• Jari-jari memiliki kuku• Genitalia eksterna sudah dapat dibedakan

antara laki dan perempuan• Volume cairan amnion 30 ml• Peristaltik usus sudah terjadi dan memilki

kemampuan menyerap glukosa

Kehamilan 16 minggu

• Panjang 14 – 17 cm• Berat 100 gram• Terdapat HbF• Pembentukan HbA mulai terjadi

Kehamilan 20 minggu

• Berat 300 gram• Detik jantung dapat terdengar dengan

menggunakan stetoskop DeLee• Terasa gerakan janin• Tinggi fundus uteri sekitar umbilikus

Kehamilan 24 minggu

• Berat 600 gram• Timbunan lemak mulai terjadi• Viabilitas mungkin dapat tercapai meski amat

jarang terjadi

Kehamilan 28 minggu

• Berat 1050 gram ; panjang 37 cm• Gerakan pernafasan mulai terlihat ; surfactan

paru masih sangat rendah

Kehamilan 32 minggu

• Berat 1700 gram dan panjang 42 cm• Persalinan pada periode ini 5 dan 6 neonatus

dapat bertahan hidup

Kehamilan 36 minggu

• Berat 2500 gram dan panjang 47 cm• Gambaran kulit keriput lenyap• Kemungkinan hidup besar

Kehamilan 40 minggu

• Berat 3200 – 3500 gram ; panjang 50cm• Diameter biparietal 9.5 cm

Growth and Functional Development of Fetus

• 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 size

• But 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 cm

Development of Organ Systems

• Gross 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 neonate

• Cellular 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 development

Circulatory System• Heart:

Begins beating during the 4th week after fertilization ± 65 bpm and increases to ± 140 bpm before birth

• Blood 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 tissue

Respiratory System• Respiration cannot occur during fetal life

• At the end of 1st trimester of pregnancy: respiratory movements caused by tactile stimuli or fetal asphyxia

• During 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

Nervous System

• Most of skin reflexes are present by 3rd – 4th month of pregnancy

• However, functions of central nervous system that involve cerebral cortex are still mainly undeveloped, even at birth

• Myelinization of some major tracts of central nervous system becomes complete only after ± 1 year of postnatal life

Gastrointestinal Tract

• By midpregnancy: fetus ingests and absorbs large quantities of amniotic fluid

• During the last 2-3 months: gastrointestinal function approaches that of normal neonate

• Small quantities of meconium are continually formed in gastrointestinal tract and excreted from bowel into amniotic fluid

• Meconium is composed of: - Residue from amniotic fluid- Excretory products from gastrointestinal mucosa and glands

The Kidneys

• Fetal kidneys are capable of excreting urine during at least the latter half of pregnancy and urination occurs normally in utero

• However, 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

Fetal Metabolism

• Fetal uses mainly glucose for energy

• Fetal has a high rate of storage of fat and protein

• Most of fat being synthesized from glucose, rather than being absorbed from mother’s blood

• Some special problems of fetal metabolism in relation to:- Calcium and phosphate- Iron- Some vitamins

Metabolism of Calcium and Phosphate• ± 22.5 gr of calcium and 13.5 gr of phosphorus are

accumulated during gestation:± ½ 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 gain

• During the earlier part of fetal life, fetal bones are relatively unossified and have mainly cartilagous matrix until ± 4th month of pregnancy

• Total amount of calcium and phosphate needed during gestation represent only ± 1/50 quantities of these substances in mother’s bone → minimal drain from mother

• A much greater drain occurs after birth during lactation

Metabolism of Iron

• Iron accumulates in fetus more rapidly than calcium and phosphates

• Most of iron is in the form of Hb, which begin to be formed at 3rd week after fertilization

• Small amounts of iron are concentrated in mother’s 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 birth

Metabolism of Vitamins

• Fetus needs vitamins equally as much as adult and in some instances to a far greater extent

• Vitamins 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 fetus

But more important for adequate absorption of calcium from mother’s gastrointestinal tract → large quantities will be stored by fetal liver to be used for several months after birth

…..Metabolism of Vitamins- Vit E: necessary for normal development of early embryo although the mechanisms are not clear

In 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 factors

When vit K is insufficient in mother: Factor VII and pro-thrombin become deficient in fetus as well as in mother

Because 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