Alaqah 1

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Alaqah 1

  1. 1. ALAQAH • (Blood clot or Leech; something suspended or attached to a surface.) • This term is so important to remember that there is a complete surah in Qur’an called Surah Al- Alaq. • The first five ayyat of Surah Al-Alaq is the first revelation sent to Muhammad (SAS) in the cave of Hira. • Its importance is very much increased when we see that in the very first revelation the terminology of “alaq” is used.
  2. 2. • Read (O Prophet), in the name of your RABB (Lord), Who ceated • HE created insan from alaq (a clot of congealed blood). • Read: and your RABB is Most Generous. • Who taught knowledge by “qalam” (pen). • HE taught insan what he did not know. • Al-Alaq. Surah 96, Ayat 1-5, Para 30
  3. 3. • This Qur’anic term refers to the presomite embryo. • It starts when the implantation begins and ends when formation of somites begins. • It extends for about 14 days. • It starts on day 7 with the embedding of blastocyst and is completed on day 20 when first pair of somites appears.
  4. 4. • We created man from a quintessence (gentle extraction) of clay. We then placed him as Nutfah in a place of rest firmly fixed. Then we made Nutfah into Alaqah and then we changed Alaqah into Mudghah. Then we made Izam (bones) out of that Mudghah. Then we clothed Izam with Lahm (muscles). Then we developed out of him another creation. So blessed ALLAH the best to create. Then after that you shall all die. Then most surely you shall be raised up on the Day of Resurrection. • (Surah 23, Al-Mu’minun, Ayat 12-16, Para 17)
  5. 5. • According to modern scientific knowledge we can discuss Alaqah in two stages: 1.Alaqah-1. This is bilaminar germ disc. 2.Alaqah-2. This is trilaminar germ disc.
  6. 6. •ALAQAH-1 •Bilaminar Germ Disc •2nd week
  7. 7. IMPLANTATION • Implantation of the blastocyst begins at the end of the first week and ends by the end of second week. • At about 6th day after fertilization the embryonic pole of the blastocyst becomes attached to the endometrium and start penetrating into it.
  8. 8. IMPLANTATION SITE • The blastocyst usually implants in the midpoint of the body of the uterus, more frequently on the posterior than on the anterior wall. • Implantation almost always occurs between the openings of the glands and it is always close to a maternal capillary suggesting some type of tropism toward maternal blood. • Implantation only occurs in stratum compactum and never beyond that in normal cases.
  9. 9. EMBEDDING The trophoblasts now start proliferating rapidly and soon differentiate into two layers: 1. An inner cytotrophoblast (cellular trophoblast) consisting of mono-nucleated cells. 2. An outer syncytial trophoblast (syntrophoblast or syncytiotrophoblast) consisting of a multinucleated protoplasmic mass without individual cell boundaries.
  10. 10. Day-8. Blastocyst is partly buried in stratum compactum
  11. 11. • Mitotic figures are found in cytotrophoblast, but never in syncytial trophoblast yet the thickness of the latter increases considerably. • The cells of the cytotrophoblast multiply and migrate into the syncytial trophoblast, where they fuse • The finger like processes of the syncytial trophoblast grows into the endometrial epithelium and start invading the endometrial stroma but they never go beyond stratum compactum. • The erosion of the endometrial stroma results from proteolytic enzymes produced by syntrophoblast.
  12. 12. FORMATION OF BILAMINAR GERM DISC (DAY 8) • Small spaces appear between the embryoblast and trophoblast. By the 8th day, these spaces have coalesced to form a small cavity between the embryoblast and trophoblast called amniotic cavity. • Concurrently, morphological changes occur in the embryoblast resulting in the formation of a flattened, essentially circular plate of cells called the embryonic disc. The cells of the embryoblast also differentiate into two layers: 1. A superior layer of high columnar cells adjacent to the amniotic cavity, the epiblast. 2. An inferior layer of small cuboidal cells adjacent to the blastocyst cavity the hypoblast.
  13. 13. Day-8. Blastocyst is partly buried in stratum compactum
  14. 14. FORMATION OF AMNIOTIC CAVITY • Small spaces appear between the embryoblast and trophoblast. By the 8th day, these spaces have coalesced to form a small cavity between the embryoblast and trophoblast called amniotic cavity. • As the amniotic cavity enlarges, it acquires a dome- shaped thin epithelial roof of amnion, which is continuous with the edges of epiblast layer of the bilaminar germ disc. • The amnion develops from epiblast on day 8. Flat cells develop from epiblast and form a thin membrane called amnion. The flat cells constituting the amnion are called amnioblast. The amnion lines trophoblast and surrounds the amniotic cavity. So amniotic cavity has its own covering now called amnion.
  15. 15. On eighth day three events occur: 1. Trophoblast forms two layers, cytotrophoblast and syncytial trophoblast. 2. Embryoblast gives rise to two layers epiblast and hypoblast. 3. Amniotic cavity develops
  16. 16. Lacunar stage (Days 9 to 11) • The naughty trophoblast shows considerable progress in the development particularly at the embryonic pole. • The growth is so rapid that isolated spaces or vacuoles appear in the syncytiotrophoblast. • These vacuoles fuse to form large lacunae. The adjacent lacunae by fusion form a lacunar network throughout the syncytial trophoblast. • By the 9th day the conceptus is more deeply embedded and the penetration defect in the surface epithelium is closed by a fibrin coagulum.
  17. 17. FORMATION OF PRIMARY YOLK SAC • By the 9th day, a crop of flattened cells develops inside the cytotrophoblasts. • These cells either originate from the cytotrophoblasts or from the hypoblast. ALLAH The Creator knows better. • These cells form a thin membrane, known as the exocoelomic (Heuser’s) membrane, which lines the blastocyst cavity. • Exocoelomic (Heuser’s) membrane is continuous superiorly with the hypoblast of the embryonic bilaminar germ disc and circumscribes a large cavity called exocoelomic cavity or primary (primitive) yolk sac.
  18. 18. Establishment of utero-placental circulation (Days 11 to 12) As the conceptus penetrates the endometrial stroma, the endometrial capillaries become more and more congested and dilated and become sinusoids. As the syncytial cells penetrate deeper in the stroma, they finally erode endothelial lining of maternal capillaries. The syncytial lacunae then become continuous with the sinusoids and maternal blood enters the lacunar system.
  19. 19. As trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through lacunar system, thus establishing the primitive utero-placental circulation. By the 12th or 13th day of development the blastocyst is completely embedded in the endometrial stroma the surface defect in the endometrium has usually healed and the surface epithelium covers entirely the original defect.
  20. 20. FORMATION OF EXTRA-EMBRYONIC MESODERM • A new population of cells develops between the inner surface of the cytotrophoblast externally and the outer surface of the amnion and exocoelomic cavity internally. • These cells form a fine loose connective tissue (mesenchymal tissue) called extra-embryonic mesoderm. It is derived from cytotrophoblast probably (ALLAH knows better). • On the 11th day a thick zone of extra-embryonic mesoderm is formed.
  21. 21. • Now isolated coelomic spaces appear in it. These spaces rapidly fuse to form large isolated cavities of extra-embryonic coelom. Soon these become confluent and a continuous crescent shaped extra-embryonic coelomic cavity is established • This cavity surrounds the primitive yolk sac and amniotic cavity except on the caudal end of the developing germ disc, where extra-embryonic mesoderm remains solid and is given the name connecting stalk.
  22. 22. • The formation of extra-embryonic coelomic cavity divides the extra- embryonic mesoderm into two layers. 1. The outer layer lines the cytotrophoblast and is called somatic mesoderm. 2. The inner layer covers the amniotic cavity and yolk sac. The part covering the amniotic cavity is also called somatic mesoderm and the part covering the yolk sac is called splanchnic mesoderm.
  23. 23. CONNECTING STALK • Connecting stalk determines the side of the embryo because it develops on the caudal aspect of bilaminar germ disc. • The connecting stalk is the pathway along which the blood vessels of the embryo later establish communication with those of the chorion. • Subsequently the connecting stalk is converted into part of the umbilical cord and establish communication between embryo and placenta. •
  24. 24. FORMATION OF SECONDARY YOLK SAC • As the extra embryonic coelom increases in size primary yolk sac decreases in size. Part of primary yolk sac is drawn out and pinched off into the mesodermal strands. • The hypoblast cells produce additional cells that migrate along the exocoelomic or Heuser’s membrane. These cells proliferate and gradually replace the primitive yolk sac or exocoelomic cavity. • This new cavity is known as secondary or definitive yolk sac.
  25. 25. FORMATION OF CHORIONIC CAVITY • As primary yolk sac is replaced by a smaller secondary yolk sac, the extraembryonic coelom increases in size, and now it is usually called chorionic cavity. But still we can call it extraembryonic coelom, a better and explanatory name. • The trophoblast (both cytotrophoblast and syncytial trophoblast) and the extraembryonic somatic mesoderm lining the trophoblast together constitute chorionic plate.
  26. 26. DECIDUA REACTION • As the conceptus erodes and sinks into the endometrium, the endometrial stroma around the implantation site becomes edematous and highly vascular. • Adjacent large tortuous glands start secreting abundant glycogen and mucus. • The endometrial stromal cells enlarge and become laden with glycogen and lipids and they become polyhedral in appearance, now called decidual cells. • All these cellular, vascular and glandular changes are collectively called decidua reaction.
  27. 27. • This decidua reaction is first confined to the area immediately surrounding the implantation site, but soon spreads throughout the endometrium and by the days 13 to 14 there is marked decidua reaction throughout the endometrium. • Some of the decidual cells degenerate in the region of the penetrating syncytiotrophoblast and provide a rich source of material for embryonic nutrition. • Later on the conceptus receives nutrients directly from the maternal blood.

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