Important Points of Embryology for FCPS Part 1

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Embryology is too much important for the exam of FCPS Part 1. You have to do Embryology with hard work so that you can easily solve MCQs in exam. There are many Books available for Embryology. You can use Langman, High Yeild Embryology and NBDE First Aid for Embryology. Also you have to cover the important Points or Random Pearls for Embryology, which will be regularly updated on this Blog.

We have made this article for Embryology Preparation by the name of Important Points of Embryology for FCPS Part1. These points are very much important for your preparation.






The site of Fertilization is Ampulla. When we talk about Menstruation, during menstruation Basal Layer does not not slough off, but Compact and Spongy Layer Slough Off during Menstruation. Oogonia Arrest at Meiosis 1 Prophase before Ovulation. At Ovulation Secondary oocyte arrest at MetaPhase. Ovarian Follicle develops under the influence of Follicle Stimulating Harmone. Cyclic changes in Ovaries occur under the influence of Follicle Stimulating Harmone and Leutinizing Harmones.
Now we will talk about few functions of Follicle Stimulating Harmone and Leutinizing Harmones.

It causes the development of Follicle, it causes Corpus leutum formation. It has a role in ovarian cycle and causes the growth of Primordial follicle. These were few important functions of Follicle Stimulating Harmone and Leutinizing Harmones.

Cumulus Oophorus are Follicular Cells surrounding Oocytes. Zona Pellucida is secreted by Granulosa cells. Corpus Leutum is formed by Ruptured Graffian Follicle. Corpus Leutum secretes Progesterone and it maintains Endometrium layer of Uterus. Corpus Leutum secretes Progesterone till the fourth Month of Pregnancy. Placenta Secrete Progesterone after 4 Month of Pregnancy. Proliferative Phase of Menturation cycle (until Ovulation) is under the influence of Estrogen. Secretory Phase starts after ovulation phase under the Influence of Progesterone. Primary Oocyte begun 1st Meiotic Division before Birth. Ovulation is completed at Prophase. 2nd Meiotic division form 4 spermatids. Spermatogenesis is the process of formation of 4 Spermatoza (mature sperm). Prenatal Maturation is from fetal life till puberty.

Primary Oocyte Arrests in Diplotene stage of prophase i.e before Ovulation. Secondary Oocyte releases at the time of Ovulation. Secondary Oocyte surrounded by Zona Pellucida and corona Radiata. Acrosin and Neuraminidase facilitate the passage of Sperm through Zona Pellicuda.

Capacitation(modification) is followed by Acrosome Reaction (sperm perforate corona radiata), which is followed by Zona Reaction(sperm penetrate Membrane of Secondary Oocyte). After the Zona Reaction, Fusion of male and female Pronucleus occurs which causes Zygote formation.

During Fertilization in first 12-24 hours there is Differentiation of sex, Initiatail cleavage and Restoration of 46 chromosomes.

Bastomere is 8 cell stage while Morula (3-4 days) is 16 Cell stage, which enters uterus.

During 2nd Week of  embryological development Implantation of Blastocyst completes, there is formation of Epiblast and Hypoblast (bilamilar disc).

Human chorionic gonadotrophin Is produced by Corpus Leutum. Extra embryonic Coelom split the extra embryonic mesoderm into Somatic during 10-12 Days. Chorion is two layers of Trophoblast and extra Embryonic Mesoderm. Prochordal plate is the thickening of Hypoblasts cellin head region (indicate mouth of embryo). Remanent of Primitive Yolk Sac forms Exocoelomic cyst.

During 3rd week of embryological development Gastrulation occurs, there is formation of Notochord and Somities. Gastrulation is the formation of 3 Layers, which are Ecto derm, Mesoderm and Endoderm. Primitive Streak is a thick linear band of epiblast, it forms embryonic Mesoderm and is degenerated at end of 4th week of development. Notochordal process induces Ectoderm to form neural plate. Endoderm is formed by Hypoblast while Epiblast forms Ectoderm and Mesoderm. Ectoderm and Endoderm fuse to form Oropharyngeal membrane. Allantois is Involved in early blood formation and development of urinary bladder. At the end of 3rd Week there is development of 1st Pair of Somite. Cephalic Neuropore forms at 25 Day, Caudal Neuropore at 27 Day. Embryonic Period is from 3 to 8 Weeks of development. Fetal Period is from 19 to 38 Weeks of development in which there is growth and differentiation of tissues and organs.

Organogenesis process is during 4-8th weeks of development. Eyes of embryo open at 8th Week. Vascular Plexus of Scalp develops at 8th Week. 4 Pairs of Brachial Arch, 3 Primary Brain Vesicles and Limb bud Appearance at 4th Week.  Primary Chorionic villi, Syncytiotrophoblast and Cytotrophoblast formation occur at 2nd Week. Cervical Sinus is Visible at 5th Week. Fetal sex can be recognization during 13-16th Weeks. Rapid eye movement starts at 21 weeks. Type 2 Pneumocytes(surfactant) forms at 24 Weeks. Hemopoiesis begins in yolk sac. Liver is the major site of hemopoises (9thweek). Spleen is the major site of hemopoises ( 12th week).  Erythropoises ends in spleen by 28th week and begins in bone marrow. Birth usually takes place at 266Days / 38th week after Fertitlization.

If we talk about Dizygotic twin, it is 2 Oocytes and 2 Different Sperms, Monozygotic Twin is 1 Oocyte & 1 Sperm. HCG is a Glycoprotein, which is produced by Synsytiotrophoblast. Failure of matching Pair of Chromosome to split properly during division leads to Non disjunction(Down’s syndrome). klienfielters syndrome in which Extra chromosomeis present is XXY. Turners syndrome which lack Chromosome is XO. Villous Chorion is the site of development of Decidoa Basalis.

NOTE:-

THYROID GLAND ARISES FROM MIDLINE THYROID DIVERTICULUM AND FORM FROM ENDODERM IN FLOOR OF PHARYNX. THYROID REACH FINAL POSITION IN 7TH WEEK(INFRONT OF TACHEA)

DORSAL WING OF 3RD POUCH gives rise to INFERIOR PTH, VENTRAL WING OF 3RD POUCH gives rise to THYMUS, TOUNGE DEVELOPMENT is at 4TH WEEK. DORSAL PART OF 1ST CLEFT gives rise to EXTERNAL AUDITORY MEATUS. FORMATION OF PHARYNGEAL POUCHES OCCUR PRIOR TO NEURAL CREST MIGRATION. POUCHES ARE FORMED BY MIGRATION OF ENDODERMAL CELL LATERALLY. BRACIAL FISTULAS OCCUR WHEN 2ND PHARYNGEAL ARCH FAILS TO GROW CAUDALLY OVER 3RD AND 4TH ARCH. NEURAL CREST CELL DEFECT leads to 1ST ARCH  DEFECT which leads to TREACHER COLLIN’S SYNDROME and ROBIN SEQUENCE.

By Dr Maryum Malik 

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