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EMBRYOLOGYDr.D.KRUPA DANIEL (Ph.D)Associate Professor of AnatomySPERMATOGENESIS

SPERMATOGENESIS

SPERM

SPERMIOGENESIS

PARTS OF SPERM

AXIAL FILAMENT

FEMALE REPRODUCTIVE SYSTEM

OOGENESIS

STAGES

OVULATIONSecondary oocyte covered by follicular cells , Cumulus oophorecus. Follicular cells secrete actively Estrogen.Day 14 ovulation takes place.Graffian follicle enlarges,bulges on the surface of the ovary and burst open.By the time ovum is surrounded by Corona radiata cells.Ovum is released into the peritoneal cavity and is taken up by fimbriated end of Uterine tube.Sudden dip &raise of body temperature,mild pain in abdomen at the of ovulation.CORPUS LUTEUMThe empty graffian follice is converted into corpus luteum.C.L lasts for 10 -12 days,if Ovum is not fertilized.C.L lasts for 2-3 months,if ovum is fertilized and pregnancy continues.Cells of Graffian follicle secretes Estrogen.Cells of Corpus luteum secrete Progesterone.

Layers of Uterine WallOuter wall : PerimertiumMiddle wall: MyometriumInner wall: EndometriumEndometrium consists of lining epithelium which is columnar.Endometrial Dip Invagination.Glands are formed & projects into Myometrium,Perimetrium.

PARTS

Endometrial LayerBasal layer is thick and supporting the superficial layers.Endometrium shows 3-parts.Stratum Basale: Thin,Outer layerStratum Spongiosum: Thick,Middle layerStratum Compactum: Thin, Inner layer.S.basale permanently present throughout cycle.S.c & S.s are shed during Menstruation.B.S : Uterine artery-Spiral arteries.Endometrial Layer

Early Development of EmbryoSecondary oocyte is covered by Acellular,Amorphous Glycoprotein layer called ZONA PELLUCIDA.Zona pellucida is covered by Corona radiata cells.

PHASES OF FERTILIZATIONPassage of Sperm through Corona Radiata.Penetration of Zona pellucida.Fusion of plasma membranes of the Oocyte and sperm.Completion of 2nd meiotic division of oocyte &formation of female pronucleus.Formation of Male pronucleusFusion of both Male & Female Pronuclei.Zygote has formed (2n)Phases of Fertilization

Phases of Fertilization

Penetration

Penetration

Penetration

Cleavage of Zygote

Cleavage of Zygote

Cleavage of Zygote

2 celled stage

4-celled stage

2,4,8,16 celled stage

FORMATION OF BLASTOCYST16 celled stage is called MORULA.Morula is converted to Blastocyst.As the Morula moves towards the uterine cavity,fluid enters the Morula through zona pellucida and partially seperates the cells into Outer cell mass and inner cell mass.As fluid as entered a cavity is formed.Cavity enlarges ,Outer cell mass becomes flattened called as Trophoblast.Inner cell mass is called Embryoblast.This results in the formation of BLASTOCYST.BLASTOCYST

BLASTOCYSTBlastocyst enlarges &Zona pellucida disappears.Blastocyst is now Implanted in the wall of the uterus.Trophoblast forms future Placenta.Inner cell mass forms Embryo proper.FIRST WEEK ENDSSECOND WEEKIMPLANTATION Implantation is completed by the end of 2nd week-time between 6-10 days after Ovulation.Trophoblast differentiates into outer synctiotrophoblast and inner Cytotrphoblast cells.Synctiotrophoblast invades the Endometrial wall layer and the Blastocyst is Superficially Implanted by the end of SECOND WEEK.Synctiotrophoblast secretes Human chorionic gonadotrophin hormone.9th Day.IMPLANTATION

FORMATION OF GERM LAYERSBilaminar Germ DiscEctodermEndodermAmniotic cavityPrimary yolk sac

Prochordal plate14th day Embryo has a flat Bilaminar Germ disc.At one end of embryonic disc near its margin a round area becomes thicker than the rest of the disc.The rounded area is called Prochordal plate.In this region flattened endodermal cells becomes Columnar and are firmly adherent to ectoderm.With the formation of prochordal plate the cranial & caudal ends of embryonic disc is identified.

Prochordal Plate

SECOND WEEK ENDSTHIRD WEEKDURING 3RD WEEKAppearance of Primitive Streak.Differentiation of Three germ layers.NotochordNeural plateNeural tubeFormation of Intra-embryonic mesoderm.PRIMITIVE STREAKBeginning of 3rd week & dissapears by end of 4th week. Longitudinal ridge or elevation that appears at caudal end of embryo.Primitive streak visible on the upper surface towards the amniotic cavity of Embryonic disc.Ectodermal cells proliferates and move towards the midline and the cells elevates to form an elevation called as PRIMITIVE STREAK.Intially it is at Caudal end.. Now it elongates Cranially.At the cranial end Primitive streak proliferate to form PRIMITIVE NODE or KNOT or Hensens node.

PRIMITIVE STREAKPrimitive streak invaginate deep between ectoderm and endoderm.These cells extends now and forms Intraembryonic Mesoderm.Anterior to Prochordal plate the Mesoderm of two sides is continous with each other to form SEPTUM TRANSVERSUM.Now embryonic disc enlarges and becomes pear shaped.Cranial end is Broad & Caudal end is narrow.At caudal end IEM passes beyond embryonic disc and becomes Connective stalk. (EXTRA EMBRYONIC MESODERM)Primitive streak after giving rise to MESODERM gradually disappears.PRIMITIVE STREAK

Sacrococcygeal TeratomaRemants of Primitive streak persists and gives rise to Sacrococcygeal teratoma.Common in New borns.Prevalence : 1:35,000Affected : 80 % female babies.Surgically excised.

NOTOCHORDNEURAL TUBEIntra embryonic mesodermThird week

THIRD WEEK ENDSEmbryo is straight.Has 12 somites.Neural tube formed.Day :24 First & Second arch develops. (Mandibular,Hyoid).Maxillary prominence starts upper jaw formation.Now embryo is slightly folded due to Head & Tail folds.Day :26 3 pairs of pharyngeal arches are visible.Day : 26 Rostral Neuropore closes.Forebrain starts developing.FOURTH WEEKDay :26.27 - Upper limb buds , Otic pits.Lens placodes appears.Day :28 - 4th pair of Pharyngeal arch develops.Day:28 - Lower limb bud appears.End of 4th week : Caudal neuropore closes,CVS develops.FOURTH WEEK

Rapid Head development due to development of Brain.Rapid development of 2nd ,3rd ,4th pharyngeal arches.Mesonephric kidney starts developing

FIFTH WEEKEmbryo show reflex response to touch.Upper limb shows regional differentation-Elbow and Hand plates ,Primordia of digits develop called as Digital rays.Spontaneous movements of Trunk &limbs.Development of Lower limb occurs 4 or 5 days later than Upper limb.External Acoustic meatus develops.(External Ear).Retinal pigment in eye formed.(eye formation).Head is now much Larger,Bending in cervical region.Trunk & Neck begin to straighten.formation of Intestines.SIXTH WEEK

SIXTH WEEK

SIXTH WEEKDEVELOPMENT OF LIMBS

SEVENTH WEEK

Limb undergoes considerable changes during 7th week.Notches appears between Digital rays,Handplates clearly indicating future digits.By the end of 7th week Ossification of the bones of the Upper limb appears.7th Week

7th Week

EIGHTH WEEK

Digits of the Hand are Webbed.Notches are clearly visible between the Digital rays of Feet.Digits are lengthened & seperated completely.Profuse Limb movement occurs.Ossification begins in Femur.Head size is large comparably.Scalp vascular plexus appears around the Head.Neck region is established.Eye lids are formed.Eye lids are closing.

8th week

8th week

EIGHTH WEEKAuricles assume their final shape.Sex differences appear.External genitalia are clearly distinct so,accurate sexual identification is not permitted.8th week

8th week

9th Week to 12th Week Head size more increased and increases rapidly upto 12th week.Early in 9th week Legs are long,Thighs are relatively short.9th week face is Broad,Eyes are widely placed,Eyelids are fused,Low set Ears.9th week Liver is the site for Erythropoiesis.End of 9th week External genitalia develops both male & females appears similar.9th Week to 12th Week End of 10th week intestinal coils appears.End of 11th week intestinal coils placed in abdomen proper. End of 12th week Upper limb has almost reached final development.End of 12th week Primary Ossification centers appear in the skeleton (skull & Long bones). End of 12th week Activity of Rbc is decreased and in spleen it starts.Between 9th -12th week Urine formation begins and discharged into Amniotic fluid.

9th week

9th week

9th week

9th week

9th week

10th week

11th week

11th week

11th week

12th week

12th week

13th Week to 16th Week By 14th week : Slow eye movements occurs .By 14th week : Scalp hair patterning is determined.By 16th week : Head is relatively small when compared to 12th week.By 16th week : Lower limbs have extended & Limb movements appears.By 16th week : Ossification of Fetal skeleton & Bones are clearly visible.By 16th week : Ovaries are differentiated.By 16th week : Eye faces anteriorly (before its antero-laterally).By 16th week : External ears are placed in its position.Between 12th -16th weeks : sexes can be determined.13-16th weeks

80Genital organs

17th Week to 20th Week Fetal movements quickened commonly felt by the mother.Skin is now covered greasy,cheeselike vernix caseosa.(consists of mixture of dead epidermal cells and fatty subustance .)Vernix caesosa protects delicate fetal skin from abrasions,hardening,chapping results from exposure to amniotic fluid.Brown fat is formed &prevents from heat production.(Neck,sternum,perirenal areas).18th week : Uterus has formed.20th week : Testes has formed.20th week : Eye brow hair & Head hair clearly visible.

17-20 weeks

17-20 weeks

21st Week to 25th Week Fetus is proportionately better & weighted.Skin is wrinkled & colour is pink to red .21st week : Rapid eye movements visible.24th week : Type II pneumocytes appear in the lung. (secretory epithelial cells)24th week : Finger nails are developed.Babies born between 22-25 weeks survived in intensive care.Some cases babies die due to because Respiratory system has not developed or immature.21-25th weeks

21-25th weeks

21-25th weeks

26th Week to 29th Week Lungs & Pulmonary vasculature has developed.Central nervous system starts matured.Rythemic breathing movements &Control over body temperature occurs.26th week : Eye lids opens 26th week : Head hair fully develops.26th week : Toe nails are visible.26th week : Quantity of white fat increases.26th week : Fetal spleen has been important site for Erythropoiesis.

26th Week to 29th Week

26th Week to 29th Week

26th Week to 29th Week

26th Week to 29th Week

26th Week to 29th Week

26th Week to 29th Week

26th Week to 29th Week

30th week to 34th Week 30th week : Papillary light reflex of the eye can be elicited.Skin is smooth, Upper limb & Lower limbs are chubby in appearance.

35th week to 38th Week Fetuses born at 35th week have firm grasp & exhibit spontaneous orientation to light.36th week circumference of head and abdomen are equal in size.Full term fetus has 360mm CRL.3400 gms in weight.Male foetuses are larger in weight than female.Thorax is promonent.Testes are usually in the scrotum.38TH WEEK

PARTURING

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