EARLY_EMBRYOLOGY

EXTENDS FROM FERTILIZATION (DAY 1) TO END OF 8TH WEEK (DAY 56)

-ZYGOTE: CELL THAT RESULTS FROM UNION OF EGG AND SPERM

-EMBRYO: EARLY STAGES IN UTERO (DAY 1 - 56)

-CONCEPTUS: "PRODUCTS OF CONCEPTION", EMBRYO AND ASSOCIATED MEMBRANES (EMBRYO, EMBRYONIC PART OF PLACENTA, AMNION, CHORIONIC SAC, YOLK SAC)

EXTENDS FROM 9TH WEEK (DAY 57) TO BIRTH; PRIMARILY PERIOD OF DIFFERENTIATION AND GROWTH OF TISSUES AND ORGANS

CRITICAL PERIOD FOR SENSITIVITY TO STRUCTURAL TERATOGENESIS

3RD THROUGH 8TH POST-FERTILIZATION WEEK IS THE PERIOD DURING WHICH ALL THE MAJOR ORGAN SYSTEMS OF THE BODY ARE BEING FORMED.

• DAYS WEEKS MONTHS
• FERTILIZATION: 266 38 8.75

LNMP: 280 40 9.25

1) REDUCTION TO HAPLOID NUMBER GAMETES

2) RANDOM ASSORTMENT OF MATERNAL & PATERNAL CHROMOSOMES BETWEEN GAMETES

3) CROSSING OVER ALLOWING RECOMBINATION OF GENETIC MATERIAL

1) NEONATE -- ONE MONTH TO 1 YEAR

2) INFANT -- 1-YEAR-OLD OR YOUNGER

3) PUBERTY

4) MENARCHE

FEMALE GERM CELLS THAT PROLIFERATE BY MITOSIS DURING EARLY FETAL LIFE

FORM PRIMARY OOCYTES BEFORE BIRTH

1) OOGONIA ENLARGE TO FORM PRIMARY OOCYTE

2) PRIMARY OOCYTE BEGIN FIRST MEIOTIC DIVISION BEFORE BIRTH; PROPHASE IS NOT COMPLETED 'TIL AFTER PUBERTY, ARESTED DUE TO MATURATION INHIBITOR RELEASED BY FOLLICLE CELLS

3) PRIMARY OOCYTE + SUROUNDING LAYER OF FLATTENED EPITHELIAL FOLLICULAR CELLS = PRIMORDIAL FOLLICLE

1) ZONA PELLUCIDA FORMS BETWEEN PRIMARY FOLLICLE CELLS AND OOCYTE TO MATURE 15-20 PRIMARY OOCYTES EACH MONTH

2) ONE PRIMARY OOCYTE COMPLETES 1ST MEIOTIC DIVISION JUST BEFORE OVULATION, FORMING SECONDARY OOCYTE AND 1ST POLAR BODY

3) SECONDARY OOCYTE BEGINS 2ND MEIOTIC DIVISION, BUT STOPS IN METAPHASE

4) 2ND MEIOTIC DIVISION COMPLETED WHEN SPERM ENTERS SECONDARY OOCYTE, FORMING A FERTILIZED OOCYTE (ZYGOTE) AND 2ND POLAR BODY

NORMAL PROCESS OF PROGRAMMED CELL DEATH IN PRIMARY OOCYTES AND PRIMARY FOLLICLES

1) FSH STIMULATES 15-20 PRIMARY FOLLICLES TO GROW

2) 1 REACHES MATURITY AND OTHERS UNDERGO ATRESIA

3) THECAL CELLS SURROUND AND PROMOTE GROWTH OF BLOOD VESSLES

4) FOLLICLE CELLS PROLIFERATE AND PRODUCE FLUID TO FORM CAVITY (ANTRUM); NOW CALLED SECONDARY FOLLICLE

5) PRIMARY OOCYTE IN SECONDARY FOLLICLE SURROUNDED BY CUMULUS OOPHORUS (FOLLICLE CELLS)

6) FOLLICLES PRODUCE ESTROGEN

1) SURGE OF LH CAUSES PRIMARY OOCYTE TO COMPLETE 1ST MEIOTIC DIVISION

2) INTRAFOLLICULAR PRESSURE, SMOOTH MUSCLE CONTRACTION IN THECA, AND ENZYMATIC DIGESTION CAUSES RUPTURE OF SECONDARY FOLLICLE

3) SECONDARY OOCYTE AND 1ST POLAR BODY (SURROUNDED BY ZONA PELLUCIDA AND CUMULUS OOPHORUS) ARE EXPELLED

4) CUMULUS OOPHORUS REARRANGES TO FORM CORONA RADIATA

5) WALLS OF FOLLICLE AND THECA FORM CORPUS LUTEUM, WHICH SECRETES PROGESTERONE & ESTROGEN

6) PROGESTERONE AND ESTROGEN PREPARE ENDOMETRIUM OF UTERUS

7) IF NO PREGNANCY THEN MENSTRUAL CYCLE OCCURS

1) DURING OVULATION, FIMBRIAE OF UTERINE TUBE MOVE OVER OVARY

2) CILIA OF MUCOSAL CELLS OF FIMBRIAE SWEEP SECONDARY OOCYTE INTO INFUNDIBULUM OF UTERINE TUBE

3) OOCYTE PASSES INTO AMPULLA OF UTERINE TUBE AS RESULT OF PERISTALSIS; MOVES TOWARD UTERUS

4) FERTILIZED WITHIN 12 HOURS AFTER OVULATION, CANNOT AFTER 24 HOURS

1) AT PUBERTY, SPERMATOGONIA PROLIFERATE BY MITOTIC DIVISION

2) SPERMATOGONIA TRANSFORM INTO PRIMARY SPERMATOCYTES

3) 1*SPERMATOCYTES UNDERGO 1ST MEITIC DIVISION TO FORM TWO 2*SPERMATOCYTES

4) 2*SPERMATOCYTES UNDERGO 2ND MEIOTIC DIVISION TO FORM 4 HAPLOID SPERMATIDS

1) SPERM PENETRATES CORONA RADIATA USING ACROSOMAL ENZYMES & TAIL

2) PENETRATES ZONA PELLUCIDA USING ACROSOMAL ENZYMES. ZONA REACTION FROM OOCYTE STOPS OTHER SPERM

3) FUSION OF SPERM & OOCYTE PLASM MEMBRANES

4) COMPLETION OF OOCYTE 2ND MEIOTIC DIVISION. FORMATION OF FEMALE PRONUCLEUS AND 2ND POLAR BODY

5) FORMATION OF MALE PRONUCLEUS; BOTH MALE & FEMALE REPLICATE DNA

6) PRONUCLEI FUSE TO FORM ZYGOTE

1) AFTER THE 9-CELL STAGE, BLASTOMERES CHANGE SHAPE AND ATTACHMENTS TO UNDERGO COMPACTION (REQUIRED TO SEGREGATE INNER CELL MASS GIVING RISE TO EMBRYO PROPER)

2) MORULA ENTERS THE UTERUS ABOUT 3 DAYS AFTER FERTILIZATION

RAPID MITOTIC DIVISIONS OF THE ZYGOTE RESULTING IN EMBRYONIC CELLS CALLED BLASTOMERES

EMBRYO CONSISTING OF 12-32 BLASTOMERES

1) FLUID-FILLED BLASTOCYSTIC CAVITY APPEARS INSIDE MORULA ABOUT 4 DAYS AFTER FERTILIZATION

• 2) BLASTOMERES SEPARATE INTO 2 GROUPS:
• ---TROPHOBLAST FORMS A THIN OUTER CELL LAYER WHICH GIVES RISE TO EMBRYONIC PLACENTA
• ---INNER CELL MASS (EMBRYOBLAST) MADE OF CENTRALLY LOCATED BLASTOMERES GIVING RISE TO EMBRYO

3) CONCEPTUS NOW CALLED BLASTOCYST; AFTER ABOUT 2 DAYS THE ZONA PELLUCIDA DEGENERATES AND THE BLASTOCYST "HATCHES"

1) ABOUT 6 DAYS AFTER FERTILIZATION, BLASTOCYST ATTACHES TO ENDOMETRIAL ENDOTHELIUM AT POINT CLOSEST TO INNER CELL MASS (EMBRYONIC POLE)

• 2) TROPHOBLAST PROLIFERATES AND DIFFERENTIATES INTO 2 LAYERS:
• --- INNER LAYER CALLED CYTOTROPHOBLAST
• --- OUTER MULTINUCLEATED LAYER CALLED SYNCYTIOTROPHOBLAST WHICH INVADES ENDOMETRIUM AND RELEASES ENZYMES ALLOWING BLASTOCYST TO BURROW

3) DAY 7 AFTER FERTILIZATION, PRIMARY ENDODERM (HYPOBLAST) DELAMINATES FROM THE EMBRYOBLAST ON THE DEEP SURFACE FACING THE BLASTOCYSTIC CAVITY

1) INVADES ENDOMETRIAL CONNECTIVE TISSUE; THESE CELLS MUST BE IN RECEPTIVE STATE FOR INVATION

2) SPECIALIZED DECIDUAL CELLS OF ENDOMETRIUM DIE AND ARE ENGULFED BY STB FOR FOOD (GLYCOGEN AND LIPIDS)

3) PRODUCES hCG WHICH MAINTAINS HORMONAL ACTIVITY OF CORPUS LUTEUM

4) LACUNAE FORM EITHIN STB AND FILL WITH BLOOD WHICH PROVIDES FOOD

5) ERODED ENDOMETRUAL CAPILLARIES COMMUNICATE WITH THE LACUNAE AND ESTABLISH THE PRIMORDIAL UTEROPLACENTAL CIRCULATION

6) DECIDUAL CELLS REACTION OF THE ENDOMETRIUM PRIVIDES IMMUNOLOGIAL PROTECTION FOR BLASTOCYST

7) 12 DAYS AFTER FERTILIZATION: LACUNAR NETWORKS FORM WITHIN STB

IMPLANTATION OUTSIDE OF UTERUS

>90% OF THESE OCCUR IN AMPULLA AND ISTHMUS OF URERINE TUBE (TUBAL PREGNANCY)

BLASTOCYST EXPELLED INTO THE PERITONEAL CAVITY AND IMPLANTS IN THE RECTOUTERINE POUCH

BLASTOCYST IMPLANTS NEAR THE THE INTERAL OS "OPENING" OF THE UTERUS

PLACENTA COVERS OS -- THUS PLACENTA WILL PRECEDE THE BABY IN DELIVERY

* WEEK 2

*APPEARS AS SPACE IN EMBRYOBLAST (INNER CELL MASS)

* CELLS MIGRATE FROM THE EPIBLAST AND FORM THE AMNION

* WEEK 2

* EPIBLAST FORMS FLOOR OF AMNIOTIC CAVITY CONTINUOUS WITH AMNION

* HYPOBLAST FORMS ROOF OF EXOCOELOMIC CAVITY

* PRECHORDAL PLATE (DAY 14) FORMS AS ATHICKENED AREA OF HYPOBLAST. INDICATES FUTURE SITE OF MOUTH.

* WEEK 2

* CELLS OF HYPOBLAST AND EXOCOELOMIC MEMBRANE LINE THE PUV (YOLK SAC)

* EXTRAEMBRYONIC COELOM SURROUNDS AMNION AND UMBILICAL VESICLE, AND BECOMES LINED WITH EXTRAEMBRYONIC MESODERM

* ENDOMETRIAL CELLS MIGRATE FROM HYPOBLAST TO FORM SECONDARY UMBILICAL VESICLE; PUV PINCHES OFF AND SHRINKS/DISAPPEARS

* WEEK 2

* CYTOTROPHOBLAST CELLS PROLIFERATE AND REARRANGE TO FORM "FINGERS" THAT PROJECT INTO THE SYNCYTIOTROPHOBLAST

* PART OF CHORIONIC SAC DEVELOPMENT

* WEEK 2

* EXTRAEEMBRYONIC SOMATIC MESODERM LINES TROPHOBLAST, COVERS AMNION

* EXTRAEMBRYONIC SPLANCHNIC MESODERM SURROUNDS UMBILICAL VESICLE

* PART OF CHORIONIC SAC DEVELOPMENT

* WEEK 2

* WALL OF CHORIONIC SAC MADE OF EXTRAEMBRYONIC SOMATIC MESODERM + PRIMARY CHORIONIC VILLI + SYNCYTIOTROPHOBLAST

* EXTRAEMBRYONIC COELOM NOW = CHORIONIC CAVITY

* PART OF CHORIONIC SAC DEVELOPMENT

* PART OF CHORIONIC SAC DEVELOPMENT

WEEK 3

FORMATION OF GERM LAYERS

• CONVERTS BILAMINAR EMBRYONIC DISC INTO TRILAMINAR EMBRYONIC DISK:
• ---ECTODERM
• ---MESODERM
• ---ENDODERM

BEGINNING OF MORPHOGENESIS

BEGINS WITH PRIMITIVE STREAK ON DORSAL SURFACE OF EPIBLAST

EMBRYO IS NOW CALLED A GASTRULA

WEEK 3

MOST SUPERIOR PART OF TRILAMINAR EMBRYONIC DISK. BETWEEN AMNION (DORSAL SIDE) AND MESODERM (VENTRAL SIDE)

GIVES RISE TO EPIDERMIS, CENTRAL AND PERIPHERAL NERVOUS SYSTEMS, AND RETINA

WEEK 3

MEDIAL PART OF TRILAMINAR EMBRYONIC DISK BETWEEN ECTODERM AND ENDODERM

GIVES RISE TO SMOOTH MUSCLE COATS, CONNECTIVE TISSUE AND VESSELS, MOST OF CARDIOVASCULAR SYSTEM, BLOOD CELLS AND BONE MARROW, SKELETON, STRIATED MUSCLES, REPRODUCTIVE AND EXCRETORY ORGANS

WEEK 3

MOST INFERIOR PART OF TRILAMINAR EMBRYONIC DISK. BETWEEN EMBRYONIC MESODERM AND HYPOBLAST.

GIVES RISE TO EPITHELIAL LININGS OF RESPIRATORY PASSAGES AND GASTROINTESTINAL TRACT, AND TO GLANDULAR CELLS OF ASSOCIATED ORGANS

WEEK 3

APPEARS CAUDALLY AND MEDIALLY ON DORSAL SIDE OF EPIBLAST

PRIMITIVE GROOVE AND PIT ALLOW ID OF CRANIAL/CAUDAL AND LEFT/RIGHT AXES

MESENCHYMAL CELLS FORM EITHER MESODERM OR ENDODERM (MUST DISPLACE HYPOBLAST)

REGRESSES AND DISAPPEARS EARLY ON WEEK 4

MOST COMMON TUMOR IN NEWBORNS

RESULTS FROM PERSISTENCE OF PRIMITIVE STREAK

WEEK 3

FORMED FROM INVAGINATING MESENCHYMAL CELLS OF EPIBLAST THAT MIGRATE CRANIALLY ALONG MIDLINE

DORSAL CELLS PERSIST AS FLAT NOTOCHORDAL PLATE, WHICH FOLDS TO BECOME THE RIGID NOTOCHORD

WEEK 3

LUMEN OF NOTOCHORDAL PROCESS

WEEK 3

SMALL CIRCULAR STRUCTURE CRANIAL TO NOTOCHORDAL PROCESS WHERE ECTO AND ENDODERM ARE IN CONTACT

BLOCKS EXTENSION OF NOTOCHORDAL PROCESS CRANIALLY

PRIMORDIUM OF THE OROPHARYNGEAL MEMBRANE (ORAL CAVITY)

WEEK 3

TEMPORARY COMMUNICATION BETWEEN AMNIOTIC AND UMBILICAL VESICLE CAVITES

LAST AND TEMPORARY STRUCTURE OF NOTOCHORDAL CANAL

WEEK 3

FORMED IN SEVERAL STEPS DURING GASTRULATION BY MESENCHYMAL MESODERM CELLS

INDUCES OVERLYING ECTODERM TO BECOME NEURAL PLATE

INDICATES FUTURE SITE OF VERTEBRAL BODIES

WEEK 3

FORMED FROM ECTODERM INDUCED BY THE NOTOCHORD

PRIMORDIUM OF THE CNS

WEEK 3

CAUDAL TO PRIMITIVE STREAK

MADE UP OF FUSED ENDO AND ECTODERM

PRIMORDIUM OF ANUS

WEEK 3

EMBRYONIC MESODERM ON EACH SIDE OF NOTOCHORD PROLIFERATES TO FORM COLUMN OF PARAXIAL MESODERM

END OF 3RD WEEK, PARAXIAL MESODERM DIVIDES INTO BLOCKS CALLED SOMITES

SOMITES GIVE RISE TO MOST OF THE AXIAL SKELETON AND ASSOCIATED MUSCLES, AND TO THE ADJACENT DERMIS OF SKIN

OCCURS NATRALLY

MOST COMMON DURING 3RD WEEK

15% OF PREGNANCIES END BY THIS

50% RESULT FROM CHROMOSOMAL ABNORMALITIES OF THE CONCEPTUS

CAN BE CAUSED BY A TRISOMY AS A RESULT OF NONDISJUNCTION (EXCEPTION, DOWN SYNDROME)

SPORADIC AND RECURRENT SPONTANEOUS ABORTIONS ARE COMMON GYNECOLOGICAL PROBLEMS

CAUDAL DYSGENESIS

INSUFFICIENT MESODERM IN THE CAUDAL REGION OF EMBRYO DUE TO DISRUPTION OF GASTRULATION

• RESULTS IN:
• ---ABNORMAL LUMBOSACRAL VERTEBRAE
• ---HYPOPLASIA AND FUSION OF LOWER LIMBS
• ---RENAL AGENESIS
• ---IMPERFORATE ANUS

TRANSPOSITION OF THE VISCERA IN THE THORAX AND ABDOMEN

MAY BE DUE TO GENETIC ABNORMALITIES IN CILIA (KARTAGENER SYNDROME) WHICH ARE PRESENT ON THE CELLS OF THE PRIMITIVE NODE

DEVELOPS FROM PLURIPOTENT CELLS THAT ARE REMNANTS OF THE PRIMITIVE STREAK

MAY CONTAIN TISSUES DERIVED FROM ALL THREE GERM LAYERS