OBJ - Early Embryogenesis Flashcards
(24 cards)
Fertilization vs Gestational age
Gestational age/menstrual age):
- Origin is the woman’s last normal menstrual period (LMP)
= Fertilization age + 14 days
Fertilization Age/embryonic age/fetal age
- Origin is fertilization
= Gestational Age - 14 days
Timeline:
LMP—-14 days—-Fertilization
Nomenclature
From fertilization
Pronuclear
Zygote: 2 cell stage to Morula
2 cell - 4 cell - 8 cell - Morula
Morula Day 3
Blastocyst Days 4 - 6
Embryo –> until the end 8th week
Fetus Week 9 to birth
Conceptus
- all structures that develop from zygote – embryonic and extra embryonic
Phases of Fertilization
PHASES
1) Ovulation (viable for 24 hrs)
2) Intercourse
3) Sperm Capacitation
- Glycocalyx lost in uterine tube
- Sperm (Viable 24-48 hours)
4) Fertilization
A. Penetration of Corona Radiata
Hyaluronidase
Tube Enzymes
Tail Wagging
B. Penetration of Zona Pellucida
Enzymes released from acrosome &
form pathway through ZP
C. Ovum-Sperm membrane Fuse
- Cortical & zona reactions –
cortical granules released
- Ovum completes meiosis II
(because have right amount of DNA
- Sperm mitochondria are destroyed
(maternal only)
4) Male Pronucleus – FORMS
Female Pronucleus – already present
5) Pronuclei Replicate their DNA
6) Pronuclear membranes degenerate ->
ZYGOTE
7) Chromosomes line up for mitosis & first
cleavage
—-> Cleavage & Transport down uterine tube
Pronuclear -> 2 cell -> 4 cell -> 8 cell -> morula -> blastocyst -> blastocyst hatches from zona pellucida & implants
—-> IMPLANTATION
Zona Reaction
Alteration of the ZP by acosomal enzymes & ZP becomes impenetrable to more sperm
Cortical Reaction
Ovum membrane altered by cortical granules
Results of Fertilization
1) Initiates completion of Meiosis 2
2) Restores to 2n chromosomes
3) Determines genetic sex
4) Activates metabolism
5) Initiates cleavage
Characters of Fertilization
1) Ovum
Ovulation:
ovum completes first meiotic division & arrests at metaphase II -> haploid chromosomes but diploid DNA b/c only X
Zona Pellucida – Glycoprotein coat – clear layer, glycoproteins act as receptor for sperm
Corona Radiata Cells – help nourish & take car of ovum (ovum’s groupies) & serve as barrier
Uterine tube = Fallopian tube = Oviduct (all the same structure)
Uterine Tube Mucosa = simple columnar
- PEG CELLS
secrete nutritive material for ovum
- Ciliated cells move fluid down the tube
2) Sperm
Glycocalyx over Acrosomal Cap over Head
Mitochondiral sheath = body
Tail = microtubules
Made in seminiferous tubule
Epididymus – matured, gain motility & stored
Vas Deferens – leave through ejaculation
Haploid in chromosomes & DNA content – 23 X or 23 Y
Recall the events of the first week, including cleavage, hatching, early implantation and the formation of the blastocyst with its inner cell mass and trophoblast.
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Events of the first Week
1) Cleavage
2) Hatching of ZP
3) Early implantation
4) Blastocyst formation with inner cell mass
Trophoblast – cells on outside
Blastocoel – fluid filled cavity
Inner Cell Mass - becomes embryo
– embryonic Pole -> site of implantation
Day 0: Fertilization & Pronuclear stage
Day 1: 2 Cell
Day 2: 4 cell
Day 3: 8 cell
Day 4: Morula
Day 5: Blastocyst floating around nucleus
Day 6: Hatching Blastocyst
Inner Cell Mass - attaches
Blastocyst Cavity
Trophoblast
Day 7: Implantation
Cytotrophoblast proliferation &
integration of vessels & glands
HYPOBLAST formation
Cytotrophoblast
Inner layer of trophoblast
Essential for implantation of blastocyst
- Once made contact with endometrium - begins to rapidly proliferate & absorb/breakdown vessels & glands to get nutrients
- Then lets Synctiotrophoblast take over
Pre-eclampsia - failure to invade uterus & its vasculature
Synctiotrophoblast
Outer layer of trophoblast
Epithelial covering of the highly vascular embryonic placental villi
Invade endometrium, surround glands & absorbs nutrients, surround vessels -> Lakes -> feeding conceptus
Establishes nutrient circulation
Events of the Second Week
Day 8: Continuing Implantation
Bilaminar Disc formation with
EPIBLAST formation
Amniotic Cavity
Primary Yolk Sac
Day 9: Decidua Reaction
Formation of EE Coelom
Formation of EE Mesoderm
Day 10:
Day 11:
Day 12: Lacunae Coalesce
Uterine wall continuous again
Utero-placental Flow & Primary Villi
Formation of EE Cavity
Day 13: Blastocyst floating around nucleus
Formation of Chorionic Cavity
Formation of Connecting Stalk &
Secondary yolk sac
Formation of Somatic EEM
Formation of Chornion
Portions that become the Embryo
Inner Cell Mass -> Epiblast & Hypoblast
Week 2 = Week of 2’s
2 Weeks
2 Layers
2 layers of inner cell mass:
Epiblast & hypoblast
2 layers of trophoblasst:
Cytotrophoblast & synctiotrophoblast
2 yolk sacs – primary then secondary
2 new cavities – amnion & chorion
2 layers of EEM = chornionic cavity
2 layered membranes = become
Amnion, chorion & yolk sac
Bilaminar Disc
Epiblast
Hypoblast
Decidual Reaction
Changes in endometrium of the uterus that prepare it for implantation of a fertilized zygote
Generalized area where the blastocyst contacts the endometrial decidua (what would be shed during menstration
-> Increase in secretory functions of the endometrium at the area of implantation, as well as a surrounding stroma that becomes edematous
Chorionic villi
Baby’s BV surrounded by pools of maternal blood - separated/isolated
1st formed = primary villi = formed by cytotrophoblastic cells
Chorion
Fetal portion of placenta
Made of:
- Syntrophoblast
- Cytotrophobast
Amnion
Large sac containing amniotic fluid in which the fetus is suspended by the umbilical cord to support/insulate
Gastrulation
3 weeks = 3 layers
Migration to form 3 germ layers; formation of trilaminar disc
Ectoderm = BLUE
- Thickens as a precursor to neural/skin systems
Mesoderm = RED
- Thickens as precursor to many organ/stromal systems
Endoderm = YELLOW
- Migrate deepest and replace hypoblast – lines the floor of the disc
Formation of the notochord
Notocord:
Extends from oropharyngeal membrane to the primitive node (the medial end of the primitive streak, distal end = cloacal membrane = anus)
Functions as the primary signaling center in early embro
Induces overlying ectoderm to thicken & form neural plate (gives rise to CNS)/axial skeleton
Primitive streak
- Establishes body axes/polarities:
R/L head & feet
- Cells detach from epiblast & migrate/invaginate beneath it -> notocord
- Epiblast -> Ectoderm
- Mesoderm -> filler
Cord of cells between endoderm & ectoderm that form region of oropharyngeal membrane – 2 layers @ other end become mouth
Cranial edge
Primitive streak: now a deep groove & portal for cells -> Primitive Pit
Cells stream into the streak towards the head/Cranial edge
Neurulation
Formation of neural tube
Ectoderm -> neural groove & neural crests becomes U and fuses to become a O tube -> Neural plate (neural groove = CNS; neural crest -> spinal column)
Mesoderm -> organizing itself
Paraxial/Lateral layers
Parietal/ Visceral layers
Starts cranially and “zips” down to form caudal region
Closes by 25 days
Folding of layers in 2 directions:
- Cranial/caudal folding - assuming fetal position – heart above head -> below brain
- Lateral folding – zipping up & creates gut surrounded by parietal cavity
http: //www.indiana.edu/~anat550/genanim/latfold/latfold.swf
Causing:
- Each germ layer can induce each other
- Closure of ventral body wall – except for where umbilical tube is growing
- Tube with 2 tubes within it – neural & future gut
1) Intra-embryonic cavity
= Yolk sac -> gut tube & umbilical cord
2) Amniotic cavity
Abnormal Embryos
Almost ANY defect in this process
Neural tube defects – Spina Bifida
Prevented by Folic Acid
Abnormal pregnancies
Tubal Ovarian Intramural Cervial Abdominal
**Any other place than uterus
Ectopic pregnancy = VERY dangerous for mom
