Lecture 6: Fertilization and Gastrulation Flashcards
What are the order of structures of the Human Ovum from superficial to deep?
- Corona Radiata (superficial) –> follicular cells
- Zona Pellucida
- Perivitelline Space
- Plasma Membrane
- Cytoplasm
- Nucleus
Where does fertilization of the egg take place at?
Distal 2/3 of the ampulla (uterine tube)
Fertilization Step 1: Capacitation
- sperm “mature” and prepares enzymes for fertilization (takes 7 hrs as sperm travels)
- uses hyaluronidase to move through corona radiata
Fertilization Step 2: Penetration
- sperm uses acrosin to errode zona pellucida
- zona reaction: blocks polyspermy by freezing meshwork of zona pellucida
Fertilization Step 3: Fusion
- plasma membranes of oocyte and sperm merge
- head/tail of sperm enter oocyte cytoplasm
Fertilization Step 4:
- complete second mitotic division
- generation of male pronucleus and fusion w/female pronucleus
How long does fertilization usually take?
24 hrs
- 46 chromosomes
- determination of sex (X or Y)
- metabolic activation of oocyte (initiation of cleavage)
Cleavage: what is it and what is generated?
- increase in cell number and decrease in cell size
- 2 cell stage (blastomeres) –> 4 cell stage –> 8 cell stage –> MORULA (Day 3 after fertilization)
- takes place 30 hrs after fertilization
What day does the Morula reach the uterus?
Day 4
Blastocyst: What is happening from Day 5-Day 7?
Day 5: inner cell mass (embryonic stem cells), trophoblast outer layer, degenerating zona pellucida
Day 6: implantation in uterus
Day 7: zona pellucida gone (“embryo hatching”), cells get bigger
What is the Trophoblast and what two structures does it give rise to?
- trophoblast secretates Early Pregnancy Factor (no rejection)
1. Cytotrophoblast: stem cell layer (mitotically active)
2. Syncytiotrophoblast: responsible for implantation and initial signal of pregnancy (hCG) –> see on preg. test
Hydatidiform Mole (Complete vs Partial) and symptoms
- abnormal trophoblastic prolif., excessive hCG prod.
1. Complete: fert. of empty oocyte, duplication of sperm OR fert. of empty oocyte by TWO sperm
2. Partial: fert. of normal oocyte by TWO spem
symptoms: vaginal bleed, pelvic pressure, morning sickness
What happens in Week 1, Week 2, and Week 3?
Week 1: development of inner cell mass (1 layer)
Week 2: development of epiblast and hypoblast (2 layer)
Week 3: development of ectoderm, mesoderm, endoderm
Week 2 structures
Epiblast –> ectoderm, amnion, amniotic cavity
Hypoblast –> extraembryonic endoderm
What does the Hypoblast help develop? (3)
- Prechordal plate = future mouth
- Primary/Secondary Yolk Sac (umbilical vesicle)
- primary yolk sac degrades
- Extraembryonic mesoderm
What is primitive blood and where does it form?
- extraembryonic splanchnic mesoderm
- forms in wall of yolk sac
Placenta Previa
- implant close to interal os of cervix
- vaginal bleeding beyond 20 weeks of gestation
- DO NOT PALPATE –> can cause severe hemorrhage
What structures do the ectoderm, mesoderm, and endoderm form?
ectoderm: skin, hair, CNS
mesoderm: muscle, bone, blood, spleen
endoderm: GI tract, bladder, liver, lungs
What are the possible causes of Sacral-coccygeal and Oropharyngeal Teratomas?
- persistence of the primitive streak
2. abnormal movement of primordial germ cells
What is the Notochord and why is it important?
- midline that extends from primitive node to prechordal plate
- template for vertebral column
- induces neural plate (SONIC HEDGEHOG)
What are Chordomas?
- rare, slow growing aggressive neoplasms of bone
- from remnants of NOTOCHORD
- in spheno-occipital region of skull, sacral region
What is the allantois?
- posterior midline (ENDODERM)
- template for umbilical arteries and veins (gives position where they will form around)
- becomes urachus
Paraxial, Intermediate, and Lateral Plate Mesoderm
Paraxial - somites (muscle, vertebral, dermis)
Intermediate - urogential (kidneys and gonads)
Lateral Plate - CT (blood, lymph, mesenteries, cardio)
- somatic layer (nxt to ectoderm)
- splanchnic layer (nxt to endoderm –> viscera)
