pregnancy & human development ex. 44. fertilization: it’s all in the timing! oocyte is only...
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Pregnancy & Human Development
Ex. 44
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Fertilization: It’s all in the timing!
• Oocyte is only viable for ~ 24 hours.
• Sperm is viable for 12 – 24 hours (some “super sperm” may be viable for up to 72 so be careful!)
• Therefore, usually, coitus must occur within a 24 hour window on either side of ovulation.
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Barriers to fertilization• Low vaginal pH
• Getting lost (50/50 chance of getting the right uterine tube)
• Numerous defective sperm
• Uterine contractions
• Phagocytes
• By the time they get to the oocyte, there are only a few dozen to a couple hundred
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Penetration
Secondaryoocyte
Head of sperm
1650X
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No Polyspermy!
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Fertilization&
First cleavage
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What’s this thing called, Love?• Zygote – a the single cell after fusion of
the pronuclei of the oocyte & the sperm.
• Conceptus – covers the period of develop following first cleavage and differentiation of cells into an embryo.– Morula – the conceptus as a solid ball of 16
cells (about day 3).– Blastocyst – a hollow ball of cells, from day 4.
“Hatching” occurs at this stage, when the blastocyst emerges from the zona pellucida.
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Development from zygote to implantation.
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Then what ?• The blastocyst differentiates into:
– the trophoblast, the outer ball of cells that eventually becomes the placenta and “extraembryonic” membranes.
– the inner cell mass (ICM) becomes the embryo.
• The above occurs over the course of the second week following conception.
• Implantation – occurs on about day 6 or so, as the blastocyst burrows into the endometrium.
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Implantation – Day 6
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Implantation – Day 7
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Hormone levels in
early pregnancy
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Placental hormones
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Implantation
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Placentation
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Fetus & placenta: 13 weeks
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Embryonic Development
Differentiation of the three primary germ layers
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Germ layer formation, Part II
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Neurulation: Part I
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Neurulation: Part II
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GastrulationFormation of the
primitive gut
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Gasturlationpart II
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Organogenisisin a 5
week embryo
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Differentiation of Mesoderm
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Differentiation of Mesoderm continued
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The Primary Germ Layers
All nervous tissue Muscle G.I. epithelium
Epidermis & Derivatives
Connective tissue Digestive glands
Cornea & lens Lymphoid tissue Reproductive ducts & gland epithelium
Oral, nasal & anal epithelium
Endothelium of blood vessels
Thyroid, thymus & parathyroid
Tooth enamel Serosae Urethra & bladder epithelium
Pineal, pituitary & adrenal medulla
Eye’s fibrous & vascular tunics
Respiratory tract epithelium
Melanocytes Synovia
Flat bones of cranium Urogenital organs
ECTODERM MESODERM ENDODERM
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Fetal circulation
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Pregnancy from the mother’s perspective
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Hey Ma! It’s getting crowded in here!
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Labor:the
beginning of the end
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The “let-down” reflex
or, more fun with oxytocin