Download Pregnancy & Human Development

Pregnancy & Human
Development
Ex. 44
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.
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
Penetration
Secondary
oocyte
Head of
sperm
1650X
No
Polyspermy!
Fertilization
&
First
cleavage
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.
Development from zygote to
implantation.
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.
Implantation – Day 6
Implantation – Day 7
Hormone
levels in
early
pregnancy
Placental hormones
Implantation
Placentation
Fetus & placenta: 13 weeks
Embryonic Development
Differentiation of the three primary germ layers
Germ layer formation, Part II
Neurulation: Part I
Neurulation: Part II
Gastrulation
Formation of the
primitive gut
Gasturlation
part II
Organogenisis
in a 5
week embryo
Differentiation
of Mesoderm
Differentiation of Mesoderm continued
The Primary Germ Layers
ECTODERM
MESODERM
ENDODERM
All nervous tissue
Muscle
Epidermis &
Derivatives
Cornea & lens
Connective tissue Digestive glands
Lymphoid tissue
Reproductive ducts &
gland epithelium
Oral, nasal & anal
epithelium
Endothelium of
blood vessels
Thyroid, thymus &
parathyroid
Tooth enamel
Serosae
Pineal, pituitary &
adrenal medulla
Eye’s fibrous &
vascular tunics
Urethra & bladder
epithelium
Respiratory tract
epithelium
Melanocytes
Synovia
Flat bones of cranium Urogenital organs
G.I. epithelium
Fetal circulation
Pregnancy from the mother’s
perspective
Hey Ma!
It’s getting
crowded
in here!
Labor:
the
beginning
of the end
The “let-down”
reflex
or, more fun
with oxytocin