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8/3/2019 Embryology Lecture 4
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Beginning the Developmental
Program: Gametogenesis
Comparing Oogenesis and
Spermatogenesis
8/3/2019 Embryology Lecture 4
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Only genetic information from Germ Cells can be passed to the
next generation. [Wolpert Fig. 1.6]
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Gamtes are produced by Meiosis [Wolpert Fig. 12.17]
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Comparing Eggs (Ova) & Sperm
Haploid
Products of Meiosis
Produced by female parentin ovary
Non-motile gamete
Large size
Cytoplasm contains RNA
and Protein, nutrients
Haploid
Products of Meiosis
Produced by male parent intestis
Motile gamete -flagellum
Small in comparison
Minimal amt. Cytoplasm
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Structure of a Human Sperm [Wolpert Fig. 12.21]
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[Gilbert Fig. 7.3]
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Spermatogenesis produces 4 haploid Gametes [Wolpert Fig. 12.18]
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Spermatogenesis takes place in the seminiferous tubules in
the testis. [Gilbert Fig. 19.19]
Meiosis is initiated continuously in a mitotically dividing
stem cell population (= spermatogonia).
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Oogenesis vs. Spermatogenesis
(Mammals) Germ Cells enter ovary
Diploid oogonia multiply by
mitotic divisions duringembryogenesis
Enter prophase of Meiosis Ibefore birth
Further growth and
development of primaryoocyte delayed untilpuberty
Germ Cells enter testis
Arrest in G1 of cell
cycle until after birth
After birth, esp. after
puberty,
spermatogonia
multiply by mitoticdivisions
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Oogenic Meiosis
Oocytes in the human
ovary completed the
first meiotic prophase
before birth.
Puberty induces
completion of meiosis 1.
Each month, ovulation
triggers development
through metaphase of
meiosis 2.Fertilization triggers
completion of meiosis 2.
[Gilbert Fig. 19.30]
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Graafian follicle in a mammalian ovary [Balinsky Fig. 21]
Follicle cells synthesize Estrogen.
Estrogen stimulates liver to produce vitellogenin
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Oogenesis produces 1 Ovum & 3 Polar Bodies [Wolpert Fig. 12.8]
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Oogenesis vs. Spermatogenesis
Growth and development
occurs before completion
of Meiosis 1 One ovum & 3 polar bodies
are produced from each
primary oocyte
Unequal cytokineses
Differentiation occurs after
completion of Meiosis 1 &
2 Four sperm are produced
from each primary
spermatocyte
Equal cytokineses
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Regulation of
Gametogenesis by
hormones made in theAnterior Pituitary Gland
FSH (= follicle
stimulating hormone)
LH (= Luteinizinghormone)
[Gilbert Fig. 19.30]
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Oogenesis vs. Spermatogenesis Regulated by
pituitary hormones:
FSH and LH Ovarian hormones:
estrogen and
progesterone
Regulated by
pituitary hormones:
FSH and LH Testicular hormones
testosterone and
androgen binding
protein
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Timing of Fertilization in relation to development of the
oocyte [Wolpert Box 2A]
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The Cycle Continues.
The egg and the sperm will both die if they
do not meet.
The elements that unite are single cells,
each on the point of death; but by their
union a rejuvenated individual is formed,
which constitutes a link in the eternalprocess of life. Frank R. Lillie (1919)