embryology lecture 4

8/3/2019 Embryology Lecture 4

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Beginning the Developmental

Program: Gametogenesis

Comparing Oogenesis and

Spermatogenesis


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Only genetic information from Germ Cells can be passed to the

next generation. [Wolpert Fig. 1.6]


3/18

Gamtes are produced by Meiosis [Wolpert Fig. 12.17]


4/18

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


5/18

Structure of a Human Sperm [Wolpert Fig. 12.21]


6/18

[Gilbert Fig. 7.3]


7/18

Spermatogenesis produces 4 haploid Gametes [Wolpert Fig. 12.18]


8/18

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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10/18

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


11/18

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]


12/18

Graafian follicle in a mammalian ovary [Balinsky Fig. 21]

Follicle cells synthesize Estrogen.

Estrogen stimulates liver to produce vitellogenin


13/18

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


15/18

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


17/18

Timing of Fertilization in relation to development of the

oocyte [Wolpert Box 2A]


18/18

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)

embryology lecture 4

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