BIO1022 Lecture Notes - Lecture 14: Zygote, Cell Potency, Allantois
30 May 2018
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BIO1022 – Lecture 14
- organogenesis - various regions of the threee embryonic germ layers develop
into the rudiments of organs
- frist structure to take shape in vertebrate organogenesis are the notochord and
the neural tube
• the notochord - rod like - forms from dorsal mesoderm
- endoderm - archenteron - digestive system -
- developmental adaptation of amniotes
• all vertebrate embryos require an aqueous environment for development
• two effective structures that have allowed vertebrates to reproduce in dry
environments
•
o shelled egg of birds, reptiles and some mammals - monotremes
o uterus of marsupial and eutherian - placental mammals
o
▪ within the shell or uterus the embryo is surrounded by fluid
within a sac formed by a membrane called the amnion
▪
▪ therefore called amniotes
▪ Amnion protects the embryo in a fluid-filled cavity
that prevents dehydration and cushions mechanical
shock.
• The three germ layers in these organisms also give rise to the four
extraembryonic membranes that surround the developing embryo:
•
o Amnion protects the embryo in a fluid-filled cavity that prevents
dehydration and cushions mechanical shock.
o Allantois functions as a disposal sac for certain metabolic wastes.
Also functions with chorion as a respiratory organ.
o Chorion and the membrane of the allantois exchange gases
between the embryo and the surrounding air. Oxygen and carbon
dioxide diffuse freely across the egg’s shell.
o Yolk sac expands over the yolk, a stockpile of nutrients stored in
the egg. Blood vessels in the yolk sac membrane transport
nutrients from the yolk into the embryo. Other nutrients are
stored in the albumen the egg white.
- mammalian development
• eggs of placental mmammals are small and contain few nutrients
•
o exhibit holoblastic cleavage
o show no obvious polarity
- early human embryonic development
• fertilisation
•
o gives rise to an embryo
o embryo secretes human chorionic gondadotrophins which
maintains secretion of progesterones and estrogens to help
maintain lining of uterus
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Document Summary
Organogenesis - various regions of the threee embryonic germ layers develop into the rudiments of organs. Frist structure to take shape in vertebrate organogenesis are the notochord and the neural tube the notochord - rod like - forms from dorsal mesoderm. Endoderm - archenteron - digestive system - Also functions with chorion as a respiratory organ: chorion and the membrane of the allantois exchange gases between the embryo and the surrounding air. Oxygen and carbon: yolk sac expands over the yolk, a stockpile of nutrients stored in the egg. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are dioxide diffuse freely across the egg"s shell. stored in the albumen (cid:523)the (cid:498)egg white(cid:499)(cid:524). Mammalian development: eggs of placental mmammals are small and contain few nutrients, exhibit holoblastic cleavage, show no obvious polarity.
