Transcript Embryonic Dev

Chapter 15
Human Development
United Streaming Video:
Fertilization – Part 4
United streaming: Fertilization
- Part Five
Hormones Secreted During
Pregnancy
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The embryonic period occurs during the first two
months of the first trimester.
Cleavage follows, with successive mitotic cell
divisions, leading to the formation of a blastocyst,
consisting of an outer trophoblast layer and an inner
cell mass.
The blastocyst implants in the uterine wall, and
secretes human chorionic gonadotropin, which
prevents menstruation.
Functions of the Placenta
Nutritional
functions
• transports nutrients (for example, glucose, amino acids, fatty acids,
minerals, and vitamins) from the mother’s blood to the fetus’s blood
• stores nutrients, such as carbohydrates, proteins, iron, and calcium, in
early pregnancy and releases them to the fetus later, when fetal demand is
greater than the mother can absorb from her diet
Excretory
functions
• transports wastes (such as urea, ammonia, and creatinine) from the fetal
blood to the mother’s blood
Respiratory
functions
• transports oxygen from the mother to the fetus and carbon dioxide from
the fetus to the mother
Endocrine
functions
• secretes hormones, such as estrogen, progesterone, and human chorionic
gonadotropin
• allows hormones from the fetus to diffuse into the mother’s blood and
hormones from the mother to diffuse into the fetus’s blood
Immune functions
• transports antibodies from the mother into the fetus’s blood to provide
passive immunity
United Streaming: Biologix Fetal Development
and Birth – Lessons 4-6 (?)
In the placenta, chorionic villi that extend from the embryo are in
contact with pools of blood from the mother. Nutrients and
oxygen pass by diffusion from the maternal blood to the embryo,
and wastes diffuse in the opposite direction.
Organs and body systems that develop
from the three primary germ layers.
Major Events,
by Month, in
Prenatal
Development
Fetal Growth
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The fetal period occurs during the last month
of the first trimester and over the remaining
two trimesters.
In the fetal period, existing structures formed
via morphogenesis are elaborated and refined.
Throughout prenatal development, teratogens
exposed to or ingested by the mother can
affect the health of the embryo and fetus.
Critical Phases of Prenatal
Development
Three Stages of Parturition
Parturition: Positive Feedback
Mechanism
Reproductive Technologies
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Some reproductive technologies (such as in
vitro fertilization and superovulation) are
designed to enhance reproductive potential.
Some reproductive technologies (such as
condoms and surgical sterilization) are
designed to restrict or suppress reproductive
potential.
In a variation of in vitro fertilization, performed when a sperm is unable to
penetrate the egg in vitro, sperm may be injected into the egg—a technique
called intracytoplasmic sperm injection. It is used to help men with very low
sperm counts, high numbers of abnormal sperm, or injuries or illnesses that
prevent men from providing a sperm sample through ejaculation.
Sterilization