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Unit 2 AOS 1 6.2 Prenatal Development
Transcript of Unit 2 AOS 1 6.2 Prenatal Development
Once fertilisation occurs, the prenatal stage of development commences.
Even though the foundations of
ntellectual development start at this stage, the
aspect of development is the most noticeable.
Development during this stage is the most rapid of all lifespan stages.
The germinal stage starts at fertilisation and ends with implantation.
begins around day five and ends around days 10–12.
When fertilised, the newly formed cell (
) travels down one of the fallopian tubes while constantly dividing.
3-4 days after fertilisation, when there are about 16 cells, the zygote takes on a spherical shape and is now known as a
5 days after fertilisation, when it is made up of around 64 cells, the morula transforms to include an outer cell mass, an inner cell mass and a hollow, fluid-filled centre called the blastocyst cavity. At this stage, the morula is known as a
The inner cell mass of the blastocyst will become the embryo and the outer cell mass will eventually become the placenta.
When it reaches the uterus, the blastocyst implants itself in the endometrium. At this point, it becomes known as an ‘embryo’.
The embryonic stage starts at implantation and ends at the eighth week.
characterised by cell differentiation
cells start taking on specialised roles such as heart cells, skin cells and bone cells
most internal and external organs and systems are formed during this stage
brain and spinal cord are almost complete by the end of it (although they will grow in size and increase in complexity for years to come).
although sex is determined at conception, the internal sex organs begin to form during the embryonic stage but will not be complete for another eight weeks.
by Week 8 the embryo becomes distinctly human looking, although the head and neck still account for around half the embryo’s total length and the brain makes up almost half of its body weight.
The Foetal Stage
The foetal stage starts at the ninth week of pregnancy and continues until birth at around 40 weeks.
During this stage the unborn baby is referred to as a ‘foetus’.
The foetus measures only a few centimetres in length at the beginning of this stage and about 50 centimetres by the end.
This stage is characterised by rapid growth.
Physical development from conception to birth, including the features of the germinal, embryonic and foetal stages
Because major organs and systems are formed during this time, the embryo is very sensitive to environmental influences.
Teratogens such as tobacco, alcohol and medication are particularly influential during this stage of development.
At the eighth week, the embryo has begun to form every major organ and system, and many are close to completion.
( 90 per cent of the structures found in an adult human can be found in an eight-week-old embryo!)
All organs and systems mature and are functioning in the early stages of foetal development.
The placenta is fully developed and functioning at 14 weeks.
- acts like a kidney, lung and digestive system for the foetus by supplying the foetus with oxygen, nutrients and immune support, and removing wastes such as urine and carbon dioxide.
- connected to the foetus by the umbilical cord, which is made up of two arteries and one vein. The umbilical vein supplies the foetus with nutrient-rich oxygenated blood from the placenta, and the umbilical arteries return deoxygenated and nutrient-depleted blood to the placenta.
The placenta is also connected to the uterus of the mother, and her blood forms pools in the placenta. The blood vessels of the umbilical cord complete a ‘U-turn’ while passing through pools of the mother’s blood in the placenta. This allows the exchange of nutrients, oxygen and wastes through the thin walls of the placenta without the foetal blood coming into direct contact with the blood of the mother (see figure 6.8).
In the foetal stage, Sex organs start taking shape
By the 15th week, the sex of the foetus may be identifiable (Ultrasound).
A female foetus will have produced millions of eggs but this number will be reduced by the time she is born.
The testes of a male foetus will be producing testosterone.
in Workbook - 6.2
Q1 - Q4
Complete Handout task
Cut up the sentences describing characteristics of each stage.
Arrange them in chronological order to demonstrate your understanding.
Paste into your workbook after having them checked :)
Complete the handout "CH6 Worksheet Teratogens"
CH6 Activity Cut & Paste Prenatal
HANDOUT: Prenatal Development Summary Table
As we work through the following content, use the summary table to record your notes on each of the stages of prenatal development.