Transcript Human Embryo Development

Honours
Development of the Embryo
The hormonal control of the
menstrual cycle
Human Embryo Development
Honours
Learning Objectives
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List the sequence of development of an embryo
Explain the term fertilized egg
Explain the term blastocyst
Explain the term amnion
Explain how the placenta is formed
Explain how the embryo develops up to the third
month of gestation
Human Embryo Development
Sequence of development from fertilised
egg
Early stages
Human Embryo Development
Sequence of development from
fertilised egg
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The zygote contains
46 chromosomes,
twenty three from the
egg and 23 from the
sperm
Human Embryo Development
It divides rapidly by
mitosis to produce
2 cells, then 4,
then 8, 16 etc. and
continues to divide
Human Embryo Development
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At this point the
developing
individual is referred
to as the morula
Human Embryo Development
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Around 5 days after
fertilisation the
morula forms a
hollow ball of cells
called the
blastocyst
Human Embryo Development
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The outer layer of
the blastocyst forms
the trophoblast.
This will later
develop into the
layer of membranes
that surround the
embryo (placenta
and amnion)
Trophoblast
Human Embryo Development
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The inner cells (called
the inner cell mass) of
the blastocyst will
eventually form the
embryo. These cells
are not yet specialised.
They have a
phenomenal ability to
differentiate – divide to
give rise to many
different types of tissue
Inner cell mass
Human Embryo Development
Stem cells
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Huge research potential to renew or repair damaged
body parts.
Learning check
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How many chromosomes in a fertilised egg?
Is a fertilised egg haploid or diploid?
What is the developing individual referred to when it
is made up of 8 cells?
What is it referred to after a number of days?
What is unusual about the cells of the inner cell
mass?
Human Embryo Development
The morula/blastocyst is pushed along the
fallopian tube until it enters the uterus
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Human Embryo Development
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Here it will implant into
the uterus wall. The
endometrium now
provides nourishment for
the developing blastocyst
Connections with the
mother will begin to form
(placenta and umbilical
cord)
This point marks the beginning of
pregnancy
Human Embryo Development
Sequence of development from fertilised egg
Development of the embryo
Human Embryo Development
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About 10 days after fertilisation the inner cell mass
forms the embryonic disc
This usually consists of three layers called germ
layers
Ectoderm (outside)
 Mesoderm (middle)
 Endoderm (inside)
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Human Embryo Development
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Each of these layers gives rise to specific structures
in the developing embryo
In humans the mesoderm is split by a layer called
the Coelom
This allows space for more complex organs such as
heart, lungs and kidneys to develop
Human Embryo Development
Ectoderm – skin, nervous system
Coelom – heart, lungs
Mesoderm – muscles, skeleton
Endoderm – inner lining of
digestive system
Human Embryo Development
The Amnion
Human Embryo Development
The Amnion
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When first formed the amnion is in contact with the
embryo, but at about the fourth or fifth week fluid
begins to accumulate within it (amniotic fluid)
The primary function of the amnion and amniotic
fluid is the protection of the embryo for its future
development
Human Embryo Development
Four to five weeks after fertilisation
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The heart forms
and starts to beat
The brain also
develops
The limbs have
started to form
Human Embryo Development
Human Embryo Development
By the 6th week
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Eyes are visible
The mouth, nose
and ears are
forming
The skeleton is at
the early stages of
development
Human Embryo Development
By the 8th week
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the major body
organs are formed
Sex glands have
developed into
testes or ovaries
Bone is beginning
to replace cartilage
Human Embryo Development
By the 8th week
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At this stage the
embryo has taken
on a recognisably
human from.
From this point it is
referred to as a
foetus
The foetus
continues to grow.
No new organs are
formed from this
Human Embryo Development
By the 12th week (3 months)
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The nerves and muscle
become co-ordinated
allowing the arms and legs to
move
The feotus sucks its thumb,
urinates and even releases
feaces into the amniotic fluid
Human Embryo Development
By the 12th week (3 months)
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The gender of the
foetus can be seen
in scans
Human Embryo Development
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The time from
fertilisation to birth
(the gestation
period) lasts about
38 weeks (9
months)
Learning Check
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What are germ layers?
Name them
What features have already appeared by the fifth
week?
At what stage is the developing individual referred to
as a feotus?
Human Embryo Development
Placenta formation
Human Embryo Development
Placenta formation
Human Embryo Development
Placenta formation
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The placenta forms from a
combination of the tissues of
the uterus and the embryo
Soon after implantation a
membrane called the chorion
completely surrounds the
amnion and embryo
Human Embryo Development
Human Embryo Development
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The chorionic villi
emerge from the
chorion and invade
the endometrium
allowing the transfer
of nutrients from
maternal blood to
fetal blood
Human Embryo Development
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This combination of the chorionic villi and the
endometrium will eventually form the placenta which
becomes fully operational about three months into
the pregnancy
Human Embryo Development
The Placenta
Mother’s
blood
Placent
a
Chorion
Embry
o
Wastes, Carbon Dioxide,
Water
Nutrients, Oxygen,
antibodies
Mother
Embryo
Amnio
n
Amniotic
Umbilical cordfluid
Embryo’s
blood
Human Embryo Development
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Placenta allows gases, nutrients, waste, antibodies,
some drugs, hormones and micro-organisms to be
exchanged between mother and baby
Placenta also produces hormones
Human Embryo Development
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Blood supplies of mother and embryo do not mix
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Blood types may not be compatible
Mother’s blood pressure might damage embryo
Human Embryo Development
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Umbilical cord
connects the
embryo with the
placenta
it takes blood from
the embryo to the
placenta and back
again
It must be cut at
birth to separate
mother and baby
Human Embryo Development
45 seconds after birth!
Learning check
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Name the structures that move into the endometrium
and eventually become part of the placenta
At what point does the placenta become fully
operational?
Why is it important that the blood of the mother and
baby do not mix?
Hormonal Control of the
Menstrual Cycle
(Honours)
Learning objectives
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Outline the stages in the menstrual cycle
Discuss the role of hormones in the menstrual
cycle
Discuss the Cause/Prevention/Treatment for
fibroids or for endometriosis
Menstrual Cycle
Hormonal control in the menstrual
cycle
 Four hormones involved:
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FSH (Follicle Stimulating Hormone)
Oestrogen
LH (Luteinising Hormone)
Progesterone
 Each hormone causes the production of the
hormone following it and inhibits the hormone
preceding it (an example of a negative feedback
mechanism)
FSH – Follicle Stimulating Hormone
 Produced by pituitary gland
 Produced early in the cycle (days 1-5)
 Stimulates a few potential eggs to develop,
surrounded by graafian follicles
 Only one usually survives
 Sometimes used in fertility treatments to stimulate
ovaries to produce eggs – often lots of eggs
develop. This explains some multiple births
 Each graafian folllicle then produces oestrogen
Oestrogen
 Produced by the graafian follicle in the ovary
 Produced from days 5 -14
 Causes the endometrium to develop
 Inhibits FSH ensuring no further eggs develop
(useful in contraceptive pill)
 High levels of oestrogen just before day 14
stimulate release of LH
LH - Luteinising Hormone
 Produced by the pituitary gland
 Produced on day 14
 Causes ovulation
 Causes the remains of graafian follicle to
develop into corpus luteum
 Corpus luteum makes final hormone in the cycle
progesterone (along with small amounts of
oestrogen)
Progesterone
 Produced by the Corpus Luteum in the ovary
 Produced from days 14-28
 Maintains structure of endometrium
 Inhibits FSH to stop further eggs developing
 Inhibits LH to stop further ovulation and
pregnancies
 Prevents contractions of the uterus
The hormonal control of the menstral cycle demonstrates
the fine control of negative feedback mechanism in nature.
(1)FSH stimulates the production of oestrogen
(2)But Oestrogen inhibit the production of FSH and itself.
(3)And Oestrogen stimulates the production of LH
(4)LH stimulates the production of progesterone
(5)But progesterone inhibits LH and FSH.
(6)If the egg is not fertilised the corpus lutem dies – nó
progesterone and the cycle begins again
(7)FSH produced again
Learning Check
 List the four hormones involved in the menstrual
cycle
 In each case state where it is produced
 Give a function for each hormone
Events when pregnancy
does not occur
Menstrual disorder (Fibroids)
 Fibroids are tumours of
the uterus
 They are the result of
the overproduction of
cells
 They do not invade
other tissues and do
not spread (benign)
Menstrual disorder (Fibroids)
 Slow growing and range from the size of a pea
to the size of a melon
 Common between ages of 35 and 45
 Small fibroids often produce no symptoms
 As they enlarge they produce heavy and
prolonged menstrual bleeding (this can lead to
anaemia, pain, miscarriage or infertility)
Cause
 Cause is uncertain
 May be an abnormal response to oestrogen
 Can occur in women taking the contraceptive
pill
Prevention and treatment
 Small fibroids require no treatment just
monitoring to check their growth
 Large fibroids can be removed by surgery
 If many large fibroids are present a
Hysterectomy may be necessary. This is where
the uterus is removed
Menstrual disorder (Endometriosis)
 Growth of endometrial cells outside the uterus (often
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in fallopian tube)
Normally endometrium is shed each month in the
menstrual cycle. In endometriosis misplaced
endometrium is unable to exit the body
Results in internal bleeding, inflammation of
surrounding area and pain
Formation of scar tissue may result
If in the fallopian tube this can interfere with the
passage of eggs to the uterus (infertility)
Cause
 Exact cause remains unknown
 Several theories (response to excess oestrogen
creation)
Prevention and treatment
 No known cure
 Hysterectomy (removal of uterus) - no guarantee
that symptoms will disappear
 Medication can be taken to interfere with
hormones resulting in a reduction or elimination
of menstrual flow
Syllabus
Depth of treatment
 Detailed study of the menstrual cycle and
hormonal control
Contemporary issues and technology
 Menstrual disorders
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one example of a menstrual disorder from the
following: endometriosis and fibroids
one possible cause, prevention and treatment