Download Sequence of development from fertilised egg

Higher level- Menstrual Cycle
Hormonal control in the menstrual cycle
• Four hormones involved:
– 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
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
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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
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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
Insemination
• Insemination is the release of sperm into the female
• Contractions of uterus and fallopian tubes move the
sperm to the fallopian tubes within 5 minutes
• If an egg is present it releases chemicals to attract
the sperm this is called chemotaxis
Fertilisation
Fertilisation is the fusion of the egg and sperm nuclei to form a diploid zygote.
This usually occurs in the fallopian tube.
Fertilisation
The acrosome releases enzymes to digest the egg membrane
A number of sperm may reach the egg at the same time.
The sperm loses its tail and the head enters the egg.
The sperm and egg nuclei fuse to form a zygote
A chemical reaction at the membrane prevents other sperm cells entering.
Implantation
Implantation is the embedding of the fertilised egg into the
lining of the uterus
•This occurs 6 - 9 days after fertilisation.
•By this time the zygote has grown into an
embryo.
•During implantation a membrane called the
amnion develops around the embryo. This
secretes amniotic fluid which will surround the
developing embryo and act as a shock absorber.
•After implantation the placenta forms.
Sequence of development
from fertilised egg
Early stages
Sequence of development from
fertilised egg
• The zygote contains
46 chromosomes,
twenty three from
the egg and 23
from the sperm
It divides rapidly by mitosis to produce 2 cells,
then 4, then 8, 16 etc. and continues to divide
• At this point the
developing
individual is
referred to as the
morula
• Around 5 days after
fertilisation the
morula forms a
hollow ball of cells
called the
blastocyst
• 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
• 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
The morula/blastocyst is pushed along the fallopian
tube until it enters the uterus
• 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
Sequence of development
from fertilised egg
Development of the embryo
• 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)
• 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
Ectoderm – skin, nervous system
Coelom – heart, lungs
Mesoderm – muscles, skeleton
Endoderm – inner lining of digestive
system
The Amnion
• 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
Four to five weeks after fertilisation
• The heart forms
and starts to beat
• The brain also
develops
• The limbs have
started to form
By the 6th week
• Eyes are visible
• The mouth, nose
and ears are
forming
• The skeleton is at
the early stages of
development
By the 8th week
• the major body
organs are formed
• Sex glands have
developed into
testes or ovaries
• Bone is beginning
to replace cartilage
By the 8th week
• 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
point
By the 12th week (3 months)
• The nerves and muscle
become co-ordinated
allowing the arms and
legs to move
• The foetus sucks its
thumb, urinates and
even releases faeces into
the amniotic fluid
By the 12th week (3 months)
• The gender of the
foetus can be seen
in scans
• The time from
fertilisation to birth
(the gestation
period) lasts about
38 weeks (9
months)
Placenta formation
Placenta formation
Placenta formation
• 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
• The chorionic villi
emerge from the
chorion and invade
the endometrium
allowing the
transfer of
nutrients from
maternal blood to
fetal blood
• This combination of the chorionic villi and the
endometrium will eventually form the
placenta which becomes fully operational
about three months into the pregnancy
The Placenta
Placenta
Chorion
Embryo
Mother’s blood
Wastes, Carbon Dioxide, Water
Nutrients, Oxygen, antibodies
Mother
Embryo
Amnion
Amniotic fluid
Umbilical cord
Embryo’s blood
• Placenta allows gases, nutrients, waste,
antibodies, some drugs, hormones and microorganisms to be exchanged between mother and
baby
• Placenta also produces hormones
• Blood supplies of mother and embryo do not mix
– Blood types may not be compatible
– Mother’s blood pressure might damage embryo
• 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
Birth
1
The hormones oestrogen and progesterone are
produced throughout pregnancy firstly by the corpus
luteum (3 months)
and then by the placenta. The
placenta acts as an endocrine gland.
2
Immediately before birth the placenta stops making
progesterone. The walls of the uterus begin to contract
as a result.
3
The pituitary gland releases the
hormone called
oxytocin. This causes further contractions of the uterus
Labour has now begun
Breastfeeding
Lactation
• The secretion of milk
from the mammary
glands
• The first days after
birth colostrum
produced
• Milk production
triggered by release of
prolactin by pituitary
Breastfeeding
Breastfeeding is better than bottle feeding because:
• Colostrum and breastmilk provides the baby with
essential antibodies protecting it against infection
• Ideal balance of nutrients for baby
• Has little fat making it is easier to digest than milk
Birth control
• Birth control refers to the methods employed to limit
the number of children that are born
• Removing the possibility of conception is called
contraception.
• This is achieved by preventing the egg and sperm
from meeting
• There are a number of methods:
Mechanical contraception -male
• The use of condoms
• Surgical contraception
– Sperm ducts are cut
and tied
Mechanical contraception - female
• The use of diaphragms
Chemical contraception
• Use of ‘the pill’. The
pill contains oestrogen
and progesterone
which prevents
ovulation and hence
conception.
• Use of spermicide
Surgical contraception
• The fallopian tubes and
sperm ducts can be cut
and tied
Natural contraception
- Not having sexual intercourse during the fertile
period of the menstrual cycle
- Natural methods of contraception try to identify the
time of ovulation based on:
•
monitoring the body temperature. This
rises slightly after ovulation
•
-
mucous secreted in the cervix (which
changes its texture after ovulation)
Infertility
Infertility is the inability of a couple to achieve
conception.
Male infertility disorders
• Low sperm count – Refers to a low number of sperm
per ml of seminal fluid.
• Low sperm mobility - If movement of the sperm is
slow, not in a straight line or both, the sperm may
have difficulty passing through the cervical mucous
or penetrating the shell of the egg.
• Endocrine gland failure – A failure of the testes to
produce sperm
Low sperm count
Causes:
• The persistent use of drugs such as alcohol,
cigarettes and anabolic steroids.
• Abnormalities in sperm production or obstruction
of the tubes through which sperm travels.
• Stress
Treatment
• A change in diet.
• A change in lifestyle e.g. stopping alcohol
consumption, smoking.
• A reduction in stress levels.
Female infertility disorders
• Blockage of the Fallopian Tube
– Scarring of the fallopian tube can block the
passage of the egg to the uterus
• Endocrine gland failure
– A failure of the ovaries to produce an egg
Blockage of the fallopian tubes
Causes:
• Fragments of the uterus lining may spread to the
fallopian tube
• Inflammation as a result of infection
Treatment
• In-vitro fertilisation (I.V.F.)
In-vitro fertilisation (IVF) is a method
of treating infertility
It involves removing eggs from an
ovary and fertilising them outside
the body
During IVF fertility
drugs are given to
the female to
stimulate the ovaries
to produce more
than one egg
During the natural
menstrual cycle an
egg is produced by
the ovary every
month
These eggs are
then taken from
the females
body and into
the laboratory
In the
meantime a
sperm sample
is taken from
the male
The eggs and sperm are mixed together in the
hope that fertilisation will occur
The sample is placed in the most ideal
conditions for fertilisation to occur
The main aim of the procedure is to obtain a
zygote. If successful the zygotes development
will be monitored closely
If successful the zygote develops into a
morula, blastocyst and eventually becomes
an embryo
The developing embryo can now be placed
back into the females body for implantation
to take place
• Babies born as a result of IVF are often
incorrectly called ‘test tube’ babies.
• While fertilisation takes place in the
laboratory (‘in vitro’ – in glass) the fertilised
egg is re-inserted into the mother’s body and
develops naturally in the uterus
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 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