Sexual Reproduction in Humans
OBJECTIVES
By the end of the lesson, the student should be able to:
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Identify parts of the male and female reproductive systems and
state their functions
Compare male and female gametes in terms of size, structure,
motility and numbers
Define fertilisation, and outline what happens during fertilisation
State and explain the adaptive features of sperm and egg cell
Outline what happens to the zygote in early development
State and describe the functions of the umbilical cord, placenta,
amniotic sac and amniotic fluid
State that some toxins e.g. nicotine and pathogens e.g. rubella virus,
can pass across the placenta and affect the fetus
The male reproductive system
(front view)
The male reproductive organs
(side view)
Functions of parts of the male
reproductive system
The female reproductive organs
(Front view)
The female reproductive organs
(Side view)
Functions of parts of the female
reproductive system
Human gametes
Sperm
Adaptive features of sperm
 Flagellum
– for swimming or
movement
 Many mitochondria – for providing
energy
 Enzymes in the acrosome – for
digestion of jelly coat to reach the
ovum
 Streamlined shape – for efficient
swimming
Human gametes
Ovum (egg cell)
Human gametes
Ovum (egg cell)
Adaptive features of egg cells
 Energy
stores – contains food that
supports the embryo after
fertilisation
 Jelly coat – changes at fertilisation
to ensure that on one sperm
fertilizes the egg
Male and female gametes compared
Feature
Sperm cell
(male)
Egg cell (female)
Size
Smaller
Larger
Motility (movement)
Moves by itself
Moved by cilia and
swimming using the peristalsis in the oviduct
flagellum
Numbers produced
Many all the time
One or few per month
Food store OR
No food store
Cytoplasm
Less
Food stored in the
cytoplasm
More
Site of production
Testes
Ovary
Chromosome OR
X or Y
X only
No. of chromosomes
23
23
Flagellum
Present
Absent
Fertilisation
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It is the fusion of the nuclei from a male gamete
(sperm) and a female gamete (egg cell /ovum)
It occurs in the oviduct after ovulation
Outline of events at fertilisation
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A sperm cell secretes enzymes from acrosome
to digest a way through the jelly coat
The sperm attaches to, and enters the egg cell
The egg membrane changes so no other sperm
can enter
The nuclei of the sperm and egg fuse,
To form a diploid zygote
After fertilisation to implantation
• The zygote divides by MITOSIS
• To form a ball of cells called the EMBRYO
• The embryo is moved in the oviduct by cilia
movement and peristalsis to the uterus
• The embryo then embeds (sinks) into the
thickened uterus lining, a process called
IMPLANTATION
Development of the embryo
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As the embryo grows, so does a placenta, which
connects it to the wall of the uterus
The embryo develops into a fetus after 11 weeks
The placenta is joined to the fetus by the umbilical
cord
Inside the cord are two arteries and a vein
The arteries take blood from the fetus into the
placenta, and the vein returns the blood to the fetus
The fetus is surrounded by a strong membrane
called the amniotic sac (or amnoin)
Inside the amniotic sac is the amniotic fluid
Functions
Placenta
 Acts as a barrier to toxins and pathogens
 Supplies nutrients e.g. glucose, amino acids to the
fetus
 Supplies oxygen to the fetus
 Supplies water to the fetus or removes water from
the fetus
 Removes carbon dioxide from the fetus
 Removes urea from the fetus
 Transfers antibodies from the mother
 Secretes hormones e.g. oestrogen and progesterone
Functions
Amniotic sac
Secretes the amniotic fluid
Prevents the entry of pathogens from the vagina
 Amniotic fluid
Supports the fetus
Cushions it against bumps or damage
Provides a constant temperature
Allows fetus to move
Provides a sterile environment
Needed for bone or muscle development
Collects fetal wastes
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Note
 Event
though the placenta acts a
barrier to toxins and pathogens, some
toxins e.g. nicotine and pathogens e.g.
rubella virus, can pass across the
placenta and affect the fetus
Ante-natal care (care before birth)
Special dietary needs:
 More calcium – to help form the fetus’s bones
 More iron – to make more red blood cells to carry
more oxygen for the mother and fetus, and also to
allow the fetus to form blood cells
 More carbohydrate – to help provide extra energy
to help move the mother’s heavier weight around
 More protein – to help the fetus to form new cells
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Ante-natal care contd.
Avoid smoking
 Nicotine and carbon
monoxide in cigarette smoke
can cross the placenta and
cause premature birth or
underweight babies
 Avoid alcohol
consumption
 Alcohol can cross the
placenta and cause birth
defects and mental
retardation
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Labour and birth
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processes involved in labour
and birth are:
breaking of the amniotic sac
contraction of the muscles in the uterus
wall
dilation of the cervix
passage through the vagina
tying and cutting the umbilical cord
delivery of the afterbirth
Breast-feeding
Advantages over bottle-feeding using formula
milk:
 Provides the most complete food
 Easy to digest
 Contains no additives
 Contains antibodies that provide passive immunity
 Its sterile
 It is at the correct temperature
 Its always available (no preparation)
 Its free
 Allows bonding between mother and baby
 It reduces risk of allergies
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Breast-feeding contd.
Possible disadvantages:
 Transfer of viruses e.g. HIV and Hepatitis B
 Painful nipples
 May be stressful or embarrassing
 Mother may not be able to produce enough
milk
 Mother cannot see how much the baby has
consumed
 Task cannot be shared with the other parent
 Medications can pass to the baby
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Sex hormones in humans
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The period when a person approaches sexual maturity
is called adolescence
The point at which sexual maturity is reached is called
puberty
During adolescence, secondary sexual characteristics
develop
These developments are brought about by hormones
The male hormone is testosterone, and is produced in
the testes
The female hormone is oestrogen, and produced in
the ovaries
Secondary sexual characteristics
In males:
 hair on face
 pubic hair
 increase in muscles
 growth of genitals
 deep voice
 broad shoulders
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In females:
 widening of hips
 development of
breasts
 growth of pubic hair
 fat deposition
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Roles of hormones in the menstrual
cycle
Menstrual cycle
FSH (secreted from
the pituitary gland)
 stimulates follicle cells
 to grow and to mature
 and to secrete oestrogen
 low FSH after ovulation
prevents further follicle
development
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Oestrogen (secreted
by ovaries)
 Stimulates repair of the
uterus lining
(endometrium)
 by stimulating the
development of blood
vessels
 so the uterus is ready
for implantation
 it inhibits the release of
FSH,
 so stops further follicle
development
 it stimulates release of
LH
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LH (secreted by
the pituitary
gland)
 triggers ovulation
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Progesterone (secreted
by the corpus luteum)
 maintains the thickened
endometrium
 so it is ready for implantation
 it promotes the development
of more blood vessels in the
endometrium
 inhibits the release of FSH
and LH
 so prevents further follicle
development
 [Promotes development of
mammary glands in
pregnancy]
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Birth control in humans
Birth control methods should either:
• Stop sperm from reaching the egg
• Stop the eggs from being made, or
• Stop the fertilised egg from being implanted
Natural
 Abstinence
 Monitoring of body
temperature
 Cervical mucus
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Chemical
 IUD
 IUS
 Contraceptive pill
 Implant
 Injection
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Barrier
 condom
 femidom
 diaphragm
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Surgical
 vasectomy and
female
 sterilisation
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Hormones in birth control
Oestrogen/progesterone  Progesterone only
pills
 they are contraceptive pills
 they inhibit FSH release, so  they inhibit sperm
prevent follicle development movement through the
cervix
 they also inhibit LH release,
 they prevent
so prevent ovulation
implantation
 prevent sperm reaching
the egg
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Hormones in fertility treatments
Causes of infertility:
Infertility is inability to produce children in spite of
unprotected sexual co-habitation after two (2) years
In males:
In females:
 inability to produce
 low concentration
sperm
of FSH
 sperm cannot swim
 inability to ovulate
 low sperm count
 blocked oviduct
 blockage of
 inability of embryo
epididymis
to implant
 problems with
ejaculation
FSH/LH
 Injected at the
beginning of the cycle
 Stimulate egg
production in the
ovary, and follicle
development
 So more eggs are
available
 Stimulate ovulation
 So increase chance of
fertilisation
 Makes eggs available for
IVF
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Progesterone
 Causes the lining of
the uterus to thicken
 So increases the
chance of implantation
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Testosterone
 Stimulates sperm
production
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Artificial insemination
Collect sperm from male
or a donor
 Injection female to
stimulate corpus luteum
to secrete more
progesterone
 Inject the sperm into the
uterus
 Near the time of
ovulation
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NOTE
 near the time of
ovulation because:
 it increases the
chance of fertilisation
 sperm can survive
only for a few days
 so sperm is less likely
to die
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In vitro fertilisation (IVF)
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IVF is the fertilisation of egg (oocyte) in a glass dish
Procedure / Outline:
 Ovulation is stimulated using hormones
 Eggs (oocytes) are collected using a fine tube
 The eggs are placed in a glass dish with motile sperm
 Fertilisation occurs, and after three (3) days, the
embryos are inspected
 More than one (1) embryo is collected and placed
into the uterus
 Hormonal treatment is used to maintain
endometrium
Social implications of using fertility
treatments
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religious objections to use of fertility drugs
issues with elderly parent(s)
problems with unused embryos when used with
IVF
high cost of the treatment
can be used to increase populations, especially in
countries with falling birth rates
may lead to multiple births
may not treat infertility successfully
storage of eggs or embryo is possible during
chemotherapy
it has allowed stem cell research on embryos
Social implications of using contraception
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Less poverty/starvation
Greater care of children
More women work
More promiscuity
More STIs
Decrease in population
Sexually transmitted infections (STIs)
An infection that is transmitted via body fluids
through sexual contact
 Human immunodeficiency virus (HIV) is an example
of an STI
 HIV infection may lead to AIDS
 Other examples of STIs are gonorrhoea, syphilis,
genital herpes, chlamydiasis, genital warts,
trichomoniasis
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Methods of transmission of HIV
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unprotected sexual intercourse
across placenta
at birth
in breast milk
sharing needles or syringes
in blood products or in blood for transfusion
blood to blood contact
Control of spread of STIs
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use of condoms or femidoms
provide education
publicity campaigns
needle exchange schemes for drug addicts
sterilisation of needles
screening of blood or blood donors
HIV mothers should bottle-feed
How HIV affects the immune system
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The virus attacks lymphocytes
So antibodies are not produced,
So phagocytes are not as effective
So existing immunity is lost
This results in increased susceptibility to infections
Opportunistic infections thrive