Aspects of
Human
Reproduction
Histology of ovary
Histology of testis
Gametogenesis
• The process of formation of gametes from
the germ cells in the testes and ovaries.
• The timing of the developmental stages of
gametogenesis, and the number of
gametes produced are very different in
male and female germ cells.
• In the male spermatogenesis occurs from puberty to old
age, at an average rate of 1.5 million spermatozoa per
minute.
• In females all oocytes ever to be formed in females are
produced during foetal life.
• At birth the ovaries contain about 2 million oocytes.
• All the oocytes go into meiotic arrest when they reach
the first meiotic division during foetal life.
• The primary oocytes remain in prophase of the first
meiotic division until the time of puberty, when they are
gradually released to complete meiosis at regular
intervals known as the ovarian cycle.
• On the average only one oocyte matures during each
cycle, which occurs at approximately monthly intervals,
so that the total amount of oocytes to be ovulated is
about 500 oocytes in a lifetime.
Spermatogenesis
• It occurs in the seminiferous tubules of the
testes.
• The process begins at the outer edge in
the germinal epithelium and moves in
towards the lumen.
• The beginning cells are called
spermatogonia and they divide by mitosis.
Some develop
into primary
spermatocytes
which divide by
meiosis.
The first division
produces
secondary
spermatocytes
which are
haploid.
Spermatogonia
• The second
division forms
spermatids
which are also
haploid.
barrier)
The tails sticks into the lumen.
The spermatozoa head is
attached to a Sertoli cell which
nourishes and protects the cell
Oogenesis
• Occurs in the ovary while the girl is still an
embryo.
• Germinal epithelial cells divide by mitosis
to form diploid oogonia.
Some start to
divide by meiosis
and are called
primary oocytes.
At puberty some
divide into two
haploid cells. One
large one
(secondary oocyte)
and a small one
(polar body)
• The secondary
oocyte divides
up until
metaphase II.
• Only after
ovulation does
the final stage
of meiosis occur
and the polar
bodies fall
away.
• The developing oocytes are found inside follicles
in the ovary.
• The wall of the follicle contains granulosa cells
which protect and secrete hormones.
Menstrual Cycle
• There are a number of
hormones involved in the
control of the human
menstrual cycle.
• Two are produced by
the ovaries:
– Oestrogen (produced by
follicle cells)
– Progesterone (produced by
corpus luteum)
• Two are secreted by the
anterior pituitary gland:
– Luteinising Hormone (LH)
– Follicle Stimulating
Hormone (FSH)
• Oestrogen is secreted at the onset of
puberty, causing an increase in the size
of the reproductive organs and the
development of secondary sexual
characteristics.
• The main role of oestrogen is to prepare
the endometrium (lining of the uterus).
• The duration of a normal menstrual cycle
is 28 days – day 1 is the first day of
menstruation.
• The main hormonal changes during the
cycle are as follows:
• FSH and LH increases slightly during the
first few days causing a number of primary
follicles to develop. (only one in one ovary
continues to develop)
• The granulosa cells of the developing
follicle secrete oestrogen.
• The increase in the level of oestrogen
inhibits FSH and LH
• The oestrogen causes the endometrium to
thicken – by day 12 it is 3 – 4mm thick
• Day 12 LH rises very sharply inhibiting
oestrogen in granulosa cells and starting
secretion of progesterone.
• Ovulation day 14
• When egg released, remaining granulosa cells
fill up with a yellow substance and is called a
corpus luteum or yellow body,
• This continues to secrete large amounts of
progesterone and small amounts of oestrogen.
• The progesterone develops the endometrium,
increasing its supply of blood.
• Its thickness reaches 5 – 6 mm and it is
prepared for implantation, if the egg has been
fertilised.
• If no fertilisation, the oestrogen and
progesterone inhibit FSH and LH from the
anterior pituitary gland and the corpus luteum
degenerates.
• All four hormones fall to a low level and, once
the oestrogen and progesterone have dropped
far enough, the anterior pituitary again begins to
secrete FSH and LH and the cycle begins again.
• The fall in oestrogen and progesterone causes
the endometrium to break down and
menstruation occurs during the next four to
seven days of the cycle.
The oestrogen/progesterone
contraceptive pill
•
•
•
•
It contains oestrogen and progesterone
changes the hormone balance of the body,
and ovulation does not take place.
The high levels of oestrogen and
progesterone inhibit the release of FSH
and LH from the anterior pituitary gland.
• It also causes the mucus made by the
cervix to thicken, forming a ‘mucus plug’ in
the cervix – this makes it more difficult for
the sperm to get through to the uterus.
• It also makes the lining of the uterus
thinner
With most oral contraceptives, a woman will
take the pill for 21 days and then stop for 7.
During the 7 days, menstruation takes
place. (sometimes a different coloured pill is
taken at this time, that has no effect, but it
keeps the routine going.
Morning After Pill
Works for up to 72 hours after intercourse,
by preventing embryo from being implanted
into the uterus.
The biological, social and ethical implications
of the use of contraception
• Biological implications
• methods of contraception which do not involve
hormones (e.g. barrier methods etc.) do not
have any biological implications. But hormonal
ones have many.
• Benefits:
– Reduces the risk of developing certain ovarian cysts
– Reduces the risk of developing cancer of the ovary or
uterus
– Menstruation is more regular and can relieve premenstrual tension
– Reduces the risk of pelvic infection – the mucus plug
may prevent bacteria getting into the uterus
• Side effects and possible risks:
–Some women may develop nausea
and head aches
–Tiredness and mood changes
–Rise in blood pressure
–Increased risk of thrombosis. May
cause a stroke or a blood clot in the
lungs
–Small increased risk of breast
cancer
• Social implications
• Contraception means that it is easier to choose
when to have or not to have children.
• Plan families around careers and other
considerations, such as financial circumstances.
• Population control can be good and bad.
– Some places have too few children to be able to
sustain the population in the future.
– Other places continue to have problems of
overpopulation and the implications that this has for
supply of food, water and other resources.
• Ethical implications
• The benefits:
– a woman can decide when and if she will
conceive
– countries can control their population growth
– those at medical or psychological risk if
pregnant, can avoid such pregnancy
– reduced chance of unplanned pregnancy in
sexually active teenagers
• artificial contraception seen as morally
wrong
In vitro fertilisation
• In-vitro is Latin for ‘in glass’
• Eggs are fertilised outside the woman’s body.
• By controlling ovulation through the
administration of hormones, removing eggs from
the ovaries and allowing sperm to fertilise them
in a fluid medium.
ovarian stimulation
• Treatment starts on the third day of
menstruation.
• Hormones stimulate the development of
multiple follicles in the ovaries.
• About 10 days of injections necessary.
• The oocytes are collected using a hollow
needle inserted through the vaginal wall
and into the developing follicles.
• The egg is sucked out.
• The sperm are collected on the same day
and placed in special medium which only
strong motile sperm can swim through.
• Each oocyte is placed in a dish and
100 000 sperm are added with a nutrient
medium.
• If fertilisation does not occur then DNA is
injected directly into the oocyte.
• Left for 3 days.
• Two or three fertilised ones are chosen
and implanted into the uterus wall.
Ethical issues
• The fate of the unused embryos
• Embryos can be used as stem cells.
• Should we have the power to choose
whose sperm is used?