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Sexual Reproduction in Humans
How to make a Human Being
Male Reproductive System
Testes
• Male gonads (animal organs
that produce sex cells)
• Temperature of testes is
maintained at 35°C (optimal
temp for meiosis)
• Each testis contains spermproducing cells
• Testosterone is also produced
– stimulates sperm production
– promotes sexual maturity
– induces secondary sexual characteristics
Structure
Function
Scrotum
Sac of skin in which the testes are held
Testes
Produces sperm and testosterone
Epididymis
Sperm storage and maturation
Sperm Duct (vas
deferens)
Carries sperm from the epididymis to the urethra
Seminal Vesicles
Produce milky seminal fluid (sugary alkaline fluid in which sperm are
suspended, nourished and protected from the acidic vagina)
Cowper’s Gland
Produces clear sticky fluid which neutralises any urine which remains in
the urethra.
Prostate
Produces another milky nourishing fluid which goes to make up part of
the semen (semen = sperm plus fluid)
Penis
Transfer of sperm into the vagina. Becomes engorged with blood during
sexual arousal. Once hard and erect, it can penetrate the soft tissue of
the vagina.
Urethra
Carries sperm along and out of the penis.
Structure of a Sperm Cell
Tail
Sperm Cells
• Diploid cells in the testis divide by meiosis to
produce haploid sperm cells
• First produced in the testes at the onset of
puberty (12-13 years old in males)
• The acrosome in the head contains digestive
enzymes to allow it to penetrate the ovum.
• The collar contains lots of mitochondria to
provide energy for movement using the tail
• The nucleus contains 23 chromosomes
Male Reproductive Hormones
• Testosterone
– causes primary and secondary male characteristics
– produced in the testes
– production increases at puberty
• FSH
– produced by the pituitary gland at puberty
– stimulates cells in the testis to produce sperm cells
• LH
– produced in the pituitary at puberty
– stimulates the testes to produce testosterone
• HL
• OL
2007 Q15 a
2010 Q15 a
2010 Q14 a
2014 Q14 a
2010 Q15 a
Female reproductive system
Female Reproductive System
Ovaries
• Each ovary contains many sac-like structures
– these are called Graafian follicle
• Each follicle produces a potential female
gamete by meiosis
– female gametes are called ova or eggs
• Only one Graafian follicle releases a mature
ovum every 28 days
– Ovulation is the release of an egg from the
Graafian follicle
https://www.youtube.com/watch?
v=dwtFYOLFeNw
Female Reproductive System
Structure
Function
Ovary
Produce eggs (ova) and female hormones
Fallopian Tubes
• Have funnel-shaped ends that catch the eggs as they are released from
the ovaries
• Carry eggs to the uterus by cilia and peristalsis
• Site of fertilisation
Uterus (Womb)
• Site of implantation
• Outer muscular wall which contracts to push baby our during birth
• Inner lining (endometrium) nourishes and protects embryo.
Cervix
• Opening between the uterus and the vagina containing a plug of mucus
which protects uterus from infection
• Dilates during labour to allow passage of baby into the vagina
Vagina
• Receives penis and sperm during intercourse
• It is the birth canal - allows the exit of the baby during birth
• Acid produced by normal resident bacteria protect from infection
Secondary Sexual characteristics
• Features that distinguish males from females,
other that the presence of the sex organs
Male
Female
Growth of underarm, facial and
pubic hair
Growth of underarm and pubic hair
Enlargement of the larynx,
deepening of the voice
Enlargement of breasts
Widening of the shoulders
Widening of the pelvis
Increase in sebum production in the
skin
Increase in body fat
Menstrual Cycle
• A series of changes that occurs in the female
reproductive system every 28 days on average
– changes in hormone levels cause changes in the
endometrium
• Begins at puberty and ends at menopause
– menopause is the end of a womans reproductive
life (usually between 45 and 55)
• Ranges from 21 to 40 days in length
• The Fertile period is the time during the
menstrual cycle in which fertilisation is most
likely to occur
https://www.youtube.com/watch?
v=l_wX285vrrU
Day 1 to 5
• Meiosis occurs in new oocytes in the ovary
• Oestrogen and progesterone levels fall
– this allows the pituitary to secrete FSH
• Low oestrogen causes menstruation
• Menstruation occurs
• Menstruation is the shedding of the bloodfilled lining of the womb.
Days 6-14
• FSH stimulates the production of an egg within a
Graafian follicle
• The developing Graafian follicle produces
oestrogen
• Oestrogen causes the thickening of the
endometrium
• Rising oestrogen levels inhibit FSH production
– this prevents further follicles from maturing
– normally only one Graafian follicle is produced during
each cycle
• Very high oestrogen levels eventually stimulate the
production of LH just before day 14
Day 14
• LH causes the release of the egg from the
Graafian follicle
– Ovulation occurs
• The egg passes into the funnel of the Fallopian
tube and begins to move along towards the
uterus
• LH causes the remains of the Graafian follicle
to become the corpeus luteum
Days 15-26
• Oestrogen and progesterone are secreted by
the corpeus luteum (in the ovary)
• High progesterone levels
– further causes the building and up of the
endometium and maintains it
– inhibits the secretion of FSH and LH from the
pituitary gland
– prevents uterine contractions
• An unfertilised egg will die by day 16
• The corpus luteum starts to degenerate (day
22)
Days 26-28
• The corpeus luteum dies if implantation does not
occur by day 26
• This causes a drop in progesterone (and oestrogen)
– the corpus was producing these hormones
• Low levels of progesterone and oestrogen eventually
cause (day 28)
–
–
–
–
uterine contractions
loss of the endometrium
a new cycle begins with menstruation
a rise in FSH production (no more FSH inhibition)
Egg
Graafian Follicle
Oestrogen
Degenerating
Corpus luteum
Role of Oestrogen
• Produced in the ovary (by the Graafian follicle)
• Causes the endometrium to thicken for first 14
days
• Inhibits FSH production (negative feedback)
– prevents further Graafian follicles from maturing
– this ensures only one egg produced per cycle
• High levels stimulate the pituitary to produce
LH
Role of Progesterone
• Produced in the ovary (by the corpus luteum)
• Causes the endometrium to thicken for last 14
days and maintains its structure
• Inhibits FSH production (negative feedback)
– stops the development of more Graafian follicles
• Inhibits LH production
– prevents ovulation
• Prevents muscular contractions of the uterus
Role of Follicle Stimulating Hormone
• Produced in the pituitary
• Causes Graafian follicles (containing
eggs) to develop and mature
• Indirectly causes the production of
oestrogen
– since the Graafian follicle produces
oestrogen
Role of Luteinising Hormone
• Produced in the pituitary gland
• Causes ovulation
• Causes the remains of the Graafian follicle to
become the corpus luteum
• Indirectly results in the production of
progesterone
– since the corpus luteum produces progesterone
Menstrual Disorder - Fibroids
• Benign tumours of the uterus
• Most common in 35-45 year olds
• If they grow too large they can cause pain, heavy
bleeding, miscarriage, infertility
• Cause is thought to be abnormal response to
oestrogen
• Treatment
– if small, no treatment
– if large, surgery to remove them
– hysterectomy in severe cases
Infertility
• Infertility (male or female) is the inability to
produce offspring
• Affects 1 in 6 couples, but 50% are
successfully treated
Infertility
Cause
Treatment
Male
Low sperm count due to
smoking, alcohol/drug abuse,
stress.
Stop or reduce smoking,
drugs, alcohol, stress.
Female
Failure to ovulate (due to
hormone disorder).
Hormone treatment (e.g.
FSH stimulates ovulation)
Male Infertility
• Male infertility is the inability to produce
sperm capable of fertilizing an egg cell
• Cause: low sperm count
– due to excessive alcohol or drug use; stress
• Treatment: avoidance of possible reasons for
low sperm count
– alcohol and drug use
– stress
Female Infertility
• Female infertility is the inability to conceive.
• Cause: failure to ovulate
– due to hormone deficiency
• Treatment: hormone therapy
2009 Q14 a
In-vitro fertilisation (IVF)
• Method of treating infertility
• Eggs are removed from the ovary
• Fertility drugs are given to encourage egg
development.
• Eggs are surgically removed on day 14.
• Sperm and eggs are incubated together in
vitro (in a glass dish).
• If fertilisation occurs, a number of embryos
are placed in the uterus to implant.
Stages in Sexual Intercourse
• Sexual Arousal
– penis becomes erect
– vagina becomes lubricated
• Copulation
– coitus or sexual intercourse
• Orgasm - involuntary muscle spasms cause
– ejaculation in males
– uterine and vaginal contractions in female
• Insemination
– Release of semen into the vagina
Fertilisation
• Fertilisation is the fusion of the sperm nucleus with
the nucleus of the egg to form a diploid zygote
• Occurs in the Fallopian tube, usually at the top near
the ovary
• Digestive enzymes produced by acrosome in the
head of the sperm make an opening in the egg
• Once the sperm nucleus enters the egg, the
membrane of the egg changes to prevent entry of
other sperm.
Conception
• Implantation is the embedding of the fertilised egg
into the lining of the womb
• Occurs 6-9 days after fertilisation
• Fertilisation followed by implantation is called
conception
• The embryo then secretes a hormone (hCG)
– this prevents the degeneration of the corpus luteum
– progesterone continues to be produced
– the endometrium is maintained
– the menstrual cycle stops
Stages to Implantation
BIRTH CONTROL
• Abortion – the termination of a pregnancy.
• Contraception – using methods to prevent
fertilisation.
Natural contraception
• – intercourse is avoided at times in the menstrual
cycle when it may result in fertilisation.
Body temperature recorded – rises after ovulation.
Mucus secreted by cervix – texture changes after
ovulation.
Past menstrual cycles – rhythm method.
Mechanical contraception
• – using physical barriers to stop the sperm and egg
meeting.
Condom – male on penis, female in vagina.
Diaphragm – dome shape fitted into vagina before
intercourse.
Cap – small rigid rubber device, covers cervix.
Chemical contraception
• – using chemicals to kill sperm or hormones to
prevent ovulation.
Spermicides – used along with mechanical
methods.
The ‘Pill’ – oestrogen and progesterone,
prevents ovulation
Surgical contraception
- involves surgery (usually irreversible).
Female sterilisation – cutting tying the fallopian
tubes.
Vasectomy – The vas deferens (sperm duct) is cut.
Sperm is not present in the semen.
•
Early Development of the Zygote
• The zygote divides several times to form a ball of
cells called the morula
• 5 days after fertilisation the morula develops a cavity
and further divides to become a blastocyst
• The outer cell layer of the blastocyst is the
trophoblast which later forms the membranes
surrounding the embryo
– i.e. the chorion and the amnion
• The inner cell mass of the blastocyst later forms the
embryo
Development of the Blastocyst
Embryonic Development
• The inner cell mass of the blastocyst forms 3
germ layers
• Each germ layer gives rise to different tissues
Germ Layer
Tissue/Organ
Ectoderm
Nervous system, epidermis of skin
Mesoderm
Muscles, skeletal and circulatory system, kidneys.
Endoderm
Digestive system, liver, pancreas
Formation of the Placenta
• After implantation, the embryo forms an outer
membrane
– this is called the chorion
– It later forms the placenta along with tissue from
the mothers of the endometrium.
• Therefore the placenta is formed from the
tissue of 2 different individuals, the mother
and the embryo
The Placenta
• Pancake-shaped temporary organ
• Contains blood vessels of mother and foetus
• Mothers blood and foetal blood do not mix
– blood groups may not be compatible
– mother’s blood pressure would be too great
• Vessels are close enough to allow exchange of
materials
• Waste is transferred from
foetus to mother
• Nutrients and antibodies
are transferred from
mother to foetus
Functions of the Placenta
1. Supply of Nutrients
2. Gas exchange
– O2 and CO2
3. Production of Hormones
4. Removal of Waste
– Urea, CO2 etc.
The first 8 weeks
• Heart forms and is beating after 4 weeks
• By week 5, other internal organs are forming
• By week 6, ears, nose, eyes and mouth are
distinguishable
• By week 8
– ovaries and testes have formed
– ossification of cartilage to bone starts to occur
• The tail is no longer a feature and we now
refer to the embryo as a foetus
By 12 weeks
•
•
•
•
•
All major organs are formed
Nerves and muscles become co-ordinated
Limbs begin to move, the foetus can kick
Teeth grow, breathing starts
Urinary system begins to work
Week 12 to birth
• No new organs are formed
• Growth and development is rapid
• Gestation is the length of time spend in the
uterus from fertilisation to birth
• Gestation time is 38 weeks from the day of
fertilisation
https://www.youtube.com/watch?
v=-jlPdMKPyZY
Hormones during Pregnancy
• The corpus luteum produces progesterone
and oestrogen during the first 10 weeks
• The placenta takes over this role after this
• Just before birth
– Progesterone production stops
– Oestrogen production increases
Birth
• Stage 1 - Dilation
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–
–
–
Cervix dilates to allow passage of the baby
Amniotic fluid is released from the amniotic sac
Muscular contractions begin
The mucus plug in the cervix is lost
• Stage 2 - Delivery
– Contractions increase as oxytocin levels increase
– Baby passes through the birth canal head first
• Stage 3 - Placental
– Release of the placenta and foetal membrane
Lactation
• Milk Production by the mammary glands
• Colostrum is the first milk produced in the
days just after the birth
– rich in protein and antibodies (passive natural
immunity)
• Prolactin is produced
– this hormone promotes milk production
– progesterone inhibits prolactin secretion during
pregnancy
Benefits of Breast-feeding
• Mother milk is the perfectly balanced source
of nutrients for the baby
• Contains antibodies which provide natural
passive immunity to the baby
• Helps the mother recover after the birth by
helping the uterus to tighten again
• Helps the mother lose fat put on during
pregnancy