CHAPTER 18
Reproduction in Humans
• Ultrasound is a type of imaging. It uses high-frequency
sound waves to look at organs and structures inside the
body. Health care professionals use it to view the heart,
blood vessels, kidneys, liver, and other organs. During
pregnancy, doctors use ultrasound to view the fetus
What you would learn
in this section…
(18.1) The Male Reproductive System
(18.2) The Female Reproductive System
(18.3) Puberty
(18.4) Sexual Reproduction in Humans
(18.5) Sexually Transmitted Infection
(18.1) The Male Reproductive System
Male reproductive system
prostate gland
seminal vesicle
Cowper’s
gland
sperm duct
penis
urethra
testis
spermatic cord scrotum
epididymis
(18.1) The Male Reproductive System
Male reproductive system
• Testis
produces sperms and male sex
hormones such as testosterone
• Epididymis
stores inactive sperms from the
testis before they are released
into the sperm ducts
• Spermatic cord
testis
supplies blood to the testis
spermatic epididymis
cord
(18.1) The Male Reproductive System
Male reproductive system
• Scrotum (scrotal sac)
pouch-like sacs located outside
the body cavity to help maintain
sperm a lower temperature for the
duct development of sperms
• Sperm duct (vas deferens)
the pathway travelled by sperms
after they are released from the
testis
scrotum
(18.1) The Male Reproductive System
Male reproductive system
• Seminal vesicle
stores sperms temporarily
before they are released
seminal
vesicle
through the urethra
• Seminal vesicle, prostate
gland, and Cowper’s gland
activate sperms by secreting a
prostate slippery fluid that contains
gland Cowper’s nutrients and enzymes
gland
• The mixture of this fluid and
sperms is called semen.
(18.1) The Male Reproductive System
Male reproductive system
• Urethra
a tube that extends from the
bladder, through the penis, to
outside the body
• Both urine and semen exit the
body through the urethra, but
never at the same time.
• The sphincter muscles at
the base of the urinary
bladder prevent urine from
exiting the body during
urethra
ejaculation.
(18.1) The Male Reproductive System
Male reproductive system
• Penis
erectile organ that becomes
erect and hard during sexual
intercourse in order to enter
and deposit semen into the
vagina
• An erection occurs when
the spongy tissue in the
penis penis is filled with blood.
(18.1) The Male Reproductive System
Sperm
Sperms (spermatozoa) are produced throughout
the lifetime of a male human after he reaches
physical maturity.
acrosome
head cytoplasm
nucleus
middle piece
cell surface
membrane
tail mitochondrion
(18.1) The Male Reproductive System
Sperm
1) The head contains:
acrosome
• a nucleus that carries
head cytoplasm one haploid set of
chromosomes,
nucleus
• small amount of
cytoplasm, and
• an acrosome that
contains enzymes for
breaking down part of
the egg membrane for
sperm penetration.
(18.1) The Male Reproductive System
Sperm
2) The middle piece:
• contains numerous
middle mitochondria that
piece mitochondria provide energy for
sperm to swim to the
egg.
3) The tail (flagellum):
tail
• beats to enable the
sperm to swim
towards the egg.
A sperm is motile = it can move on its own
What you would learn
in this section…
(18.1) The Male Reproductive System
(18.2) The Female Reproductive System
(18.3) Puberty
(18.4) Sexual Reproduction in Humans
(18.5) Sexually Transmitted Infection
(18.2) The Female Reproductive System
Female reproductive system
oviduct
ovary
uterus
uterine lining
cervix
vagina
vulva
(18.2) The Female Reproductive System
Female reproductive system
• Ovary
produces eggs and female sex
hormones such as oestrogen
and progesterone
• Oviduct (fallopian tube)
a narrow muscular tube with a
oviduct funnel-like opening at the ovary
ovary • Mature eggs are released
from the ovary into the
oviduct to be fertilised.
(18.2) The Female Reproductive System
Female reproductive system
• Uterus (womb)
the location where the
foetus develops; it has
elastic muscular walls that
enable contraction during
birth to expel the foetus
uterus • Uterine lining
(endometrium)
uterine the soft, smooth inner lining
lining of the uterus that is important
for embryo implantation
Why do menstrual
cramps occur?
• During a woman's menstrual cycle an excessive
amount of the endometrial prostaglandin F is
released.
• This hormone increases the contraction of the
muscle of the uterus. If the uterus contracts too
strongly, it can press against nearby blood
vessels. The pressure on the blood vessels
decreases blood flow therefore, the oxygen supply
to the muscle tissue of the uterus is decreased.
• Pain results when part of the muscle briefly loses
it's supply of oxygen and ischemia occurs.
• Menstrual pain from secondary dysmenorrhea is
caused by a disease in the woman's reproductive
organs.
The zygote is the first diploid cell
formed from the fusion of the
nucleus of a male and female
gamete.
The embryo is a ball of cells
formed from a zygote undergoing
mitosis. Organs begin to develop
at this stage.
The fetal stage begins about 8
weeks after fertilisation (right after
the embryonic stage). At the fetal
stage, all the major organs have
been formed.
(18.2) The Female Reproductive System
Female reproductive system
• Cervix
the lower portion of the uterus;
Enlarges/dilates to allow
passage of fetus during birth.
• Vagina (birth canal)
the location where semen is
deposited during sexual
intercourse; spans the area
cervix
from the cervix to the vulva.
vagina
vulva
(18.2) The Female Reproductive System
Ovum
Ova (eggs) are present in the ovaries of a female
at birth.
Eggs are released into the oviducts from the time
a female reaches puberty until she reaches 45-55
years of age.
A female baby is born with about
70 000 potential eggs. However,
An ovum
only about 500 of these eggs will
mature in the ovaries.
(18.2) The Female Reproductive System
Ovum
nucleus The ovum is made up of a:
cytoplasm
• large nucleus containing
one haploid set of
chromosomes,
• large amount of
cytoplasm which may
contain a small amount of
yolk, and
• cell surface membrane
cell surface outer
that is surrounded by an
membrane membrane outer membrane.
What you would learn
in this section…
(18.1) The Male Reproductive System
(18.2) The Female Reproductive System
(18.3) Puberty
(18.4) Sexual Reproduction in Humans
(18.5) Sexually Transmitted Infection
(18.3) Puberty
Puberty
Puberty refers to the stage of human growth and
development in which a person’s body becomes
capable of reproduction.
During this period:
• Sex organs mature
• Sex organs secrete sex hormones:
• Testosterone (male)
• Oestrogen and progesterone (female)
• Sex hormones cause secondary sexual
characteristics to develop.
(18.3) Puberty
Puberty
Secondary sexual characteristics:
In males In females
• Hair starts to grow in the • Hair starts to grow in the
pubic region, at the pubic region and at the
armpits and on the face. armpits.
• The penis and testicles • Breast and uterus enlarge
increase in size
• Hips broaden
• Larynx enlarges and
• Menstruation and ovulation
voice deepens
begin
• Production of sperm
begins
(18.3) Puberty
The menstrual cycle
The cycle of events that takes place in the female
reproductive organs every month
• Menstruation: Breakdown of the uterine lining, which
is discharged out of the body, together with blood and the
unfertilized ovum, via the vagina.
• In a female adult, the average length of a menstrual cycle
is 28 days.
• There is a natural variation in the length of the menstrual
cycle; ranging from 21 to 33 days.
• The menstrual cycle can be affected by stress, illness,
unbalanced diet, and/or malnutrition.
• At the age of 45-55, the eggs in a female’s ovaries will
stop maturing and stop being released
The menstrual cycle stops.
• At this age, the ovaries will also stop producing the sex
hormones, oestrogen and progesterone.
This phase in a female’s life is termed as menopause.
(18.3) Puberty
Changes in a follicle during the
menstrual cycle
potential egg cell • The ovary contains
layer of developing follicles.
follicle cells
• Young follicles are called
primary follicles.
primary follicle
• Each primary follicle
consists of a potential egg
cell surrounded by a layer
of smaller cells known as
ovary
follicle cells.
(18.3) Puberty A Graafian follicle is
also known as a
mature follicle.
Changes in a follicle during the
menstrual cycle
• A primary follicle may develop
fluid-filled space into a Graafian follicle that
haploid egg cell contains a mature egg
surrounded by follicle cells
and a fluid-filled space.
Graafian follicle • The egg is now ready to be
released into the oviduct.
• Generally, one egg is released
every month. The ovaries
ovary take turns to release an egg.
(18.3) Puberty
Changes in a follicle during the
menstrual cycle
ovulation
• Ovulation occurs when
the Graafian follicle
ruptures and releases
the egg into the oviduct
funnel.
• Ovulation typically
occurs on the 14th day
from the start of
Definition of ovulation:
menstruation.
Release of a mature ovum
from the ovary.
(18.3) Puberty
Changes in a follicle during the
menstrual cycle
• After ovulation, the ruptured
Graafian follicle develops
into a corpus luteum.
• The corpus luteum
corpus luteum
breaks down produces hormones that
prepare the body for
pregnancy.
corpus • If fertilisation does not
luteum occur, the corpus
luteum will eventually
break down.
(18.3) Puberty
Stages in the menstrual cycle
ovulation (day 14)
progesterone
oestrogen concentration
concentration highest
highest
corpus
follicle stage luteum stage
(day 6–13) (day 15-28)
menstrual flow
stage (day 1–5)
(18.3) Puberty
Stages in the menstrual cycle
Menstrual flow stage (Day 1–5)
• The first day of menstruation
is the first day of the
menstrual cycle.
• The uterine lining breaks
down and flows out of the
body through the vagina.
• The anterior pituitary gland
secretes follicle-stimulating
hormone (FSH) into the
bloodstream.
FSH and LH not in syllabus
(18.3) Puberty
Stages in the menstrual cycle
Follicle stage (Day 6–13)
• FSH stimulates:
• follicle development in the
ovaries, and
• oestrogen secretions by
the follicles.
• Oestrogen causes the repair
and growth of the uterine
lining.
Uterine lining becomes thick
and spongy and full of blood
capillaries
(18.3) Puberty
Stages in the menstrual cycle
Follicle stage (Day 6–13)
High concentration • A high concentration of
of oestrogen oestrogen in the blood:
1) inhibits FSH production,
which prevents the
maturation and growth of
more follicles, and
2) stimulates the pituitary
gland to secrete
luteinising hormone (LH).
(18.3) Puberty
Stages in the menstrual cycle
Ovulation (Day 14)
• LH causes ovulation
and the formation of the
corpus luteum.
• The corpus luteum
secretes progesterone
and some oestrogen.
Recall: corpus luteum is
formed from the ruptured
Graafian follicle
(18.3) Puberty
Stages in the menstrual cycle
Corpus luteum stage (Day 15–28)
• Progesterone prepares
High the uterine lining for the
concentration of fertilised egg by:
progesterone – Further thickens the
uterine lining and
maintains it by
– supplying it with blood
capillaries.
• Progesterone inhibits:
• ovulation, and
Video: Ovulation • FSH production.
(18.3)
Ovulation occurs after the concentration Puberty
of oestrogen in the blood peaks. (High
levels of oestrogen result in LH secretion, and LH causes ovulation.)
Progesterone secretion rises with the formation of the corpus luteum (after the
rupture of the Graafian follicle, i.e. after ovulation). Progesterone secretion
Stages in the menstrual cycle
results in the further thickening and maintenance of the uterine lining.
Follicle
development
progesterone
Hormone
oestrogen
concentration
Uterine
lining
thickness
Day 0 14 28
If fertilisation occurs, the corpus luteum is
(18.3) Puberty
prevented from breaking down although the high
progesterone level results in lower LH level
If fertilisation does not occur
Egg breaks down
High concentration of progesterone inhibits LH production.
Lowered LH levels result in the corpus luteum breaking down.
Progesterone is no longer secreted.
Uterine lining breaks down
Uterine lining is discharged together with blood through the vagina
(This marks the beginning of menstruation.)
FSH is produced by the pituitary gland and the menstrual cycle repeats.
The hormone that the implanted embryo secretes, which helps maintain the
(18.3) Puberty
corpus luteum, is human chorionic gonadotropin (hCG). hCG signals the corpus
luteum to continue its secretion of progesterone, thereby enabling the
maintenance of the uterine lining.
If fertilisation occurs
Fertilization results in the formation of a zygote, which
undergoes mitosis and develops into an embryo.
The embryo will move down the fallopian tube to the uterus, by peristalsis
and the action of cilia. It will embeds itself in the uterine lining, in a process
called implantation.
The embryo secretes a hormone that prevents
the corpus luteum from breaking down.
The corpus luteum continues to secrete oestrogen and
progesterone until the placenta forms and is able to
take over the production of both hormones.
(18.3) Puberty
Fertile and infertile periods of the
menstrual cycle
• Ovulation occurs on day 14.
• The egg can be fertilised up to 48 hours after its release
from the ovary.
• Sperms can live for up to three days in the female
reproductive system.
• Therefore, if sexual intercourse takes place between
days 11 to 16, there is a higher chance of fertilisation.
This period is known as the fertile period.
• The rest of the days make up the infertile period of the
menstrual cycle.
What you would learn
in this section…
(18.1) The Male Reproductive System
(18.2) The Female Reproductive System
(18.3) Puberty
(18.4) Sexual Reproduction in Humans
(18.5) Sexually Transmitted Infection
(18.4) Sexual Reproduction in Humans
Sexual intercourse (copulation)
Sexual arousal oviduct
Penis becomes erect as blood is
pumped into the spongy erectile tissue fertilisation
egg
Semen containing millions of sperms
is ejaculated into the vagina. ovary
Sperms swim up the oviduct to meet the
egg. **Fertilization happens
in the oviduct.
(18.4) Sexual Reproduction in Humans
Fertilisation
Fertilisation occurs when the a nucleus of a sperm (n) fuses
with the nucleus of an ovum (n) to form a zygote (2n).
(18.4) Sexual Reproduction in Humans
Fertilisation
follicle cell
• For fertilisation to happen, the
egg nucleus sperm has to penetrate the egg.
• When the sperm makes contact
with the egg, the sperm’s
acrosome releases an enzyme
that:
• disperses the follicle cells,
and
sperm • breaks down part of the egg
enzymes membranes to allow the
released by sperm to enter.
sperm
(18.4) Sexual Reproduction in Humans
Fertilisation
follicle cells
dispersed
• Only one sperm nucleus
enters the egg
• The haploid sperm nucleus
fuses with the haploid egg
nucleus, to form a zygote
(a fertilised egg).
only one sperm
enters the egg
(18.4) Sexual Reproduction in Humans
Fertilisation
diploid nucleus • As soon as a sperm enters
the egg, the membrane of
the egg changes such that
no other sperms can enter.
• The sperms that were
unable to fertilise the egg
eventually die.
zygote
(18.4) Sexual Reproduction in Humans
Development of the embryo
1) Implantation embryo
oviduct
• The cilia lining the
oviduct sweep the
fertilised egg towards zygote
the uterus.
fertilisation
• As the zygote travels
along the oviduct, it egg
undergoes mitosis to
form an embryo.
• It typically takes the embryo ovary
five days to reach the uterus.
Approximately
(18.4) Sexual Reproduction how many
in Humans
days after fertilisation does
implantation occur?
Development of the embryo
1) Implantation
• The embryo may float
freely in the uterus for
two days before it gets
implanted into the
uterine lining. embryo
implanted
• Implantation refers to the
event where the embryo
becomes embedded in the
uterine lining.
Video: Human Fertilization
(18.4) Sexual Reproduction in Humans
Development of the embryo
2) Development of the placenta placenta
• After implantation,
finger-like projections embryonic uterine blood
called villi grow from the villi lining capillaries
embryo into the uterine
lining. They contain the
blood capillaries of the
embryo
• The embryonic villi and the umbilical
uterine lining make up the cord
placenta.
• The umbilical cord attaches
the embryo to the placenta.
Majority of
monozygotic twins
(60–70%) share the
same placenta but
have separate
amniotic sacs.
Fraternal twins each
have their own
placenta and own
amniotic sac.
(18.4) Sexual Reproduction in Humans
Development of the embryo
3) Development of the amniotic sac
• The amniotic sac is the
membrane that encloses
the embryo in a fluid-filled
space called the amniotic
cavity. fetus
• The fluid in this cavity is amniotic cavity amniotic
called the amniotic fluid. containing sac
amniotic fluid
• The embryo continues to develop, and once all major
organs are formed, it is known as a fetus.
The fetal blood system
fetal blood capillaries
placenta umbilical umbilical
artery vein
Note:
The colour of the umbilical artery in the diagram is blue because it
carries deoxygenated blood.
The colour of the umbilical vein is red because it carries
oxygenated blood.
(18.4) Sexual Reproduction in Humans
The fetal blood system
fetal blood capillaries
metabolic waste • Fetal blood capillaries are
products not connected to the maternal
blood capillaries.
oxygen
and food • The fetal blood capillaries are
substances surrounded by the maternal
blood spaces.
maternal
• Diffusion of dissolved
blood
substances can occur across
spaces
the maternal blood spaces.
(18.4) Sexual Reproduction in Humans
The fetal blood system
The fetal blood system is separated from the maternal
blood system because:
• the mother’s blood pressure would be too high
for the fetus, and
• the fetus’s and mother’s blood type may be
different.
If both blood systems were allowed to mix, the
maternal antibodies would cause the fetus’s
blood to agglutinate. This could be fatal to both
the mother and fetus.
(18.4) Sexual Reproduction in Humans
Allows oxygen and dissolved
Allows excretory
food substances (glucose, aa
products (urea and CO2)
and mineral salts) to diffuse
to diffuse from the fetus’s
from the mother’s blood into the
blood into the mother’s
fetus’s blood
blood
Functions of
the placenta
Video: Structures
and Functions of the
Placenta
Produces progesterone Allows antibodies to diffuse
to maintain the uterine from the mother’s blood into
lining the fetus’s blood to protect
the fetus against diseases
(18.4) Sexual Reproduction in Humans
The umbilical cord is made up of two
umbilical arteries and one umbilical
vein.
Functions of umbilical
the umbilical cord
cord
Umbilical vein Umbilical arteries
transports oxygenated transport deoxygenated
blood and food blood and metabolic
substances from the waste products from
placenta to the fetus the fetus to the placenta
(18.4) Sexual Reproduction in Humans
• The amniotic sac encloses amniotic
the fetus in the amniotic cavity. sac
amniotic
• It contains amniotic fluid. fluid
Allows the fetus Supports and
to move freely Functions of the
cushions the
during growth amniotic fluid
fetus
Lubricates the Protects the fetus against
vagina during physical injury by
birth absorbing shock
What you would learn
in this section…
(18.1) The Male Reproductive System
(18.2) The Female Reproductive System
(18.3) Puberty
(18.4) Sexual Reproduction in Humans
(18.5) Sexually Transmitted Infection
(18.5) Sexually Transmitted Diseases
Sexually transmitted diseases
• A sexually transmitted infection (STI) is a
disease that is spread through sexual intercourse.
• STIs are caused by bacteria or viruses.
• STIs can be transmitted from an infected person to
an uninfected person via:
What are some possible situations
1) semen, in which blood could be transferred
2) fluid in the vagina, and from one person to another?
3) blood. Answer: blood transfusion, sharing
of things that could result in blood
being transferred: syringe needles,
acupuncture needles, razors, etc.)
(18.5) Sexually Transmitted Diseases
Acquired Immune Deficiency Syndrome
(AIDS)
• AIDS is a STI.
• It is caused by the Human Immunodeficiency Virus
(HIV).
• HIV destroys the body’s immune system.
• A person infected with AIDS is not able to produce
sufficient antibodies to protect his or herself from
other infections.
• Infections that are normally mild may become fatal for
a person with AIDS.
Video: Understanding HIV and AIDS. Stop video at 3:09 min
(18.5) Sexually Transmitted Diseases
Severe diarrhoea that
lasts for months
Chronic Symptoms of Pneumonia
fever AIDS
Widespread Brain Kaposi’s
tuberculosis infection sarcoma =
cancer of the
blood vessels
(18.5) Sexually Transmitted Diseases
Unprotected sexual Passed from mother
intercourse with to fetus during
an infected person pregnancy
Modes of
transmission
of AIDS
Blood Sharing of
transfusion with hypodermic
blood from an needles with an
infected person infected person
(18.5) Sexually Transmitted Diseases
Do not have sex.
Keep to one Use a condom
sex partner. when having
How to prevent sexual
intercourse.
HIV infection
Make sure that Do not abuse
the needles Do not share drugs as drug
used in instruments that can addicts tend to
acupuncture, break skin and get share needles.
ear-piercing contaminated with
and/or tattooing blood (e.g. razors,
are sterilised. toothbrushes).
