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Ch15: Sex Organs & Hormonal
Control
Higher Human Biology
Male Reproductive
System
Testes are the site of:
• sperm production
• manufacture of the male
sex hormone testosterone
Sperm Production
Sperm are formed by meiosis in the tiny
seminiferous tubules of the testes, which unite
forming coiled tubes that connect to the sperm duct.
Sperm
duct
Sperm
forming by
meiosis
Pathway of sperm
Pathway of sperm
during sexual intercourse
Sperm are
motile. This
requires a fluid
medium &
a source of
energy.
Image source: www.fertility.com
Testosterone
….the male sex hormone
• Produced by interstitial cells, in the tissue
between the seminiferous tubules of the testes
• Released directly into the bloodstream
Image source: http://faculty.une.edu
Seminal Vesicles
Males have 2 seminal vesicles, which secrete a
thick liquid rich in:
• fructose – a sugar that provides sperm with
energy for motility
• prostaglandins –
hormone-like
compounds that
stimulate
contractions of the
female reproductive
tract. Help sperm to
move more quickly
towards the egg.
Prostate Gland
Secretes a thin lubricating liquid containing
enzymes. The enzymes keep the fluid at the
optimum viscosity (thickness) for sperm motility.
Semen is a milky
liquid composed
of:
•sperm,
•fluid from
seminal vesicles
•fluid from
prostate gland
Female Reproductive System
Oviduct / Egg tube
Where the egg is fertilised
Ovary
Produces eggs
Uterus / Womb
Where the baby grows
Vagina
The penis is
put here when
mating.
Uterus lining
Lining of the womb
Cervix
The neck of the uterus
which connects to the
vagina.
Developing Egg
Eggs are formed by meiosis in the ovaries. Each
ovum (egg) is contained by a developing Graafian
follicle which secretes oestrogen (a hormone).
After ovulation
(release of the
egg), the
Graafian
follicle develops
into a corpus
luteum which
secretes the
hormone
progesterone.
Image source: http://resources.schoolscience.co.uk
Hormones
Hormones are chemical
messengers, produced
in the endocrine
(ductless) glands (e.g.
pituitary and thyroid
glands) then secreted
into the bloodstream.
Thyroid
gland
Pituitary
gland
When a hormone reaches
its target tissue it brings
about a specific effect
Gonadotrophic hormones
The gonads (reproductive organs) are the target
organs of two of the hormones produced by the
pituitary gland, thus these hormones are called
gonadotrophic hormones:
1. FSH: follicle-stimulating
hormone
2. ICSH: interstitial cellstimulating hormone (males)
LH: Luteinising hormone
(females)
These hormones begin to be released from
the anterior pituitary at puberty.
Male Gonadotrophic hormones
The functions of the testes are
regulated by these hormones:
FSH
Anterior
(front)
lobe
In bloodstream
stimulates
interstitial
cells to
produce
ICSH testosterone
promotes
sperm
production in
the
seminiferous
tubules
Testosterone
Activates
secretion from
prostate gland +
seminal vesicles
Self Regulation of Testosterone
The body has self-regulating mechanisms, called
negative feedback control, that allows the body
to correct changes.
When the
concentration of
testosterone gets to
a certain level it
inhibits the
secretion of FSH &
ISCH, which in turn
causes a decrease in
testosterone
concentration.
Negative Feedback Control
When a factor
affecting the
body’s internal
environment
deviates from
its norm (or
set-point) the
body responds
to correct the
change.
Image source: www.hw.ac.uk
Female Gonadotrophic hormones
FSH stimulates:
• Development and maturation
of each Graafian follicle
• Secretion of oestrogen
from ovary tissue
LH triggers:
• Ovulation
• Development of corpus luteum
• Secretion of progesterone
Oestrogen & Progesterone
are the ovarian hormones.
Oestrogen
Oestrogen stimulates:
• cell division
(proliferation) of the
endometrium (inner
layer of the uterus)
allowing it to repair
after menstruation.
• the secretion of LH
by the anterior
pituitary
Image source: www.beliefnet.com
Progesterone
Progesterone stimulates:
• the thickening of the endometrium
• inhibits the secretion of FSH & LH by the
anterior pituitary
Effect of
Hormones
in
females
GnRH =
Gonadotrophin
Releasing
Hormone
Menstrual
Cycle
• 28 day cycle
• each cycle
continuous with
previous cycle
and next cycle
Ovulation
• 2 phases
View the animation on
menstruation:
http://resources.schoolscience.co.uk/abpi/n
Endometrium
ew/resources/hormones/horm4.asp
Image source: www.medicine4faith.net
follicular phase luteal phase
Menstrual Cycle: Follicular Phase
• First half of cycle
• FSH from pituitary
stimulates development &
maturation of a Graafian
follicle and production of
oestrogen from ovarian tissues
• Repair & proliferation of
the endometrium (due to
increase in Oestrogen)
• At day 14 - high Oestrogen
levels cause a surge in the
production of LH (& FSH)
causing ovulation.
Ovulation
• Occurs on day 14
• Surge in LH causes the
wall of the Graafian
follicle to rupture &
release the egg
• after ovulation the egg
moves along the oviduct
• for 3-4 days the egg
can be fertilised if it
meets a sperm
Ruptured follicle
Protective cells
Egg
Menstrual Cycle: Luteal Phase
FSH
LH
oestrogen
• Second half of cycle
• LH stimulates Graafian follicle
to become corpus luteum, which
then secretes oestrogen &
progesterone
• Endometrium becomes thick,
vascular & spongy, due to
increase in progesterone, ready
to accept & nourish the embryo
if fertilisation has occured
• FSH drops due to high
oestrogen + progesterone so no
new follicles
Menstrual Cycle: Luteal Phase
FSH
LH
• Low LH causes
degeneration of corpus
luteum (day 22)
• Followed by rapid drop in
progesterone (& oestrogen)
oestrogen
• If NO fertilisation,
Menstruation begins at
Day 28 because the ovarian
hormones (oestrogen +
progesterone) are so low
that the endometrium can’t
be maintained
Why do pregnant women not
menstruate?
The fertilised egg secretes a hormone called human
chorionic gonadotrophin (HCG) which maintains the
corpus luteum which secretes progesterone
preventing menstruation.
After 6 weeks the
placenta secretes
progesterone instead.
Pregnancy tests,
test for the
presence of HCG in
urine.
Image source: staff.um.edu.mt
Role of cervix
The cells that line the
cervix secrete mucus
which lubricates the vagina.
High levels of oestrogen
stimulate these cells to
secrete a watery mucus
which help sperm enter
the reproductive tract.
to transport, nourish &
filter sperm
Endometrium (food
lining) develops
High levels of progesterone
cause the cervical mucus to
Prostaglandins in the
thicken. During pregnancy
semen also help transport this forms a semi-solid
Endrometrium
plug
(+ some blood) is
discharged
the sperm by inducing
to protect the
fertilised
muscular contractions in egg from infection.
the uterus & oviduct.
Image source: www.fertilityet.org.uk
Body Temperature
Body temperature rises
by 0.5°C at ovulation
and stays high during
the luteal phase.
Changes in viscosity of
cervical mucus & body
temperature are used
by some people as
indicators for the
rhythm method of
birth control.
Image source: http://en.wikipedia.org
Continuous v Cyclical Fertility
Male fertility is continuous because they secrete a
steady level of testosterone and produce a steady
quantity of sperm.
Female fertility is cyclical due to the delicate
balance of gonadotrophic and ovarian hormones.
Females are usually only fertile for 3-4 days
immediately after ovulation.