GONADS
Gonads are the male and female primary
reproductive organs. The male gonads are
the testes and the female gonads are the
ovaries.
 Function : to produce gametes for sexual
reproduction and secrete sex hormones
needed for the growth and development of
primary and secondary reproductive
organs and structures.
 The gametes and sex hormones differ in
Males and Females.
Female
reproductive
system
Male
Reproductive
System
Male and female sex hormones are steroid
hormones and as such, can pass through
the cell membrane of their target cells to
influence gene expression within cells.
 Gonadal hormone production is regulated
by hormones secreted by the
anterior pituitary in the brain and hormone
secreted by the hypothalamus.
 Hormones that stimulate the gonads to
produce sex hormones are known as
gonadotropins.

The pituitary secretes the gonadotropins
luteinizing hormone (LH)and folliclestimulating hormone (FSH).
 LH stimulates the testes to secrete the sex
hormone testosterone and the ovaries to
secrete progesterone and estrogens.
 FSH aids in the maturation of ovarian
follicles (sacs containing ova) in females
and sperm production in males.

Female Gonad Hormones
The primary hormones of the ovaries are
estrogen and progesterone.
 Estrogens - Group of female sex
hormones important for reproduction and
the development of female sex
characteristics.

 responsible
for growth and maturation of the
uterus and vagina; breast development;
widening of the pelvis;
Female Gonad Hormones
 greater
fat distribution in the hips, thighs, and
breast; uterus changes during the menstrual
cycle; and increased growth of body hair
Progesterone - Hormone that functions to
prepare the uterus for conception; regulates
uterus changes during the menstrual cycle;
increases sexual desire; aids in ovulation; and
stimulates gland development for milk
production during pregnancy.
Female Gonad Hormones
Androstenedione - Androgen hormone
that serves as a precursor to testosterone
and estrogens.
 Activin - Hormone that stimulates the
production and release of folliclestimulating hormone (FSH). It also assists
in menstrual cycle regulation.
 Inhibin - Hormone that inhibits the
production and release of FSH.

Male Gonad Hormones

Androgens are hormones that primarily
influence the development of the male
reproductive system. Although found in
much higher levels in men, androgens are
also produced in women. Testosterone is
the main androgen secreted by the testes.
Male Gonad Hormones

Testosterone - Sex hormone important
for the development of male sex organs
and sex characteristics.
 Testosterone
is responsible for
increased muscle and bone mass; increased
growth of body hair; development of broad
shoulders; deepening of the voice; and growth
of the penis.
Male Gonad Hormones
Androstenedione - Hormone that serves
as a precursor to testosterone and
estrogens.
 Inhibin - Hormone that inhibits the release
of FSH and is thought to be involved in
sperm cell development and regulation.

Gonads: Hormonal Regulation
 Sex hormones may be regulated by other
hormones, by glands and organs, and by a
negative feedback mechanism.
 Hormones that regulate the release of
other hormones are called tropic
hormones.
 Gonadotropins are tropic hormones that
regulate the release of sex hormones by
gonads. The majority of tropic hormones
and the gonadotropins FSH and LH are
secreted by the anterior pituitary.
Gonads: Hormonal Regulation
Gonadotropin secretion is itself regulated
by the tropic hormone gonadotropinreleasing hormone (GnRH), which is
produced by the hypothalamus.
 GnRH released from the hypothalamus
stimulates the pituitary to release the
gonadotropins FSH and LH. FSH and LH
in turn stimulate the gonads to produce
and secrete sex hormones.

Gonads: Hormonal Regulation
The regulation of sex hormone production
and secretion is also an example of a
negative feedback loop.
 The release of GnRH stimulates the
pituitary to release LH and FSH.
 LH and FSH stimulate the gonads to
release testosterone or estrogen and
progesterone. As these sex hormones
circulate in the blood, their rising
concentrations are detected by the
hypothalamus and pituitary.

Gonads: Hormonal Regulation

The sex hormones help to inhibit the
release of GnRH, LH, and FSH, which
results in decreased sex hormone
production and secretion.
Negative Feedback for FSH and LH by
Testosterone
Negative Feedback for FSH and LH by
Estrogen and Progesterone
Gonads: Gamete Production
The production of sperm cells is known as
spermatogenesis. This process occurs
continuously and takes place within the
male testes. The male germ cell or
spermatocyte undergoes a two part cell
division process called meiosis.
 Meiosis produces sex cells with one half
the number of chromosomes as the parent
cell.
 Haploid male and female sex cells unite
during fertilization to become
one diploid cell called a zygote.

Gonads: Gamete Production
Oogenesis(ovum development) occurs in
the female ovaries.
 After meiosis I is complete, the
oocyte(egg cell) is called a secondary
oocyte. The haploid secondary oocyte will
only complete the second meiotic stage if
it encounters a sperm cell and fertilization
begins.
 Once fertilization is initiated, the
secondary oocyte completes meiosis
II and is then called an ovum.

Gonads: Gamete Production

When fertilization is complete, the united
sperm and ovum become a zygote. A
zygote is a cell that is at the earliest stage
of embryonic development.
Female Reproductive System
Menstrual Cycle
 28 days.
 4 phases:

menstruation
 follicular
 ovulation
 luteal
Female Reproductive System
Flow Phase (days 1 to 5)- menstruation
 Menstruation is the elimination of the
thickened lining of the uterus
(endometrium) from the body through the
vagina.
 Shedding of endometrium (menstruation).
 Menstrual fluid contains blood, cells from
the lining of the uterus (endometrial cells)
and mucus.
 Used to mark beginning of menstrual
cycle.
Female Reproductive System
Follicular Phase (days 6 to 13) - follicular




Development of follicles in ovary.
Prompted by the hypothalamus, the pituitary
gland releases follicle stimulating hormone
(FSH). This hormone stimulates the ovary to
produce around five to 20 follicles (tiny nodules
or cysts),
Each follicle houses an immature egg. Usually,
only one follicle will mature into an egg, while
the others die.
Estrogen secreted.
 Triggers thickening of endometrium.
Female Reproductive System
Ovulatory Phase (day 14) - ovulation
 Ovulation is the release of a mature egg
from the surface of the ovary.
 Secondary oocyte released from ovary.
 During the follicular phase, the developing
follicle causes a rise in the level of
estrogen. The hypothalamus in the brain
recognises these rising levels and
releases a chemical called gonadotrophinreleasing hormone
GnRH prompts the pituitary gland to
produce raised levels of luteinizing
hormone (LH) and FSH.
 ovulation is triggered by the high levels of
LH. The egg is funnelled into the fallopian
tube and towards the uterus by waves of
small, hair-like projections. The life span of
the typical egg is only around 24 hours.
Unless it meets a sperm during this time, it
will die.

Female Reproductive System
Luteal Phase (days 15 to 28)
 During ovulation, the egg bursts from its
follicle, but the ruptured follicle stays on
the surface of the ovary
 the follicle transforms into a structure
known as the corpus luteum (Corpus
luteum develops.)
 Corpus luteum secretes estrogen and
progesterone.
 Progesterone
continues to stimulate growth of
endometrium and prepares uterus for an
embryo.

If a fertilized egg implants in the lining of
the uterus, it produces the hormones that
are necessary to maintain the corpus
luteum. This includes human chorionic
gonadotrophin (HCG), the hormone that is
detected in a urine test for pregnancy. The
corpus luteum keeps producing the raised
levels of progesterone that are needed to
maintain the thickened lining of the uterus.

If pregnancy does not occur, the corpus
luteum withers and dies, usually around
day 22 in a 28-day cycle. The drop in
progesterone levels causes the lining of
the uterus to fall away. This is known as
menstruation. The cycle then repeats.
Common menstrual problems




Premenstrual syndrome (PMS) – hormonal events before a
period can trigger a range of side effects in women at risk,
including fluid retention, headaches, fatigue and irritability.
Treatment options include exercise and dietary changes.
Dysmenorrhoea – or painful periods. It is thought that the
uterus is prompted by certain hormones to squeeze harder
than necessary to dislodge its lining. Treatment options
include pain-relieving medication and the oral contraceptive
pill.
Menorrhagia – or heavy menstrual flow. If left untreated, this
can cause anaemia. Treatment options include oral
contraceptives and a hormonal intrauterine device (IUD) to
regulate the flow.
Amenorrhoea – or absence of menstrual periods. This is
considered abnormal, except during pre-puberty, pregnancy,
lactation and menopause. Possible causes include low or high
body weight and excessive exercise.
*Males and females both have male and
female sex hormones, but in varying
levels.