Reproductive Endocrine

1. Reproductive Endocrinology

2. Testis
Function:
1. Spermatogenesis.
2. Androgen synthesis and secretion.
Consists of:
1. Seminiferous tubules: nurtures the sperm as
they develop. Each tubule is made up of germ
cells and Sertoli cells
2. Leydig cells: steroid synthesizing cells.

3. Gross and microscopic anatomy of
human testis

4. Androgens
• In males, androgens are secreted by Leydig cells of the testis,
with only a small contribution from the adrenal.
• In male embryos androgen secretion by the Leydig cells is
initiated by human chorionic gonadotropin (hCG).
• T is converted to dihydrotestosterone (DHT) by 5α-reductase
in peripheral tissues.
• Embryonically, T stimulates the male external genitalia, while
DHT is responsible for the development of the internal
genitalia
• In adolescence, androgens stimulate skeletal growth and
muscle protein synthesis.
• Androgens induce aggression and libido
• They also promote the development of both primary and
secondary male sexual characteristics

5. Synthesis pathway of gonadal hormones

6. Testicular biosynthesis and hepatic metabolism of
testosterone

7. Hormonal control
• Spermatogenesis requires both FSH and T.
• T is released from the Leydig cells and is
concentrated in the tubules.
• LH binds to Leydig cells and stimulates T synthesis.
• FSH binds to Sertoli cells, it also enhances the
number of Leydig cell LH receptors.
• Prolactin controls the number of Leydig cell LH
receptors
• Inhibin secreted by Sertoli cells inhibit FSH
• Testosterone acts directly on some tissues and must
be converted to either DHT or Estradiol to mediate
its action in some other tissues

8. Androgens
Aromatase 5α-reductase
Estradiol
E2
Dihydrotestosterone
DHT
Testosterone
T

9. Hormonal regulation of steroidogenesis and
spermatogenesis in the testis
Leydig cells Sertoli Cells
Ant Pituitary
Hypothalamus
GnRH
T
LH
Inhibin
FSH
-
-
- -

10. Action of LH and FSH on Sertoli
and Leydig Cells

13. Female Gonads

14. Female reproductive system

15. Estrogens
• Estrogens are secreted by the ovary in women. In
men it is formed by the peripheral conversion of
androgens.
• In the embryo, estrogen production is stimulated
by hCG.
• During puberty, estrogen stimulates skeletal
growth as androgens, but induces muscle protein
synthesis far less.
• Estrogens cause behavioral changes and promote
development of both primary and secondary
female sexual characteristics.

16. Oogenesis
• From birth, the ovaries of the human female
contain about one million of immature oocytes,
called primordial follicles.
• Primordial follicle: oocyte surrounded by a
single flat layer of granulosa cells.
• Primary follicle: oocyte surrounded by a single
cuboidal layer of granulosa cells.
• Secondary follicle: Under hormonal stimulation
during puberty, bigger oocyte and several layers
of granulosa cells. Formation of theca externa
and interna layers from the interstitial tissue
surrounding the follicle.

19. Graafian Follicle
• Graafian follicle: it is marked by the
formation of a fluid-filled cavity adjacent to
the oocyte called the antrum. Granulosa and
theca cells continue to undergo division
concomitant with an increase in antrum
volume.
• Graafian follicles are dependent on the
availability of FSH
• Corpus Luteum: After the egg cell has been
released, the follicle remains and the
granulosa and thecal cells increase in
number and becomes known as the corpus
luteum.
• It secretes progesterone and estradiol under
the effect of LH.
• It maintains uterine endometrium in early
pregnancy.
• If fertilization does not occur, it degenerates
until it becomes only as scar tissue called
corpus albicans.
Graafian Follicle

20. Follicles

21. Pederson and Peter
• Classification of follicles
on population of
Granulosa cells

22. Ovarian Hormonal synthesis
• Menstrual Cycle consists of 4 phases: follicular, ovulation,
luteal and menstrual phases.
• Follicular phase lasts for 10-14 days.
• Starts with FSH developing primordial follicles into primary
follicles.
• LH stimulates steroidogenesis from the follicle’s theca interna.
Androstenedione and testosterone are produced due to lack
of aromatase.
• They are then transported to the adjacent granulosa cells
where they are converted to E2 by a FSH-induced aromatase

23. Synthesis of Estrogens

24. Menstrual Cycle
• The control circuit of the hormonal cycle has two
essential control elements:
• The pulsatile liberation of GnRH, as well as FSH and
LH
• The long-loop feedback-effect of estrogen and
progesterone on the hypothalamic-hypophysial-
system (these two hormones are synthesized in the
[ready to rupture] follicle and so originate in the
ovary, thus the name "long loop").

25. • The menses (bleeding or periods): this commonly lasts from
day 1 to day 5.
During this phase, if fertilisation of the egg did not occur, the
lining of the womb or uterus, which is called the
endometrium, comes away from the uterus wall and the
blood and tissues pass out via the vagina.
• The follicular phase: this phase is so-named because it is
when the follicles in the ovary grow and form an egg. About 3
to 30 follicles grow between days 8 and 10. Each follicle
contains an egg, but by days 10 to 14 one follicle has
overtaken the rest and has reached the correct stage of
maturity.
• During days 6 to 14, the lining of the uterus is repaired and
builds up to be thicker. This is why this phase is also known as
the proliferative phase. This is stimulated by oestrogen
secreted from the ovaries. The lining of the uterus will now be
about 3 mm thick and is also more velvety again.

26. • Ovulation: A surge of luteinising hormone occurs roughly just before day 14 in a
28-day cycle. This surge stimulates the mature follicle in one of the ovaries to
release its egg (ovulation) 16 to 32 hours later. Oestrogen also peaks during this
surge.
• An egg is released from the right or left ovary at random and takes about 5 days
to travel down the fallopian tube to the uterus.
• The luteal or secretory phase: This phase follows ovulation and lasts from about
day 15 to day 28. After the follicle ruptures as it releases its egg, it closes and
forms a corpus luteum. The corpus luteum secretes more and more
progesterone, which acts on glands in the endometrium and causes them to
make a secretion. The purpose of this secretion is to feed the embryo for a few
days until a placenta has formed. Even if the egg is not fertilised and pregnancy
has not happened, the secretion is still produced.
• The progesterone secreted by the corpus luteum causes the temperature of the
body to rise slightly until the start of the next period.
• If the woman has not become pregnant the corpus luteum lasts about 14 days
and then starts to break down. This is when progesterone production rapidly
drops and the oestrogen level decreases. This lack of hormones causes blood
vessels in the endometrium to go into spasm and they cut off the blood supply to
the top layers of the endometrium. Without oxygen and nutrients from the
blood, the endometrial cells begin to die, tissue breaks down and there is
bleeding from the damaged blood vessels and so this is how the new menstrual
cycle begins on about day 28.

27. Role of FSH and inhibin in the control of
gonadal function

28. Menstrual
cycle