Female reproductive system

1. Reproductive system-3
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
RDGMC

2. Female reproductive physiology
 Female reproductive physiology is more complex than male
reproductive physiology.
 Release of ova is intermittent.
 Secretion of female sex hormones displays wide cyclic
swings.
 The tissues influenced by these sex hormones also undergo
cyclic changes.
 The most obvious of which is the monthly menstrual cycle
(menstruous means “monthly”).

3. Female reproductive physiology
 During each cycle, the female reproductive tract is prepared for
the fertilization and implantation of an ovum released from the
ovary at ovulation.
 If fertilization does not occur, the cycle repeats.
 If fertilization does occur, the cycles are interrupted while the
female system adapts to nurture and protect the newly conceived
human.
 Furthermore, the female continues her reproductive functions after
birth by producing milk (lactation) for the baby’s nourishment.

4. Female reproductive physiology
 During each cycle, the female reproductive tract is prepared for
the fertilization and implantation of an ovum released from the
ovary at ovulation.
 If fertilization does not occur, the cycle repeats.
 If fertilization does occur, the cycles are interrupted while the
female system adapts to nurture and protect the newly conceived
human.
 Furthermore, the female continues her reproductive functions after
birth by producing milk (lactation) for the baby’s nourishment.

5. Female reproductive physiology
 The ovaries perform the dual function
1. producing ova (oogenesis)
2. secreting the female sex hormones, estrogen and progesterone.
 These hormones act together to promote fertilization of the ovum
and to prepare the female reproductive system for pregnancy.
 The actions of estrogen are important to preconception events.
 progesterone, called the “hormone of pregnancy.”

6. Female reproductive physiology
 Being steroids, estrogen and progesterone exert their multiple
effects by binding with their respective receptors in the cytoplasm
of their target cells.
 Hormone-receptor complex
 Moves to the nucleus
 Binds with a hormone specific DNA hormone-response element.
 Gene transcription
 Synthesis of designated proteins
 Exert the hormone’s dictated response in the target cells

7. Selective estrogen receptor
modulators
 Like raloxifene, are drugs that selectively bind with a specific
estrogen receptor.
 Raloxifene is approved to treat osteoporosis.
 Because it selectively binds with estrogen receptors in bone,
where it mimics estrogen’s beneficial effect on maintaining bone
density.
 Not exerting any effect on reproductive organs.
 Extra estrogen like influence could increase the risk of cancer.

8. Oogenesis
 Oogenesis contrasts sharply with spermatogenesis in several
important aspects.
 The undifferentiated primordial germ cells in the fetal ovaries,
divide mitotically to produce about 7 million oogonia by the fifth
month of gestation, when mitotic proliferation ceases.
 During the last part of fetal life, the oogonia begin the early steps
of the first meiotic division but do not complete it.
 The primary oocytes remain in this state of meiotic arrest for years
until they are prepared for ovulation.

9. Oogenesis
 Before birth, each primary oocyte is surrounded by a single layer
of connective tissue–derived granulosa cells.
 Together, an oocyte and surrounding granulosa cells make up a
primordial follicle.
 At birth, only about 2 million primordial follicles remain, each
containing a single primary oocyte capable of producing a single
ovum.
 How 7 million become 2 million?

10. Oogenesis
 Primary oocytes that are not incorporated into follicles self-
destruct by apoptosis (cell suicide).

11. Oogenesis
 Once it starts to develop, a follicle is destined for one of two fates:
 It will reach maturity and ovulate, or it will degenerate to form scar
tissue, a process known as atresia.
 Until puberty, all the follicles that start to develop undergo atresia
in the early stages without ever ovulating.
 For the first few years after puberty, many of the cycles are
anovulatory (that is, no ovum is released).
 Of the original total pool of follicles at birth, about 300,000 remain
at puberty, and only about 400 will mature and release ova.

12. Oogenesis
 The primary oocyte within a primordial follicle is still a diploid cell
that contains 46 doubled chromosomes.
 The mechanisms determining which follicles in the pool develop
during a given cycle are unknown.
 Just before ovulation, the primary oocyte, whose nucleus has
been in meiotic arrest for years, completes its first meiotic
division.
 This division yields two daughter cells, each receiving a haploid
set of 23 doubled chromosomes.

13. Oogenesis
 However, almost all the cytoplasm remains with one of the
daughter cells, now called the secondary oocyte, which is
destined to become the ovum.
 The chromosomes of the other daughter cell, together with a small
share of cytoplasm, form the first polar body.
 The nutrient-poor polar body soon degenerates.
 In this way, the ovum-to-be loses half of its chromosomes.

14. Oogenesis

15. Formation of a Mature Ovum
 The secondary oocyte, and not the mature ovum, is ovulated and
fertilized.
 Sperm entry into the secondary oocyte is needed to trigger the
second meiotic division.
 Unfertilized secondary oocytes never complete this final division.
 During this division, a half set of chromosomes, along with a thin
layer of cytoplasm, is extruded as the second polar body.
 The other half set of 23 unpaired chromosomes remains behind in
what is now the mature ovum.

16. Formation of a Mature Ovum
 These 23 maternal chromosomes unite with the 23 paternal
chromosomes of the penetrating sperm to complete fertilization.
 If the first polar body has not already degenerated, it too
undergoes the second meiotic division at the same time the
fertilized secondary oocyte is dividing its chromosomes.
 The older age of ova released by women in their late 30s and 40s
is believed to account for the higher incidence of genetic
abnormalities, such as Down syndrome, in children born to
women in this age range.

17. Ovarian cycle
 After the onset of puberty, the ovary constantly alternates between
two phases:
 The follicular phase- dominated by the presence of maturing
follicles.
 The luteal phase- characterized by the presence of the corpus
luteum.
 Normally, this cycle is interrupted only if pregnancy occurs and is
finally terminated by menopause.
 The average ovarian cycle lasts 28 days, but this varies among
women and among cycles in any particular woman.

18. Ovarian cycle
 At any given time throughout the cycle, a portion of the primordial
follicles is starting to develop under paracrine influence.
 However, only those that reach a certain stage of development
during the follicular phase, when the gonadotropin hormone
environment is right to promote their final maturation, continue
beyond the earlier stages of development.
 The others, lacking hormonal support, undergo atresia.
 During follicular development, as the primary oocyte is
synthesizing and storing materials for future use if fertilized.

19. Pre antral follicle
 The first stage of follicular development is conversion of selected
primordial follicles into preantral follicles.
 A preantral follicle is a follicle that has begun to grow but has not
yet formed an antrum.
 Antrum - a fluid-filled cavity within the follicle’s interior.
 Primordial follicle has single layer of granulosa cells covered.
 These cells proliferate and increase in thickness and form multiple
layers in pre antral follicle
 The glycoprotein layer will be formed that separates oocyte from
granulosa cells.
 This intervening membrane is known as the zona pellucida.

20. Pre antral follicle
 Gap junctions penetrate the zona pellucida and extend between
the oocyte and surrounding granulosa cells.
 Glucose, amino acids, and other important molecules are
delivered to the oocyte from the granulosa cells through these
connecting tunnels.
 Also, signaling molecules pass through the gap junctions in both
directions, helping coordinate the changes that take place in the
oocyte and surrounding cells as both mature and prepare for
ovulation.

21. Developing antral follicle
 Enlargement of oocyte.
 Granulosa cells proliferates.
 Granulosa cells secrete paracrine substances.
 Thecal cells will be formed around granulosa cells
 Granulosa cells + thecal cells = follicular cells
 Follicular cells can secrete estrogen
 Beginning of formation of antrum

22. Antral follicle
 Antrum = fluid filled cavity.
 Antrum is formed in the middle of granulosa cells.
 The follicular fluid originates partially from transudation
(passage through capillary pores) of plasma and partially
from follicular cell secretions.
 As the follicular cells start producing estrogen, some of this
hormone is secreted into the blood for distribution
throughout the body.
 A portion of the estrogen collects in the hormone-rich antral fluid.
 Estradiol is the principal ovarian estrogen.
 What are other physiological forms of estrogen?

23. Antral follicle
 Three physiologically important estrogens in order of
potency
1. Estradiol
2. Estrone
3. Estriol

24. Antral follicle
 The oocyte reaches full size during early development of the
antrum.
 The shift from a preantral follicle to an antral follicle initiates
a period of rapid follicular growth.
 Part of the follicular growth is the result of continued
proliferation of the granulosa and thecal cells.
 but most results from a dramatic expansion of the antrum.
 This early antral development takes another 45 days.

25. Follicular phase
 Only antral follicles that have developed to the point of
becoming extremely sensitive to FSH are “recruited” for
further rapid development at the beginning of the follicular
phase when FSH levels rise.
 Typically during each cycle, about 15 to 20 follicles are
recruited.
 Whereas the diameter of a preantral follicle is still less than
1 mm, that of a recruitable antral follicle is 2 to 5 mm, and
that of a recruited mature follicle reaches 15 to 20 mm
shortly before ovulation.

26. Follicular phase
 Of the follicles recruited, one, the “dominant” follicle,
usually grows more rapidly than the others, developing into
a mature (preovulatory, tertiary, or Graafian) follicle.
 Rapid growth of recruited follicle
 Development of mature follicle
 Under influence of FSH
 14 days duration (approx)
 What criteria decides to become mature follicle?
 Presence of more FSH receptors so more sensitivity to FSH

27. Mature follicle
 The antrum occupies most of the space in a mature follicle.
 The oocyte, surrounded by the zona pellucida and a single
layer of granulosa cells, is displaced asymmetrically at one
side of the growing follicle.

29. Ovulation
 The greatly expanded mature follicle bulges on the ovarian
surface.
 Creating a thin area that ruptures to release the oocyte at
ovulation.
 Rupture of the follicle is facilitated by enzymes released
from the follicular cells.
 Release of these enzymes is triggered by a burst in LH
secretion.
 Enzymes digest the connective tissue in the follicular wall.
 The follicular wall become further weakened
 it can no longer contain the rapidly expanding follicular
contents.

30. Ovulation
 Just before ovulation, the oocyte completes its first meiotic
division.
 The ovum (secondary oocyte), still surrounded by its zona
pellucida and granulosa cells.(now called the corona
radiata).
 Secondary oocyte is swept out of the ruptured follicle into
the abdominal cavity by the leaking antral fluid.
 The released ovum is quickly drawn into the oviduct, where
fertilization may or may not take place.
 Rupture of the follicle at ovulation signals the end of the
follicular phase and ushers in the luteal phase.
 What is fate of other follicles that started the race??

31. Fate of other follicles in the race
 The other developing follicles that failed to reach maturation
and ovulate undergo degeneration, never to be reactivated.

32. Fraternal twins
 Dizygotic twins
 Occasionally, two (or perhaps more) follicles reach
maturation and ovulate around the same time.
 If both are fertilized, fraternal twins result.
 Fraternal twins arise from separate ova fertilized by separate
sperm.
 They share no more in common than any other two siblings
except for the same birth date.

33. Identical twins
 Monozygotic twins
 Develop from a single fertilized ovum.
 that completely divides into two separate, genetically
identical embryos at an early stage of development.
 Identical twins share all of their genes.
 Are always of the same sex.

34. Luteal phase
 The ruptured follicle left behind in the ovary after release of
the ovum changes rapidly as the granulosa and thecal cells
remaining in the remnant follicle undergo a dramatic
structural and functional transformation.
 These old follicular cells form the corpus luteum (CL), a
process called luteinization.
 Follicular cells converts into luteal cells.
 Luteal cells are very active steroid hormone–producing
tissue.
 Why corpus luteum is in yellow color?

35. Luteal phase
 Why corpus luteum is in yellow color?
 Abundant storage of cholesterol, the steroid precursor
molecule, in lipid droplets within the corpus luteum gives
this tissue a yellowish appearance
 Hence its name (corpus means “body”; luteummeans
“yellow”).

36. Corpus luteum
 The CL secretes into the blood abundant quantities of
progesterone, along with smaller amounts of estrogen.
 Estrogen secretion in the follicular phase followed by
progesterone secretion in the luteal phase is essential for
preparing the uterus for implantation of a fertilized ovum.
 The CL becomes fully functional within 4 days after
ovulation, but it continues to increase in size for another 4
or 5 days.

37. Fate of Corpus luteum
 Depends on fertilization
 If fertilization do not occur
 the CL degenerates within about 14 days after its formation
 The luteal cells degenerate and are phagocytized
 Connective tissue rapidly fills in to form a fibrous tissue
mass.
 The luteal phase is now over, and one ovarian cycle is
complete.
 Signals the onset of a new follicular phase.

38. Fate of Corpus luteum
 Depends on fertilization
 If fertilization and implantation occurred
 the corpus luteum continues to grow and produce
increasing quantities of progesterone and estrogen instead
of degenerating.
 Now called the corpus luteum of pregnancy.
 It provides the hormones essential for maintaining
pregnancy until the developing placenta can take over this
crucial function.

39. THANK YOU