Advanced Reproduction Physiology (Part 2)

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Advanced Reproduction Physiology(Part 2)

• Isfahan University of Technology
• College of Agriculture, Department of Animal
  Science

Prepared by A. Riasi http//riasi.iut.ac.ir
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Oogenesis Folliculogenesis
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Overview
1 ovary, 2 tertiary follicle, 3 proper ovarian
ligament, 4 fallopian tube, 5 ovarian artery
and vein
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Overview
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Overview
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Overview
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Overview

• The ovaries have two distinct functions
• Producing the sex steroids and protein hormones
• Prepare the vagina and fallopian tubes to assist
  in fertilization
• Prepare the lining of uterus to accept and
  implant a zygote
• Maintain hormonal support for the fetus before
  placenta capacity
• Act on diverse target organs

• Ovogenesis and folliculogenesis
• Maintain and nurture the resident oocyte
• Mature the oocyte and release it at the right time

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The biology of oogenesis

• Primordial germ cells migrate from the yolk sac
• The primordial germ cells proliferate by mitosis
  to form primary oocytes
• In cattle, the first meiotic prophase in days
  75-80
• The first meiotic division is not completed befor
  ovulation

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The biology of oogenesis

• In contrast the male, the female cannot
  manufacture new oogonia
• It must function with continuously declining
  number of primary oocytes.

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Folliculogenesis

• The first stage of development of the ovarian
  follicle parallels the prophase of the oocyte.
• As an oocyte enters meiosis, it induces a single
  layer of spindle cells to surround it completely.
• Cytoplasmic processes from these cells attach to
  the plasma membrane of the oocyte.

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Folliculogenesis

• In the next phase, the spindle-shaped cells
  become cuboidal and granulosa cells and a primary
  follicle is formed.
• Then secondary follicle is created.
• After that the zona pellucida is formed.

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Folliculogenesis
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Folliculogenesis

• During the initial deposition of zona pellucida
  material some changes occur in oocyte
• Formation of cortical granules within the oocyte
  cytoplasm
• Onset of oocyte RNA synthesis
• Gonadotrophin responsiveness

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Folliculogenesis

• Primordial, primary and secondary follicles
  appear in the fetal ovary on Days 90, 140 and
  210, respectively (Russe, 1983).
• The second stage of follicular development is
  take place during in postnatal and in puberty.

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Folliculogenesis

• Follicular growth in prepubertal heifers occurs
  in waves.
• Each wave is preceded by a peak in serum FSH
  concentrations (Fortune, 2004).
• There is a marked but transient increase in blood
  concentrations of both LH and FSH.

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Folliculogenesis

• From 30-80 days before the first ovulation, the
  LH pulses frequency result
• Increases in follicle diameter
• Increase in serum estradiol concentrations
• Enhancing antral follicle development

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Folliculogenesis

• The transition to the tertiary follicle includes
• Development of the theca interna and externa
• Formation of basal lamina
• Formation of cumulus cells
• Formation of a fluid-filled antral cavity

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Folliculogenesis

• The fluid in the antrum contains different
  chemicals
• Mucopolysachrides
• Plasma proteins
• Electrolytes
• Glycosoaminoglycans
• Proteoglycans
• Gonadal steroid hormones
• FSH, Inhibin and other factors

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Folliculogenesis
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Folliculogenesis
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Folliculogenesis

• The final stage of follicular development occurs
  only in the postpubertal reproductive ovary.
• Some event in third stage
• The granulosa cells spread apart
• The cumulus oophorus loosens
• The follicle generally ruptures, releasing the
  oocyte with adherent cumulus oophorus
• At this time the initial meiotic division complete

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Follicular waves

• Follicles develop in waves.
• Emergence of a new follicular wave is preceded by
  a rise in FSH.
• Suppression of FSH prevents further growth of 3-5
  mm follicles.

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Follicular waves

• The FSH surge peaks, on average, when the largest
  follicle is about 5 mm.
• Rather than selection of a dominant follicle,
  selection involves an action against the other
  follicles in the wave (Ginther et al, 2003).

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Follicular waves

• A subordinate follicle remains viable for at
  least 1 day after deviation starts
• Administration of FSH when a dominant follicle is
  present does not consistently hasten emergence of
  the next wave

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Follicular waves

• With decreasing serum FSH concentrations,
  follicles begin to undergo changes
• Reduced production of estrogens
• Reduced levels of higher molecular weight (MW)
  inhibins
• Increased amounts of lower MW insulin-like growth
  factor (IGF)-binding proteins
• Culminating in granulosa cell apoptosis

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Follicular waves

• FSH stimulates the production of estradiol,
  activin-A and inhibin-A (Glister et al, 2001).
• These FSH-stimulated factors have intrafollicular
  roles in deviation.
• Both estradiol and inhibin act alone (as well as
  synergistically) to suppress blood FSH
  concentrations.

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Follicular waves

• The estradiol secretion by dominant follicle
  increase the expression of genes in granulosa
  cells for
• Aromatase
• 3-beta-HSD
• Receptors for FSH and LH

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Follicular waves
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Follicular waves
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Follicular waves
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Follicular waves

• The IGF system is involved in cell growth and
  differentiation and consists of
• IGF-1
• IGF-2
• IGF receptors
• A family of binding proteins (IGFBPs)
• IGFBP proteases

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Follicular waves

• It appears that pregnancy-associated-plasma
  protein-A (PAPP-A) is the earliest change
  detectable in the future dominant follicle.
• PAPP-A is a protease and increase intrafollicular
  IGF-I concentrations.

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Follicular waves

• Increased IGF-I acts together with FSH to
  increase estradiol synthesis.
• It is noteworthy that estradiol stimulates the
  production of IGF-1 and IGF-1 stimulates the
  production of estradiol.

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Follicular waves

• In the early estrogenic follicle some changes
  occur for receptors
• The mRNAs for the FSH receptor and aromatase are
  elevated within the granulosa layer.
• Theca cells have increased abundances of LH
  receptor and 17a-hydroxylase.

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Follicular waves
Two cell, two-gonadotropin theory of ovarian
steroidogenesis
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Follicular waves

• Dynamic changes are evident within the inhibin
  family
• In estrogen-active follicle the large molecular
  weight inhibins (i.e., gt160 kDa) are elevated.
• In estrogen-inactive follicles the smaller
  inhibins (32 to 34 kDa) are increased.

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Follicular waves

• FSH secretion by pituitary gland will reduce by
• The increased secretions of estradiol
• The increased secretion of large MW inhibin
• Lack of FSH prevents further growth of
  subordinate follicles, which are also
  nonestrogenic due to low concentrations of free
  IGF-I.

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Follicular waves

• Once the dominant follicle reaches 10 mm its
  granulosa cells begin to express LH receptors.
• Continued growth and dominance of the dominant
  follicle beyond10 mm appears to be dependent upon
  LH secretion.

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Follicular waves
Ovarian follicular and corpus luteum development
correlated with endocrine changes during the
bovine estrous cycle. E2 Estradiol IGFBP-4 and
-5 insulin-like growth factor binding proteins
4 and 5 OvF ovulatory follicle.
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Follicular waves

• Dominant follicles continue to grow for a few
  days after selection.
• If there is an LH surge the dominant follicle
  continues to grow and the oocyte within
  undergoes
• Final maturation
• Culminating in follicle rupture
• Ovulation

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Follicular waves

• Final maturation includes
• Expansion of the cumulus cover
• Disruption of the contact between the corona
  radiata cells and the oocyte membrane
• Perivitelline space formation
• Increase lipid content in oocyte cytoplasm
• Decrease golgi compartment in oocyte cytoplasm

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Follicular waves

• Final maturation includes
• The cortical granules are aligned just inside the
  oocyte membrane
• The chromosomes condense and progress through the
  final stages of meiosis I and arrest at metaphase
  of meiosis II

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Follicular waves

• The peak and average plasma concentrations of FSH
  and inhibin A are lower in the two non-ovulatory
  waves than a three-wave cycle

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Follicular waves

• Higher fertility in three-wave cycles could be
  due to
• A shorter interval for development of the
  ovulatory follicle (Townson et al, 2002).
• Delayed regression of the corpus luteum.

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Atresia
Follicular Size
Ovulation
FSH Sensitive Pool
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Ovulation
Day After Ovulation
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Ovulation

• Ovulation takes place about 10-14 hours after the
  end of oestrus.
• The gonadotropin surge is important for
  ovulation
• Increase progesterone production
• Increase estrogen production
• Increase prostaglandins (PGE2 PGF2a)

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Corpus luteum formation

• In its early stages of growth the corpus
  haemorrhagicum is difficult to palpate.
• The corpus luteum (CL) is palpable at about five
  days post ovulation.

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Corpus luteum formation

• It frequently has a distinct crown
• About ½ cm in diameter
• About ½ cm high
• The corpus luteum enlarges progressively to two
  to three cm by day-8 or 9 and has a liver like
  consistency.

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Corpus luteum formation

• Actually the CL is made up two cell groups
• The large luteal cells, which originated from
  granulosa cells.
• The small luteal cells which originated from
  theca cells.
• The luteal cells are steroidogenic and secrete
  progesterone.

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Corpus luteum formation

• Progesterone has the following functions during
  pregnancy
• It prevents the cow from coming on heat.
• The function of the hormone oxytocin is blocked.
• It regulates the changes in the mucous membranes
  in the uterus.
• It plays a role in the formation of udder tissue.

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Some research papers associated to this lecture

• Beg, M. A. et al. 2002. Follicle Selection in
  Cattle Dynamics of follicular fluid factors
  during development of follicle dominance. Biology
  of Reproduction. 66 120126.
• Bisinotto, R. S. Et al. 2010. Follicular wave of
  the ovulatory follicle and not cyclic status
  influences fertility of dairy cows. J. Dairy Sci.
  93 35783587.
• Rýfat, M. et al. 2005. Evaluation of the corpus
  luteum size throughout the cycle by
  ultrasonography and progesterone assay in cows.
  Turk. J. Vet. Anim. Sci. 29 1311-1316.