(PhD in Animal Nutrition & Physiology) By: A. Riasi (PhD in Animal Nutrition & Physiology) http://riasi.iut.ac.ir Isfahan University of Technology, Isfahan, Iran Advanced Reproductive Physiology (part 3)

Two distinct functions for ovaries Gamete production in female animals Two distinct functions for ovaries 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

Gamete production in female animals Fallopian tube Ovarian artery and vein Ovarian ligament Ovary Tertiary follicle

Gamete production in female animals

Gamete production in female animals Ovogenesis is started during the fetal period: Primordial germ cells (PGCs) migrate from the yolk sac The primordial germ cells proliferate by mitosis to form primary oocytes The first meiotic division is not completed before ovulation In cattle, the first meiotic prophase in days 75-80 The formation of primordial germ cells (PGCs) indicates the commencement of oogenesis. During early fetal life the primordial germ cells which arise in the yolk sac migrate to the presumptive gonads. In cattle the first potential primordial germ cells were identified in an 18-day-old embryo. When the gonadal ridge develops (about day 27) it contains a certain number of primordial germ cells. It is well known that PGCs play an indispensable role in the induction of gonadal development.

Gamete production in female animals The gonad emerges on the ventromedial surface of the mesonephros at the 4th week of gestation. The migration of the primordial germ cells from the wall of the yolk sac along the dorsal mesentery of the hind gut to the gonadal ridge is shown as blue circles. Adapted from Kousta et al., 2010

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

Gamete production in female animals 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.

Gamete production in female animals First 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.

Gamete production in female animals 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

Gamete production in female animals 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.

Follicular growth in prepubertal heifers occurs in waves. Gamete production in female animals 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.

Gamete production in female animals 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

The transition to the tertiary follicle includes: Gamete production in female animals 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

The different chemicalsin antrum fluid: Gamete production in female animals The different chemicalsin antrum fluid: Mucopolysachrides Plasma proteins Electrolytes Glycosoaminoglycans Proteoglycans Gonadal steroid hormones FSH, Inhibin and other factors

Gamete production in female animals

Gamete production in female animals

Gamete production in female animals Final stage of follicular development occurs only in the postpubertal reproductive ovary: 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

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.

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).

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

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

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.

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

Follicular waves

Follicular waves Follicular Size Day After Ovulation Selection Dominance Ovulation Follicular Size Day After Ovulation 9 16 21 Recruitment Atresia Progesterone

Follicular waves

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

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.

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.

In the early estrogenic follicle some changes occur for receptors: 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 17α-hydroxylase.

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

Dynamic changes are evident within the inhibin family: Follicular waves Dynamic changes are evident within the inhibin family: In estrogen-active follicle the large molecular weight inhibins (i.e., >160 kDa) are elevated. In estrogen-inactive follicles the smaller inhibins (32 to 34 kDa) are increased.

FSH secretion by pituitary gland will reduce by: 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.

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 beyond 10 mm appears to be dependent upon LH secretion.

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.

Dominant follicles continue to grow for a few days after selection. 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

Final maturation includes: 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

Final maturation includes: 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

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

Higher fertility in three-wave cycles could be due to: 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.

Follicular Size Day After Ovulation Progesterone Atresia Recruitment Dominance Ovulation Selection FSH Sensitive Pool 9 16 21 Ovulation Day After 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 & PGF2α)

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.

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.

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.

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.

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: 120–126. 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 :3578–3587. 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.