Estrus, Ovulation & Oogenesis Lecture 14 PDF

Lecture 14 Estrus, Ovulation & Oogenesis AGSC310 –Physiology of Reproduction Luis Fernando Schutz, Ph.D. 1  Reproductive cyclicity Learning objectives: Ø Know the functions of estradiol during the...

Lecture 14 Estrus, Ovulation & Oogenesis AGSC310 –Physiology of Reproduction Luis Fernando Schutz, Ph.D. 1  Reproductive cyclicity Learning objectives: Ø Know the functions of estradiol during the follicular phase Ø Understand the process of ovulation Ø Understand the process of oocyte maturation Ø Know how the corpus luteum is formed 2  Reproductive cyclicity Group activity: review Ø Discuss in groups of four stress pregnancy nutrition season v hfftiggy Person 1: what are the types and stages of estrous cycle? What are the causes of anestrus? seasonal monoestrus polyestrus structures, mainluteum estradiol follicle progphase (dominant corpus v Person 2: characterize the follicular and luteal hormones, stages of estrous cycle). Characterize the four processes of folliculogenesis. recruitment selection dominance ovulation v Follicular proestrus estrus luteal metestrus Person 3: how is the hormonal regulation of the release of GnRH and diestrus gonadotropins? How does that affect recruitment, selection, dominance, and ovulation? v Person 4: explain the synthesis of estradiol by the antral follicle (what are the roles of the FSH and LH in the production of steroids?). 3  Estrus Actions of Estradiol (E2) Ø during the follicular phase, E2 is high and P4 is low follicle present v in response to high E2: ü the female becomes sexually receptive (estrus) ü the reproductive tract prepares for copulation ü the reproductive tract contracts to aid sperm motility 4  Estrus Actions of Estradiol (E2) Ø the female becomes sexually receptive (estrus) v increased locomotion movement helpful for the v increased vocalization bull to find bellowing them distance v cows mount each other ü cows will start mounting each other during proestrus (beginning of the follicular phase), but will only accept to be mounted when in estrus (standing estrus) v lordosis (mating posture) 5  Estrus Actions of Estradiol (E2) Ø the reproductive tract prepares for copulation v mucosa of caudal vagina increases in thickness mucus dripping from volva v the cervix and cranial vagina produce mucus v uterine glands develop from the luminal epithelium an penetrate into the submucosa of the endometrium v the epithelium of the oviduct increase its secretory rate v the cilia within the oviduct increase their beat frequency v blood flow of the reproductive tract increases (hyperemia) more of a red color 6  Estrus Actions of Estradiol (E2) Ø the reproductive tract prepares for copulation v mucosa of caudal vagina increases in thickness ü mechanically protects the vagina during copulation ü prevents microorganisms from gaining entrance to the vasculature in the submucosa v the mucus produced by the cervix and cranial vagina has three functions: ü lubricate the vagina and cervix in preparation for copulation can cause ü friction infection flush foreign material such as bacteria out of the tract following copulation ü in the cow, low viscosity mucus aids sperm transportation through the cervix and into the uterus 7  Estrus Actions of Estradiol (E2) Ø the reproductive tract prepares for copulation v uterine glands develop from the luminal epithelium an penetrate into the submucosa of the endometrium nourish the embryo ü uterine glands will secrete factors that nourish the preimplantation embryo v the epithelium of the oviduct increase its secretory rate ü secretes substances that support embryo survival and development v the cilia within the oviduct increase their beat frequency ü increased beat frequency allows for gamete and fluid transport cilia beat highly specialized differently 8  Estrus Actions of Estradiol (E2) Ø the reproductive tract prepares for copulation v blood flow of the reproductive tract increases (hyperemia), which has the following functions: ü facilitates secretion of mucus and factors important for embryo survival throughout the reproductive tract kills off foreign material exeranong ü allows for delivery of leukocytes into submucosal region of reproductive tract so that invading foreign material (including sperm) may be phagocytized after copulation (this process is called leukocytosis) ü in the cow, hyperemia induces the swelling of the vulva (edema), which may serve as a diagnostic indicator of estrus important for dairy cows 9  Estrus Actions of Estradiol (E2) Ø the reproductive tract contracts to aid sperm motility v E2 increases tone and motility of the muscularis in all regions of the reproductive tract ü this increase in tone and motility is responsible, at least in part, for sperm transport 10  Ovulation Ovulation is regulated by LH cuisine Ø the preovulatory surge of LH a through a series of biochemical events will induce ovulation v these events lead to the rupture of preovulatory follicle to release the egg via two mechanisms: ü increase of follicular pressure ü weakening of the follicle wall 11  Ovulation Ovulation is regulated by LH Ø the preovulatory surge of LH: v stimulates the synthesis of factors critically important for the rupture of preovulatory follicle to release the egg v these factors include: ü progesterone (P4) ü prostaglandin E2 (PGE2) ü prostaglandin F2 ⍺ (PGF2⍺) 12  Ovulation Ovulation is regulated by LH Ø progesterone and ovulation: v P4 starts to be produced by follicular cells in response to LH in the beginning of the ovulatory process ü P4 stimulates the synthesis of collagenase by the cells of theca interna ü collagenase breakdowns the connective tissue of the tunica albuginea, the outer covering of the ovary ü enzyme breakdown of the tunica albuginea is accompanied by an the enzymatic increase of follicular fluid volume inside the preovulatory follicle ü these events will weaken the follicle wall 13  Ovulation Ovulation is regulated by LH Ø prostaglandins and ovulation: v PGE2, together with histamines, stimulates an increased blood flow to the follicle (hyperemia) ü together with increased blood flow, cells of the theca interna become edematous, which increases the hydrostatic pressure that may facilitate the eventual rupture of the follicle (increase of follicular pressure) v PGF2⍺ ü causes the release of lysosomal enzymes that cause digestion of connective tissue of the follicle, which weakens the follicle wall ü causes contractions of the myoid (smooth muscle) components of the follicle (increase of follicular pressure) 14  Ovulation Ovulation is regulated by LH Preovulatory LH surge P4 PGF2⍺ PGE2 synthesizes weff.ie message increases pressure Release of Contraction of Collagenase lysosomal ovarian smooth Blood flow to the ovary and follicle enzymes muscle weakening of the follicle wall increase of follicular pressure 15  Oocyte maturation Oogenesis and Oocyte maturation: Ø prior to ovulation and subsequent fertilization, oocytes need to be fully mature Ø oocyte maturation occurs throughout the lifetime of the female conceptus, beginning during embryonic development of the female and continuing throughout her reproductive lifetime Ø oogenesis refers to the events of oocyte maturation that occur throughout the lifespan of the female 16  Oocyte maturation Oocyte maturation: Ø oocyte maturation consists of four phases: v mitotic division of primordial germ cells (prenatal) v nuclear arrest (dictyotene) v cytoplasmic growth v resumption of meiosis 17  Oocyte maturation Oocyte maturation: Ø mitotic division of primordial germ cells (prenatal) v mitotic divisions occur only prenatally v mitotic divisions ensure that the female is born with a complete supply of germ cells that will provide a future follicular reservoir v the last mitotic division from oogonia to the primary oocyte marks the entrance of the primary oocyte into the first meiotic prophase multiplication of oocytes thats it and its a limited pool of oocytes 18  Oocyte maturation Oocyte maturation: Ø nuclear arrest (dictyotene) v after the last mitotic division, the primary oocyte is arrested at meiotic prophase I and the nucleus of the oocyte becomes dormant v the nucleus of the oocyte will remain dormant until puberty, when it will be stimulated by gonadotropins they get stimulated by release of GnRH v the purpose of this nuclear arrest is to inactivate the DNA in the female gamete so it may not be vulnerable to possible insult during the lifetime of the female 19  Oocyte maturation Oocyte maturation: Ø cytoplasmic growth v after birth, some of the primary oocytes begin to accumulate larger volumes of cytoplasm and develop a translucent membrane around the cytoplasm called zona pellucida translucent membrane ü the presence of the zona pellucida characterize the secondary follicle stage cround of oocytes cytoplas ü at this stage, junctional complexes between the oocyte and adjacent granulosa cells (called gap junctions) are formed § gap junctions allow the diffusion of material between the oocyte and cumulus cells, which is important to oocyte growth important for oocyte growth 20  Oocyte maturation Oocyte maturation: Ø resumption of meiosis v resumption of meiosis occurs in response to ovulatory LH surge ü the gap junctions between cumulus/granulosa cells and oocyte deteriorate after the LH surge, releasing the oocyte from inhibitors provided by the granulosa cells § cAMP provided by the cumulus cells is a major inhibitor of meiosis resumption ü LH also stimulates the activity of the maturation promoting factor and the germinal vesicle breakdown § germinal vesicle breakdown: the nucleus of the oocyte (also known as germinal vesicle) dissolves, which is followed by chromosome condensation and the completion of first meiotic division 21  Oocyte maturation Oocyte maturation: Ø resumption of meiosis v resumption of meiosis characterizes the final oocyte maturation that occurs just prior to ovulation v once the follicle has entered the dominance phase, the oocyte becomes ready to interrupt the nuclear arrest at metaphase I and resume meiosis v following the resumption of meiosis, the primary oocyte becomes the secondary oocyte during the first meiotic division and subsequently becomes the ootid, which is ready to be fertilized to be ready 22 fertilized  Oocyte maturation Oocyte maturation: Ø resumption of meiosis v following resumption of meiosis, a 1st polar body will be formed ü the formation of the first polar body begins with a peripheral migration of the oocyte nucleus; the bivalent chromosomes in the nucleus will then line up and the chromatids are separated by a microtubule system ü the 1st polar body is a sign of the initiation of final oocyte maturation v after fertilization, the second meiotic division will occur, forming the 2nd polar body 23  Oocyte maturation Oogenesis: Primordial germ Oogonia avoidsgetting destroyed infected 2N overtime PRENATAL Taste Primary oocyte 2N Primary oocyte Puberty Nuclear arrest 4N LH Surge Resumption of meiosis: 1st meiotic division AFTER PUBERTY PB1 1st polar body Secondary oocyte 2nd polar body not equal not symmetric affiliation PB2 2nd meiotic division only half of i PN 1N male pronucleus matters Ootid Zygote PN 1N female pronucleus PB1 fertilization 24 PN 1N see female has in PB2 biggest her body PN 1N females only get a certain amount of eggs for their lifetime  Luteinization Luteinization (formation of corpus luteum): Ø shortly before ovulation: v the basement membrane of the follicle undergoes partial disintegration and the physical separation of the theca and granulosa cells disappear Ø during ovulation: v many small blood vessels rupture, causing hemorrhage ü this will give rise to the corpus hemorrhagicum (which will last from 1 to 3 days and will then be replaced by the corpus luteum) v the follicular fluid leaks from the ruptured follicle v the wall of the follicle collapses ü this allows theca and granulosa cells to mix and form luteal cells 25  Luteinization Luteinization (formation of corpus luteum): Ø the luteal phase begins immediately after ovulation Ø after ovulation, the theca interna cells and the granulosa cells of the ruptured antral follicle undergo a dramatic transformation known as luteinization IETF mation v luteinization = follicular cells will become luteinized ü granulosa cells will become large luteal cells ü cells of the theca interna will become small luteal cells ü both small and large luteal cells will produce progesterone Ø luteinization is governed by LH Leutinizing hormone 26