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REPRODUCTIVE SYSTEM:CHAPTER 35 Control of Gonadal and Gamete Development…

- - - - Eg : Gonadotropin releasing hormone (GnRH) is secreted from the hypothalamus and stimulates gonadotropic cells in the anterior pituitary gland to release luteinizing hormone and follicle-stimulating hormone, which in turn regulate the gametogenic and steroidogenic functions of the gonads in male and female.
        
        Synthesis of GnRP produces GnRH-associated protein (GAP)
        
        GAP able to inhibit prolactin secretion
  - - - anterior lobe has three subdivisions,pars distalis, pars tuberalis and pars intermedia
        
        makes and secretes GH,PL, FSH,LH ,ACTH and GH
      - Posterior lobe composed of mainly neural tissues, has subdivisions: Pars nervosa, median eminence, infundibulum
        
        secretes hormones made by hypothalamus, eg oxytocin and vasopressin
- - - - inhibit LH
    - - inhibit FSH
    - - dopamine, GABA and GAP inhibit secretion
        
        bromocriptine and cabergoline, can be used to suppress prolactin secretion in cases of hyperprolactinemia
      - estrogen and removal of pituitary gland increase secretion
        
        estrogen suppress sensitivity of dopamine, increase no. of thyrotrtopin-releasing hormone
  - - - If GnRH is continue administer, receptors are occupy,interrupt the signal for gonadotropin secretion and release, pulse generator system will be downregulated, less gonadotropin is release
        
        Estrogen decreases the pulse amplitude, and progesterone decreases the pulse frequency of gonadotropin secretion.
  - - - During first 10 ten days, theca cell develop receptors and bind with LH
        
        secretes androstenedione
        
        Granulosa cell develop FSH receptor first ,then develop LH receptor afterwards
        
        Produce aromatase
        
        converts androstenedione into 17B-estradiol (member of estrogen family)
        
        Follicle grows, increased level of estrogen act as -ve feedback signal,inhibit pituitary from releasing FSH
        
        FSH decreased, some follicles regress, only the follicle with most FSH receptors continues grow,undergoes ovulation
        
        1 more item...
        
        feedback site: arcuate nucleus
      - During follicular phase, no progesterone, pulse frequency increases, have estrogen, pulse amplitude decreases
    - - After ovulation, corpus luteum (consists luteinized granulosa and theca cells)
        
        Theca cells secrete androstenedione, coverted to 17B-estradiol by granulosa cells
        
        Granulosa cells respond to LH by increase activity
        of cholesterol side chain cleavage enzyme ,p450scc
        
        converts cholesterol into pregnenolone (progesterone precursor)
        
        Progesterone > estrogen
        
        Progesterone act as -ve feedback mechanism signal , decrease release of FSH n LH
        
        low FSH ,low estrogen
        
        1 more item...
        
        Secrete inhibin, inhibit FSH
- - - - RNA is synthesised
        
        follicle cells begin to divide and form a granulosa
        
        secrete zona pellucida
        
        Primary follicle formed
  - - - theca produces androgens (testoster
        one and androstenedione) under the influence of LH,
        
        granulosa is incapable of forming
        androgens
        
        theca has limited capacity for producing estrogens
        
        two-cell mechanism
        
        These estrogens have a positive-feedback
        effect on the granulosa; they stimulate the cells to undergo mitotic division
        
        antral follicle becomes increasingly sensitive to FSH as it develops
  - - - Increasing secretion of estrogen initiates the preovulatory
        surge of gonadotropins
- - - - In the absence of androgens, the hypothalamus is organized
        as female
        
        conversion (aromatization) of androgens to estrogens is essential for maleness
        
        if is male, will have active intervention
        
        (2) within the hypothalamus for conversion to estrogen
        
        (1) within the internal genitalia for conversion to more potent androgen
    - - wolffian duct is maintained,
        müllerian duct regresses
        
        formation of the penis and the scrotum
    - - müllerian duct is maintained,
        Wolffian duct regresses
        
        labia form the vulva, and a clitoris
        develops
  - - - Wolffian duct becomes the epididymis, vas deferens, and urethra
      - Invagination of sex cords continues into medulla of embryonic gonad
      - Germ cells -> genital ridge -> develops into sertoli cell and leydig cell
    - - Ovulation : a process releasing oocyte from ovary
      - müllerian ducts develop into oviducts
        
        wolffian duct
        regresses
        
        Fimbria enable oocte to be released from ovary.
      - Germ cells -> Genital ridge -> contribute to follicle cells and granulosa cell -> surround oocyte
- - - - 3 compartment :
      - 1) interstitial compartment : leydig cell (produce testosterone),
      - 2) Basal part of seminiferous : Sertoli cell (provide nourishment & support to spermatogenesis), spermatogonia undergo mitosis into spermatocyte
      - 3) adluminal (inner) : blood-testis barrier (spermatid→spermatozoa)
      - size of testicles influence sperm production
      - size depends on age, body condition score , breed, species
      - -larger testes, more sperm produced, measured by scrotal circumference/ ultrasonographic measurement
    - - 3 parts : head ,body, tail
        
        Head and body: spermatozoa undergo maturation and motility ,capable to fertile.
        Tail : spermatozoa storage
    - - *PGs, above all PGE, occur in testicle tissue, have a modulating effect on the LH-dependent steroid synthesis and possibly influence sperm density and sperm function.help in fertility
    - - seminiferous tubule →retes testis → epidydimis (store sperm)→ ductus deferens → seminal gland → prostate gland → bulbo-urethra gland →urethra → penis
- - - - **how about internal testes animal?
        
        E.G :birds develop spermatogenesis at Elevated temperature. The mechanisms that maintain an
        efficient avian spermatogenesis at the high core body temperature of 40^41³C are unknown at present. They have special thermoregulation mechanism, some believe have lower core body temp.
- - - - for better performance during epididymal maturation and in oviduct
      - Oxidative : aerobic,for epididymal maturation, motility and differentiation
      - Glycolytic: anaerobic, for motility, capacitation, acrosomal rxn
        
        What is capacitation?
        
        Change in structure& motility for sperm
        
        motility : chemical change in tail so increase motility (hyperactive)
        
        Structure: removal of glycoprotein on acrosome membrane (protective layer), for better release of enzyme during acrosomal rxn
        
        why need that? for better survival n performance
        
        What is acrosomal rxn?
        
        process of acrosomal enzyme exocytosis, fusion of acrosome with plasma membrane of egg cell
        
        produce enzyme for penetrate---granulosa cell & zona pellucida
        
        hyaluronidase ---hyaluronic acid on granulosa cell
        
        Acrosin ----zona pellucida
        
        Increase the tail flagellar beat
  - - - cuz need to wait for maturition of oocyte
      - due to delayed completion of meiosis
        
        especially in horse and dog
- - - - Fetus adrenal cortex convert it into androgen
        
        Placenta convert androgen into estrogen
- - - - HOW IT PRODUCED ?
        
        Fetus hypothalamus -->stimulate anterior pituitary ----> produce ACTH -----> stimulate adrenal cortex-----> produce cortisol ----> stimulate uterus ---> produce prostaglandin
- - - - neonatal undergo changes, foramen ovale close by left ventricle, closure of ductus arteriosus n venosus
- - - - Proestrus
        
        Period of follicle development, occur subsequently to luteal regression , ending at estrus
        
        usually begins within 48 hours
        after the end of the luteal phase
        
        proestrus in the dog delayed by the anestrus phase (2 to 3 months) and proestrus in the pig not occurring for 5 to 6 days.
      - Estrus
        
        Period of sexual receptivity
      - Metestrus
        
        Period of initiation development of CL
      - Diestrus
        
        Period of mature phase of CL
      - Anestrus
        
        the period of sexual quiescence between two periods of sexual activity
      - Behavioral : estrus or nonestrus
        Gonadal activity : Differentiation of follicle and CL (Ovarian status-follicular or luteal.)
        
        Ovarian status in dog and cat can be determined by performing vaginal cytology (estrogen effect) and measure serum progesterone level
        
        Identify CL as CL represents the culmination of
        follicle growth and ovulation
- - - - E.g: 6-12M (cat & dog) , 7-8M (goat & sheep), 8-12 M (cow), 12-18M (horse)
    - - the sensitivity of the hypothalamus to decrease in response to negative estrogen feedback.
  - - - Gonadotropin secretion can be increased, or can be normal,
        because of the lack of estrogen and therefore lack of negative
        feedback on gonadotropin secretion
- - - - In sheep and goats, estrus occurs in response to estrogen only
        if the animal has been exposed previously to progesterone
      - The requirement of progesterone
        for sexual receptivity means that the first follicular phase of the breeding season, which leads to ovulation
  - - - preovulatory gonadotropin surge is the result of
        an increased rate of pulsatile release of gonadotropins
- - - - A positive response to a change in the photoperiod usually occurs relatively soon after the occurrenceof the summer or winter solstice
      - A negative response to a change in photoperiod usually requires a longer duration for an effect
    - - Exposure to artificial lighting regimen (for mare)
        
        If the photoperiod is established before the end
        of ovarian activity in the autumn, cyclical ovarian activity continues through the time associated with anestrus.
      - Melatonin can be orally fed/systemic administrated to sheep & goat to make them cycle during anestrus
  - - - sows do not come into
        estrus until after piglets are weaned
      - importance of suckling with its related stimulation
        of prolactin synthesis
        
        Inhibiting factors for prolactin
        synthesis, including dopamine and the GnRH-associated peptide,
        need to be suppressed
        
        GnRH-associated peptide are essential links in the synthesis of
        gonadotropins
        
        Increase prolactin= decrease inhibiting factor = decrease GnRP synthesis n release =reduce ovarian activity
  - - - Sex pheromone affects sex behavior
        
        Arise from sebaceous gland, reproductive tract and urinary tract
    - - synchronization of estrus in female mice through the sudden
        introduction of a male
        
        stimulate the synthesis of GnRP
        
        influence the onset
        of puberty in pigs.
        
        Manipulate estrus cycle
    - - blockage of pregnancy
        development
        
        effect of the odor of the strange male is to block the release of prolactin
        
        CL regress and causes fetal loss
    - - methyl-p-hydroxybenzoate, isolated from the vaginal secretions of dogs
        
        produced intense anogenital
        interest by males
      - sight of the male by the female, as well as physical contact, influence gonadotropin secretion and thus
        ovarian activity.
  - - - extra nutrition in the postpartum period to reestablish ovarian activity because they have requirements for growth as well as for lactation
- - - - mechnoreceptor send impulses when by suckling n milking stimulation to hypothalamus
        
        hypothalamus release oxytocin form pos.pituitary, block the prolactin-inhibiting neuron
        
        oxytocin causes contraction of myoepithelial on alveolar cell
        
        lactotrophic cell produce more prolactin for milk secretion
- - - - produce connective tissue to wall off infection , limit area for duct n alveoli proliferation, reduce milk-producing potential
  - - - exposure of to ovarian hormone, increase chance
        
        less chance of getting neoplasia if being oviaroectomized before first estrus cycle
  - - - why this happened?
        
        fetal RBC pass into maternal system, causes formation of antibody ,concentrated in colotrum ,absorb by neonate
      - need blood transfusion,as hemolytic crisis happened
  - - - unable to respond immediately to the calcium drain from
        the blood by the mobilization of calcium
        
        lose their ability to maintain normal muscle activity;
- - - - 2 different phases in final antral follicle development : slow phase n acceleration phase ,terminate in ovulation (4-5 days per phase)
        
        for final growth phase, initiated by slow pulse rate of gonadotropin release during luteal phase , rapid growth phase required fast pulse gonadotropin release by day 3-4.
        
        antral follicle must be acted
        on through proper gonadotropin stimulation during rapid growth phase, if not they regress
      - maintain its status by producing other follicle developing inhibitant . e.g:inhibin that inhibit FSH
        
        dominant follicle is able to compensate
        for the lower FSH concentrations and continue tp grow because of the numbers of FSH receptors it has compared withcompetitor follicles.
  - - - LH block oocyte-inhibiting factor and luteinizing-inhibiting factor which allows oocyte from resuming meiosis and granulosa cell from becoming luteal tissue
        
        surge of LH causes
        
        formation of first polar body
        
        transform cell to secrete progesterone
        
        cause the granulosa to produce substances, such as relaxin and prostaglandin F2α
        
        affect the continuity of the connective
        tissue of the thecal layers
        
        development of vesicles (within fibrocytes) that contain hydrolytic enzymes that break down the collagen matrix of connective tissue.
        
        follicle rupture
- - - - Allow newly formed conceptus to synthesise and release factor to maintain CL
    - - For nonpregnant animal to return potentially fertile state
  - - - The mode of transfer of PGF2α from the uterus to the ovary occur by
        
        Countercurrent transfer
        
        involves the movement of molecules across the blood vascular system
        
        general systemic transfer
        
        through the general circulatory system.
      - pattern of synthesis and release of PGF2α is essential to its luteolytic effect
        
        must be pulsatile, with pulses occurring at about 6 hour intervals for luteolysis to be affected
        
        PGF2α synthesis ceases 6 to 12 hours after progesterone concentrations have become basal,that is, with the completion of luteolysis
        
        PGF2α affect
        the CL to cause both a reduction in progesterone production and the release of luteal oxytocin.
        
        Oxytocin then interacts with receptors
        within the uterus to initiate another round of PGF2α synthesis
        
        Changes in PGF2α
        Synthesis,changes luteal life span
        
        Prolonged luteal phase due to :Presence of embroyo that blocks synthesis , Uterus infection and absence of uterine horn, bacterial contamination on endometrium
- - - - In primates: no significant follicle growth occurring until luteolysis is complete
      - large domestic animals, much of the follicle growth is
        telescoped into the luteal phase
  - - - Copulation replaces estrogen as the
        stimulus that induces the ovulatory release of gonadotropins.
        
        cohorts of follicles develop, are maintained in
        a mature state for a few days, and then regress
        
        Follicle growth
        patterns can be distinctly separated,
  - - - Copulation initiates the release of prolactin
        
        prolongation of luteal activity for up to 10 or
        11 days in the absence of pregnancy.(pseudopregnancy)
- - - - In mares, More light =less melatonin= higher GnRH level=stimulation of ovaries
      - In goat& sheep : more light =less melatonin= lower GnRH = less stimulation of ovaries
        
        so they are short day breeder
        
        Cyclical ovarian cycle in diifferent animal
        
        Long day : Sexually active in spring /summer(Horses,cats,hamster)
        
        short day: Sexually active in fall/winter (goat &sheep)
      - Cat very sensitive,a total photoperiod change as brief as 15mins can be translate into ovarian activity