Summary Reproduction and fertility

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Summary - Reproduction and fertility

  • 4 Puberty

  • when has a male of female reached puberty and what does it contain?
    when its able to release gametes and to manifest complete sexual behavioural sequences
    • Females mammals: the age at which first oestrus (excluding primates) with ovulation occurs, followed (in non-pregnant mammals) by regular cycles
    • Male vertebrates: the age at which the animal can produce an ejaculate with fertile sperm cells
  • what is the definition of puberty?
    The whole period in which an enhanced growth of the reproductive organs take place and in wich the secondary sex characteristics appear
  • what is the function of the pituitary gland, steroids and gametes in males/females by puberty
    • Pituitary gland: producing LH and FSH
    • Steroids: in females = oestrogens, in males = testosterone
    • Gametes: in females = oocytes, in males = sperm cells
  • what is causing the onset of puberty?
    stepwise desensibilisation of the hypothalamus for the negative feedback of the circulating seks steroids --> the hypothalamus becomes less sensitive to this negative feedback.
    • Causes a rise of GnRH / LH / FSH / seks steroids
  • By the onset of puberty the pituitary becomes more responsive to GnRH. this results in:
    • Higher levels of gonadotropins
      • increase as a result of an increase in both the amplitude and frequency of the pulses of gonadotropins
      • Results in oestrus with ovulation/oocytes and ejaculation of fertile sperm cells
    • Higher levels of sex steroids
  • what is the cyclical pattern of females and males?
    • Females: cyclical pattern, resulting in periodic oestrogen (oestradial E2) peak -> Induce an LH surge (golf) --> ovulation
    • Males: dont have the cyclical pattern
  • what causes the differences between male and female in prenatal development?
    • Fetal ovaries (females): produce oestrogens (E2) that bound to alpha-fetoprotein, which prevents them from entering the brain. 
    • Fetal testicles (males):  produce testosterone (T), can not bound to alpha-fetoprotein -> testosterone freely enters the brain -> is there converted into estradiol (defeminises the brain) -> males do not develop an GnRH surge centre after puberty
  • Age of first oestrus of rabbits, sheep/goat/pig, cattle, horses is:

    3-4 months
    Sheep, goat, pig
     6-7 months
    11-12 months
    15-18 months
  • what influences age at first oestrus?
    • Insemination
      • Sheep at puberty
      • Cattle 15 months because it is more economically beneficial:
        • less calving dificulties, higher milk production, longer lifespan
      • Pigs 7-8 months, more economically beneficial:
        • lower weight loss during first lactation, improved reproductive performance after first lactation, longer lifespan
    • Age is genetically determined: differences in age at first oestrus betweens breeds of species
    • Influenced by the environment
      • Physical environment, light, temperature, nutrition
    • Genotype-environment interaction: the influence of a certain environmental parameter does not affect all genotypes similarly
  • why is nutrition important for puberty?
    Suboptimal nutrition extends the pre-pubertal phase. 
    • Puberty can not take place until the animal has reached a certain physiological development or body weight
    • In contrast to cattle, age at pubery in pigs is more influenced by age and less by feeding level and growth rate
  • what are seasonal factors?
    Influence of ambient temperature and hours light per day
    • Short day breeders: sheep, feral pig
    • Long day breeders: horses
      • Young in the spring: environmental temperature and food availability ensure high survival chances for their offspring
  • what are social factors in case of puberty in pigs?
    clear influence of mature boar contact on puberty attainment.
    • Auditory, visual, olfactory and tactile
    • Pheromones: most important olfactory stimuli 
      • In boars 3alpha-androstenol
  • 5 male gametes

  • what is spermatogenesis?
    The production of sperm cells from stems cells, spermatogonia.

    Development A1 spermatogonia through spermatocytes and spermatids into spermcells. 
    Round spermatids into sperm cells
  • what are Seminiferous tubules?
    basal membrane + seminiferous epithelium
  • Sertoli cells consists of?
    germ cells
  • what is the foetal phase?
    germ cells divide several times before they become gonocytes
  • what happens in the prepubertal phase?
    Gonocytes develop into A1 spermatogonia
  • What are A and B spermatogonia and what forms do they have and what is the right order?
    A1 -> A2 -> A3 -> A4 -> B spermatogonia
    • Single spermatogonia are called type A and spermatogonia clusters of more than 4 cells are called type B
    • Type B divide once or twice and then become the primary spermatocytes, that are still diploid
      • These cells duplicate their DNA -> undergo meiosis 1 -> secondary spermatocytes -> meiosis 2 -> haploid spermatids
  • What is the function of LH in relation to spermatogenesis?
    LH stimulates Leydig cells to pulsatile release of androgens -> androgens diffuse to the Sertoli cells  -> to the blood -> negative feedback on the hypothalamus and pituitary
  • What is the function of FSH in relation to spermatogenesis?
    FSH stimulates Sertoli cells to produce inhibin and ABP -> ABP forms a complex with the androgens from the leydig cells -> released to the lumen of the seminiferous tubules with the sperm cells -> causes high androgen content of testes secretions
    • Androgen binding protein
    • Inhibin has a negative feedback on FSH production 
  • What is the function of the epidymis?
    transports the sperm cells into the vas deferens
  • What happens with sperm cells during transport to the epidymis?
    Sperm cells undergo a maturation process, and are not able to fertilize ova
  • Where are the sperm cells stored?
    In the caudal portion of epidymis
  • what triggers ejaculation and what is the content?
    pressure and temperature, sperm cells and seminal plasma
  • what is the function of seminal plasma?
    • Transport of sperm cells from the male to the female reproductive tract
    • Isotonic and neutral
  • there are 3 different phases of abnormal sperm cells. what are these phases and what do they do?
    Failure of spermatogenesis

     Passage through the epididymis
    Tailless heads

    Damage during or after ejaculation
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