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Summary: Adp-21803

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  • puberty

    This is a preview. There are 56 more flashcards available for chapter 09/02/2020
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  • Two possible mechanisms leading to puberty

    - caused by a stepwise desensibilization of the hypothalamus for the negative feedback of oestrogen and testosterone -> rise in levels of GnRH, LH/FSH and sex steroids
    -
    the pituitary could become more responsive to GnRH and the resulting levels of gonadotropins results in higher levels of sex steroids
  • Changes in the reproductive organs during puberty

    Males:
    - Testes growth -> interstitial tissue (mostly leydig cells) + seminiferous tubulus develop  
    - high increase of Leydig cells during puberty as a consequence of LH

    Females:
    - the first antral follicles appear long before the first oestrus
    - complete follicular development and ovulation are observed only when LH and FSH have reached post-pubertal cyclic profiles      
  • Factors for age at first oestrus

    - nutritional factors: suboptimal nutrition extends the pre-puberal phase. Puberty cannot take place until the animal has reached a certain physiological development 
    - seasonal factors: are mainly the result of ambient temperature and hours of light per day.
    - social factors: in pigs there is an influence of mature boar contact on puberty attainment, as this offers auditory, visual, olfactory and tactile stimuli
  • 2-cell-2-gonadotropin model

    - Theca cells produce androgens (mostly testosterone) when LH binds to LH receptors
    - These androgens diffuse to the granulosa cells which have FSH receptors
    - after binding FSH -> aromatase activity converts testosterone into oestrogens
  • Follicle development during pregnancy and lactation

    - pregnancy -> high progesterone levels -> prohibit follicle development and ovulation
    - after pregnancy -> progesterone concentrations drop
    - during lactation -> follicle development remains suppressed
  • Morphology of sperm cells

    head:
    - consists of the nucleus
    - anterior end is covered by the acrosomal cap
    - containing hydrolytic enzymes -> important role in the fertilization of an oocyte

    tail:
    - central part of the tail -> fromed by an axoneme, composed of nine pairs of microtubules around two central filaments
    - axoneme is responsible for the motility
    - middle piece: axoneme is surrounded by fibres that are surrounded by a circle of mitochondria
    - principal piece: axoneme is surrounded by fibres
    - end piece: contains only the axoneme convered by the plasma membrane          
  • Passage of sperm cells through the epididymis

    - immature spermatozoa -> released into the lumen of the seminiferous tubulus -> swept to the rete testis by fluid secretions -> epididymis -> vas deferens 
  • Abnormal sperm cells

    Primary:
    - due to failure of spermatogenesis
    - include abnormalities of the mid piece and tail
    - selection occurs by selective resorption or lysis
    secondary:
    - occurs during the passage through the epididymis 
    - include tailless, heads, cytoplasmatic droplets or bent tails
    tertiary:
    - occuring during or after ejaculation
  • Cyclicity of sexual behaviour in female mamals

    Pro-oestrus:
    - females become more attractive
    - proceptivity by searching for mates
    Oestrus: 
    - attractivity, proceptivity and receptivity
    - at the end -> surge in LH from the anterioir lobe of the pituitary -> ovulation
    Metestrus:
    - luteal phase of the reproductive cycle 
    - occurring after ovulation
    - development of the corpus luteum 
    - increased progesterone
    - decreased oestrogen
  • fertilisation

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  • Transport of oocytes to the site of fertilisation

    - oocyte transport -> movements of the cilia on the fimbriae
    - coordinated contractions of the fimbriae, the utero-overian ligaments and the mesovarium

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