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• puberty

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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