Summary Class notes - adp-21803

- adp-21803
- Nicoline Nieuwenhuizen-Soede
- 2018 - 2019
- Wageningen University (Wageningen University, Wageningen)
- Dierwetenschappen
135 Flashcards & Notes
1 Students
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Summary - Class notes - adp-21803

  • 1581202801 puberty

  • Puberty
    - reached when the animal is able to release gametes and manifest complete sexual behaviour
    - the whole periode in which an enhanced growth of reproductive organs takes place
    - period in which the secondary sex characteristics appear
  • Puberty in female mammals
    - The age at which the first oestrus with ovulation occers followed by regular cycles 
  • Puberty in male mammals
    - The age at which the animal can produce and ejaculate with fertile sperm cells 
  • Puberty is the result of...
    - an adjustment between increasing gonadotropic activity of the anterior pituitary lob (LH and FSH)
    - the ability of gonads to reacts to these gonadotropins by producing steriods (oestrogen and testosterone) and gametes (oocytes and sperm cells)
  • 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
  • Concentrations of gonadotropins
    - the concentration increase as a result of both the amplitude and frequency of the gonadotropins pulses
    - when the level of sex steroids is high enough the secondary sex characteristics can develop and reproductive organs can grow
  • The difference between males and females
    - lies in pre-natal development
    - foetal ovaries produce oestrogens (E2) -> are bound to alpha-fetoprotein -> prevents it from entering the brain -> hypothalamus feminizes -> develop a GnRH surge centre  - foetal testicles produce testosterone (T) -> can freely enter the brain -> converted into estradiol -> defeminises the brain
  • Changes in the reproductive organs during puberty
    - Testes growth -> interstitial tissue (mostly leydig cells) + seminiferous tubulus develop  
    - high increase of Leydig cells during puberty as a consequence of LH

    - 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      
  • Age at first oestrus
    - is highly variable among species
    - it is genetically determined 
    - can also be influenced by environmental factors
  • 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
  • Oogenesis
    - the formation of ova (oocytes) in a procces that follows 5 steps. 
    1. diploid primordial germ cells to ->
    2. diploid oogonoia through meiotic divisions ->
    3. diploid primary oocytes with their first nuclear development at the prophase of the first meiotic division to ->
    4. haploid secondary oocyte in the metaphase of meioisis 2 after LH surge to ->
    5. zytoge with a male and female pronucleus  
  • Menopause
    - all potential gametes are present in the ovaries as primary oocytes
    - the numbers are reduced by artersia or ovulation and when the follicle pool is depleted -> menopause
    - in males -> spermatogonia continue to multiplicate and differentiate to form sperm cells    
  • Follicle development
    - follicles develop around each oocyte
    - develop from a primordial follicle to an antral follicle (80-100 days)
    - most follicles go into atresia but under the right conditions a selection from the antral follicle pool will be stimulated to develop and finally ovulate   
    - oocyte matures -> The zona pellucida is formed and the oocyte develops and grows by own synthesis and incorporation of material from the surrounding granulosa cells 
  • Primordial follicle
    - a primary oocyte with zona pellucida -> surrounded by one layer of flat epithelial cells. 
    - from the primordial follicle pool groups of follicles start their developement
  • Primary follicles
    - the oocyte increases in size and epithelial cells become more cubic
  • Secondary follicles
    - become surrounded by several layer of epithelial cells (granulosa cells now) -> producing theca-cell0organiser factor -> transform the interstitial tissue into a theca interna layer surrounding the follicle
  • Tertiary follicles (antral follicles)
    - the layer of granulosa cells form fluid filled cavities -> antrums
    - for antrum formation FSH and LH are necessary
  • 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
  • Recruitment
    - escape from atresia -> initiated by the hypothalamus
    - GnRH leads to pulse wise of LH + continuous FSH secretion by the pituitary -> antral follicle pool develop into Graafian follicles
    - progesteron dominance -> suppression of GnRH -> antral follicles cannot escape from the follicle pool
  • Selection
    - the larger follicles in the antral pollicle pool will reach the stage of Graafian follicle 
    - these larger follicles secrete inhibin -> blocks the FSH release as FSH is no longer necessary -> LH stimulates their future development 
    - smaller follicles still require FSH and will go into atresia
  • Dominance
    - selected follicles produce increasing amounts of estrogens
    - this stimulates the proliferation of granulosa cells and production of follicle fluid
    - these estrogens give negative feedback to the hypothalamic GnRH release
  • Ovulation rate
    - recruitment, selection and dominance result in a limited number of pro-ovulatory follicles 
  • Spontaneous ovulators
    - the endocriene processes in the follicular phase result in ovulation and without an external simulus 
  • Reflex ovulators
    - ovulation only occurs after mating
    - mating stimulates sensory nerves in the vagina and cervix -> activates GnRH surge in the hypothalamus through the spinal cord 
  • Pre-ovulatory processes
    - The apex or apical side of the follicle lies at the outside of the ovary and contains multiple tissue layers
    - ovulation is not possible until all these layers have disappeared
    - through cellular and biochemical changes
  • Cellular changes
    - at the apex -> granulose cells disappear
    - the oocyte can now move freely in the antrum
    - lysosomes from the surface in the apex secrete lysozymes that hydrolyse the underlying tunica albuginea and thecal cells
    - results in a weaking of the apical follicular wall -> the weakened part is the stigma
  • Biochemical changes
    - LH surge -> follicle starts to produce progesterone -> necessary for ovulation 
    - concentrations of prostaglandins (PGF2a and PGE2-alpha) increase -> important role in follicle rupture 
    - PGF2-alpha influences the lysosome to release lysozomes
    - smooth muscle contractions (by PGE2) cause rupture of the stigma -> the oocytes are expelled from the follicle 
  • Nuclear maturation
    - the changes that occur in the nucleus of the oocyte after the LH surge
    -  The oocyte resumes meiosis and matures up to the metaphase of the second meiotic division 
    - second meiotic division continues after fertilization
  • Cytoplasmatic maturation
    - changes in the cytoplasma of the oocyte related to changes in matabolism of the granulosa cells and composition of the follicle fluid 
  • Cyclicity
    - estrous cycles consist of a series of predictable vents beginning at oestrus (or ovulation) and ending at the subsequent estrus
  • Oestrus cycle
    - is divided into two phases
    1. follicular phase
    2. luteal phase  

  • Follicular phase
    - stage in which the secreted follicles develop
    - produce estrogens
    - induce a LH surge
    - and ovulate
  • Luteal phase
    - corpora lutea have developed from the follicle
    - produces increasing amounts of progesterone, inhibiting GnRH secretion and thereby LH and FSH release
    - follicle development is limited
    - at the end of the luteal phase -> the corpus luteum goes into regression -> except in the case of pregnancy
  • Cyclicity patterns
    - poly-oestrous: series of oestrous cycles when not interrupted by pregnancy
    - seasonally poly-oestrous: series of oestrous cycles but not in a certain period of the year
    - mono-oestrous: showing only one oestrus at irregular intervals
  • 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
  • Seasonal breeders
    - some species do not cycle all year and the cycle depends on the day lengths and temperature 
    - especially the changes in day light influence cyclicity 
    - photoreceptors in the eye stimulate the pineal gland to produce melatonin during dark hours -> short days result in high melatonin levels    
    - melatonin affects the sensitivity of the hypothalamus to oestrogens -> negative feedback and GnRH change, affecting follicle development  
  • Spermatogenesis
    - development of sperm cells within the male reproductive organs 
    - takes place in the seminiferous tubulus -> consisting of a basal membrane and the seminiferous epithelium
    - the latter consists of Sertoli cells and the deviding and differentiating of germ cells
    - consists of three stages: spermatocytogenisis, spermoiogenesis and spermation      
  • Spermatocytogenesis
    - developement from type A1 spermatogonia to type B to spermatids 
  • Spermiogenesis
    - the morphological transformation from the round spermatids into sperm cells
    - mostly under influence of the Sertoli cells
    - No cell division takes place 
    - the cell almost loses all of its cytoplasma
  • Spermation
    - release of complete sperm cells in to the lumen of the tubuli seminiferi 
  • Morphology of sperm cells
    - consists of the nucleus
    - anterior end is covered by the acrosomal cap
    - containing hydrolytic enzymes -> important role in the fertilization of an oocyte

    - 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          
  • Blood-testes barrier
    - sperm cells in the tubulus are protected against blood by a special barrier to prevent antibodies being made against the own haploid sperm cells
    - to create a stable environment
    - consists of contractile myoid cells in the basal membrane of the tubulus   
  • LH (spermatogenesis)
    - stimulates the Leydig cells to a pulsatile release of androgens
    - these diffuse to the sertoli cells -> from there to the blood -> negative feedback on the hypothalamus and pituitary
  • FSH (spermatogenesis)
    - stimulates the Sertoli cells to produce inhibin and androgen binding protein (ABP)
    - inhibin has a negative feedback on FSH
    - ABP forms a complex with the androgens from the Leydig cells -> high androgen content -> needed for the normal function of epididymus epithelium and for the maturation of the spermatids   
  • 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 
  • Epididymis
    - sperm cells undergo a maturation process
    - involving several functional changes leading to fertility 
    1. development of sustained motility
    2. progressive loss of water
    3. distal migration and eventuel loss of the cytoplasmatic droplet
    4. cell organelles and acrosome mature + chromatin of the nucleus changes

    - the caudal epididymis stores 70% of spermatozoa
  • Unejaculated sperm
    - gradually eliminated by excretion into the urine
    some degenerate and are re-absorbed by the epididymis and ductus deferens  
  • The ejaculate
    - triggered by stimulation of the sensory nerve cells in the penis
    - by a combination of pressure and temperature 
    - causing contraction of the muscle cells of the vas epididymis, vas deferens, urethra and accessory sex glands
    - ejaculate contains sperm cells and seminal plasma for the transport of sperm cells to the female reproductive tract     
  • Seminal plasma
    - originates from a number of sources
    - testes, epididymis and accessory glands
    - contains organic components such as fructose, ascorbic amino acids, lipids, immunoglobulins and hormonal substances
  • Abnormal sperm cells
    - due to failure of spermatogenesis
    - include abnormalities of the mid piece and tail
    - selection occurs by selective resorption or lysis
    - occurs during the passage through the epididymis 
    - include tailless, heads, cytoplasmatic droplets or bent tails
    - occuring during or after ejaculation
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