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Summary - Reproduction and fertility
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:
Sheep, goat, pig
what influences age at first oestrus?
- 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?Primary:
Failure of spermatogenesis
Passage through the epididymis
Damage during or after ejaculation
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