Lecture 20: Reproduction during the lifetime Flashcards
What is Sex determination?
commitment of the Indifferent gonad to a testis or an ovary
-regualted in one gene by humans
When the bi-potential gonad which arises from mesodermal tissue in the early developing body’s gonadal ridge, and by default the gonad will become an ovary, if the Y chromosomes is present, the gonad will develop as testes, if there is a mutation in the SRY gene the gonad will develop into an ovary
How is sex determination controlled in mammals?
genetically
How many chromosomes does a human have?
46 chromosomes
22 pairs of autosomes
1 pair of sex chromosomes
What does XX represent?
Normal female
y-chromosome is absent
female gonads develop as ovaries
could be X or XXX
What does XY represent?
Normal male
y-chromosome present
Male gonads/testes develop
What is the sex determining factor?
SRY gene on the Y chromosome
chromosomally activated
Sex-determining Region on the Y chromosomes
What does the Sex determining Region on the Y chromosome provide?
SRY gene provides the Path for the tests to develop
The presence of testis determines the sexual fate of the embryo, against the basic female trend
In the absence or mutation of SRY, the embryo developed int a female
What occurs with menopause?
Loss of oestrogen
When does differentiation occur?
After the Gonad has been determined
What does the Y chromosome contain?
a Sex determining region on the Y gene
basis for testes to develop
determines the sex in humans
with it you will form a penis
What is the basic human trend?
Everything in the body will become female unless and intervention (y chromes) causes it to form male testes via male testicular hormones - interfere with trend to become female
What happens in the absence of the SRY gene?
the human becomes a female
What is the hormonal intervention in sex determination?
masculinity must be imposed against an inherent trend towards females
or in other words, hormonal intervention to stop body becoming female
What is sex differentiation?
the phenotypic development of genital structures due to the action of hormones produced following gonadal development - affect external and internal genetalia
What is the Internal Genetalia?
the female structure (Mullerian duct) and male structure (Wolffian duct)
both present early on in development
When and from where do the gonads develop?
Gonads develop from the intermediate mesoderm
during the 5th week of development
What is the Mullein duct?
eventually forms structures of the reproductive system in females
What is the Wolffian duct?
eventually develop into male reproductive system
When is the undifferentiated state?
5th week embryo
What is the undifferentiated state?
EARLY in development,
BOTH sets of internal genital ducts are present
- Mullerian duct (female) and Wolffian duct (male)
What is the internal female genital?
uterine tube uterus upper part of vagina \+ male parts regress = happens by default
Overall what does the Male differentiation involve?
Mullerian duct regressions + Wolffian duct development and maintenance
The testis descend from its internal position (para-renal)/High in the Pelvic Cavity to –> the scrotum,
usually after the 7th month
What are the two different types of cells involved in male differentiation?
Lydia cells
Sertoli cells
What does the Mullerian duct regression involve?
occurs under the control of AMH - Anti-Mullerian Hormone
AMH is secreted by the Sertoli cells
What does the Wolffian duct development and maintenance involve?
is due to the testosterone
Testosterone is secretes by the testis –> Leydig cells
This Actively maintains the Wolffian ducts
The wolffian ducts develop into the (male Internal geneitalia) epididymis, vas deferens, and seminal vesicle
What do the Wolffian ducts develop into?
Epidiymis
Vas deferens
Seminal Vesicle
What do the sertoli cells produce?
AMH
What produces AMH?
Sertoli cells
How many hormones do the testes make and which ?
Two
AMH and Testosterone
What is no intervention equivalent to?
No male hormones (No AMH or Testosterone present)
At what time in a males life do the testis descend into the scrotum?
7months
What does female differentiation occur?
9th week
What does female differentiate involve?
occurs about the 9th week
is Slower than male differentiation due to there being no active hormonal intervention
What happens in the Wolffian ducts in female differentiation?
The wolfing ducts begin to spontaneously regress slowing from about 10 weeks
What happens in the Malarian ducts in female differentiation?
The Malarian ducts persists and develop to give rise to : Uterine (fallopian) tubes uterus cervix upper vagina
What is external genetalia?
the male and female external genetalia develop from a single bipotential precursor
What is the bipotential precursor?
early undifferentiated state, no action of androgens yet
What happens during male differentiation?
ANDROGENS produced by the testes convert testosterone –> 5a DHT, this brings about most changes in external male genetalia
FUSION of the urethral folds ENCLOSING the urethral tube form the shaft of the penis
-if insufficient androgen, doesn’t occur. won’t urinate from tip of the penis but will from the side (hypospadia)
Labioscrotal swellings tube in midline forming the scrotum (-empty for testes) (scrotalisation)
the genital tubercle (glans area) expands forming glans penis
What is hypospadia?
If there is INSUFFICIENT ANDROGEN during the developmental process, the enclosing of the urethral folds to form the urethral tube doesn’t occur and won’t form the shaft of the penis
therefore the male won’t urinate from the tip of the penis, but will urinate from the side
What happens during female differentiation?
the urethral folds and labioscrotal swellings remain separate, thus forming the labia minor and major
the genital tubercle (glans area) forms the clitoris
What another name for the glans area?
genital tubercle
What is Androgen resistance syndrome?
- the person is XY and has testes - but the genital ducts and/or external genetalia are female
- the person has a Mutation in their Androgen Receptor Gene which prevents androgen function
- in the absence of androgen action, the external genetalia which prevents androgen function
- in the absence of androgen function the external genetalia will appear female - can have testes inside labia
What is puberty?
The development of secondary sexual characteristics
and the potential for reproduction is achieved
the physical, emotional and sexual transition from childhood –> adulthood
marked by pulses of LH due to pulses of GnRH, mostly occurs during sleep and becomes something in the day
What is the transition of puberty like?
the transition is GRADUAL and is Punctuated by well defined events ad milestones
What happens when there is hormonal changes during puberty?
BEHAVIOURAL responses physical changes (e.g. body shape in boys/girls determines by diff effects (androgen and oestrogen)
When does the repro system “go to sleep”?
following activity in the developing embryo to produce internal and external genitals, the reproductive system “goes to sleep” during childhood –> = about 10 years
What is puberty is relation to the endocrine system?
puberty is the RE-awakening of the reproductive ENDOCRINE system, which leads to full secondary maturation with the capacity of reproduction –> hormone lectin
What is the mechanism which holds reproductive function?
the mechanisms for keeping reproductive function on hold during childhood are largely unknown, as the neuroendocrine events that trigger puberty
What happens to the plasma levels during puberty?
plasma levels of gonadotrophin (FSH and LH) are low during childhood and until initiation of events leading up to puberty and the RISE
What is the Diurnal changes in pulsatile release of LH at puberty?
an increase in plasma LH (pulses) levels is the first endocrine sign of puberty - it is the results of an increase in GnRH release
Gonadotropin release (both LH and FSH) occurs EARLY in puberty at night during sleep
At LATE puberty, daytime LH pulses also increase
SEX steroids rise in response to the increase in plasma LH (males testosterone)(female - some follicles growth -produce granulose cells -oestradiol)
What are the sexual characteristics?
characterisits devleop at different chronological ages in different individuals sequence of these events/changes are characteristic for each sex staging criteria (tanner stage) allows for abnormalities to be detected, and comparisons made between individuals
What are the 4 Tanners stages during female puberty?
- breasts
- sexual hair development
- growth spurt
- manarche
(5-ovulation)
What is the first tanner stage in the female sequence of puberty?
Breasts
first sign of 2 secondary maturation
What happens to the breasts during the first stage of female reproduction?
- first sign around 10-11
- Secretion of oestradiol by ovarian follicle leads to the appearance of a breast BUD, followed by the formation of a breast MOUND
- high LH causes estradiol production, by granulosa cells of small follicles, which don’t ovulate until later, and don’t mature properly
- Ovulation, with corpus luteum and therefore subsequent progesterone secretion, leads to full breast development
What is the second event in the female sequence of puberty?
Sexual hair development
second sign
What is the role of the male genetalia?
provide the link between the inside of the reproductive system –> to the outside world
Where are the testes early on in development?
essentially where the ovaries are in woman
What temperature do the testes need to be at to be effective?
Below core body temperature
How often does male differentiation occur?
in Most boys
-not all, especially boys born EARLY
Does female or male differentiation lag behind?
female differentiation is slower as there is NO active hormonal intervention driving the process
What is the Malarian duct essentially in a woman?
the structures which take the e.g. out to the vagina
What does the early external genetalia look like?
undifferentiated
couldn’t tell the difference
(5th week)
same in both males and females
Where are the labia scrotal swellings?
on the outside of the external genetalia
What is the first endocrine sign of puberty?
rise in LH
What is the first real sign of puberty?
rise in GnRH which leads to a rise in LH
Why do we have the Tanner stages?
age and sequence of steps to ensure everything is okay
-some develop early or late due to some serious reasons
therefore have the Tanner staging criteria to allow for any abnormality to be detected. and to allow for some comparison between individuals
What sort of steps does puberty arise in?
Puberty arises in a series of discrete steps
What happens to sexual hair development during the second event in the female sequence of puberty?
sexual hair development is the second sign of 2 secondary sexual maturation
- occurs usually within 6 months of the appearance of the breast bud at age 10-12
- due to the exposure of hair follicles to Androgens
- slow process
- occurs after breast development
- auxillary hair (armpit hair) follows= one year after pubic hair
What is auxiliary hair?
armpit hair
When does auxiliary hair form?
1 year after the growth of pubic hair
What does the early exposure of sexual hair development indicate?
Earlier than 6 months after first appearance of breast
Indicate Excess Androgen
What is the third event in the female sequence of puberty?
growth spurt
body shape - breasts, redistribution go fat due to oestrogen’s
increases pelvis width - for child birth
When does the growth spurt occur in girls?
11-12 years
(2 years earlier than males)
smaller height gain
shorter time period of growth
When does the growth spurt occur in males?
13-15
–>grown LATER but grow for a LONGER period –> therefore TALLER
What happens during the third event in the female sequence of puberty?
Body shape - breasts -redistribution of fat due to oestrogen’s
-increased width of pelvis - for childbirth
Growth is stimulate by steroid hormone (Oestrogen and Androgen)
with an Epiphyseal closure (bony ends) by oestrogen
What is the mechanism to end the growth of bones?
Epiphyseal closure (closure of the boney ends) driven by oestrogen
What do males need Oestrogen, even at just low levels?
As the Oestrogen triggers the mechanism which ends bone growth,
Epiphyseal closure occurs, closing the boney ends
What is the fourth event in the female sequence of puberty?
Menarche is the First menstrual bleed
What happens during the fourth event in the female sequence of puberty?
Menarche occurs at an average age of 12-13 years - first bleed
the first ovulation does not take place until 6-9 months after menarche as the Positive feedback mechanism of Oestrogen have not yet developed
Regular ovulatory cycles are established 1-2 years after menarche
- Most woman only form ager of 20 onwards
What is the average age for menarche to occur?
12-13 years
When is woman normally fertile?
a woman is actually fertile/have her first ovulation until 6-9 months after her first menarche
When the menstrual cycle consolidate itself?
in most woman, not until the age of 20
What is the order of 4 events in the male sequence of puberty?
- Testis
- Pubic Hair
- Penis
- Growth spurt
What is the first event in the male sequence of puberty?
Testicular (and Penile) Enlargement
What happens in the first event in the male sequence of puberty?
Testicular enlargement
First sign of secondary sexual development is the enlargement of the testicles
Lydia cells enlarge and release TESTOSTERONE –> it is this which gives rise to an increased testicular size
due to increased activity
What is the second event in the male sequence of puberty?
Sexual hair growth
What happens during the second event in the male sequence of puberty?
- Pubic hair appears about 6 months after beginning of testicular enlargement of peripheral
- Auxillary hair - about 18months later –>
- Then facial hair later than that
Androgen brings about the chance in auxiliary hair, larynx and voice drops
What is the third event in the male sequence of puberty?
Enlargement of the penis
What happens during the second event in the male sequence of puberty?
Elongation and enlargement of the penis begins within a year testicular enlargement
Induced by the activity of more potent form of testosterone (5 a dihydrotestosterone)
What is the fourth event in the male sequence of puberty?
Growth spurt
What happens during the second event in the male sequence of puberty?
Growth spurt is 2 years later in boys but prolongs for longer
Body shape - More muscular, in response/due to androgens
What is Spermache?
Motile sperm is seen in urine at 13-14 years onwards(surrogate marker)
First conscious ejaculation occurs soon after
“End point of spermatogenesis, first sight that boy is consciously fertile”
What does the timing of a girls first menstruation how?
The age at which girls first menstruate shows a clear trend toward Early Menarche in girls
What must occur before HPG axis activation in girls?
In girls, a critical weight (=47 kg) must be attained before the activation of the hypothalamic-pituitary-gonadal axis can occur
- mechanism unknown, could be weight or fat (muscle ratio)
- possibility of hormone actin
What is the mean weight of girls at the beginning of menarche?
Mean weight of girls at the beginning of menarche is - about 47 kg
-but there is large margin of error
What is the importance of the critical weight in girls?
Attainments of a critical weight due to improvements in nutrition, healthcare and social living conditions – obesity?
signifies that sufficient storage is required to sustain pregnancy and lactation
What is precocious puberty?
Early onset puberty
What occurs during precocious puberty?
the appearance of the physical and hormonal signs of puberty -before 7 years in girls (more common)
- before 9 years in boys
usually DUE TO a GnRH dependant problem, often due to a CND lesion or injury (e.g. tumour in hypothalamus or pituitary)
What is delayed puberty?
Late onset puberty
What occurs during delayed puberty?
Shellack of appearance of the physical and hormonal signs of puberty - 13 years in girls - 14 years in boys (more common)
Occurs when the Gonadotrophin signals from he Pituitary are inadequate for sex steroid secretion
What is Menopause?
ovaries run out of follicles and the cessation of the menses
End of reproductive life
When does Menopause occur?
occurs between 50-52 years of age
What occurs during menopause?
The last episode of natural menstrual bleeding signifies the end of her reproductive life (menopause)
What is the time line of follicular numbers?
During fetal development, around = 7 million follicle develop
By birth the number of follicles has decline to 1-2 million
There is a GRADUAL decline of follicles from:
a. Puberty - 400,000 follicles
through to –>
b. menopause -
What occurs during the pre menopause period?
regular periods
What occurs during the menopausal transition?
variable duration
menstrual bleeds are irregular –> longer bleeds
What occurs during post menopausal oestrogen production?
By about 1 year after Menopause, the ovary has essentially ceased/stopped producing hormones -ovarian senescence Oestragen production (oestradiol primarily) resduces to less than 1/10th of previous levels Oestrogen (oestrone) arises mainly from production of it in stream cells of adipose tissue (only oestrogen produced) - weak oestrogen
What are the Perimenopausal symptoms?
Most woman experience a variety of diueal symptoms of Oestrogen Deprivation during the perimenopause -- more than age Vasomotor Genitourniary symptoms Bone metabolism Behavioural and Psychological changes
What does the Peri-menopausal symptom of vasomotor include?
Blood vessels change the shape leading to vascular problems
- hot flush - overwhelming overheating and out of control, associated with panic
- night sweats -hard to adjust body temp, don’t sleep well, discomfort
What does the Peri-menopausal symptom of Genitourinary symptoms include?
No production of oestrogen
Vaginal dryness
-reverse of puberty when there are secretions
ain during intercourse
What does the Peri-menopausal symptom of Bone metabolism include?
increased risk of osteoporosis
What does the Peri-menopausal symptom of Behavioural and Psychological changes include?
find that these changes hard to deal with
depressions
tension
anxiety
mental confusion
decrease in libido (due to changes in testosterone levels)
What is the treatment for Perimenopausal symptoms?
HRP or hormone replacement (given woman oestrogen back) therapy
can reverse, prevent or arrest symptoms by oestrogen treatment
-but there are associated risks (e.g. breast and endometrial cancer more likely)
but for some the pain is so severe that it is needed
Where does spermatogenesis occur in men?
Prior to the height spurt
What is the order of facial hair development in males during puberty?
- pubic hair (6 months after testicular enlargement)
- auxillary hair (18 months later)
- facial hair
- changes in layrnx
What is changes in the larynx mediated by?
testosterone
What is a surrogate maker in relation to spermache?
Easier to have urine samples, and observe motile sperm
What are some physical development differences between males and females?
woman have more fat
- different body shape
- woman fat resides on hips, pelvic anatomy - to assure birth canal is more optimal
What happens when female hormones stop presenting themselves during puberty?
Females start presenting a more male shape
What is a clear evolutionary change shown in woman?
Time of menarche
we get it earlier (150)
prior puberty = 17 years
Now an extra 5 years of reproductive life as a woman
What does an early reaching of 47kg suggest?
critical weight
girls will reach menarche earlier
How do girls periods sometimes stop?
The woman loses weight and goes below 47kg
this is what often leads to a girl’s period stopping
What does the critical weight of 47 kg signal?
There is sufficient weight to maintain pregnancy and
an ability to lactate afterwards
What is the age range of a woman with precocious puberty?
before 7 years
What is the age range of a male with precocious puberty?
before 9 years
What is precocious puberty usually due to?
GnRH
normally tumour in hypothalamus or pituitary
What is the age range of a woman with delayed puberty?
over 13 years
What is the age range of a man with delayed puberty?
over 14 years
What is delayed puberty usually due to?
inadequate levels of GnRH
problem with hypothalamus and pituitary
Do many species go through menopause?
no
humans are one of the few
How many follicles does a woman begin with?
around 7 million follicles
How many follicles is a woman born with?
1-2 million follicles
Has the age of menarche changed dramatically?
yes 17 –> 12
Has the age of menopause changed dramatically?
no always 50
By what age has the majority of a woman’s good follicles gone?
40
can no longer be guaranteed to have a baby
By menopause how many follicles do you have?
1 or 2
But the DONT respond to hormones
What is a woman’s menstrual cycle like from the age of 40 onwards?
regular
What is a woman’s menstrual cycle like from the age of 46 years?
irregular
What is the name for the last menstrual bleed?
menstruation
50yrs-52yrs
What is the time of regular menstrual bleeds called?
pre menopause
40-45
What is the time of irregular menstrual bleeds called?
menopausal transition
large bleeds too
5 ish years
Which phase in the end of a female reproductive life is highly variable among woman?
menopausal transition
What is the function of the ovary like after menopause?
continues to work for another year prudces a small amount of hormones The bstios (ovarian senescence)
What is ovarian senescence?
when the ovary stops producing hormones
1 year after menopause (the last menstruation)
What does the peri menopause mean?
time around menopause
When does peri-menopause occur?
Beginning of menopausal transition –> beginning of ovarian senescence(year or two after menopause)
What happens to oestrogen concentration after menopause?
Drops significantly
Primarily oestradiol concentrations
instead OESTRONE is produced
-SMALLER amount of a WEAKER oestrogen
Where do men get all their oestrogen from?
OESTRONE
from ADIPOSE tissue
(is weak)
What do the permenopausal symptoms resemble?
the reduction of oestrogen production in woman in this age
What is the time period of female reproduction?
female reproduction is time limited
menarche –> menopause
BUT most woman still aren’t fertile during menopause - due to decrease in oestrogen
What is menopause (in conclusion)?
The complete cessation of menstruation
What are the most common peri menopausal symptoms in woman?
hot flushes
night sweats
vaginal dryiness
