Reproduction Flashcards
What is sexual determination?
- Genetically controlled process
- Dependent on the “molecular switch” on the Y chromosome
Chromosomal determination of male, or female
What is sexual differentiation ?
- Process by which internal, and external genitalia develop
- As male, or female
• Both of these processes = contiguous , happen at the same time
They consist of several stages
What is the process of sex differentiation- embryo (has genotypic sex, either has a y chromosome or it does not)
- Genotypic sex is present in all eggs, gonadal sex is whether it has ovaries or testes which secrete hormones –> rest of development
- Gender identity = how the patient feels - there are cases where these things are not the same
Genotypic –> gonadal –> phenotypic –> legal sex –> gender identity
What is Gonadal sex - what creates the testis
- “does it have ovaries or testes”
- In the absence of Y chromosome
- Gonads secrete hormones that influence the rest of development,
- which then affects the phenotype, then the ovaries / testes will develop
- Phenotypic sex, whether we have the structure of male or female
- Sertoli cells = anti mullerian hormones
What is Gonadal sex - what is the role of the sex determining region Y (SRY)
Sex determining region Y
- SRY expressed = goes down the male pathway, says “make a testes” - rather than an ovary. SRY = testes
- This will switch on briefly
- During embryo development
- (after week 7)
• This will make the gonad into a testis
○ When there is no SRY7 - an ovary is formed
The testis develops cells that make 2 important hormones - what are they?
sertoli cells + leydig cells
what is the role of sertoli cells
produces anti mullerian hormone, AMH
what is the role of leydig cells
makes testosterone
Describe the process of gonadal development:
BIPOTENTIAL EMBRYO
- After fertilisation, a pair of gonads will develop, that are bipotential
- Their precursor is from common somatic mesenchymal tissue precursors (The genital ridge primordia) - (3.5 to 4.5 weeks)
- On posterior wall of lower thoracic lumbar region.
- Purple ridges = the gonadal, genital ridge which develop into the gonads - there are 2 of them which will either become 2x ovaries or 2x testes
- Hormones that they secrete as a result of this will influence the rest of the development of the embryo
- These 2 ducts determine what is going to be the internal architecture (men: vas deferens and prostrate)
Mullerian = becomes uterus
Wolffian = becomes male architecture
All embryos are capable of differentiation into male or female - this has to be triggered, by a switch of 1 gene on the x chromosome, which is the smallest chromosome and has very few genes on it
what do mullerian ducts become
uterus
what do wolffian ducts become
male architecture
What are the 3 waves that invade the genital ridge
- Primordial Germ Cells
- Primitive Sex Cords
- Mesonephric Cells
role of 1. Primordial Germ Cells?
- Become sperm (male)
- Or oocytes (female)
role of 2. Primitive Sex Cords
- closely associated with the primordial germ cells*
- Become sertoli cells (male)
- Granulosa cells (female)
Associated to the developing sperm / eggs
- 3 cell types that are really critical in the ovaries and testes that are functional = derive from the same cellular origin
- From week 3 they go from the yolk site and colonise the genital ridges
- These germs cells can still be sperm, or eggs. Begin building a gonad as the actual germ cells
role of 3. Mesonephric Cells?
- These will become blood vessels
- And Leydig cells (male)
Theca cells (female)
Describe Primordial Germ Cell Migration
- An initially small cell cluster in the epithelium of the yolk sac; which expands by mitosis [approx. 3 weeks].
- They migrate to the connective tissue of hind gut, to region of the developing kidney and then onto the genital ridge. [completed by 6 weeks]
Describe the primitive sex cords (Sertoli/Granulosa)
- Cells that are from the germinal epithelium that are overlying the genital ridge
- Mesenchyme migrates inwards
- As columns called the primitive sex cords
Describe the primitive sex cords (Sertoli/Granulosa) - what happens in males?
- SRY expression
- Penetrates medullary mesenchyme
- & surrounds PGCs to form testis cords - Eventually become Sertoli Cells
- Sertoli cells can express Anti-mullerian hormone (AMH)
- Germ cells move inside, on the outside surface there is the primitive sex cord that migrate inwards and combine intimately with the germ cells that are already there
- This combination differs depending on whether you are male or female
- SRY expressed = tells cells to become a sertoli cell, which is the cell in the testes that is associated to sperm
- Antimullerian hormone (AMH) causes female architecture to be suppressed
Describe the primitive sex cords (Sertoli/Granulosa) - what happens in females?
- There is not any SRY expression
- The sex cords are ill defined
- They do not penetrate deeply
- But instead they condense in the cortex
- They condense as small clusters
- That are around PGCs - Eventually they will become Granulosa Cells
- If there is no expression of SRY then tells surrounding cells to become female architecture
Mesonephric Cells - How mesonephric cells act in males?
- Originate in Mesonephric Primordium
- Which are just lateral to the genital ridges
- Act under the influence of pre sertoli cells
• Which themselves express SRY
These form: - Vascular tissue
- Leydig cells
• Synthesise lots of testosterone
• Do not express SRY - Basement membrane
• Contributes to formation of seminiferous tubules and rete-testis
How mesonephric cells act in females?
- In females, without the influence of SRY
They form: - Vascular tissue
- Theca cells
Synthesise androstenedione which is a substrate for estradiol production by the granulosa
Summary of Gonadal Sex in males
PGCs —> Spermatozoa.
Primitive sex cords —> Sertoli cells (SRY, AMH).
* Mesonephric cells —>Leydig cells (testosterone).
* Mullerian ducts regress in males
* Wolffian ducts become epididymis, vas deferens, seminal vesicles and ejaculatory ducts.
Summary of Gonadal Sex in females
PGCs —> Oocytes.
Primitive sex cords —> Granulosa cells (estradiol).
Mesonephric cells —> Theca cells (androstenedione).
Mullerian ducts become uterus and fallopian tubes.
Wolffian ducts regress in females
These secretions are not that significant in an early stage
Describe the internal reproductive organs
- There are 2 main structures involved:
- SRY flicks a switch to determine certain development
1. Mullerian Ducts - Most important in females, inhibited in the male
§ By AMH, which is produced by the sertoli cells of the newly developed testes
§ Ducts require testosterone to develop otherwise they will regress
2. Wolffian Ducts - Most important in the males
- Stimulated by testosterone
- Lack of stimulation by testosterone
- Means that there is regression in females
- In females there is NO AMH OR TESTOSTERONE. So there is no testes, and
Describe internal sexual differentiation in males
- Still inside the body - do not descend until later
- Producing AMH and testosterone
- Mullerian ducts regress because of the AMH
- Wolffian ducts keep developing because of the testosterone
Describe internal sexual differentiation in females
- No AMH
- Mullerian ducts therefore continue to develop
- Uterine tube, uterus and vagina develop because there is no AMH
- Male wolffian ducts regress because there is no tetstosterone
describe 5 alpha reductase
And its role in external differentiation?
- Testosterone converted in the genital skin, tomore potent androgen DHT (DHT = dihydrotestosterone)
- This conversion is by 5 alpha reductase in the skin - this just adds a H group to testosterone. Makes dihydroteststerone in the local area
- In the male embryo there is testosterone circulating around, and DHT = influences formation of the external genitalia
- Little or no testosterone in Females - so nothing to convert this DHT
what does DHT do?
- Also binds to testosterone receptor
- But it is more potent than testosterone
- Causes differentiation
- Of the male external genitalia
• Clitoral area enlarges into a penis
• The labia will fuse together and will become ruggated to form the scrotum
• Prostrate will form
describe external differentiation in males
- In presence of DHT you will get genital tubercle becoming phallus of penis
- Urethral fold folds over on itself to make a hollow tube that becomes the shaft of the penis and folds over on itself until it becomes circular
- line = marks where the urethral fold joins, and evidence of sexual differentiation
describe external differentiation in females
- External genitals are similar to begin with
- Little testosterone and DHT so genital tubercle becomes clitoris and the labia = from the swellings
Urethral fold becomes the opening of vagina
Outline some of the disorders within sexual differentiation - gondal dysgenesis
- Sexual differentiation = incomplete
- Usually missing SRY gene in males
- Partial / complete deletion of the second X in females
+ used as general description of abnormal development of gonads
Outline some of the disorders within sexual differentiation - Sex reversal
- Phenotype and genotype do not match
- May be male genotypically
- And look female phenotypically
Outline some of the disorders within sexual differentiation - Intersex
- Have some components of both tracts
- Or have ambiguous genitalia
- Sex of infant = hard to determine
Gonadal dysgenesis 1
What happens if XY person:
Testosterone made but there is no effect + how would this happen
- Androgen insensitivity syndrome
AIS
Gondal Dysgenesis 2
What happens If XY person has testosterone made but not DHT
5 alpha reductase deficiency
- Gonad itself has not developed properly, which can cause other issues in development.
- Sex reversal = ambiguous gender / genitals : get this with a mixture of wolffian and mullerian ducts
- Testosterone would not have an effect, in ANDROGEN INSENSITIVITY SYNDROME (AIS)
○ Receptors are not responding to the high amounts of testosterone
○ AMH made, so there is regression of the mullerian ducts
○ Testosterone is not active therefore the wolffian duct, which needs testosterone to develop, will not grow - therefore no internal genitalia of any kind.
○ External genitalia = you would have female external genitalia , no external male genitals
○ DHT = also binds to testosterone receptors,
AIS -androgen insensitivity syndrome
- 1 in 20k
- Appearing totally female at birth and assigned female gender despite being XY - undescended testes
- Primary amenorrhea - lack of body hair, ultrasound scan with male levels of androgen : ultrasound scan and karyotype with male levels of androgens and never responded to androgens, so appear and feel female
Might even start to develop male external genitalia.
Describe what happens in a 5 alpha reductase deficiency enzyme
- Variance in incidence, as autosomal recessive and can depend on inter related marriage
- Testes form. AMH and testosterone both act. This will cause the internal structures to form and the external structures do not develop. Therefore the person will appear mainly female and could have ambiguous genitalia
- Degree of the enzyme block will vary - Therefore presentation also varies.
What will happen at puberty:
- Need to assess potential
- As high testosterone level which will occur at adrenarche
- And puberty
- May induce virilisation
Gonadal Dysgenesis - 3
What happens if there is a 45 XO (Turners)
In turners there is just a missing chromosome = x but no y.
- There is only one x chromosome - All descendants of that chromosome will have the same X suppressed - Women need 2x X chromsomes, some of the genes on the suppressed chromosome are actually needed
What are the characteristics of Turner Syndrome
- Failure of ovarian function
- “Streak” ovaries - get 2X in some cases but not in others, there are lots of morphological issues that come from only having one X
• Ovarian dysgenesis
• Illustrates that we need 2 X for ovarian development - The uterus + tubes are present but small, as well as other defects in growth and development
- May be fertile, could have mosaicism. There is hormone support of the bones and uterus
Gonadal Dysgenesis - 4
What happens when XX female gets exposed to lots of androgens in utero
- Congenital adrenal hyperplasia = the most common cause of this
The hypothalamic pituitary adrenal axis (HPA)
- CRH ○ Corticotropic releasing hormone ○ Stimulates pituitary gland ○ To secrete ACTH - ACTH ○ Adrenocorticotropic hormone ○ Stimulates the rapid uptake of cholesterol ○ Into the adrenal cortex ○ Will upregulate the cholesterol side chain cleavage enzume § P450scc ○ Increases glucocorticoid secretion
What is congenital adrenal hyperplasia (CAH)
- The completeness of the block baries
- If there is an enzyme absent
- Then children can be wrongly gender assigned at birth - ambiguous genitalia
- Also in CAH = have to be aware of possibility of salt wasting
- Due to lack of Aldesterone - which can be lethal
- Need treatment with glucocorticoids to correct feedback
what are the things that have to be done to reproduce?
- Differentiation
• Into male or female - Sexual maturation - puberty needs to have occurred
- Produce + store enough egg and sperm
- Right number of chromosomes in egg and sperm
- Egg and sperm have to meet - sexual intercourse
• I.e. in gamete transport - Creation of new individual with genes from both of the parents
- Nurture individual until capable to “independent” life
- Fertilisation, implantation, embryonic and placental development - nurture until capable of independent life
describe the control of reproduction?
- Male and female gonadal function
- This controlled by hormonal feedback by the following:
• Hypothalamic and pituitary peptides
• Gonadal steroids
○ And peptides - This all fits together in the Hypothalamic / Pituitary / Gonadal (HPG) axis
HPG axis
HPG AXIS is the master controller of reproduction
- Controlled by feedback
- Hypothalamus acts on the pituitary which act on receptors within the gonads
- Feedback in negative feedback which regulates the drive from the hypothalamus to the pituitary
- + feedback occurs in menstrual cycle - there is a mid cycle surge in oestrogen and LH
- LH is a setup of positive feedback
Hypothalamus (RH) = Gonadotrpohin releasing hormone, Kisspeptin
Pituitary (SH) = follicle stimulating hormone and LH
Gonad = F = oestradiol
GnRH definition
- Decapeptide is synthesised
- And is secreted
- By specialised neurones
- That are within the hypothalamus
- HAS TO BE IN A PULSATILE FASHION
GnRH pulse generators definition?
- Collective group
- Of neurones
- That discharge GnRH
In orchestrated manner
Gonadotrophs definition?
- Cells in the anterior pituitary
- That synthesise and secrete LH and FSH
- In response to GnRH
Gonadotrophins definition?
- LH
- FSH
- Stimulate the ovary and the testis
What is the action of GnRH
- Released in a pulsatile fashion = continual release, secretion this way is key to its function
- Released from special pulse generator that is within the hypothalamus
The GnRH release has to be pulsatile - why?
- In males this is around every hour or so
- LH surge occurs = this causes the pulse to be more frequent
- Pulse of GnRH = stimulates pulse of FSH + LH from pituitary
- Pulsatile GnRH secretion is vital for the stimulation of LH and FSH
- Slow frequency pulse, favours FSH release. Rapid pulse frequency, favours LH.
Continuous release results in the cessation of response
What are the clinical applications of GnRH
- Synthetic GnRH is the same structure as native GnRH = stimulatory
- GnRH analogues which are modified versions of GnRH = various modifications within the GnRH structures
- Analogs are always used to downregulate / inhibit the GnRH structure
- They work in slightly different ways
- Discovery of decapeptide structure of GnRH
- = development of new drugs
- GnRH = synthetic but had same structure as native GnRH
- GnRH analogues
• Single peptide replaced in chain
• Prevents breakdown by enzymes at pituitary and receptor internalisation
• Longer half life
• Loss of pulsatility - Can be used to stimulate or suppress release of LH / FSH
- GnRH is a GPCR –> activation of signalling on binding –> stimulatiion of gonadotrophin synthesis and secretion.
• Agonist = THEN dissociation of GnRH from GnRHR –> GnRHR response to next GnRH
• Antagonist = uncoupling of GnRHR from Gprotein signalling –> GnRHR non responsive to GnRH
What are the characteristics of the GnRH analogues
- Inhibition of the stimulations of gonad
- By removing LH + FSH
- By the loss of pulsatility
- Never used for stimulation
- Always used for inhibition
• Testicular cancer - dependent on testosterone for growth
• Uterine fibroids prior to surgery
○ Oestrogen dependent
• Prevention of premature ovulation in IVF
What are the characteristics of the GnRH analogues - continued
- Old versions = tended to be agonists
- Bind to and activate the receptor
• This stimulates the massive release of gonadtrophins initially
• Until the gonadotrophins in the gonadotrophs are depleted
• Even receptors down regulation - Newer versions = antagonists
• These will bind to and block the receptor
• Without activation
• Gonadarelin
• Triptorelin
• About £900pa for prostrate cancer
describe the GONADOTROPHINS LH/FSH/hCG
- HETERODIMERIC = made up of 2 different subunits
- peptide hormones with common α sub-unit and specific β sub-units
• β sub-unit confers specificity of action
• sub-units are glycosylated - glycosylation (+ various versios of glycosylations) are required for activity - LH & FSH always released in pulses for normal reproductive function
- Why pulses?
• The pulses are lost in “unfit to reproduce” conditions
• The correct release = dependent on extra hypothalamic and extra pituitary signals
• Heterodimeric peptides –common a-subunit and hormone-specific b-subunit
• N-linked carbohydrate side chains (+ O-linked in hCG) = microheterogeneity, required for biological function
• Free subunits have no biological action
• a-subunits are synthesized in excess with b-subunit limiting the hormone concentration
Pulsatile secretion due to pulsatile GnRH release from hypothalamus but pulsatile secretion not necessary for biological activity
Normal follicular phase gonadotrophin pulses
- Release of LH every 90 minutes and a smaller release of FSH
- Underweight person = lose amplitude of LH pulse and there is diminishing of LH = much lower level of FSH
Get downregulation of the HPG axis and therefore impairment
describe the gonadotrophin pulses in underweight patient
- LH = binds to receptors on the testes and stimulates the leydig cell androgen synthesis. On the ovary it causes theca cell androgen synthesism ovulation, progesterone production of CL
FSH = regulates sertoli cell metabolism, follicular maturatio and granulsa cell estrogen synthesis of the ovary
Gonadotrophins = day and night sensitive
- During puberty, first rise in secretion = during sleep
- This coincides with GH rise
- Sleep related rise in patients, persists in adulthood
- Lost in weight loss related amenorrhoea
- Delayed puberty in children with sleep disorders
- “travellers amenorrhoea” = due to jet lag
Gonadotrophins / receptors actions
- Gonadotrophins act via G protein coupled receptors
- There are 2 x distinct receptors
- There is the same secondary messenger –> cAMP
- FSH low cAMP, LH high cAMP
Receptor distribution in the ovaries
- FSH receptors only on granulosa cells
- Make oestrogen
- LH receptors always on theca cells - cause the LH reeceptor to produce androgens
• + on differentiated granulosa cells
• + the corpus luteum
Receptor distribution in the testes
- FSH receptors on sertoli cells
- Sertoli cell metabolism = spermatogenesis
• Make oestrogen and AMH
• FSH + LH receptors are on the Leydig cells
• Makes testosterone and oestrogen
General rule of LH and FSH
- LH = Stimulates androgen production, usually
- FSH = always stimulates oestrogen production
- And positive feedback on the hypothalamus and the pituitary
Outline the characteristics of the steroids : oestrogens
- Oestradiol 17beta
Also oestrone
Outline the characteristics of the steroids : progesterone
- Synthetic progesterones
- Are known as progestagens
Outline the characteristics of the steroids : androgens
- Androstenedione
- Testosterone
dihydrotestosterone
What is puberty?
- When secondary characteristics develop, the primary characteristics = at birth. @ adolescence there is a growth spurt, and physiological changes.
- Gonads will make mature gametes, the testes make spermatozoa and the ovaries make oocytes.
- HPG axis before this is waiting for reactivation, in a quiescent state
- Testes make spermatozoa
- Ovaries make oocytes
What are the 2 endocrinological events in puberty
adrenarche + gonadarche
independently regulated processes
what is adrenarche
- Awakening of the adrenals
- Pubic hair and axillary hair, growth in height
what is gonadarche
- Reawakening of the HPG axis, denoted by LH and FSH secretions
describe LH + FSH (both released during gonadarche)
LH
- Steroid synthesis, secondary sex characteristics
FSH
- Testes growth (M) - Steriod synthesis / folliculogenesis (F)
Describe adrenarche
- Change in adrenal androgen secretion. There is a gradual rise from 8-15 years. 20 fold increase which peaks at about 20-25years.
- Adrenal androgens, from the zona reticularis. Dehydro-epiandrosterona (DHEA)
- Dehydro-epiandrosterone sulfate (DHEA-S)
• Not taling about any other adrenal steroids = these are the only 2 adrenal steroids that are actually produced in Adrenarche - No changes in levels of cortisol, androstenedione, 11-hydroxy-androstenedione
- Decline thereafter = adrenopause
- We do not understand mechanisms involved in adrenarche.
- Adrenal = separated into cortexes of different zones
- Elevated DHEA + DHEA-S which peaks at 20-25, then there is a decline
- There is no change in any other adrenal androgens - no idea what the trigger of adrenarche is yet. Can compare post natal adrenal to the one that is at the point of adrenarche = is highly differentiated
- Zones = develop at different stages but we do not know what causes this
Pubarche
Result of adrenarche
- Appearance of pubic / axillary hair. Induced because of adrenal androgen secretion and associated with a rise in sebum production (=acne), infection, abnormal keratinization = acne.
- If before 8 years for girls or 9 years for boys = precocious.
Gonadarche - Reawakening of the HPG axis and happens around age 11
- Several years after adrenarche, activation of gonadal steroid production.
- This is dependent on hypothalamic GnRH.
- Puberty depends on reactivation of GnRH release
- Kisspeptin at the top = see this slide
- HPG axis is first activated during gestation
- Pulsatile GnRH remains until 1-2 years postnatally - then it is restrained
What is puberty dependent on?
Reactivation of GnRH release
GnRH characteristics?
- It is made and secreted by GnRH neurones. This will stimulate the pituitary directly and the gonads. 16th gestational week activation of the HPG axis.
- Pulsatile GnRH secretion in the fetus, and 1-2 years post natally. Declines until 9-10 years.
- Neurones are restrained during postnatal period - 10 years or more
- At puberty a gradual rise in pulsatile release of GnRH.
- There is a nocturnal increase in GnRH secretion = pulse of GNRH –> pulse of LH
- LH is always used as a measure for GNRH pulsatility
What are the factors that stimulate the onset of puberty
- Maturational event within the CNS • Lots of things are said to implicate its starting - Inherent - genetic maturation of 1000-3000 GnRH synthesising neurones. - Environmental and genetic factors - Body fat / nutrition - Leptin - Other gut hormones - Kisspeptin
Nutrition + body fat involvement in the central generator
- Link between fat metabolism and reproduction
- Anorexia / intensive physical training causes a reduced response to GnRH, fall in gonadotrophin levels, amenorrhea, restored when nourished and exercise stopped.
- Body fat hypothesis is that, a certain % fat:body weight is needed for menarche (17%) and need (22%) to maintain female reproductive ability.
Leptin could be trigger to puberty - how?
- A rise in leptin occurs about 2 years before puberty. This leads to increased GnRH pulsatility.
- In starvation, low leptin levels. Decreased activity of HPG axis.
- Obesity increases leptin and earlier puberty occurs
- Low levels of Leptin, decreased LH
- Receptors for leptin protein are in the hypothalamus
- A permissive role for leptin, not the driver.
Neurohormone - Kisspeptin. Describe its actions
Kisspeptin / Metastin
- Found in hypothalamic neurones, receptors for kisspeptin (GPR54) are expressed on GnRH neurones - Directly regulates GNRH secretion
- In the arcuate nucleus
Kisspeptin + puberty
- Mutations of the GPR54, or gene that is coding for kisspeptin
- Abnormal development of GnRH neurones leads to hypogonadism (low levels of LH + FSH gonadotrophins, so small testes and ovaries because of inactivating mutatios), failure to enter puberty
- Hypothalamic hypogonadism
- Activating mutations of GPR54 - precocious puberty (where the receptor is active all the time)
KISSPEPTIN - what is it critical for
- Critical in the initiation of puberty, and reproductive function
Interplay with energy homoestasis and kisspeptin
Factors that stimulate onset of puberty?
- Inherent genetic maturation of 1000-3000 GnRH synthesising neurones. Environmental and genetic factors. Body fat + nutriton. Leptin, and other gut hormones
- Kisspeptin is critical in starting puberty + reproductive function
what is Consonance?
- Smooth and ordered progression of changes - order of pubertal changes is uniform
- Wide inter individual differences in timing and how long each of these stages take
Girls physical change in puberty?
Breasts enlarge - Thelarce. 1st sign, in response to E2
Pubic / axillary hair
Uterus enlarges
• Secretions in response to E2
• Uterine tubes + Vagina/cervical changes
• Dormant follicles start to grow and increase in size
Height - Earlier onset than boys, peak height velocity (PHV) = 9cm/y
• This is reached at 12 years old HPG axis
- Rise in ovarian size and follicular growth
Menarche
- Not equated with fertility onset
- First period = for the first year this might not be associated with fertility as the HPG axis is being established -
Fertility - In first year there is about 80% menstrual cycles
- Anovulatory, irregular cycles
What is prader orchidometer
- Numbers represent the volume in millimetres.
- Measures centiles of testicular size
Androgen effects on differentiation of pilosebaceous units (PSUs)
- Androgens have different effects on the pilo sebaceous units
- Terminal PSUs make the beard and mustache
- If we get sebaceous gland increased secretions and infection/ abnormal keratinisation this can lead to acne
Growth spurt
Growth spurt
- GH and Oestrogen in boys and girls - Complex interaction between the 2
What is the biphasic effect of oestrogen on epiphyseal growth
- Low levels = linear growth and bone maturation - the initial growth spurt is supported by low levels of oestrogen
- High levels = epiphyseal fusion (decrease in growth spurt )
What is consonance
- Smooth ordered progression of changes
- Order of pubertal changes is uniform
- Age of onset, pace and duration of changes - wide inter individual difference
- Average age of menarche onset (UK) = 12.5yrs
- There are difference in the age of pubertal development - discuss this.
- Can be precocious / delayed sexual maturation
○ Precocious sexual development, is development of any 2ndary sexual characteristics before the age of 8 in girls and before age 9 in boys.
○ Precocious puberty is when pubertal changes are early but in consonance- Tanner stages of puberty: scale of physical measurements of development - breasts, pubic and axillary hair growth, male genitalia.
Precocious puberty / sexual development 1
pubertal delay = rare
Early puberty = precocious puberty (early, but in consonance)
- Getting secondary sex characteristics before 8 years in girls and 9 in boys
- Gonadotrophin dependent/ central precocious puberty - consonance
• XS GnRH secretion : idiopathic / secondary
• XS gonadotrophin secretion : pituitary tumour
- Gonadotrophin independent secretion = pituitary tumour.
- Gonadotrophin precocious pseudo puberty loss of consonance
• Testotoxicosis : activating mutation of LH receptor
• Sex steroid secreting tumour / exogenous steroids
• Primary hypothyroidism (High TSH –> LH / FSH receptors)
what happens in McCune Albright?
• McCune Albright: mutation of alpha subi=unit of GPC activation of adenylate cyclase = hyperactivity of signalling pathways and hormone over production
what is Testotoxicosis
- Small testes, absent gonadarche
- Lack of FSH
- Activating mutation of the LH receptor, this is a child that is 20 months old
- Tanner stage 3 already though = so in mimd puberty
Result of activating mutation of LH receptor which is why there is virilisation
McCune Albright Syndrome - describe.
- Café au lait skin pigmentation
- Mutations in the GNAS1 gene
- Activating mutation of LH receptor
What mutation causes McCune Albright syndrome
- Mutation in the GNAS1 gene
- Fibrous dysplasia
- Autonomous endocrine function - most common gonadotrophin independent precocious puberty
Precocious sexual development 2 - can also get psuedo precocious puberty. Describe this.
- Premature adrenarche / pubarche
- Precocious development of pubic and axillary hair, also CAH congenital adrenal hyperplasia/ Cushings.
- Premature thelarche - precocious breast development
• Isolated cyclical (less than 2 years) without other pubertal development
• Variant (more than 2 years) proceeding to precocious puberty
how would you do Investigations of precocious sexual development
- Auxology - meta term covering study of all aspects of human physical growth
- Accurate measurements of height including body proportions and weight
- Pubertal staging, bone age estimation
- LH, FSH, sex steroids measurements
- LH response to 100micrograms of GnRH - normal stage of puberty in central precocious puberty, suppressed in testotoxicosis.
- Adrenal steroids - high in tumours, precursors high with CAH
- MRI scans of hypothalamic pituitary area
- Ultrasound scans of the pelvis - uterus and ovaries
How would you treat precocious sexual development?
- Antiandrogens
- 5alpha reductase inhibitor
- Aromatase inhibitor
- Long acting GnRH analogue - central precocious puberty
Pubertal Delay -
what is constitutional delay
- Affects both growth and puberty, about 90% of cases. (most common type of delay that one would see)
- 10x more common in boys and 2ndary to chronic illnesses like CF, diabetes
Pubertal Delay - what is Hypogonadotrophic hypogonadism
- Kallmans syndrome (X linked KAL gene - GnRH neurone migration) - GnRH originate in the nasal cavity and migrate backwards into the hypothalamus
- KAL mutation = neurones cannot migrate in the hypothalamus which leads to hypergonadism
- (Other genetic causes, hypopituitarism)
- Low levels of gonadotrophin horrmones, hyperplastic ovaries and testes which can be due to a genetic disorder
Investigations of delayed puberty
- Family history, dysmorphic features, anosmia, auxology
- Pubertal staging
- Bone age estimation
- LH / FSH / Sex steroid measurements
- LH response to 100micrograms of GnRH
- Adrenal steroids, high with tumours, precursors high with CAH
- MRI scans of hypothalamo-pituitary area
- Ultrasound scans of pelvis, uterus and ovaries.
- Similar to investigations of precocious puberty.
treatment for delayed puberty?
- Testosterone (males), oestrogens (females) - oxandralone is a synthetic steroid.
- People can sometimes just go through puberty at a later stage = e.g. over exercising can make puberty be held up
What has to be achieved to reproduce
- Goes beyond just sexual intercourse
- Differentiation into male and female
- Sexual maturation
- Production + storage and release of sufficient supply of eggs and sperm
- The right number of chromosomes in eggs and sperm
- The eggs and sperm have to meet
• Gamete transport - Creation of new, individual with genes from both parents
- To nurture individual until capable of independent life
What has to be achieved to reproduce?
- Goes beyond just sexual intercourse
- Differentiation into male and female + Sexual maturation
- Production + storage and release of sufficient supply of eggs and sperm
- The right number of chromosomes in eggs and sperm
- The eggs and sperm have to meet
• Gamete transport - Creation of new, individual with genes from both parents
- To nurture individual until capable of independent life
What has to be achieved to reproduce?
- Germs enter the gonad
2. If the PGCs enter ovary, they will become oocytes
what happens when Germs enter the gonad?
- Cells that are going to become eggs
- Or sperm
- Are called Primordial Germ Cells (PGC)
- PGCs first identifiable in the yolk sac of the developing foetus at 3 weeks after conception, and go through many cycles of mitosis + migrate to the genital ridge in the foetus, and the genital ridge becomes the gonad
Further differentiation of the PGC depend on the development of the gonad i.e. ovary or testis
what happens when germ cells enter the ovary?
- Germ cells become oogonia when they are in the ovary
- Oogonia = egg precursors
○ Diploid, and multiply by mitosis - Once the mitosis stops, and they enter into meiosis
- They are known as primary oocytes
describe the process of Going from Germ cells to Eggs?
- All the eggs that a woman will ever have are made at this stage
- The mitotic divisions are therefore critical
- Once the oogonia enter the 1st stage of meiosis no more division occurs and they become primary oocytes
- The primary oocytes remains in the first phase of meiosis until it is ovulated (or dies)….maybe for 52 years!
describe Primary oocytes?
- Are packed into the outer layer of the ovary
The cortex
with Primary oocytes - the primordial follicle - describe its characteristics.
- Oocyte arguably the most important cell in the body and will in the vulnerable 1st meiotic phase for many years
- Therefore each one becomes surrounded by protective layers and protective cells
In the foetal ovary, the surrounding cells condense around the oocyte and differentiate into the granulosa cells
Folliculogenesis - this is the growth of a follicle: what happens during this?
- Defined as the growth and development of follicles from the earliest “resting” stages as laid down in the foetus, through to ovulation
- Most of the follicles in the ovary are not growing – after puberty only a few grow each day
- As the follicles start to grow, the oocyte secretes another protective acellular layer called zona pellucida….which stays attached after ovulation
- Once growth of the follicles has started a second layer of cells then differentiate around the basal lamina: the theca
describe the control of follicle growth?
- We don’t really know or understand the factors that control the initiation of growth
- Early stages = unknown
FSH - Drives most folliculogenesis
- Early growth = independent of FSH
• Driven by local factors
○ You can tell this from FSH deficient patients
○ Or with patients that have mutations of the FSHr
○ Means that when FSH is suppressed e.g. on COCP - the follicles will continue early growth but then die
When the follicle starts to grow:
- Increases rapidly in diameter
- Granulosa cell divisions increase
- Gaps start to form in granulosa cell layers
• These gaps = consist of fluid filled spaces
○ These spaces form an antrum
• 2 main phases of follicle growth (labelled by absence/presence of the antrum)
Follicles that have an antrum = antral, or secondary follices.
What is follicle initiation?
- The cohort of early follicles that leave the resting pool and grow continuously
What is follicle recruitment?
- Fact that the follicles will not keep growing unless they get to a size where they will respond to changes in FSH which occur in the menstrual cycle
How does the ovarian follicle produce steroids?
- The LH interacts with the LH receptor and this triggers the synthesis of androstenedione, from cholesterol. This then becomes estradiol, in reaction that is enabled by aromatase, and then the estradiol goes to the follicle.
FSH binding to the FSH receptor is what binds to
explain Ovarian steroidogenesis.
cholesterol => progesterone => testosterone => oestradiol
explain control of folliculogenesis
hypothalamus makes GnRH => ant pituitary.
Ant pituitary makes FSH/LH => acts on ovary.
ovary produces oestrogen + progestone which acts on hypothalamus and ant.pituitary.
Factors that have to be achieved to reproduce?
- Differentiation into male, or female
- Sexual maturation
- Production, storage and release of enough eggs and sperm - right # of chromosomes in eggs and sperm, plus they have to meet in gamete transport
- Create new individual genes from both parents
- To nurture individual until it is capable of independent life
describe the Aims of menstrual cycle?
- This is the selection of a single oocyte, regulator spontaneous ovulation. Correct # of chromosomes in eggs.
- Cyclical changes in vagina, cervix, fallopian tube
- Preparation of uterus
- Support of the fertilised dividing egg
What does the empty follicle become
- Corpus luteum
what happens in the Luteal phase?
- Progesterone = negative feedback - made by the CL, and feedbback is onto the hypothalamus and pituitary, reducing their output
- Like in males there is constant negative feedback by testosterone
Always negative feedback
what happens in the Follicular phase
- Release of negative feedback
- Negative feedback reinstated
- Switch from negative to positive feedback
Like a brake on the car = break is cause by progesterone, when you lift off the brake you allow it to start secreting GnRH and gonadotrophin
Then start to make estrogen from the growing antral follicle which will feedback to reinstate the negative feedback = there
Switching between negative and positive feedback.
Late luteal, early follicular
Intercycle rise in FSH
- Progesterone declines - negative feedback.
Allows hypothalamus and pituitary to start working again - Selectively raises FSH
- Inter cycle rise
Allows antral follicles that are at the right size to keep on growing
what happens phases in the mid follicular phase
- As they grow they increase their production of oestrogen, which is made by the granulosa cells.
- E2 increases, negative feedback
- FSH falls (FSH turned off) - which will cause lots of the follicles to die off apart from one, which will become the dominant follicle.
- Massive proliferation of granulosa cells + the amount of oestrogen, pumping oestrogen out
- High sustained levels of oestrogen for about 48hrs = this then acts back on the hypothalmus and pituitary to produce positive feedback, preferentially on LH.
what happens Mid cycle?
- 2 days of E2, more than 300pmol
- Positive feedback when there are sustained high levels of estrogen
- LH surge, which produces final maturation
what happen mid luteal phase?
- High progesterone
- Negative feedback, low LH/FSH (from progesterones negative feedback)
- P overcomes E2.
describe the Intercycle rise in FSH
- Intercycle rise and fall in FSH is important because it allows selection of single follicle
This happens at start to cycle because progesterone decreases = allows antral follicles to continue to grow and produce
what is the “Window of opportunity”
- There are cohorts of follciles = ones that reach antral stage, at this part of the cycle when FSHS is low they cannot sustain their growth so will die.
- When FSH is starting to rise = can contine their growth and estrogen made
As FSH is falling, any other follicles that are coming across will not be able to progress
Follicle selection?
- When there is raised FSH, this presents a window of opportunity
- FSH threshold hypothesis - one follicle from the group of antral follicles in ovary is just @ right stage @ right time. This becomes the dominant follicle which goes onto ovulate. This is known as selection. Can happen in either ovary.
- One follicle becomes the dominant follicle.
- Oestradiol levels rise, which reinstated negative feedback @ pituitary. This causes FSH levels to fall prevents further follicle growth
- The dominant follicle survives the fall in FSH.
Follicular phase gonadotrophins?
- As FSH falls, LH increases
- Dominant follicle, will make LH receptors on the granulosa cells, couple much more effectively to their downstream signalling pathways
- Granulosa cells need LH receptors
- Other follicles do not, so they will lose their stimulant, and die.
What are the rules of receptors on follicles
- Theca always has LHr, but never FSHr
- LH drives androgen + progesterone production from theca
- Granulosa have FSHr, then LHr acquired from mid follicular phase, onwards. Primarily on the dominant follicle
- FSH and LH drive oestrogen production in follicular phase.
in Steroidogenesis…?
- Aromatase in the granulosa cells and not in the theca
The menstrual cycle overview:
- Day 1 = 1st day of bleeding, and Menstruation = 3-8days (written as 7/28 (7 days bleeding with a regular 28 day cycle), or 5-6/27-32)
- Regular cycle shouldn’t have more than 4 days variation between months
- CL has a fixed lifespan
- 32 day cycle would mean that you had a longer follicular phase because the luteal phase is constant.
describe Follicle selection process?
- The dominant follicle is selected, and grows rapidly - it doubles in diameter in 7 days from 7mm to 14mm, large structure
- Needs masses of growth factors, nutrients and steroids
- Rapid neoangiogenesis (new blood vessels)
- Oestrogen comes from follicle into the circulation.
- Does not just rely on estrogen but relies on other growth factors and nutrients that can feed the dominant follicle and allow growth to occur
characteristics of The dominant antral follicle
Theca is intact and there are follicular cells buried inside
How does ovulation occur?
- Cascade of events that causes ovulation:
- Blood flow to follicle, increases massively and there is an increased in the vascular permeability increases intra follicular pressure. Follicle has moved to the apex of the ovary. Dominant follicle has to be able to release the oocyte from the ovarian wall
- Appearance of the apex or stigma on the ovary wall, like a weakening that allows the release of various proteases (Local release of proteases)
- Enzymatic breakdown of protein of the ovary wall.
- 18hrs after the LH peak, the hold appears in the follicle wall and ovulation will occur.
- The oocyte with cumulus cells = extruded from the ovary under pressure. Follicular fluid might pour into the pouch of douglas.
- The egg is collected by the fimbria of the fallopian tube
- Egg progresses down the tube, by peristalsis and the action of cilia.
- The fallopian tube will move around and picks up the egg as it is released. If you have fibroids the follopian tubes are not patent
- Egg travels down the tube and can meet a sperm that make their way up vagina and cervix. Sperms main job is to reach the egg to fertilise it. + sperm can survive for a few days
what happens In ovulation detection?
- Certain hormones are being detected, LH being detected
Preparation of oocyte? what happens?
`- Have to grow oocyte within the follicle and have to create a haploid oocyte. In the fetus the eggs enter into meiosis 1 and then stop. This will allow the oocyte to keep all of the DNA.
- From its formation as primary oocyte in the fetal ovary up until ovulation, oocyte has been arrested - in the first meiotic division
- This allows the oocyte to retain all of the DNA and stay as large as possible during its long wait.
- In response to the surge of LH, oocyte nucleus in the dominant follicle will complete 1st meiotic division, but it does not divide.
describe Meiosis and extrusion of the polar body?
- Half of the chromosomes are put into a small package, in the egg which is called the 1st polar body
- The egg is now a secondary oocyte
- The 1st polar body plays no further part in the process and does not divide again
- 1st polar body is extruded and then there is arrest again in meiosis 2, until it is fertilised. If it is successfully fertilised then it will complete meiosis 2.
- Oocyte begins the 2nd meiotic division, but then will arrest again
- There is unequal division, to keep the size because has everything that is necessary to look at preimplantation
What is the 1st polar body
What is the 1st polar body
- Package which contains half of the chromosomes
describe the Secondary oocyte?
- Unlike sperm we only want a single oocyte
- The oocyte is the largest cell in the body (sperm are smallest…..but fastest!)
- The oocyte has to support all of the early cell divisions of the dividing -embryo until it establishes attachment to the placenta
- Spends 2-3 days in the uterine tube
- So the oocytes if now on its way into the tube….will it meet a sperm?
Fertilisation = will complete meiosis 2
Formation of the corpus luteum?
- Dissected CL showing exit hole of oocyte
- After ovulation, the follicle will collapse, and the corpus luteum is formed, “yellow body” because it looks yellow.
- Progesterone production is greatly increased, also E2
- CL contains large number of LH receptors
- CL supported by LH and hCG - if a pregnancy occurs. Has inbuilt lifespan, and dies after 14 days - if a pregnancy occurs the trophoblast will produce HCG which will maintain and support the CL.
Secretions of CL
- Progesterone
- Supports oocyte in its journey, prepares the endometrium
- Controls cells in fallopian tubes
- Alters secretions of cervix
Oestradiol
- For endometrium
