Repro Flashcards
What is sexual differentiation?
The process by which interval and external genitalia develop as male or female.
Contiguous with sexual determination.
What are the different ‘stages’ of gender in sexual differentiation?
- genotypic sex
- gonadal sex
- phenotypic sex
- legal sex
- gender identity
What is the gonadal development (bipotential embryo)?
After fertilisation w pair of gonads develop which are bipotential.
Their precursor is derived from common somatic mesenchymal tissue precursors called the genital ridge primordial on the posterior wall of the lower thoracic lumbar region.
The ridges will develop into the go add and the hormones they secrete as a result will influence the rest of the development of the embryo.
The are also two series of ducts and these represent what will become in internal sexual architecture.
The mullerian duct becomes the uterus in females.
The wolffian duct becomes the male architecture.
What is the SRY switch?
The SRY gene creates the testes. It is a gene for a transcription factor on the short arm of the Y chromosome. SRY switches on briefly during development to make the gonad into a testis. In its a sense and ovary is formed.
Testis develops cells that make two important hormones:
- Sertoli cells produce anti-Mullerian hormone (AMH)
- leydig cells make testosterone
What are the three waves of cells that invade the genital ridge?
- Primordial germ cells - these become sperm (males) or oocytes (females)
- Primitive sex cords - becomes Sertoli cells (males) or granulosa cells (females)
- Mesenephric cells - become blood vessels and leydig cells (males) or theca cells (females)
What is sexual determination?
The genetically controlled process dependent on the ‘switch’ on the Y chromosome. Chromosomal determination of male or female.
What is primordial germ cell migration?
An initially small cluster of cells in the epithelium of the yolk sac expands by mitosis at around three weeks.
They then migrate to the connective tissue if the hind gut, at the region of the developing kidney and into the genital ridge - completed by six weeks.
What are the primitive sex cords?
Cells from the germinal epithelium that overlies the genital ridge mesenchyme migrate inwards as columns called the primitive sex cords.
The combination is slightly different depending on whether you are make or female, these are the cells in males that express SRY. SRY says to this wave of cells to become settling cells, otherwise they will become granulosa cells in females.
MALE: sry expression, penetrate the medullary mesenchyme and surround the PGCs to form testis cords, eventually they become granulosa cells
FEMALE: no sry expression, sex cords are ill defined and do not penetrate deeply but instead condense in the cortex as small clusters around PCGs, eventually they become granulosa cells
What are mesonephric cells?
These cells exist just lateral to the genital ridges and they also move inwards. They become leading cells in males and the a cells in females. Both of these cells synthesise androgens. Females synthesise a lot of testosterone.
In males they act under the influence of pre-sertoli cells to form…
- vascular tissue
- leydig cells
- Basement membrane - contributing to formation of seminiferous tubules and rete-testis
In females without the influence of sry they form…
- vascular tissue
- theca cells
What does 5-alpha-reductase do?
Testosterone is converted in the genital skin to the most potent androgen DHT (dihydrotestosterone).
DHT also binds to the testosterone receptor, and is much more orient than testosterone.
what does DHT cause?
- clitoral area enlarges to penis
- labia fuse and become rug gated to form scrotum
- prostate forms
What is gonadal dysgenesis?
Sexual differentiation is incomplete. Usually missing sry in a,e, or partial or complete deletion of second X in females. Also used as a general description of a normal development of the gonads.
What is sex reversal?
Phenotype does not match the genotype. Ie may be genetically male, but externally look like a female
What is intersex?
Have some components of both tract or have ambiguous genitalia. Sex of infants is difficult to determine.
What is androgen insensitivity syndrome (AIS)?
Type of gonadal dysgenesis. There may be a problem with the receptor in that it doesn’t bind or that the receptor doesn’t function. The sufferer will have AMH so the Müllerian ducts will regress. The testes will male testosterone but the testosterone won’t be active so the wolffian ducts won’t develop. Therefore they will have testes but with female ester all genitalia.
Can be complete or partial. Quite often a spectrum.
Usually present with primary amenorrhoea. Lack of body hair is a clue. Ultrasound scan and karyotype with male levels of androgens. Never responded to androgens so look and FEEL female.
What is Turner syndrome?
XO have failure of ovarian function. “Streak” ovaries = ovarian dysgenesis - illustrates that we need 2 X’s for ovarian development. Uterus and tubes are present but small, other defects in growth and development. May be fertile, many have mosaicism. Hormone support of bones and uterus.
What is the basis of steroidogenesis?
All the steroids have the same structure as cholesterol…
3 X 6 sided rings
1 X 5 sided ring
Tail
To make the differentiated steroids just cut different parts of the tail off and the occasional group is moved around the rings.
What does corticotrophin releasing hormone do?
Stimulates the pituitary to secrete ACTH
What does adrenocorticotrophic hormone do?
Stimulates the rapid uptake of cholesterol into the adrenal cortex
Upregulates cholesterol into the adrenal cortex
Upregulates cholesterol side chain cleavage enzyme (P450scc)
Increase glucocoticoid secretion
What is congenital adrenal hyperplasia (CAH)?
- completeness of the block varies
- if the enzyme is absent then children may be wrongly gender assigned at birth, or may have ambiguous genitalia
- also need to be aware of possibility of ‘salt-wasting’ due to lack of aldosterone, this can be lethal
- need treatment with glucocorticoids to correct feedback
You get male and female internal architecture. External genitalia is male - there are androgens so you will get DHT.
What is puberty?
Transition from non reproductive to reproductive state.
Secondary characteristics develop, adolescent growth spurt, profound physiological changes, profound psychological changes, gonads produce mature gametes
What are the two endocrine events of puberty?
Adenarche and gonadarche
What is adenarche?
Adenarche is the first endocrine event of puberty. It originates from the adrenal and is investigated by the maturation of cells in the adrenal cortex. This results in the release of androgens from the adrenal. Changes that occur include the growth of pubic and axilliary hair and growth in height. This is independently regulated.
What is gonadarche?
Gonadarche follows adrenarche. It is HPG driven. The synthesis and secretion of pituitary peptide hormones - LH and FSH, which activate gonadal function. LH causes secondary sex characteristics and FSH causes the growth of testes (make), steroid synthesis, folliculogenesis (female)
Several years after adrenarche around 11 years
Reactivation of GnRH
Activation of gonadal steroid production - production of viable gametes and ability to reproduce
What change in secretion occurs in adrenarche?
Change in adrenal androgen secretion (from zona reticularis)
DHEA and DHEAS
There is a gradual increase from 6-15 years with a 20 fold increase peaking at 20-25 years.
- decline in DHEA/DHEAS thereafter = adrenopause
- no change in other adrenal androgens
- no known mechanism for trigger if adrenarche
What is pubarche?
Appearance of pubic/axilliary hair
Induced by adrenal androgen secretion
Associated with increased serum production = acne,
Infection and abnormal keratinisation = acne
If before 8 years (girls) or 9 years (boys) = precocious
What is GnRH?
GnRH is synthesised and secreted by specialist hypothalamic centres - GnRH neurones
Pulsatile secretion is essential for GnRH function
HPG axis is first activated at 16th gestational week - pulsatile GnRH secretion in foetus until 1-2 years postnatally web creases, reactivation at about 11 years
GnRH neurones ‘restrained’ during postnatal period - 10 years or more
At puberty a gradual rise in pulsatile rise in pulsatile release of GnRH
Changes in LH secretion begin nocturnally. LH acts as a surrogate for GnRH, and LH is a lot easier to measure so this is what may be graphically represented to show changes of GnRH occurring during pubertal development.
What stimulates the onset of puberty?
- inherent maturation of 1000-3000 GnRH synthesising neurones
- environmental/genetic factors
- body fat/nutrition - need to be fit and healthy to reproduce and body knows this (need 17% fat for menarche and 22% to maintain female reproductive ability)
- leptin
- other gut hormones
- kisspeptin
What is consonance?
The smooth, ordered progression of changes
Order of pubertal changes in uniform: age of onset, pace and duration of changes - wide inter-individual differences, average age of menarche onset (uk) is 12.5 years
What physical changes occur in girls during puberty?
Breasts enlarge
Pubic/axilliary hair
Uterus enlarges, cytology changes, secretions in response to E2
Uterine tubes
Vagina
Vertical changes
Height
Body shape
HPG axis - increase in ovarian size and follicular growth
Menarche - not equated with onset of fertility
Fertility - in 1st year ~80% menstrual cycles anovulatory, irregular cycles
What physical changes occur in boys during puberty?
External genitalia Vas deferens Seminal vesicles and prostate Facial/body hair Pubic/axilliary hair Larynx Height Body shape Onset of fertility
What is the parader orchidometer?
- numbers represent the volume in millimetres
10th, 50th, 90th ce tiles of testicular size in boys at different ages
Used to measure testis size
What hormones are involved in the pubertal growth spurt?
Growth hormone
Oestrogen
Low levels of oestrogen: linear growth and maturation
High levels of oestrogen: epiphyseal fusion
What are the effects of androgens on the differentiation of pilosebaceous units (PSUs)?
Androgens stimulate sebum secretion and together with infection this can cause acne.
Androgens can induce differentiation of vellum PSUs to terminal PSUs encouraging moustache and beard.
Androgens can induce differentiation of vellum hairs to apo-PSUs encouraging increased growth in areas of pubic and axillary hair.
What psychological changes occur in puberty?
Increasing need for independence
Increasing sexual awareness/interest
Development of sexual personality
Latter muturation = better adjustment
What is precocious sexual development?
Development of any secondary sexual characteristic before the age of 8 in girls and before the age of 9-10 in boys. Precocious puberty is when puberty is when pubertal changes are early but in consonance.
Gonadal-dependent (or central) precocious puberty - consonance
Excess GnRH secretion - idiopathic or secondary
Excess gonadotrophins secretion - pituitary tumour
Gonadotrophin-independent precocious puberty - loss of consonance
Testotoxicosis - activating mutation of LH receptor
McCune Albright - constitutive activation of adenylyl Cyclades»_space;hyperactivity of signalling pathways and over production of hormones
Sex steroid secreting tumour or exogenous steroids
What is McCune Albright syndrome?
Cafe au lair skin pigmentation
Autonomous endocrine function - most common gonadotrophin-independent precocious puberty
Fibrous dysplasia
Mutations in the GNAS1 gene
What is pseudo-precocious puberty?
Premature adenarche/pubarche
- precocious development of pubic and/or axillary hair
Also CAH/Cushings
Premature thelarche - precocious breast development
- can be unilateral
- isolated ‘cyclical’ with absence of other pubertal development
- other variant proceeding to precocious puberty
What are ways of investigating precocious puberty?
Auxology LH, FSH, sex steroid measurements LH response to 100 micrograph GnRH Adrenal steroids MRI scans of hypothalamic-pituitary area Ultrasound scans of pelvis
How is precocious sexual development treated?
Anti-androgens
5-alpha-reductase inhibitor
Aromatase inhibitor
Long acting GnRH analogue
What is pubertal delay?
Absence of secondary sexual maturation by 13 years in girls or 14 years in boys
What is constitutional delay?
- affecting both growth and puberty. Approximately 90% of all pubertal delay cases
- about 10 times more common in boys
- secondary to chronic illness eg diabetes, cystic fibrosis
What is hypogonadotrophic hypogonadism?
Low LH and FSH
Kallman’s syndrome
Other genetic causes, hypopituitarism
What is hypergonadotrophic hypogonadism?
High LH and FSH
Gonadal dysgenesis, low sex steroid levels:
- congenital - klinefelters and turners
- gonadal dysgenesis with normal karyotype, viral eg mumps
What might be done to investigate delayed puberty?
Family history, dystrophic features, anosmia Auxology Pubertal staging Bone age estimation LH, FSH, sex steroid measurements LH response to 100 micrograms GnRH Adrenal steroids - high with tumours, precursors high with CAH MRI scans of hypothalamo-pituitary area Ultrasound scans of pelvis
How do we treat delayed puberty?
Testosterone in males
Oestrogens in females
Oxandralone (synthetic steroid)
What do we need to reproduce?
- correct process of sex determination and differentiation
- sexual maturation
- production and storage of sufficient supply of eggs and sperm
- correct number of chromosomes in egg and sperm
- actual sexual intercourse - egg and sperm have to be transported and meet
- fertilisation, implantation, embryonic and placental development
- once delivered/born, to nurture individual until capable of independent life
How is gonadal function controlled by feedback?
- hypothalamic and pituitary peptide hormones
- gonadal steroid and peptide hormones
What are the hormones of the HPG axis?
Hypothalamus: (releasing hormones) gonadotrophin releasing hormone (GnRH), kisspeptin
Pituitary: (stimulating hormone) FSH and LH
Gonad: in females oestradiol (E2), progesterone (PS), in males testosterone (inhibins and activins)
What is the HPG axis there to do?
Coordinate gonadal function for viable gamete production (male), growth and development (both)
The u,it ate coordination of gonadal function to facilitate viable gamete production, growth and development.
What does GnRH do in the HPG axis?
GnRH positively drives the gonadotrope cells of the anterior pituitary where it stimulates synthesis and secretion of LH and FSH which positively stimulates the production of gonadal steroid (oestrogen positive and negative feedback, progesterone and androgens negative feedback only).
What is GnRH?
Decapeptide (10aa)
Synthesised and secreted from GnRH neurones
Secreted in a pulsatile fashion - pulse generator orchestrated
Brings to the GnRH receptor (GnRHR) on gonadotrophin cells of the anterior pituitary to stimulate the synthesis and secretion of gonadotrophin hormones LH and FSH
After release GnRH binds to its receptor which is a GPCR on gonadotroph cells of the anterior pituitary
What is the pulsatile release of GnRH stimulated by?
Hypothalamic neurotransmitters
What happens following the release of GnRH?
It binds and increases gene transcription of alpha and beta subunits of LH and FSH. These hormones are then translated, packaged and secreted from gonadotroph cells and also released in a pulsatile fashion. Pulse of GnRH also corresponds with release of LH. Lots of things regulate it.
What is the importance of the pulsatile release of GnRH?
GnRH pulse stimulates a pulse of LH and FSH secretion from the pituitary
Pulsatile GnRH secretion is vital for stimulation of LH/FSH secretion
Slow frequency pulse favours FSH release, rapid frequency favours LH release
Continuous release results in cessation of response
What are the clinical applications of GnRH?
Synthetic GnRH - same structure as native GnRH –> stimulatory …… Used in the stimulation of hypothalamic pituitary axis eg delayed puberty
GnRH analogues - modified GnRH peptide structure, loss of pulsatility –> inhibitory… Either agonists or antagonists ……. This is a,ways used to down regulate/inhibit the HPT axis
What is the mechanisms of action of synthetic GnRH and GnRH analogues?
Brings to receptor
Activation of signalling - GPCR
Stimulation of gonadotrophin synthesis and secretion
Dissociation of GnRH from receptor
Responsive to next GnRH pulse as it occurs
Agonists work in a similar way until we don’t get the dissociation. We get a constant GnRH binding to agonist as modified in a way that prevents dissociation from the receptor. After 2-3 weeks of treatment resulting in uncoupling if GnRHR from G protein signalling.
Antagonists bind to the receptor and block the receptor are all competitive inhibitors of GnRH itself.
What are the clinical used of GnRH analogues?
Ovulation indication and IVF
GnRHR/GnRH and ovarian and endometrial cancers
Really and breast cancer in pre-menopausal women
PCOS
Endometriosis
Uterine fibroids
Prostrate cancer
The two biggest uses in terms of clinical applications and grossing money wise is ovulation induction and IVF, and also in prostate cancer. The one controversial application is gonadal protection prior to chemotherapy. In order to try and preserve fertility in child cancer patients.
What is the structure of gonadotrophins?
They are comprised of two different subunits. They have a common alpha subunit and there is a hormone specific beta subunit which confers biological specificity for each are all glycosylated. This allows recombinant heterogeneity.
About the gonadotrophin hormones; FSH, LH and hCG…
Heterdimeric peptides - common alpha subunit and hormone specific beta subunit
N-linked carbohydrate side chains and o linked in hCG - microheterogeneity required for biological function
Free subunits have no biological action
Alpha subunits are synthesised in excess with beta subunit limiting the hormone concentration
Pulsatile secretion due to pulsatile GnRH release from the hypothalamus but pulsatile secretion not necessary for biological activity
The three subunits don’t have any biological activity independently. The beta subunit is the rate limiting step. Alpha is synthesised in excess and released in a pulsatile fashion. However, the pulsatile release isn’t essential for their function.
What are the functions of LH?
Testis: stimulation of leydig cell androgen synthesis
Ovary: theca cell androgen synthesis, ovulation, progesterone production of corpus Luteum
What are the functions of FSH?
Testis: regulation of Sertoli cell metabolism
Ovary: follicular maturation, granulosa cell oestrogen synthesis
What is the basics of female gonadal steroid production?
Androgens transported from theca cells into granulosa cells under control of FSH receptor they become Oestrogens. This used AROMATASE.
What is the definition of puberty?
transition from no-reproductive to reproductive state
What are the main features of puberty?
- secondary characteristics develop (primary are present at birth)
- adolescent growth spurt
- profound physiological changes
- profound psychological changes
gonads produce mature gametes (testes: spermatozoa, ovaries: oocytes)
What are the names of the two main endocrine processes of puberty?
Adrenarche
Gonadarche
What is adrenarche?
Originates from the adrenal and is instigated by the maturation of cells in the adrenal cortex. This results in the release of androgens from the adrenal.
Changes that occur include the growth of pubs and axillary hair and growth in height. This is independently regulated.
What is gonadarche?
Occurs following adrenarche. This is HPG driven. The synthesis and secretion of pituitary peptide hormones - LH and FSH, which activate gonadal function. LH causes secondary sex characteristics and FSH causes the growth of testis (male), steroid synthesis, folliculogenesis (female)
What are the substances that change in adrenarche?
Dehydroepiandrosterone (DHEA) Dehydroepiandrosterone sulphae (DHEAS)
There is a gradual increase form 6-15 years with a 20 fold increase peaking at 20-25 years.
- decline in DHEA/DHEAS thereafter = adrenopauqe
- no change in other adrenal androgens
- no known mechanism for trigger of adrenarche
What is pubarche?
- appearance of pubic/axiallary hair
- induced by adrenal androgen secretion
- associated with: increased serum production = acne, infection, abnormal keratinisation = acne
- if before 8 (girls) and 9 (boys) it is precocious
What are the features of gonadarche?
- several years AFTER adrenarche (typically ~11 years of age)
- reactivation of hypothalamic GnRH
- activation of gonadal steroid production –> production of viable gametes and ability to reproduce
What is GnRH?
- synthesised and secreted by specialise hypothalamic centres - GnRH neurones
- pulsatile secretion is essential for GnRH function
- HPG axis is first activated at 16th gestational week: pulsatile GnRH secretion in foetus until 1-2 years postnatally when ceases, re-activation at ~11 years
- GnRH neurones ‘restrained’ during postnatal period –> 10 years or more
- at puberty a gradual ise in pulsatile release of GnRH
What stimulates onset of puberty?
It is clear that it is a maturational event within the CNS.
- inherent (genetic) maturation of 1000-3000 GnRH synthesising neurones
- environmental/genetic factors
- body fat/nutrition
- leptin
- other gut hormones
- kisspeptin
- What drives the central generator???
??
What is the link of nutrition and body fat to puberty?
- link between fat metabolism and reproduction
- anorexia nervosa/intensive physical training: reduced response to GnRH, decreased gonadotrophin levels, amenorrhea, restored when nourished/exercise stopped
What is the Frisch et al. body fat hypothesis?
Certain % fat:body weight necessary for menarche (17%) and required (22%) to maintain female reproductive ability
What is kisspeptin?
- found in hypothalamic neurones
- kisspeptin receptors expressed in GnRH neurones
What is the relation between kisspeptin and puberty?
mutations of GPR54 or the gene coding for kisspeptin.
- abnormal development of GnRH neurones - hypogonadism
- failure to enter puberty
- hypothalamic hypogonadism
activating mutations of kisspeptin receptor - precocious puberty
What is ‘consonance’?
smooth ordered progression of changes
order of pubertal changes in uniform:
- age of onset, ice and duration of changes: wide inter-individual differences
- average age of menarche onset (UK) = 12.5 years
What are physical changes in girls during puberty?
- breasts enlarge (thelarche)
- pubic/axilliary hair
- uterus enlarges, cytology changes, secretions in response to E2
- uterine tubes
- vagina
- cervical changes
- height (earlier onset then boys, peak height velocity 9cm/y reaches at 12 years)
- body shape
- HPG axis (increase in ovarian size and follicular growth)
- menarche (not equated with onset of fertility)
- fertility (in 1st year ~80% menstrual cycles anovulatory, irregular cycles)
What are physical changes in boys in puberty?
- external genitalia (increase in testiular volume >4ml, growth of penix, scrotum, scrotal skin changes)
- vas deferens (lumen increases)
- seminal vesicles and prostate
- facial/body hair
- pubic/axilliary hair
- larynx (androgens - enlarge larynx, adams apple (projection of thyroid cartilage), voice deepens)
- height (PHV = 10.3cm/y reached at 14 years)
- body shape
- onset of fertility (testosterone form leydig cells stimulates meiosis and spermatogenesis in sertoli cells, boys fertile at the beginning of puberty)
What is a trader orchidometer?
- measures testicular size
- numbers represent the volume in millimetres
- 10th, 50th, 90th centimes of testicular size in boys at different ages
What causes the growth spurt in puberty?
Complex interaction between growth hormone and oestrogen.
Earlier in girls - approximately 2 years
biphasic effect of oestrogen in epiphyseal growth
- -> low levels: linear growth and bone maturation
- -> high levels: epiphyseal fusion
What are the effects of androgens on the differentiation of pilosebaceous units (PSUs)?
- androgens stimulate sebum secretion and together with infection this can cause acne
- androgens can induce differentiation of villus PSUs to terminal PSUs encouraging moustache and beard
- androgens can induce differentiation of villus hairs to apo-PSUs encouraging increased growth in areas of pubic and axillary hair
What are the psychological changes the accompany puberty?
- increasing need for independence
- increasing sexual awareness/interest
- development of sexual personality
later maturation = better adjustment
What is precocious sexual development?
development of any secondary sexual characteristic before the age of 8 in girls, and before the age of 9-10 in boys.
precocious puberty is when pubertal changes are early but in consonance.
- gonadal-dependent (central) precocious puberty : consonance
- gonadotrophin-independent precocious puberty : loss of consonance
What happens in gonadal-dependent (central) precocious puberty?
CONSONANCE
- excess GnRH secretion: idiopathic or secondary
- excess gonadotrophin secretion: pituitary tumour
What happens in gonadal-independent precocious puberty?
LOSS OF CONSONANCE
- testotoxicosis: activating mutation of LH receptor
- McCune albright: constitutive activation of adenylyl cyclase»_space; hyperactivity of signalling pathways and over-production of hormones
- sex steroid secreting tumour or exogenous steroids
What is pseudo-precocious puberty?
PREMATURE ADENARCHE/PUBARCHE
- precocious development of pubic and/or axillary hairs
also CAH (congenital adrenal hyperplasia)/cushings
PREMATURE THELARCHE - PRECOCIOUS BREAST DEVELOPMENT
- can be unilateral
- isolated ‘cyclical’ (2 years) proceeding to precocious puberty
What investigations might be done into precocious puberty?
- auxology: accurate measure of height, including body proportions and weight
- pubertal staging
- boen age estimation
- LH, FSH, sex steroid measurements
LH response to 100micrograms GnRH: normal for stage of puberty in central precocious puberty, surpassed in testoxicosis - adrenal steroids: high with tumours, precursors high with CAH
- MRI scans of hypothalamic-pituitary area
- ultrasound scans of pelvis (uterus and ovaries)
How might we treat precocious sexual development?
- anti-androgens
- 5alpha-reductase inhibitor (T –> 5a-DHT)
- aromatase inhibitor
- long-acting GnRH analogue (central precocious puberty
What is pubertal delay?
absence of sexual maturation by 13 years in girls (or absence of menarche by 18years) or 14 years in boys
- CONSTITUTIONAL DELAY
- HYPOGONADOTROPHIC HYPOGONADISM (low LH and FSH)
- HYPERGONADOTROPHIC HYPOGONADISM (high LH and FSH)
What is constitutional delay?
- Affecting both growth and puberty. Approximately 90% of all pubertal delay cases.
- About 10 times more common in boys.
- Secondary to chronic illness eg diabetes, cystic fibrosis.
What is hypogonadotrophic hypogonadism?
low LF and FSH
•Kallman’s syndrome (X-linked KAL gene, GnRH migration)
•Other genetic causes, hypopituitarism
what is hypergonadotrophic hypogonadism?
high LH and FSH
- Gonadal dysgenesis, low sex steroid levels:
oCongenital – Klinefelter’s syndrome (XXY) 1:500 males, Turner’s syndrome (XO) 1:3000 girls
oGonadal dysgenesis with normal karyotype, viral eg mumps
How might we investigate delayed puberty?
- Family history, dysmorphic features, anosmia
- Auxology (accurate measurement of height, including body proportions, and weight)
- Pubertal staging
- Bone age estimation … based on above
- LH, FSH, sex steroid measurements
- LH response to 100µg GnRH
- Adrenal steroids – high with tumours, precursors high withCAH
- MRI scans of hypothalamo-pituitary area
- Ultrasound scans of pelvis (uterus and ovaries)
How might we treat delayed puberty?
- testosterone (in males)
- oestrogens (females)
- oxandralone (synthetic steroid)
What are the aims of the menstrual cycle?
- selection of a single oocyte
- regular spontaneous ovulation
- correct number of chromosomes in eggs
- cyclical changes in the vagina, cervix and fallopian tube
- preparation of the uterus
- support of the fertilised dividing egg
What controls the menstrual cycle?
The hormones produced by the follicle in the ovary which feedback to control the main production of GnRH and gonadotrophins which go on to control the whole cycle.
What are the two phases of the menstrual cycle?
Follicular phase
Luteal phase
What is the follicular phase of the menstrual cycle?
growth of follicles up to ovulation – dominated by oestradiol production from dominant follicle
What is the luteal phase of the menstrual phase?
formation of corpus luteum from the empty follicle – dominated by progesterone production from the corpus luteum
What are the basic sequence of events in the menstrual cycle?
- Two phases separated by ovulation
- Cycle begins on day 1 - first day of bleeding
- Next 14 days are follicular phase – ie growth of follicle
- Ovulation occurs at the end of the follicular phase
- Empty follicle becomes the corpus luteum
- The next 14 days are luteal phase, ie dominated by the corpus luteum
- Menstruation occurs at the end
What are the feedback changes in follicular phase?
- Release of negative feedback
- Negative feedback then reinstated
- Switch from negative to positive feedback
The switching of feedback determines the control of the cycle. We start in the luteal phase which is dominated by progesterone produced from the corpus luteum which feedback back to down regulate the secretion of GnRH and gonadotrophons so it is negative feedback.
In males there is constant negative feedback but in women it is more complicated. In females the negative feedback at the start of the follicular phase is released at the end of the luteal phase. The break is lifted, allowing the HPG axis to work again and this stops in the follicular phase and allows the increase of secretions again.
Oestrogen is started to be produced for the growing follicle and this feeds back to reinstate the negative feedback. Towards midway through the cycle there are sustained high levels of oestrogen for the dominant follicle and the feedback switches to positive.
What does the inter-cycle rise in FSH allow?
allows the selection of a single follicle
What is the window of opportunity?
The exact stage of development that a follicle has to be in to be selected
How does follicle selection occur?
•Raised FSH present a ‘window’ of opportunity
•FSH threshold hypothesis
-One follicle form the group of antral follicles in the ovary is just at the right stage at the right time…
-This becomes the dominant follicle which goes on to ovulate
-This is known as selection
-Can be in either ovary, and doesn’t have to be alternating
•Oestradiol levels rise reinstating negative feedback at pituitary causing FSH levels to fall, and this prevents further follicle growth.
What happens to the gonadotrophins during the follicular phase?
As FSH falls, LH increases. The dominant follicle acquires LH receptors on granulosa cells. Other follicles do not, so they loose their stimulant and die.
It is also thought that it has more FSH receptors than in other follicles, so it is able to catch any FSH around even if levels are really low. FSH couples maybe to their downstream signalling pathway very effectively.
What are the rules of receptors on follicles?
- Theca always has LHr, never FSHr – remember LH drives androgen and progesterone production from theca
- Granulosa cells have FSHr, then LHr acquired from mid-follicular phase onwards – FSH and then LH drive oestrogen production in follicular phase
What is steroidogenesis?
Just be aware that all steroids originate from cholesterol and are made by sequential removal of carbon atoms by a series of enzymes (in blue) which are distributed through the cellular compartments of the follicle.
What are the basic timings of the menstrual cycle?
- Day 1 is the first day of bleeding
- Menstruation lasts 3-8 days, written in notes as 7/28 or 5-6/27-32
- A regular cycle should have no more than 4 days of variation from month to month
Most womens cycles are 30 days. The variation is in the follicular phase because the corpus luteum has a fixed lifespan, after 14 days it will die.
How is the follicle selected during the menstrual cycle?
- Dominant follicle selected
- Grows rapidly, doubling in diameter in 7 days… from 7mm to 14mm
- Needs masses of growth factors, nutrients and steroids
- Rapid neoangiogenesis
- Oestrogen released from follicle into circulation
It doesn’t only rely on oestrogen. There is a very rich vasculature in the dominant follicle allowing nutrients to be fed to it and growth can occur. There is also neoangiogenesis.
What does the LH surge do in the menstrual cycle?
• Throughout the follicular phase E2 feedback was negative
• At the end of the follicular phase E2 levels are raised for long enough feedback switches from negative to positive
• This causes massive release of LH from the pituitary
• Exponential rise in LH in serum
• Triggers ovulation cascade
- Egg is released
- Above result in changes in follicle cells = luteinisation ie formation of the corpus luteum
- E2 production falls and P is stimulated
What happens during ovulation?
- Ovulation occurs via a cascade of events
- Blood flow to the follicle increases dramatically – increase in vascular permeability increases intra-follicular pressure
- Appearance of apex or stigma on ovary wall
- Local release of proteases
- Enzymatic breakdown of protein of the ovary wall
- 18 hours after peak of LH, hole appears in follicle wall and ovulation
The follicle has by now moved back to the cortex of the ovary. As they grow they move into the medulla which has a rich blood supply and as they get bigger and bigger they grow back up to cortex as they need to be able to release the oocyte from the ovarian wall.
The stigma is a kind of weakness in the wall – proteases degrade the wall to allow the oocyte to be released.
- Oocyte with cumulus cells is extruded from the ovary under pressure
- Follicular fluid may pour into the Pouch of Douglas
- The egg is ‘collected’ by fimbria of Fallopian tube
- The egg progresses down the tube by peristalsis and action of cilia
Egg collected by fimbria due to signal from fluid. Fluid may move into the pouch of Douglas but Fallopian tube will move around and pick up egg as it is released. Therefore, if you have fibroids or anything that means the follicular tubes are latent then may not get pregnancy as can’t move to pick up the egg. The egg moves down the tubes – cilia – and hopefully meets with the sperm to be fertilised in the ampulla.
On what day in a regular cycle does ovulation occur?
day 15
Hoe do home ovulation detection methods work?
Ovulation “sticks” that detect the LH surge.
Home ovulation methods are based on the detection of these hormone products in urine or saliva, or the changes in other body fluids such as cervical mucus in the vagina. The simplest and least expensive method is the detection of the LH surge in urine. Many women refer to this as “pee on a stick” although there are different ways of performing the test depending on the kit. Many kits are available in the drug stores. For most women, this is adequate and accurate. Ovulation occurs approximately 12 to 24 hours after the detection of the LH surge in the urine.
What happens in preparation of the oocyte?
- From its formation as a primary oocyte in the fetal ovary up until ovulation, the oocyte has been arrested in the first meiotic division.
- This permits the oocyte to retain all of the DNA and remain as large as possible during its long wait.
- In response to the LH surge, the nucleus of the oocyte in the dominant follicle completes the first meiotic division, but it does not divide
We have got to create haploid oocytes. We are in meiotic arrest as the oocyte has entered into meiosis I and stopped.
What is the extrusion of the polar body?
Undergoes meiosis I and packages all the chromosomes into astute known and the first polar body. Maintains majority of cytoplasm because we need everything that is necessary to sustain the implantation for fertilisation of the egg.
The egg is now called secondary oocyte. It goes into meiosis II and arrests again. It stays in meiosis II until it is fertilised. If successfully fertilised will complete meiosis II, if not then it will be lost in menstruation.
What is the secondary oocyte?
- Unlike sperm we only want a single oocyte
- The oocyte is the largest cell in the body (sperm are smallest… but the fastest!)
- The oocyte has to support all o 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 oocyte is now on its way into the tube… will it meet a sperm? The story continues later…
How is the corpus lute formed?
- After ovulation the follicle collapses
- The corpus luterum is formed, ‘yellow body’
- Progesterone production increases greatly, also E2
- CL contains large numbers of LH receptors
- CL supported by LH and hCG… if a pregnancy occurs
The second peak of E2 in the luteal phase is made by the corpus luteum
What is the basic physiology of the uterus?
The uterus is mainly muscle. It has an endothelium lining
which is lost each month. The sperm swim up the uterine
tube and meet the egg in the ampulla.
What changes occur in the uterus and cervix?
- Maternal steroids increase the size of the newborn uterus
- growth with height during infancy
- myometrium dependent on oestradiol
- corpus of uterus undergoes greater increase in size than the cervix
In the newborn, the uterus has been exposed to a huge amount of oestrogen. Therefore, the uterus in the new born is disproportionately large and by the age of 4 it has shrunk to be smaller in the first place.
In a menopausal woman the uterus shrinks to a similar size as it would be during puberty.
What does ‘parous’ and ‘nullparous’ mean?
parous: have given birth
nullparous: never given birth
What is the myometrium?
- The outer muscular myometrium grows gradually throughout childhood
- Increases rapidly in size and configuration during puberty
- Changes in size through the cycle and is capable of vast expansion during pregnancy
The inner layer is of circular fibres.
The middle layer is figure of 8 or spiral fibres.
The outer layer is longitudinal fibres.
Together these produce a highly dynamic organ.
What is the endometrium?
- Very thin in childhood. Begins to thicken at puberty
- Dependent on steroids. Responds cyclically to hormone changes. Can be seen and measured on an ultrasound scan. Good ‘bioassay’ of oestradiol level
- Changes in glandular and epithelial cells through the cycle. At menstruation most of the endometrium is lost
- After menstruation – stromal matrix with small columnar cells with glandular extension 2-3mm thick glands are simple and straight
The endometrium is the inner layer that is shed each month. The arteries supplying it become very convoluted to increase surface area and can get more nutrients in. Around a week after ovulation it is at its peak of activity it has grown the glands for adhesion factors, growth factors etc on the surface where implantation will take place.
There are changes throughout the cycle and the first part of the cycle is dominated by oestrogen which causes proliferation. After ovulation the corpus luteum is producing progesterone instead which causes the differentiation of this layer eg maturation of secretory glands.
What is the endometrial proliferative phase?
Proliferative phase stimulated by oestradiol from the dominant follicle.
Stromal cell division, ciliated surface. Glands expand and become tortuous giving increased vascularity, neoangiogenesis also occurs. There is minimal cell division by days 12-14.
When the endometrium >4mm induction of progesterone receptors occurs and there are small muscular contractions of the myometrium.
What is the endometrial secretory phase?
The secretory phase (luteal phase of ovary) 2-3 days after ovulation, the gradual rise in progesterone causes a reduction in cell division. Glands increase in tortuosity and distend – secretion of glycoproteins and lipids commences.
Oedema, increased vascular permeability arterioles contract and grow tightly wound. Myometrial cells enlarge and movement is suppressed and blood supply increases.
