Section 7- Reproductive endocrinology

Question 1

Sequential process of sexual differentiation

Answer 1

1. Establishment of genetic sex
2. Translation of genetic sex into gonadal sex
3. Translation of gonadal sex into phenotypic sex

Question 2

Which duct is typical for males and which is for females?

which organs does each of those ducts give rise to?

Answer 2

Females: mullerian duct-> Female tract (oviduct, uterus, upper vagina)

Males: Wolffian duct-> Male tract (Epididymis, vas deferens, seminal vesicle)

Question 3

What is urogenital sinus?

Answer 3

common primordium for external genitalia

Will develop in either Clitoris and vulva in females, or penis and scrotum in males

Question 4

What happens if we remove testes from embryos? What happens to female embryos that had their gonads removed?

What does that mean?

Answer 4

embryos developed a female reproductive tract and female genitalia.

But, gonadectomised female embryos also developed into female features

it means that The TESTES are essential for male sexual differentiation, but the ovaries are NOT necessary for female differentiation

-> embryos develop in females by default and a switch is requried for an embryo to start developign in a male

Question 5

Which of the developmnet pathways (male or female) are dependent on hormones? Why

Answer 5

Male development pwathway is hormonal dependent as hormones act as a switch to swith from default female pathway into male pathway

Question 6

Pre-requisites for normal sex differentiation

Answer 6

Normal intact chromosome complement
Fully functioning sex determination genes

Intact steroidogenic pathway and receptors

Question 7

Is female fomration abolutelty default?

Answer 7

No, it stil requires some signalling but less than in males

Question 8

Allozome vs isozome

Answer 8

allozome= sex chromosomes
isozome= all chromosomes

Question 9

What are the functions of sexes that result form sexual differentiation

Answer 9

Males: provision of sprem, provision of different set of chromosomes

Females: Provision of eggs, Fertilization, Pregnancy, Lactation

Question 10

Classification of sexual differences: Chromosomal, gonadal, inernal ducts, external genitalia, Phenotypic, behavioural

Answer 10

Question 11

What are all the possible male and female phenotypes?

Answer 11

Question 12

Presence of _ = MALE

Answer 12

Presence of Y = MALE

Question 13

How does sexual reproduction produce new combinations of genes? Why is it beneficial?

Answer 13

recombination occurs between homologous chromosomes-> genetic variation-> benefit for survival

Question 14

Which regions of sex chromosomes can participate in recombination

Answer 14

only a small portions on either ends of X and Y that can participate in recombination-> these are called pseudoautosomal regions

Question 15

What is MSY region

Answer 15

MSY does not participate in recombination at all; it is the whole of Y chromosome, but the PAR region (Pseudoautosomal region that participates in recombination)

Question 16

Does the whole X chromosome participate in recombination?

Answer 16

The whole X chromosome participates in recombintion only if 2 Xs are present

if X and Y are present, only the PAR regions of X participate in recombination

Question 17

What is SRY? Where is it found?

Answer 17

Sex determining region of Y

Present in MSY (Male specific region of Y)

Question 18

Proof of the role of the SRY gene

Answer 18

male Y chromosome was cut up in chunks
DNA pieces were injected into pronuclei in hope for integration into a sex chromosome

Some embryos contained ovaries, some contained testis

They were interested in those, that contained tesits as they had male phenotype, but had female chromosomal pattern XX

some fetuses had XX but yet had testes due to SRY gene DNA- Thus SRY is required for testis development and male phenotype

Question 19

What is the effect of SRY on Bipotential Genital ridge

Answer 19

Converts Bipotential Genital ridge into testis

Question 20

Why is the location of SRY in MSY a bit problematic

Answer 20

SRY is oacted close to the region that participates in recombination

1) Can lead to XX male
2) Y chromosome can have abnormal SRY-> Deleted/mutant SRY gene-> XY female

Question 21

What is the role of HMG proteins

Answer 21

bend the DNA after they bind to it

Question 22

SRY has DNA __ capability

Answer 22

SRY has DNA binding capability

Question 23

in which region of DNA are SRY genes found?

Answer 23

In DNA binding domain

Question 24

SRY protein binds to DNA to __ because it is a __

Answer 24

SRY protein binds to DNA to induce trancription of other genes because it is a transcription factor

Question 25

What is the consequence of SRY absence in sex determination? Se

Answer 25

SRY absence: Ovary is formed-\> female SRY presence: SOX9-\> testis-\> male

Question 26

At what day is SRY expressed in bipotential gonad?

Answer 26

day 10-12

Question 27

SOX9 expression is __ throughout embryonic development in the gonad

Answer 27

SOX9 expression is continuous throughout embryonic development in the gonad

Question 28

SOX9 and SRY relationship

Answer 28

SOX9 is the target gene of SRY ## Footnote As pregnancy progesssess: SOCS9 takes over the role of SRY SOCS9 inhibits the expression of SRY

Question 29

How does SOX prevent the embryo from becoming a female

Answer 29

other factors + SOX9 lead to amh expression - anti mullerian hormone (or MIS Mullerian inhibiting substance)-\> responsible for destruction of mullerian duct (which transforms into female reproductive organs) Wolffian duct takes over-\> male is formed Female phenotype requires other hormones and proteins (WNT4 and RSPO1) along with TF FOXL2 determines ovary formation and thus female phenotype - these have to be present to form fa female (thus it is not formed by default)

Question 30

What is the site of GnRH production?

Answer 30

hypothalamus is the site of GnRH production as there ar GnRH neurones

Question 31

WHat are the 2 centers of the hypothalamus that release GnRH?

Answer 31

It is synthesized in two different centres of the hypothalamus, the tonic (male) and the ovulatory or surge centre (female).

Question 32

Estradiol entrance to the brain: male vs female fetus What is the consequent effect

Answer 32

In male fetus, testosterone freely enters brain and converted to estradiol by aromatase * as testosterone is not bound to a protein that is produced only during fetal period * this protein is called alpha-fetal protein; produced by fetal liver In female, estradiol cannot cross the blood-brain barrier (binds to alpha-Fetoprotein) * this is why estradiol doesn’t end up in the brain and de-feminize the surge center absence of estrogen causes the surge center to mature and become functional post-puberty * Female retains surge center + tonic center to control LH/FSH after puberty this **estrogen** presence in the brain is responsible for **de-feminization**, lack of maturation of another center called surge center

Question 33

what is the imortance of the surge center in females?

Answer 33

surge center is important for females in the post puberty period where there’s a surge release of GnRH, leading to a surge release of gonadotropins that are responsible for ovulation and reproductive cycle

Question 34

The hypothalamo-pituitary-gonadal axis

Answer 34

hypothalamus produces GnRH which stimulates the production of FSH and LH from the pituitary They act upon gonads to produce gonadal hormones that can have negative impact on hypothalamus and pituitary

Question 35

The function of the gonads

Answer 35

1. Gametogenesis 2. Hormonogenesis (mostly steroids) 1. Electrolyte homeostasis 2. Fuel and protein metabolism 3. Adiposity and muscle mass

Question 36

Effect of plasma testosterone levels at various ages in human males

Answer 36

testosterone levels at **fetal** stage are responsible for Sexual differentiation (maturation of testis and their descent, formation of reproductive organs, formation of tonic center and inhibition of surge center) testosterone levels at **neonatals** stage are a tiny bit hihger than at fetal, but the function is unknown; some infants show pimple development because of this increase Pre-puberty: Gonads quiescent in both sexes Surge in pubertal perdiod and remains high durign adulthood (same increases are seen in estradiol in females )

Question 37

What are the chnages that occur in puberty

Answer 37

Includes all physiological, morphological & behavioral changes v Gonads/brain/phenotype change from adolescent to adult v In females, first menstrual cycle – menarche v In males, first ejaculation - semenarche

Question 38

GnRH, FSH and Lh levels: Prepubertal period vs Puberty

Answer 38

Prepubertal period * minimal GnRH release; low amplitude and low frequency * FSH and LH low * minimal to no folliculargenesis or spermatogenesis Puberty * increase in the pulse frequency and amplitude of GnRH release * once the puberty occurs, the tonic center produces more frequent GnRH pulses; in case of adult females only, the surge center becomes active and results in massive release of GnRH * increase in FSH and LH pulses * folliculargenesis and spermatogenesis occur

Question 39

What are the changes in that occur in hypothalamic senstitivity to estradiol and negative feedback that allow puberty to occur

Answer 39

Question 40

Gonadotrophin Releasing hormone- structure

Answer 40

vSmall peptide of 10 a.a. cleaved from a larger precursor vSynthesized by about 1000-3000 neurons in the hypothalamus

Question 41

Where do axons of neruones that release Gonadotrophin Releasing hormone terminate? What is their consequent role? Where else is GnRh made and what is the role?

Answer 41

vMost axons terminate in the hypophyseal portal capillaries and release GnRH → Stimulation of gonadotrophs in the anterior pituitary vSome axons terminate in other brain areas and may affect sexual behavior GnRH is also synthesized in the placenta, gonads, breast, lymphocytes and the pituitary, but function unknown

Question 42

Structure of Gonadotropins LH and FSH

Answer 42

Glycoprotein

Question 43

What are the subunits of Gonadotropins LH and FSH

Answer 43

Common α-subunit and different β-subunit that provides specificity (there’s LH-beta and FSH-beta gene). the alpha-gene is not only common for gonadotropins, but also for TSH

Question 44

What are the consequences of changes in glycosylation of Gonadotropins LH and FSH that may occur in circulation

Answer 44

different isoforms with slightly different biological properties

Question 45

What is the receptor and pathways used by LH and FSH

Answer 45

G-linked: Activation of adenylate cyclase and also phospholipase C (PKA and PKC pathways)

Question 46

What is the release pattern of LH and FSH

Answer 46

Pulsatile release (in response to GnRH)

Question 47

Which cells have LH receptors? What is the pathways tiggered by LH binding in these cells?

Answer 47

Thecal cells in females; Leydig cells in males 1) Adenylel cyclase-\> cAMP-\> PKA 2) Phospholipase C-\> DAG-\> PKC 2) Phospholipase C-\> IP3-\> Ca2+

Question 48

Which cells have FSH receptors? Which pathways are triggered in these cells by FSH binding?

Answer 48

Granulosa cells; sertoli cells Adenylel cyclase-\> cAMP-\> PKA

Question 49

What is the overall effect of gonadotropins on gonads

Answer 49

Oogenesis, spermatogenesis, steroidogenesis Target cells and actions differ in male and female * Testis: Only LH is steroidogenic (acts on Leydig cells)-\> produce testosterone * Ovaries: Both LH and FSH are steroidogenic act on two cell types (theca and granulosa cells)

Question 50

What are the actions of LH and FSH in non-gonadal tissues?

Answer 50

v Increase of intracellular cholesterol. v Transport of cholesterol to the inner mitochondrial membrane by StAR v Conversion to pregnenolone; effect and mechanism similar to ACTH action in adrenal cortex

Question 51

What is the role of sertoli cells?

Answer 51

sertoli cells main role is to support spermatogenesis, but they can also produce some estrogen when stimulated by FSH; thus sertoli cells also have some steroidogenic role

Question 52

What are the 2 stages of follicules

Answer 52

- primordial - primary - secondary

Question 53

What are the types of somatic cells in follicles

Answer 53

1) Theca cells are the endocrine cells associated with ovarian follicles that play an essential role in fertility by producing the androgen substrate required for ovarian estrogen biosynthesis. 2) A **granulosa** cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete

Question 54

What is a follicular antrum?

Answer 54

The follicular antrum is the portion of an ovarian follicle filled with follicular

Question 55

What is the role of corpus luteum?

Answer 55

it is the main producer of progesterone which is essential for the establishment of pregnancy and maintenance

Question 56

Positive and netative feedback of estrogen

Answer 56

low estrogen can have a negative effect at the level of pituitary and tonic center as a negative feedback loop. It will inhinbit LH and FSH release but higher levels of estrogen can act upon the surge centre as a positive feedback which results in GnRH surge release-\> pre-ovulatory FHS and LH surge-\> ovulation

Question 57

Do we have just 1 follicule growing at one particular time?

Answer 57

group of follicles grow together at a certain period of time, but there is one follicle that will continue to grow; other follicles will undergo attrition (death) this one follicle becomes large- dominate follicle

Question 58

When would dominant follicule ovulate?

Answer 58

dominant follicle doesn’t ovulate unless there’s and LH surge; will die if it doesn’t occur

Question 59

Hormonal profile changes during estrous cycle

Answer 59

LH peak in the beginning- responsible for ovulation of the dominant follicle from the previous cycle One at the end- initiation of the next cycle LH has one peak per cycle, and then remains at a lower concentration for the rest of the cycle Progesterone concentrations starts to increase after the begging of the cycle This is because there’s a corpus luteum that is formed in the beginning of the cycle after ovulation Remains functional for some time; then undergoes luteolysis and progesterone levels decrease When progesterone levels are high: luteal phase Low levels of progesterone: follicular phase as there’s only the follicle that is present (releases estrogen); responsible for LH surge Estrogen there are periodic increases and decreases Estrogen surge preseeds LH surge; this is the postive feedback that results in LH release FSH surge along with LH surge Smaller periodic increases in FHS Peak estrogen levels is associated with low levels of FSH; low estrogen levels are associated with peak FSH levels- reverse relationship between FHS and estrogen- negative feedback regulation

Question 60

how does the level of estrogen change as follicule growth?

Answer 60

as follicle growth, estradiol levels increase as dominant follicle is the main source of estrogen in females

Question 61

What happens when a dominant follicule dies\>

Answer 61

As dominant follicle dies, estrogen levels go down -\> no negative feedback-\> increase in FSH-\> next wave

Question 62

Surge in which hormone leads to ovulaion

Answer 62

FSH

Question 63

What are the hormonal levels durign the Follicular phase

Answer 63

low progesterone levels, increased levels of estrogen-\> stimulation of pre-ovulation gonadotropin surge-\> ovulation