Sex Differentiation and Gametogenesis Flashcards
what determines if a foetus is male or female
whether they have an XX or XY chromosome
When is genotypic Sex established in mammals
At fertilisation
what is Turner Syndrome and what does it result in
- when someone has an XO chromosome
- results in a female that:
> is sterile
> has poorly developed breasts
> has very small sexual organs
sexual differentiation
what is sexual differentiation
the development of any male- or female-specific physical or behavioral characteristic, to equip organisms with the necessary anatomy and physiology to allow sexual reproduction to occur.
genotypic sex
what is Klinefelter syndrome and what 3 thinks does this result in
for second part think height, testes and breasts
- someone who possesses XXY chromosomes
results in a male that:
- is above average height
- has Underdeveloped testes
- has Occasional breast development
Grastrulation
what is Gastrulation?
- the process by which agastrulaforms from ablastula.
PGCs
How can primordial germ cells (PGCs) be characterized
think density, outline and diameter
- high electron cytoplasm density
- irregular outline
- diameter of 10 -20 µm (depending on species, stage, shape)
PGCs
What in PGCs are used as an indicator enzyme and why
for second part think of activity in cytoplasm of PGC
alkaline phosphatase as there is high activity of it in PGCs peripheral cytoplasm
PGCs
Outline how the testis develop from PGCs if male leaning
think medulla of something and then something else regressing
- develops from the medulla of the primordial (undifferentiated) gonad causing the cortex to regress
PGCs
Outline how the ovary develop from PGCs if female leaning
think cortex of something causing the regression of something else
- develops form the cortex of the primordial (undifferentiated) gonad causing the medulla to regress
sex determining region on Y chromosome
Outline how male development occurs in the developing goand in the presence of the SRY gene (Sex determining Region on the Y chromosome)
for step 1, think SRY directing cells to differentiate
for step 2, think about 3 things what these differentiated cells
- SRY directs somatic cells in developing goand to differentiate into Sertoli cells instead of follicle cells
- Sertoli Cells then:
- induce primordial germ cells to commit to sperm development
- secrete anti-Mullerian hormone, causing the Mullerian duct to regress
- Help induce other somatic cells to differentiate into Leydig cells, which secrete testosterone
SRY
Outline how female development occurs in the developing gonad in the absence of SRY gene (SEX determining Region on Y chromosome)
- In absence of SRY, Primordial germ cells commit to egg development, so somatic cells develop into:
- follicle cells (to support egg development)
- theca cells (which secrete oestrogen)
SRY
When do theca cells begin secreting oestrogen?
puberty
gonadal differentiation
Why does an indifferent gonad develop into a testis and when does an ovary develop instead of a testis
think TDF for first part
for second part think TDF and critical window
- develops into testis in response to Testis Differentiation Factor (TDF) before WEEK 9 of development
An ovary will develop instead of a testis if:
- TDF is not present
- TDF is only present after the Week 9 critical window has passed.
gonadal differentiation
what 3 hormones does further male pattern sexual differentiation depend on and which of these hormones is produced by the testis and which of these is converted into by peripheral tissues?
3 hormones:
- Testosterone
- Dihydrotestosterone (DHT)
- Anti-mullarian hormone (AMH)
- testosterone and AMH produced by testis
peripheral tissues convert testosterone to DHT
testicular differentiation
What 3 cell types make up the testicular cords?
- Peritubular myoid cells
- Sertoli cells
- Primordial germ cells
What is the rete testis?
think interconnected tubules and sex cords and what this creates
a system of interconnected tubules formed by the primitive sex cords creating an outlet for sperm
ovarian differentiation
Outline the 5 stages of ovarian differentiation in female embryos
stage 1, think what regresses and what thickens in pGCs and what this gives rise to
for stage 2 think about how many oogonia in ovaries in week 8 and then what that number is in week 20
for stage 3 think what happens to a large number of oogonia and what the remainder are surrounded by
for stage 4 think what stage all oocytes are locked in by week 20 and until what point it is like this
for stage 5 think how many primordial follicles will be available for reproduction at birth
- medulla of gonad regresses while cortex thickens due to mitotically dividing PGCs, giving rise to oogonia
- by week 8 developing ovaries contain 600,000 oogonia, increasing to 6-7 million by week 20
- large number of oogonia die and are resorbed, and remainder are surrounded by single layer of Granulosa cells, forming primordial follicles
- by week 20 all oocytes are locked at prophase I of meiosis and remain that state until the follicle is selected for maturation or death later in life
- At birth, each ovary holds around 1 million primordial follicles that will be available for reproduction for the rest of the female’s life
oogenesis and primordial follicle formation
Define primordial follicle
think oocyte in a specific stage and what surrounds it
Oocyte locked in Prophase I (of meiosis I) that is surrounded by a single layer of flat granulosa cells
external genitalia
What week does the genital tubercle begin to enlarge to form the phallus in both sexes
week 4
external genitalia
outline how external genitalia develops in males
think genital tubercle, urogenital folds and laboscrotal swellings and what they become
- genital tubercle becomes the glans penis (tip of penis)
- urogenital folds fuse to form the shaft of penis
- labioscrotal swellings become the scrotum
external genitalia
Outline how external genitalia develops in females
think about genital tubercle, urogenital folds, labioscrotal swellings and the ventral (anterior) labioscrotal swellings and what they become
- genital tubercle becomes clitoris
- urogenital folds remain separate as the labia minora
- labioscrotal swellings become labia majora and remain unfused
- ventrally, the labioscrotal swellings fuse to form the mons pubis
puberty and gametogenesis
what 2 physiological processes does puberty involve?
- gonadarche
- adrenarche
puberty and gametogenesis
what is gonadarche and what is it induced by?
for first part think maturation of gonads and what they produce as a result
for second part think about hormones released by anterior pituitary
- physical and functional maturation of the gonads, such that they produce gametes and sex steroids
- induced by increased production of FSH and LH by anterior pituitary
