Lecture 18 - Sex Determination: Fetal Endocrine Flashcards
chromosomes:
- how many somatic chromosomes are there in the body
- how many matched somatic chromosomes are there in the body
- how many sex chromosomes are there in the body
slide 4
- 46 chromosomes diploid
- 22 matched pairs of autosomes
- 2 sex chromosomes, 1 matched pair
sex determination:
- what are the gamete combinations to be male or female
slide 5
- male = XY, female = XX
- whichever two gametes fertilizes the egg first = the sex of the child
bipotential primordium:
- what is bipotential primordium and what determines it and when does it occur
- what structures does one develop if they are XX vs XY
slide 6
- bipotential primordium = a default structure that has the potential to become many different anatomical structures dependent on the sex of the child
- it is determined by the sex chromosome of the child, and any hormones/receptors present
- @6 weeks fetus has bipotential primordium
- if XX: bipotential primordium –> ovary –> mullerian duct –> fallopian tube, uterus, upper vagina
- if XY: bipotential primordium –> testis –> wolffian duct –> epididymis, vas deferens, seminal vesicle
XX development of structures:
- what happens @ 10 weeks to develop female structures (2)
- what happens @birth in relation to AMH hormone? forms 4 structures
slide 7
- @ 10 weeks: (1) bipotential primordium –> ovary in the absence of SRY protein and under the influence of female specific genes (2) absence of testosterone = wolffian duct disintegrates
- @ birth: absence of AMH (anti mullerian hormone) = develops fallopian tube, uterus cervix, and upper vagina
Speciality of the Y chromosome:
- what is the gene on the Y chromosome that forms testes?
- what does this gene code for?
- what happens if you have an XY chromosome but lack this gene?
slide 9-10
- SRY promotes testes development
- SRY is a gene regulatory protein/ transcription factor which develops tests (endocrine gland) and interacts with DNA
- lacking SRY as an XX or XY promotes female structures (thus NEED SRY for male structures)
Function of SRY:
- what is the pathway from the bipotential gonad to the development of testes + additional cells– name them (involves 1 factor and 1 gene and 2 hormones)
slide 11
- Steroidogenic factor 1 SF1/ bipotential primordium/gonad –> XY –> codes SRY gene –> expresses SOX9 –> expresses AMH (and others) –> develops testes (from SRY), develops sertoli cells/repression of female structures (from AMH) and develops leydig cells (testosterone)
role of SOX9 gonadal development:
- how does high levels vs low levels of SOX9 in XY vs XX individuals effect SRY expression, reproductive organ development, and the repression/expression of a specific protein for male vs female structure development
slide 12
- the bipotential primordium can either be XY or XX dependent on whats present.
- if inc. SOX9 and functional SRY = XY = testis development = positive feedback loops to increase SOX9 more and develop pro-like male structures/genes/proteins (suppresses B-catenin)
- if dec. SOX9 and no functional SRY = XX = ovary development = inc. B-catenin (inhibits SOX9) and develops female structures
SOX9
- what male cell in the seminiferous tubules is SOX9 responsible for?
- what does SOX9 do for this cell (2)
slide 13
- SOX9 is responsible for sertoli cell differentiation/proliferation (1)
- differentiates into precursors that will begin to develop the testes structure (2)
cellular events downstream of SOX9:
- what do these cellular events downstream of SOX9 code for
- how does this differ to XX individuals
slide 14
- in XY: @week 6 the bipotential primordium/gonad is present –> with SRY and SOX9 forms testes and sertoli cell differentiatior –> causes proliferation, vascularization, and leydig cell differentiation
- in XX there is no SOX9 or functional SRY thus none of this happens
XY development of structures:
- what happens @ 10 weeks to develop male structures (2) - what protein and hormone is needed here
- what happens @birth in relation to AMH hormone? forms 3 structures (what other hormone is present here)
- what structure is DHT hormone responsible for (1)
slide 15
- @ 10 weeks = (1) SRY protein stimulates testis development, (2) expression of AMH from testis sertoli cells causes mullerian duct to disappear
- @ birth = testosterone from testis converts wolffian duct into seminal vesicle, vas deferens, and epididymis.
- DHT (derivative from testosterone) hormone controls prostate development
hormones regulate structural differentiation:
- in males XY, state the pathway from SRY gene to development of genitalia, accessory structures, and regression of mullerian duct
- what hormones and cells are responsible for each?
slide 17
- SRY protein expression –> produces multiple proteins that cause gonad to become testis
- sertoli cells in testis –> secrete AMH –> reduces mullerian duct
- leydig cells in testis –> secretes testosterone –> development of wolffian duct into accessory structures
- testosterone –> 5-alpha reductase –> DHT –> develop male external genitalia
localization of testosterone vs DHT:
- what structures are testosterone vs DHT responsible for developing?
slide 18
- testosterone = internal structures = epididymis
- DHT = external structures = scrotum, penis, prostate (internal), pubic hair
Function of B-Cat:
- what is the pathway from the bipotential gonad to the development of ovaries + additional glands (instead of SRY, SOX9, and AMH)
- what hormones are female organs responsible for
- what does B-cat suppress in male development?
slide 19
- bipotential gonad –> XX –> factor –> WNT4 (instead of SOX9) –> beta catenin (inhibits SOX9 instead of AMH) –> female tissue and organs –> estrogen and estradiol
- note: does not produce AMH or testosterone
Variations in sex determination:
- if an XY has atypical androgen synthesis, ex hindered 5alpha-synthesis, what will happen to the male body
- if an XX has excessive exposure to androgens during early development, what will happen
slide 20
- XY: atypical androgen synthesis = effect DHT conversion and responsibility ie external structures and of the prostate
- XX: excess exposure to androgens = atypical development of secondary sexual characteristics and reproductive structures
puberty:
- what is it
- which sex has an earlier typical onset of puberty
- what are the signs of puberty for each sex
- how is frequency of hormones affected during the onset of puberty?
- what is the activation complex when the hormones are affected? (develops 2 things)
slide 23-25
- puberty: rapid growth and development
- girls have earlier onset of puberty than males
- girls = growth, pubic hair, breasts, males = growth, penis, pubic hair
- puberty reactivates GnRH-LH/FSH cycle to a higher frequency –> causes development of sex steroids, secondary sex characteristics
