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Reproductive and Endocrine > Sex-Differentiation > Flashcards

Sex-Differentiation Flashcards

1
Q

What is the sex-determining region of the Y chromosome?

A

SRY gene

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2
Q

At which point is genetic sex determined?

A

Fertilisation, depends on the sperm.

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3
Q

In humans, which type of sex are males and which type are females?

A

Males are heterogametic (XY)

Females are homogametic (XX)

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4
Q

What term is used to describe the Y chromosome because it is small and has lots of heterochromatin and doesn’t carry many genes?

A

Transcriptionally quiet

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5
Q

What term is used to describe SRY because it is the same in many species?

A

Conserved sequence.

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6
Q

What is the condition called where the genotype is female (XX) but the person develops as a male, and what causes it?

A

XX sex reversal, there has been translocation of the SRY box onto the X chromosome.

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7
Q

What is the condition called where the genotype is male (XY) but the person develops as a female, and what causes it?

A

XY sex reversal, the SRY gene on the Y chromosome is missing or mutated.

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8
Q

What do the gonads develop from in the foetus?

A

Genital ridge primordia (bipotential structures)

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9
Q

What do the genital ridge primordia develop from on either side of the central dorsal aorta?

A

Mesenchymal knots.

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10
Q

What is the first wave of migrating cells into the genital ridge primordia?

A

The primordial germ cells (which do not express SRY) migrate from where they form in the yolk sac, through the cloaca, and into the genital ridge primordial.

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11
Q

Where in the genital ridge primordia do the PGCs migrate into in the male, and where in the female?

A

In the male they migrate into the medulla and the cortex degenerates. In the female they migrate into the cortex and the medulla degenerates.

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12
Q

What is the second wave of migrating cells into the genital ridge primordia?

A

Coelomic/germinal epithelial cells (which express SRY in the male) migrate into the genital ridge primordia as primitive sex chords.

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13
Q

What happens to the coelomic epithelial cells in the male?

A

They proliferate vigorously and project deep into the medulla. They surround the PGCs to form testis cords which are the precursors of seminiferous tubules. The coelomic epithelial cells form pre-Sertoli cells, and the PGCs they surround form prospermatogonia.

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14
Q

What happens to the coelomic epithelial cells in the female?

A

The coelomic epithelial cells don’t express SRY so the primitive sex cords are ill-defined and don’t project far into the genital ridge. Instead, the coelomic epithelial cells condense cortically and surround the PGCs in small clusters to form primordial ovarian follicles. The coelomic epithelial cells will form granulosa cells and the PGCs form oogonia and then eventually oocytes.

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15
Q

What is the third wave of migrating cells into the genital ridges?

A

Mesonephric cells from the mesonephric primordia (don’t express SRY).

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16
Q

What 3 things do mesonephric cells contribute to in the male?

A

Leydig cells between the testis cords to produce androgens.
Vascular tissue of the testes.
Myoid cells, which form the tubules of the rete blastema and rete testis.

17
Q

What two things do mesonephric cells contribute to in the female?

A

Vascular tissue

Thecal cells, which cluster around the developing primordial follicles

18
Q

What is the function of SRY?

A

To act as a transcription factor and activate the transcription of SOX-9.

19
Q

What are 5 functions of SOX-9?

A

Stimulates the production of prostaglandin-D2 by the pre-Sertoli cells
Activates transcription of more SOX-9
Inhibits the FoxI2 gene to stop theca cells and vascular tissue being formed so ovaries aren’t formed
Activates production of Fibroblast Growth Factor 9
Stimulates production of anti-Mullerian hormone

20
Q

What does prostaglandin-D2 do?

A

Stimulates SOX-9 production in neighbouring Sertoli cells.

21
Q

What does Fibroblast Growth Factor 9 do?

A

Promotes SOX-9 production

Acts as a chemotactic factor for the 3rd wave of migrating cells (mesonephric cells)

22
Q

What does a defect in the SOX-9 gene cause?

A

Production of ovo-testes.

23
Q

What happens to the cell division of PGCs in foetal testes?

A

After being enclosed in the developing sex cords, they cease mitosis and enter a long period of mitotic arrest, until puberty when mitosis is reactivated.

24
Q

What happens to the cell division of PGCs in foetal ovaries?

A

The oogonia cease meiosis and enter the first meiotic division to produce all the primary oocytes a woman will ever have.
The primary oocytes are encased in primordial ovarian follicles by condensation of the granulosa cells from the invading sex cords.

25
Q

Which duct produces the male reproductive tract, and which produces the female reproductive tract?

A

Mesonephric/Wolffian duct produces the male reproductive tract.
Paramesonephric/Mullerian duct produces the female reproductive tract.

26
Q

Which two hormones are essential for male development, and what are their functions?

A

Androgens produced by Leydig cells - cause the mesonephric duct to remain and develop
Anti-Mullerian Hormone produced by Sertoli cells - causes the paramesonephric duct to regress

27
Q

When do (phenotypic) secondary sexual characteristics begin to become visible?

A

At puberty, begin at gonadarche

28
Q

What are some phenotypic sexual characteristics of women?

A 
Breast development 
Oestrous/menstrual cycle (cyclic changes in hormone levels and periodic egg production)
Ovaries
Oviducts, uterus, cervix, vagina
Oocytes in small numbers
29
Q

What are some phenotypic sexual characteristics of men?

A 
More continuous (not cyclical) reproductive processes
Testes
Vas deferens, seminal vesicles
Spermatozoa in vast numbers
Musculature
Deeper voice
More likelihood of baldness
Androgenous hair patterning.
30
Q

What does perinatal exposure to androgens result in?

A

The hypothalamus being insensitive to oestrogen later in life, so being functionally male.

31
Q

What is Turner’s syndrome, and what are the characteristics?

A

Unpaired X chromosome (X0) due to nondisjunction.
Ovaries present but underdeveloped female reproductive tract, breasts underdeveloped, infertility, amenorrhea, small stature, nevi (brown spots on skin), fold of skin in the neck.

32
Q

What is Klinefelter’s syndrome?

A

Genotype XXY. Testes present but underdeveloped, infertile, tall stature, breast development, testicular atrophy, osteoporosis.

33
Q

What is Androgen Insensitivity Syndrome?

A

The intracellular androgen receptors are absent, or a mutation has altered their structure, so androgens are secreted by the testes but the target tissues fail to respond.

34
Q

What are the characteristics of Androgen Insensitivity Syndrome?

A

Genotype XY but phenotypically female and infertile. No internal genitalia, as AMH is produced which degenerates the paramesonephric tract, but androgens can’t rescue the mesonephric tract, testes are present.

35
Q

What is guevedoces?

A

Penis at 12. A form of Androgen Insensitivity Syndrome which is due to a deficiency in the enzyme 5-alpha reductase, which causes the XY person to appear phenotypically female until puberty. The increase in androgen production after puberty overcomes the tissue insensitivity, the clitoris expands into a penis, the testes descend, and the person begins to function as a normal male.

36
Q

What is congenital adrenal hyperplasia?

A

When the genotype is XX but both the paramesonephric and mesonephric ducts are retained due to the hyperactive foetal adrenal glands trying to overcome the low production of corticosteroids.
The person will have external male genitalia.

37
Q

What is the difference between sex and gender?

A

Sex is determined by your chromosomal make-up, gender is a result of a combination of genetics and environment, and is usually decided at birth based on your external genitalia.

Reproductive and Endocrine (11 decks)

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