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Physiology 2 > Sexual Differentiation and Disorders > Flashcards

Sexual Differentiation and Disorders Flashcards

1
Q

What is sexual differentiation?

A

How we become a boy or a girl

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2
Q

When does sexual determination and differentiation occur?

A

They both occur side by side (contiguously)

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3
Q

What is sexual determination?

A

Commitment to either the male or female pathway. It is genetically controlled by a molecular switch on the Y chromosome, the SRY gene.

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4
Q

What is sexual differentiation?

A

The process by which our internal and external genitalia develop as male or female

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5
Q

By when is our genotypic sex decided?

How does the embryo develop from this?

A

When we are an 8 cell embryo we have a genotypic sex, either XX or XY.

The embryo then develops it’s gonadal sex (i.e. it develops ovaries/ testes) and these contribute to the rest of development.

The phenotypic sex then develops (you outwardly become male or female), followed by your legal sex (what is on your passport) and then gender identity (what gender you feel you are)

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6
Q

How do the genotypic, gonadal and phenotypic sexes link?

A

Usually each of them should be aligned with eachother (i.e. genotypic sex = gonadal sex = phenotypic sex) but sometimes this isn’t the case

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7
Q

What is the SRY gene?

A

The sex determining region Y

A gene on the Y chromosome only

Codes for a TF/ DNA binding protein that cause cascade of events to create testes from gonad

Gene switches on during embryo development past the 7th week

Gene also causes testes to develop sertoli cells (AMH - anti-mullerian hormone - production) and Leydig cells (testosterone production)

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8
Q

What other areas of sexual differentiation do the hormones produced by the testes influence?

A

Influence further gonadal and phenotypic sexual development

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9
Q

What happens in the absence of a Y chromosome or absence of the SRY gene?

A

Ovaries form and develop

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10
Q

What evidence is there that the early embryo is bipotential (can become male or female)?

A

Has 2 sets of ducts, the mullerian duct (which develops into the uterus, uterine tube) and wolffian duct (which develops into the vas deferens and part of the prostate)

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11
Q

What would happen is an embryo has a Y chromosome but no SRY gene?

A

The embryo develops into a female

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12
Q

In the early embryo, what goes on to form the testes/ ovaries?

A

The genital ridges.

After fertilisation a pair of gonads develop which are bipotential (can form testes or ovaries).

Somatic mesenchymal tissue (making up the genital ridge, was originally part of mesoderm) have precursors called the genital ridge primordia (precursors to the genital ridges)

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13
Q

Which 3 types of primordial cells invade the genital ridge?

A
  1. The primordial germ cells - become sperm in males and oocytes in females
  2. The primitive sex cords - become sertoli cells in males (and express the SRY gene) and granulosa cells in females

The sertoli cells and granulosa cells are intimately connected to egg or sperm cells

  1. The mesonephric cells - become blood vessels, leydig cells in males or theca cells in females

Both leydig and theca cells produce androgens

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14
Q

What is the pathway for primordial germ cells to go to the genital ridges?

A

An initially small cluster of cells in the epithelium of the yolk sac expands by mitosis at around 3 weeks

The yolk sac connects to the embryo and later becomes the placenta - see https://biology.stackexchange.com/questions/17049/do-birds-have-navels

The cells then migrate to the connective tissue of the hind gut (make up last part of adult gut), to the region of the developing kidney (retroperitoneal organ so towards the back of the embryo) and on to the genital ridge – completed by 6 weeks

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15
Q

Up to what point do primordial germ cells stay non-committed to forming either sperm or egg cells?

When are they triggered to form them?

A

They are non-committed even when they have reached the genital ridge

By the end of 6 weeks they are ready to be triggered to form either egg or sperm cells

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16
Q

What is the wave of invading cells of the genital ridge following the primordial germ cells?

A

Primitive sex cords (that form sertoli and granulosa cells)

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17
Q

What is the route of the primitive sex cords to get to the genital ridges?

A

Since they are germinal ridge epithelium cells
That overlie the genital ridges mesenchymal cells
They just migrate inwards as columns (the primitive sex cords)

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18
Q

When and where do the genital ridge primordia develop?

A

At 3.5-4.5 weeks

On posterior wall of the lower thoracic lumbar region

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19
Q

What do the primitive sex cords express?

A

The SRY gene

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20
Q

What are the primitive sex cords route/ actions following inwards migration into the genital ridges in males?

A

They penetrate the medullary mesenchyme

They surround the primordial germ cells and then form testes cords

They then become Sertoli cells - release AMH

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21
Q

What are the primitive sex cords route/ actions following inwards migration into the genital ridges in females?

A

They do not express SRY

Rather than penetrating deeply, they condense in the cortex of the mesenchyme in small clusters around the primordial germ cells

Then they become granulosa cells

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22
Q

What is the first difference between male and female differentiation?

A

The primitive sex cords either penetrating the medullary mesenchyme and eventually becoming Sertoli cells, or not penetrating and becoming Granulosa cells

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23
Q

How is the migration of primitive sex cords in the genital ridges foreshadow for testes/ follicle formation?

A

In males, upon migrating in they become tubular structures with the primordial germ cells (sperm cells) on the inside

In females the cords surround the primordial germ cells (egg cells) in clumps

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24
Q

Where do the mesonephric cells originate from and where do they migrate?

A

The mesonephric primordium, which are lateral to the genital ridges

They also migrate into the genital ridges

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25
Q

What influences the mesonephric cells to become Leydig cells in males and what do Leydig cells synthesize as a result?

A

The AMH already produced by Sertoli cells + Sertoli cell products

They synthesize testosterone.
They form vascular tissue
They form a basement membrane
(helps form seminiferous tubules and the rete-testis - anastomosing network of tubules located in the hilum of the testicle that carries sperm from the seminiferous tubules to the efferent ducts)

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26
Q

What happens to mesonephric cells in females?

A

They form theca cells
Which synthesize androstenedione - substrate for estradiol production by granulosa cells
Do not produce androgens at this early stage, this occurs later in development

They also form vascular tissue

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27
Q

How do the products of the male and female gonads influence development?

A

The male gonads produce AMH and testosterone which influence their development; in females these hormones are not produced, so their absence causes female development

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28
Q

What are the internal reproductive organs?

A

Testes and vas deferens

Uterus and uterine tubes

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29
Q

What are the 2 ducts called involved with the internal reproductive organs?

Which is most important for each sex

A

Mullerian and Wolffian ducts

Mullerian is most important for females and Wolffian for males

30
Q

What are the Mullerian and Wolffian ducts inhibited and stimulated by

A

Mullerian - inhibited to grow (regressed) by AMH from Sertoli cells

Wolffian - stimulated to grow by testosterone; without testosterone the duct regresses

31
Q

What do the Wolffian and Mullerian ducts develop into?

A

The Wolffian duct develops into the rete testis, the ejaculatory ducts, the epididymis, the ductus deferens and the seminal vesicles; the Mullerian duct develops into uterine tube/ uterus/ other third of vagina

32
Q

Where is the enzyme 5 alpha reductase found, what does it do and how does it do it?

A

It is found in the genital skin of both males and females
It converts testosterone to dihydrotestosterone (DHT) which binds the same receptor as testosterone but is 10x more powerful
Conversion is by an addition of H from NAFPH

33
Q

Why does 5 alpha reductase have no effect in females?

A

They have no testosterone

34
Q

What does DHT cause?

A

Clitoral area enlarges into penis
Labia fuse and become ruggated to form scrotum
Prostate forms

35
Q

What are the parts of the primitive genitalia?

A

Genital tubercle, genital swelling, urethral fold and urogenital membrane

36
Q

What happens to the parts of the primitive genitalia in both male and female development?

A

Male:

Genital tubercle becomes the phallus and then the glans penis

Urethral fold folds over itself to form a tube to become the shaft of the penis (line that runs at the bottom of the shaft of the penis; it is where the penis has folded over)

Female:

Genital tubercle becomes the clitoris

Urethral fold becomes the labia

Urogenital groove becomes vagina

37
Q

What are 3 disorders of sexual differentiation?

A

Gonadal dysgenesis, sex reversal and intersex

38
Q

What is gonadal dysgenesis?

A

A sexual differentiation disorder

Incomplete sexual differentiation

Usually missing SRY in male/ deletion of second X in female

39
Q

What is gonadal dysgenesis a general term for?

A

Abnormal development of the gonads

40
Q

What is sex reversal?

A

A sexual differentiation disorder

Phenotype does not match genotype

e.g. genotypic male (XY) but externally looks like femaleness

41
Q

What is intersex?

A

A sexual differentiation disorder

Have components of both Mullerian and Wolffian tracts

Ambiguous genitalia (e.g. small penis/ large clitoris)

Difficult to determine sex of infant

42
Q

What is DSD?

A

What patients with disorders of sexual differentiation are known as

43
Q

What is androgen insensitivity syndrome?

A

AIS is an intersex condition

Partial or complete inability of the cell to respond to androgens (e.g. testosterone)

Wolffian duct does not form as no testosterone, Mullerian duct does not form as AMH still made

No internal or external male genitalia but since insignificant impact on Mullerian duct, female external genitalia

44
Q

What are the features of complete AIS? What is it’s incidence?

A

Appear completely female at birth

Have undescended testes and no uterus

Rare - 1 in 20,000 people

45
Q

How can people with AIS vary pathophysiologically?

A

Degree of androgen insensitivity varies

Degree of genitalia varies (e.g. large clitoris/ more penis or testes)

46
Q

What can happen to people with AIS when they hit puberty?

A

Their undescended testes may start producing more androgen which pushes the person to a more masculine form

47
Q

What do people with complete AIS present with?

A

Amenorrhoea - absence of period in woman of reproductive age

Lack of body hair

Male levels of androgen seen via ultrasound/ karyotype

Appear and feel female

48
Q

What do people with partial AIS present with?

A

Varying degrees of penile and scrotal development from ambiguous genitalia to large clitoris

49
Q

What happens in an XY individual if DHT is not made but testosterone is?

A 
Testes form (via Wolffian duct)
but stay ascended 
so internal genitalia is male

Mullerian duct does not form (due to AMH)

External genitalia does not develop as DH not made (DH responsible for fusion of labial scrotal folds, growth of phallus and prostate)

So external genitalia is female

50
Q

What causes testosterone to not convert to DHT?

A

5 alpha reductase deficiency, perhaps due to gene mutation

Not complete deficiency so testosterone has some effect

51
Q

What can happen to people with 5 alpha reductase deficiency when puberty hits them?

A

External male genitalia may start to develop

52
Q

How does incidence of alpha 5 reductase vary?

A

A lot since it is an autosomal recessive disorder + depends on inter-related marriage (e.g. marrying cousin)

53
Q

How do people with 5 alpha reductase deficiency present?

A

Present as female/ with ambiguous genitalia

54
Q

Why does presentation of 5 alpha reductase deficiency vary?

A

Degree of enzyme blocking varies

55
Q

What happens if you only have 1 X chromosome as in 45XO (Turner Syndrome)?

Answer in terms of if you have an ovary or testes, which duct you have and which external genitalia you have

A

Ovary

Mullerian duct but no Wolffian duct

Female external genitalia

56
Q

What happens to the ovaries in turner syndrome, and what happens in extreme cases of it?

A

Streak ovaries - they work sub-optimally (showing how we need 2 X’s for it’s development)

Extreme cases - failure of ovarian function

(Ovaries produce oocytes)

57
Q

How do the uterus and uterine tubes appear in turner syndrome?

Any other effects of the syndrome?

A

They are present but small

Defects in growth and development
May be fertile
Many have mosaicism (presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg)

58
Q

What support can ovaries get if they are working sub-optimally?

A

Steroid hormones from the bones/ uterus

59
Q

In what XX female affecting condition is there exposure to high levels of androgens?

A

Congenital adrenal hyperplasia - 1 in 15,000 people

60
Q

Where does steroidogenesis occur?

A

Adrenal gland on top of kidney

61
Q

Which steroid hormones are produced in the adrenal gland and which ones are produced in the gonads?

A

Adrenal gland - aldosterone and cortisol

Gonads - testosterone, oestrogen, progesterone

62
Q

What is the starting molecule of steroidogenesis? Describe it’s structure

A

Cholesterol - all steroids based off this

3 x 6 sided rings
1 x 5 sided ring
Long chain of C

63
Q

What is the first thing that happens to cholesterol upon importing into a cell? How do the hormones differ?

A

Cleaving of C’s from 21st C onwards to form all the progesterones (17 alpha hydroxyl pregnenolone, progesterone and pregnenolone; all with 21 Cs)

Only difference between them all is the different hydroxyl groups and oxygen groups around the rings

64
Q

What happens when you cleave 2 C’s off the progesterones? How do the hormones differ?

A

you get all the androgens (testosterone, androstenedone etc.)

The difference between them all are the movements of the hydroxyl and oxygen groups

65
Q

What happens when you cleave 1 C off the androgens? How do the hormones differ?

A

You get all the oestrogens

Oestrone, estradiol, estriol; all differ according to the number of OH groups on them

Estradiol has 2 hydroxyl groups, estriol has 3 and estrone has 1

66
Q

From which pathway do aldosterone and cortisol form? What other molecules do their production involve?

A

The progesterone pathway - requires 21 hydroxylase for the conversion

67
Q

What happens if 21 hydroxylase fails to convert the progesterone’s?

A

Cortisol isn’t made and the progesterone’s build up

68
Q

How is cortisol made?

A

The hypothalamus makes CRH, causing the anterior pituitary to make ACTH and the adrenal gland to make cortisol. There is negative feedback involved in this.

69
Q

What happens in the hypothalamic pituitary adrenal axis when there is no cortisol (e.g. when the 21 hydroxylase enzyme fails)?

A

No negative feedback on the pituitary/ hypothalamus so an increase in ACTH and CRH occurs.

ACTH causes more cholesterol to be taken up; so more androgens are formed and so in the baby girl, the adrenal glands start producing testosterone

70
Q

What happens when an XX foetus has a failure of the 21 hydroxylase enzyme, so has more testosterone?

A

Testosterone causes Wolffian ducts to grow, producing male external genitalia

As no AMH is produced the Mullerian ducts grow too

(ovary already developed as XX)

This is congenital adrenal hyperplasia (CAH)

Hyperplasia - the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells

71
Q
  1. In CAH, what occurs at birth/ can be seen at birth?
  2. What can the lack of aldosterone in CAH cause?
  3. How do you treat CAH?
A
  1. Wrong gender assignment at birth/ may have ambiguous genitalia
  2. ‘Salt-wasting’ due to lack of aldosterone - can be lethal
  3. Need treatment with glucocorticoids to correct feedback.

Physiology 2 (10 decks)

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