Sex Determination and Differentiation

Question 1

What are the aims of the male reproductive system?

Answer 1

• to produce, maintain, transport and nourish sperm an semen
• to discharge sperm within the female reproductive tract
• to produce and secrete male sex hormones

Question 2

What are the male external genitalia?

Answer 2

penis and scrotum

Question 3

What is the male gonad?

Answer 3

testis

Question 4

What are the male internal genitalia?

Answer 4

• seminal vesicle
• ejaculatory duct
• vas deferens
• epididymis

Question 5

What are the aims of the female reproductive system?

Answer 5

• to release eggs, which can potentially be fertilised by sperm
• to produce and secrete female sex hormones
• to provide an environment for a fertilised egg to develop during pregnancy
• to facilitate labour and childbirth

Question 6

What are the female external genitalia?

Answer 6

• clitoris
• labia
• vagina

Question 7

What is the female gonad?

Answer 7

ovary

Question 8

What are the female internal genitalia?

Answer 8

• uterine duct
• uterus
• vagina (upper 1/3)

Question 9

What are the 3 levels that determine the sex of a person?

Answer 9

1. genetic sex
2. gonadal sex
3. phenotype sex

Question 10

When is genetic sex determined?

Answer 10

at the time of fertilisation

Question 11

How many chromosomes do somatic and gamete cells have respectively?

Answer 11

• somatic = 46 (23 pairs)
• gamete = 23

Question 12

What are the sex chromosomes in males and females respectively?

Answer 12

• male = XY
• female = XX

Question 13

What does genetic sex determine?

Answer 13

gonadal sex

Question 14

What determines gonadal differentiation?

Answer 14

presence or absence of a Y chromosome

Question 15

What can the gonadal ridge form?

Answer 15

either ovary or testis

Question 16

What happens at 1.5 months of gestation?

Answer 16

• all embryos have a potential to differentiate along either male or female lines
• the developing reproductive tissues of both sexes are identical and undifferentiated

Question 17

When is gonadal sex determined in males and females respectively?

Answer 17

• males = week 7
• females = week 9

Question 18

What is the SRY gene?

Answer 18

the sex determining region of the short arm of the Y chromosome that encodes the protein TDF (testis-determining factor)

Question 19

What does TDF do?

Answer 19

act as a TF for the genes necessary for testicular differentiation, including MIF and androgen receptors

Question 20

What does MIF do?

Answer 20

initiate the development of male glands

Question 21

Why do females not produce TDF?

Answer 21

they lack the SRY gene

Question 22

What does the cloaca form?

Answer 22

the male and female external genitalia

Question 23

Which ducts form the male and female internal genitalia?

Answer 23

• male = Wolffian
• female = Müllerian

Question 24

What happens if the undifferentiated glands are removed before testes have developed at 7 weeks?

Answer 24

the Wolffian gland development is inhibited and so no MIF is produced and ovaries form

Question 25

What is required for male differentiation?

Answer 25

- Y chromosome must be present - SRY gene must work to produce MIF - hormones must be present

Question 26

What does testosterone do?

Answer 26

convert to DHT which allows the Cloaca to form the external male genitalia

Question 27

What enzyme converts testosterone to DHT?

Answer 27

5α reductase

Question 28

What is aneuploidy?

Answer 28

abnormal number of chromosomes

Question 29

What causes Turner's syndrome?

Answer 29

having a single X chromosome

Question 30

What are the symptoms of Turner's syndrome?

Answer 30

webbed feet, short stature, failure of ovaries to develop, absence of menstrual cycle

Question 31

Give an example of a gonadal sex disorder

Answer 31

abnormal development of gonads (incomplete differentiation) and so not functional to induce puberty

Question 32

Give an example of a phenotypic sex disorder

Answer 32

male/female pseudo hermaphroditism

Question 33

What is pseudo hermaphroditism?

Answer 33

a condition in which an organism is born with secondary sex characteristics or a phenotype that is different from what would be expected on the basis of the gonadal tissue (ovary or testis)

Question 34

What is an hermaphrodite?

Answer 34

one bearing characteristics of both sexes

Question 35

What is lacking in male pseudo hermaphroditism?

Answer 35

- hormones (testosterone, MIF) - enzymes (5α-reductase, enzymes involved in steroid synthesis) - receptors (androgen receptors, LH receptor)

Question 36

What does female pseudo hermaphroditism arise from?

Answer 36

exposure to androgens (male sex hormone) by maternal exposure or androgen excess in foetus

Question 37

What are the symptoms of 21-hydroxylase deficiency in females?

Answer 37

- abnormal menstrual periods - deep voice - early appearance of pubic and armpit hair - excessive hair growth and facial hair - failure to menstruate - genitals that look both male and female (ambiguous genitalia), often appearing more male than female

Question 38

What is a significant stage in sexual development of males?

Answer 38

descent of the testes in the 7th month of gestation

Question 39

What is undescended testes into adulthood and what is its incidence?

Answer 39

cryptorchidism and its incidence is 3% of full-term babies and 30% of premature babies

Question 40

What is spermatogenesis dependent on?

Answer 40

temperature (needs to occur 2ºC cooler than normal body temperature)

Question 41

How long does spermatogenesis take?

Answer 41

64 days

Question 42

What cell type produces testosterone?

Answer 42

Leydig cells

Question 43

What provides nutrients and support for spermatogenesis?

Answer 43

Sertoli cells

Question 44

What does the hypothalamus do at puberty?

Answer 44

secrete GnRH to stimulate the anterior pituitary to make and release LH and FSH

Question 45

How are LH and FSH secreted?

Answer 45

in a pulsatile manner ~every 1-3 hours

Question 46

What happens if there is continuous exposure of gonadotrophs to GnRH?

Answer 46

desensitisation of GnRH receptors, leading to a decrease in LH and FSH release

Question 47

How is GnRH a tropic hormone?

Answer 47

it stimulates the testes to make testosterone

Question 48

What does the negative feedback loop of testosterone levels do?

Answer 48

decrease GnRH release by acting on the hypothalamus to indirectly decrease both LH and FSH release

Question 49

How does testosterone work?

Answer 49

by binding to plasma proteins in circulation (can also bind to albumin but not with the same affinity)

Question 50

What are the effects of testosterone?

Answer 50

- internal male genitalia (differentiation) - pubertal growth spurt - penis (growth) - deepening of voice - spermatogenesis - libido - muscle mass and recovery

Question 51

What are the effects of taking exogenous hormone (anabolic steroid)?

Answer 51

the testes would not achieve normal testosterone levels since they are not receiving normal stimulatory input causing testosterone secretion and sperm production to decrease and the testes to shrink

Question 52

How much more active is DHT than testosterone?

Answer 52

more than 2x

Question 53

Where is 5α-reductase high?

Answer 53

skin, prostate gland, seminal vesicle, epididymis, testes and liver

Question 54

What are the effects of DHT?

Answer 54

- external male genitalia (differentiation) - sebaceous glands - prostate (growth) - male hair pattern baldness

Question 55

What does DHT do to hair?

Answer 55

cause shrinkage in the overly sensitive hair follicles which causes them to fall out

Question 56

What is spermatogenesis?

Answer 56

production of sperm

Question 57

Give an example of a post testicular abnormality

Answer 57

failure in sperm storage, transport, nourishment, and release

Question 58

Give an example of a pretesticular abnormality

Answer 58

- failure in the entire male repo functions - GnRH deficiency