Sexual differentiation

Question 1

What effect does the secretion of T from the testis have?

Answer 1

Stimulates Wolffian duct formation and Mullerian inhibiting hormone (MIH) which causes the Mullerian duct to degenerate
=absence of uterus

Question 2

MIH the same as and what is it?

Answer 2

(AMH) - Anti-Mullerian Hormone
Large molecular weight glycoprotein - part of TGF-beta super family

Question 3

What is the jost hypothesis?

Answer 3

Secretion of androgens and AMH by fetal testis during critical stages of development accounts for tor the full range of sexually dimorphic urgogenital traits observed at birth.

Question 4

What is maleness conferred by?

Answer 4

The SRY gene - small region at the tip of the Y chromosome

Question 5

Is the embryo sexually differentiated at an early embryo?

Answer 5

No

Question 6

Role of sertoli cells
(in the testis)

Answer 6

Germ support cells
- Secrete substances initiating meiosis and testicular fluid
- Concentrate testosterone locally with androgen binding protein
- Release AMH, prevent formation of ovarian duct
- Protect spermatids from the immune system

Question 7

Role of Leydig cells

Answer 7

Androgen production

Question 8

Events in the sex-neutral early embryo

Answer 8

Question 9

Germ cells
XX
XO
XY
XX
XXY

Answer 9

Migrate to the gonadal region in early development
Cells survive in ovarian environment and produce follicles
Cells cannot produce follicles and germ cells die
Cells die in ovarian environment
Cells die in testicular environment
Klinefelter’s syndrome dies in testicular environment

Question 10

Must be a ________ to ensure survival of female germ cell

Answer 10

X-linked dosage mechanism
- 2 Xs renders cell sensitive to cytotoxic effects of MIH?

Question 11

Model for differentiation

Answer 11

Question 12

Nuclear hormone receptor action

Answer 12

Testosterone acts with 5alpha DHT on a common receptor which directly binds to DNA

Question 13

Cascade of development and Behavioural pathways

Answer 13

Early embryo - SRY switch - Testis develop - sex steroids produced

Question 14

Testosterone

Answer 14

Multiple action on other genes

• Spermatogenesis
• Testicular descent
• Wolffian duct growth
• Gonadotrophin hormone regulation
• Differentiation of brain via oestrogen

Question 15

5 alpha dihydrotestosterone

Answer 15

Multiple action on other genes

• External virilization
• ## Maturation at puberty

Question 16

Klinefelters

Answer 16

Double dose of X plus Y chromosome
Small testis, low T production, limited breast development, no spermatozoa produced, scant body
XXY germ cells cannot survive in testicular environment

Question 17

Testicular feminisation

Answer 17

Lack of androgen receptor
Body cannot perceive testosterone
Testicular oestrogen drives breast development
Voluptuous breasts - no T signal opposing oestrogen
No uterus present - MIH produced by testis
Testis do not descend
Vagina short and blind ending
XY testicular feminised indivudals raised as girls

Question 18

Turner’s syndrome

Answer 18

[Female phenotype] - XO
Ovaries/streak gonads (no germ cells, no steroids)
Mullerian ducts present (no production of MIH - no testis present)
Wolffian ducts absent
No penis
Lack of germ cells = lack of sex steroid production - no breast development
Thickened neck

Question 19

X-linked suppressor of SRY

Answer 19

Male karyotype
Underdeveloped female appearance
no testicular development
Ovaries develop but degenerate as streaks
Uterus and vagina normal
No ovaries = no sex steroids no pubic hair no breast development