Lecture 20 - Sex Determination and Development Flashcards
What are the 6 biological classifications of sex?
Morphological sex, secondary, primary, gonads, sex hormones, chromosomes/gene
Is sex binary?
NO!! There are intersex (aka Diverse Sexual Development) peeps (sex characteristics that fall between “male” and “female”)
Chromosomal sex
Sex chromosomes present in somatic (non-germ line) cells
ie. XY (male) and XX (female)
Gene that is responsible for initiating male typical sex development
SRY gene
Gonadal sex
Anatomy of the gonad which determines which type of gametes are produced (ie. sperm or eggs)
What are the 2 sets of internal ducts during early developmental stages?
Wolffian duct and Mullerian duct
What are the 3 functional cell classes in mature gonads?
- Steroid secreting cells
- Support (nurse) cell
- Germ cells
True or False? At early developmental stages, all embryos will already be determined which gonad they will develop, therefore, will only have 1 set of internal duct
False - at early stages of developmental stages, all embryos have 2 undifferentiated gonads and 2 sets of internal ducts
Presence of SRY gene
Will determine whether the gonad will develop into a testis or ovary by expressing testes-determining factors
XY -> SRY+ -> testes determining factor (TDF, SOX9+) -> testes
Without SRY, ovarian-determining genes are expressed
What do the sertoli cells secrete?
They are support cells in the testes that secrete Anti-Mullerian Hormone (AMH), leading to male typical development of ducts
How is estrogen secreted from the ovaries?
Ovaries —> Follicular cells (steroid secreting cells) and granulosa and germ cells —> mostly estrogen
How is testosterone secreted from the testes?
Testes—>Leydig cells (steroid secreting cells) —> mostly testosterone
Key points of the production of steroid hormones
- 5 classes of steroid hormone receptors
- Some hormones are precursors to other hormones
- Converting enzymes can be found in non-endocrine tissues
- Many reactions are irreversible
Morphological sex
The anatomy of the external genitalia which develop in response to androgen receptor signalling
When androgen is present, how is the male external genitalia formed?
Testes —> Leydig cells —> testosterone —> dihydrotestosterone —> male external genitalia
Process of sexual maturation during puberty
Hypothalamus increases GnRH production, which produce the gonadal hormones:
FSH —> gamete production initiated
LH —> sex hormones are released; initiating secondary sex characteristics and behaviour
What are examples of secondary sexual characteristics of testosterone?
- Body hair
- Bone growth - and then closure of epiphyseal plates
- Myofibre hypertrophy
- Activational effects on sex drive and sexual behaviours
- Increased red blood cell production
- Growth of larynx
- Development of accessory structures and sperm production
What are examples of secondary sexual characteristics of estrogen?
- Mammary glands
- Bone growth - rapid closure of epiphyseal plates
- Some myofibre hypertrophy
- Activational effects on sex drive and sexual behaviours
- Reduced blood cholesterol levels
- Development of uterine lining and accessory reproduction structures
True or False. Some effects of the steroid hormones on secondary sex characteristics are reversible, some are not.
True
