Sex differences Flashcards
What determines sex in mammals at the genetic level?
The SRY gene, located on the Y chromosome, turns the fetal gonad into a testis. In its absence, the gonad develops into an ovary.
What two hormones are produced by the early testis in males?
Anti-Müllerian hormone (AMH) – Defeminizing effect
Androgens – Masculinizing effect
What happens if the early testis does not produce AMH and androgens?
Female sex organs develop in the absence of these hormones.
What are the precursors of internal sex organs in early fetal development?
Müllerian system – Precursor to female internal sex organs
Wolffian system – Precursor to male internal sex organs
How do external genitalia develop in early fetal stages?
Initially, external genitalia are indistinguishable. By the 7th-12th week, they differentiate into either male (penis and scrotum) or female (clitoris and labia) structures.
What role does Dihydrotestosterone (DHT) play in sex development?
The presence of DHT leads to male sex organ development, while its absence leads to female sex organ development.
What are the two types of hormone actions?
Organisational effects – Permanent changes, usually occurring during a sensitive period.
Activational effects – Temporary and reversible changes, depending on hormone presence.
What roles do sex hormones play during puberty?
Organisational and activational effects
Development of secondary sexual characteristics
Androgen-sensitive pubic and axillary hair growth in both sexes
What triggers the onset of puberty?
A developmental timing mechanism starts puberty.
The hypothalamus releases Gonadotropin-releasing hormone (GnRH), which signals the anterior pituitary gland to release gonadotropins.
What are the functions of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)?
FSH: Sperm production (males), follicle ripening (females)
LH: Testosterone production (males), ovulation and corpus luteum formation (females)
What is the hypothalamus-pituitary-gonadal axis?
A feedback system where:
- Hypothalamus releases GnRH.
- Pituitary gland releases gonadotropins into the bloodstream.
- Gonadotropins stimulate the gonads to produce:
Ovaries: oestradiol, progesterone.
Testes: testosterone.
How does the HPG axis function in males?
It operates as a negative feedback loop.
What happens if males take anabolic steroids?
The hypothalamus produces less GnRH, leading to reduced testosterone production by the testes, causing testicular shrinkage due to the body relying on external testosterone from steroids.
What are the phases of the human menstrual cycle?
Menstrual flow
Follicular
Ovulation
Luteal
Premenstrual
What happens during the follicular phase?
FSH stimulates ovarian follicles to grow.
Follicles release oestrogens like oestradiol.
Oestrogens increase FSH and LH release from the anterior pituitary.
What is the role of the LH surge in ovulation?
It causes one of the follicles to rupture and release its ovum.
What happens to the ruptured follicle after ovulation?
It becomes the corpus luteum, which produces progesterone to prepare the uterus lining for implantation.
What happens if the ovum is not fertilized?
Progesterone and oestradiol levels fall.
The uterus lining sheds, starting a new menstrual cycle.
