Reproduction/ Sex Steroid Axis Flashcards
What hormone does the hypothalamus release to start the reproductive axis?
gonadotropin-releasing hormone (GnRH)
How is GnRH secreted from the hypothalamus?
GnRH is secreted pulsatile, which is important for normal function
What hormones are released by the anterior pituitary in response to GnRH?
- Luteinizing hormone (LH)
- Follicle-stimulating hormone (FSH).
What is the role of luteinizing hormone (LH) in females?
= LH triggers ovulation in females
= stimulates the production of oestrogen from the ovaries
What is the role of follicle-stimulating hormone (FSH) in females?
FSH stimulates follicle maturation in the ovaries and promotes the production of oestrogen
What is the role of luteinizing hormone (LH) in males?
LH stimulates the production of testosterone from the testes
What is the role of follicle-stimulating hormone (FSH) in males?
FSH stimulates sperm production in the testes
What hormones are produced by the ovaries in response to LH and FSH in females?
- Oestrogens (e.g., estradiol)
- Progesterone in response to LH and FSH
What are the functions of oestrogen in females?
Oestrogen is responsible for the development of female secondary sexual characteristics (eg, breasts) and regulates the menstrual cycle
What is the function of progesterone in females?
Progesterone prepares the uterus for implantation and maintains pregnancy
What hormones are produced by the testes in males in response to LH and FSH?
testosterone and inhibin
What are the functions of testosterone in males?
Testosterone regulates male secondary sexual characteristics
(eg, facial hair, deep voice), sperm production, and libido
What is the role of inhibin in males?
Inhibin inhibits FSH production to regulate sperm production
What type of feedback mechanism is primarily used to regulate the sex steroid axis?
The sex steroid axis is primarily regulated by negative feedback
How do high levels of sex steroids
(eg, oestrogen, testosterone) affect the hypothalamus and pituitary?
High levels of sex steroids inhibit the release of GnRH, LH, and FSH from the hypothalamus and pituitary
What is the positive feedback mechanism in the reproductive axis?
Positive feedback occurs during the ovulatory cycle in females, when high levels of oestrogen increase GnRH secretion, leading to a surge in LH, which triggers ovulation
What are the phases of the menstrual cycle in females?
The menstrual cycle has the following phases
(1) Follicular phase
= FSH stimulates follicle development and oestrogen increases
(2) Ovulation
= LH and FSH surge due to high oestrogen
(3) Luteal phase
= Post-ovulation, the corpus luteum secretes progesterone
(4) Menstruation
= If pregnancy doesn’t occur, progesterone drops, leading to the shedding of the uterine lining
How do sex steroids contribute to sexual development?
In females, oestrogen regulates the development of breasts, wider hips, and other female secondary sexual characteristics
In males, testosterone regulates the development of a deeper voice, facial and body hair, and muscle growth
What are LH and FSH, and where are they produced?
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are glycoproteins produced and secreted by the anterior pituitary gland
What stimulates the release of LH and FSH?
Gonadotropin-releasing hormone (GnRH)
How do sex steroids affect the secretion of LH and FSH?
Sex steroids exert a negative feedback effect on the secretion of LH and FSH
How do LH and FSH levels vary during the menstrual cycle in females?
LH and FSH levels rise in the follicular phase, peak around ovulation, and then fall.
LH reaches higher plasma concentrations than FSH at ovulation
What is the function of FSH in males and females?
(1) In males, FSH acts on Sertoli cells to support spermatogenesis
(2) In females, it stimulates follicular development and oestrogen production
What is the function of LH in males and females?
(1) In males, LH acts on Leydig cells to produce testosterone
(2) In females, LH helps in corpus luteum development and progesterone production
What is hypergonadotropic hypogonadism, and which conditions are associated with it?
Characterised by higher-than-normal levels of FSH and LH.
It is associated with conditions such as 1. ovarian failure
= postmenopausal, premature ovarian failure
2. Klinefelter syndrome
What is hypogonadotropic hypogonadism, and what causes it?
Characterised by lower-than-normal levels of FSH and LH.
It can be caused by conditions like
1. hypopituitarism
2. prolactinoma
3. anabolic steroid use
4. Kallmann’s syndrome
FSH and LH are secreted by which structure?
The anterior pituitary gland
What does the mid-cycle LH surge trigger?
Ovulation
What is the hormone produced as a result of the stimulation of follicle-stimulating hormone (FSH) on its target tissue?
Oestradiol
What are the target organ and target cells of the follicle-stimulating hormone (FSH)?
Ovary - granulosa cells
What is the hormone produced as a result of stimulation by luteinising hormone (LH) on its target tissue?
Progesterone/testosterone
What is the mechanism of action of Domperidone?
Dopamine D2 receptor antagonist
Urinary pregnancy tests identify the presence of which molecule?
beta-HCG
What are the target organ and target cells of the luteinising hormone (LH)?
Ovary - theca cells
What is the term used to describe hormones which act on their target tissues to induce secretion of another hormone?
Tropic hormones
Which enzyme is deficient in 95% of Congenital Adrenal Hyperplasia cases?
21-hydroxylase
What does the corpus luteum secrete?
Progesterone
A healthy 36-year-old man being assessed for infertility is found to have a low sperm count of 10 million/mL (normal >15 million). He has no past medical history or drug history of note.
What blood result could explain this finding?
reduced FSH levels
