The HPG Axis, Puberty + The Menstrual Cycle Flashcards
Outline the anterior pituitary gland and its hormones involve in menstruation
- GnRH (every 1-3 hours) travels in hypophysis portal system + stimulates APG to secrete gonadotropin hormones:
- follicle stimulating hormone FSH
- luteinising hormone LH
Outline the HPG axis in males
- FSH stimulates Sertoli cells > spermatogenesis + secretes inhibin (negative feedback on APG + FSH)
- LH stimulates Leydig cells > testosterone released
FSH - Sertoli
LH - Leydig
Outline the HPG axis in females
- FSH stimulates granulosa cells > follicular development
- LH stimulates theca interna cells > release androgens (converted to oestrogen by granulosa cells)
Role of FSH in males
Stimulates Sertoli cells
- spermatogenesis
- inhibin releases > negative feedback on APG + FSH
Role of LH in males
Stimulates Leydig cells
- testosterone released
Role of FSH in females
Stimulates granulosa cells
- follicular development
Role of LH in females
Stimulates theca interna cells
- releases androgens > converted to oestrogen
Define gonadarche
Activation of the gonads
Define adrenarche
‘Awakening of adrenal glands’ > public/axillar hair + oily skin
Define thelarche
The onset of breast development occurring near the beginning of puberty in girls
Define menarche
The onset of menstruation at puberty
Define pubarche
Onset growth of pubic hair
What influences the timing of puberty
- pineal glands
- body weight
- Leptin
- environment
- genetics
What is the critical weight for girls to start puberty?
47kg
Where is Leptin released from?
Adipose tissue
Outline puberty in boys
- age 9-14 years
- starts with genital development
- pubic hair growth
- spermatogenesis
- growth spurt
.
+ male secondary sexual characteristics
Secondary male sexual characteristics
- increased + thickened hair on trunk, pubis, axillary+ face
- increased laryngeal size (adams apple)
- deepened voice
- increased bone + muscle mass + strength due to testosterone
What scale is used to measure puberty?
Tanner scale
Outline puberty in girls
- age 8-13 years
- start with thelarche
- adrenarche
- growth spurt
- menarche
.
+ female secondary sexual characteristics
Secondary female sexual characteristics
- pubic + axillary hair
- enlargement of labia majora + minora
- keratinisation of vaginal mucosa
- uterine enlargement
- increased fat in hips/thigh
How long is the luteal phase of the menstrual cycle?
Always 14 days
What is the menstrual cycle controlled by?
HPG axis
What two cycles occur in the menstrual cycle?
Ovarian cycle
Uterine cycle
What are the phases of the ovarian cycle?
Follicular phase
Ovulation on day 14
Luteal phase
What are the phases of the uterine cycle?
Menstrual phase
Proliferative phase
Secretory phase
Outline the early follicular phase
- days 0 to 5
- no ovarian hormone production
- granulosa cells secrete activin > ^ FSH production + FSH receptors on granulosa cells
- FSH stimulates follicle growth, theca interna appears + increased oestrogen
- dominant follicle granulosa cells produce inhibin instead of activin
Outline the late follicular phase
- days 5 to 14ish
- oestrogen produced > ^ FSH receptors (initally negative feedback on HPG axis) + ^ LH receptors (prep for ovulation)
- inhibin produced > v FSH receptors + helps LH to increase androgen production in theca cells
- oestrogen and inhibin continue to rise
Outline the ovulatory phase
- day 14
- LH surge > oestrogen rises + exerts positive feedback on HPG axis
- ovulation occurs
Outline the luteal phase
- always 14 days
- LH stimulates remaining follicle to develop into corpus luteum > secretes oestrogen +progesterone
Outline the uterine cycle
- Menstrual phase: menstrual bleeding
- Proliferative phase: proliferation of endometrium in response to oestrogen > glands become more coiled
- Secretory phase: glands become secretory under influence of progesterone
What are the uterine layers?
Endometrium, myometrium + perimetrium
What are the endometrial changes in the uterine cycle?
- early proliferation: sparse straight glands
- late proliferation: thicker functional layer + coiled glands
- secretory phase: max endometrial thickness, very coiled glands + coiled arterioles
What occurs at the end of the menstrual cycle if fertilisation doesn’t occur?
- corpus luteum becomes corpus albicans
- fall in oestrogen, progesterone + inhibin
- menstruation
What occurs if fertilisation is successful?
Syncytiotrophoblasts produce hCG
Corpus luteum lifespan extends
Actions of oestrogen
- proliferation of endometrium + myometrium
- fallopian tube motility
- thin, alkaline cervical mucus
Action of progesterone
- produces secretory endometrium
- thickening + reduction of motility of myometrium
- thick, acidic cervical mucus (prevents further entry of sperm)
- development of breast tissue
Normal duration of menstrual cycle
21 to 35 days
What is variation in the menstrual cycle length due to?
Follicular phase
What factors can disrupt the menstrual cycle
- pregnancy
- lactation
- emotional stress
- body weight
- infertility
How do the pineal glands affect the onset of puberty?
Children with lesion in the pineal glands undergo precocious puberty
Why is there not a rise in FSH levels during ovulation?
Presence of inhibin
Causes negative feedback on APG axis
Where is inhibin released from?
Sertoli cells in testicles
dominant granulosa cells in ovary
Action of inhibin
Inhibits secretion of FSH from anterior pituitary gland through negative feedback
What are the layers of the endometrium?
What are their functions?
- function layer: responsive to horomones + sheds in menstruation
- basal layer: allows regrowth at start of a new cycle
What are the affects of low and high levels of oestrogen?
- low levels: reduces amount of GnRH released > reduces FSH+LH
- high levels: promote GnRH release > increases FSH+LH
