Female reproduction Flashcards
What are the components of the HPG axis?
Hypothalamus
Anterior pituitary gland
Gonads (Ovaries or testes)
What hormones are produced by the ovaries?
Oestrogen
Progesterone
What are the 3 main forms of oestrogen?
Oestrone - Menopause
Oestrodiol - Reproductive
Oestriol - Pregnancy
What affect does oestrogen and progesterone have on the hypothalamus and anterior pituitary?
They can both stimulate or inhibit hormone production from them, forming the axis
How is GnRH released from the hypothalamus in females?
From neurones in a pulsatile manner
The frequency of pulses then corresponds to the hormones produced by the pituitary
How does GnRH pulse frequency affect pituitary secretion?
Increased frequency ⇒ Increased LH levels
Decreased frequency ⇒ Increased FSH
How does oestrogen increase GnRH pulsatility?
Oestrogen increases pulsatility,
How does progesterone affect GnRH pulsatility?
Progesterone decreases pulsatility
How do oestrogen and progesterone affect GnRH pulsatility, when GnRH neurones do not contain their receptors?
They interact with receptor on kisspeptin hormones, which then go on the activate the neurones
How long is the average menstrual cycle?
28 days
What are the 2 main phases of the menstrual cycle?
- Follicular (Proliferative) Phase
- Luteal (Secretory) phase
Which of the 2 menstrual stages is most variable in length?
Follicular, lasting 14 days, but varying by around 7 days either side
Describe the changes in hormones during the follicular phase of the menstrual cycle
- GnRH stimulates LH and FSH release
- Follicular phase causes increase of FSH
- FSH stimulates oestrogen release from ovarian follicles
- Oestrogen causes decrease of FSH
- Oestrogen also stimulates LH surge
- LH surge leads to ovulation
On what day of the menstrual cycle is ovulation?
14 days
Describe the changes in hormones during the luteal phase of the menstrual cycle
- LH surge also leads to corpus luteum formation
- This produces progesterone
- Progesterone decreases LH
- Lack of pregnancy causes cessation of progesterone release from corpus luteum, causing period
How long does bleeding usually last in the menstrual cycle?
<7 days
What are the functions of oestrogen in the menstrual cycle?
- Increase the thickness of the endometrium
- Regulating LH surge
- Reducing vaginal pH through increase in lactic acid production
- Decreasing viscosity of cervical mucus to facilitate sperm penetration
What is the corpus luteum?
The corpus luteum is the cholesterol filled remnant of the ovarian follicle responsible for progesterone release, used in pregnancy
What are the functions of progesterone in the menstrual cycle?
- Maintaining endometrial thickness
- Maintaining infertile thick mucus (Prevent sperm transport and prevents infection)
- Relaxing the myometrium
- Increasing basal body temperature
What causes bleeding in the menstrual cycle?
Depleting levels of progesterone then cause shedding of the uterine lining and unfertilised egg, leading to a ‘period’, which causes bleeding lasting <7days
What is caused by removal of progesterone in pregnancy?
Termination of the pregnancy
What makes up an overian follicle?
Oocyte (Egg)
Follicular cells
Antrum containing follicular fluid
What are the 2 types of follicular cells?
- Granulosa cells
- Theca cells
What is the function of the follicle?
Allow for oocyte maturation and play a role in oestrogen production
How do follicular cells allow for production of oestrogen?
LH binds to receptors on theca cells and stimulates the conversion of cholesterol to androgen
This androgen is shuttled to the granulosa cells, where FSH binding and aromatase allow for the conversion of androgen into oestrogen
How many primordial follicles are found in each developing ovary?
7 million
How many primordial follicles are found in each ovary at birth?
2 million
How many primordial follicles are found in each ovary at puberty?
0.5 million
Describe the selection process of a follicle for ovulation
Early stages of growth occur independently of gonadotrophins, however, once a follicle reaches a certain size, they become dependant on FSH to grow
During each cycle around 7 follicles are picked up as they are at the right size during the FSH peak
Only 1 (Dominant follicle) will be selected for ovulation, totally dependant on FSH levels
What occurs when a follicle grows, but not in line with FSH spike?
Atresia, meaning it cannot grow further
Describe the formation of the corpus luteum
Granulosa and theca cells transform to form luteal cells
LH stimulates angiogenesis, allowing for cholesterol delivery to the corpus luteum
Cholesterol is then stored for conversion to progesterone
Describe the histology of the cervix
Stroma (In the wall) is made up of collagen matrix and fibroblasts
Epithelium is made up of columnar epithelium
What is the function of the stroma of the cervix?
Regulates rigidity of the cervical wall
What is the function of the epithelium of the cervix?
Mucus secretion
Describe the course of the cervix
The cervix contains a series of folds or grooves, some of which are not much wider than the head of the sperm
What is thought to be the functions of the grooves and folds of the cervix?
Allows for better sperm selection
Describe the changes that occur in different regions of the cervix
The fluid secretion, immune cells and mucus thickness varies in different regions of the cervix
What are some ways of predicting ovulation?
- Ovulation predictor kits
- Spinnbarkeit
- Basal body temperature
How do ovulation predictor kits work?
Detect LH surge which occurs 24-36 hours before ovulation
What is spinnbarkeit?
Spinnbarkeit is the ability to form a thread by mucus from the cervix uteri when spread onto a glass slide and drawn out
Maximum length usually precedes or coincides with the time of ovulation
How does basal body temperature change in menstruation?
It shifts up by 0.2-0.4ºC
