Discuss the physiology of the HPO axis and normal menstrual cycle Flashcards
What happens during the secretory phase of the uterine cycle if fertilisation has not occurred?
- corpus luteum hormones decline
- spiral arteries spasm
- endometrium degenerates
- menstruation follows in approx. 24 hours
What is the uterine cycle and what is its purpose?
- the uterine cycle consists of changes occurring in the uterus
- to prepare the endometrium for possible implantation by the fertilised embryo
What is the duration of the uterine cycle and what does it correspond with?
- 28 days approx.
- the ovarian cycle
Describe the process of ovulation
- the follicle ruptures and the 2º oocyte is expelled into the abdominal cavity
- the oocyte enters the fimbriated end of the fallopian tube
When does the proliferative phase of the uterine cycle start?
- when bleeding ceases
- corresponding with follicular phase of ovarian cycle
What does the follicular phase end with?
ovulation
How are FSH and LH released?
In a cycle by the anterior pituitary
Why is there a mid-cycle surge in LH?
- FSH and LH are produced in response to stimulation of the pituitary by oestrogen reaching a critical point.
- It is to stimulate ovulation and the formation of corpus luteum
True or false? Changes in the duration of the ovarian cycle can be due to either the follicular or luteal phase
False - the duration of the luteal phase remains unchanged
What 3 phases make up the uterine cycle?
- proliferative
- secretory
- menstrual
Which phase occupies days 15-28 of the ovarian cycle?
The luteal phase
What happens in the luteal phase?
- the ruptured (from ovulation) follicle caves in and fills with a blood clot
- granulosa and theca cells increase and form the corpus luteum
How long does the menstrual phase of the uterine cycle last?
3-6 days
When does the secretory phase of the uterine cycle occur?
- in correspondence with the luteal phase of the ovarian cycle
- 14 days duration
What is the corpus luteum?
- essential in preparing for fertilisation and for maintaining pregnancy
- secretes progesteronee and oestrogen
- degenerates after 12-14 days if fertilisation does not occur
How do FSH and LH control the release of oestrogen and progesterone?
- FSH + LH stimulate initial follicular development and oocyte maturation
- small amounts of oestrogen produced by the follicle inhibits FSH+LH by negative feedback
- oestrogen levels reach critical point
- this causes oestrogen to stop inhibiting and start stimulating the anterior pituitary to release FSH and LH (+ve FB)
- following ovulation, the corpus luteum secrets oestrogen and progesterone to inhibit FSH/LH
- if pregnancy does not occur, the fall in LH causes the corpus luteum to degenerate and reduce levels of O+P
- this removed the inhibition and enables the pituitary to secrete FSH and LH again, starting a new cycle
What happens in the follicular phase of the ovarian cycle?
- primordial follicles become 1º follicles
- 1º follicles mature into 2º follicles
- the zona pellucida and theca folliculi are formed
- cells of the theca produce oestrogen during the maturation process
- mature graffian follicles are ready to release a 2º oocyte at ovulation
Which hormones control the ovarian cycle?
FSH and LH
What happens during the menstrual phase of the uterine cycle?
- spiral arteries dilate and bleed into the necrotic stratum functionalis
- clotting of the menstrual blood flow is prevented in the uterus by release of fibrinolysins
- the uterus contracts in response to prostaglandins to expel the blood
What is the HPO axis and what is its role?
- Hypothalamic pituitary ovarian axis
- the system controlling female reproduction
Describe the features of the secretory phase of the uterine cycle that prepares for an embryo
- progesterone causes the glands in the endometrium to secrete glycogen (to nourish the embryo at implantation)
- cervical mucus changes to a thick plug (blocking the cervical canal and protecting embryo)
Describe the proliferative phase of the uterine cycle
- following menstruation, only the basal layer of the endometrium remains (stratum basalis)
- the release of oestrogen results in cell proliferation and regeneration of the stratum functionalis
- phase ends with the maturation of the graffian follicle and ovulation at approx. day 14
Which phase occupies days 1-14 of the ovarian cycle?
the follicular phase, including ovulation
What is the duration of the ovarian cycle?
approximately 28 days
