Reproduction: Menstrual Cycle and Drug Flashcards
What is the purpose of the menstrual cycle?
Preparation of
- Gamete via the ovarian cycle
- Endometrium by the uterine cycle
What are the control mechanism of the menstrual cycle?
Gonadotrophins acting on the ovary
Ovarian steroids:
- Acting on tissues of the reproductive tract
- Acting to control the cycle
Outline the HPO axis control of the menstrual cycle
- GnRH produced by the hypothalamus
- Acts on the anterior pituitary to release the gonadotrophins: FSH and LH
- Gonadotrophins act on the ovary to promote follicular development and produce ovarian hormone like steroid hormones and inhibit
- The gonadal hormones act to control the system
What happens if GnRH release is continuous rather than intermittent?
- Continuous exposure of the GnRH receptors to GnRH lead to them becoming desensitised
- FSH and LH production stops
- Gonadal steroid production stops
What are the feature of the start of the menstrual cycle?
- No ovarian hormone
- Early development of follicles begin
- Low steroid and inhibin levels
- Little inhibition at hypothalamus or anterior pituitary
- Free from inhibition
- FSH levels are rising
What is the effect of FSH in the menstrual cycle?
- Bind to granulosa cells
- Follicular development continues
- Theca interna appears
- Follicle now capable of oestrogen secretion
- Inhibin secretion begins
What occurs in the mid-follicular phase?
- Need a nominate a dominant follicle
- Prevention of recruitment of any further follicles
- The follicular oestrogen is now at a concentration that it can exert positive feedback at hypothalamus and anterior pituitary
- Gonadotrophin levels rise
- Follicular inhibit rising which seleively inhibits FSH production for m the anterior pituitary
- Effect on LH only
What are the hormonal changes resulting in ovulation?
- Circulating estradiol and inhibit rise rapidly
- Oestradiol production no longer dependant on FSH
- Surge in LH production
- Progesterone production begins as the granulosa cells become responsive to LH
- Modulation of GnRH pulse generator
What is completed and started in ovulation?
Meiosis 1 is completed
Meiosis 2 is started
How is the mature oocyte extruded?
It is extruded through the capsule of the ovary
What are the effects of LH after ovulation?
- Folicle is lutenised
- Oestrogen and progesterone are secreted in large quantities
- Inhibin continues to be produced
What is the effect of progesterone on LH production?
-LH is suppressed by progesterone via negative feedback
Describe the luteal phase.
- Corpus luteum formed and produced progesterone, oestrogens from androgens. It also produced inhibin
- Production of progesterone is promoted
- Corpus luteum regresses spontaneously however in the absence of further rise in LH
What is the effect of oestrogen on the endometrium?
-Proliferates and secretes
What is the effect of progesterone on the endometrium?
-Secretion
What is the endometrium?
Specialised epithelium
What is the uterus made of?
- Muscular wall called the ‘Myometrium’
- Endometrium which is the epithelial layer. Has a functional layer which is hormone responsive and sheds if no pregnancy occurs. Functional layer is developed on the basal layer
What occurs at the end of the menstrual cycle?
- Absence of further rise in LH means the corpus luteum regreses
- Dramatic fall in gonadal hrmone
- Relieving of the negative feedback
- Resets to start again
What are the series of changes the uterus undergoes in the menstrual cycle?
- Early proliferative: Glands sparse and straight
- Late proliferative: Functional layer has doubles and the glands are now coiled
- Early secretory: Endometrium max thickness and very pronounced coiled glands
- Late secretory: Glands adopt characteristic saw tooth appearance
If the ovum is fertilised, which hormone is produced to support the corpus luteum and what by?
-Human chorionic gonadotrophin (HCG) by the Syncytiotrophoblast
How does the corpus luteum support the pregnancy?
It produces steroid hormone which support the pregnancy
What controls the HPO axis throughout most of pregnancy?
- The placenta
- Oestrogen and Progesterone
- Responsible for maintaining the pregnancy state
- Take over from corpus luteum by 11th week
What are the actions of progesterone in the luteal phase?
- Further thickening of the endometrium into secretory form
- Thick, acid cervical mucus
- Thickening of the myometrium but reduction of motility
- Changes in mammary tissue
- Increased body temperature
- Metabolic changes
- Electrolyte changes
What is the normal duration of the menstrual cycle?
21-35 days
