Normal Menstrual Cycle Flashcards
What are the four hormones involved in the menstrual cycle?
Follicle stimulating hormone
Luteinising hormone
Oestrogen
Progesterone
What are the phases of the menstrual cycle in the ovary?
Follicular phase
Ovulatory phase
Luteal phase
What is the normal length of a cycle?
~21 - 28 days - can be shorter or longer
If the cycle is shorter or longer, which phase stays constant and which phase changes?
The follicular phase changes in duration
Luteal phase is always 14days
What does the hypothalamus secrete?
Gonadotrophin releasing hormone GRH
What does the GRH act on?
The anterior pituitary gland
What does the anterior pituitary gland release?
Follicule stimulating hormone
Luteinising hormone
What is the role of the FSH?
Acts on the ovaries and stimulates the development of follicles
What is the role of LH?
Causes ovulation
What happens in the follicular phase?
FSH stimulates the development of 15-20 follicles in the ovary
The surrounding granulosa cells secrete increasing oestrogen
What is the role of oestrogen?
Oestrogen = steroid sex hormone
Development of secondary sex characteristics e.g. breast tissue & genital development
Influences the endometrium to proliferate - causing increase in capillary formation (proliferative phase of the menstrual cycle)
Causes thinning of the cervical mucous for sperm to fertilise the egg easily
Rise in oestrogen suppresses FSH and LH in the negative feedback loop
When does ovulation happen?
Day 14 in a 28 day cycle
What happens in the luteal phase?
After ovulation, the follicle that release the ovum collapses to form the corpus luteum
What is the purpose of the corpus luteum?
It secretes high levels of progesterone which maintain the endometrial lining
What is the role of progesterone?
Thickens and maintains the endometrium
Thickens the cervical mucus to become less penetrable
Causes a slight increase in body temp
What else does the corpus luteum secrete?
Small amounts of oestrogen
What happens if the egg is fertilised?
The synctiotrophoblast of the embryo releases human chorionic gonadtrophin (HCG)
The placenta takes over production of progesterone from 5-10 weeks
What is the role of the HCG?
It keeps the corpus luteum alive
Pregnancy tests check for the levels of HCG
What happens if the egg is not fertilised?
No HCG is released
The CL degenerates and stops producing oestrogen and progesterone
Why does menstruation occur?
Due to the fall in oestrogen and progesterone when the CL degenerates causing the endometrium to break down
What do stromal cells of the endometrium release and what does this do?
They release prostaglandins
Prostaglandins encourage the endometrium to break down and the uterus to contract
When does menstruation start?
Day 1 of the menstrual cycle
What happens to the levels of FSH and LH?
The cycle restarts –> The drop in oestrogen and progesterone removes the negative feedback loop to the hypothalamus and FSH and LH will rise again
Which layers of the endometrium are involved in menstruation?
The superficial and middle layers - the functionalis layer - separates from the lower one third of the endometrium - the basalis layer
