Flashcards in The Ovarian and Menstrual Cycles Deck (23):
What are the 3 stages of the ovarian cycle?
Follicular, ovulatory and luteal phases
Describe the follicular phase of the ovarian cycle
5-12 primordial follicles are stimulated to grow and develop --> one will for Graafian follicle --> releases the oocyte at ovulation
Describe the ovulatory phase of the ovarian cycle
Graafian follicle bulges from ovary wall and ovulation occurs when the wall rupture and expels the oocyte into the peritoneal cavity
Describe the luteal phase of the ovarian cycle
Granulosa cells of the Graafian follicle divide to form the corpus luteum which secretes hormones to maintain the endometrium to allow a fertilised oocyte to implant and grow
When does the LH surge occur?
Just prior to ovulation
What are the 3 stages of the menstrual cycle
Menstrual, proliferative and secretory phases
Describe the menstrual phase
When there is withdrawal of steroid support (oestrogen and oestrogen) --> endometrium collapses and is shed with blood from the ruptured arteries and the detached endometrial tissue and blood pass out of the vagina
Describe the proliferative phase
Oestrogen from the Graafian follicle stimulates the thickening of the endometrium --> glands and spiral arteries form --> oestrogen stimulates synthesis of progesterone receptors on endometrial cells
Describe the secretory phase
Progesterone from corpus luteum acts on endometrium to stimulate gland enlargement to increase mucus and glycogen secretion in preparation for implantation of a fertilised oocyte. If fertilisation doesn't occur, the corpus luteum degenerates, progesterone levels fall, endometrium degenerates and the cycle restarts
Describe what happens instead of the menstrual phase if fertilisation occurs
The blastocytst implants into the endometrium --> developing placenta secretes hCG (syncytiotrophoblasts)--> corpus luteum doesn't degenerate --> progesterone levels don't fall and this maintains the endometrium
What is the role of FSH and where is it produced?
Responsible for the maturation and growth of the follicles in the ovary; produced in the anterior pituitary gland
What is the role of LH and where is it produced?
Causes release of mature oocyte into the fallopian tube; produced by the anterior pituitary gland
What is the role of oestrogen and where is it produced?
Stimulates the growth of the endometrial lining and prepares the endometrium to be as nourishing to a possible fertilised egg; produced by follicles/immature eggs
What is the role of progesterone and where is it produced?
Helps endometrium prepare for implantation by increasing vascularity and secretions of the tissue and halts oestrogen secretion to prevent overgrowth of the endometrial cells; produced in the corpus luteum
What is the role of hCG and where is it produced?
Produced when a women is pregnant; by syncytiotrophoblast in the placenta
Outline the hormones involved in the follicular phase
GnRH (hypothalamus) --> LH and FSH (anterior pituitary) --> stimulates maturation and growth of follicles --> Graafian follicle secretes oestrogen --> oestrogen inhibits further LH and FSH via negative feedback (large amounts of oestrogen cause positive feedback) --> oestrogen stimulates growth of endometrium
Outline the hormones involved in the ovulatory phase
Oestrogen levels in high enough quantities --> positive feedback of FSH and LH --> LH and FSH surge --> stimulates meiosis I completion in primary oocyte --> secondary oocyte --> meiosis II in secondary oocyte --> surge in LH involved in facilitating ovulation
Outline the hormones involved in the luteal phase
Granulosa cells of the ruptured follicle go on to form the corpus luteum --> oestrogens and progesterone, where the progesterone works to prepare the endometrium for implantation
Describe the normal process of ovulation
Release of secondary oocyte from a Graafian follicle into the oviduct, uses intrafollicular pressure (due to proteoglycan presence) as well as the LH surge
What is the function of spiral arteries in the menstrual phase?
These arteries contract in order to reduce bleeding from the shedding of the endometrium
What is the normal age range for menarche?
Usually 12-15 but can be as early as 8 and be normal
Why are there fluctuating oestrogen levels at the start of puberty?
Due to follicular development failing to reach ovulation and as a result, the endometrium is affected and undergoes cycles of proliferation and regression which eventually lead to the first period