Cell reproduction and the Continuity of Life: The menstrual cycle Flashcards
Test review
What is the menstrual cycle?
A monthly hormonal change in womens’ bodies that prepares the uterus for possible pregnancy
What are the 4 stages of the menstrual cycle and which days do they occupy?
- Menstruation (Day 1-5)
- Follicular stage (Day 5-13)
- Ovulation (Day 14)
- Luteal stage (Day 15-28)
What happens in menstruation (the period)?
- Progesterone levels fall
- Endometrium breaks down
- Blood and endometrium fluid exit the body from the vagina
What happens in the follicular stage?
- Follicles enclose immature eggs
- Anterior pituitary secretes FSH and LH, causing follicles to grow upon reaching the ovary
- One follicle grows faster, stopping development of all others. This one fills with fluid and sticks out from surface of the ovary
- Follicle secretes estrogen, thickening the endometrium and increasing it’s blood supply to prepare uterus for possible pregnancy (Lasts 10-14 days)
What happens in ovulation?
- High levels of estrogen in blood just before day 14 makes the pituitary secrete more LH (and minor FSH)
- Follicles rupture due to heightened LH levels in blood vessels, and egg is released into the abdominal cavity where it is swept into the oviduct
What happens in the luteal stage?
- Post ovulation, LH turns ruptured follicle into a corpus luteum (yellow body)
- Corpus luteum produces progesterone, further preparing the endometrium
- If fertilization occurs, corpus luteum produces progesterone for weeks which also prevents further secretion of FSH and ovulation
- If fertilization does not occur, egg disintegrates after about 1 day, corpus luteum breaks down, and progesterone levels fall after about 11 days
What controls negative feedback of GnRH, FSH, and LH in women?
Estrogen and progesterone
What controls negative feedback of GnRH, FSH, and LH in men?
Inhibin and testosterone
What happens to estrogen and progesterone levels during pregnancy?
They remain high
What happens to estrogen and progesterone levels if pregnancy does not occur?
They fall
How long does the menstrual cycle last?
28 days, starting when the decrease in progesterone levels causes the anterior pituitary to secrete FSH (menstruation)
How do oral contraceptives work?
They maintain high levels of estrogen and progesterone so as to prevent the secretion of FSH and LH, resulting in no eggs releasing. Some also thin the endometrium and reduce cervical mucus.
When do women usually stop menstruation?
Age 40-50 (Menopause)
What is the most fertile period of the menstrual cycle?
Day 10-14 (Due to life span of sperm)
When does puberty typically begin in North American females?
Ages 9-10 (Due to good diet, exercise, and health care)
