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Biology and the Menstrual Cycle

Menstrual cycle is regulated by fluctuatinglevels of sex hormones

These hormones produce certain changes in

the ovaries and uterus

Humans are nearly unique among species in

having a menstrual cycle

Other species of mammals have estrous

cycles

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The Phases of the Menstrual

Cycle

The menstrual cycle has 4 phases: 1. Follicular phase - proliferative phase or

preovulatory phase

2. Ovulation

3. Luteal phase - secretory phase or

postovulatory phase

4. Menstruation

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Hormones and What Happens in

the Ovaries

Follicular phase - high levels of FSH secreted Function is to stimulate follicles in the ovaries

One follicle begins to ripen and brings an egg

to maturity

Follicle secretes estrogen

Ovulation - follicle ruptures open and releases theripened egg

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Hormones and What Happens in

the Ovaries

Luteal phase - after releasing an egg, the follicleturns into the corpus luteum

The corpus luteum manufactures progesterone

Menstruation - shedding of the inner lining of theuterus

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What Happens in the Uterus

Follicular phase - endometrium proliferates Luteal phase - progesterone secreted by the

corpus luteum stimulates the glands of the

endometrium to start secreting the

nourishing substances

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What Happens in the Uterus

Corpus luteum continues to produceestrogen and progesterone for about 10 to

12 days

If pregnancy has not occurred, its hormone

output declines

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Length and Timing of the Cycle

Normal menstrual cycle = 20 to 36 to 40 days;average is about 28 days

Menstruation begins on day 1 and continues until about

day 4 or 5 Follicular phase extends from about day 5 to about day

13

Ovulation occurs on day 14 Luteal phase extends from day 15 to the end of the

cycle, day 28

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Length and Timing of the Cycle

Mittelschmerz- middle pain; cramping in lowerabdomen that occurs during ovulation

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Other Cyclic Changes

Two other physiological processes fluctuatewith the menstrual cycle:

The cervical mucus cycle

The basal body temperature cycle

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Menstrual Problems

Dysmenorrhea - painful menstruation Possible cause - prostaglandins

Amenorrhea - absence of menstruation

Primary amenorrhea - when girl has not

menstruated by about age 18

Secondary amenorrhea - absence ofmenstruation if she has had at least one period

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Fluctuations in Mood

Premenstrual syndrome - PMS PMS is a combination of severe physical

and psychological symptoms, such as

depression and irritability, occurring just

before menstruation

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Fluctuations in Performance

Research on intellectual or athleticperformance generally shows no

fluctuations over the cycle

Research on academic performance,

problem solving, memory, or creative

thinking shows no fluctuations over thecycle

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Fluctuations in Sex Drive

Results of one study indicated thattestosterone levels peaked at ovulation

Other studies have indicated contradictory

results

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What Causes the Fluctuations in

Mood

Biological factors Fluctuations in levels of hormones

Environmental factors

Menstrual taboos and cultural expectations

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Cycles in Men

One study found evidence of behavioralcycles in men

Another study identified that high

testosterone levels were correlated with

depression

Other researchers have found cycles inmens emotional states