Menstruation I. Estrus v. Menstruation II. Menstruation A. Evolution of menstruation B. Menstrual cycle overview C. Physiology of menstruation D. Menstrual symptoms E. Menstruation and the environment

I. Estrus v. Menstruation Estrus = “frenzy” Species with estrus cycles, females are generally only sexually active Females of species with menstrual cycles

A. Phases of Estrus Proestrus  one or several follicles of the ovary are starting to grow,folliclesovary Estrus  ovarian follicles are maturing and estrogen secretions exert their maximal influence. The animal exhibits a sexually receptive behavior, a situation that may be signaled by visible physiologic changes. Metestrus  Estrogen declines, and the corpus luteum starts to form Diestrus

B. Hormonal control & variation in cycles: Time line specific for canines Hamster14 Sheep217 Horse521 Dog760 Lion955 Species Estrus Cycle AVERAGE LENGTHS (days) OF ESTRUS AND ESTROUS CYCLES

The female on the left is in estrus: note the swelling around the top of the vagina and the presence of a small opening as well as the bright red color.

II. Menstruation Myths

A. Evolution of menstruation Inflammatory response? Only humans & great apes exhibit menstrual cycles, in contrast to the estrus cycle of most mammalian species.

B. Menstrual cycle overview Series of cyclic changes that the uterine endometrium undergoes each month in response to changing levels of hormones in the blood

C. Physiology of menstruation Remarkable events: Dependant upon interrelationships between the brain, pituitary gland, ovaries & uterus Preparation of egg for fertilization, preparation of uterus for pregnancy, evaluation of pregnancy status, reabsorption and excretion, begin again… Phases:

Days 1-5 Ovarian hormones at lowest point, Prostaglandin level is high in menstrual By day 5,

Days 6-14,  Follicular phase

Day 14: Ovulation

Days Endometrium Rising levels of progesterone from corpus luteum act on endometrium causing changes

IF fertilization occurs – Shortly after implantation,

No fertilization – Days 24-28, Premenstrual phase Degeneration of endometrium

D. Menstrual symptoms

E. Menstruation and the environment Amenorrhea – Oligomenorrhea – Effect of exercise  28% competitive females experience athletic amenorrhea or oligomenorrhea Diet Stress Menstrual synchrony –