Menstruation

I. Estrus v. Menstruation

II. MenstruationA. 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, 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

Hamster 1 4

Sheep 2 17

Horse 5 21

Dog 7 60

Lion 9 55

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 http://news.bbc.co.uk/2/hi/south_asia/4250506.stm http://www.mum.org/

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 menstruationRemarkable 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 15-28

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 –