Menstruation
Estrus v. Menstruation
Menstruation
I.
II.
A.
B.
C.
D.
E.
Evolution of menstruation
Menstrual cycle overview
Physiology of menstruation
Menstrual symptoms
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
Species
Estrus Cycle
Hamster
1
4
Sheep
2
17
Horse
5
21
Dog
7
60
Lion
9
55
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 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 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 –