Hysteroscopic view of endometrium during menses

*Ever wonder why you have cramps during period?
*My speculation: The shredding of the endometrium and blood clots fills up the uterus, triggering irritation, leading to cramps.
 *Try taking a warm shower, moving around, contracting lower-abdomen, and attempting to expel the endometrium+clots.

Here's some picture of what your uterus looks like inside during menses
Src:
http://humrep.oxfordjournals.org/content/early/2009/03/11/humrep.dep036/F2.expansion
"

A re-appraisal of the morphological changes within the endometrium during menstruation: a hysteroscopic, histological and scanning electron microscopic study"

First day of menstruation.
(A) Hysteroscopic image of the earliest Day 1 appearance with the first evidence of menstrual blood loss from a single linear break in the surface (black arrow) and extensive areas of subepithelial haemorrhage.
(B) Hysteroscopic view of the partial detachment of surface epithelium and superficial endometrium from the underlying basalis on the first day of menstrual bleeding.
(C) Hysteroscopic appearance of a portion of endometrium that is completely detached from the underlying stroma and is floating free within the distended uterine cavity.
(D) A low-power SEM image of a Day 1 endometrium illustrating localized endometrial shedding exposing underlying stroma and protuberant gland stumps with the retention of adjacent surface epithelium.
(E) The white arrow indicating the hysteroscopic appearance of an unshed endometrium adjacent to a zone of shed surface epithelium, demonstrating the piecemeal nature of endometrial shedding (black arrows indicate multiple fine tubes) on Day 1 of menstruation.
(F) A hysteroscopic image of a more extensive area of coalesced shed endometrium, with white arrow indicating a small island of residual unshed endometrium and the black arrows showing the semi-transparent endometrial glands viewed end on.