The layer of cells that line the uterus is called the endometrium (red). It is this layer that proliferates in response to estrogen and later, develops into a secretory lining in response to progesterone. If implantation of a fertilized egg does not occur, the endometerium is shed and the cycle begins all over again.

This daily doodle illustrates endometriosis, a condition where the endometrium of the uterus is found outside the uterine cavity. I tried to highlight the endometrium in red to show how it is found inside the uterus and in the case of endometriosis, outside the uterine cavity.

The endometrium can be found on the ovary, the fallopean tube, the intestines, the bladder, almost anywhere in the abdominal cavity and **exceedingly rare, in the lungs and brain**. Like the endometrium in the uterine cavity, this tissue responds to estrogen and progesterone and it follows the same menstrual cycle – growing and shedding. Depending on where the endometrium is located, the symptoms may be different. For example, if it grows in the recto/sigmoid area, the patient may present with dyschesia (difficulty defecating).

The triad of symptoms include:
1) Dysmenorrhea (painful menstruation)
2) Dyschesia
3) Dysparenia (pain during intercourse)

Diagnosis is done through laproscopy and biopsy. Red endometriosis lesions are “active” while the dark spots that look like “chocolate” indicate areas of nflammation. White lesions are inactive or scarred areas.