Uterus, before menarche, is lined by: September 2011
**Core Concept**
The uterus, before menarche, is composed of a thick fibromuscular layer of the myometrium and a thin layer of endometrium. The endometrium is crucial for menstrual cycle regulation and is influenced by hormonal changes.
**Why the Correct Answer is Right**
During the premenarchal period, the endometrium is primarily composed of **simple tubular glands** that are not yet fully developed. These glands are influenced by estrogen and progesterone, but the **estrogen levels are higher**, causing the endometrium to be thinner and less responsive to progesterone. The presence of these simple glands is essential for the eventual development of the endometrium and the initiation of menstrual cycles.
**Why Each Wrong Option is Incorrect**
**Option A:** The uterus is primarily composed of smooth muscle in the myometrium, but this does not accurately describe the lining of the uterus before menarche.
**Option B:** The endometrium is not composed of a thick layer of squamous epithelium, which is more characteristic of the vaginal lining.
**Option C:** The endometrium is not composed of a thick layer of columnar epithelium, which is more characteristic of the mature endometrium after menarche.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the premenarchal endometrium is thinner and less responsive to progesterone due to higher estrogen levels, which eventually leads to the initiation of menstrual cycles.
**Correct Answer: D. Simple tubular glands**