1. The uterus is a muscular sac, lined with that undergoes cyclic changes.

2. The wall is made up of thick, smooth muscle, organized in interlacing bundles that run randomly. It is called the .

3. The uterine lining consists of glands that are called .

4. As the ovary and oviduct are undergoing changes with the cycle, the uterine lining is being prepared to receive an .

5. The normal human menstrual cycle is divided into three phases by the hormonal events and changes in the uterine lining.  The first phase is called the phase.

6. This coincides with the rise in early in the cycle and is distinguished in the uterus by lengthening endometrial glands.

7. After ovulation, the uterine lining becomes more torturous.  The lining is now under the control of .  This steroid hormone stimulates the lining to secrete material that may help nourish both sperm and a potential pregnancy.  The glands expand and the lumina are wide and contain products of secretion.

8. If a does not occur, the lining breaks down about two weeks after ovulation.  Spiral arteries supplying the outer region of the uterine lining constrict and deprive the region of oxygenated blood.  The cells lose fluid and cease to function.  The stroma is invaded by leukocytes.

9. continues and the uterine lining is shed.  This is the menstrual phase of the uterine lining.  After the third or fourth day, all of the lining is shed except basal regions containing glands that can regenerate during the proliferative phase of the subsequent cycle.

10. The myometrium is responsive to the hormone, , that is particularly high during labor.