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What is Uterine contraction and explain in detail?
Uterine contractions are muscle contractions of the uterine smooth muscle that occur during the menstrual cycle and labour. Uterine contractions occur throughout the menstrual cycle in the non-pregnant state and throughout gestation.

Throughout menstrual cycle
Uterine contractions that occur throughout the menstrual cycle, also termed endometrial waves or contractile waves, appear to involve only the sub-endometrial layer of the myometrium.

Follicular and luteal phase
In the early follicular phase, uterine contractions in the non-pregnant woman occur 1—2 times per minute and last 10–15 seconds with a low intensity of usually 30 mmHg or less. This sub-endometrial layer is rich in estrogen and progesterone receptors. The frequency of contractions increases to 3–4 per minute towards ovulation. During the luteal phase, the frequency and intensity decrease, possibly to facilitate any implantation.

Menstruation
If implantation does not occur, the frequency of contractions remains low; but at menstruation the intensity increases dramatically to between 50 and 200 mmHg producing labor-like contractions. These contractions are sometimes termed menstrual cramps, although that term is also used for menstrual pain in general. These contractions may be uncomfortable or even painful, but they are generally significantly less painful than contractions during labour. Painful contractions are called dysmenorrhea.

Directionality of contractions
A shift in the myosin expression of the uterine smooth muscle has been hypothesized as arising for changes in the directions of uterine contractions during the menstrual cycle.

Labour
Uterine contractions are part of the process of natural childbirth (i.e., not by Caesarean section). During labor, uterine contractions changes from episodic and uncoordinated to highly-coordinated. This change typically occurs at night, suggesting neural control, and significantly increases intrauterine pressure. Some women may experience contractions before labour is due. These are Braxton Hicks contractions, which are sometimes referred to as "false labour." There are several endogenous compounds involved in coordinating uterine contractility in labour, including oxytocin and prostaglandins.

Oxytocin
The hormone oxytocin has been identified as inducing uterine contractions, and labour in general. Oxytocin is produced by the body naturally and since the 1950s has also been available in synthetic pharmaceutical form.  In either form, oxytocin stimulates uterine contractions to accelerate the process of childbirth. Production and secretion of oxytocin is controlled by a positive feedback mechanism, where its initial release, either naturally or in pharmaceutical form, stimulates production and release of further oxytocin. For example, when oxytocin is released during a contraction of the uterus at the start of childbirth, this stimulates production and release of more oxytocin and an increase in the duration, intensity and frequency of contractions. This process compounds in intensity and frequency and continues until the triggering activity ceases.

Prostaglandins
The concentration of prostaglandins in the blood plasma and amniotic fluid increases during labor. These inflammatory mediators encourage myometrial contractions to induce labor. Prostaglandins are also related to the changes in gap junction formation and connexin-43 expression during labor.

In orgasm
Uterine and vaginal contractions usually take place during female sexual stimulation, including sexual arousal, and orgasm.

Monitors
Uterine contractions can be monitored by cardiotocography, in which a device is affixed to the skin of the mother or directly to the fetal scalp