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.
Feeding bites
Feeding bites have characteristic patterns and symptoms, a function of the feeding habits of the offending pest and the chemistry of its saliva. Microscopic appearance
The histomorphologic appearance of insect bites is usually characterized by a wedge-shaped superficial dermal perivascular infiltrate consisting of abundant lymphocytes and scattered eosinophils. This appearance is non-specific, i.e. it may be seen in a number of conditions including:
Drug reactions,
Urticarial reactions,
Prevesicular early stage of bullous pemphigoid, and
HIV related dermatoses. See also
List of biting or stinging arthropods
Spider bite
Insect bite relief stick
Schmidt sting pain index
Bee  sting
Allergy

References
External links

Venomous Arthropods chapter in United States Environmental Protection Agency and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual
Burns, Boyd (Bo) D (2020-12-06). "Insect Bites: Background, Pathophysiology, Epidemiology". Medscape Reference. Retrieved 2021-01-22.