The myometrium is the thick middle layer of the uterine wall, made of interlacing bundles of smooth muscle. It forms most of the uterus's bulk. During pregnancy its cells enlarge greatly, and in labour they contract powerfully and rhythmically to push the baby out.
| Location | Middle layer of the uterine wall between the endometrium and perimetrium |
|---|---|
| Parts |
|
| Nerve Supply | Uterovaginal plexus (from the inferior hypogastric plexus); Sympathetic fibres T10-L1 (pain from the uterine body); Pelvic splanchnic nerves S2-S4 (parasympathetic, pain from the cervix) |
| Blood Supply | Arcuate and radial arteries (from the uterine artery) |
| Venous drainage |
|
| Lymphatic drainage |
|
Contracts during labour, menstruation and orgasm, and clamps uterine blood vessels after delivery.
Oxytocin and prostaglandins stimulate the myometrium and are used to induce labour and to control bleeding after birth. After delivery, its crossing fibres squeeze the blood vessels shut ('living ligatures'), so poor contraction leads to postpartum haemorrhage. Fibroids grow from myometrial cells, and a previous caesarean scar is a weak point that can rupture in a later labour.
Benign smooth muscle tumours arising in the myometrium.
A tear through the myometrium in labour, usually at a previous caesarean scar; a serious obstetric emergency.
Endometrial glands within the myometrium causing an enlarged, painful uterus.
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