What are the three muscle layers of the uterus?

• Outer longitudinal layer
• Middle vascular layer (contains the large vessels)
• Inner layer with both longitudinal and oblique fibres (the interlacing 'living ligatures')

The interlacing arrangement allows the myometrium to compress the vessels passing through it during contraction - the basis of post-delivery haemostasis.

Clinical relevance. The interlacing myometrium's compression of vessels is the basis of haemostasis after delivery and why atony causes PPH.

More Detail

Uterine musculature

The myometrium's layered, interlacing structure is functionally important.

The layers

• Outer longitudinal layer.
• Middle vascular layer - contains the large blood vessels.
• Inner layer with both longitudinal and oblique muscle fibres.

Functional significance

• The interlacing fibres act as 'living ligatures': when the uterus contracts after delivery, they kink and compress the vessels running through the middle vascular layer, achieving haemostasis at the placental bed.
• Failure of this contraction (atony) causes postpartum haemorrhage despite normal clotting.

Other

The myometrium hypertrophies enormously in pregnancy and generates the contractions of labour.