Myometrium
| Myometrium | |
|---|---|
 Uterus and uterine tubes (myometrium labeled at center right) | |
 Histology of myometrium | |
| Details | |
| Location | Uterus |
| Identifiers | |
| Latin | tunica muscularis |
| MeSH | D009215 |
| TA98 | A09.1.03.025 |
| TA2 | 3520 |
| FMA | 17743 |
| Anatomical terminology | |
The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells (also called uterine myocytes[1]) but also of supporting stromal and vascular tissue.[2] Its main function is to induce uterine contractions.
Structure
The myometrium is located between the endometrium (the inner layer of the uterine wall) and the serosa or perimetrium (the outer uterine layer).
The inner one-third of the myometrium (termed the junctional or sub-endometrial layer) appears to be derived from the
Muscular structure
The molecular structure of the smooth muscle of myometrium is very similar to that of smooth muscle in other sites of the body, with myosin and actin being the predominant proteins.[1] In uterine smooth muscle, there is approximately 6-fold more actin than myosin.[1] A shift in the myosin expression of the uterine smooth muscle may be responsible for changes in the directions of uterine contractions during the menstrual cycle.[1]
Function
Contraction
The myometrium stretches (the smooth muscle cells expand in both size and number, and crisscrossing fibres of middle layer compress the blood vessels to minimize blood loss. A positive benefit to early breastfeeding is a stimulation of this reflex to reduce further blood loss and facilitate a swift return to prepregnancy uterine and abdominal muscle tone.
Uterine smooth muscle has a phasic pattern, shifting between a contractile pattern and maintenance of a resting tone with discrete, intermittent contractions of varying frequency, amplitude and duration.[1]
As noted for the macrostructure of uterine smooth muscle, the junctional layer appears to be capable of both
Resting state
The
This resting potential undergoes rhythmic oscillations, which have been termed slow waves, and reflect intrinsic activity of
Excitation-contraction
The excitation-contraction coupling of uterine smooth muscle is also very similar to that of other smooth muscle in general, with intracellular increase in calcium (Ca2+) leading to contraction.
Restoration to resting state
Removal of Ca2+ after contraction induces relaxation of the smooth muscle, and restores the molecular structure of the sarcoplasmic reticulum for the next contractile stimulus.[1]
References
- ^ PMID 20551073.
- ^ "NCI Dictionary of Cancer Terms". National Cancer Institute. Retrieved 2017-12-27.
- ^ Steven's and Lowe Histology p352
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