adj.

子宮筋の、子宮筋層の

関: myometrium、uterine muscle

WordNet

the smooth muscle forming the wall of the uterus

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/07/26 10:31:39」(JST)

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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. Its main function is to induce uterine contractions.

Macrostructure

The myometrium is located between the endometrium (the inner layer of the uterine wall), and the serosa or perimetrium (the outer uterine layer).

Myometrium has 3 layers: outer longitudinal smooth muscles, middle crisscrossing (figure of eight) muscle fibres, and inner circular fibres.^[2] Middle crisscross fibres act as living ligature during involution of the uterus and prevent blood loss.

The inner one-third of the myometrium (termed the junctional or sub-endometrial layer) appears to be derived from the Müllerian duct, while the outer, more predominant layer of the myometrium appears to originate from non-Müllerian tissue, and is the major contractile tissue during parturition and abortion.^[1] The junctional layer appears to function like a circular muscle layer, capable of peristaltic and anti-peristaltic activity, equivalent to the muscular layer of the intestines.^[1]

Molecular 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]

Contractile patterns

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 be capable of both peristaltic and anti-peristaltic activity.^[1]

Resting state

The resting membrane potential (V_rest) of uterine smooth muscle has been recorded to be between -35 and -80 mV.^[1] As with the resting membrane potential of other cell types, it is maintained by a Na⁺/K⁺ pump that causes a higher concentration of Na⁺ ions in the extracellular space than in the intracellular space, and a higher concentration of K⁺ ions in the intracellular space than in the extracellular space. Subsequently, having K⁺ channels open to a higher degree than Na⁺ channels results in an overall efflux of positive ions, resulting in a negative potential.

This resting potential undergoes rhythmic oscillations, which have been termed slow waves, and reflect intrinsic activity of slow wave potentials.^[1] These slow waves are caused by changes in the distribution of Ca²⁺, Na⁺, K⁺ and Cl⁻ ions between the intracellular and extracellular spaces, which, in turn, reflects the permeability of the plasma membrane to each of those ions.^[1] K⁺ is the major ion responsible for such changes in ion flux, reflecting changes in various K⁺ channels.^[1]

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. However, the stimulating factors for uterine smooth muscle differs from other types of.

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]

Functions

The myometrium stretches (the smooth muscle cells expand in both size and number^[3]) during pregnancy to allow for the uterus to become several times its non-gravid size, and contracts in a coordinated fashion, via a positive feedback effect on the "Ferguson reflex", during the process of labor. After delivery the myometrium contracts to expel the placenta, 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.

Pathology

Lack of contraction at this stage is termed uterine atony. After pregnancy the uterus returns to its nonpregnant size by a process of myometrial involution.

Benign neoplasms of the myometrium are very common, termed uterine leiomyomata or fibroids. Their malignant version, leiomyosarcoma, is rare.

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Aguilar, H. N.; Mitchell, S.; Knoll, A. H.; Yuan, X. (2010). "Physiological pathways and molecular mechanisms regulating uterine contractility". Human Reproduction Update. 16 (6): 725–744. PMID 20551073. doi:10.1093/humupd/dmq016.
^ Miller-Keane Encyclopedia & Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition.
^ Steven's and Lowe Histology p352

External links

Myometrium at the US National Library of Medicine Medical Subject Headings (MeSH)

UpToDate Contents

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1. 分娩の生理学 physiology of parturition
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English Journal

Bioelectrical activity of porcine oviduct and uterus during spontaneous and induced estrus associated with cyclic hormone changes.

Pawliński B1, Domino M1, Aniołek O1, Ziecik A2, Gajewski Z3.
Theriogenology.Theriogenology.2016 Dec;86(9):2312-2322. doi: 10.1016/j.theriogenology.2016.07.029. Epub 2016 Aug 4.
It is widely accepted that uterine contraction is initiated by spontaneous generation of electrical activity at a cellular level in the form of action potentials. Such action potential events, when they involve many myometrial cells and occur in immediate succession, are described by their amplitude
PMID 27590095

Exercise during pregnancy in normal-weight women and risk of preterm birth: a systematic review and meta-analysis of randomized controlled trials.

Di Mascio D1, Magro-Malosso ER2, Saccone G3, Marhefka GD4, Berghella V5.
American journal of obstetrics and gynecology.Am J Obstet Gynecol.2016 Nov;215(5):561-571. doi: 10.1016/j.ajog.2016.06.014. Epub 2016 Jun 16.
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Loss of stiffness in collagen-rich uterine fibroids after digestion with purified collagenase Clostridium histolyticum.

Jayes FL1, Liu B2, Moutos FT2, Kuchibhatla M3, Guilak F2, Leppert PC4.
American journal of obstetrics and gynecology.Am J Obstet Gynecol.2016 Nov;215(5):596.e1-596.e8. doi: 10.1016/j.ajog.2016.05.006. Epub 2016 May 10.
BACKGROUND: Uterine fibroids are a significant health problem. These common benign tumors occur in 70-80% of women before age 50 years and often cause bleeding and pain and can interfere considerably with daily life. Current treatment options are limited. Fibroids contain substantial amounts of alt
PMID 27177523

Japanese Journal

ISP-16-5 Preoperative and intraoperative assessment of myometrial invasion in endometrial cancer : Comparison of magnetic resonance imaging and frozen section diagnosis(Group 16 Oncology 7,IS Poster,International Session)

Nogami Yuya,Kisu Iori,Banno Kouji,Umene Kiyoko,Tsuji Kosuke,Masuda Kenta,Ueki Arisa,Yamagami Wataru,Susumu Nobuyuki,Aoki Daisuke,Yoshimura Yasunori
日本産科婦人科學會雜誌 65(2), 1023, 2013-02-01
NAID 110009639802

子宮びまん性平滑筋腫症を認めた姉妹例

野溝万吏,馬場長,鈴木彩子 [他],山西恵,山口綾香,角井和代,松村謙臣,吉岡弓子,近藤英治,佐藤幸保,濱西潤三,小阪謙三,万代昌紀,小西郁生
産婦人科の進歩 65(1), 40-45, 2013
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The Activity and Localization of 3β-hydroxysteroid Dehydrogenase/Δ⁵-Δ⁴ Isomerase and Release of Androstenedione and Progesterone by Uterine Tissues During Early Pregnancy and the Estrous Cycle in Pigs

WOJCIECHOWICZ Bartosz,KOTWICA Genowefa,KOLAKOWSKA Justyna [他],FRANCZAK Anita
Journal of Reproduction and Development 59(1), 49-58, 2013
… In this study, we examined 1) endometrial and myometrial expression of 3β-HSD mRNA, 2) uterine 3β-HSD protein activity and 3) in vitro production of A4 and P4 by uterine slices harvested from pigs on days 10 to 11, 12 to 13 and 15 to 16 of pregnancy and the estrous cycle. …
NAID 130001854905

Related Pictures

★リンクテーブル★

リンク元	「uterine muscle」
拡張検索	「myometrial contraction」

「uterine muscle」

Myometrium
	Uterus and uterine tubes (Myometrium labeled at center right)
	Microscopic slide of the myometrium.
Details
Identifiers
Latin	tunica muscularis
TA	A09.1.03.025
FMA	17743
	Anatomical terminology [edit on Wikidata]