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）』「2015/10/29 14:20:42」(JST)

wiki en

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 made of longitudinal smooth muscles, middle from crisscrossing (figure of eight) muscle fibres and inner circular fibres.^[2] Middle crisscross fibres act as living ligature during involution of 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 myometrium appears to originate from non-Mullerian tissue, and is the major contractile tissue during parturition and abortion.^[1] Also, 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 smooth muscle of the myometrium is basically very similar in molecular structure to smooth muscle in other sites of the body, with myosin and actin being the predominant proteins expressed.^[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 has been hypothesized to avail for changes in the directions of uterine contractions that are seen 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]

Also, 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 basically 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 basically very similar to 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 smooth muscle, availing for separate coordination of uterine smooth muscle.

Restoration to resting state

Removal of Ca²⁺ after contraction induces relaxation of the smooth muscle, and restores the molecular structure of the sarcoplasmic reticulum to avail 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 harboring of the pregnancy, 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 reduce blood loss; where the crisscrossing fibres of middle layer compress the blood vessels. Thus a positive benefit to early breast feeding is a natural stimulation of this reflex to reduce 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.

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. doi:10.1093/humupd/dmq016. PMID 20551073.
^ 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

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 子宮腺筋症 uterine adenomyosis
2. 分娩の生理学 physiology of parturition
3. 患者情報：異常子宮出血（不正性器出血および過多月経）（詳細） abnormal uterine bleeding beyond the basics
4. 子宮鏡下子宮筋腫摘出術 hysteroscopic myomectomy
5. 癒着胎盤、嵌入胎盤、および穿通胎盤の臨床的特徴および診断 clinical features and diagnosis of placenta accreta increta and percreta

English Journal

Sonographically Guided Hysteroscopic Endomyometrial Resection.

Wortman M.SourceDirector, Center for Menstrual Disorders, Clinical Associate Professor of Gynecology, University of Rochester Medical Center, Rochester, New York.
Surgical technology international.Surg Technol Int.2012 Dec 1;XXI:163-169. [Epub ahead of print]
Hysteroscopic endomyometrial resection (EMR) was first reported by this author in 1994.[1] Several refinements have been made through the years including the addition of sonographic guidance as well as its adaptation into an office-based environment. EMR has many outstanding benefits including its a
PMID 22504986

Relaxant effect of a novel calcium-activated potassium channel modulator on human myometrial spontaneous contractility in vitro.

Rosenbaum ST, Larsen T, Joergensen JC, Bouchelouche PN.SourceDepartment of Gynecology and Obstetrics, Holbaek Hospital, Holbaek, Denmark Smooth Muscle Research Center, Department of Clinical Biochemistry, Koege Hospital, Koege, Denmark.
Acta physiologica (Oxford, England).Acta Physiol (Oxf).2012 Jun;205(2):247-54. doi: 10.1111/j.1748-1716.2011.02384.x. Epub 2011 Dec 22.
Aim: To investigate the effect of 4,5-dichloro-1,3-diethyl-1,3-dihydro-benzoimidazol-2-one (NS4591), a novel SK/IK channels positive modulator, on human myometrial activity. Methods: Organ bath studies were performed on myometrial preparations obtained from women undergoing elective caesarean
PMID 22099068

Japanese Journal

An in vivo mouse model of primary dysmenorrhea

YANG Lu,CAO Zhengyu,YU Boyang,CHAI Chengzhi
Experimental Animals 64(3), 295-303, 2015
… The area of uterine myometrium significantly decreased along with the increased thickness in the oxytocin-induced estrogen pretreated mice model. …
NAID 130005091027

子宮体部から漿膜側へ有茎性に発育した子宮内膜間質肉腫の1例

李泰文,小林史昌,稲田収俊 [他],山村省吾,坂田晴美,吉田隆昭,中村光作,小野一雄
産婦人科の進歩 67(2), 101-106, 2015
子宮体部から漿膜側へ有茎性に発育する悪性腫瘍はまれである．今回われわれは，子宮内膜間質肉腫が子宮体部の漿膜側に有茎性に発育した症例を経験したので報告する．症例は61歳，未経妊．腹痛のため当院救急外来を受診した．超音波検査とMRI検査にて骨盤内に，壁が緊満に乏しく，内部に出血を伴う腫瘤（長径20cm）の存在と，骨盤内に内容液の漏出を疑う所見を認め，卵巣癌の破裂が疑われた．開腹手術を行ったところ，骨盤 …
NAID 130005085384

An in vivo mouse model of primary dysmenorrhea

YANG Lu,CAO Zhengyu,YU Boyang,CHAI Chengzhi
Experimental Animals advpub(0), 2015
… The area of uterine myometrium significantly decreased along with the increased thickness in the oxytocin-induced estrogen pretreated mice model. …
NAID 130005066236

Related Pictures

★リンクテーブル★

リンク元	「子宮」「myometrial」「子宮筋層」「uterine muscle」

「子宮」

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

　　[★]

英: uterus (Z), womb, metra
関: 内性器

発生学的由来

中腎傍管

解剖

支持構造

子宮広間膜
子宮支帯(膀胱子宮靭帯、基靭帯、子宮仙骨靭帯)

組織

子宮

子宮の大きさ

鶏卵大。(非妊娠時)逆位の前後にやや扁平な西洋梨状で長さ約7cm、幅約4cm、厚さ約2.5cm、重さ30～40g。

妊娠と子宮の大きさ、子宮底の高さ、恥骨結合上縁から子宮底までの長さ

妊娠月数	子宮の大きさ	子宮底の高さ	恥骨結合上縁から子宮底までの長さ
第1月末	鶏卵大
第2月末	鵞卵大
第3月末	手拳大
第4月末	小児頭大	恥骨結合上2-3横指	12cm	（妊娠月数x3)
第5月末	成人頭大	恥骨結合と臍との中央	15cm	（妊娠月数x3)
第6月末		臍高	21cm	（妊娠月数x3+3)
第7月末		臍上2-3横指	24cm
第8月末		剣状突起と臍との中央	27cm
第9月末		剣状突起下2-3横指	30cm
第10月末		剣状突起と臍との中央	33cm

産褥0日分娩直後		臍下3横指	11cm
産褥0日12時間後		臍高(右に傾く)	15cm
産褥1-2日		臍下1-2横指	12cm
産褥3日		臍下3横指	10cm
産褥5日		臍高と恥骨結合上縁との中間	9cm
産褥7日(産褥1週)	手拳大	恥骨結合上縁
産褥10日		腹壁から触れない
(産褥6週)	鶏卵大