UTERUS
Is a pear shape organ consist of body, lower cylindrical part called cervix and the dome shaped part of the body above the openings of uterine tubes called fundus.The wall of the uterus is relatively thick and consist of three layers:
serosa or adventitia:the outer most layer.
myometerium : thick layers of smooth muscles.
endometrium:the inner layer of mucosa of uterus.
The fundus and the body of the uterus have the same histological features which differ than that of the cervix.
MYOMERTRIUM:
Composed of bundles of smooth muscle fibers separated by connective tissues . they form four poorly defined layers . the 1st and the 4th layers are longitudinally arranged (parallel to the axis of the uterus ) while the middle two layers are irregular and contain the larger blood vessels.
During pregnancy the myometrium increase ingreatiy inits proportion both due to hyperplasia (increase in number of smooth muscle cells) and hypertrophy (increasein cells size).
During pregnancy those smooth muscle cells have the character of protein secreting cells and they synthesis collagen leading to significant increase in collagen content of the uterus .
After pregnancy some smooth muscle cells will be destructed and others will decrease in size with enzymatic degradation of collagen and so the uterus will retrun to its pregnancy size.
ENDOMETRIUM:
Consist of epithelium and lamina propria containing simple tubular uterine glands .The epithelium consist of amixture of ciliated and secretory columner cells . The epithelium that line the uterine glands is similar to the surface epithelium of the uterus however ciliated cells are rare within the glands .
Connective tissue lamina propria is rich in fibroblasts with abundant ground surface .
The endmetrium can be divided in to layers:
stratum basalis: the deepest layer adjacent to the myometrium it consist of lamin propria and the beginnings of the uterine glands .
stratum functonalis: contain the remaining parts of the lamina propria uterine glands and covered by surface epithelium , this layer undergo profound changes during the menstrual cycle while the basalis layer remain unchanged.
The blood vessels supplying the endometrium are very important , the arcuate arteries are found within the myometrium they give 2 sets of arteries:
straight arterioles: supplying stratum basalis.
Spiral arterioles: supplying stratum functionalis.
MENSTRUAL CYCLE:
After puberty the ovarian hormones (estrogen and progesterone ) which are under stimulus of the anterior lobe of pituitary causes the endometrium to undergo cyclical structural changes during the menstrual cycle.The average of each cycle is about 28 days , day one of the cycle is taken as the day when the menstrual bleeding begins. The menstrual discharge consist of degradating endometrium mixed with blood from the ruptured blood vessels .
The menstrual phase lasts for 3-4 days on average . The next phase of the cycle are called the proliferative and secretory phases.
1.proliverative phase(follicular,estrogen phase)
Begins after the menstrual phase and its duration is variable (usually last from day 5 to day 15 or 16 ) . At its beginning the uterine mucosa are relatively thin (0.5mm) and its coincids with rapid growth of small group of ovarian follicles which start secreting increasing amount of estrogen .Estrogen hormone will have its effect on the endometrium so it will enhance cellular proliferation and induce rebuilding of the endometrium lost during menstruation .
During this phase the endometrium is covered by a simple columner epithelium .
The glands also formed of simple columner cells and they are straight tubules with narrow lumen .
At the end of the proliferative phase the endometrium is 2-3 mm thick.
2.Secretory phase(luteal phase):
It starts after ovulation under effect of progesterone secreated from the corpus luteum. Progesterone secreation will stimulate further growth of the uterine glands where they become higly coiled & their lumen will be filled with glycoprotein secretion.In this phase the endometrium reach its maximum thickness which is about 5mm. due to accumulation of secretion & edema in the stroma.
If fertilization occure the embryo will reach the uterus during its secretory phase & it is thought that the secretion of the gland is the major source of nutrition for the embryo before its implantation .
Proesterone hormone will also inhibits the contraction of the smooth muscle cells of the myometrium that might otherwise interfere with the implantation of the embryo.
Menstrual phase :
If fertilization does not occur the corpus luteum only programmed to act for 10-12 days after ovulation . After that marked decrease in estrogen & progesterone levels occur causing contraction of the spiral arterioles supplying struatum functionalis. Immediately prior to menstruation the endometrium regress, endometrial venous drainge is inhibited & an intense vasoconstriction of the spiral arterioles followed by vaso-relaxation is generated.
These events leads to tissue ischemia & damage, with shedding of the stratum functionalis & bleeding occur from fragments of arterioles remaining in the stratum basalis.
Menstruation cease as the damaged spiral arterioles vasoconstrict & the endometrium regenerate.Later repair of the endometrium & new blood vessels formation lead to complete cessation of bleeding within 5-7 days from the start of the menstrual cycle.