UTERUS Is a pear shaped organ. consist of consist of 1. Body. 2. lower cylindrical part called cervix 3. 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. they form four poorly defined layers. the 1st and the 4th layers are longitudinally arranged (parallel to the axis of the uterus ) 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 greatly in its proportion both due to hyperplasia (increase in number of smooth muscle cells) and hypertrophy (increase in 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 return to its prepregnancy size.

ENDOMETRIUM: Consist of epithelium and lamina propria containing simple tubular uterine glands. The epithelium consist of a mixture of ciliated and secretory columnar 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. 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 lamina propria and the beginnings of the uterine glands. stratum functionalis: 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 degenerating endometrium mixed with blood from the ruptured blood vessels. The menstrual phase lasts for 3-4 days on average. The next phases of the cycle are called the proliferative and secretory phases.

 Proliferative 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 it coincides with rapid growth of small group of ovarian follicles which start secreting increasing amount of estrogen. At its beginning the uterine mucosa are relatively thin (0.5mm) and it coincides 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.

Proliferative phase (follicular, estrogen phase) During this phase the endometrium is covered by a simple columnar epithelium. The glands also formed of simple columnar cells and they are straight tubules with narrow lumen. At the end of the proliferative phase the endometrium is 2-3 mm thick.

Secretory phase (luteal phase): It starts after ovulation under effect of progesterone secreted from the corpus luteum. Progesterone secretion will stimulate further growth of the uterine glands where they become highly 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 occur 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 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 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

 Full term placenta: At full term, the placenta is discoid in shape with a diameter of cm. It approximately 2-3cm. in thickness& about gm. in weight. The placenta has two surfaces: a fetal surface which is very smooth, in contact with fetus a maternal surface which is rough, irregular & in contact with wall of the uterus, it consist of about polygonal areas, which are known as cotyledons.

The formation of the placenta is fully established by the end of the fourth month. The human placenta has a complex villous structure that greatly increases the contact surface area between maternal blood & fetal capillaries so giving greater nutritional support for the fetus.

The umbilical cord The umbilical cord connects the body of the fetus to the placental disc. It is formed of two umbilical arteries & one umbilical vein supported by loose gelatinous connective tissue called Wharton’s jelly.

THE FETAL PART OF PLACENTA: consists of a chorionic plate & branching processes or villi, which arise from it. These chorionic villi are the basic functional units of the placenta. These chorionic villi are the basic functional units of the placenta. The villi that arise from the chorionic plate are usually called stem villi, those villi that are attached to the basal plate are anchoring villi, and those villi which ends free in the intervillous spaces are the terminal villi.

Villi are alike histologically. In each villous there is a fetal capillary lined with endothelium & is contained in the loose connective tissue core of the villous. In each villous there is a fetal capillary lined with endothelium & is contained in the loose connective tissue core of the villous. IN the core there are a few bundles of collagen fibers & fibroblasts also some scattered smooth muscle fibers. Larger cells with large eccentric spherical nuclei (cells of Hofbauer) are also present; possibly these are phagocytic cells.

The trophoblast cells covering each villous consists of two well defined layers cytotrophoblasts & syncytiotrphoblast until approximately the middle of the third month of the pregnancy, the cytotrophoblast layer will progressively disappear until at term only a few isolated clumps of cells are left.

The cytotrophoblast layer: (langhan’s cells) consist of large, pale cells. In early stages of pregnancy these cells form a complete layer between syncytial cells & the basement membrane. The nuclei of these cells were large & rounded with high nucleo-cytoplasmic ratio. In mature placenta langhan’s cells don’t form a complete layer, their number decrease greatly, but they could still be recognized. Cytotrophoblasts cells function mainly as stem cells for the overlying syncytiotrphoblasat.

The syncytiotrphoblasat layer: is a dark variably thick layer. in which numerous small nuclei are found & no intercellular boundaries can be distinguished. This layer becomes progressively thinner through out pregnancy.

The maternal part of the placenta is formed by the decidua basalis, which consist chiefly of the connective tissue stroma, the cells of which are decidual in nature. The endometrial cells become large, polygonal & rich in glycogen & lipid droplets. Endometrial glands, fibrinoid substance, & small clumps of trophoblastic cells are also present.

In the initial placenta, the placental barriers between fetal & maternal circulations are composed of 4 layers: In the initial placenta, the placental barriers between fetal & maternal circulations are composed of 4 layers: (a) the endothelial lining of the fetal vessels (b) the connective tissue in the villous core (c) the cytotrophoblastic layer (d) the syncytium.

From the fourth month onward the placental barriers are formed only from the endothelial lining of fetal vessels and the syncytium. This will greatly increase the rate of exchange through them.