د. مها السماك
Lec.3Menstrual and ovarian cycles
Histology of the uterus : The wall of the uterus is composed of three layers :
Endometrium : the mucosa lining the inside wall and is formed from compact , spongy and basal layers , it contains glands and vessels.
Myometrium : thick layer of smooth muscle.
Perimetrium : the peritonium covering the outside wall.
Histology of the ovary : the ovary consists of :
Medulla : formed of blood vessels and connective tissue.Cortex : formed of connective tissue and covered by cuboidal epithelia it contains the ovarian follicles.
At time of puberty the females undergo regular monthly cycles involving the endometrium (known as the menstrual cycle) and the ovaries (known as the ovarian cycle) , preparing the reproductive system for pregnancy. the cycles are controlled by the hypothalamus , the hypothalamus secretes gonadotropin releasing factors which act on the anterior pituitary gland , which in turn secretes FSH and LH (gonadotropins) that stimulate and control the cyclic changes in the ovary and endometrium.
The duration of the menstrual cycle is variable but averages 28 days , it can be divided into 3 phases , during which the ovarian cycle is also in operation (i.e. the menstrual cycle is coincides with the ovarian cycle).
Menstrual phase ( menses ) : the period of bleeding it takes the first five days of the cycle . it is caused by sudden reduction in estrogen and progesterone. during which the compact and spongy layers (containing the glands and arteries )are expelled from the uterus , while the basal layer remains in the uterus. During this phase ovarian cycle begins and a number of follicles start to grow under influence of FSH. the follicles start to produce estrogen from their theca and follicular cells.
Proliferative or preovulatory phase : the period between the menses and ovulation ( i.e. from 6-13 days in a 28 days cycle ). during which FSH and LH stimulate the follicles to grow further in turn produce more estrogen , this estrogen will repair the endometrium form the basal layer. the follicles continue their growing but usually only one reaches full maturity and only one oocyte discharged. the other follicles degenerated and replaced by connective tissue forming the corpus atreticum. The estrogen from the growing follicles will stimulate the pituitary Gland to secrete more LH which is important for the final stages of follicle maturation and to induce ovulation .
Ovulation : shedding of the oocyte and some of the cumulus oophorus cells out of the ovary. these cells will rearrange around the zona pellucida forming the corona radiata. at the moment of ovulation the secondary oocyte is in the stage of spindle formation. ovulation occur in the day 14 , the oocyte will enter uterine tube by the sweeping movements of the fimbriae and the motion of the cilia on the epithelial lining. in the tube the oocyte loss contact with the corona radiata and it is pushed forward the uterine lumen if it is fertilized it will reaches the lumen in about 3-4 days .
Secretary or post ovulatory phase :the period between ovulation and the onset of the next menses (i.e. from 15-28 days ) during which the following : cells remaining in the wall of the raptured follicle in the ovary are vascularized and under LH stimulation they will change to luteal cells thus forming the corpus luteum (CL) which will secrete progesterone and estrogen . these hormones cause the endometrium to enter the secretory phase in preparation for implantation of the endometrium so the glands show increase secretory activity and the arteries of endometrium become tortuous , and the three layers of endometrium Become well recognized.
If the oocyte is not fertilized the estrogen and progesterone increase thus decrease gonadotropin releasing factor , so LH decrease and thus corpus luteum (CL) degenerates 9-12 days after ovulation forming corpus albicans thus estrogen and progesterone decrease , precipitating menses.
If fertilization occur (CL) will continue to grow by the effect of gonadotropic hormone secreted by the trophoblast of the developing embryo , forming the (CL) of pregnancy , it will continue to secrete progesterone until the end of the fourth month , then after it regress since progesterone will be secreted in adequate amount from the trophoblastic part of the placenta for maintenance of pregnancy.