238 UROGENITAL SYSTEM 



THE UTERUS DURING MENSTRUATION AND PREGNANCY: PLACENTA AND 



DECIDUAL MEMBRANES 



Two sets of important changes take place normally in the wall of the uterus. 

 One of these is periodic and is the cause of menstruation (monthly flow). These 

 periodic changes may also be regarded as preparatory to the second set of changes 

 which take place if pregnancy occurs and give rise to the decidual membranes and 

 placenta. 



Menstruation. — The periodic changes which accompany the phenomenon of 

 menstruation form a cycle which occupies 28 days. This period is divided into 

 (1) a phase of uterine congestion lasting six or seven days; (2) a phase of hem- 

 orrhage and epithelial desquamation, duration three to five days; (3) a phase of 

 regeneration of the uterine mucosa lasting four to six days; (4) finally an interval 

 of rest or slight regeneration, varying from twelve to sixteen days duration. 



During the first phase, the uterine mucosa is thickened to two or three times 

 its normal condition, both because of vascular congestion and on account of the 

 actual increase in amount of reticular tissue. The uterine glands become longer 

 and their deeper portions especially are dilated and more convoluted because 

 they are filled with secretion. From the enlarged veins and capillaries blood 

 escapes into the reticular tissue beneath the epithelium and forms haematomata. 

 At the end of this phase the uterine mucosa shows a deep spongy layer and a 

 superficial compact layer, these corresponding to similar layers in the decidual 

 membranes of pregnancy. 



During the second phase, which is menstruation proper, blood escapes into 

 the uterine cavity between the epithelial cells of the mucosa and there is an active 

 discharge of secretion from the uterine glands. The surface epithelium and a 

 portion of the underlying tissue may or may not be desquamated. In some 

 normal cases the surface epithelium and most of the compact layer may be ex- 

 pelled, aided by painful contractions of the uterus. 



In the third stage, the mucosa has become thin with straight narrow glands 

 between which are fusiform, closely packed stroma cells. Any surface epithelium 

 which has been desquamated is regenerated from the epithelium of the glands and 

 gradually the mucosa returns to a resting condition during which, however, there 

 is a slow process of cell proliferation. ' 



The premenstrual changes of the first phase are regarded as the most impor- 

 tant part of the whole process, the uterine mucosa being prepared for the reception 

 of a fertilized ovum and for the development of the decidual membranes. Men- 



