MD-22 II. 56-3100 HUMAN FEMALE REPRODUCTIVE SYSTEM SET BOBBITT I:~ 1-'- LABORATORIES BURLINGTON, ",ORT", CAROLINA Carolina Biological Supply Company Main Office Powell laboratories Division Burlington, N. C. 27215 Gladstone, Oregon 97027 Printed in U.S.A. © 1968 Carolina Biological Supply Company Dorsocranial Fig.l Ventrocaudal Fig.3 II 56-3100 to 56-3120 Human Development The female reproductive system includes the ovaries, the fallo­ pian tubes, the uterus, the vagina, and the external genital organs. The uterus in its most usual position is turned forward so that the fundus is directed ventrally toward the abdominal wall. In this position the fallo­ pian tubes lie anteriorly and the ovaries are on the upper surface of the broad ligament. Figs. 1 and 2 show these structures from the upper (dorsocranial) and lower (ventrocaudal) aspects. The entire system lies in an invagination of the peritoneum and is thus not within the peritoneal cavity. The heavy lines around the uterus in Fig. 3 represent the peri­ toneum. The most usual representation of the system shows a frontal section through the uterus, ovary, and fallopian tubes. To obtain such a section the uterus must be reflected along the line shown in Fig. 3. The paired ovaries are the source of all of the eggs produced by the mature female. These occur in the cortex of the ovary and are in an undeveloped form called the primary germ cell. There are some 400,000 of these in the ovary at puberty and the supply is exhausted at about 50 years of age. Many of these potential eggs do not develop fully but are lost. The first phases in the development of the egg occur before birth. Small masses of cells appear in the ovarian cortex as it develops. The cell masses, called primordial follicles, each consist of a central germ cell (oogonium) surrounded by a single layer of flattened epithelial cells. From the third month to birth the germ cells undergo a maturation peri­ od during which they enlarge and their nuclei begin the first meiotic di­ vision. They are called primary oocytes at this time and measure about 40 mu in diameter. No further changes occur until puberty. In the mature individual, several of the primary follicles undergo maturation every 28 days, though usually only one reaches full maturity.' This maturation consists of a proliferation of the epithelial cells and a two-fold increase in the size of the germ cell. A heavy membrane, the zona pellucida, appears around the germ cell (oocyte), As the epithelium (granulosa) continues to proliferate, it becomes several cells thick and small pockets of fluid appear between the cells. These fluid -filled spaces move together into the center of the cell mass to form a single pocket, the antrum. The oocyte lies to one side of the antrum and is surrounded by a mass of granulosa cells called the cumulus oophorus. 3 ", fi~~'Mis,.,--- P o l a r body I --,~~_Cytoplasm '!tI14~~+-p.~--Nucieus Vitelline membrane T he sur rounding ovar ian ti s sue bec om es mo dified to form a she ath or the ca which will di fferentiate int o two lay ers, the inter nal and exter ­ nal th ecae. T he follicle enlarges until it forms a distinct bulge on the surface of the ovary. T he surface of the follicle the n thin s down until it r up tur es, releasing the oocyte. A layer of follicular cells, the co rona ra­ di ata , su r r ounds the free oocy te (Fig. 4). T he oocyte is car ried through the ab domina l orifice of the fa llopian tube by c iliary actio n. The fi rst m e iotic division i s now completed with th e extrusion of th e fi r s t polar body, and the c ell be c ome s a secondary oocyte . The second m ei oti c di­ vision is initiated im mediately . T his div ision is co mpleted after e ntry of the spe r m and usually occurs as the cell is car ried through th e ovi ­ duc t. T he second m eioti c division r esults in a haploid egg and a second pol ar body . At thi s time the egg m easure s abou t 130 mu in diameter . The sper m head i s mo dified to bec ome the male pronucleu s , which then unite s with the fe male nucleu s. With th is fusion, the zygote i s formed. Cleavage i s init iated by the divi sion of the zygo te into two unequal bl a stom er e s. The large r of the two cells soon divide s again , r esulting in a three-celled em bryo. Rep eat e d irregular divi sions give rise to a solid m a s s of cells called the m orula. A cavity appears in the ce nter of this cell m a s s a nd in cre a se s in s ize until the em bryo r e semble s a hollow ball. F our t o five days af ter fe r tilizatio n the embryo (bla stocyst) con­ s ists of an outer shell of cells, the cho r io n, surrounding an inner cell mass, the embryoblast, and a large liquid -filled cavity, th e blastoc oele (Fi g. 5). As these divi sions take pla ce, the embryo migrate s from the 4~~~~~~~~~~~EmbrYOblast V, Endoderm Trophoblast 4 uterine tubule into the uterus and enl arges to abo ut 200 mu in diamete r. Implantation occurs at ab out 7 -1 / 2 day s afte r fertiliz ation. T he ute r in e epith elium di s s olves away at th e point at whi ch the bl a stocyst touches it and the embryo sinks into the s uperfic ial layers of the endometrium. The blastocyst be com e s or iented so that th e inner cell mas s is toward the uterus . T he wall of the embryo fa cing the uterus be­ com e s thickened and differentiates int o two ti s su e l ay er s. The deeper l ayer, th e s yntrophobla st, is in contact with the ut erus. It has no cell wall s a nd s hows little mitotic activity. T he out e r layer , the cytotropho ­ blast, is cellular ancl i s m itotically very active. These two ti s su e layers m ak e up the chorion of the em bryo. .- ... -­ .. ... == :-"","::...:.:.o;; Ifl:i! ~ ':7- - A mnio n 1lt\-:......,.c:..o:!lOi~,:-,.,.- E m b r y o n i c d isc ~-+~-E n d o de r m -iI'''f--Mesod er m Ao',;~- 'Cy tot r o p h o b las t '; ......:"',J Synt rophoblast :~~".;@""",,_~~:~; ..;o-' i\. small s pace , the a mnio tic cav ity , appears in the inner cell m a s s . The po rtion of the cell m a s s ext er nal to the cav ity is th e em bryonic di sc. i\. lo osely or ganized m a s s of cells exter nal to th e em bryonic disc is the e ndode r m . The cells of the endoderm pr oliferate rapidly, spreading away from th e disc to line the ca vity of the bl a stocyst. This cavity is now the primary yolk sa c . The portion of th e bl a stocoel e external to the y olk sac becomes loo sel y fi lled with primary m e soderm (Fig . 6) . By th is time (about ]2 clay s) the bla stoc yst, which is about 1 mm in di amet er, ha s been com ple te ly covered over by r egenerating t issue of the ut erine epi ­ thelium . T he are a of penetration is m arked by a mass of tissue debris c alled th e op erculum. Spaces or lacunae now begin to appear in the synt r ophoblast of the embryo. Many of th e se spaces are I'ilIed with maternal bl ood, sup­ plied from s m all s piral arter ies in the endom etrium of t he uterus. TI1e trophobla stic tis sues rapidly increase in extent, eve ntually completel y s ur round ing the e mbryo. TI1e cytotrophobla st forms numerous projec­ ti ons ext ending towar d the maternal tis sue. The se ar e c overed with s yn­ trophobla stic ti.ssue and fo r m the prim ary villi. The se villi enlar ge, ac ­ quire a m e senchymal core and Circul a tory tissue, a nd u sually give r ise to many secondary br anches ( Fig. 7) . At the tips of s ome of the s e villi , the cy t otrophoblastic cells multiply to form columns whi ch per fo r ate the synt r ophoblast and r each the maternal tissue. Such villi s erve to attach 5 F;g. 7 Q ~ ~ 7; -:- ~' IJ .... ---Decidua basali s i,;:::;:f;?~::: :'; · · \ ...:<O' inle rvilio us },~. ; ' i . ,~, spa ce '. ;:. 'i=;{ C yl rophobla sl m,.cl¥ .",,---Mesoderm th e placenta securely to th e ut erine tissues. T he inte r vi llou s spaces are com pletely line d w ith sy ntrophobla s tic tissue. At ab out th ree weeks th e blastocy st i s appr oxim a te ly 8 111m in diameter.