Genital Glands. The first appearance of the genital gland is essentially the same in the two sexes, and consists in a thickening of the epithelial layer which lines the peritoneal cavity on the medial side of the urogenital fold. The thick plate of epithelium extends deeply, pushing before it the mesoderm and forming a distinct projection. This is termed the genital ridge, and from it the testis in the male and the ovary in the female are developed. At first the mesonephros and genital ridge are suspended by a common mesentery, but as the embryo grows the genital ridge gradually becomes pinched off from the mesonephros, with which it is at first continuous, though it still remains connected to the remnant of this body by a fold of peritoneum, the mesorchium or mesovarium. About the seventh week the distinction of sex in the genital ridge begins to be perceptible.

            The Ovary.—The ovary, thus formed from the genital ridge, is at first a mass of cells derived from the celomic epithelium; later the mass is differentiated into a central part or medulla covered by a surface layer, the germinal epithelium. Between the cells of the germinal epithelium a number of larger cells, the primitive ova, are found, and these are carried into the subjacent stroma by bud-like ingrowths (genital cords) of the germinal epithelium. The surface epithelium ultimately forms the permanent epithelial covering of this organ; it soon loses its connection with the central mass, and a tunica albuginea develops between them. The ova are chiefly derived from the cells of the central mass; these are separated from one another by the growth of connective tissue in an irregular manner; each ovum assumes a covering of connective tissue (follicle) cells, and in this way the rudiments of the ovarian follicles are formed. According to Beard the primitive ova are early set apart during the segmentation of the ovum and migrate into the germinal ridge.

           Waldeyer taught that the primitive germ cells are derived from the “germinal epithelium,” covering the genital ridge. Beard, on the other hand, maintains that in the skate they are not derived from this epithelium, but are probably formed during the later stages of cell cleavage, before there is any trace of an embryo; and a similar view was advanced by Nussbaum as to their origin in amphibia. Beard says: “At the close of segmentation many of the future germ cells lie in the segmentation cavity just beneath the site of the future embryo, and there is no doubt they subsequently wander into it.” The germ cells, “after they enter the resting phase, are sharply marked off from the cells of the embryo by entire absence of mitoses among them.” They can be further recognized by their irregular form and ameboid processes, and by the fact that their cytoplasm has no affinity for ordinary stains, but assumes a brownish tinge when treated by osmic acid. The path along which they travel into the embryo is a very definite one, viz., “from the yolk sac upward between the splanchnopleure and gut in the hinder portion of the embryo.” This pathway, named by Beard the germinal path, “leads them directly to the position which they ought finally to take up in the `germinal ridge’ or nidus.” A considerable number apparently never reach their proper destination, since “vagrant germ cells are found in all sorts of places, but more particularly on the mesentery.” Some of these may possibly find their way into the germinal ridge; some probably undergo atrophy, while others may persist and become the seat of dermoid tumors.

            Descent of the Ovaries. In the female there is also a gubernaculum, which effects a considerable change in the position of the ovary, though not so extensive a change as in that of the testis. The gubernaculum in the female lies in contact with the fundus of the uterus and contracts adhesions to this organ, and thus the ovary is prevented from descending below this level. The part of the gubernaculum between the ovary and the uterus becomes ultimately the proper ligament of the ovary, while the part between the uterus and the labium majus forms the round ligament of the uterus. A pouch of peritoneum analogous to the saccus vaginalis in the male accompanies it along the inguinal canal: it is called the canal of Nuck. In rare cases the gubernaculum may fail to contract adhesions to the uterus, and then the ovary descends through the inguinal canal into the labium majus, and under these circumstances its position resembles that of the testis.

Fallopian tubes. The fallopian tubes are about 10 cm long and begin as funnel-shaped passages next to the ovary. They have a number of finger-like projections known as fimbriae on the end near the ovary. When an egg is released by the ovary it is caught by one of the fimbriae and transported along the fallopian tube to the uterus. The egg is moved along the fallopian tube by the wafting action of cilia hairy projections on the surfaces of cells at the entrance of the fallopian tube and the contractions made by the tube. It takes the egg about 5 days to reach the uterus and it is on this journey down the fallopian tube that fertilisation may occur if a sperm penetrates and fuses with the egg. The egg, however, is only usually viable for 24 hours after ovulation, so fertilisation usually occurs in the top one-third of the fallopian tube.

Uterus
The uterus is a hollow cavity about the size of a pear (in women who have never been pregnant) that exists to house a developing fertilised egg. The main part of the uterus (which sits in the pelvic cavity) is called the body of the uterus, while the rounded region above the entrance of the fallopian tubes is the fundus and its narrow outlet, which protrudes into the vagina, is the cervix.

The thick wall of the uterus is composed of 3 layers. The inner layer is known as the endometrium. If an egg has been fertilised it will burrow into the endometrium, where it will stay for the rest of its growth. The uterus will expand during a pregnancy to make room for the growing fetus. A part of the wall of the fertilised egg, which has burrowed into the endometrium, develops into the placenta. If an egg has not been fertilised, the endometrial lining is shed at the end of each menstrual cycle.

The myometrium is the large middle layer of the uterus, which is made up of interlocking groups of muscle. It plays an important role during the birth of a baby, contracting rhythmically to move the baby out of the body via the birth canal (vagina).

Uterus

“Hystera” and “Uterine” redirect here. For the state of mind, see hysteria. “Womb”

The uterus (from Latin “uterus”, plural uteri) or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. Two uteri usually form initially in a female fetus, and in placental mammals they may partially or completely fuse into a single uterus depending on the species. In many species with two uteri, only one is functional. Humans and other higher primates usually have a single completely fused uterus, although in some individuals the uteri may not have completely fused. In English, the term uterus is used consistently within the medical and related professions, while the Germanic-derived term womb is more common in everyday usage.

The uterus consists of a body and a cervix. The cervix protrudes into the vagina. The uterus is held in position within the pelvis by condensations of endopelvic fascia, which are called ligaments. These ligaments include the pubocervical, transverse. cervical ligaments cardinal ligaments, and the uterosacral ligaments. It is covered by a sheet-like fold of peritoneum, the broad ligament.^[2]

The uterus is essential in sexual response by directing blood flow to the pelvis and to the external genitalia, including the ovaries, vagina, labia, and clitoris.

The reproductive function of the uterus is to accept a fertilized ovum which passes through the utero-tubal junction from the fallopian tube. It implants into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, attaches to a wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even during pregnancy the mass of a human uterus amounts to only about a kilogram (2.2 pounds).

Humans may have a bicornuate uterus, a uterine malformation where the two parts of the uterus fail to fuse completely during fetal development.

The uterus is located inside the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum. The human uterus is pear-shaped and about 3 in. (7.6 cm) long. The uterus can be divided anatomically into four segments: The fundus, corpus, cervix and the internal os.

Regions

From outside to inside, the path to the uterus is as follows:

• Cervix uteri – “neck of uterus”
  • External orifice of the uterus
  • Canal of the cervix
  • Internal orifice of the uterus
• corpus uteri – “Body of uterus”
  • Cavity of the body of the uterus
  • Fundus (uterus)

Layers

The three layers, from innermost to outermost, are as follows:

Endometrium

The lining of the uterine cavity is called the “endometrium”. It consists of the functional endometrium and the basal endometrium from which the former arises. Damage to the basal endometrium results in adhesion formation and/or fibrosis (Asherman’s syndrome). In all placental mammals, including humans, the endometrium builds a lining periodically which is shed or reabsorbed if no pregnancy occurs. Shedding of the functional endometrial lining is responsible for menstrual bleeding (known colloquially as a “period” in humans, with a cycle of approximately 28 days, +/-7 days of flow and +/-21 days of progression) throughout the fertile years of a female and for some time beyond. Depending on the species and attributes of physical and psychological health, weight, environmental factors of circadian rhythm, photoperiodism (the physiological reaction of organisms to the length of day or night), the effect of menstrual cycles to the reproductive function of the uterus is subject to hormone production, cell regeneration and other biological activities. The menstrual cycles may vary from a few days to six months, but can vary widely even in the same individual, often stopping for several cycles before resuming. Marsupials and monotremes do not have menstruation.

Myometrium

The uterus mostly consists of smooth muscle, known as “myometrium.” The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis.

Parametrium

The loose connective tissue around the uterus.

Support

The uterus is primarily supported by the pelvic diaphragm, perineal body and the urogenital diaphragm. Secondarily, it is supported by ligaments and the peritoneum (broad ligament of uterus)

Axes

Normally the uterus lies in anteversion & anteflexion. Anteversion is a forward angle between the axis of the cervix and that of the vagina measuring about 90 degrees, provided the urinary bladder and the rectum are empty. Anteflexion is a forward angle between the body and cervix at the isthmus measuring about 125 degrees, provided the bladder and rectum are empty.

Major ligaments

It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):

Position

The uterus is in the middle of the pelvic cavity in frontal plane (due to ligamentum latum uteri). The fundus does not surpass the linea terminalis, while the vaginal part of the cervix does not extend below interspinal line. The uterus is mobile and moves under the pressure of the full bladder or full rectum anteriorly, whereas if both are full it moves upwards. Increased intraabdominal pressure pushes it downwards. The mobility is conferred to it by musculo-fibrous apparatus that consists of suspensory and sustentacular part. Under normal circumstances the suspensory part keeps the uterus in anteflexion and anteversion (in 90% of women) and keeps it “floating” in the pelvis. The meaning of these terms are described below:

Sustentacular part supports the pelvic organs and comprises the larger pelvic diaphragm in the back and the smaller urogenital diaphragm in the front.

The pathological changes of the position of the uterus are:

• retroversion/retroflexion, if it is fixed
• hyperanteflexion – tipped too forward; most commonly congenital, but may be caused by tumors
• anteposition, retroposition, lateroposition – the whole uterus is moved; caused by parametritis or tumors
• elevation, descensus, prolapse
• rotation (the whole uterus rotates around its longitudinal axis), torsion (only the body of the uterus rotates around)
• inversion

In cases where the uterus is “tipped”, also known as retroverted uterus, women may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, difficulty conceiving, and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.

Schematic diagram of uterine arterial vasculature seen as a cross-section through the myometrium and endometrium.

The uterus is supplied by arterial blood both from the uterine artery and the ovarian artery.

Nerve Supply

The nerves are derived from the hypogastric and ovarian plexuses, and from the third and fourth sacral nerves.

Development

The bilateral Müllerian ducts form during early fetal life. In males, MIF secreted from the testes leads to their regression. In females these ducts give rise to the Fallopian tubes and the uterus. In humans the lower segments of the two ducts fuse to form a single uterus, however, in cases of uterine malformations this development may be disturbed. The different uterine forms in various mammals are due to various degrees of fusion of the two Müllerian ducts.

     Vagina
The vagina is a fibromuscular tube that extends from the cervix to the vestibule of the vulva. The vagina receives the penis and semen during sexual intercourse and also provides a passageway for menstrual blood flow to leave the body.

The Metanephros and the Permanent Kidney.—The rudiments of the permanent kidneys make their appearance about the end of the first or the beginning of the second month. Each kidney has a two-fold origin, part arising from the metanephros, and part as a diverticulum from the hind-end of the Wolffian duct, close to where the latter opens into the cloaca. The metanephros arises in the intermediate cell mass, caudal to the mesonephros, which it resembles in structure. The diverticulum from the Wolffian duct grows dorsalward and forward along the posterior abdominal wall, where its blind extremity expands and subsequently divides into several buds, which form the rudiments of the pelvis and calyces of the kidney; by continued growth and subdivision it gives rise to the collecting tubules of the kidney. The proximal portion of the diverticulum becomes the ureter. The secretory tubules are developed from the metanephros, which is moulded over the growing end of the diverticulum from the Wolffian duct. The tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct. One end expands to form a glomerulus, while the rest of the tubule rapidly elongates to form the convoluted and straight tubules, the loops of Henle, and the connecting tubules; these last join and establish communications with the collecting tubules derived from the ultimate ramifications of the diverticulum from the Wolffian duct. The mesoderm around the tubules becomes condensed to form the connective tissue of the kidney. The ureter opens at first into the hind-end of the Wolffian duct; after the sixth week it separates from the Wolffian duct, and opens independently into the part of the cloaca which ultimately becomes the bladder.

  The secretory tubules of the kidney become arranged into pyramidal masses or lobules, and the lobulated condition of the kidneys exists for some time after birth, while traces of it may be found even in the adult. The kidney of the ox and many other animals remains lobulated throughout life.

The External Organs of Generation—As already stated, the cloacal membrane, composed of ectoderm and entoderm, originally reaches from the umbilicus to the tail. The mesoderm extends to the midventral line for some distance behind the umbilicus, and forms the lower part of the abdominal wall; it ends below in a prominent swelling, the cloacal tubercle. Behind this tubercle the urogenital part of the cloacal membrane separates the ingrowing sheets of mesoderm.

  The first rudiment of the penis (or clitoris) is a structure termed the phallus; it is derived from the phallic portion of the cloaca which has extended on to the end and sides of the under surface of the cloacal tubercle. The terminal part of the phallus representing the future glans becomes solid; the remainder, which is hollow, is converted into a longitudinal groove by the absorption of the urogenital membrane.

  In the female a deep groove forms around the phallus and separates it from the rest of the cloacal tubercle, which is now termed the genital tubercle. The sides of the genital tubercle grow backward as the genital swellings, which ultimately form the labia majora; the tubercle itself becomes the mons pubis. The labia minora arise by the continued growth of the lips of the groove on the under surface of the phallus; the remainder of the phallus forms the clitoris.

  In the male the early changes are similar, but the pelvic portion of the cloaca undergoes much greater development, pushing before it the phallic portion. The genital swellings extend around between the pelvic portion and the anus, and form a scrotal area; during the changes associated with the descent of the testes this area is drawn out to form the scrotal sacs. The penis is developed from the phallus. As in the female, the urogenital membrane undergoes absorption, forming a channel on the under surface of the phallus; this channel extends only as far forward as the corona glandis.

  The corpora cavernosa of the penis (or clitoris) and of the urethra arise from the mesodermal tissue in the phallus; they are at first dense structures, but later vascular spaces appear in them, and they gradually become cavernous.

  The prepuce in both sexes is formed by the growth of a solid plate of ectoderm into the superficial part of the phallus; on coronal section this plate presents the shape of a horseshoe. By the breaking down of its more centrally situated cells the plate is split into two lamellæ, and a cutaneous fold, the prepuce, is liberated and forms a hood over the glans. “Adherent prepuce is not an adhesion really, but a hindered central desquamation” (Berry Hart).

The Mammæ (Mammary Gland; Breasts)

The mammæ secrete the milk, and are accessory glands of the generative system. They exist in the male as well as in the female; but in the former only in the rudimentary state, unless their growth is excited by peculiar circumstances. In the female they are two large hemispherical eminences lying within the superficial fascia and situated on the front and sides of the chest; each extends from the second rib above to the sixth rib below, and from the side of the sternum to near the midaxillary line. Their weight and dimensions differ at different periods of life, and in different individuals. Before puberty they are of small size, but enlarge as the generative organs become more completely developed. They increase during pregnancy and especially after delivery, and become atrophied in old age. The left mamma is generally a little larger than the right. The deep surface of each is nearly circular, flattened, or slightly concave, and has its long diameter directed upward and lateralward toward the axilla; it is separated from the fascia covering the Pectoralis major, Serratus anterior, and Obliquus externus abdominis by loose connective tissue. The subcutaneous surface of the mamma is convex, and presents, just below the center, a small conical prominence, the papilla.

  The Mammary Papilla or Nipple (papilla mammæ) is a cylindrical or conical eminence situated about the level of the fourth intercostal space. It is capable of undergoing a sort of erection from mechanical excitement, a change mainly due to the contraction of its muscular fibers. It is of a pink or brownish hue, its surface wrinkled and provided with secondary papillæ; and it is perforated by from fifteen to twenty orifices, the apertures of the lactiferous ducts. The base of the mammary papilla is surrounded by an areola. In the virgin the areola is of a delicate rosy hue; about the second month after impregnation it enlarges and acquires a darker tinge, and as pregnancy advances it may assume a dark brown or even black color. This color diminishes as soon as lactation is over, but is never entirely lost throughout life. These changes in the color of the areola are of importance in forming a conclusion in a case of suspected first pregnancy. Near the base of the papilla, and upon the surface of the areola, are numerous large sebaceous glands, the areolar glands, which become much enlarged during lactation, and present the appearance of small tubercles beneath the skin. These glands secrete a peculiar fatty substance, which serves as a protection to the integument of the papilla during the act of sucking. The mammary papilla consists of numerous vessels, intermixed with plain muscular fibers, which are principally arranged in a circular manner around the base: some few fibers radiating from base to apex.

Development.—The mamma is developed partly from mesoderm and partly from ectoderm—its bloodvessels and connective tissue being derived from the former, its cellular elements from the latter. Its first rudiment is seen about the third month, in the form of a number of small inward projections of the ectoderm, which invade the mesoderm; from these, secondary tracts of cellular elements radiate and subsequently give rise to the epithelium of the glandular follicles and ducts. The development of the follicles, however, remains imperfect, except in the parous female.

Structure—The mamma consists of gland tissue; of fibrous tissue, connecting its lobes; and of fatty tissue in the intervals between the lobes. The gland tissue, when freed from fibrous tissue and fat, is of a pale reddish color, firm in texture, flattened from before backward and thicker in the center than at the circumference. The subcutaneous surface of the mamma presents numerous irregular processes which project toward the skin and are joined to it by bands of connective tissue. It consists of numerous lobes, and these are composed of lobules, connected together by areolar tissue, bloodvessels, and ducts. The smallest lobules consist of a cluster of rounded alveoli, which open into the smallest branches of the lactiferous ducts; these ducts unite to form larger ducts, and these end in a single canal, corresponding with one of the chief subdivisions of the gland. The number of excretory ducts varies from fifteen to twenty; they are termed the tubuli lactiferi. They converge toward the areola, beneath which they form dilatations or ampullæ, which serve as reservoirs for the milk, and, at the base of the papillæ, become contracted, and pursue a straight course to its summit, perforating it by separate orifices considerably narrower than the ducts themselves. The ducts are composed of areolar tissue containing longitudinal and transverse elastic fibers; muscular fibers are entirely absent; they are lined by columnar epithelium resting on a basement membrane. The epithelium of the mamma differs according to the state of activity of the organ. In the gland of a woman who is not pregnant or suckling, the alveoli are very small and solid, being filled with a mass of granular polyhedral cells. During pregnancy the alveoli enlarge, and the cells undergo rapid multiplication. At the commencement of lactation, the cells in the center of the alveolus undergo fatty degeneration, and are eliminated in the first milk, as colostrum corpuscles. The peripheral cells of the alveolus remain, and form a single layer of granular, short columnar cells, with spherical nuclei, lining the basement membrane. The cells, during the state of activity of the gland, are capable of forming, in their interior, oil globules, which are then ejected into the lumen of the alveolus, and constitute the milk globules. When the acini are distended by the accumulation of the secretion the lining epithelium becomes flattened.

  The fibrous tissue invests the entire surface of the mamma, and sends down septa between its lobes, connecting them together.

  The fatty tissue covers the surface of the gland, and occupies the interval between its lobes. It usually exists in considerable abundance, and determines the form and size of the gland. There is no fat immediately beneath the areola and papilla.

Vessels and Nerves.—The arteries supplying the mammæ are derived from the thoracic branches of the axillary, the intercostals, and the internal mammary. The veins describe an anastomotic circle around the base of the papilla, called by Haller the circulus venosus. From this, large branches transmit the blood to the circumference of the gland, and end in the axillary and internal mammary veins. The nerves are derived from the anterior and lateral cutaneous branches of the fourth, fifth, and sixth thoracic nerves.