The female reproductive system is an intricate arrangement of structures that can separate into external and internal genitalia. The external genitalia comprises the structures outside of the true pelvis, including the labia majora and minora, vestibule, Bartholin glands, Skene glands, clitoris, mons pubis, perineum, urethral meatus, and periurethral area. The internal genitalia is the structures within the true pelvis, including the vagina, cervix, uterus, fallopian tubes, and ovaries, the latter being the focus of this article. It is vital for medical professionals, especially those in the field of obstetrics and gynecology, studying the female reproductive system to understand anatomy exclusive to females.

The uterus is the central anatomical landmark of the female internal genitals and pelvic anatomy. It is a highly muscular, childbearing organ in females, approximating 3 x 2 x 1 inches in size in a nulliparous. Even though the uterus is primarily a pelvic organ, but during later stages of pregnancy due to hypertrophy and hyperplasia of the myometrium, it can reach up to the epigastric region. The most common anatomical position of the uterus is anteverted-anteflexed. Anteversion is the angulation between the long axis of the cervix and the vagina, which nears the right angle.[1][2] Anteflexion is the angulation between the long axis of the body and the cervix, which is an obtuse angle around 120 to 125 degrees. In an anteverted-anteflexed position, the uterine body sits within the vesicouterine space. In rare cases, the uterus may be retroverted-retroflexed, causing the uterine body to be within the Douglas pouch. The shape of the uterus has been described as “pyriform” on examination in a sagittal plane. It has four parts: the fundus, body, isthmus, and cervix.[3][4] The uterine body is the largest portion, while the uterine isthmus is the location where the uterine body meets the cervix.[4] The fundus is that part of the uterus, which is above the opening of the fallopian tubes into the uterine cavity. The whole of the uterine cavity has a very special lining membrane called the endometrium. This endometrium will shed during menstruation; inflammation of this membrane is endometritis, which, when chronic, can be lead to infertility.[5] 

The ovaries are the primary organs of the female reproductive system. They are oval-shaped gonadal structures, approximately 3 x 1.5 x 1 cm in size, and homologous with the testis in males. They are present in pairs with the long axis oriented downward and forward. The ovaries are within the pelvis, just lateral to the uterus. They lie within the ovarian fossa, in front of the ureters, and behind the external iliac vessels.[3] In nulliparous females, they are pinkish with a smooth outer surface, but in multiparous, they are more greyish with a puckered surface due to repeated ovulations. The ovaries are entirely covered with peritoneum except for the mesovarian (anterior) border through which all the blood vessels, nerves, and lymphatics pass. They contain thousands of follicles. Each month, one follicle will develop into the dominant follicle (Graafian follicle), which releases an ovum during ovulation.[4] On ultrasound, the ovary appears as having an echoic central area and a peripheral region, with the former corresponding to the stroma and the later corresponding to the cortex.[3] The ovaries secrete two steroid hormones, estrogen, and progesterone under the direct control of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secreted by the pituitary. These hormones play a significant role in many different aspects of the life of a female.[6][7][8][7] The lower, short, but broad cylindrical part extending from the internal os to the external os is the cervix. It has a narrow central lumen, which opens into the uterine cavity as internal os and into the vagina as the external os. The external os is seen as circular opening in nulliparous and as a horizontal slit in multiparous. This horizontal slit divides the cervix into an anterior and posterior lip. The narrow upper third of the cervix is the isthmus, which defines the lower uterine segment and is the site for the lower segment cesarean sections (LSCS).[9]

The ovaries link to the uterus through fallopian tubes, which function to carry the zygote to the uterine cavity for implantation. The fallopian tubes (also known as oviduct, uterine tube) divide into the fimbriated infundibulum, ampulla, isthmus, and intramural parts.[10] The ampullary part is the usual site for fertilization.[11] The fallopian tube also helps in bringing the sperm and ovum to this site of fertilization. The infundibulum is the most later part, that is funnel-shaped with finger-like projections hanging from the sides called fimbriae. This part opens into the peritoneal cavity and is in contact with the ovaries through some of its fimbriae. The intramural is the most narrow and medial part of the fallopian tube that is present within the wall of the uterus. Each region represents characteristic physiologic features. Salpingitis is a bacterial infection of the fallopian tube. It may be acute or chronic inflammation and most commonly results from Neisseria gonorrhoeae or Chlamydia trachomatis. It may lead to scarring of the fallopian tubes and predispose to infertility and ectopic tubal pregnancy. Tubal infertility caused by disruption of the integrity of the fallopian tubes by infusion, endometriosis, or surgical complication is an important consideration when evaluating women with unexplained infertility.[10] Ectopic tubal pregnancy most commonly occurs in the ampulla of the fallopian tube. Common predisposing factors include salpingitis, pelvic surgery, or pelvic inflammatory disease. This diagnosis may be confused with appendicitis in a young woman, and early differentiation of the two diagnoses is crucial.

The vagina is a fibromuscular canal ranging from 6 to 8 cm. in length. It is anatomically located anteriorly to the rectum and posteriorly to the wall of the urinary bladder and the urethra. This canal directs downwards and forwards. Because of the oblique nature of the vagina, the anterior wall is slightly shorter, i.e., about 6 cm compared to the posterior wall, which is about 8 cm. The upper segment of the vaginal forms a vaginal vault by being enclosed within the vaginal portion of the cervix.[12] The cervix extends into the vagina, forming a channel between the two structures. Thus the cervix is divided into a supravaginal and a vaginal part. The narrow space between the cervix and the wall of the vaginal is the fornix. The recess between the anterior lip of the cervix and the anterior wall of the vagina is the anterior fornix. Similarly, the recess between the posterior lip of the cervix and the wall of the vagina is the posterior fornix. The space on either side between the cervix and the lateral wall of the vagina is known as the lateral fornices. The posterior fornix is the deepest and is a common site for ruptures, foreign bodies, and malignancies.[13][14][15][16]

Before the determination of phenotypic sex, the gonads are classified as "unisex" and have the potential to develop into testes or ovaries.[17] The embryologic development of the female internal genitals has been a topic of research in recent years. The determination of female sexual differentiation is by the absence of the SRY (sex-determining region on Y) gene, a gene on the short arm of the Y chromosome (Yp11). When present, the SRY gene will cause the indifferent embryo to develop into the male phenotype.

The belief is that the ovaries derive from the gonadal ridge. But the primordial germ cells develop in epiblast and migrate to endoderm cells in the yolk sac. They finally appear in the genital ridges in 6th week. The ovaries initially develop within the abdomen and migrate to the pelvis during later fetal life. Even though they migrate into the pelvis, they still retain their blood supply, nerve supply, and lymphatic drainage back to their site of origin, the upper abdomen.[18] The gubernaculum is involved in the formation of the ovarian ligament and the round ligament of the uterus. In the recent decade, there has been ongoing research to identify a female determining sex gene. So far, the "Z" gene hypothesis, which names FoxL2 as a possible ovary determining factor, has been identified. Other genes believed to be involved, including Dax1 and Wnt4, which may have similar effects; however, many unanswered questions remain in this pathway.[17] 

The paramesonephric duct (Mullerian duct) is the embryologic derivative of the genital ducts. The cranial portions form the uterine tubes, while the caudal parts form the uterovaginal primordium. The uterovaginal primordium gives rise to the uterus, cervix, and superior third of the vagina. The vaginal plate is a derivative of the sinovaginal bulbs. It canalizes to form the lower two-thirds of the vagina. All of these derivatives are surrounded by a layer of myometrium that develops from mesenchyme. The outermost covering is the perimetrium that develops from folds of the peritoneum.

Embryologic defects that are important to consider including unicornuate uterus anomalies, where one paramesonephric duct fails to develop, Didelphys anomalies, where there is a complete lack of fusion of the paramesonephric duct and bicornuate uterus anomalies where there is a partial fusion of the paramesonephric duct.[19] Bicornuate uterus anomalies are associated with the highest risk of infertility. 

The mesonephric (Wolffian) duct disappears in the case of females, except a small cranial part that remains as epoophoron and paroophoron. The remnant of the mesonephric duct is called the Gartner's duct. A small caudal portion of this duct is seen and referred to as Gartner's duct cyst within the wall of the uterus or vagina.[20]

The Ovarian artery is a branch of the abdominal aorta; it reaches the ovary through the suspensory ligament of the ovary. Even though ovaries are pelvic organs, they derive their blood supply from the abdominal aorta indicating their site origin. The uterine artery originates from the anterior division of the internal iliac artery along with the umbilical artery in a common trunk.[21] It serves as the main arterial supply of the uterus. The uterine artery that is highly tortuous travels across the pelvic floor in the cardinal ligament runs anteriorly and superiorly to the ureter close to the lateral fornix of the vagina. It ends by anastomosing with the ovarian artery within the broad ligament of the uterus. Ligation of the uterine artery during a hysterectomy is typically at the level of the internal cervical os.[21] The small, inferior branch of the uterine artery becomes the vaginal artery and supplies the cervix and vagina. The vaginal artery may also arise from the internal iliac artery.

The veins of the female internal genitals usually correspond to the arteries. The uterine vein follows the course of the uterine artery and is also contained within the cardinal ligament; it drains into the internal iliac vein. The ovarian veins receive blood from the ovaries; the right ovarian vein drains directly into the IVC while the left ovarian vein drains into the left renal vein. Malignancies in the pelvis may metastasize to the vertebral column or spinal cord via connections of the pelvic veins.

The lymphatic flow from the uterus, cervix, and vagina drains into the internal and external iliac nodes. Lymph vessels from the ovary and fallopian tube drain directly into the paraaortic nodes. 

The nerve fibers that feed the pelvis are both parasympathetic and sympathetic. The preganglionic fibers are in the sacral parasympathetics (S2-S4) in the spinal cord. Their processes run into pelvic splanchnic nerves and relay inside the pelvic organs within the intramural plexus (the postganglionic neuron). The sensory fibers from S2-S4 dorsal root ganglia travel with parasympathetic fibers and carry pain sensations from the organs. Sympathetic fibers of preganglionic neurons (T12-L2) form the sacral splanchnic nerves. They contribute to the inferior hypogastric plexus, which is the location of the postganglionic neurons. The pudendal nerve provides sensory innervation to the lower vagina. A pudendal nerve block is an option during early labor to relieve pain for the mother.[22] It may be blocked by piercing the vaginal wall posterolaterally, using the ischial spine as a landmark. It may also be performed percutaneously along the medial side of the ischial tuberosity. However, this method does not affect the pain from uterine contractions and is no longer commonly used.