CHAPTERS
- Anatomy of the Male and Female Reproductive SystemMir Jaffar, BV Srinivas
- Oogenesis and FolliculogenesisMandeep Kaur, PM Gopinath
- Regulation of Menstrual CycleArveen Vohra, Nameeta Mokashi Bhalerao, Kamini A Rao
- Sperm Production and MigrationManishi Mittal, Kamini A Rao
- Ultrastructure of Human Gametes, Fertilization and Embryos in Assisted Reproduction: A Personal SurveyA Henry Sathananthan
- Endometrial ReceptivityDeepika K
- Implantation
INTRODUCTION
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Even though the reproductive system is not essential for the sustenance of an individual but it is essential for the sustenance of species. The male reproductive system is a series of organs mainly located outside the body with the primary function of generation of male gamete (sperm) and deposition of the same inside the female reproductive tract for the fertilization of female gamete (ovum). The female reproductive system is a series of organs primarily located inside the body. The two main functions of female reproductive system is to produce female gamete and to nourish the developing offspring until birth.
MALE REPRODUCTIVE SYSTEM
The male reproductive axis of hormones and organs is a remarkably efficient, well-orchestrated, and precisely managed biological system that has evolved over millions of years. It is responsible for reproductive tract formation and development, maturation of fertility potential at puberty and the maintenance of maleness in the adult. Understanding the basis of male infertility is becoming a growing trend among the infertility specialists because of progressive decrease in semen parameters over recent years. To understand the basic pathophysiology and the cause of male infertility, it is imperative to have a reasonable knowledge about the anatomy, physiology, development and hormonal control of the male genital and duct system for effective evaluation and treatment of male infertility.
Anatomy
During the embryonic development the male genital tract is a straight duct system with the developing testes high up inside the abdomen and the ejaculatory organ (penis) outside the body. Since testes need about 2 to 3°C lower than normal body temperature to function normally, it descends down in the scrotum normally during birth outside the body forming a loop of duct system. Though the ducts of testes (vasa deferentia) run parallel to the urethra but in the opposite direction. The initial secretory part of the duct begins outside the body (scrotum), the middle part intra-abdominal and the terminal ejaculatory part ends outside.
Male genital system includes the testes (singular = testis), epididymides (singular = epididymis), ductus deferentes (singular = ductus deferens), seminal glands, ejaculatory ducts, prostate, bulbourethral and urethral glands (Fig. 1).
The Scrotum
The scrotum is a heavily pigmented cutaneous sac of the lower part of the anterior wall of abdomen containing the testes, epididymides and the lower part of the spermatic cords. Scrotum is developed by the fusion of two embryonic labioscrotal swellings, which is demarcated externally by the scrotal raphe and internally divided into left and right compartments by the septum of scrotum each lined by an isolated portion of the peritoneum known as the tunica vaginalis. The subcutaneous fat is absent. The scrotum provides the position to the testes which is safe from physical and thermal damage outside the body in an environment which is about 3°C below that of the body cavity, a condition necessary for the development and storage of normal sperm. The wall of the scrotum contains two muscles, a subcutaneous involuntary dartos muscle supplied by sympathetic nerves, contraction of which causes the skin to wrinkle when cold. The other muscle is cremasteric muscle supplied by genital branch of genitofemoral nerve, contraction of which pulls the testes close to the superficial inguinal ring.
Contraction of these skeletal muscles lifts the scrotum closer to the body when external temperatures are too cold.
The Testis
The testes (testicles) are the male gonads ovoid in shape that lie in the scrotum on either side of a septum. The main function of these reproductive glands is to produce sperm and male hormones, primarily testosterone. The testes are suspended in the scrotum by the corresponding spermatic cord, with the left testis usually suspended more inferiorly (1 cm) than the right testis. Normally, the testis lies in the scrotum vertically with the epididymis behind. Horizontal testes are more prone for torsion injuries. Each normal testis has a volume of 15 mL or more measured on modified Prader orchidometer with right testis slightly larger than left testis. The size of less than 15 mL is indicative of damage to the seminiferous epithelium which forms the major portion of the testicular volume. Small and firm testes, usually less than 3 mL in volume are found in Klinefelter's syndrome associated men. Patients with hypogonadotropic hypogonadism also have small testes but the size usually measures between 5 mL and 12 mL. The normal consistency of testes is rubbery.
The testes have a tough fibrous, nearly avascular and inelastic outer surface, the tunica albuginea which gives the testes the eggshell appearance when explored during any operative procedure on testes. Any pathology or injury to the testes, which will induce edema, will raise the intratesticular pressure, which may hamper the blood supply to the testis. This sort of injury might thus result in either temporary or even permanent damage to the spermatogenic elements of the testes.
Posteriorly, the tunica albuginea thickens and extends inward into each testis to form the mediastinum testis. A thin connective tissue septum extends from the mediastinum testis anteriorly and subdivides each testis into about 250 incomplete compartments or testicular lobules, each containing 1 to 4 coiled seminiferous tubules. The mediastinum lodges a network of channels known as the rete testis which receives the terminal segments of the seminiferous tubules (straight tubules) in which the sperm are produced (Fig. 2).
Individual lobule of the testis is covered by a vascular layer called the tunica vasculosa, which contains many blood vessels suspended in a loose connective tissue. During open testicular biopsy, it is this layer which bleeds after incising the avascular tunica albuginea.5
Each testicular lobule contains tightly packed seminiferous tubules and sparse interstitial connective tissue. Each seminiferous tubule is lined by stratified germinal epithelium, containing proliferative spermatogenic (germ) cells and nonproliferating supporting (sustentacular) or sertoli cells. It is in these seminiferous tubules where spermatogenic cells divide, mature, and are transformed into sperm (Fig. 3).
Surrounding each seminiferous tubules are connective tissue cells, blood vessels, nerves and lymphatic vessels. In addition to these cells, between the seminiferous tubules are clusters of steroid-secreting cells, the interstitial cells (of Leydig) that produce the male sex hormone testosterone. There are two main types of cells found inside the seminiferous tubules: (1) Sertoli cells and (2) spermatogenic cells. Spermatogenic cells of different stages are incorporated into the cytoplasm of Sertoli cells for growth (nurse cells). The cytoplasmic extensions (tight junctions) of the adjacent Sertoli cells form the blood-testes barrier which prevents the spermatogenic cells from the exposure to the body's immune system. Seminiferous tubules comprise 95 percent of testicular volume, and are devoted to the production of spermatozoa. There are approximately 500 tubules per testis. The tubules are divided by fibrous septae, and surrounded by the tough tunica albuginea. Each tubule is 30 to 70 cm long and 200 to 300 μm in diameter. Each tubule is highly convoluted and forms a loop within the lobule to accommodate a long tubule in a very small lobule. Sometimes very tight convolutions of the seminiferous tubules may result in their incomplete obstruction. As the tubule reaches the mediastinum, convolutions decreases and ultimately straightens out to form tubuli recti (straight ducts), which connects to the developmentally different set of network of tubules called rete testes. Sperm produced by the seminiferous tubules pass out of the testis into the ductal system, beginning with the rete testis and on into the epididymis then to the vas deferens. Sperm in the vas deferens is joined by seminal vesicle secretions as they pass through the prostate via the ejaculatory ducts into the urethra.
Testes are mostly supplied by the long testicular arteries arising high up from the abdominal aorta just inferior to the renal arteries. The testicular artery anastomosis with the artery of the ductus deferens. The veins draining the testis and epididymis form the pampiniform plexus of veins, a network of 8 to 20 veins surrounding the testicular artery in the spermatic cord. The heat conveyed by the arteries of the testes is mostly absorbed back by the veins of the pampiniform plexus of veins. This architecture of vessels along with the cremasteric and dartos muscle helps the testes to maintain a constant temperature. The veins of each pampiniform plexus converge superiorly, forming a right testicular vein, which drains into the inferior vena cava in an acute angle, and a left testicular vein, which drains into left renal vein almost at a right angle.
The autonomic nerves of the testis arise as the testicular plexus of nerves surrounding the testicular artery, which contains vagal parasympathetic and sympathetic fibers derived from the T10 and T11 segments of the spinal cord. Most of the times patient complains of pain around umbilical region either during testicular surgery or postoperatively especially when the testis is pressed hard or squeezed, and this can be justified by the segmental innervation.
The Epididymis
The epididymis is an elongated structure along the posterolateral border of each testis. It is made up of tightly packed convoluted tubules with little supporting loose connective tissue. Clinically, the epididymis can be divided into three main segments. The upper most (head = caput); the middle (body = corpus) and the lower most (tail = cauda). Head, the most expanded part, is composed of lobules formed by the coiling of 12 to 14 efferent ductules called lobules of epididymis. These ductules are so tightly packed that the head appears solid. These efferent ductuli are very fine and lined by highly ciliated columnar epithelium for maximum absorption of water, both to increase the concentration of sperm as well as to transport the sperm from testes to epididymis by creating the suction effect. The walls of these tubules are composed of myoid cells which undergo frequent autonomous contractions to enhance the absorption of fluid as well as mobilization of sperm (Fig. 4).
All these minute ductules of the head of epididymis join together and form one single duct which coil on itself called the canal of epididymis or epididymal duct. It forms most of the body and tail of the epididymis and lies alongside the posterolateral border of the testis.
Fig. 4:
Drawing of the human epididymis showing regionalization of the ductal epithelium and muscle layer. Epididymal segment locations are shown in cross-section and are identified by number
The epididymal duct is approximately 6 m in length and its walls contain smooth muscles which contract during ejaculation to propel semen toward vas deferens. The duct is lined by pseudostratified columnar epithelium with nonmotile stereocilia which are nonmotile because of absence of axoneme. This epithelium has very important secretory activity. The passage of sperm across the epididymis has been reported to be 7 to 10 days. However, the transit time is dependent on the amount of sperm produced, high the sperm production, less the transit time it takes. From head to tail, it moves by spontaneous peristaltic movements during which sperm attain their maturity, motility and fertilization capacity. The tail of the epididymis is evolved as the sperm storage organ only in animals forced to wait for female ovulation. For the normal functioning of the epididymis for the maturation of sperm is dependent on luminal flow of testosterone. Prominent dilatation of epididymal head is known as “Bayle's sign,” which is palpable in case of epididymal obstruction or men without vas deferens.
The Vas Deferens
The vas deferens (ductus deferens) is the continuation of the epididymal duct from the tail of the epididymis. The initial part of the vas is coiled and loses its convolutions soon after joining the spermatic cord in the scrotum itself. In adult men, the vas measures about 25 cm in length and can be palpated as a 3 to 5 mm thick string in both sides of the scrotum. It has relatively thick muscular walls and a minute lumen, giving it a whipcord-like firmness, so easily differentiated during the physical examination for the presence of the same. It penetrates the anterior abdominal wall via the inguinal canal and ends by joining the duct of the seminal gland to form the ejaculatory duct. The ductus deferens enlarges to form the ampula of the ductus deferens (2 cm in length) before its termination. It is said that like the tail of epididymis, ampula also serves as the storage for the sperm prior to the ejaculation but is controversial because of the temperature issues. Because of the long and complicated course of the duct, absence of the duct or multiple blocks in the duct, surgical retrieval of sperm followed by the assisted reproductive technology is preferred over corrective surgeries.
The vas deferens has three robust layers of smooth muscles—outer longitudinal inner longitudinal and middle circular layers. The luminal surface is highly convoluted. These muscles are under the sympathetic stimulation and shows mass contraction when stimulated which transports the spermatozoa from the tail of epididymis to the prostatic urethra within a second.
The Seminal Glands (Vesicles)
Each gland is formed by the coiling of a single duct with numerous lateral diverticula on the inner side of the gland. These diverticula are held together by connective tissue.
Each seminal gland is an elongated structure of about 5 cm in length. The seminal glands are obliquely placed superior to the prostate between the urinary bladder in front and the ampulla of the rectum behind and do not store sperm contrary to the previous belief (Fig. 5). The seminal glands have a thick muscular wall that contracts powerfully during ejaculation whereby the contents are emitted to the urethra.
They are lined by a columnar mucus-secreting epithelium containing many goblet cells. The secretion of the gland is viscid, yellowish-white alkaline fluid and forms the bulk of the semen which is rich in fructose, prostaglandin and a coagulating enzyme—vesiculase. The activity of the mucous membrane is regulated by the secretion of the androgen. Fructose is believed to serve as an energy source of sperm. The seminal glands contain 40 million times higher concentrations of prostaglandins than the blood, and their physiological role other than uterine contractions also remains to be clearly determined.
In cases of absent vas deferens, the seminal glands are also absent in most of such cases because of the same developmental origin (Wolffian duct system).
The Ejaculatory Duct
The ejaculatory ducts are formed by the union of the ducts of the seminal glands with the ductus deferentes just distal to the ampula (Fig. 5). The ejaculatory ducts (approximately 2.5 cm long) arise near the neck of the bladder and pass anteroinferiorly through the posterior part of the prostate between the median and the lateral lobes of the prostate and opens at the colliculus seminalis, one on each side of the prostatic utricle. Although the ejaculatory ducts traverses the glandular prostate, prostatic secretions do not join the seminal fluid until the ejaculatory ducts have terminated in the prostatic urethra. The walls of the ducts are thin and are made up of smooth muscles, and is lined by columnar epithelium which may be two celled-thick. Ejaculatory duct obstruction can be suspected in fructose negative cases, which can be resected through transurethral resection of duct.
The Prostate
The prostate (approximately 3 cm long, 4 cm wide and 2 cm anteroposterior depth) is a conical fibro-musculo-glandular organ which surrounds the proximal part of the male urethra (Fig. 5). It corresponds in development with the paraurethral glands of female. The glandular part makes up approximately two-thirds of the prostate and the other third is fibromuscular. The fibrous capsule of the prostate is dense and neurovascular, incorporating the prostatic plexus of veins and nerves. The prostate is divided into three lobes, namely two laterals and a median lobe. The median (middle) tends to undergo hormone-induced hypertrophy in advanced age, forming a middle lobule that lies between the urethra and the ejaculatory ducts and gives rise to benign hypertrophy of the prostate. A series of small ducts (20–30) open on the posterior wall of the prostatic urethra on either side of the seminal colliculus. Prostatic fluid, a thin and milky fluid, forms a considerable part of semen (approximately 20% of semen). Its secretion is slightly acidic and biochemically very active. Prostatic secretions contain large amount of enzymes which plays a role in both semen clotting as well as liquefaction. The enzyme vesiculase induces clotting and a number of proteases, peptidases and hyaluronidase which cause the breakdown of the clot.
The prostatic secretions also contain large amounts of enzyme acid phosphatase which is a classical marker of prostatic function. This enzyme is commonly used in forensic department as a marker of the presence of semen stains because of its high stability compared to other prostatic enzymes. Abundant amount of citrate are also present in the semen secretions which can be used as an indicator of prostatic function.
Prostate-specific antigen is one of the important markers secreted by prostate, clinically used in suspected cases of carcinomas.
Inorganic elements like zinc, magnesium and calcium, are also present in prostatic fluid. Zinc is known to provide protection of spermatozoa against spermiophagic cells in the female genital tract and its role in protection of free sulfhydryl groups on the protamines to prevent “super-stabilization” of the condensed chromatin of sperm.
The Bulbourethral and Urethral Glands
The bulbourethral glands (Cowper's glands) are mucus secreting two pea-size glands situated in the deep perineal pouch surrounded by sphincter urethrae muscle. These glands correspond in development with the greater vestibular glands of female. Their ducts open through minute apertures into the proximal part of the spongy urethra.
The urethral glands are very small mucus secreting glands that open into the entire roof of the penile urethra, numerous in the fossa navicularis-distal dilated portion of the penile urethra.
The volume of the mucus secreted by these glands is very small and their secretions are rich in mucoproteins. Their mucus like secretion enters the urethra during sexual arousal to lubricate the urethra and to facilitate the ejaculation of the seminal fluid. These secretions are also referred as pre-ejaculate. These glands also produce the secretory immunoprotein-immunoglobulin G (IgG). These IgGs can on occasions be directed against the sperm as antisperm antibodies and could become a cause of infertility.8
Ejaculation
Seminal fluid or semen is the mixture of secretion of the testis, epididymis, prostate, seminal glands and bulbourethral glands. The propulsion of these secretions into the prostatic part of urethra is known as emission, and to the exterior from the penile urethra is known as ejaculation (Table 1).
The first part of the semen comes from the cauda of the epididymis suspended in prostatic fluid. Spermatozoa in zinc rich prostate fluid preserve motility, vitality and the stability of their nuclear chromatin. The second part is mainly composed of a fluid from the seminal glands, which is rich in fructose and prostaglandin. The first part of the ejaculate is deposited on to the cervical mucus comprising of spermatozoa in prostatic fluid and the second part of the semen mainly from seminal glands forms the plug to prevent backflow of the first part of the ejaculate. Semen collected in predetermined sequence is known as a “split ejaculate”. Emission is controlled by autonomic nerves while ejaculation is governed by striated muscles under voluntary control (pudendal nerve). Seldom men with premature ejaculation are advised to practice training voluntary muscles under the control of pudendal nerve.
The Endocrinology of Testes
The endocrine and exocrine functions of the testis are closely linked anatomically and physiologically. There are two main types of endocrine cells in the testis, namely the Leydig cells, which secrete testosterone and the Sertoli cells, lying within the seminiferous tubules, which mainly secrete inhibin and androgen-binding protein (ABP).
For the process of normal spermatogenesis, an intact endocrine testicular axis is mandatory (hypothalamic-pituitary-testicular axis). The endocrine secretions of the testis are largely controlled by the pituitary gonadotropins, namely follicle stimulating hormone (FSH) and luteinizing hormone (LH) which in turn is controlled by hypothalamic hormone, gonadotropin releasing hormone (GnRH).
The gonadotropin LH acts on Leydig cells through its specific receptors, which in response secrete androgenic steroid testosterone. The gonadotropin FSH finds its receptors on Sertoli cells where it stimulates the production of ABP, which has very high affinity for testosterone to increase the concentration of testosterone many folds in the seminiferous tubules for the normal production of sperm and maturation in epididymis. FSH is also known to stimulate the mitotic division of spermatogenic germ cells. The Leydig cells via the Sertoli cells with the help of androgen binding protein (ABP) thus provide a high concentration of testosterone for normal spermatogenesis in the seminiferous tubules, rete testis, the efferent ductules and the proximal portion of the epididymis for the maturation of sperm. Testosterone also enters the general circulation and acts on the organs with testosterone receptors for the normal function. The circulating testosterone by its action on the pituitary also provides negative feedback for LH. The Sertoli cells also produce the hormone inhibin, which is the major negative feedback for FSH secretion from pituitary (Fig. 6). Inhibin represents two glycoprotein hormones—inhibin A and inhibin B. The inverse relationship is known to exist between inhibin B and FSH in male sera. It is now considered one of the best markers of predicted normal spermatogenesis before employing any surgical sperm retrieval technique.
FEMALE REPRODUCTIVE SYSTEM
The female reproductive system consists of a pair of ovaries, a pair of uterine (Fallopian) tubes, a single uterus, vagina and external genitalia (Fig. 7). Mammary glands are also closely associated with the female reproductive system. Figure 8 shows Fallopian tube and ovary on one side.
Ovaries
The ovaries are a pair of female reproductive glands located deep in the pelvic cavity one on each side of the uterus connected to the broad ligament by a short peritoneal fold, the mesovarium below and behind the distal end of corresponding uterine tube. The ovary is an infraperitoneal organ, almond shaped and dull gray in color located in the ovarian fossa in nulliparous women. After repeated pregnancies, it may be prolapsed in the rectouterine pouch. In prepubertal females, the connective tissue capsule, the tunica albuginea is covered by a smooth layer of ovarian mesothelium, also known as germinal epithelium, a single layer of cuboidal cells. Located below the tunica albuginea is the cortex of the ovary, and deep to the cortex is the highly vascularized connective tissue core of the ovary, the medulla. After puberty, the ovarian surface becomes scarred and irregular due to repeated rupture of ovarian follicles and discharge of oocytes during ovulation. The scarring is seen less in women who have been taking oral contraceptives that inhibit ovulation.
During the embryonic development, the germ cells are differentiated into oogonia, which divide mitotically and then enter the first phase of meiotic division without completing it. They become arrested in this state of development and are now called the primary oocytes. During fetal life the primary oocytes are surrounded by a single layer of squamous cells-primordial follicle. Before puberty the cortex contains only primordial follicles. Beginning at puberty under the influence of pituitary hormones (FSH), the primordial follicles grow and enlarge to become primary, secondary and the large mature follicles, which can occupy the part of medulla also. Postpubertal ovary contains numerous follicles in various stages of development. In addition to the follicles, the ovary may contain a large corpus luteum of an ovulated follicle or corpus albicans of a degenerated corpus luteum.
At birth the cortex contains about one million or more primordial follicles. Most of the follicles degenerate before puberty by the process of apoptosis (programmed cell death). About 40,000 follicles persist at puberty and exhibit periodic changes during the rest of the reproductive life. Out of 40,000 primordial follicles about 5 to 10 follicles undergo a process of maturation in each menstrual cycle. Mostly one follicle from any one of the two ovaries fully matures, ruptures and discharges a secondary oocyte in the peritoneal cavity and subsequently picked up by the fimbriae of the respective Fallopian tube. Thus on an average about 400 attain such maturity during reproductive life.
Ovary is mainly supplied by the gonadal (ovarian) artery which is a branch of abdominal aorta and partly by the branches of uterine artery (branch of internal iliac artery) by its terminal branches, course along the lateral aspect of uterus and reaches the ovary before it terminates. Veins draining the ovary form a pampiniform plexus of veins, which joins further to form a single vein in the suspensory ligament of ovary. The right ovarian vein ascends to drain into inferior vena cava at an acute angle; the left ovarian vein drains into left renal vein almost at a right angle.
Uterine (Fallopian Tubes, Oviducts) Tubes
The uterine tubes are a pair of ducts (12 cm long) which conduct the monthly discharged oocyte from the ovary to the uterine cavity and also provide the usual site of fertilization. One end of the uterine tube penetrates and opens into the uterus; the other end opens into the peritoneal cavity near the ovary. Within each tube is a tiny passageway no wider than a sewing needle. Each tube is situated in the medial three-fourth of the upper free margin of the broad ligament of uterus. When an ovary does ovulate and release the oocyte, it is swept into the lumen of the uterine tube by the fimbriae which is further facilitated by the longitudinal grooves on the inner aspect of these fimbriae, suction created by the ciliary beats of the tube and also by the peristalsis of the tubal musculature. In “immotile cilia syndrome,” the transport of ova takes place only by peristalsis if at all carried by the tube to the uterine cavity. During ovulation the uterine tubes literally comes close to the ovary to pick up the oocyte which may be hormone regulated. Each tube presents two openings (ostia): (1) uterine ostium which is 1 mm in diameter and opens into the superolateral angle of the uterus and (2) the other, pelvic (abdominal) ostium which is 3 mm in diameter, opens at the bottom of infundibulum near the corresponding ovary.
The uterine tubes are normally divided into four continuous regions from lateral to medial (Fig. 9):
- Infundibulum: The funnel-shaped distal end of the tube, closest to the ovary and about 1 cm long, opens into the peritoneal cavity through the abdominal ostium, the circumference of which is provided with the fimbriae. One of the fimbria is longer (ovarian fimbria) than the rest and is attached to the upper end of the ovary.
- Ampulla: The widest and longest part of the tube (5 cm) is thin-walled, dilated and tortuous. Fertilization of the ova usually takes place in the ampulla.
- Isthmus: It is rounded and cordlike because the walls are thicker than the lumen and resembles the spermatic cord in men.
- Uterine (interstitial/intramural/pars uterine tube): It is about 1 cm long, and traverses the thick musculature of the uterus at the junction of the fundus and the uterus to open into the uterine cavity via the uterine ostium.
Uterus
The uterus (womb) is a thick-walled, shaped like an inverted pear, hollow muscular organ. The non-gravid (non-pregnant) uterus usually lies obliquely in the lesser pelvis between the urinary bladder below and in front, and the rectum and sigmoid colon above and behind. It is primarily concerned with the implantation of embryo and development of the fetus. On each side the uterus receives opening of the corresponding uterine tube at the superolateral angle, and external os which communicates with the vagina below. The uterus is possibly the most dynamic structure in human anatomy, the size and the proportion of which changes during the various stages of life. Although its size varies considerably, the non-gravid uterus is approximately 7.5 cm long, 5 cm wide and 2 cm thick and weighs approximately 90 gm. The uterus contains some of the strongest muscles in the female body, which can contract rhythmically in both the directions as needed. These muscles can expand and contract to very extremes to accommodate the growing fetus and push the fetus out during labor respectively. The uterus is only three inches long and two inches wide, but its dimensions change rapidly and dramatically during pregnancy. At birth, the uterus is relatively large and has adult proportions (body to cervical ratio = 2:1) due to the influence of maternal hormones during the intrauterine life. Several weeks after birth, childhood dimensions and proportions are obtained. The body and cervix are approximately of equal length (body to cervix dimensions = 1:1), with the cervix being of greater diameter. Because of the small size of the pelvic cavity, the uterus remains in the abdomen and descends down afterward and becomes pelvic organ. Typical angulation between the uterus and vagina is not established. During puberty, the uterus (especially the body) grows rapidly in size there by again assuming adult proportions because of hormonal exposure.
Axes of Uterus
Normally the adult uterus lies in anteversion and anteflexion (Fig. 10).
Anteversion: The angle between the cervix relative to the axis of the vagina, measuring about 90°, provided the bladder and the rectum is empty. The anteversion is maintained by: the forward pull on the uterine fundus by the traction of the round ligaments of the uterus, backward pull on the cervix by the traction of the uterosacral ligaments and the intrinsic growth of the uterine musculature. Maintenance of the anteversion angle is an important prerequisite to prevent the prolapse of the uterus.
Anteflexion: The forward angle between the body and cervix at the isthmus, creating the angle of flexion measuring about 125° so that the main bulk of the uterus rests on the bladder for better support. Consequently when the bladder is empty, the uterus typically lies in a transverse plane.
Flexion of uterus takes place around a transverse axis passing through the internal os. Normally the uterus rotates forward around this axis known as anteflexion. When it rotates backward (reverse direction) it is referred as retroflexion. A retroverted uterus will not necessarily prolapse but is more likely to do so. The condition is exacerbated in the presence of disrupted perineal body or week pelvic floor muscles and ligaments.
Usually the uterus lies in the median plane and is twisted to the right or left side. Sometimes the fundus is tilted more to the right pelvic wall, is known as dextrorotation of the fundus. In such situations the right uterine tube comes in more close contact with the lateral pelvic wall, and may be related to the pelvic type of the vermiform appendix. Consequently the cervix is tilted more to the left side, is known as levorotation of the cervix.
The uterus is divided into the fundus, body and cervix. Fundus is the rounded dome shaped part that lies above the opening of the Fallopian tubes (ostia). The body or the corpus is the main part of the uterus and extends from 12the fundus to a constriction known as the isthmus, which corresponds internally with the internal os of the cervical canal. The cervix of the uterus is the lower, narrower and terminal portion of the uterus located below the body or corpus, approximately 2.5 cm long in an adult nonpregnant woman. For descriptive purpose the cervix is divided into two parts: (1) a supravaginal part between the isthmus and the vagina, and (2) a vaginal part, which protrudes into the vagina. The rounded vaginal part surrounds the external os of the uterus and is surrounded in turn by a narrow recess, the vaginal fornix. The slit-like cavity of the uterus is approximately 6 cm in length from the external os to the wall of the fundus. The uterine cavity in particular the cervical canal and the lumen of the vagina together constitute the birth canal through which the fetus passes at the end of the gestation.
Upper one-third of the cervical canal including the internal os behaves more of the body than the lower part of the cervix and is known as the functional isthmus. It undergoes changes in menstrual cycle and is taken by the uterine cavity during the end of first trimester to form the lower uterine segment but fetal membranes unlike the uterine body are not adherent to this segment. The cervical mucosa does not undergo physical changes during the menstrual cycle rather exhibit functional changes of cervical glands that are related to sperm transport through the cervical canal. During the proliferative phase (especially during ovulation) of menstrual cycle, the secretion from the cervix gland is thin and watery, conducive to the sperm to gain the entry into the uterus through the cervix. During the secretory (luteal) phase of the cycle as well as during pregnancy, the cervical gland secretions under the influence of progesterone, become highly viscous and forming a mucous plug in the cervical canal forming a protective measure that hinders the passage of sperm and microorganisms from the vagina into the uterus.
The wall of the uterus is composed of three coats or layers:
- Perimetrium: The serosa or outer serous coat consists of peritoneum supported by a thin layer of connective tissue.
- Myometrium: The middle coat consists of three ill-defined layers of smooth muscles. The growth of the myometrium during puberty is stimulated by the estrogenic hormone. The muscle fibers increase further in length and in number during pregnancy by the stimulation of placental estrogen. The length of the muscle fibers increases tenfolds in fully gravid uterus. The main branches of the blood vessels and nerves of the uterus are located in this coat. Contraction of these muscles is hormonally controlled. On contraction, the muscles stop the uterine bleeding in menstruation or during the separation of the placenta. During the menses, myometrial contractions may produce cramping.
- Endometrium: The endometrium or mucous membrane of the body of the uterus consists of surface epithelium and lamina propria of variable thickness depending on the stage of menstrual cycle. Before puberty the surface is lined by the ciliated columnar cells; during reproductive period it is lined by simple columnar epithelium because cilia cannot grow due to repeated destruction of the superficial part of the endometrium. Functionally the endometrium consists of outer basal layer and inner functional layer (Fig. 11). In a non-pregnant female, the inner functional layer with the uterine glands and blood vessels is sloughed off or shed during menstruation, leaving intact the deeper basalis layer with the basal remnants of the uterine glands—the source of cells for regeneration of new functional layer. The basal layer is supplied by straight basal arteries, whereas the functional layer is supplied by the spiral arteries, which are highly sensitive to the hormonal changes in the blood and undergo vasoconstriction before menstruation with eventual casting of endometrium due to ischemic necrosis followed by hemorrhage.
Menstruation occurs only in primates and in mankind who possess the spiral arteries of the endometrium.
Fundus and body are developed by the fusion of the intermediate parts of the two paramesonephric (Müllerian) ducts.
13While cervix is developed from the upper part of the uterovaginal canal which in turn is formed by the fusion of the lower vertical parts of the two paramesonephric ducts and the lower part of the uterovaginal canal forms the major portion of the vagina.
The blood sutpply is mostly supplied by the uterine arteries, with the potential collateral supply from the ovarian arteries. The uterine veins enter the broad ligaments with the corresponding arteries and form a uterine venous plexus on each side of the cervix. Veins from these plexus drain into the internal iliac veins.
Vagina
The vagina is a musculomembranous tube lined by stratified epithelium (7–9 cm long) extends from the middle cervix of the uterus to the vaginal orifice. The anterior wall is about 7.5 cm long and the posterior wall 9 cm long. It runs upward and backward (at an angle of 60 degrees) up to the vaginal part of the cervix, where the vagina forms four fornices around the cervix—anterior, posterior and two lateral. The posterior vaginal fornix is the deepest and is closely related to the rectouterine pouch. The vagina does not have any glands in its wall. Mucous produced by cells in the cervical glands lubricate the vaginal lumen. In a nulliparous adult the vagina is H shaped in section with transverse folds called vaginal rugae which renders the vagina highly distensible. Before puberty rugae are absent. In the elderly, the vagina becomes less elastic and appears pale and smooth due to loss of rugae. Vagina is closely related to many pelvic floor muscles, which provide support and acts as potential sphincters for the vagina. All these muscles rhythmically contract during the orgasm. Levator ani muscles are closely related to the vagina on its lateral side, and any pathology to these muscles is significantly responsible for either the painful intercourse or orgasm. The authors have come across many such patients during their clinical practice, especially suffering from coccydenia (tail bone pain), in which levator ani muscle is mostly tender on rectal examination and surprisingly the same mechanism is seen in males as well.
The vaginal epithelium exhibits minimal changes during the menstrual cycle. During the proliferative (follicular) phase of menstrual cycle, under the influence of high estrogen secretion, the vaginal epithelium increases in thickness and stimulates the vaginal cells to synthesize and accumulate increased amount of glycogen as these cells migrate toward the vaginal lumen, into which they are shed off. The fermentative action of Doderlein bacillus on glycogen rich desquamated cellular debris (glycogen is converted to lactic acid) renders the vaginal fluid acidic, which inhibits the growth of microorganisms or pathogenic invasion. Hence, the vaginal infections are more common after menopause as the glycogen content becomes lesser.
The vagina:
- Receives the male partner's erect penis and semen during sexual intercourse.
- Routes for menstrual fluid.
- Forms the inferior part of the birth canal.
- Checks the growth of microorganisms to enter the uterus by maintaining acidic environment (pH 4.0).
CONCLUSION
For proper diagnosis and treatment, one needs to have an adequate knowledge about the anatomy and physiology. The evaluation and treatment for both the partners in an infertility set-up must go in parallel, so one needs to have a brief knowledge about the reproductive system of both male as well as female.
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