Keywords Genital tract, hormones, FSH, LH
Genital organs are classified as external and internal organs. External genital organs in female are mons veneris, labia majora, labia minora, clitoris and vestibule. Genital tract is under the influence of HPO axis. Ovaries respond to FSH and LH secreted by pituitary and uterus responds by menstruation. If the ova is fertilized, it grows in uterus. Male genital organs are also divided as external and internal organs. External organs are mons pubis, penis, scrotum and testicles. Internal organs are prostate, seminal vesicle, coopers gland and bulbourethral glands. Genital tract also responds to FSH and LH. In this chapter the anatomy and physiology of genital tract has been discussed.
Formation of genital organs depends primarily upon chromosome y and a endocrine structures which are testis in a male and ovaries in female. Differentiation depends upon secreting gonads (Table 1.1). After birth, gonads remain in quiescent stage till adolescence. Then they are activated by gonadotropins. Gonads have two functions—one is gametogenesis and the other is production of androgens in males, sexhormones and estrogen in females.
Genital organs can be divided as external and internal in both male and female.
External Genitalia of Female
External genitalia of the female are hidden compared to male genitalia. They can be seen separating thighs.
The Part of external genitalia as in Fig. 1.1 are:
- Mons Veneris
- Labia majora
- Labia minora
- Clitoris and
Mons Veneris: This is a pad of fat, on which pubic hair grows in a triangular form.
Labia Majora: These are folds of skin and fat and forms the lips of vulva. Inner surface of labia majora are hairless. They join medially to form posterior commissure.
Labia minora: These are thick folds of skin devoid of fat within labia majora. Anteriorly they enclose clitoris and behind clitoris form prepuce or frenulum. Lower portion forms fourchette.
Clitoris: It is 2.5 cm erectile body situated in the most anterior part of vulva. It consists of glans, a body and two crura and it is attached to the under surface of symphysis pubis.
Vestibule: It is a triangular space bounded anteriorly by clitoris, posteriorly by fourchette and on either side by labia majora. There are 4 openings in the vestibule,
- Urethral opening,
- Vaginal orifice
- Opening of 2 Bartholin ducts.
Vaginal orifice is incompletely closed by a membrane called hymen. The shape of the opening varies but usually cresentric in virgins. Hymen is ruptured at the consummation of the marriage and during, childbirth it is extremely lacerated. The cicatrized nodules are called as carunculae myrtiformis.
Bartholin glands are situated close to the end of vestibule. During sexual excitement it secrets abundant alkaline mucus for the lubrication. Ducts open outside the hymen on both sides.
Vestibular bulbs: These are bilateral elongated masses of erectile tissue situated beneath mucus membrane of the vestibule.
Perineum: It is 1–2 cm between anus and vaginal orifice.
Internal Genital Organs
The internal genital organs in female include vagina, uterus, fallopian tubes and ovaries as given Fig. 1.2.
Vagina: It is a fibromuscular membraneous sheath communicating the uterine cavity to the vulva, through which uterine secretion, menstrual blood are excreted. It forms 45 degrees to the horizontal plane, diameter is 2.5 cm and it is widest in its upper part. The length of anterior wall is about 7 cm and posterior 9 cm. The walls of the vagina are opposed to form “H” shaped in varies transverse section. It is lined by stratified squamous epithelium. The pH of the vagina on average is 4.5. The pH is acidic due to conversion of glycogen in the exfoliated cells to lactic acid by the Doderlein's bacilli which are dependent on estrogen.
Uterus: It is a pyriform shaped muscular organ, measuring 7.5 cm × 5 cm, × 2.25 cm, weighing 30 g. The upper portion is fundus followed by body and isthmus. The mucus lining of the cavity is called as endometrium. Cavity is triangular and 2 fallopian tubes are attached at the upper end and the internal os of cervix opens at the lower end.
Cervix: It is the composed of fibrous, connective tissue and smooth muscle. It 2.5 cm in length cervical glands secrete alkaline mucus with the pH of 7.8. The functions of the cervix are ascent of sperm, descent of menstrual blood, fetus, prevents infections.
Endometrial cycle: The endometrium undergoes changes according to the phase of the menstrual cycle. There are 3 phases.
Menstrual phase — auto digestion of functional zone resulting in bleeding for 3–5 days. But the blood does not clot due to presence of fibrinolysin. Endometrium grows up to 1 to 4 mm. This is called as stage of regeneration.
Hypothalamus, Pituitary and ovaries take part in menstrual cycle:
Proliferative phase — endometrium grows up to 4–8 mm from D5-14. Glands and stroma grow.
Secretory phase — grows from D14. Glands and vessels grow. Endometrium grows up to 6–8 mm.
Fallopian Tubes: These are paired structures measuring about 10 cm, distal end opens as finger like projections called as fimbriae.
Each tube has two openings one, communicating with the lateral angle of uterine cavity, and the other to the abdomen. Ovum and sperm travel in the tube.
Ovaries are paired sex organs in female which are concerned with steroidogenesis, maturation of germ cells, storage and release of ova. It contains 400000 immature eggs. Regulation of menstruation depends upon hypothalamo pituitary ovarian and uterine axis. The Pituitary secrets FSH by the stimulation of GnRh from hypothalamus. Ovarian follicles grow due to FSH. One of the follicles becomes dominant. From the ovary estrogen is secreted. This in turn suppresses the ovary along with inhibin by negative feedback mechanism. Ovary secretes LH by positive feedback by estrogen. At the mid peak of LH surge, ovulation occurs and progesterone is secreted. Both estrogen and progesterone suppress the pituitary. Withdrawal of both hormones lead to menstrual bleeding.
Oogenesis: Essence of maturation is reduction of chromosome to half. There are 22 pairs of chromosomes and one set of sex chromosome [XX]. The first stage of maturation occurs just prior to ovulation and final maturation only after fertilization.
Blood supply: Uterus is supplied by uterine artery. Uterine artery encircles the uterus on both sides as arcuate artery which gives branches as radial artery ultimately ending as basal and lastly spiral artery. Ovary is supplied by the ovarian artery and vagina by vaginal artery the branch of internal iliac of uterine artery. Venous drainage from uterus, vagina, cervix directly drained into internal iliac vein.
Breasts: These are not reproductive organs but they are part of sexual organs. They are symbol of feminity, sexuality and attraction. Breasts vary in size. Areola are circular colored area about 1’ width, at the center nipple can be seen. Each mammary gland ends in the nipple through mammary ducts, which are 15–20 in number.
Male Reproductive Organs
External organs are (Fig. 1.4);
- Mons pubis
Mons Pubis: It is smaller compared to women and the distribution of hair is triangular towards the umbilicus.
Penis: It is partially hidden in the perineum and partially free. It droops on the Scrotum. The length of the penis in a flaccid state varies from 2 and half to 4” and thickness 1”–1”quarter. Erect penis can be 3–7” It is formed by 3 cylindrical bodies of erectile tissue. They are 2 corpora cavernous lie parallel to each other and above the single corpus spongiosum, which contains the urethra along the under surface of the penis. The corpora cavernosa are surrounded by a thick fibroelastic membrane called tunica albugenia. The skin of the shaft of the penis contains sweat glands but devoid of hair. The upper shaft of the penis is covered by a fold of skin called as prepuce or foreskin. It is movable. Urethra runs from the bladder to the glans penis, urine and semen are discharged through the urethra and they do not mix, as there is bivalve mechanism. It is a copulatory organ.
Scrotum: It is a loose bag of rugous skin which contains 2 testicles separately. The Scrotum maintains the temperature 1–2° lesser than the body. Scrotal temperature is 32 degrees.
Musculature: Cremasteric muscle covers the testis, raises or lowers the scrotum to help regulate temperature and promotes spermatogenesis. Dartos muscle — it is a layer of smooth muscle fiber outside the external spermatic fascia below the skin, it also helps in heat loss of testicles by expansion to increase the surface area available to promote heat loss Pubococygeus muscle contracts rhythmically during erection, where as ischeocavernosus compresses the base of penis, retarding venous return and bulbocavernosus surrounds corpus spongiosum. Contraction of these muscle help in erection.
Testicles: 10–40 g, The size is 4 × 3 × 2.5 cm, are 2 in number covered by fibrous capsule tunica albuginea — sends partition through its interior dividing lobules, each lobule is 70–80 cm long and opens into Rete testis which form ductus deferens which in turn drains into epididymis. Which continues as vasdeferens. Testis contains 2 types of cells. Leydigs cells which produce testosterone and sertoli cells are rich in glycogen which nourish germ cells of sperm and secrete ABP (androgen binding protein) inhibin, MRF and also convert androgen to estrogen. Functions of the testes are storage of sperms and secretions of androgenic hormone. Spermatogenesis occurs within 74 days from germ cells to mature sperm, sperm is rich in DNA and non-motile. In the presence of androgenic hormones spermatids are converted to sperms. Hot bath of 43–45° may result in sterility.
Endocrine function: Testis is responsible for the maintenance of spermatogenesis through Follicle-stimulating hormone (FSH).
Development of sex organs
Inhibits feedback on Luteinizing hormone (LH)
Acts on epiphysis to stop the growth
Retention of calcium, phosphate, water, KCL.
Control of testicular activity: Hypothalamus secretes FSH and LH. LH is also called as Interstitial Cell Stimulating Hormone (ICSH) acts on leydig cells to produce testosterone which is necessary for the growth of the reproductive organs. Both FSH and LH are necessary for the spermatogenesis. Testosterone has inhibitory effect on the pituitary. Testosterone and inhibin B from sertoli cells inhibit FSH.
Epidydimis: It is comma shaped lies at the back of the testis. It stores mature sperms.
Internal pudendal artery, branch of internal iliac artery gives off dorsal artery which runs on the dorsum of the penis in tunica albuginea and deep arteries run longitudinally through each corpus cavernosum. Dorsal artery gives off small circumflex branches along its length which run in the fibrous sheath of cavernosum and anastomosis with deep arteries. Bulbourethral arteries run in corpus spongiosum.
Venous drainage is from both superficial and deep dorsal vein, cavernous vein. Both superficial and deep veins anastomose and superficial vein drains into saphenous vein, where as deep veins drain into pudendal veins.
Sensory nerve is from sacral root by pudendal nerve. Efferent is also pudendal nerve parasympathetic stimulates secretion from seminal, prostate and cowper's gland. Ejaculation is by symphatic fibers from T11-T12 and L1-L2.
Spermatogenesis takes place inside the testis in seminiferous tubules, epididymis receives mature sperms, and sperm travels through ductus deferens, ejaculated through the urethra.
Prostate Gland: It is situated between the bladder and urethra. Prostatic secretions contain, zinc citric acid, sodium, PSA, plasmin, acid phosphate, and forms 20% of the semen. The ejaculatory ducts open in the prostatic urethra. The secretions provide nourishment to the sperms.
Spermatic cord: Thick cord contains ductus deferens blood vessels, nerves enveloped in white fibrous tissue.
Seminal vesicles: These are two elongated sacs, 7 cm length which is posterior to bladder. The seminal fluid together with the contents of the ampulla of the vas are discharged into the prostatic part of the urethra during emission, prior to ejaculation, and the contents are fructose, citric acid, ascorbic acid, hyaluronidase, phosphatidyl choline, prostaglandins, etc. Seminal fluid forms 60% of semen volume.
Cowper's gland: These are pea sized glands below the prostatic gland and it secrets mucoid alkaline secretion which is discharged in penile urethra. They lie on each side of the urethra near its bulbous portion. They produce a few lubricating drops of pre-ejaculatory mucous secretion which may contain a small number of sperms.
Pea sized part on either side of urethra; gelatinous fluid called pre-ejaculate for lubrication urethra for spermatozoa to pass through and helps to flush out any urine or foreign material.
Prostate Gland-prostate gland secrete a thin milky fluid that contains calcium, citrate ion, clotting enzyme, and fibinolysin. During emission the capsule of prostate gland contraction at same time contraction of vas deference the fluid from prostate mixes with semen bulk.
Spermatogenesis: The spermatogoonia — primitive germ cells matures to primary spermatocytes. They undergo meiotic division and convert to secondary spermatocytes. These contain 23 Chromosomes (haploid sperms). Sperm is rich in DNA as in Fig. 1.3. Spermatozoa in testes are not mature, they acquire maturation during their passage through epididymis. Testes normally maintain a temperature of 32 degree celcius (at a lower temperature than the normal body temperature). When retained in the abdomen or close to body sterility results.
It contains the sperms and the secretions from the seminal vesicles, prostate, cooper's glands, urethral glands. The normal volume is 2.5 to 3.5 mL. 100 million sperms are present per ejaculate. If the count is less than 20 million it results in sterility. The normal speed of the sperm is 3 mm per minute, hence they reach the uterine cavity 30–60 minutes after copulation. Erection is maintained by the dilatation of the arterioles of penis, veins are compressed, blocking the outflow adding to the turgor of the organ. The nerve innervation is from the lumbar segment of the spinal cord. Efferent nerves are nervi ergentis and parasympathetic supply is by pelvic splanchnic nerve. The fibers contain acetylcholine and VIP as cotransmitters. Acetylcholine acts on muscarinic receptors to decrease the release of vasoconstrictor; norepinephrine. VIP also produces vasodilatation. However, injection of PGE1 (intraurethral) also dilates the penile smooth muscle and has been used clinically to facilitate erection.
There are non-adrenergic, non-cholinergic fibers in nervi ergentis and these contain large amounts of NO synthatase, the enzyme that catalyses the formation of nitric oxide (NO) this in turn activates cGMP, a potent vasodilator. Normally is terminated by sympathetic vasoconstrictor impulses to the penile arterioles.
Penile Erection: Penile erection is first effect of male sexual desire and stimulation. The degree of erection depends on degree of stimulation — due to psychic or physical. Erection is caused by parasympathetic impulses—pass to-from sacral portion of spinal cord through pelvic nerves to the penis.
This process has two parts — emission and ejaculation. Afferent fibers are touch receptors in glans penis, that reach spinal cord through internal pudendal nerves. Emission is a sympathetic response in the upper lumbar segment of spinal cord and effected by contraction of smooth muscles of the vasa deferens, seminal vesicles in response to hypogastric nerves. Semen is propelled out of the urethra by contraction of bulbocavernous muscles.
Puberty: Transition from adolescent to progression form appearance of secondary sexual characters to sexual development (reproductive maturity) and development of adult mental process.
Tanner's and Marshal have classified 5 stages depending upon the development of pubic hair, axillary hair, breast development, growth spurt, menstruation. In the order of growth spurt — breast budding, pubic and axillary hair development, phallic growth, menstruation. Age: 10–16 years.
Changes in Female
Prepubertal state there will be elevation of papilla only. This is followed by breast buds and papilla slightly elevation, areola begins to enlargement (median age: 9.8 years), further enlargement of entire breast tissue, secondary mould of areola and papilla projecting above the breast tissue (median age: 12.1 years) and areola recessed to general contour of breast (median age: 14.6 years). In the same way, no pubic hair present in prepubertal stage later followed by sparse, long hair on either side of labia majora (median age: 10.5 years), darker, coarser and curly hair over the mons pubis, adult type hair covering the mons only (median age: 12 years), and lastly adult hair with inverse triangle distribution (female escutcheon) covering the median thighs (median age: 13.7 years).
Changes in Male
Growth of testes and penis occurs. This is followed by curly coarse development of hair, and the shape is upside down triangular hair. Other changes are voice braking, facial hair growth, erections, sexual orientation, etc.
Fertilization is the process of fusion of ovum and sperm which takes place in the fallopian tube. The objective of fertilized ovum is to restore the number of chromosome and to initiate the embryonic development. Implantation occurs on 5th day. The duration of pregnancy is 40 weeks. Placenta acts as respiratory, nutritive and excretory organ of the fetus apart from producing hormones.