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[Academic Script] Accessory Sex Organs, Sex determination & Sex differentiation Subject: Zoology Course: B.Sc. 2nd Year Paper No. & Title: Z-203B Vertebrate Endocrinology and Reproductive Biology Topic No. & Title: Topic – 10 Accessory Sex Organs and their dependence as steroid hormones. Sex determination & Sex differentiation Lecture Title: Accessory Sex Organs, Sex determination & Sex differentiation Academic Script 1. Introduction The male reproductive tract can be divided into a sequence of ducts and three major secretory glands. Moving from testes to penis, sperm pass through the epididymis, ductus deferens, ejaculatory duct, and urethra. The major accessory sex glands, which provide most of the semen, are the seminal vesicles, prostate, and bulbourethral gland. The female reproductive tract consists of two oviducts, the uterus and the vagina. The oviducts (or fallopian tubes), which connect the ovaries to the uterus, can be divided into three segments. The most lateral part is the fimbriated infundibulum, which picks up the mature ovum when it leaves the ovary. Next is the ampulla, which is the site of fertilization; it leads into the isthmus, a relatively short straight tube running into the uterus. The major accessory sex glands are bartholin’s glands and mammary glands. ACCESSORY ORGANS OF THE MALE REPRODUCTIVE SYSTEM EPIDIDYMIS It is the start of the male reproductive tract, is a coiled tube bound to the posterior border of the testis. It is almost 7 meters long, the epididymis is divided into caput, corpus and cauda segments. It stores and protects Sperm and facilitates their Functional Maturation. A spermatozoon passes through the epididymis in about two weeks and completes its functional maturation at that time under the strict control of hormones. THE DUCTUS DEFERENS OR VAS DEFERENS It is 40–45 cm long. It begins at the tail (cauda) of the epididymis. Just before the ductus deferens reaches the prostate gland and seminal vesicles, its lumen enlarges. This expanded portion is known as the ampulla (distae part). The junction of the ampulla with the duct of the seminal vesicle marks the start of the ejaculatory duct. This short passageway penetrates the muscular wall of the prostate gland and empties into the urethra near the opening of the ejaculatory duct from the opposite side. In addition to transporting spermatozoa, the ductus deferens can store spermatozoa for several months. During this time, the spermatozoa remain in a state of suspended animation and have low metabolic rates. URETHRA Urethra shares by urinary and reproductive systems. It has 3 regions: 1. prostatic urethra: connects to urinary bladder and ejaculatory duct, passes through prostate 2. membranous urethra: passes through body wall (urogenital diaphragm) 3. spongy/penile urethra: length of penis, opens at external urethral orifice. SEMINAL VESICLES The Seminal Vesicles are glands embedded in connective tissue on either side of the midline, sandwiched between the posterior wall of the urinary bladder and the rectum. It contributes about 60 percent of the volume of semen. In particular, the secretion of the seminal vesicles contains (1) higher concentrations of fructose, which is easily metabolized by spermatozoa; (2) prostaglandins, which can stimulate smooth muscle contractions along the male and female reproductive tracts; and (3) fibrinogen, which after ejaculation forms a temporary clot within the vagina. PROSTATE GLAND The Prostate Gland is a small, muscular, rounded organ about 4 cm in diameter and encircles the proximal portion of the urethra as it leaves the urinary bladder. It produces prostatic fluid, a slightly acidic solution that contributes 20–30 percent of the volume of semen. These secretions are ejected into the prostatic urethra by peristaltic contractions of the muscular wall. THE BULBOURETHRAL GLANDS, OR COWPER'S GLANDS They are situated at the base of the penis, covered by the fascia of the urogenital diaphragm and are compound, tubuloalveolar mucous glands that secrete thick, alkaline mucus. The secretion helps neutralize any urinary acids that may remain in the urethra and lubricates the glans. ACCESSORY ORGANS OF THE FEMALE REPRODUCTIVE SYSTEM THE UTERINE (FALLOPIAN) TUBES, OR OVIDUCTS These are bilateral muscular ducts. They are about 4 in long, and the margin of the dilated end, or ampulla, is surrounded by a number of fringelike processes called fimbriae. The functions of the uterine tubes are to convey the ova from the ovaries to the uterus, to aid in the upward passage of the spermatozoa, and to provide circular folds within which the ovum is nourished and delayed of the elapse between fertilization and implantation so that the uterine wall will be properly prepared for growth and development of the embryo. THE UTERUS OR WOMB The uterus is a hollow, thick-walled, pear-shaped muscular organ about 3in long, situated in the pelvis cavity between the rectum and the bladder. Three parts of the uterus can be distinguished: (1) the body with its superior expanded portion called the fundus extending above the entrance of the uterine tubes; (2) the isthmus, or middle, slightly constricted portion; and (3) the cervix, or cylindrical lower part, that surround the cervical canal and projects into the vagina. The cavity of the uterus is small because of the thickness of its walls. The part of the cavity within the body is triangular and has three openings. The uterus is the organ of the reproductive tract in which the embryo grows and develops until the time of delivery. THE VAGINA The vagina is a fibro muscular tube, 7.5 to 10cm in length, situated anterior to the rectum and anal canal and posterior to the bladder and urethra. It is the organ of copulation, for the deposition of semen in the female, and during parturition it serves as the exit from the uterus. BARTHOLIN’S GLANDS It secrete mucus-like lubricating fluid. DEPENDENCE OF SEX ORGANS ON STEROID HORMONES Androgens and estrogens play a major role in the development of both sex secondary characteristics. Androgens, or testosterone give the male its sex characteristics during puberty and for promoting tissue and muscle growth. Androgens play a key role in maintenance of accessory sex organs, and their functions. Similarly, estrogens are synthesized in the ovaries, which control female secondary characteristics and regulation of the menstrual cycle. Another steroid hormone is needed for preparing the uterus for implantation of the ovum, this hormone is progesterone. SEX DETERMINATION Surprisingly, it is only in the last 50 years that we have begun to understand the nature of the biological events which determine our sex. It is not so long ago that women were blamed if they failed to produce a son for their husband and clearly it was thought that the power of sex determination lay within the body of the woman. Sex determination (male/female) at the biological level is determined by the presence or absence of the Y chromosome. "Female" is the default sex; due to the absence of the Y. There are many possible sex determination mechanisms in the animal kingdom. Here we consider only chromosomal sex determination mechanism in human. Chromosomal Sex Determination The basic mammalian sex determination mechanism arises from the possession of a small but important gene located on the Ychromosome. The Y-chromosome has very few functional genes and nearly all-important genes for development of early embryonic form are spread among the remaining somatic chromosome or on the X chromosome. There are indeed hundreds of genes that are necessary to construct the basic reproductive system of vertebrates during early development, but the trigger to take on a female or a male form arises from testes determining factor, the TDF genes. For years, biologists speculated that such a factor must reside on the Y chromosome and it has now been isolated in at least a few vertebrates more specifically present in p arm of Y chromosome called as sex determining region (SRY) on Y chromosome. The presence (XY) or absence (XX) of this gene takes the embryo down two alternative pathways male versus female. If the gene is absent, then the organism develops into a female with ovaries and a system of endocrine glands that regulate female reproduction and behaviors. If the gene is present, the organism develops testes rather than ovaries, and the testes in turn produce testosterone, which further organizes the neuroendocrine system. Human Sex Determination In humans, sex is determined by a specific set of chromosomes. Females have two X chromosomes (XX), whereas males have an X and a Y chromosome (XY). A mature female will produce eggs, each with one X chromosome; a mature male will produce sperm with either an X chromosome or a Y chromosome. When an egg and a sperm fuse during reproduction, the chromosome that the sperm carries determines the sex of the child. SEX DIFFERENTIATION After the determination of sex, a series of events occur to promote the appearance of three things: 1. Right type of gonadThe appearance of ovaries or testis occurs early in development. This establishes the "gonadal sex". 2. Right set of duct systemAdult sexual phenotype requires, besides the gonad, the presence of proper system capable of transporting and storing gametes, and adaptations that ensure gametes are brought together.3.The right genitals-proper external genitalia for copulation. Sex differentiation in humans 1. Differentiation of gonad At 5th week of gestation, gonads develop as paired bulges of tissue near the midline at the back of the abdominal cavity forms genital ridges. The gonad at this stage is "indifferent" or "bipotential", and has no germ cells (oogonia spermatogonia). Both cortex and medulla are present. or If Y chromosome is not present, the cortex grows into "cortical cords". Germ cells migrate from elsewhere and reside in cortical cords (future follicles), and medulla largely degenerates. Enlarging cortex becomes the ovary, and primordial germ cells become oogonia. Mitosis occurs in oogonia to give rise to primary oocytes. Human female infants are born with about 4,00,000-5,00,000 primary oocytes in primordial follicles at birth. From 7th-9th months, the ovaries descended from abdomen to pelvis. If Y chromosome (SRY) is PRESENT, at 43-50 days, the medulla grows into "medullary cords". Germ cells migrate from elsewhere and reside in medullary cords (future seminiferous tubules), and the cortex degenerates largely. Leydig cells appear at about 60 days and can be stimulated to secreted testosterone. From 3rd-9th months, the testes descended into scrotum (stimulated by testosterone).Thus, SRY of Y chromosome plays a pirotal role in testis formation, whole absence leads to ovary. 2. Differentiation of ducts At 6th week of gestation, the embryo also has indifferent sex ducts, consisting of two pairs. One pair, the Wolffian duct (mesonephric duct, or archinephric duct as a more general term), is derived from ducts of the primitive embryonic kidney (the mesonephros) which later form the male duct system. Second pair, the Mullerian duct (paramesonephric duct), is derived from the dorsal lateral lining of body cavity which gives rise to the female duct system. If testes develop-testosterone secreted by testes will cause the development of Wolffian duct into: epididymis, vas deferens, seminal vesicle and ejaculatory duct. Prostate and bulbourethral glands develop from another duct (urogenital sinus, which gives rise to urethra) and not Wolffian ducts. Embryonic testes also secrete Mullerian inhibiting substance (MIS). MIS causes the regression of the Mullerian ducts. If ovaries develop no testosterone is secreted, and Wolffian ducts regress. No MIS is secreted, so Mullerian ducts are retained and develop into: oviduct, uterus cervix, upper vagina. Lower vagina is developed from another duct (Urogenital sinus, which also gives rise to urinary bladder and urethra). 3. Differentiation of external genitalia If testes are present in embryos. Testosterone supports wolffian duct development, and is converted to DHT i.e 5-alpha dihydrotestosterone by 5-α-reductase to support development of external genitalia and prostate. DHT stimulates the male external genitalia to development. Genital develop tubercle during form the most 8th of week the of penis, urogenital folds forms ventral aspect of penis shaft, labioscrotal swelling form scrotum. Both bulbourethral and prostate glands enlarge. If no testes are present (e.g., ovaries present), no testosteron. Genital tubercle form clitoris, urogenital folds forms labia minora, labioscrotal swelling form labia majora ,this is a process that is estrogen-independent. Summary The male accessory sex organs can be divided into a sequence of ducts and three major secretory glands. Moving from testes to penis, sperm pass through the epididymis, ductus deferens, ejaculatory duct, and urethra. The major accessory sex glands, which provide most of the semen, are the seminal vesicles, prostate, and bulbourethral gland. The female accessory sex organs consist of two oviducts, the uterus and the vagina. The major accessory sex gland is bartholin’s glands. Chromosomal sex determination in humans (male/female) at the biological level is determined by the presence or absence of the Y chromosome (SRF). "Female" is the default sex; due to the absence of the Y. After the determination of sex, in sex differentiation a series of events occur to promote the appearance of three things: Right type of gonad, Right set of ductwork, the right genitals. Thus in this manner complete accessory sex organs and their dependence on steroid hormones. Sex determination and sex differentiation has been studied.