BSC1005 STUDY GUIDE Unit 4 Human Reproduction Study Guide whatever is underline will be on the Exam Causation one event being the direct cause of another Correlation two unrelated events occurring at the same time Both male and female reproductive systems are divided into sets of internal structures in the body cavity and external structures outside the body In most cases the genetic female XX is born with appropriate female internal and external reproductive structures and a genetic male XY is born with male reproductive organs In an embryo it is not evident the sex until about the seventh week Sexual differentiation begins with the gonads testes or ovaries before proceeding to the internal structures and then the external genitals It is the presence of the Y chromosome that causes the differentiated gonad to become a testis It is the presence of the Y chromosome that stimulates the indifferent gonads to differentiate into testes The testis will produce two important hormones testosterone and anti Mullerian hormone Prior to the differentiation of these gonads the body has both Wolffian ducts and Mullerian ducts The anti Mullerian hormone in males causes the Mullerian ducts to regress so not females structures can be formed Testosterone will include normal internal structures and external structures of a male In the female Mullerian ducts will differentiate into female structures if not exposed to anti Mullerian hormone Without any hormonal stimulation the embryo then fetus will develop as a female Testosterone potent male hormone belonging to the androgen class of hormones The mullerian ducts when NOT exposed to androgens develop into female structures Genitalia external and internal reproductive structures Although male and female structures are anatomically different at birth their reproductive structures develop from the same tissues homologous structures during pregnancy Homologous structures structures that are similar in developmental origin include Male structure Scrotum Penis Cowper s Glands Testes Female Structure Labia majora Clitoris Bartholin s Glands Ovaries Androgen insensitivity syndrome All individuals will have the genotype of XY All individuals will have abdominal testes Will have external genitalia of a female In the AIS the cells of the body do not respond to androgen from the abdominal testes 2 to 5 out of 100 000 births will have complete AIS Receptors are the key Testes are the only internal organs that these XY females will have Androgenital syndrome clinical condition caused by excess secretion of male hormones by the adrenal glands This shows that sexual differentiation of the reproductive structures is controlled by hormones and that female external reproductive tissues exposed to male hormones during prenatal development differentiate into male like structures Sexual differentiation Genetic sex Established at fertilization o XX female o XY male Y chromosome induces the indifferent gonads neither male nor female to become testes This differentiation of reproductive structures begins approximately at the 7th week of development The testes produce 2 types of hormones in utero Androgens male hormones which act on the Wolffian duct system to induce internal male structures These hormones diffuse to act on the duct system In addition these hormones travel via the blood to act on external genitalia to induce male structures Testosterone is diffusing from testes into the Wolffian duct Also the testis induce a anti Mullerian hormone to regress the Mullerian In summary the Wolffian ducts are induced by testosterone to form the Male sexual differentiation o Seminal vesicles o Vas deferens o Epididymis External genitalia in the male respond to a potent androgen called dihydrotestosterone to become male structures including the scrotum penis and prostate gland Receptors only respond to testosterone and cell changes in DHT Mullerian duct inhibiting hormone anti Mullerian hormone This hormone dihydrotestosterone is also produced by the testes and will cause the Mullerian ducts to degenerate If the Mullerian ducts do not degenerate they will become the internal female reproductive structures An individual with a genotype of XXY would have testis If we prevented testosterone from being changed to dihydrotestosterone we would not find fully developed penis This is because dihydrotestosterone deals with external development Female sexual differentiation In female sexual differentiation we find that if androgens are absent the Mullerian ducts will develop into the internal female reproductive structures including o Oviducts fallopian tubes Uterus and a portion of the vagina We don t need a stimulant for them to develop If no androgens are present then female external female structures develop into clitoris labia and vagina Clitoris small erectile structure located beneath the prepuce that is very sensitive to sexual stimulation Homologous structures It s clear that male and female are anatomically different but the reproductive structures develop from the exact same tissues If androgen are present the tissue become male structures and without androgen they become female structures The structures are termed homologous structures The critical role of the y chromosome So we see that if there s a Y present then the developing embryo fetus will assume male reproductive structures due to testes It s the androgen male hormones from the developing testes that are critical The scrotum is homologous to labia major Androgenital syndrome clinical condition caused by excess secretion of male hormones by the adrenal glands Androgenital syndrome This syndrome will cause an excess of male sex hormone androgen to be produced The syndrome can affect both genders and toughly 1 in every 10 000 to 18 000 children are born with the condition As a result regardless of whether the child is a male or female the male external characteristics will begin to develop Everything else is the same Sexual differentiation Androgenital syndrome illustrates the role of male hormones on development with excess male hormones in utero in a genetic female XX Since there are male hormones being produced in large amount in utero its possible that the girls genitals will look like the genitals of both genders at the same time called ambiguous genitalia T must diffuse to induce Wolffian ducts There are no testes here so no male structures internally The external genitalia of both sexes are the last to
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