Question

Describe the factors that promote sexual differentiation in utero. Discuss the process of puberty, focusing on the three critical endocrine changes that occur and the role of the anterior pituitary gland. Diagram normal female reproductive anatomy. Describe the normal female reproductive cycle, including changes in hormone levels and cellular events. Diagram normal male reproductive anatomy. Discuss the vascular and hormonal sequence of events required for ejaculation of motile sperm. Discuss the sequence of events that occurs during ovulation and menstruation. Identify the male and female hormones that regulate secondary sexual characteristics and reproductive functions. Describe the functions of the female breast and discuss the cyclical, hormone-mediated changes in breast tissue that occur during the reproductive years and in pregnancy. Discuss the normal age-related changes in the male and female reproductive systems.

Answer 1

1.Describe the factors that promote sexual differentiation in utero.

The sexual differentiation in utero occurs during the embryonic stage. The embryonic stage consists of a sexually indifferent stage in which the embryo will have the chance to develop either male or female organs. Nearby the developing gonads, there are two primitive ducts which are capable of developing into either the male or the female reproductive tracts. The more medial one is the Wolffian (mesonephric) ducts and the more lateral is Müllerian (paramesonephric) ducts. In later period its fuse in the midline more caudally.

Sexual differentiation process starts with the sex determination and it is based on the sex chromosomes, X and Y. The development of gonads as either testes or ovaries leads to the sexual determination.

In case of XY embryo, there will be a sex-determining region of the Y chromosome or the SRY gene is present. The gene network which directs the gonads to develop as testes will be activated by the protein produced by SRY. In the absence of a Y chromosome in an embryo (XX) the SRY also will be absent and in that case, the gonads develop as ovaries.

Female development proceeds when there is an absence of the SRY gene. No testosterone or MIS is made. The Wolffian ducts regress, and the Müllerian ducts persist, developing into the fallopian tubes, the uterus and the upper part of the vagina.

When the gonad starts to develop as a testis, support cells in the testis differentiate and form the main regulatory molecules that lead to sexual differentiation. The testosterone produced by the Leydig cells stimulate the development of the Wolffian ducts. They will differentiate later to form the structures of male reproductive tract the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts. The Müllerian inhibiting substance (MIS or Anti-Müllerian hormone, AMH) produced by the Sertoli cells leads to the degeneration of Müllerian ducts.

In Female development SRY gene is not present and it cause the absence of testosterone or MIS. The function of Wolffian ducts regress, but the Müllerian ducts persist. They will develope into the fallopian tubes, the uterus and the upper part of the vagina.

2. Discuss the process of puberty, focusing on the three critical endocrine changes that occur and the role of the anterior pituitary gland.

The stage of sexual development in which individuals become sexually mature is known as puberty. The hormonal control of the process in male and female are very similar but the result of puberty for boys and girls are very different.

The release of hormones from the hypothalamus (Gonadotropin Regulating Hormone GnRH), the anterior pituitary (Latinizing Hormone LH and Follicle stimulating Hormone FSH), and the hormones either testosterone or estrogen produced by the gonads is the causative factor for the maturation of the reproductive systems and the development of secondary sex characteristics.

The first developments of puberty start around the age of eight or nine with the notable production of LH. The LH release is more at night during sleep and precedes the physical changes of puberty.

When an individual approaches puberty the sensitivity in the hypothalamus and pituitary to negative feedback decreases. The more concentrations of sex steroid hormones will be needed to stop the production of LH and FSH. The second change in sensitivity is that the sensitivity of the gonads to the FSH and LH signals will be more. As a result of these two changes in sensitivity the levels of LH and FSH slowly increase and lead to the development of the gonads. The maturation of gonads leads to increased secretion of sex hormones which will, in turn, leads to the initiation of spermatogenesis and folliculogenesis.

The gonadotrophins i.e. the luteinising hormone and follicle stimulating hormone are produced by the anterior pituitary gland. These gonadotrophins can act on the ovaries or testes to stimulate sex hormone production and causes the egg and sperm maturity. The hormone prolactin produced by pituitary gland stimulates milk production in females in later life.

3. Diagram normal female reproductive anatomy.

4. Describe the normal female reproductive cycle, including changes in hormone levels and cellular events.

  
The female reproductive cycle describes the changes occurs within the female reproductive system which makes the pregnancy possible. Menarche is the beginning of a menstrual cycle which begins at puberty and usually lasts around 28 days, before its end – the menopause

The hormones which control and coordinate menstrual cycle are the :

§ Pituitary hormones (FSH and LH) which is released from the anterior pituitary gland and stimulates the ovaries to develop follicles

§ Ovarian hormones (estrogen and progesterone) excreted from the ovaries helps to maintain and regulate pregnancy.

Events in the Menstrual Cycle:

There are four key events in a Menstrual Cycle and they are distinguished by changes in hormonal levels, follicular development and the development of the endometrium

1.  Follicular Phase

§ In this phase, the Follicle stimulating hormone (FSH) secreted by the anterior pituitary will stimulate the growth of ovarian follicles. The estrogen, produced by the dominant follicle inhibits FSH secretion as a negative feedback, to prevent the growth of other follicles. The thickening of the endometrial layer of the uterus is stimulated by the estrogen.
2.  Ovulation

§ Around the midway of the cycle, the estrogen stimulates the anterior pituitary to secrete luteinizing hormone (LH) and a lesser surge of FSH. The LH leads to the rupture of the dominant follicle release an egg or secondary oocyte.

3.  Luteal Phase

§ The ruptured follicle forms into a slowly degenerating corpus luteum and which secretes high levels of progesterone and lower levels of oestrogen. The Estrogen and progesterone will cause thickening of the endometrial lining of the uterus as in preparation for pregnancy and inhibit secretion of FSH and LH.

4.  Menstruation

If fertilization does not occur the corpus luteum eventually degenerates and develops into a corpus albicans after 2 weeks. The degeneration of corpus luteum causes the drop of estrogen and progesterone levels. There by the endometrial layer is sloughed away and discarded from the body as menstrual blood flow.

The cycle again begins after the one.

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