Chapter 22: The Reproductive System

GnRH, or gonadotropin-releasing hormone, is indeed secreted by the hypothalamus and it plays a crucial role in regulating the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary gland. When GnRH is released, it stimulates the anterior pituitary to release FSH and LH, which are important hormones involved in the regulation of the reproductive system. Therefore, the statement that GnRH stimulates the secretion of both FSH and LH from the anterior pituitary is true.

The inner layer of the uterine wall is called the endometrium. This layer is highly vascularized and undergoes cyclic changes during the menstrual cycle. It is responsible for supporting the implantation of a fertilized egg and, if pregnancy does not occur, it is shed during menstruation. The endometrium is essential for the proper functioning of the uterus and plays a crucial role in reproductive processes.

The corpus luteum is a temporary structure that forms in the ovary after ovulation. Its main function is to produce and secrete progesterone. Progesterone plays a crucial role in preparing the uterus for implantation of a fertilized egg and maintaining pregnancy. It helps to thicken the uterine lining, promote the growth of blood vessels, and inhibit contractions of the uterus. Estrogens, on the other hand, are primarily secreted by the developing follicles in the ovary. While the corpus luteum does produce some estrogens, its main hormone secretion is progesterone.

During the last 6 months of pregnancy, the placenta secretes estrogens and progesterone. The placenta is an organ that develops during pregnancy and is responsible for providing oxygen and nutrients to the fetus. It also produces hormones that are necessary for maintaining the pregnancy, such as estrogen and progesterone. These hormones play a crucial role in the development of the fetus and the preparation of the mother's body for childbirth. The ovaries, on the other hand, are not actively involved in hormone production during pregnancy.

Fertilization usually occurs in the uterine tube, also known as the fallopian tube. This is the site where the sperm and egg meet and fertilization takes place. The uterine tube provides the necessary environment for the sperm to reach the egg and for fertilization to occur. Once fertilization occurs, the fertilized egg travels down the uterine tube towards the uterus for implantation. Therefore, the uterine tube is the correct answer for where fertilization usually occurs.

The degeneration of the corpus luteum, which is the temporary structure formed in the ovary after ovulation, leads to hormonal changes in the body. These hormonal changes signal the shedding of the uterine lining, resulting in menstruation.

The second half of the ovarian cycle is called the luteal phase. This phase begins after ovulation and lasts until the start of the next menstrual cycle. During the luteal phase, the ruptured follicle transforms into a structure called the corpus luteum, which produces hormones like progesterone to prepare the uterus for possible pregnancy. If pregnancy does not occur, the corpus luteum degenerates, hormone levels drop, and menstruation begins.

LH (luteinizing hormone) is responsible for triggering ovulation. It is produced by the pituitary gland and plays a crucial role in the menstrual cycle. LH surge occurs around the middle of the menstrual cycle, causing the dominant follicle to release a mature egg from the ovary. This process is known as ovulation. FSH (follicle-stimulating hormone) also plays a role in the menstrual cycle by stimulating the growth and development of follicles in the ovary, but it is LH that specifically triggers ovulation.

During the proliferative phase of the uterine cycle, the lining of the uterus thickens under the influence of rising estrogen levels. This phase occurs after menstruation and is characterized by the growth and development of the endometrium, preparing it for potential implantation of a fertilized egg. Estrogen, which is produced by the developing ovarian follicles, stimulates the proliferation and growth of the endometrial cells, leading to an increase in thickness. This phase is crucial for creating a favorable environment for implantation and subsequent pregnancy.

FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are classified as gonadotropins. Gonadotropins are hormones that are released by the pituitary gland and act on the gonads (testes in males and ovaries in females). FSH stimulates the growth and development of follicles in the ovaries and the production of sperm in the testes. LH triggers ovulation in females and the production of testosterone in males. Therefore, both FSH and LH play important roles in regulating reproductive function and are classified as gonadotropins.

Spermatogenesis is the process of sperm cell development. It is stimulated by testosterone, a hormone produced by the testes. In addition to testosterone, another hormone called follicle-stimulating hormone (FSH) also plays a crucial role in spermatogenesis. FSH targets Sertoli cells, which are located in the seminiferous tubules of the testes and provide support and nourishment to developing sperm cells. FSH helps in the maturation of sperm cells and promotes their release into the epididymis for further development. Therefore, FSH is the correct answer as it is one of the hormones involved in stimulating spermatogenesis.

During the secretory phase of the uterine cycle, the uterine conditions are prepared for possible implantation of a fertilized egg. This phase is primarily regulated by progesterone. Progesterone inhibits the secretion of gonadotropins, which are hormones that stimulate the development and release of eggs from the ovaries. By inhibiting gonadotropin secretion, progesterone helps to maintain the uterine lining and create a suitable environment for potential pregnancy.

In meiosis I, maternal and paternal chromosomes do not segregate into separate daughter cells. Instead, homologous chromosomes pair up and exchange genetic material through a process called crossing over. This results in genetic variation in the daughter cells. The separation of maternal and paternal chromosomes occurs in meiosis II, during the process of sister chromatid separation. Therefore, the statement is false.

Gonadotropin-releasing hormone (GnRH) is responsible for stimulating the secretion of gonadotropins (FSH and LH) from the anterior pituitary gland in both males and females. GnRH acts as a regulator of reproductive function by signaling the release of FSH and LH, which in turn stimulate the production of sex hormones (estrogen and progesterone in females, and testosterone in males) and the development of gametes (eggs and sperm). Inhibin, androgens, and growth hormone-releasing hormone (GHRH) may also play roles in the regulation of gonadotropin secretion, but GnRH is the primary stimulator.

The head of a sperm contains chromosomes and an acrosome, which is a vesicle containing enzymes needed for fertilization. These enzymes help the sperm penetrate the protective layers of the egg and facilitate the fusion of the sperm and egg membranes, leading to fertilization. The acrosome plays a crucial role in ensuring successful fertilization and the transmission of genetic material from the sperm to the egg.

In the first step of spermatogenesis, spermatogonia differentiate into primary spermatocytes. This is the correct answer because spermatogonia are the stem cells that undergo division and differentiation to produce sperm cells. The primary spermatocytes are the first cells formed from spermatogonia and they undergo meiosis to produce secondary spermatocytes. Therefore, primary spermatocytes are the immediate product of spermatogonia differentiation and are crucial for the continuation of spermatogenesis.

During the early to mid-follicular phase of the ovarian cycle, the granulosa cells in the ovary are primarily stimulated by follicle-stimulating hormone (FSH). FSH promotes the growth and development of ovarian follicles, which contain the eggs. It stimulates the granulosa cells to produce estrogen, which is important for the maturation of the follicles. Progesterone, LH (luteinizing hormone), and GnRH (gonadotropin-releasing hormone) have roles in different phases of the ovarian cycle, but during the early to mid-follicular phase, FSH is the primary hormone responsible for stimulating granulosa cell functions.

The proliferate phase in the uterine cycle refers to the phase where the endometrium of the uterus thickens in preparation for potential pregnancy. The menstrual phase, which is the shedding of the endometrium, occurs right before the proliferate phase. This shedding is a result of the previous cycle not resulting in pregnancy. Therefore, the correct answer is menstrual phase.

In the late luteal phase, estrogen and progesterone levels fall because of the degeneration of the corpus luteum. The corpus luteum is formed from the ruptured dominant follicle after ovulation and is responsible for producing estrogen and progesterone. However, if fertilization does not occur, the corpus luteum degenerates, leading to a decrease in hormone production. This decrease in estrogen and progesterone levels prepares the body for menstruation and the start of a new menstrual cycle. The other options mentioned (rupture of dominant follicle, inhibitory effect of LH on secretory activity of corpus luteum, inhibitory effect of inhibin on the secretory activity of granulosa cells) are not the primary reasons for the decrease in estrogen and progesterone levels in the late luteal phase.

In oogenesis, meiosis I occurs just before ovulation. This is the process where a diploid cell called a primary oocyte undergoes division to form two haploid cells called secondary oocytes. Meiosis I is initiated during fetal life and remains arrested until just before ovulation, which is when the secondary oocyte is released from the ovary. After ovulation, the secondary oocyte will proceed to meiosis II, but this will only be completed if fertilization occurs. Therefore, the correct answer is just before ovulation.