Chapter 15 | Reproduction and Development

  1. Figure 15.2 Which of the following statements about the male reproductive system is false?
    1. The vas deferens carries sperm from the testes to the penis.
    2. Sperm mature in seminiferous tubules in the testes.
    3. Both the prostate and the bulbourethral glands produce components of the semen.
    4. The prostate gland is located in the testes.
      Illustration shows a cross section of the penis and testes. The penis widens at the end, into the glans, which is surrounded by the foreskin. The urethra is an opening that runs through the middle of the penis to the bladder. The tissue surrounding the urethra is the Corpus spongiosum, and above the Corpus spongiosum is the Corpus cavernosum. The testes, located immediately behind the penis, are covered by the scrotum. Seminiferous tubules are located in the testes. The epididymis partly surrounds the sac containing the seminiferous tubules. The Vas deferens is a tube connecting the seminiferous tubules to the ejaculatory duct, which begins in the prostate gland. The prostate gland is located behind and below the bladder. The seminal vesicle, located above the prostate, also connects to the seminal vesicle. The bulbourethral gland connects to the ejaculatory duct where the ejaculatory duct enters the penis.
      Figure 15.2 The reproductive structures of the human male are shown.
  2. Figure 15.9 Which of the following statements about hormone regulation of the female reproductive cycle is false?
    1. LH and FSH are produced in the pituitary, and estradiol and progesterone are produced in the ovaries.
    2. Estradiol and progesterone secreted from the corpus luteum cause the endometrium to thicken.
    3. Both progesterone and estradiol are produced by the follicles.
    4. Secretion of GnRH by the hypothalamus is inhibited by low levels of estradiol but stimulated by high levels of estradiol.
      Hormone levels during the follicular phase, ovulation, and the luteal phase are compared. During the follicular phase, L H and F S H secreted from the pituitary stimulate several follicles to grow. The follicles produce low levels of estradiol that inhibit G n R H secretion by the hypothalamus, keeping L H and F S H levels low. Low levels of estradiol also cause the endometrial arteries to constrict, resulting in menstruation. During the time leading up to ovulation, L H and F S H stimulate maturation of one of the follicles. The growing follicle begins to produce high levels of estradiol, which stimulates G n R H secretion by the hypothalamus. As a result, L H and F S H levels rise, resulting in ovulation about a day later. Estradiol also causes the endometrium to thicken. After ovulation, the ovarian cycle enters the luteal phase. L H from the pituitary stimulates growth of the corpus luteum from the ruptured follicle. The corpus luteum secretes estradiol and progesterone that block G n R H production by the hypothalamus and L H and F S H production by the pituitary. Estradiol and progesterone also cause the endometrium to further develop.
      Figure 15.9 The ovarian and menstrual cycles of female reproduction are regulated by hormones produced by the hypothalamus, pituitary, and ovaries.
  3. Figure 15.11 Which of the following statements about the menstrual cycle is false?
    1. Progesterone levels rise during the luteal phase of the ovarian cycle and the secretory phase of the uterine cycle.
    2. Menstruation occurs just after LH and FSH levels peak.
    3. Menstruation occurs after progesterone levels drop.
    4. Estrogen levels rise before ovulation, while progesterone levels rise after.
      The menstrual cycle encompasses both an ovarian cycle and a uterine cycle. The uterine cycle is divided into menstrual flow, the proliferative phase and the secretory phase. The ovarian cycle is separated into follicular and luteal phases. At day zero the uterine cycle enters the menstrual phase and the ovarian cycle enters the follicular phase. Menstruation begins, and the follicle inside the uterus begins to grow. The level of the pituitary hormone F S H rises slightly, while L H levels remain low. The levels of ovarian hormones estradiol and progesterone remain low. After menses the uterine cycle enters the proliferative phase and the follicle continues to grow. The level of the ovarian hormone estradiol begins to rapidly rise. Toward the end of the proliferative phase, levels of the pituitary hormones F S H and L H rise as well. Around day fourteen, just after the levels of estrogen, progesterone and estradiol reach their peak, ovulation occurs. The follicle ruptures, releasing the oocyte. The ovarian cycle enters the luteal phase. The follicle grows into a corpus luteum and then degenerates. The uterus enters the secretory phase. Progesterone levels increase and estradiol levels, which had dropped after ovulation, increase as well. Toward the end of the secretory phase estrogen and progesterone levels decrease, reaching their baseline levels around day 28. At this point menstruation begins.
      Figure 15.11 Rising and falling hormone levels result in progression of the ovarian and menstrual cycles. (credit: modification of work by Mikael Häggström)
  4. View this time-lapse movie of a conceptus starting at day 3. What is the first structure you see? At what point in the movie does the blastocoel first appear? What event occurs at the end of the movie?
  5. Visit this site for a summary of the stages of pregnancy, as experienced by the pregnant person, and view the stages of development of the fetus throughout gestation. At what point in fetal development can a regular heartbeat be detected?

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