Chapter 13: Reproductive system, development (C7886474)


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    Continuing the list of endocrine glands, those specifically related to reproduction include–

    Gonads, which as expressed , are the organs that make gametes from germ cells. Gamete is a cell that fuses with another during fertilization, for sexual reproduction. As enlisted , these include:

    • Testes, in males, which produce sperm by spermatogenesis, which is the development of spermatogonia into sperm. It starts in the seminiferous tubules of the testes, Leydig cells are stimulated by LH to produce the steroid hormone testosterone, which stimulate spermatogenesis. Testosterone is also responsible for promoting secondary sexual characteristics, which are features distinguishing between the two sexes, including growth of pubic hair, enlargement of larynx (Adam’s apple), and growth of the penis. Testosterone is also slowly converted to estradiol, which leads to ossification of the cartilaginous epiphyseal plate into the harder epiphyseal line. As the epiphyseal plate is where long bones grow, ossification will conclude length wise growth. Also within the seminiferous tubules, Sertoli cells are stimulated by FSH, which nurtures the stages of spermatogenesis. The immature sperm undergoes maturation in the epididymis. Upon ejaculation, sperm passes through the vas deferens, and the urethra. The seminal vesicles, prostate gland and bulbourethral glands add fluid to the sperm to make semen
    • Ovaries, in females, which produce eggs by oogenesis, which is the development of oogonium into ovum. Oogonium develops into primary oocytes during fetal life (discussed ). Further development is arrested at birth, until puberty, when the menstrual cycle begins, which includes:
      • Follicular phase, which is where rising FSH induces proliferation of granulosa cells, which surround the oocyte. Granulosa cells in turn secrete zona pellucida, which is a membrane immediately surrounding an oocyte. Granulosa cells can thus be viewed as the homolog to Sertoli cells. FSH also causes granulosa cells to secrete estrogen. Estrogen stimulates a positive feedback loop, which increases production of LH. LH induces proliferation of theca cells, which surround granulosa cells. LH also induces theca cells to produce androgens (an example, being testosterone). Theca cells can thus be viewed as the homolog to Leydig cells. The complex of a single oocyte (unfertilized egg), granulosa cells and theca cells, is known as ovarian follicle. Follicular phase recruits several follicles, which compete until one follicle dominates
      • Ovulation, which is caused by the positive feedback producing large amounts of LH, known as the LH surge, which triggers the oocyte to burst through the follicular wall, known as ovulation. After being released from the ovary, the oocyte is swept into the fallopian tube by the fimbria. The ciliated fallopian tube sweep the oocyte towards the uterus
      • Luteal phase, where FSH and LH cause the remaining follicle (with its oocyte removed) to transform into the corpus luteum, which secretes progesterone and estrogen. Progesterone is a steroid hormone, which helps prepare the uterus for pregnancy by creating a uterine lining. If pregnancy doesn’t occur, the corpus luteum degenerates. Fertilization usually takes place in the fallopian tubes. A fertilized egg will implant into the uterine wall, and is referred to as a blastocyst
      • Menstruation, which is the shedding of the uterine wall into the vagina and out, indicating a woman hasn’t become pregnant

    Placenta, in females, which forms if pregnancy occurs. Placenta secretes progesterone, estrogen, and HCG. HCG (human chorionic gonadotropin) is a peptide hormone, which is analogous to LH and FSH

    Frequently asked questions
    What are the gonads?
    The organs which convert germ cells into gametes. It is the testes in men, and ovaries in women.

    What are gametes?
    Cells which fuse with another during fertilization, for sexual reproduction. They are the egg in the female, and sperm in male.

    Learning activity
    What is the reproductive system?

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    Biology - Pre-med science - MR. SHUM'S CLASSROOM