1.  How are oogenesis and spermatogenesis different from each other?

 Oogenesis refers to formation of egg cells.  Spermatogenesis is the process that produces sperm cells.  Both processes involve cell production by meiosis.  In this method of cell production, the new cells will not be identical to their parent cells because they will have half the number of chromosomes that the parent cells had. For that reason, meiosis is sometimes referred to as “reduction division”.  The process of  meiosis involves two separate divisions of genetic material. (Recall that in mitosis there is one division of previously duplicated genetic material, resulting in two offspring cells that are identical to the parent cell, having exactly the same number of chromosomes, not a reduced number.)  The new cells that result from meiosis are called gametes. They are cells that can form a new organism when two such cells join their nuclear material together (fertilization), thus producing a new cell that has the same chromosome count as each of the original parent cells had.

 One of the major differences between oogenesis and spermatogenesis is that in spermatogenesis, the final product of the two meiotic divisions is four sperm cells.  However, in oogenesis, only one potential egg cell is produced.  This is because the divisions that occur in oogenesis do not evenly divide the cellular material as is true in spermatogenesis.  Although the chromosome number is reduced by half, the cytoplasm does not divide evenly.  This results in one large cell and three smaller ones instead of four cells of the same size.

 For an illustration of spermatogenesis, see Fig. 19.5 in Hole’s Essentials of Human Anatomy and Physiology.  Compare it with Fig. 19.8 to see the difference in the outcome of oogenesis.
 

2.  What are the major hormones of the menstrual cycle?

 The four major hormones of the menstrual cycle are:
 follicle stimulating hormone (FSH)
 luteinizing hormone (LH)
 estrogen
 progesterone
 

3.  What is the effect of each of these hormones?

 FSH and LH are produced by the anterior lobe of the pituitary gland.  As its name implies, follicle stimulating hormone has an effect on the follicles -- of the ovaries.  It stimulates the development & growth in size of an ovarian follicle.  The ovarian follicle contains an egg cell which has previously developed to the stage where it is referred to as a primary oocyte.  LH stimulates cells in the ovary to produce the precursor to estrogen.  On average, about 13 days after the previous menstrual flow, there is a surge in the amount of LH produces followed by an increase in the amount of FSH produced.  The LH surge brings about the release of the oocyte from its follicle.

 Estrogen and progesterone are hormones that are produced by cells of the ovary.  Estrogen is produced by cells surrounding the ovarian follicle.   This hormone causes the lining of the uterus (endometrium) to increase in thickness.   After an oocyte has been released (ovulation), the follicle becomes a corpus luteum, and it secretes a hormone called progesterone.  Progesterone has two effects:  it brings about a dense growth of blood vessels & glands in the endometrium, and it also inhibits the secretion of FSH.  Progesterone will help to maintain the thickened uterine lining in preparation for a pregnancy.  If a sperm cell does not fertilize the released oocyte, the corpus luteum degenerates around the 24th day of the cycle.  As progesterone levels drop, the blood vessels of the lining constrict.  The lining then sloughs off.  This is known as the menstrual flow.  If a sperm cell fertilizes the released oocyte and the embryo implants in the endometrium, progesterone will continue to be produced to maintain the lining throughout the pregnancy.  As a placenta develops, it will take over production of progesterone.