Download Topic Nine

9.1 Production of Gametes
9.1.1 Draw the structure of testis tissue as seen using a light microscope.
9.1.2 Outline the processes involved in spermatogenesis including mitosis, cell growth, the two
divisions of meiosis and cell differentiation.
 Germ cells, diploid, called spermatogonia, go through mitosis many times, producing a large
population of potential sperms.
 The germ cells grow into primary spermatocytes, still diploid.
 Primary spermatocytes go through the first meiotic division, forming secondary
spermatocytes, which are haploid.
 Secondary spermatocytes undergo meiosis II, forming spermatids, also haploid.
 Spermatids differentiate into spermatozoa, which matures into sperms.
9.1.3 Outline the origin and the role of the hormones FSH, testosterone and LH in
spermatogenesis.
 FSH: stimulates sperm production in the seminiferous tubule, stimulates the first meiotic
division.
 LH: stimulates the interstitial cells outside of the tubule to produce testosterone.
 Testosterone: stimulates the secondary sexual characteristics and development into a mature
sperm.
9.1.4 Draw the structure of the ovary as seen using a light microscope.
9.1.5 Outline the processes involved in oogenesis including mitosis, cell growth, the two
divisions of meiosis, the unequal division of cytoplasm and the degeneration of polar
bodies.
During fetal development in a girl:
 Germ cells called oogonia divide by mitosis to produce many oogenia, diploid.
 Oogenia grow into primary oocytes, haploid. These primary oocytes start meiosis I, but are
stopped during prophase I.
 The primary oocyte and a single layer of follicle cells form primary follicles.
From puberty and onward until menopause:
 A few follicles start to develop during each menstrual cycle.
 Meiosis I is completed forming 2 haploid nuclei, but by unequal cytoplasmic division,
forming one large secondary oocyte, haploid, and one small polar body, haploid.
 The secondary oocyte starts meiosis II, but stops in prophase II.
 The follicle cells divide and develop into a mature follicle.
 At ovulation, the follicle bursts and the ovum is released as a secondary oocyte.
 The follicle cells develop into corpus luteum.
 Only if a sperm penetrates the secondary oocyte, does it finish meiosis II and again with
unequal cytoplasmic division, forming another polar body.
 The sperm finally fuses with the mature ovum and the polar bodies degenerate.
9.1.6 Draw the structure of a mature sperm and egg.
9.1.7 Outline the role of the epididymis, seminal vesicle and prostate gland in the production of
semen.
 Epididymis: sperms mature, become motile and are stored here.
 Seminal vesicle and prostate gland: produce and store fluid that is expelled during
ejaculation. This fluid is mixed with the sperms.
 Seminal vesicle: produces fluid containing nutrients for the sperms including fructose and
also mucus that protects the sperms and prostaglandin that stimulates contractions in
contractions in the female reproduction system.
 Prostate gland: produces alkaline fluid that can neutralize the environment in the vagina
(acidic) to optimize sperm motility. Also mucus for protection including a clotting substance
that makes the semen gelatinous.
9.1.8 Compare the processes of spermatogenesis and oogenesis including the number of
gametes and the timing of the formation and release of gametes.
 Every primary spermatocyte produces 4 sperms. Every primary oocyte produces only 1
ovum.
 Males produce millions of sperms a day. Females produce only one per 28 days.
 Males produce sperms continuously from puberty to old age. Female produces primary
oocytes before birth and one ovum per menstrual cycle from puberty to menopause.
 Sperms can be released anytime by ejaculation. Ova are released according to the menstrual
cycle, on day 14 by ovulation.
 Spermatogenesis has an equal division of cytoplasm and nutrients. Oogenesis divides the
cytoplasm unequally, leading to that all nutrients goes to one cell, the ovum, and nearly
nothing to the polar body.
 Both involve mitotic division, cell growth before meiosis, and the two divisions of meiosis.
 In male, FSH initiates meiosis I. In female, FSH stimulates the completion of meiosis I.
9.2 Fertilization and Pregnancy
9.2.1 Describe the process of fertilization including the acrosome reaction, penetration of the
egg membrane by a sperm and the cortical reaction.
 When the sperm get in contact with the zona pellucide (jelly coot), the acrosome reaction
takes place.
 Enzymes from the acrosome are released and break down the zona pellucide. This allows the
sperms to reach the plasma membrane of the ovum.
 At the plasma membrane, the sperm is recognized by receptor molecules and the plasma
membrane of the sperm fuses with the plasma membrane of the ovum.
 The ovum completes meiosis II.
 The fusion of the plasma membranes also initiates the cortical reaction.
 The cortical granules, vesicles fuse with the plasma membrane and release their content by
exocytosis. This makes the zona pellucide harden and impermeable to other sperms.
9.2.2 Outline the role of human chorionic gonadotrophin (HCG) in early pregnancy.
 Progesterone from corpus luteum made the endometrium thicker, with glands and blood
vessels to support the implanting embryo.
 The embryonic cells produce HCG that maintains the corpus luteum so that it will continue
to produce progesterone to maintain the endometrium.
 HCG is detectable in the urine at 8 days after fertilization and is therefore used in pregnancy
tests.
9.2.3 Describe the structure and functions of the placenta including its hormonal role in the
maintenance of pregnancy (secretion of estrogen and progesterone).
Structure:
 The placenta is a disc-shaped structure, approx. 2 cm thick, 20 cm in diameter.
 It is embedded in the uterine wall, attached to the fetus via the umbilical cord with blood
vessels inside (artery and vein).
 The chorionic villi in the placenta form a large surface area for exchange of materials. The
fetal blood in capillaries in the villi project into intervillus space with maternal blood.
Function:
 Nutrition: glucose, lipids, vitamins, minerals, amino acids are absorbed by fetal blood.
 Gas exchange: oxygen into the fetal blood, carbon dioxide out of the fetal blood.
 Excretion: urea, carbon dioxide and water from the fetal blood.
 Protection: antibodies fro the mother, natural passive immunity.
 Anchorage
 Heat exchange
 Endocrine gland: the placenta produces hormone and takes over the production from corpus
luteum after approx. 10 weeks. Produces progesterone which is needed to maintain the
endometrium and inhibit release of FSH. Estrogen is also produced and is needed to inhibit
FSH and stimulate further growth of endometrium and growth of breasts.