2 Topic OutlineProduction of GametesFertilization & Pregnancy
3 Topic 9.1 - Production of Gametes 9.1.1 Draw the structure of testis tissue as seen using a light microscope.The drawing will be insertedat a later date.MAIN PAGE
4 9.1.2 Outline the processes involved in spermatogenesis including mitosis,cell growth, the two divisionsof meiosis and cell differentiation.Spermatogonia, diploid cells, go throughmitosis first many times. This createslarge populations of potential sperm(at this time they are still diploid,as they have undergone mitosis only).
5 If the animal were to have a diploid number of 4, in the first division ofmeiosis,the chromosome number ofthese potential sperm cells is reducedby half. These spermatocyte chromosomesare then duplicated, consisting of twoidentical chromatids.
6 The second meiotic division produces four spermatids, each with two single chromosomes.Spermatids then differentiate intomature spermatozoa, or sperm cell
7 9.1.3 Outline the origin and the role of the hormones FSH, testosterone,and LH in spermotogenesis.FSH periodically stimulates a follicle tobegin growing again and inducesits primary oocyte to begin thesecond meiotic divisions in females.In males, however, it servesanother function.
8 The increased release of FSH combined with LH from the anterior pituitary glandsin the head induces the increasedproduction of testosterone, which inturn increases the rate of spermatogenesis.
9 LH stimulates androgen production by the interstitial cells and androgen isrequired for sperm production. Androgenis a type of testosterone, which againincreases rate of spermatogenesis.
10 9.1.4 Draw the structure of the ovary as seen using a light microscope.The drawing will be inserted at a later date.
11 involved in oogenesis including mitosis, 9.1.5 Outline the processesinvolved in oogenesis including mitosis,cell growth, the two divisions of meiosis,the unequal division of cytoplasm.and the degeneration of polar bodiesOva is produced by mitosis producingdiploid oogonia. Each oogonia developsinto a primary oocyte, which is also diploid.
12 Typically each month, an oocyte completes meiosis I. The meiotic divisions in oogenesisinvolve unequal cytokinesis. The first divisionproduces a large cell and a muchsmaller polar body.
13 The second meiotic division, which produces the ovum and a smaller polar body, occursonly if the sperm cell penetrates thesecondary oocyte (at this time thesecond polar body also divides, yieldingthree polar bodies in total).
14 After meiosis is completed and the second polar body separates from the ovum,the haploid nuclei of the sperm andthe mature ovum, haploid at last fromthe final division, fuse together in theactual process of fertilization. Afterfertilization the three polar bodiesdegenerate and rapidly die.
15 The drawing will be inserted at a later date. 9.1.6 Draw the structure of amature sperm and egg.The drawing will be inserted at a later date.
16 9.1.7 Outline the role of the epididymis, seminal vesicle and prostate glandin the production of semen.The epididymis is where the spermsmove to in order to travel out ofthe body. The seminal vesicles arein the ejaculated semen and theyrelease a sugary solution to feedthe sperm for their longswim towards the egg.
17 The prostate gland releases the alkaline solution that constitutes the seminal fluid.This fluid provides proper environment andnutrition for the sperm cells before,while and after they are ejaculated.
18 9.1.8 Compare the processes of spermatogenesis and oogenesis including the number of gametesand the timing of the formationand release of gametes.Spermatogenesis begins between agesAbout 900 sperm gametesejaculate and sperms are producedcontinuously under the effectof a certain level of testosteronein the blood.
19 In meiosis, 4 equally-sized sperm are formed. Males start producing sperm around the ageof 14. Around ages 20 to 40, maximumnumbers of sperm are produced. It thenstarts to decline gradually but doesn'tstop completely. Oogenesis beginsbetween the ages of 10 and 14.
20 Usuallly one gamete is produced per menstrual cycle (28 days). One large eggand 3 small polar bodies are producedin meiosis. Only one egg is usedin fertilization. The polarbodies are discarded and they die.
21 Females produce eggs from about the age of 13 to about the age of 50. At this age,menopause sets in and no moreeggs are produced.
22 Topic 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.The acrosome reaction is when the sperm comes into contact with the coats surrounding the egg, and as the contact takes place the acrosome (an enzyme-filled vacuole at the tip of the sperm) bursts open and releases enzymes that digest the jelly coat of the egg.MAIN PAGE
23 The sperm membrane then comes in contact with the egg cell membrane and the two membranes fuse,followed by the entry of the spermnucleus into the cytoplasmof the egg.
24 The cortical reaction results as the sperm comes in contact with the egg cell membrane, triggeringchanges to the egg cell membranemaking it impossible for othersperms to enter.
25 9.2.2 Outline the role of human chorionic gonadotrophin (HCG) in early pregnancyHuman chorionic gonadotropin is anembryonic hormone that acts likepituatary LH to mantain secretion ofprogesterone and estrogens bythe curpos luteum throughthe first trimester.
26 In the absence of hormonal override, the decline in maternal LH due to inhibition of the pituitary byprogesterone would result inmenstruation and spontaneousabortion of the embryo.
27 Levels of HCG in the maternal blood are so high that some is excreted in theurine, where it can be detectedin pregnancy tests.
28 9.2.3 Describe the structure and funtions of the placenta including its hormonal role in the maintenanceof pregnancy (secretion of estrogenand progesterone).During first 2 to 4 weeks of developmentthe embryo obtains nutrients directly fromthe endometrium. However, tissues growout from the developing embryo andmingle with the endometriumand form the placenta.
29 The placenta is disk-shaped and grows to about the size of a dinner plate weighingless than 1 kg. Diffusion of materialbetween the maternal and embryoniccirculations provides nutrients,exchanges respiratory gases, anddisposes of metabolicwastes for the embryo.
30 Blood from the embryo travels to the placenta through arteries of the umbiliicalcord and returns via the umbilical vein,passing through the liver of the embryo.The embryo secretes hormones thatsignal its presence and control themother's reproductive system (suchas HCG, mentioned above).
31 HCG acts like pituitary LH to maintain secretion of progesterone and estrogensby the corpus luteum throughthe first trimester.
32 In the absence of this hormonal override, the decline in maternal LH due toinhibition of the pituitary by progesteronewould result in menstruation andspontaneous abortion of the embryo.MAIN PAGE