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ANA301 Human EmbryologyLecturesMon and Fri 13pm in McLeod Auditorium MSB 2158 Evaluation Test 1 for 40 Lectures 19Mon Feb 11 Test 2 for 35 Lectures 1016 on material until Mar 11 Fri Mar 15Test 3 for 25 Lectures 1720Fri Apr 5 Lecture 1Mon 7 Jan Introduction Human Embryology and Teratology Why study To better understand human anatomy and to understand origin of major malformationsdiscovered at birth in 3 6100 newborns and discovered in an additional 3 later in life Professor Mike Wileymikewileyutorontoca 4169782642 MSB1178 Professor Ian Taylorfitztaylorutorontoca 4169787559 MSB1180 Lecture 2 Fri 11 Jan Gametogenesis and FertilizationObjectives Understand the significance of gametesReview the process of meiosis and understand the significance of meiotic nondisjunctionDescribe the process of gametogenesis in males and females and the steps in ovulation Understand the transit of sperm cells from the seminiferous tubules to the site of fertilization describe the glands producing seminal fluid and understand the process of capacitationDescribe the interaction between sperm and ovum at fertilization including acrosome reaction cortical reaction and zona reactionDescribe the role of male and female pronuclei and the significance of the zygote GametogenesisRefers to the production of gametes a population of cells specialized for the purpose of fertilizationGametogenesis involves the acquisition of the structural and functional characteristics necessary to ensure successful union Meiosis a type of cell division restricted to the gamete lineage meiosis occurs in two stages and halves the number of chromosomes in the gamete nucleus by separating the 23 pairs of chromosomes into 23 single chromosomes Fertilization the union of the gametes Gametes spermatozoa and oocytes special structural features half the somatic cell chromosome number Somatic cells and the Gametes somatic cell nuclei46 chromosomes diploid23 pairs of chromosomes22 pairs of autosomes XX or XY sex chromosomes pair Gamete Nuclei 23 chromosomes haploid23 single chromosomes22 autosomesEither X or Y sex chromosome Meiosisstart off with a cell with 46 chromosomes when meiosis begins they replicate their DNA then divides first in the first meiotic division meiosis I 23 chromosomes produced at meiosis I still have double DNA so there is meiosis II 23 single strand Mitosis v MeiosisMitosisDNA replication occurs separation of the chromatids 1 cell2 cells Meioticreplication and then separation of the chromosomes and in meiosis II separation of the chromatids meiosis 1 cell4 cells 1160 Newborns Have Abnormal Chromosome Number Too manyeg trisomy Downs syndrome Not enougheg monosomy Turners syndrome the 1 sex chromosome present is always an X you can only have a monosomy in the sex chromosomesstndNondisjunctionthe chromosomes dont separate properly in either 1 or 2 meiotic division instead of having 1 pair separate into the daughter cells there are some gametes with an extra and some with deficientIn meiosis II the chromatids fail to separate into daughter cells first division takes place normally but in the second division 2324 and 22 instead of the normal 23 and 23 monosomy failure of chromosomes to distribute normally during meiosis leads to the formation of gametes with abnormal numbers of chromosomes this affects 2 or 3 of sperm and 2060 as menopause is approached of oocytes in later years appears to affect women more than men if such a gamete participates in fertilization the resulting embryo will have an abnormal number of chromosomes in its cells aneuploidy Approximately 1160 newborns will haveAge 30 11000 risk of child having abnormal chromosomes Abnormal chromosome numbers the majority of aneuploid embryos never come to term Failure of paired chromosomes to separate during cell division is called nondisjunctionNondisjunction can occur during mitosis in early cleavage as well and this can result in one of the cells carrying an extra chromosome or being deficient 46 creates 46 46 and one of them 47 45 almost all monosomic will be eliminated and so person becomes mosaic some normal and some trisomic 4647 amount of cells affected by trisomy depends on how early on the nondisjunction occurs 1SpermatogenesisBeginning at puberty and continuing uninterrupted for the lifetime In the seminiferous tubules of the testes A 2 phase process First phasespermatogonia via Meiosis IIIspermatids Second phasespermatids via spermiogenesisspermatozoaFrom spermatogonium to spermatozoon takes about 10 weeks70 days Spermatogenesis starts at puberty an is a continuous process Produces 50 to 150x106 sperm cellsdaySpermatozoonHead and tail head acrosome contains hydrolytic enzymes haploid nucleus cell membrane contains binding sites for sperm receptors on the zona and on the oocyte membrane Tailmiddle piece principal piece and end piece the tail is just a long flagellumAbnormal forms are common Around 10 abnormal forms are typical but more than 20 can mean infertilitySpermiogenesis is just a part of the process From the testicle to the urethra Epididymis after 24 hours of coming in the sperm can wiggle after 48 they can circle and swim and after 46 days the sperm develop the ability to swim in a direct fashion From the epididymis the sperm cells enter the vas deferens at ejaculation they are pushed into the urethra There are two glands called seminal vesicles and they make 60 of the seminal fluid Seminal fluidproduced principally by the paired seminal vesicles 60 the prostate gland 30 and the paired bulbourethral glands 10 At the time of ejaculation the seminal fluid is added to the spermatozoa to constitute the semen The seminal fluid functions to provide a nutrient source for the spermatozoa and to neutralize vaginal acidity and promote sperm motility vagina has a natural acidity to it and the seminal fluid is alkalineA concentration of 40200x106 spermatozoa per ml of semen is considered normal Azoospermia is a lack of spermatozoa in the semen zero Oligospermia is a deficiency of spermatozoa in the semen some but not a normal number Sperm Transitfrom the vagina to the ampullathe normal site of fertilization is in the ampulla of the uterine tubeupper part of the uterine tube and so the sperm cells have to go to through the cervix to the uterus the sperm have to get through the external os and external os into the uterus Within minutes of ejaculation some spermatozoa are carried from the vagina to the ampulla of the uterine tube by contractions of the uterine and tubal musculature the remaining spermatozoa majority colonize the crypts of the cervix Some sperm cells reach via contractions of the uterine wall and the rest have to try to swimits estimated this would be only a few hundred compared to the other millions Only one tubeConnection between the tube and uterus is really tiny and hard to find the more sperm cells making contact with the uterine lining the more chance that there will be some entering the uterine tube why there are many Its estimated Over the following several days sperm cells leave the cervix and swim to the ampullae by means of means of the sperm tail beat most of the cells can survive for at least 2 days some might by able to survive as long as 5 or 6 days majority of sperm can remain viable in the female tract for at least 2 days and an oocyte lives only about 24 hours
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