Brandon Moncada 11.4 notes Review Sperm and ovum are required for fertilization and sexual reproduction to occur. These gametes are produced by the processes spermatogenesis and oogenesis. Brandon Moncada Spermatogenesis o process of producing sperm through meiosis. It occurs in the testis, which consist of narrow tubes called seminiferous tubules separated by cells called interstitial cells o o Near the outer wall of the tubules are germinal epithelial cells called spermatogonia. At any time a spermatogonia may be undergoing mitosis or meiosis. o Brandon Moncada o Spermatogonia undergo meiosis in order to produce spermatozoa which are motile sperm. They also under mitosis to replenish cells that have developed into spermatozoa. Brandon Moncada Brandon Moncada Brandon Moncada CELL TYPE CELL # CHROMOSOMES (n = # of chromosomes) PROCESS CELL ENTERS Spermatogonia 1 46 – 2n Mitosis Primary Spermatocyte 2 46 – 2n Meiosis I Secondary Spermatocyte 2 23 - n Meiosis II Spermatid 4 23 - n Spermatogenesis Spermatozoa 4 23 - n o While undergoing meiosis and developing in the seminiferous tube, spermatids are nursed (provided nutrients) by Sertoli cells. When they have fully matured and formed the flagella/acrosome (head) they release from the Sertoli cells into the tubule lumen and are swept away into the epididymis. Brandon Moncada Brandon Moncada o Seminiferous Tubule Diagram Brandon Moncada Oogenesis o the process that produces egg cells in the ovaries. o Production begins during the fourth to fifth month of pregnancy and is completed by the seventh month. o As a result, females are born having already produced their egg cells. Brandon Moncada Brandon Moncada Brandon Moncada Brandon Moncada Brandon Moncada CELL TYPE CHROMOSOMES PROCESS CELL ENTERS Oogonium 2n Mitosis Primary Oocyte 2n Meiosis I Secondary Oocyte 1n Meiosis II Ovum 1n Brandon Moncada Brandon Moncada Brandon Moncada SPERMATOGENESIS OOGENESIS Millions of sperm produced per day One secondary oocyte produced per menstrual cy 4 gametes produced for each spermatogonium 1 gamete produced for each oogonium Brandon Moncada Very small haploids Very large haploids Occurs in testes (gonads) Occurs in ovaries (gonads) Spermatozoa released during ejaculation Oocyte released during ovulation Haploid nucleus from meiosis Haploid nucleus from meiosis Continues all through life from puberty Starts at puberty and ends at menopause Brandon Moncada Cytoplasm o Sperm only contain the resources necessary to move and penetrate the egg. During differentiation, most of the cytoplasm is eliminated. As a result, the size of egg cytoplasm is significantly larger. # of Gametes o Ovulation occurs only once per menstrual cycle in humans, which typically results in one egg being released. In contrast, testes produce sperm continuously after puberty, millions per day. Fertilization Polyspermy o results when multiple sperm fertilize an egg, which is fatal. As a result, there are several mechanisms to prevent this. Brandon Moncada Brandon Moncada In animals, fertilization can take place inside or outside the body. Brandon Moncada o Aquatic animals can release gametes directly into water where fertilization occurs. Risks include predation and susceptibility to environmental factors. o Terrestrial animals utilize internal fertilization, which prevents gametes from drying out. After fertilization, embryos are protected. Development Brandon Moncada Brandon Moncada Brandon Moncada Pregnancy Some tissue from the developing embryo is used to create extra-embryonic sacs, including the amniotic sac. It is filled with amniotic fluid in which the fetus floats. Brandon Moncada Functions of the sac/fluid include: o Acting as a cushion to blunt force o Providing environment for free-movement o Providing excellent thermal stability (fluid is mainly water) Brandon Moncada Brandon Moncada Brandon Moncada ^^positive feedback loop. Very rare in the body Brandon Moncada Brandon Moncada After the baby has been delivered, the afterbirth is discharged from the mother. This consists of the placenta and fetal membranes that once surrounded the fetus. Gestation time is the period of time from conception until birth. This time varies in mammals, but in humans the average is 38 weeks. Brandon Moncada Brandon Moncada
